# M³ Project Announcement



## morsel

[size=x-small][size=small]*M³ Project Announcement*[/size]

 Morsel and AMB present a new community service project and invite your participation.
 M³ is a 3 channel MOSFET output headphone amplifier inspired by the PPA and SDS Labs amps.

*There is no ETA on boards.*

 [size=small]*Pronunciation*[/size]

 M³ is pronounced *em cubed*. The 3 in M³ is HTML *&sup3;* (Unicode 00b3). Type MMM if you are lazy. Rumor has it MMM once stood for Morsel's MOSFET Monster, but in fact it refers to the 3 MOSFET output channels. M³ is a codename subject to possible future change.

 [size=small]*Design Goals*[/size]

 AC only, no compromises for battery compatibility
 Unimpeachable discrete output stage
 Better price/performance ratio than the PPA
 KISS philosophy (Keep It Simple, Stupid)







 [size=small]*Circuit Description*[/size]

 Vbe multipliers bias IRFZ24N and IRF9Z34N 18A power MOSFET pairs into Class A operation for low distortion by establishing a constant voltage drop across the gates, which determines the quiescent current. 1µF film capacitors across the Vbe multipliers help stabilize the voltage drop and lower impedance at high frequencies. FET cascode current sources bias the opamps into Class A operation and set the drive current high enough to overcome the reactance of the MOSFET gates. 220pF capacitors between gate and source of the N channel MOSFETs compensate for the difference in Ciss between N and P channel MOSFETs to provide symmetrical bandwidth rolloff, or the N channel gate resistors may be increased 1.67x, or compensation may be omitted.

 3 amplifier channels (left, right, and ground) use the same output stage and noninverting opamp topology. The ground channel sources and sinks the return current from both transducers which would otherwise have been dumped into signal ground or power supply ground. This shifts responsibility for the high current reactive load of the headphones from signal ground to the supply rails of the output stage, thus removing the primary source of signal ground contamination. The transducers are driven by symmetrical output stages with equal impedance and transfer characteristics on both sides, rather than an output stage on one side and the large capacitor bank of the power supply ground on the other. This results in lower output impedance and greater linearity.

 [size=small]*Choices*[/size]

 We have deferred some decisions to give the community a greater opportunity to voice opinions and to give us more time to test various aspects of the developing design.

 Board dimensions are really critical as they affect cost, size, case compatibility, board mounted components, component spacing, and sound quality. We are leaning toward dimensions 2-3x bigger than a standard eurocard to allow for onboard heat sinks, a less congested layout than the PPA, possible choice of board mounted components, multiple input and output jacks, and compatibility with PAR-METAL 20 Series cases.

 Ventilation requirements exist for the MOSFET heat sinks unless the MOSFETs are arranged along one edge of the board and bolted to the case along with electrically insulating heat sink pads. Ventilation slots result in dust ingress but allow for more flexible board arrangements. Heat sink options include Aavid Thermalloy 531202b00000 2" or 531002b00000 1" free standing screw mount extrusions.






 External power supplies are best, as they are less likely to interfere with the amplifier. Internal supplies should be as far from the input stage as possible, and preferably shielded with steel or mu metal. We are considering voltage regulators on the pcb, capacitance multipliers or voltage regulators on the opamp power rails (either 3 separate, or 1 for all 3 opamps). LED power indicator current sources and zeners are pointless, since this is an AC only amp. LED and series resistor, power switch, and series diode for reverse voltage protection would be useful.

 Ciss compensation capacitors, increasing N channel gate resistors by 1.67x, or no compensation is a choice best left up to the end user, as is bass boost, assuming board space is not a problem. No crossfeed is included, although we have considered a simple resistive crossfeed to reduce the stereo image on hard panned albums from the 60s and 70s.

 We tried MOSFET diamond buffers but they had slightly worse IMD than MOSFETs driven directly by opamps. We considered BJT diamond buffers but decided to stick with studly MOSFETs because of lower output impedance, higher input impedance, negative thermal coefficient, and circuit simplicity. Low drive current requirements eliminate the need for more complex driver circuits such as the diamond buffer. We also think MOSFETs sound better than BJTs.

 [size=small]*Measurements*[/size]

 Initial tests using an M-Audio Transit and 33 Ohm dummy loads show THD and IMD comparable to sound card loopback. (THD .0015%, IMD .0025%, perhaps someday I will buy a better sound card.) Our prototype drives studio monitors impressively and should be a good match for any dynamic headphone, even the notorious AKG K1000.

 [size=small]*Team M³*[/size]

 Team M³ is Morsel and AMB. Thanks to PPL for his bountiful wisdom and lore.
NeilPeart will be helping us with listening tests.[/size]


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## Glassman

great, I like that FET+BJT opamp supply isolation better than just FETs.. as to the amp circuit itself - simple, clean and clear.. I like that.. what about different types of MOSFETs or are these really the best?


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## Voodoochile

Nice target chassis choice! 
	

	
	
		
		

		
		
	


	




 Really, I like that box a lot. Glad to see designed for AC from the ground up ('specially with MOSFETs).

 I'm in full support of more board-mounted options, such as nested pads for the DaCT attenuator and Alps, plus on-board fusing as an option that can be jumpered if rear-panel access is preferred.

 Glad you are planning to drive the MOSFETs directly from the OPAs... I like that.

 When will the boards be ready? (kidding- no reply requested!)


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## sygyzy

Very nice. From the little amount of that I actually understood, this seems like a pretty exciting time for DIY.


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## Lil_JV

Looks great! I look forward to building this amp.

 JV.


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## Earwax

Quote:


  Originally Posted by *morsel* 
_[size=small]*Design Goals*[/size]

 AC only, no compromises for battery compatibility
 Unimpeachable discrete output stage
 Better price/performance ratio than the PPA
 KISS philosophy (Keep It Simple, Stupid)
 [/SIZE]_

 

Much of the rest of the announcement is over my head, but I like this part 





 Looking forward to building one!


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## morsel

Hi Glassman,

 Renesas (formerly Hitachi) makes power MOSFETs for amplifiers such as the 2SK216/2SJ79 .5A and 2SK1058/2SJ162 7A pairs. They are really expensive, hard to get, use a nonstandard pinout, have higher Rds, lower Id, and their Ciss is not much better than the IRF parts.


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## kyrie

Looks very cool! Though I don't understand the technicalities...
 It says that the M³ is designed to have better price/performance ratio than the PPA, but would you expect it to sound better than the PPA, ignoring price?


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## morsel

Our design goals may or may not be achieved. 
	

	
	
		
		

		
		
	


	




 For those people who prefer discrete output to HA5002 buffers, it will probably sound better.


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## Sovkiller

morsel:
 Any way we could use another OPamps, like the BBs OPA627/637 or the LT1122, LT1028, etc....???

 Any way of getting included any onboard processor like crossfeed, bassboost, etc...even if optional or defeatable???


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## morsel

As with any DIY, you can choose your favorite opamps, add crossfeed, etc.


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## Nisbeth

Whoa, the wait is over! 
	

	
	
		
		

		
		
	


	



 You've mentioned this project a few times before Morsel but I thought you had given up on it. Luckily not 
	

	
	
		
		

		
		
	


	




. 

 I'll be following this thread with great interest 
	

	
	
		
		

		
		
	


	





 /U.


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## Lil_JV

Is it okay if we just write M3 in the future? It is even easier than MMM.
	

	
	
		
		

		
		
	


	




 JV.


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## morsel

M3 is a model of BMW. Why not just copy and paste M³ from a previous post?


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## Sovkiller

Quote:


  Originally Posted by *morsel* 
_As with any DIY, you can choose your favorite opamps, add crossfeed, etc._

 

Yep, but what about if you guys, consider those options as part of the initial circuit, that will make the project a more universal one, and will fit more and more persons, why not including them on the original circuit board, maybe optional, but there. And later same as the PPA, if you want them, just populate this part of the circuit, and if not, just bypass it, and period....But the bassboost can't be added later if you want it, IIRC it has to be there in the circuit I think, or am I wrong?


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## morsel

Bass boost is part of the circuit. Rbb, Cbb, Sbb are the bass boost resistor, capacitor, and switch. I thought that was obvious.


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## Sovkiller

Quote:


  Originally Posted by *morsel* 
_Bass boost is part of the circuit. Rbb, Cbb, Sbb are the bass boost resistor, capacitor, and switch. I thought that was obvious._

 

Thanks morsel for your answers. Sorry, my bad as I barely looked at the schematic.....BTW remember that sometimes what is obvious for you, is not that obvious for others, and there are a lot of members that would like to venture themselves into a first good DIY project, but they are not DIYers in any way. 
 Even though I will be really interested in trying this out, definitelly, I own a PPA, and I love it, and I was always curious about this Sheldon D. Stokes project, just that nobody seems to care too much about it, and offer it as a DIYFSE option (other that himself, a very expensive labor BTW)......


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## aos

nevertheless you should consider 2sj76 / 2sk213 series. A mosfet designed
 for amplification isn't the same as one designed for switching. Rds means much less in an amp than linearity. also I don't recall them costing more than a few bucks and easy to get from mcm or wherever.


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## drewd

The spec'd transistors look reasonably linear to me, at least from the datasheet, unless Vgs is very small.

 I would be a big fan of a well considered voltage regulation system on the board to give us a greater choice of power sources. If we can take control of the voltage regulation, then we can make it as robust as necessary. Since the circuit board is targeted for such a large size, it seems reasonable to aim for independent regulation for each channel, with, perhaps, some sort of jumper option to use a single regulator.

 Maybe a Jung regulator? Is it called that anymore?

 -Drew


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## jamont

Very nice work on this long anticipated project!

 The LaRocco and Glassman discrete buffers have shown the merit of this approach, having an integrated design - opamp voltage amplifier + discrete buffer - seems like the logical next step.

 I think it would be nice if there would be a configuration that could be built in a case smaller than the Par 20 series, especially if there is an outboard PSU. The 1455N series case used in the PPA seems to me an ideal size for a headphone amplifier. I do like the idea of the outboard PSU, and also the idea of more options for board-mounted components.

 Whatever you decide, I look forward to building it.


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## h3nG

sweet. what an exciting news for the diy audio community. you mentioned it's goign to have a better price and performance ratio than the ppa, but any idea what the price range is goign to be? (200-250, 300-350, etc...)

 cant wait to hear it/hear impressions of it.


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## amb

Hi all,

 I am glad that hardly a half day has passed and this announcement already generated so much interest. This is going to be a very exciting project because it combines the essential qualities of the PPA with that of a *very* robust class-A MOSFET output stage (I love the term "studly" that morsel used in the announcement 
	

	
	
		
		

		
		
	


	




 ), and makes several significant enhancements over the SDS Labs MOSFET amplifier as well.

 I built and tested several iterations of prototypes on breadboards, exploring some different possibilities. As Morsel said, we tried a diamond buffer output stage, except with MOSFET output devices. It worked well enough, but ultimately didn't measure as well as a simpler, directly-driven MOSFET topology. Just for kicks, here is a photo of the diamond buffer-based amp prototype:






 As for the choice of MOSFETs, we had to consider several factors. Since this amp is going to operate in class A, we would like to choose high current devices for reliability. The Ciss should not be too high, and yet high current devices always have higher Ciss due to their larger internal junctions. Stable and assured availability is also an important factor in our consideration. Linearlity, performance and suitability for the application, and last but certainly not least, the cost is also considered because we want this amp to deliver a lot for the money.

 The Hitachi 2SK213/2SJ76 series were considered. These are nice devices with low Ciss, but IMO just a bit "weak" with a Ids rating of 0.5A. The 2SK1058/2SJ162 are stronger, but the IRF devices we chose are even more robust yet with comparable linearlity, Ciss. Plus they are stocked in quantity at Digikey and Newark Electronics. The 2SK/2SJ devices are scant by comparison (at least in the US) and more expensive. The choice then became clear. The Renesas/Hitachi parts are not pin-compatible with the IRFs, so we had to choose one or the other for our PCB layout.

 As for the op amps, both Morsel and I like the AD8610. However builders/users can substitute others like the OPA637/627 just like you could with the PPA.

 We would definitely welcome more comments about the other open choices as listed in the announcement. In particular the power supply, casing, heat management, etc.

 -Ti


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## Glassman

I think it would be nice to have one larger heatsink in the center of the case, dividing it in two halves, one half for the amp itself, the other for the PSU w/ transformer.. I think having everything in one box is a better approach for such project, you're choosed rather big casing where there is enough space to prevent input section being interfered by PSU.. as for the PSU, the output section is a Class A beast and as such I'd choose a capacitance multiplier for it and keep the voltages rather high! for the opamp power I'd simply go with 78xx regulator for each channel with 317 as a preregulator for them all.. or some TL431 + pass transistor job..

 I don't think those Hitachi MOSFETs are hard to get either.. the question is if they're sonicaly better or not.. considering one bigger heatsing for all MOSFETs, you can add pads for both types of MOSFETs.. it won't take much space..


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## morsel

Aos: AMB already addressed the Renesas MOSFET issue, but I will add that the IRF IRFZ24N/IRF9Z34N 18A MOSFETs are about $1 each from Digikey, the Renesas 2SK1058/2SJ162 7A MOSFETs are about $9 each from B&D Enterprises, and the Renesas 2SK213/2SJ76 .5A MOSFETs are about $5 each. Multiply that by 6 for the 7A devices and 12 for the .5A devices and you have $54 to $60 for Renesas MOSFETs .vs. $6 for IRF MOSFETs. MCM Electronics prices are even worse.

 2SK1058 Ciss = 600pF
 IRFZ24N Ciss = 340pF
 2SK213 Ciss = 90pF
 2SJ162 Ciss = 900pF
 IRF9Z34N Ciss = 620pF
 2SJ76 Ciss = 120pF

 The 2SK1058/2SJ162 make no sense at all from either the cost or spec perspective. The 2SK213/2SJ76, once doubled up to compensate for their wimpy output, are too costly and space consuming despite the low Ciss. The IRFZ24N/IRF9Z34N are modern, 5th generation HEXFETs that sound good to us.

 Drewd: We might be talked into classic IC regulators but there is not room for a Jung regulator per channel, nor is it necessary.

 Jamont: Even with an external power supply, the eurocard format used for the PPA is probably too small for the M³, mostly because of the real estate the heat sinks require. We might be able to cram it on a eurocard if we sacrifice the Aavid extrusions, go for small clip-on heat sinks, and forego a more spacious layout, but I suspect this would not be a popular decision.

 h3ng: No ETA on boards or assembly cost.


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## morsel

Glassman: Perhaps your central heat sink idea is something best left to the individual user? Many feel that the power supply does not belong inside the case. Those that want it in the case may do so (at their own risk!) 
	

	
	
		
		

		
		
	


	




 It may be tough to have the MOSFETs spaced for Aavid extrusions and also have them mate to a central heatsink.


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## Glassman

Quote:


  Originally Posted by *morsel* 
_It may be tough to have the MOSFETs spaced for Aavid extrusions and also have them mate to a central heatsink._

 

yeah I know.. maybe you can arrange it like Kevin did with dynahi - output devices mounted horizontaly on L shaped extrusions.. that way it's possible to use Aavids as well as one big heatsink.. I'd just like to have the ability to use big heatsink profile at one side of the board.. keep that in mind when laying out the board, I think it's doable 
	

	
	
		
		

		
		
	


	




 oh and jung regs are most likely overkill here, opamps have very low current requirements as well as very good supply rejection, it's more important to focus on good bypassing close to the supply pins.. I'd go with 100n polypropylenes.. and also I'd like to have SOIC pads available..


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## PeterR

MMM, Mosfets 
	

	
	
		
		

		
		
	


	



 Have you ever tried a M² version?


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## morsel

Quote:


 and also I'd like to have SOIC pads available 
 

Hey Tangent, are you listening to this? We found someone besides Kurt who wants so8 pads. Glassman, where were you when we were working on PPA v1.1? 
	

	
	
		
		

		
		
	


	




 Peter, yes we have, I confess we have only tested with 2 channels so far. No worries though, we will be testing with 3 channels soon.


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## Glassman

ask IpsilonSound and you'll realise there's more then two people wanting SOIC pads 
	

	
	
		
		

		
		
	


	




 regarding my location at the time of discussing PPA v1.1, well I might have been busy with designing the buffers


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## 00940

what about M4 and balanced operation ?

 I agree with Glassman that having all the hot parts lined on the side for a big heatsink would be a big plus in my view.


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## amb

Quote:


  Originally Posted by *00940* 
_what about M4 and balanced operation ?_

 

Since that would require that you re-wire your headphones, I question how popular might such an amp be. I wonder how many people have built the Gilmore balanced, for example, compared to the standard Gilmore dynamic?

 One benefit of a balanced 4-channel setup is double the maximum output voltage swing, which might be useful for very high impedance and inefficient headphones, but I think that's of limited interest to most people.

 The other benefit of a balanced 4-ch design is that the output signal return is not dumped into signal ground, but our ground channel also gives the same benefit.

 Four channels will also significantly add to the size and cost (not only for the extra amplifier channel, but also increased power supply demand as well as increased PCB real estate). This would be contrary to our goal, which is KISS yet strive for excellent sound quality and performance.

 -Ti


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## Sovkiller

Well who's gonna work to try to organize the ideas and draw the first layout for the board, and maybe who knows later on organize a group buy through PCB or so....????


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## Budgie

I like the looks of this! I was thinking of adding a front end to my current class A amp, so the timing is perfect. Can't wait to see how it all turns out! 

 Thanks you, Morsel and amb!

 Do you think an active current source for the output stage might be an (optional) upgrade? Something easy like an LM317/resistor combo?


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## Earwax

Quote:


  Originally Posted by *Sovkiller* 
_morsel:
 Any way we could use another OPamps, like the BBs OPA627/637 or the LT1122, LT1028, etc....???

 Any way of getting included any onboard processor like crossfeed, bassboost, etc...even if optional or defeatable???_

 

Is a crossfeed a good use of board space? Which circuit would be used? I like the Meier crossfeed best, but maybe someone else wants a Linkwitz or something else. Overall, wouldn't a daughteboard approach for crossfeed be better? 

 Any opamp at all, including Bipolar types (LM6171)?


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## aos

Wimpy output?? You can bias them into class A from 50 to 150mA, as I did
 in my SDS labs amp (which has since fallen apart as this was 4 years ago). If 150mA isn't enough for a headphone amp, what kind of mutant 
 headphones are you trying to drive with it? Well I don't know how 
 much AKG1000 needs but what you are making then is a small speaker 
 amp. I found these Toshibas to sound much nicer than the IRF. 
 I do understand the monetary concern though - and the resourcing one
 even moreso. I guess a board can always be hacked to use the 
 other pinout. I would push for wire bridges in order to allow different 
 pinouts but that would mean that no matter what layout you use 
 you'd have to make some bridges and that wouldn't fly.

 Oh by the way, I personally like the idea of individual heatsinks as you mentioned. That works out well, as long as you don't need insane
 power. Single heatsink is by definition going to be custom, and I'd rather
 etch my own board than drill or God forbit cut a heatsink (I may exaggerate
 a bit since I do have a drill press). The same money/resource issue applies here - single heatsinks are easy to buy and relatively cheap. Consider custom heatsink ONLY if you're going to offer
 it alongside boards as well.


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## tangent

Quote:


 We found someone besides Kurt who wants so8 pads. 
 

Find ten and you enter the realm of statistical significance. >
	

	
	
		
		

		
		
	


	




 Regarding the amp, I assume from the 2N3904/6 that you're using in the power supply CCS that each channel consumes under 100mA?


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## aos

tangent, the output mosfet's are not driven by the voltage mutliplier but by the rails directly. So just the opamp will certainly not go over 100mA. There's no way they'd be talking big power if that poor thing was to have to pass that current through anyway (or they'd have made a major design mistake).

 Oh yeah, morsel, why the non-standard FETs in the voltage multiplier? Just about anyone who built PPA has probably some 5458 left over. Or is it Digikey availability? I know they have 5457.

 (tangent can probably sit back proudly, because whatever he uses becomes a "standard" part 
	

	
	
		
		

		
		
	


	




 ).


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## tangent

Quote:


 the output mosfet's are not driven by the voltage mutliplier 
 

Yes, I thought of that and came back to obliterate my post, only to find your answer already. 
	

	
	
		
		

		
		
	


	




  Quote:


 why the non-standard FETs 
 

My guess is that Digi-Key carries them, along with all the other parts they spec. You have to go to Mouser for 5484s.


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## tangent

That brings up a new question, then. How much _does_ each channel draw, quiescent?


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## tangent

Quote:


 Is a crossfeed a good use of board space? Which circuit would be used? 
 

Morsel said above, resistive crossfeed. Just a resistor between the channels to leak some sound through. Think "fixed pan slider".

 You won't see anything else on a Morsel amp, as she dislikes the nonlinear crossfeed circuits.

  Quote:


 I like the Meier crossfeed best 
 

It won't happen on that circuit, as designed. The Meier circuit depends on being isolated between two active stages, due to its impedance requirements. If you put it ahead of the amp circuit like we do with the Linkwitz, its behavior varies wildly with the source's output impedance variations.

  Quote:


 wouldn't a daughteboard approach for crossfeed be better? 
 

If it just means putting in some PPA-style mounting holes, I'm sure they could be talked into it....


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## aos

Also, you can't use Meier's circuit without permission. You can add it on your own amp if you wish but I don't think it could be included on board as default.
 That's why a daughterboard (or another kind of allowance for crossfeed)
 is a good approach to adding crossfeed.

 tangent, I guess the current draw is whatever you set the bias of the MOSFETs to. The opamp draw can pretty much be ignored (it will be
 order of magnitude less). I think they might be talking several hundred
 mA per channel, perhaps even 0.5A per channel.


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## jcx

"AC only, no compromises for battery compatibility
 Unimpeachable discrete output stage
 Better price/performance ratio than the PPA
 KISS philosophy (Keep It Simple, Stupid)"

 ?? supply splitter is "no compromise" ??

 i'm assuming you do this to allow cheap single polarity wall warts - but it is definitely a compromise

 accepting the splitters, it looks to me as if you are proposing shorting at least 2 of 3 tle2426 directly to each other - care to clarify these ground connections and show how to prevent this when the common ground of the external signal source is connected?


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## morsel

00940: Balanced operation, as AMB points out, is not very popular. We discussed this during the PPA design phase and concluded that if you want true balanced operation you can use only the left and right channels of 2 boards.

 With regards to the layout, I will try to align all the MOSFETs if possible, with the input circuit on one side and the capacitors on the other side. This would allow for one big bar bolted to all of the MOSFETs, but would not be conduicive to bolting them to the case wall. The Aavid extrusions require about 1.5 inches of linear space, that's 9 inches for all 6 if they are lined up. It may be that we will either have to sacrifice the Aavid extrusions, or rotate them 90° to reduce the length of the footprint.

 Sovkiller: Team M³ is designing the M³ with DIYer input and arranging for board manufacture when the time comes, as a community service.

 Earwax: As you say, crossfeed is best left to daughterboards. As Tangent hinted, we will probably include PPA compatible daughterboard holes.

 Aos: OK, relatively wimpy by comparison, then. 
	

	
	
		
		

		
		
	


	




 I don't want to consider any output device less than 1 Amp. May I ask if you have tried the IRFZ24N and IRF9Z34N MOSFETs? We tried the Renesas MOSFETs (if I remember correctly) and didn't find them superior.

 Regarding the non-standard FETs, I knew that would come up. 
	

	
	
		
		

		
		
	


	




 That capacitance multiplier might not be used. It has yet to face close scrutiny by Team M³. To answer more directly, the 2N5457 and 2N5460 have a low, consistent Idss of about 1mA which makes them convenient for this purpose. I was just suggesting to AMB recently that people would not be happy about this and that we could use other FETs or at least use the N channel on both rails by turning it 180° in place of the P channel FET.

 MOSFET bias is adjustable, with 80mA being the minimum we are considering for now. Once prototyping and testing has proceeded to a more advanced stage, we will study distortion .vs. bias to determine the optimum value.

 JCX: We said *no compromises for battery compatibility*, which to me means compromises like low quiescent current, class AB output, keeping the amp to a portable size, etc. The power supply is still very open ended. That is one of the issues we intend to discuss. I would get into more detail right now, but I am late for a movie. I'll be back in a few hours.

 Oh, and Jamont, going back to the eurocard format issue, perhaps that is best left to PPA v2. No, there is no info on PPA v2 at this time.


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## jamont

Quote:


  Originally Posted by *morsel* 
_Oh, and Jamont, going back to the eurocard format issue, perhaps that is best left to PPA v2. No, there is no info on PPA v2 at this time._

 

Oh, dear. I gots to know...


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## Nisbeth

Quote:


  Originally Posted by *morsel* 
_PPA v2._

 

Ugh, did you have to say that 
	

	
	
		
		

		
		
	


	




 Now we'll all be waiting for that as well 
	

	
	
		
		

		
		
	


	





 /U.


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## morsel

JCX: Regarding power issues, we could do it just like the PPA with 3 TLEs, or with a single supply for all 3 channels separate from the output rails, or one supply for everything. We could use capacitance multipliers, or voltage regulators, or FET isolation. There are many options. We are waiting for some FETs to arrive from Mouser so we can do more testing. This includes testing the performance difference between 2 and 3 channel operation. I would like to cut out anything that does not significantly contribute to amp performance, to keep the price reasonable while still providing excellent quality. As for using rail splitters, I like them. They are only being used to supply the opamps, which have miniscule power requirements. We will keep you posted on the results of our power supply tests.


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## drewd

Quote:


  Originally Posted by *morsel* 
_Hey Tangent, are you listening to this? We found someone besides Kurt who wants so8 pads. Glassman, where were you when we were working on PPA v1.1? 
	

	
	
		
		

		
			



_

 

Count mine as a vote for SO8 pads as well! The way that it's set up on the PIMETA is great - a choice between DIP or SO8. Very flexible.

 -Drew


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## ppl

thay are complementry j-fets 2N5457 and 2N5460 and are available everywhare
http://www.onsemi.com/pub/Collateral/2N5457-D.PDF
http://www.onsemi.com/pub/Collateral/2N5460-D.PDF

 You can also use the 2Sk170 and 2Sj74 J-Fets from Toshiba
http://www.ampslab.com/PDF/2sk170.pdf
http://www.ampslab.com/PDF/2sj74.pdf
 Thanks to amplabs for hosting these and other data sheets
http://www.ampslab.com/


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## morsel

PPL, you are right, they are readily available, what aos and I meant is that they are nonstandard in the sense that everyone has been using 2N5484, 2N5486, and 2N4392 FETs. By specifying yet another kind of FET, it forces people to order and stock more parts. There is some nuisance factor involved. I'm sure some people would be happier if we used the "same old" FETs as before.


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## aos

Nah, FETs are cheap. And if they are available from Digikey, it's a non-issue. I was just wondering why, since when you experiment you tend to pull something out of your drawers and go shopping only if you absolutely need to (or you're depressed).


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## ppl

Quote:


  Originally Posted by *aos* 
_Nah, FETs are cheap. And if they are available from Digikey, it's a non-issue. I was just wondering why, since when you experiment you tend to pull something out of your drawers and go shopping only if you absolutely need to (or you're depressed)._

 

LOL since im depressed dose this imply if i go shopping ill feel better never thought of that one


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## Sovkiller

Quote:


  Originally Posted by *Earwax* 
_Is a crossfeed a good use of board space? Which circuit would be used? I like the Meier crossfeed best, but maybe someone else wants a Linkwitz or something else. Overall, wouldn't a daughteboard approach for crossfeed be better? 

 Any opamp at all, including Bipolar types (LM6171)?_

 

I have tried the Meier one, and it is absolutelly stunning, after two weeks of using it, there is no way I could remove it from the system. I like it so much to the point of opening it and replace all the internal wiring by silver solid wire....
 I know that many people do not like it and others never had tried it, for the ones who have not tried it, my advice is, go for one and try it.......
 The problem with doughter boards is that they need a lot of additional wire in the signal path, if you include it at the input near the jack in the circuit you minimize this, you can even use a few levels of crossfeed with bass and highs compensation similar to the Corda Cross-1...


----------



## Sovkiller

Quote:


  Originally Posted by *aos* 
_Also, you can't use Meier's circuit without permission. You can add it on your own amp if you wish but I don't think it could be included on board as default.
 That's why a daughterboard (or another kind of allowance for crossfeed)
 is a good approach to adding crossfeed.
_

 

Meier circuit is of the public domain, it is on the Headwize projects section, and for DIY use, since a long time ago, and this amp *will be for DIY*, not for commercial use. I don't think that Jan will have any objection, that someone use his project, and circuit (or part of it), in a completely personal DIY project.
 But of course, there will be, as usual, some of the DIYFSE that will begin to make them for others, and get some profits, out of it, (this is always a consequence of the free projects, and in fact some of us that really wants them do not have the tools and knowledge to do it for ourselves) But even though not everybody is so reserved with his intellectual property. Of course if some of those DIYFSE are going to use his, it will be very polite to contact him first, just to be sure he won't mind. 

 As for the impedance issues, I don't know how he implement his in his amps then, maybe some kind of compensation or the like, but it works with any source on his amps, for sure.....
 Anyway any other circuit that works will fit as well, I'm just suggesting the one I have tried, and liked....


----------



## DCameronMauch

Add me to the SO8 statistical poll.

 Does the design take into account that the ground channel buffers will be sourcing/sinking twice as much current as the drive channels? And thus will require twice as much heatsinking.

 If power consumption is of no concern, why not use single ended pure class A output stages. Like the Nelson Pass DIY amps. Two N-type mosfets, the bottom as a constant current source. Should be more linear.

 What do you need the 10ohm output resistors for? My understanding is they are useful in bipolar output stages with multiple transistor pairs to keep any single one from running away. But mosfets have a negative temperature coefficient so that doesn't happen. Plus there is only one pair.


----------



## morsel

Cameron: The MOSFETs are going to dissipate about 1W assuming 12V × 80mA. This is no problem for the Aavid extrusions. Most of the power is due to bias, so the ground channel will not be double the signal channels. As for the Nelson Pass amps, aren't they capacitively coupled? Not my personal preference, although he does great work.

 You are free to reduce the value of your source resistors, or remove them if you dare, but AMB feels they need to be 10 Ohms to adequately balance the differences between the N and P channel MOSFETs and limit the maximum output current. I originally wanted to go with 1 or 2 Ohms. Perhaps AMB will say a few words on this subject.


----------



## DCameronMauch

I figured the biasing would be closer to the expected maximum load current. I usually go 2x to be on the safe side. But if you are going for a larger fixed bias current for everything, that should work okay. With any given bias current, I would still check to make sure the ground buffer isn't switching to class B or doing anything else weird. Just to be sure.

 The Nelson Pass amplifiers usually do have a DC offset at the output. But since the output stage would be inside the feedback loop, the opamp will take care of that. No need to worry about current limiting with resistors either. The lower mosfet current source is your limit but without adding to the utput resistance. Also why would you want to current limit anyways? There have been many instances where it was noted that buffers without current limiting sound better.

 Attached is a butt basic no-gain example schematic:


----------



## PeterR

http://www5.head-fi.org/forums/showp...0&postcount=50


----------



## morsel

Peter, thanks for that link. The entire thread is worth reading:
DC Coupled Szekeres Power Supply l7815 and lm317

  Quote:


 There have been many instances where it was noted that buffers without current limiting sound better. 
 

Cameron, in principle, I agree. The Hafler DH-200 power amp (circa 1980) does not use source resistors. I am theoretically in favor of lower or no source resistors, however AMB is the supergenius among us and he has his reasons, so I'll let him answer.


----------



## aos

OT:

  Quote:


 LOL since im depressed dose this imply if i go shopping ill feel better never thought of that one 
 

I'm dead serious here. Shopping helps a LOT when you're depressed. I thought it's well known. Shopping as in go-look-buy, not online because it's a time-delayed thing. It's even logical, you go and see stuff, get excited, buy it, run home and play/fiddle with it, changes your mood easily. It's also a form of addiction unfortunately so if you can't control your shopping implulses you'll end up with house full of gadgets and no money.

 OnT: I'm going to place an order with Mouser so I'll get a few of these parts. Eventually they'll come in handy 
	

	
	
		
		

		
		
	


	




.

 Meyer circuit is NOT in the public domain, except for your own personal use. The fact that these boards WILL be used by some for DIYFSE eliminates it from being on the default board - or eliminates possibility of DIYFSE of the boards, whichever. I'm sure Jan would object (because he mentioned that in the past) and he has every right to. If I were to include his crossfeed I'd personally be willing to pay royalties, as would be only fair. I've tried several crossfeeds over the years and Meier crossfeed was the only one that
 gave me the desired effects and made me want to use it myself.


----------



## Sovkiller

Quote:


  Originally Posted by *aos* 
_Meyer circuit is NOT in the public domain, except for your own personal use. The fact that these boards WILL be used by some for DIYFSE eliminates it from being on the default board - or eliminates possibility of DIYFSE of the boards, whichever. I'm sure Jan would object (because he mentioned that in the past) and he has every right to. If I were to include his crossfeed I'd personally be willing to pay royalties, as would be only fair. I've tried several crossfeeds over the years and Meier crossfeed was the only one that
 gave me the desired effects and made me want to use it myself._

 

There was a long discussion on what is, or not, allowed to be used, and registered, and copyright ownership in the past (IIRC was in that same thread in which Jan complained about one member using one of their same crossfeed circuits) so I will not go into that again.
 IIRC there was enough posting regarding that, from even a person that use to work in a field related to the patents registration, etc....but anyway, this will cause some problems as you wisely stated in the case of the DIYFSE part of the project that we will be sorry of that, we as customers, need that and some others as manufacturers also....here is part of that discussion....anyway, nevermind....


  Quote:


 ".......Jan can copyright the article text as well as any images, PCB layouts, and schematic diagrams, but he cannot copyright the circuit design itself. Here is the US Copyright Office's description of what can and cannot be copyrighted:
http://www.copyright.gov/circs/circ1.html#wnp
 In other words, the disclaimer text at Headwize does not prevent others from selling copies of Jan's design, as long as they make their own PCB layout (as appears to have happened here).

 Copyright simply doesn't protect device designs. The only forms of intellectual property that protect device designs are patents and trade secrets. He obviously gave up trade secret protection by publishing it online........etc....." 
 

Just for the records, I have one of his Corda Cross-1, and made by him, so even if they won't include it, I will have it anyway.....I don't care if it will be part or not of the circuit, but I would like others to have it as well, as I'm extremelly pleased with it....


----------



## morsel

Sovkiller, I already warned you in private email about derailing this thread. I am now taking moderator advice and putting you on my permanent IGNORE list, something I have never done before to anyone. Do not post here again. No posts referencing Sovkiller will be responded to.


----------



## ppl

Morsel wht is your issue with Sovekiller and might i ask how he is derailing this thred.


----------



## aos

Well, even if you could legally build it based on his circuit, I don't think it'd be right to do so. Anyhow, I can't tell others what to do, I just know what I'll do.
 I can only recommend allowing for a crossfeed daughterboard mount. People
 using crossfeed are minority anyway so it's just an inconvenience. You can
 always build it on a protoboard, it's simple enough, and just add it to the amp in that form.

 Also, even if it's "legal", you might run afoul of Head-Fi policies. Head-Fi
 policies are much stricter than the law and as Jan is one of main sponsors 
 if he complained I'm sure this thread wo go poof (if it contained crossfeed). I'm actually quite surprised this thread was not brought on Headwize, as Morsel herself stated during ppa development days that she will do so because a lot of people protested due to percieved "commercial" status of PPA. Also, there'd be less "noise" on the thread. Though right now I'm probably making some myself.

 By the way, MOSFET should be biased to the most linear region, and it should be more than the load will ever need to use. cameron made a good point 
 that ground channel might need to sink 2x.

 10 Ohm might indeed be a bit much. I say experiment.


----------



## aos

Oh yeah, MOSFETs, as I recall it was tough to find actual complementary pair. I recall looking at IRF at that time and even those few they claimed were complementary, were in fact quite apart. Of course N and P devices differ and can never have exactly same parameters (due to difference in electron and hole mobility mostly, I think) but I recall Toshibas were much better matched. Just a thought, if you're going to go with IRF, it may be worthwhile to comb their offering and see if they have matched complementary pairs - I checked the datasheet and haven't seen them actually mentioning that these two you
 specified are complementary. As their intention is to sell these for switching, they might not bother offering complementary pairs though.


----------



## amb

I know there are fans of single-ended fans out there, but I am not too keen on such a topology, just a personal preference. To me there is an elegance with push-pull. Going single-ended means either a rather large, hot running resistor (yuck), or a constant current source of some sort. The quoted article used a LM317 voltage regulator for that, and if I were to be forced to go single-ended I would instead find a MOSFET solution (a la the Borbely headphone amp), but that would require more parts. Ultimately it comes down to preference, but so far I am not convinced that there is any advantage with single-ended, measurably or sonically.

 The source resistors are there as a form of local feedback (the MOSFETs are themselves operating as simple source followers) to equalize the matching between the N and P channel devices. Without them you'd need to hand-select and match the MOSFETs from a big handful on a curve tracer, and even then it won't be too close. Better matching means lower distortion. They also happen to be very convenient for setting the quiescent current, because you just measure the voltage drop and turn the Vbe multiplier pot. 10 ohms is a good value because you could read the voltage and translate that into mA in your head without a calculator. The resistors are within the global feedback loop, so they do not contribute significantly to the output impedance. In fact, I measured an actual output impedance of less than 0.1 ohm.

 -Ti


----------



## aos

That's true, how else would you measure the bias? And matching transistors as well. You need resistors, and 10Ohm is a nice round value but there's nothing stopping the builder from going a bit lower, say 4.7Ohm.

 I'm sure you'd find a lot of buyers for matched MOSFETs if you have the ability to match them on a curve tracer 
	

	
	
		
		

		
			





.


----------



## Sovkiller

Quote:


  Originally Posted by *ppl* 
_Morsel wht is your issue with Sovekiller and might i ask how he is derailing this thred._

 

"You are with me, or against me" kind of an attitude right? Simple as that.....not a very polite attitude, for a very good professional and talented person, as her....but every single person is a separate world, modesty is a virtue not everybody have.....


----------



## Sovkiller

Quote:


  Originally Posted by *aos* 
_Well, even if you could legally build it based on his circuit, I don't think it'd be right to do so. Anyhow, I can't tell others what to do, I just know what I'll do.
 I can only recommend allowing for a crossfeed daughterboard mount. People using crossfeed are minority anyway so it's just an inconvenience. You can
 always build it on a protoboard, it's simple enough, and just add it to the amp in that form.

 Also, even if it's "legal", you might run afoul of Head-Fi policies. Head-Fi policies are much stricter than the law and as Jan is one of main sponsors if he complained I'm sure this thread wo go poof (if it contained crossfeed). _

 

Please AOS do not misunderstood me, I'm not suggesting the use of such device against Jans willingness.....even when maybe it is legal, this won't be ethical, in my book neither, and I won't do it neither, but it will be a nice addition indeed, even when now I know that this is not a posibility to consider given some attitudes 
	

	
	
		
		

		
		
	


	










 End of the "Crossfeed" chapter, for me at least......


----------



## morsel

Aos: amb put a lot of effort into studying the IRF catalog. I did the same and called IRF tech support for additional advice and confirmation before we chose the IRFZ24N and IRF9Z34N. They are not officially designated as complimentary pairs, but we feel confident about our selection.

 The source resistors are in the negative feedback loop, which makes the apparent output impedance really low, but it does not change the fact that the impedance before feedback is higher than it would be with smaller source resistors. Low output impedance before feedback correlates to good bass with low impedance headphones. I believe it is important to have the lowest possible distortion and output impedance before feedback. Unfortunately, as amb points out, lowering the source resistors may increase distortion before feedback.

 We will test the output stage in open loop configuration (without feedback) using source resistors from 10 to 0 Ohms and let you know how it goes.


----------



## aos

Quote:


 Aos: amb put a lot of effort into studying the IRF catalog. I did the same and called IRF tech support for additional advice and confirmation before we chose the IRFZ24N and IRF9Z34N. They are not officially designated as complimentary pairs, but we feel confident about our selection. 
 

If you did the research already, then all is well.


----------



## DCameronMauch

AMB: I am totally following you about the resistors as local feedback. I had forgotten about that. Makes a lot of sense. Decreasing the value also decreasing the "matching" effect. And you are right, they should have minimal on the final output impedance. The mosfets are also inside the feedback loop, so the opamp should "linearize" them. But opamps, like everything else, are imperfect. It is always best to make the output stage as linear as possible, to make the opamp's job that much easier.

 Now the single ended topology does not need any device matching. There is only one transistor driving. So there is that advantage. Free to test mosfets without matching p-type. The bias current should be similar, since this design looks to be keeping the push-pull topology class A mode all the time. Come to think of it, the single ended topology is essentially what you get when you use a current source to the negative rail with opamps. I have had the most linear results from IRF with the IRLIZ24N. 2nd and 3rd harmonics are about 4dB lower than the IRFZ24N before going into a feedback loop. But I don't think there is any matching p-type mosfet.

 Attached is the same schematic with the current source expanded. Just to show a possible implementation. And that parts count can still be quite low. One power resistor, two small resistors, and one TL431. Not bad.


----------



## morsel

Cameron: Thanks for the nice drawings. It's tempting, but don't we lose part of our supply voltage range across the current source MOSFET this way?


----------



## morsel

One output stage, both inline and folded. Oops, I just realized the MOSFETs have to be on the same side of the heat sink to make the inline folks happy. 
	

	
	
		
		

		
		
	


	




 Not that it matters, as the linear space wasted with the inline configuration seems prohibitive. The smallest PAR-Metals case is 12×8×2" which is not tall enough for 2" heat sinks. It also comes in 12×8×3". 8" is not enough depth for 3×3" long channels side by side. Rotating the board 90° means the input stage is at the back of the case, not along the side, which means the volume control leads have to run back and forth or the pot must be rear mounted with a shaft extension, whereas if the input stage is along the side, the volume leads can be shorter.


----------



## amb

DCameronMauch, thanks for the schematic. That is roughly how I would do it if I were to go single ended as well. However, there is another consideration that makes push-pull attractive to me, is the fact that push-pull is twice as efficient as a current-sourced single-ended topology in a class A stage. This is an important practical concern that cannot be overlooked for an amp that is intended to be built by many people.

 Nelson Pass describes this well in his class A 40W power amp design paper:

http://www.passdiy.com/pdf/a40.pdf

 Although this is less of a problem with headphone amps than it is with speaker amps, still we are constrained by the amount of heat sinking, ventilation, and power supply dissipation too (assuming the use of voltage regulators on the output devices, which I'd like to do). All this also directly correlate with size and cost as well.

 -Ti


----------



## aos

morsel, you're correct, you lose part of the available voltage swing on the current source (or the resistor which is a simpler version). That's actually where the loss of efficiency occurs - a lot of power is dissipated on the resistor (or current source).


----------



## DCameronMauch

Morsel: Yes, there is a DC offset at the opamp output, thus limiting your voltage swing. But the schematic you showed has the same problem. The opamp is connected to the top of the biasing circuitry. Which has to be a few volts above ground to start conduction. To avoid the problem, it would have to be connected to the middle. Of course the bias circuitry would have to be different, since this one doesn't really have a middle. I believe the original Sheldon Stokes article mention this. In a design I am playing with, I use balanced outputs, so even with the higher voltage requirements of Senn's, +-12Vdc rails is more than enough.

 AMB: Yeah, single ended is definitely not very efficient. But I thought the project statement indicated that there was no concern for power supply requirements. Also the target enclosure should have more than enough room. PCB area could be reduced by mounting the power mosfets horizontally off the end of the board. I am not sure if project cost would really be impacted that much. Another way to decrease heat dissipation is to change the bias current AND the voltage rails to match the intended load. For example, Grado's need more current and less voltage versus Senn's. But the overall power requirements of both headphones are roughly the same. Just some food for thought...


----------



## morsel

Aos: Yeah, that is an unacceptable sacrifice, given that some of us have 600 Ohm phones, and we are already losing a fair bit to bias voltage. I for one would like to stick with AD8610 opamps, despite their 24V supply limit. PPL suggested a nifty opamp bootstrapping circuit which creates a sliding voltage window to power the opamps controlled by the output voltage, but that adds quite a bit of complexity.

 Cameron: I thought our scheme only loses 1/2 of the total bias, or 4V. If we bias in the middle of the gates, I'm not sure how we would bias the opamp into Class A at the same time. We abandoned that idea a while back, but we could reconsider it.

 Amb: I don't think we care much about efficiency.


----------



## amb

The project statement says that we do not make concessions for battery compatibility since this is an AC only design (and indeed it would be impractical to run a class-A amp on battery). However efficiency is still a consideration given that it directly impacts the amount of heat we have to manage. I am comfortable with dissipating one or two watts on those Aavid/Thermalloy heatsinks we picked, but not much more. This is based on my own experience, having built the prototypes as well as a modified SDS Labs MOSFET amp using the same heatsinks. I don't want the sinks to get burning hot 
	

	
	
		
		

		
			





 .

 On the topic of max output swing, even with the fact that the op amp's output is biased a few volts above 0, we should still be able to achieve 15Vp-p swing with +/-12V rails with the "good" opamps. IMHO that is quite enough to drive most hi-Z phones to a _very_ high volume.

 -Ti


----------



## morsel

Hopefully we can do closer to 20Vpp.

 I realize that anything left behind on the previous page is swiftly forgotten, but do members of the inline heat sink camp have anything to say regarding post 73?


----------



## Wodgy

Are in-line heat sinks really practical for most DIYers? Is there a source that sells them for a reasonable price independent of a case? Also, at relatively high levels of heat dissipation, what about thermal crosstalk?


----------



## DCameronMauch

Morsel: The schematic I showed sits at 2.4Vdc above ground at the opamp output with the IRLIZ24N. Or 3.8Vdc for the IRFZ24N. For the push-pull, you could use two variable voltage drop transistors instead of the one. And connect the opamp between them. Even at the max +-13.2Vdc rails for the AD8610s, there is no way you could get 20Vpp with that 4Vdc offset.

 AMB: One or two watts per mosfet is all a single ended topology would need. My latest design sits at 1.2W (12Vdc rails at 100mA for HD650s as target load). The IRLIZ24N has a junction to case thermal resistance of 5.8C/W. So, to keep with the Nelson Pass 50C max temp guideline, a heatsink with a thermal resistance of roughly 15C/W should do it. Here is the one I have been using. Even made a sweet Eagle library for this part if anyone is interested.


----------



## amb

Quote:


  Originally Posted by *Wodgy* 
_what about thermal crosstalk?_

 

The temperature isn't going to change once it stabilizes in a class A amp, so thermal crosstalk is not going to be an issue at all. Moreover, the only things that are going to heat up are the MOSFETs and the voltage regulators, not the op amps or other items. We are also going to be using single op amps rather than duals, so there is no "dynamic" thermal crosstalk problem there either.

 The voltage swing issue is something Morsel and I had already discussed at length offline. It boils down to basically this, if you want lots of voltage swing, then you need either higher supply rails or a balanced output topology. As I said IMO what we have is perfectly adequete for most headphones unless you want to damage your hearing. We have listened to this setup with Morsel's 600 ohm (?) Beyer DT-990s and we had no trouble getting loud, very loud.

 Oh, and just to put things in perspective, the difference between 15Vp-p and 20Vp-p is only 2.5dB. Not really night and day...

 For those small fraction of people out there who wants even more SPLs, or those that don't mind a much more complex "cost no object" uber deluxe amp, I have a fully discrete MOSFET amp in the works for the future that will surely address all those concerns. However the M³ as it is (power supply, heat sinking, PCB layout, casing and other topics notwithstanding) should still be an excellent performer for most dynamic phones.

 -Ti


----------



## peranders

Morsel, isn't it wiser to have a mosfet as a temp sensing element? With a mosfet you will get a more stable bias. If a BJT is used you will get a heavy bias peak until the amp has stabilized. I noticed that myself in my QRV-01 monster. With a BS170 (in my case) I got a very good stable bias with my IRFD120/9120.


----------



## sijosae

I think, it is meaningful approach to consider a ground channel as a viewpoint of power supply rather than that of additional amplifer channel.
 Here is my idea of virtual ground power supply with two ground outputs.
 If we build this kind of power supply, we can enjoy PI-Amps (PPA Inspired headphone Amps) with almost all existing 2-channel headphone amplifer. 
	

	
	
		
		

		
		
	


	




http://www.headphoneamp.co.kr/bbs/vi...sijosae&no=181


----------



## morsel

Cameron: I like your heat sink choice. There are many other heat sinks available. I am not firmly committed to the Aavid 531202. Choosing a less obtrusive profile would open up other layout possibilities.

 Peranders: I can't imagine us using temperature sensing as it does not fit the KISS philosophy. Once the amp warms up it should be pretty stable.

 Sijosae: I think we want to use the same topology for all 3 channels. We will test M³ in 2 and 3 channel mode.

 To input the "³" character, hold down the Alt key and type 0179 on the alternate keypad (Windows), or copy it from Character Map (Windows) or the title of this thread.


----------



## peranders

Quote:


  Originally Posted by *morsel* 
_Peranders: I can't imagine us using temperature sensing as it does not fit the KISS philosophy. Once the amp warms up it should be pretty stable._

 

Ok, but since you already have the transistor... and isn't it a bit "engineering science" to have constant bias regardless if the amp is in a cold garage or in a hot listening room?


----------



## Nisbeth

Quote:


  Originally Posted by *morsel* 
_Cameron: I like your heat sink choice. There are many other heat sinks available. I am not firmly committed to the Aavid 531202. Choosing a less obtrusive profile would open up other layout possibilities._

 

Morsel, how much heat sinking is actually required (or, how much dissipated power do you expect per device)?


 /U.


----------



## morsel

Peranders, perhaps you could explain exactly what it is you are proposing and post a user friendly gif to go with it.

 Nisbeth, 1-2 Watts, typically.


----------



## DCameronMauch

I really don't see the bias current drifting slightly do to thermal variations as any kind of a problem. I have not tested the one shown with the push-pull topology. But the one I showed, the bias is set exclusively by the 25 ohm power resistor. If you get one with very low PPM and oversized to take the power dissipation easily, any drift due to ambient temperature should be very small. Also the rate of change is SO slow that there is no chance for interaction with anything in the audio band. Now, if the bias current was super critical for some reason, absolutely, a current sensing resistor would be almost mandatory.


----------



## aos

peranders, what are you talking about? Your schematics show BD139 used as VBE multiplier to bias the mosfets, not the BS170! Besides BS170 is a TO-92 device, the only way to thermally couple it would be to glue it to the 
 heatsink which is a hack.

 That amp of yours is truly a monster though.


----------



## amb

I think peranders is proposing to use a MOSFET for the Vbe multiplier and put that on the heat sink with the output MOSFETs. This provides a thermal feedback loop.

 This sort of technique is common practice with class-AB power amplifiers to prevent thermal runaway, due to the positive thermal coefficient of BJT devices (quiescent current creeps up with increasing temperature).

 Doing thermal sensing limits heat sink choices, because all three devices (both output transistors and the Vbe multiplier) must be mounted to a common heat sink to be meaningful. It also complicates PCB layout for the same reason, and we want to avoid the need to run wires from the board to the sink-mounted Vbe multiplier transistor.

 In practice this is not necessary because bias drift is not an issue with this amp at all. The negative thermal coefficient of the MOSFETs will self-regulate the bias very nicely. This is one of the major advantages of MOSFETs. There is a period of time after cold turn-on where the quiescent current goes higher than the desired target idle value, but that actually makes for quicker warm-up times. Once warmed up, the quiescent current is rock steady. This, and the fact that MOSFETs have no secondary breakdown and SOA (safe operating area) concerns is why pro-audio amps nowadays are almost exclusively MOSFET designs.

 -Ti


----------



## amb

On the subject of how much power dissipation, here is the basic rundown. With our push-pull class A topology, we want to run at least as much quiescent current through the output MOSFETs as one half the maximum output current. In fact, we want a bit more than that, to allow for headphone transducer reactance, etc.

 So, for a 32 ohm load, if we want to achieve, say, 6Vp-p (3V average) without dropping out of class A, then that's 3V / 32 ohms = 94mA. One half of that is ~50mA. Give it a healthy bit of extra margin and let's say we run at 80mA, with +/-12V rails, then each output MOSFET will dissipate 12V * 0.08A = ~1W. This is for the left and right channels. Since the ground channel has to potentially sink or source twice the current return (such as in the case of a mono signal), then the ground channel should be biased to twice that amount. If you want to get even higher output swings into 32 ohm load or if you want to run even lower load impedances with the same voltage swing, then the quiescent current must be increased or you drop out of class A at high volumes.

 For single-ended class A topology, the quiescent current (and therefore the power dissipation) must be doubled from the above calculation. This would be the case with the circuit using a current source at the output.

 For high-Z phones, the situation is much easier since we're talking about mostly voltage swing and not much current output. So whatever bias we set to optimize for low impedance will work well with higher impedances.

 -Ti


----------



## aos

Yes, I'm quite aware of the BJT thermal runoff and the advantage of mosfet's in that regard. My post was to note that while peranders said he wanted to use MOSFET in Vbe multiplier like in his monster amp, the schematics he provided doesn't actually use one. And the one he mentioned is not in a case that allows installation on a heatsink (unless there's a different version of BS170). Unless I managed to misinterpret his schematics.


----------



## ppl

if driving Headphones that require large voltage swings you might consider Bootstraping the op amp.
http://www.reed-electronics.com/ednm...ages/45890.pdf

 Also discribed in the below artical is the Classic David White Mosfet power amp in addition to the Authors own circuitry.
http://wiredworld.tripod.com/tronics/mosfet_amp.html


----------



## morsel

PPL: Thanks for the links. We did discuss opamp bootstrapping recently. It adds a lot of complexity. If it came to it I'd settle for using a 36V opamp instead.


----------



## xtreme4099

itd be nice to have an all blackgated version of this amp, with silver wire throughout, and a labpower to see how it compares to my amp, i love the ubercaps, aos can attest to the fact the high quality caps can make a difference, he's heard my amp, but ive changed it since then, morsel, are the lead holes, as big as the ppa or bigger, it would be nice to add super giant caps to this.


----------



## aos

Caps make a difference but your lab power supply (by ppl) likely made the lion share of the difference. Only now a lot of DIYers are realizing the importance of a good PS.


----------



## xtreme4099

even so, good clean power is hard to get right, ive bought my quail cables from that group buy thread and they sure made a difference, more natural, focused highs and mids, very clean sounding, i wasnt originally a power cable guy but i kept an open mind, and sure enough it made a difference, clean power is underrated by diyer's it seems. Silver wire all the way. Wooh00


----------



## morsel

As you know, I think Black Gates and silver wire are a waste of money. I will not take heroic measures to make giant caps fit, but I believe there will be room for bigger caps on the M³ than are on the PPA.


----------



## xtreme4099

Quote:


  Originally Posted by *morsel* 
_As you know, I think Black Gates and silver wire are a waste of money. I will not take heroic measures to make giant caps fit, but I believe there will be room for bigger caps on the M³ than are on the PPA._

 

i do think there is a difference in tonal qualities between caps, ones that accent more detail versus smoothness, caps of bigger values do affect the overall sound, e.g. the big caps on my diamond buffer. Silver wire is known to be a better conductor than copper, i dont think im alone in saying that adding silver to the ppa has improved the sound for the better, clearer highs, deeper bass, biggersoundstage, some other ppa diy builders can chime in and attest to this as well, ratshack parts will only take you so far, come on morsel, experiment a little, if not for the fun of it, what else is there?


----------



## amb

No capacitors in the signal path is even better than an expensive capacitor... In the M³ the input, output and global feedback are all DC coupled. The only capacitors in the design are for HF compensation, the Vbe multiplier bypass cap, and power supply reservoir and decoupling caps.

 The Vbe multiplier bypass cap is the only capacitor in our circuit that might warrant the use of something fancy. We specify a WIMA 1uF film capacitor for this purpose, which should be more than good enough.

 Costly "audio grade" capacitors are good if a coupling capacitor must be used in the signal path, and it has been clearly demonstrated that the use of inappropriate types add distortion and smear up the sound. In the M³, we should not have that problem at all. Power supply capacitors are a whole different matter. I am not convinced that the spendy Black Gates are going to make any difference as a reservoir cap over the "standard issue" Nichicons, Elnas or Panasonics. For rail decoupling it is important to use a cap with good HF performance, such as a good film cap or NP0 multilayer ceramic. That's all that matters.

 Of course, if you want to spend a lot of money and use Black Gates and such in the power supply, be my guest... it gives you bragging rights when you open the cover 
	

	
	
		
		

		
			





 .

 -Ti


----------



## digi01

amb,
 have you considered add zobels on the output?just like common 2 ch solid based amp doing.


----------



## amb

Quote:


  Originally Posted by *digi01* 
_have you considered add zobels on the output?just like common 2 ch solid based amp doing._

 

I haven't seen too many headphone amps with a Zobel. In a speaker amp that is more common due to the types of load. Do you have any reason to believe that a Zobel is desirable in a headphone amp?

 -Ti


----------



## digi01

thank you amb.


----------



## peranders

Quote:


  Originally Posted by *morsel* 
_Peranders, perhaps you could explain exactly what it is you are proposing and post a user friendly gif to go with it._

 

You could do something like this:
http://home5.swipnet.se/~w-50674/hif...0_bias_bjt.jpg
http://home5.swipnet.se/~w-50674/hif...ias_mosfet.jpg

 Check the "double" transistor at the heatsink.
http://home5.swipnet.se/~w-50674/hif...2_overview.jpg


----------



## jcx

i don't understamd mosfets for this app, particularly ones rated at 100X current

 but you should really reconsider the assumption that mosfets have a self-stabilizing positive (Vth, Rds) tempco before getting rid of the source resistors - just look at the IRFZ24 data sheet fig 1&2, the 4.5 Vgs curve shows a positive Ids tempco in the linear region, this is because Vth has negative tempco, only at high currents or near saturation does the positive Rds tempco dominate in vertical mosfets


----------



## DCameronMauch

digi01: I believe zobel networks help the amplifier deal with complex load impedances and back emf. Since headphones don't usually have crossovers, the load impedance is not that complex. And back emf is relatively small.

 jcx: Current rating is not that important, so long as it is more than enough. Voltage rating and power dissipation are of primary concern. Hum. Interesting. It looks there are some conditions where the tempco for mosfets is positive after all. News to me. Still, with a push-pull single n/p pair topology, there is no real danger of runaway. Bias current may drift a little, but that is not a big worry here either. That said, I don't think source resistance is a bad thing. Might be wise to take the better safe than sorry approach.


----------



## Nisbeth

Quote:


  Originally Posted by *DCameronMauch* 
_digi01: I believe zobel networks help the amplifier deal with complex load impedances and back emf. Since headphones don't usually have crossovers, the load impedance is not that complex. And back emf is relatively small._

 

Actually, I believe the purpose of the Zobel is to keep the amp from oscillating if the load is capacitive. Either way, it shouldn't be necessary here.


 /U.


----------



## morsel

Let's talk cases and board size. Are people happy with the 12×8×3" PAR-Metals 20 Series case? Can anyone envision wanting a larger case than that? The board could be up to 6×8" and still only take 1/2 the case, leaving the other 1/2 for the power supply, separated by an internal metal plate. I think the PAR-Metals might be a wee bit too big, but that is the smallest size listed. Does anyone have a superior case suggestion? For those on a budget, a smaller economy case could be used, along with a separately boxed STEPS or ~500mA wall wart. Probably the nicest case work I have seen is that done by Larry of LaRocco Audio. Perhaps he would be interested in making cases for us. Finally, there is Front Panel Express for designing custom panels, but they do not make cases as far as I know.


----------



## Super-Gonzo

Quote:


  Originally Posted by *morsel* 
_I think the PAR-Metals might be a wee bit too big, but that is the smallest size listed._

 

Par-Metals does custom sized enclosures, if several were purchased at once, perhaps we could get a smaller spec'd 20 series case for a reasonable price?

 Also, I think it would be a good idea leave enough room inside the enclosure for a stereo ladder attenuator, and maybe a rotary input switch.


----------



## Voodoochile

I like the Par chassis well enough. It is fairly important to request anodizing though, as their paintwork is not good at all. Also, request that they countersink the screws, or you get round-head by default.

 Backing up a little bit, I had mentioned wanting pads for the Dact attenuator within Alps Blue pads. If it is practical, I'd like to see the pads at the rear of the board, or perhaps front and rear (as the input pads on the PPA are).

 Since this will not be built in the Hammond cases, having the pot right near the input jacks is ideal (IMO), and the shaft extensions and bearings are easy to work with.

Linky to Handmade. Welborne also has them.


----------



## DCameronMauch

voodoochili: Both excellent recommendations. How much of a premium did you have to pay with Par-Metals for having the entire enclosure anozided and countersunk screws? For the pot, shouldn't it be positioned such that the leads from the pot to the AD8610s are short as possible? To avoid RC lowpass effects. A few inches difference from the audio source to the pot shouldn't make much difference.


----------



## morsel

Gonzo: I was also thinking that custom smaller PAR-Metal cases might be good, as long as we don't have to get into complex group buy issues. We will definitely have room for a stepped attenuator. 

 Elma Type A






 Elma Type R





 Elma Type N





 I prefer the surface mount Type N series attenuator. It is easy to board mount and has a short signal path with good stereo separation.

 VC: AMB and I talked a bit about using a shaft extension, but we were a bit unsure how others would feel about this. How much of a pain is it to install a shaft extension and panel bearing?

 I know about the need to order the case anodized, not painted, but what's this about countersinking the screws, can you give us more detail? I assumed no one keeps the stock screws.

 Are you OK with the 12×8×3" case size?


----------



## Super-Gonzo

Quote:


  Originally Posted by *Voodoochile* 
_Since this will not be built in the Hammond cases, having the pot right near the input jacks is ideal (IMO), and the shaft extensions and bearings are easy to work with._

 

I'm with Voodoo on this one, I like the idea of putting the pot/att. at the back and using a shaft extension. (IF it results in a shorter lead to the opamp.)


----------



## Super-Gonzo

Quote:


  Originally Posted by *morsel* 
_Elma Type N





 I prefer the surface mount Type N series attenuator. It is easy to board mount and has a short signal path with good stereo separation._

 

ooh, the Type N is pretty. And believe it or not, I prefer soldering SMD resistors to the through-hole variety. Is there a ladder version of this attenuator? I didn't see one on the elma site.

 On a related note, what are the thoughts about using SMD components for other amp components? For items where it could shorten signal path and improve performance, perhaps it should be considered?


----------



## Nisbeth

Quote:


  Originally Posted by *morsel* 
_VC: AMB and I talked a bit about using a shaft extension, but we were a bit unsure how others would feel about this. How much of a pain is it to install a shaft extension and panel bearing?_

 

It's not much of a problem really. The extender can be any piece of 1/4" or 6 mm tube or rod (with a tube it's possible to run LED wires inside for an illuminated knob). The hole for the panel bearing is just a bit larger than the thread on an Alps blue (9 mm. vs 8 mm. IIRC) and the flange around the bearings I have used have been quite wide so drilling the hole slightly larger (say 10 or 11 mm.) will give a little slack to aid in allignment if your measuring skills are less than perfect.


 /U.


----------



## Voodoochile

Quote:


  Originally Posted by *morsel* 
_VC: AMB and I talked a bit about using a shaft extension, but we were a bit unsure how others would feel about this. How much of a pain is it to install a shaft extension and panel bearing?

 I know about the need to order the case anodized, not painted, but what's this about countersinking the screws, can you give us more detail? I assumed no one keeps the stock screws.

 Are you OK with the 12×8×3" case size?_

 

The extension is a fairly simple to use, requires only a *little* more insight than a panel-mounted pot. Mainly calculating the height for the hole from the panel base, typically lower than the chassis base due to overhang. A table could be made giving the offset based on 1/8" standoffs under the PCB, 1/4", 3/8", etc. To this you would add the overhang dimension of the panel.

 As for the countersinking, you have to ask Jeannette or John at Par very specifically. They will furnish screws then. And instead of painted zinc screws, they then furnish proper black screws, and stainless for the faceplate. You may opt to not have the faceplate countersunk if you wish to use Allen-style machine heads, or button head screws. Having the entire chassis anodized in black, and the faceplate in silver, with countersunk holes throughout runs about $55 shipped for a 12"x8"x1.75"/2" (1.75 box/2"faceplate). That is also including the fist thickness upgrade on the faceplate, which is well worth it, I think. I believe it is 1/8" thick.

 As for the case size, that's tough. The case I describe above is perfect for a PPA, is almost exclusively what I have used. But it is tight vertically. The next (stock) height is the 3" case you describe. This seems tall to me, at least in the 12"x8" size. I think I would do one of the following:

 Either keep the 3" height, and get the 16"x8" or 16"x12" case to keep proportions nice, or...

 stay with 12"x8", and ask for a custom 2.5 or 2.625" height as a custom job.

 I don't believe they gouge you on price, but you will wait for it. As it is they take about 10 days to 2 weeks for a chassis or two in stock sizes, since they do make them to order, even when 'stock' sizes. I think by stock it just means that they have jigged settings or routing packages saved for these sizes. They don;t actually have them truly 'in stock'.

 They (Par) are very nice people, and the work is pretty good, but it is imperative that you are very explicit with your preferences.


----------



## Nisbeth

Quote:


  Originally Posted by *Super-Gonzo* 
_On a related note, what are the thoughts about using SMD components for other amp components? For items where it could shorten signal path and improve performance, perhaps it should be considered?_

 

I would prefer through-hole but SMD is OK with me as long as they're 0805 or larger 
	

	
	
		
		

		
		
	


	




 In my opinion SMD's should only be used in positions where they yield significant benefits.


 /U.


----------



## Voodoochile

Gonzo- the ladder is available, but it is *big*, and the price is proportionate to the size. I made one on a 5-deck Elma attenuator switch from Mike Percy, and it was modestly obscene, with a pile of Holcos to solder. The attenuator is the size of a bottle of Tabasco sauce.

 From Goldpoint it's about $250, from Dact, closer to $325. Brutal. But I do love mine. The kit from Percy was about $180 IIRC. At the time, a series Dact was $181 from DIY cable.

 So, block out a lot of soldering time if you really want one!


----------



## Super-Gonzo

Quote:


  Originally Posted by *Voodoochile* 
_The attenuator is the size of a bottle of Tabasco sauce._

 

Thats half the appeal!


----------



## morsel

Gonzo: I don't think SMD will be necessary for this project.

 Voodoochile and Nisbeth: thanks for your detailed replies on casing and shaft extensions.

Elma Series N stepped attenuators come populated with low inductance SMD metal film resistors. No soldering required. Sound more appealing now? 
	

	
	
		
		

		
			





 If you are feeling rich you can go with the HeadRoom stepped attenuator instead, which uses the Elma mechanism with proprietary circuit boards that look really nice, but do not have board mount pins.


----------



## Voodoochile

I did not know you could buy Headroom's without an amp. Interesting.

 Also, good points, Cameron. I meant to comment on that earlier.

 If the op-amp is approximately centered along the fron-to-rear dimension, then I'd prefer the rear or center for the pot as opposed to the leading edge. If that makes sense!

 Gonzo: that is true. Why not just go crazy and install some Shallco 45-position ladders!


----------



## drewd

Quote:


  Originally Posted by *morsel* 
_Gonzo: I was also thinking that custom smaller PAR-Metal cases might be good, as long as we don't have to get into complex group buy issues._

 

I bought a 6" wide type 20 case a few weeks ago for $50.00. Basically any custom work smaller than the smallest listed type 20 is $50.00. That was black anodized, but not countersunk.

 Here's a picture. The one on the right is the standard 12" wide case.

 -Drew


----------



## amb

Quote:


  Originally Posted by *drewd* 
_I bought a 6" wide type 20 case a few weeks ago for $50.00. Basically any custom work smaller than the smallest listed type 20 is $50.00. That was black anodized, but not countersunk.

 Here's a picture. The one on the right is the standard 12" wide case.

 -Drew_

 

That 6" wide case is very nice. If we could make the main PCB fit in a case like that it would be ideal. The PSU will have to be external, which is fine. Those who want to put the PSU inside could just go with the 12" wide case. If it doesn't cost that much more to have Par Metal make a 6"x8"x2.5" case then I think it would be a good target to aim for. It would be especially nice if we could get the PCB layout such that the MOSFET heat sinks sit directly below the ventilation slots on the top cover.

 As for shaft extensions for the volume control pot or stepped attenuator, is the panel bearing a standard part that vendors like Digikey/Mouser/Newark carry? The extension tube seems like it's going to have to be custom (because the length would vary depending on the specific pot or stepped attenuator used, as well as the distance to the case front panel). How would people feel about having to fab this themselves?

 -Ti


----------



## morsel

If there is enough interest in board mounted Elma Series N stepped attenuators, perhaps they could be ordered with a shaft of the proper length and sold along with the M³ pcb and panel bearings.


----------



## Nisbeth

Quote:


  Originally Posted by *amb* 
_As for shaft extensions for the volume control pot or stepped attenuator, is the panel bearing a standard part that vendors like Digikey/Mouser/Newark carry? The extension tube seems like it's going to have to be custom (because the length would vary depending on the specific pot or stepped attenuator used, as well as the distance to the case front panel). How would people feel about having to fab this themselves?_

 

The shaft extender can be any old piece of 6 mm. or 1/4" aluminium/steel plastic tube or rod. Mine are cut from a 6 mm. aluminium tube bought at the local version of home depot using a small hacksaw. This should be manageable for most people 
	

	
	
		
		

		
		
	


	




 The panel bearings I use are these (click the 2 in the bottom for a sketch)


 /U.


----------



## jamont

Quote:


  Originally Posted by *amb* 
_How would people feel about having to fab this themselves?_

 

I'd rather not


----------



## Voodoochile

You definitely only need the coupler and bearing.

 The shaft is sold in 4' lengths for about $3. at an Ace Hardware store or home center. The Welborne kit is almost $20. The Handmade Electronics kit is about $4. You end up with a pot with a 10" shaft you trim to length.

 Doing the shaft yourself is easy... finding a coupling and bearing is a little harder, and the kit is a better choice. If I can find a place that sells the individual parts in bulk, it would be cheap to make little shaft kits.

 I'm afraid that a custom order from Dact would be big money or big minimum, but perhaps not. It would be the cleanest solution. Of course trimming the stainless shaft is not quite as easy as trimming the aluminum one.


----------



## Earwax

Quote:


  Originally Posted by *jamont* 
_I'd rather not 
	

	
	
		
		

		
		
	


	


_

 

Me neither. I'd much rather solder SMD parts than have to build a shaft assembly. ( I know it's not an either/or question )


----------



## DCameronMauch

I'm not understanding people's resistance to the shaft extension. It sounds like the parts are more than easy enough to acquire. And if you can't handle cutting a little pipe (I use the one for cutting plumbing copper pipes, makes nice perfect cuts), then you probably can't handle the soldering either. The biggest challenge is the measurements. But I see that as pretty straight forward too. ???


----------



## ppl

Quote:


  Originally Posted by *DCameronMauch* 
_I'm not understanding people's resistance to the shaft extension. It sounds like the parts are more than easy enough to acquire. And if you can't handle cutting a little pipe (I use the one for cutting plumbing copper pipes, makes nice perfect cuts), then you probably can't handle the soldering either. The biggest challenge is the measurements. But I see that as pretty straight forward too. ???_

 



 Locating the volume control at the rear has its advantages and disadvantages. Most of the disadvantages disappear if some sort of impedance transformation or Buffer is used. This implies an additional active stage or transformer and this option is something to not suitable to this application at this level of anticipated complexity, or shall I say lack of expected complexity.

 An eligent solution lies in the layout and adopts what is often called localized circuit structure. This simply implies locating related circuits in as closet proximity to each other as possible yet can be somewhat detached from other connected circuits however of a different function. The Input and voltage gain stage can be one localized Block. The output stage and its power supply another localized circuit however connected to the previous localized circuit via feedback and signing lines. The power supplies for each of these localized Blocks can be remote for the Input and gain stages yet ideally the output and its supply should not be broken into separate localized Blocks.

 The Bottom line of all the above babble is that yes a rear mounted pot and even relay operated input selection if desired. This will only require DC wires to connect to the front panel and the actual signal switched right at the source into the volume control and well you get the idea.

 So Moving on to shaft coupler’s and related hardware the least expensive however quite use able is the couplers intended t convert a multi-turn pot into a panel mount. This takes care of your front panel bushing now get some ¼” rod of your choice of metals me stainless for long life lube the bussing with some silicon spray lube in the bushing. Use this in sparing amounts in bushing to maintain smooth rotation.
 The required Bushing is available from Newark
http://www.newark.com/NewarkWebComme...jsp?id=44F7418
 Less than $4 Dollar folks.

 You might also want to throw in some of these they are pretty cool and only about three dollars http://www.apmhexseal.com/switchboot...00.pdf#page=11

 Moving on to shafts and shaft couplers check these Guys out for the perfect complete package. http://www.oselectronics.com/ose_p100.htm

 Possible small mismatches between metric and English measure can result in small imbalances so check shaft size the above hardware is for a true 1/4" shaft and that excludes the Alps Blue because it is a close metric equivalent however still slightly smaller than a true 1/4" and that is wy some Knobs made for 1/4" shafts sit so funny on the Alps


----------



## Glassman

what about this kind of heatsink?


----------



## Nisbeth

Quote:


  Originally Posted by *ppl* 
_Possible small mismatches between metric and English measure can result in small imbalances so check shaft size the above hardware is for a true 1/4" shaft and that excludes the Alps Blue because it is a close metric equivalent however still slightly smaller than a true 1/4" and that is wy some Knobs made for 1/4" shafts sit so funny on the Alps_

 

PPL, a single layer of electricians tape on the shaft of the Alps is usually enough to convert the shaft from 6 mm to 1/4". 
	

	
	
		
		

		
		
	


	





 /U.


----------



## DCameronMauch

glassman: Those do look promising. But they need to be much taller. Because they are so short, their thermal resistance is too high. For four mosfets at say 1.5W each, it would need to be around 2.5C/W. Do they make any with the same dimensions but taller? The target case should allow for 2" high heatsinks.


----------



## aos

Quote:


 I'm not understanding people's resistance to the shaft extension. It sounds like the parts are more than easy enough to acquire. And if you can't handle cutting a little pipe (I use the one for cutting plumbing copper pipes, makes nice perfect cuts), then you probably can't handle the soldering either. The biggest challenge is the measurements. But I see that as pretty straight forward too. ??? 
 

You obviously haven't been in electronics for very long. There is an aversion towards doing any kind of mechanical work.

 Yes, I can easily cut a pipe with my Dremel or hacksaw. But, lots of us live in apartments, we don't have fancy workshops and even workdesks in our living room where we can hack and cut at will. The other problem is getting ahold of this stuff. Just because your local home hardware has it doesn't mean that even the same chain in Canada carries it, let alone the rest of the world. Not to mention that finding stuff in those stores is a challenge. Anyone counting on a big, popular project like this would do well to provide such stuff to DIYers (especially if it's easy for them to do so). Tangent for
 example is doing a splendid work in this regard - teflon insulator sheets, SOIC to DIP sockets, standoffs and so on. That's one of the reasons why projects he provides parts for are so popular (or rather why so many DIYers actually manage to GET THEM FINISHED).


----------



## DCameronMauch

AOS: Actually, I have been in electronics for a very long time. Any electronics project includes mechanical work. There is no way around it. And it has been made more than clear that the parts are easily gotten. You don't need a workshop to use a plumbing copper cutter. It couldn't be easier. You guys sound like a bunch of girlie men.


----------



## aos

I don't know why is it so hard to understand that having to buy extra tools (which many will never use again) and cutting metal on the carpet of your living room is not appealing to many people. For the record I have a drill press, sanding paper, files and I use them all on my living room floor and I can do my own board etching if necessary. But that attitude will eliminate a lot of builders from the project. If the goal is that only rich people and US citizens with access to home hardware can build it, then ok.


----------



## amb

ppl: Thanks for the links. The Ocean State Electronics shaft extenders and couplers look very promising. I also just ordered a sample of the HHSmith panel bearing to see if it might fit our needs (The Newark online catalog page does not show a picture, and it's not in their printed catalog). 

 aos: Yes, you have a good point, and that's why I asked. I do my own cutting and drilling in the house even though I don't have a workshop (my dining table is my workbench 
	

	
	
		
		

		
		
	


	




 ), but I think I'm the minority here. Even though I don't think this amp should be a first-time DIYer's project, I do want to make this amp as easy to build as possible, so these considerations are very important. Tangent does a great job with his projects and I hope to be able to emulate him in some fashion for the M³.

 BTW, Morsel's DSL connection is down (she is switching services), so she is offline for a day or two.

 -Ti


----------



## Earwax

Quote:


  Originally Posted by *DCameronMauch* 
_AOS: Actually, I have been in electronics for a very long time. Any electronics project includes mechanical work. There is no way around it. And it has been made more than clear that the parts are easily gotten. You don't need a workshop to use a plumbing copper cutter. It couldn't be easier. You guys sound like a bunch of girlie men. 
	

	
	
		
		

		
		
	


	


_

 

Hey, I'm no girlie man, I'm a real girl! 
	

	
	
		
		

		
		
	


	







 Soldering is ton's easier than casework. And I worked my way through college as a bicycle mechanic and I still feel that way. 

 It's not a big deal to me, but if the KISS principle is being applied to the electronic aspects, the expectation might reasonably that the case work would also be kept more or less basic. But us wimps can always run wires to a front panel mounted pot, can't we?


----------



## amb

Just for laughs, here is a picture of my humble dining table "workbench", currently with M³ breadboarded prototype in test 
	

	
	
		
		

		
		
	


	









 -Ti


----------



## kevin gilmore

where is the dead pizza??


----------



## DCameronMauch

AOS: Uh, okay. The pipe should be readily available even in Canada for like $2. You talk like it's a third world country. And the circular cutter tool is like $5. Rich Americans? What kind of salaries do you guys make up there? Someone could provide the parts for those who don't feel they are upto it. Like Tangent does for the PPA. Everyone who did that project had to make their own case and drill those. Where you thinking this wasn't going to be a DIY project, but some kind of everything supplied minimal work kinda kit?

 Earwax: Sweet.


----------



## aos

All I'm saying is that in my experience you'll get a considerably higher successful completion rate if you provide these "insignificant" things. I HAVE seen people never finishing projects because of lack of a few trinklets. And I HAVE seen Home Hardware and Radio Shack not carrying a lot of things that their namesakes carry in US (we are a much smaller market). And I know about aversion of electronics people for doing mechanical work. Please don't mistake what I'm personally capable of and what I believe a lot of potential builders are capable of (which was my concern) - and this is a project for a wide audience. I've already built amps like this years ago so I'm not desperately seeking to get a piece of pipe pre-cut for myself, that's for sure (though it'd be nice).

 amb: that's pretty innocent actually. I recall a similar thread way back on headwize (that's probably why Kevin was asking about dead pizza - your workspace is "too neat").

 And now on-topic comment: Why the 10 Ohm resistors in series with opamp rails? Both here and on PPA version 1.1? I hope you're aware that the resistor's function was actually a "poor man's" substitute (or I should
 say approximation) for a current source like FET - which you already use? It looks like unnecessary duplication, and
 it mandates good bypassing of the opamp, otherwise you'd calling for trouble with high speed chips for obvious reasons.


----------



## comabereni

RE: Shaft extensions

 I'm just catching up on this thread and haven't read all six pages yet, but I did note that there seems to be a need for shaft extensions.

 The recommendation to buy commercially available shaft extenders and cut them to length is excellent, but for those averse to learning how to use a hacksaw 
	

	
	
		
		

		
		
	


	




 , I could turn some extensions to exact length on my lathe from stock aluminum, Delrin, or 6/6 nylon. I'd only need dimensions.

 Only hitch, this would have to be in a couple months or so--I'm in the middle of a major home remodeling project and my lathe is buried deep in my shop behind all my furniture.

 I'm no pro machinist, but my other DIY hobby is making telescopes and telescope drive systems, and this is a pretty simple part. PM me if you are interested. I'd do them for cost, or even for just the cost of shipping--I have lots of cut-off ends and scrap lying around in my shop. 

 Just trying to help the DIY effort so you guys will be generous with your knowledge once I start asking lots of questions about circuits and various amp components 
	

	
	
		
		

		
		
	


	




 .


----------



## CingKrab

Quote:


  Originally Posted by *morsel* 
_If there is enough interest in board mounted Elma Series N stepped attenuators, perhaps they could be ordered with a shaft of the proper length and sold along with the M³ pcb and panel bearings._

 

I don't know if this is relevant, but like morsel says, why don't you guys just do a group order from Elma with the desired shaft length? I found this quote in this datasheet: http://www.elma.com/files/products/r...ries_n_002.pdf

  Quote:


  Originally Posted by *http://www.elma.com/files/products/rotary_components/pdfs/audio_switches_series_n_002.pdf* 
_Special shaft length
 To order, state the shaft length AL as shown in diagram, measured
 from mounting face.
 Specify dimensions on page 150._


----------



## amb

Quote:


 where is the dead pizza?? 
 

Hehe, if you were here you'd see a couple of pizza boxes on the kitchen counter.

 aos: Re: the power supply 10 ohm rail resistors: this area of the circuit is definitely not cast in stone and subject to change. Morsel took it from the PPA design but we will most likely make some changes. So far we have focused more on the amp itself. In fact all my testing so far have been done without the TLE2426 rail splitter nor the capacitance multiplier. I am using just a standard split power supply with dual IC regulators and some pretty big reservoir caps. I do like the rail splitter idea because it synthesizes a signal ground from the regulated and filtered supply rails, and should be cleaner than the more ordinary approach.

 comabereni: Thanks for your offer, we should keep that in mind. I hope though, that you understand what you might be signing up to do 
	

	
	
		
		

		
		
	


	




 .

 -Ti


----------



## amb

Quote:


  Originally Posted by *CingKrab* 
_I don't know if this is relevant, but like morsel says, why don't you guys just do a group order from Elma with the desired shaft length?_

 

Yeah, if there is enough people who want to go that route then this is definitely something we ought to look into.

 -Ti


----------



## pabbi1

I apologize in advance for not being able to read a schematic.... but guys, I'm a CPA.

 I'm so interested in this project, but can someone describe, in lay terms, how this will be a superior design to the SDS (v1.1)? Is Sheldon at all involved?

 For the record, my SDS still does the job, but I did have to increase the R11/61 values for the HD600 - will this be designed for all impedences or will it be switched?


----------



## DCameronMauch

The whole shaft extension idea is ONLY important if it allows us shorten the leads from the pot to the first opamps significantly. Careful board layout is another way to do it. So all this may just be academic.

 aos: I have been told that sometimes I can come off as being argumentative and confrontational. Just incase I did in this case, I appologize. Didn't mean to be.


----------



## amb

Quote:


  Originally Posted by *pabbi1* 
_I'm so interested in this project, but can someone describe, in lay terms, how this will be a superior design to the SDS (v1.1)? Is Sheldon at all involved?

 For the record, my SDS still does the job, but I did have to increase the R11/61 values for the HD600 - will this be designed for all impedences or will it be switched?_

 

Hi pabbi1,

 Sheldon is not involved in this project. I think Morsel had contacted him many moons ago but he wasn't interested in a project like this.

 As stated in the initial announcement, this amp is inspired by the SDS Labs MOSFET amp as well as the PPA. As such it bears some resemblance to both.

 The basic M³ amplifier is similar to the SDS Labs amp (which is a text-book opamp + discrete output buffer design), but improves upon it in a few areas:

The biasing of the Vbe multiplier and the drive from the op amp to the output MOSFETs now employ a cascoded JFET current source. This has a couple of important benefits:





> - Improved power supply rejection ratio (PSRR) because there is no longer any resistors going to the power rails.
> - The cascoded JFET current source pulls current _out_ of the op amp to bias the op amp into class A. The amount of current is also adjustable to suit differing op amps and tastes. In the stock SDS Labs MOSFET amp, a small amount of current is fed _into_ the opamp's output instead, but in reality it's not sufficient to really bias the op amp into class A, and also that causes the PNP side of the op amp's output stage to be on, rather than the NPN like the M³ design. The NPN device is typically more linear.
> - Having a constant current source provides a more robust drive to the MOSFETs. This is good because the gates of the MOSFETs are capacitive.



The three-channel architecture is inspired by the PPA and absent in the SDS Labs amp. I won't go into the benefits here because that's been written up already in the announcement as well as on the PPA web site.
Sheldon's PCB layout has the power transformer located too close to the op amp and as such induces AC mains hum (and its harmonics) into the audio signal. This is audible with sensitive headphones and is clearly visible on a spectrum analyzer. The M³ PCB will not have this problem, and will be a more deluxe two-layer plate-through board with silkscreening and soldermask.
Our parts selection differs from that of Sheldon's, in particular, the op amps (using singles instead of dual units for better channel separation), and the MOSFETs.
The amp will be suitable for use with both low impedance as well as high impedance phones. The gain of the M³ is set at 11 but builders can change this.
The power supply will be quite different as well, and other smaller details too.

 I know the above is not really a "lay person's" description, but what we are doing will hopefully result in an amp that would sound superb. Your ears will be the judge when we're done! 
	

	
	
		
		

		
		
	


	




 -Ti


----------



## Voodoochile

Quote:


  Originally Posted by *kevin gilmore* 
_where is the dead pizza??_

 

Jim Williams ate it already. 
	

	
	
		
		

		
			





 AOS:
 I see your point completely, and was in that same position myself for years.
 In the interest of this, perhaps the front mounted pot would be best.

 Or as Earwax mentioned, maybe those wishing to mount on the front could run leads to the pot. I'm flexible, so whatever works the best for the most people.


----------



## aos

Or, you could allow for two places on the board to mount the pot/attenuator - front and rear. So people not willing to get shafted (heh) would install it in front - at the cost of slightly reduced performance due to longer leads between RCA input and the pot - and the others could mount it on the rear for full benefits. If you have those two places aligned, you can still use the same panel layout for both - meaning the shaft extension would still come through the same hole in the front panel. As you'd need to have a clear path for that shaft, you will already have to dedicate some space in that area to be (tall) parts free anyway so the cost of this shouldn't be too high. Or even better, use Alps Blue for front position, and attenuator for the rear - it also makes sense, as if you're willing to pay for attenuator you want to get all that you can out of it, and if you're fine with Alps Blue then the front position will also be satisfactory for you. So you could provide attenuator + shaft kit or people can just get Alps Blue (from Tangent or wherever). That way they can even upgrade later when they get into money wihtout having to redesign and rewire their panels.


----------



## pabbi1

Thank you amb for the response... I am not an engineer, but understand the design benefits.

 I'll offer a hearty thank you for this project in advance, and look forward to building one. 

 Will heat considerations eliminate wood as a case material?


----------



## amb

Quote:


  Originally Posted by *pabbi1* 
_Will heat considerations eliminate wood as a case material?_

 

Metal cases provide shielding that helps cut down on induced noise from external sources. Sheldon's SDS Labs MOSFET amp example has the circuit board completely exposed to the elements, which is good for heat dissipation but is susceptible to noise pick-up. If you like the looks of wood, you can always add wooden endcaps or something like that to the sides of a metal case. Whatever case material you use for this amp, it will be important to have ventilation to allow the heat to escape.

 -Ti


----------



## hottyson

Quote:


  Originally Posted by *aos* 
_use Alps Blue for front position, and attenuator for the rear_

 

This sounds like the most sensible layout to me. I like the sound of this idea.


----------



## amb

I spent the past couple of days testing the M³ prototype amp. 

 I measured the frequency response, slew rate, total harmonic distortion, intermodulation distortion and signal to noise ratio. You'll see a test summary as well as pretty graphs here:

http://www.amb.org/ti/audio/mmm/2ch_proto_20040825.html

 Note that this prototype is running in two channel configuration (no ground channel), and the power supply is not as optimal as I would like it. Moreover, the prototype is built on an open breadboard, so the specs are not as good as it could be.

 Despite all that, the results are really quite remarkable, as you can see. The THD and IMD are both very close to the residual distortion of the M-Audio Transit running in loopback mode, so the amp is in fact adding very little distortion of its own to the signal.

 There is no measurable difference in distortion, regardless of whether the amp's outputs are loaded with 33 ohms or 330 ohms (or no load at all). This speaks volumes about the robustness of the MOSFET output stage.

 I have also spent some time listening to this amp. It's already excellent.

 I will be doing more testing of the circuit hopefully in three-channel mode soon, and I will also test the circuit for optimum bias settings, and tune the values of some components to see if I could achieve even better results.

 Enjoy...

 -Ti


----------



## pabbi1

OK, I know this is cheesy, but... I really Vodoochile's use of an old SCSI enclosure, and wonder would something like this work:

http://cgi.ebay.com/ws/eBayISAPI.dll...118903363&rd=1

 The enclosure has switched power, ventilation, and a fan (is the fan a sonic inteference problem?). besides, most are built like tanks, and shielded well. This one is 10.25" x 9.75" x 2.0", but would that be tall enough?


 Actually, being the SUN head, I'd probably go this way:

http://cgi.ebay.com/ws/eBayISAPI.dll...118212331&rd=1

 If nothing else, these are cheap, indestructible, plentiful, and recycled.

 And, I have this stepped attenuator that I was going to use in the SDS (to replace the Alps), but will use it here. In this case, it looks like no board pin placements will work for me, whether placed in front or back. It's Vishay, and relatively cheap (~$45).

http://home.swbell.net/pabbi/step_attenuator2.jpg


----------



## amb

pabbi1:
 You can use computer drive enclosures, but I would strongly suggest ditching the built-in swtching mode power supply (and fan). They are fine for computer equipment, but give very noisy DC output and is not suitable for a high quality audio amplifier, not to mention having the wrong voltages (typically +5V and +12V are available, sometimes also a -12 but at very low current). Tangent's TEPS would be a good choice for this amp. I would put the power supply board in a separate enclosure for maximum isolation from the amplifier. If you want it in the same enclosure, make the power transformer and any AC lines as far away from the amplifier board as possible.

 The stepped attenuator you have is definitely a "run wires to it" affair 
	

	
	
		
		

		
		
	


	




.

 -Ti


----------



## pabbi1

Sorry, I just meant the power recepticle... and not the P/s itself. The main question was the fan. I just always seem to find yet another SUN exclosure (with an Ultra 2 or Ultra10 attached to it).


 While talking P/s, Tangent, how far a step down is the Velleman K1823, and conversely, how much better would the Wellbourne PS1 be? I only ask since there are several Velleman dsitributors within 10 minutes from me. And, if we're going for the better solution, is the $150 Wellbourne price worth the difference over the ~$80 TEPS?

 In this amp design, will the P/s be a super critical consideration, or is separating the P/s from amp board more critical? Or both? 

 Will someone take pity on us lesser mortals here and add further instructions (later) about configuration and connecting the TEPS to the M³?

 Sorry to contunually define the bottom feeding segmant of the thread,

 Al


----------



## amb

Quote:


  Originally Posted by *pabbi1* 
_The main question was the fan. I just always seem to find yet another SUN exclosure (with an Ultra 2 or Ultra10 attached to it)._

 

If you could power the fan from a separate power circuit than the amp, then it would help keep the amp's power clean. Having a fan motor on the same power rail as the amp would be a bad idea, as the fan produces back-EMF pulses and pollutes the power.

 I never liked the idea of a fan in home audio gear, though. Even the quietest fan makes noise and draws dust into the enclosure. I prefer passive (heat sink) cooling as much as possible.

 I'll let Tangent answer your question about TEPS vs. other options (hope he's reading this thread).

  Quote:


 In this amp design, will the P/s be a super critical consideration, or is separating the P/s from amp board more critical? Or both?  
 

The M³ has good PSRR, so it's not _too_ critical on the power supply but the PSU should have high enough output current to handle the ~300mA to 500mA continuous draw and not burn itself up. Good clean power is "motherhood and apple pie" for amps in general, so I would advocate getting the best power supply you could afford.

 We are going the route of not putting the PSU on the same board as the amp to give DIYers more choices, and the ability to put the PSU in a separate case for best isolation.

  Quote:


 Will someone take pity on us lesser mortals here and add further instructions (later) about configuration and connecting the TEPS to the M³? 
 

Absolutely. That's what this community is all about. As I said in an earlier post, the power supply for this amp is an area that is still subject to change. Assuming it doesn't change drastically (i.e., we retain the TLE2426 rail splitter design), then the STEPS (single supply version of the TEPS) will be a good match. It would have to use the 24VCT version of the Amveco toroidal transformer instead of the 30VCT variant to prevent the regulator IC from overheating. At this time, though, I think that level of detail is a bit premature, and will be forthcoming when we're ready to release the official version of the M³.

 -Ti


----------



## digi01

any news here?I am eager finished version


----------



## morsel

No news. My new DSL is working but I am preparing to go out of town for a week. AMB and I have more testing to do when I get back. We will post more in a week or two.


----------



## gerG

Whew, what an amazing thread! I just blundered in here looking for a volume pot for a different project. Now I am hooked, and I need an M³ (I wouldn't mind an M3 as well, but that is a bigger project).

 I can only offer comments from a thermal and mechanical perspective. On the topic of heat sinking, is it feasible to mount the devices to the chassis? Morsel alluded to this in the first post, but I didn't see much discussion on the subject. External heat sinking will provide far superior thermal rejection than internal sinking with secondary convection to the chassis (the btus have to sneak out somewhere). If not, I would be tempted to provide for enhanced circulation. If the case of choice already has vents, nevermind. Their server seems to be down just now, so I haven't seen it yet.

 I am all for the back mounted attenuator (with driveshaft). I have a few commercial examples of this approach (preamps mostly). They work great and are very durable. Somehow the forward bearing gives a more solid feel to the control as well.

 For a great example of both approaches peek inside an AKG K1000 (SAC) amp.


 gerG


----------



## morsel

I talked to Elma. Series A are $44 each for 100. Series R are $71 each for 100. Series N are $152 each for 100. The single price for the DACT CT2 from DIYCable.com is $150. I sent email to DACT inquiring about direct volume purchases.

 The Elma Series A and R require hand soldering lots of leaded resistors and do not board mount, so I am currently leaning towards the DACT CT2.


----------



## ppl

Quote:


  Originally Posted by *aos* 
_And now on-topic comment: Why the 10 Ohm resistors in series with opamp rails? Both here and on PPA version 1.1? I hope you're aware that the resistor's function was actually a "poor man's" substitute (or I should
 say approximation) for a current source like FET - which you already use? It looks like unnecessary duplication, and
 it mandates good bypassing of the opamp, otherwise you'd calling for trouble with high speed chips for obvious reasons._

 

 The resistors were added to the PPA to shorten the high frequency current loop to keep it confined within the smalest area around the op amp power rails. Do not confuse power supply decoupling as we are doing hear with the simple Bypassing used in PPA version 1.0. with just simple Bypassing the actual PCB foils can become inductors and actualy hearting stability by creating a high impedence L/c Tank circuit tuned well up into the RF range and probaly lower in frequency than the unity gain bandwidth of your chosen op amp thus allowing the entire circuit to oscilate at the Tuned L/c frequency. Simply adding this small resistor kills the "q" Factor of any possible L/c tank and maintains stability. Granted quality RF grade capacitors of at least 0.1uF is min and bigger would be evean better. The Wima and BC component polypropylene types have less than 10 nH of inductence and this is added to any PCB foil's inductence.

 True the JFET isolation technique is more effective up to the point that Criss takes over however this is still farly high in frequency. My Battery operated reference trravaler that the PPA style isolation technique was first used on employed all three methods of isolation the two used on PPA v 1.1 in addition to a Capacitence multiplier.


----------



## morsel

DACT CT2 are $51 each for 100. This eliminates Elma as a contender.










TKD 2CP-2500 are ¥3000 or $27 each for 100. These are not stepped attenuators, but are perhaps the finest pots in the world, with true log, 90dB cutoff, laser trimmed conductive plastic tapers. See the picture below and read the THEL Audio World description for more detail. (edited: CP-2500 is single gang)

THEL Audio World Pots (in German)
THEL Audio World Pots (Babel Fish translation)


----------



## AndrewFischer

Quote:


  Originally Posted by *morsel* 
_DACT CT2 are $51 each for 100. This eliminates Elma as a contender._

 

That's a great price. 

 For the amp, I'm liking the TKDs. Is that price for a dual?

 I don't think you can go wrong with either choice.


----------



## Nisbeth

Quote:


  Originally Posted by *morsel* 
_DACT CT2 are $51 each for 100. This eliminates Elma as a contender._

 

That sounds very interesting, Morsel. If you want I'll go and pick them up after the order is placed 
	

	
	
		
		

		
		
	


	








 /U.


----------



## Voodoochile

That's an amazing price. Although it represents a $5K plus outlay, I have a feeling that 100 people would be willing to spend $50 on an attenuator that normally sells for $150-$180. Considering the switch alone is $38-$50, then you need to buy a pile of resistors and solder them, it's even a good alternative to building one.

 This is really more a topic for a seperate thread, I think. What a good price though. Look at how many people chipped in on silver wire- that order was significantly larger than this one would be. /hmmmm


----------



## Nisbeth

At this price, I don't think selling 100 would be much of a problem 
	

	
	
		
		

		
		
	


	





 /U.


----------



## morsel

Andrew: You were right, I did not specify stereo to TKD. I edited the previous post to correct the model number and price.

 VC: Actually this directly relates to M³ as AMB will have to provide stepped attenuators with the board if we are going to incorporate them. Also keep in mind the prices I was quoted do not include shipping, handling, insurance, and other fees either from the manufacturer to AMB or from AMB to the end user.


----------



## Voodoochile

I realize that... I meant that you would likely have more than enough interest even outside the scope of this project to be able to move 100 attenuators- even if they were $60 or $65 each. I can't stop smiling when I think about it!


----------



## aos

Quote:


 The resistors were added to the PPA to shorten the high frequency current loop to keep it confined within the smalest area around the op amp power rails. Do not confuse power supply decoupling as we are doing hear with the simple Bypassing used in PPA version 1.0. with just simple Bypassing the actual PCB foils can become inductors and actualy hearting stability by creating a high impedence L/c Tank circuit tuned well up into the RF range and probaly lower in frequency than the unity gain bandwidth of your chosen op amp thus allowing the entire circuit to oscilate at the Tuned L/c frequency. Simply adding this small resistor kills the "q" Factor of any possible L/c tank and maintains stability. Granted quality RF grade capacitors of at least 0.1uF is min and bigger would be evean better. The Wima and BC component polypropylene types have less than 10 nH of inductence and this is added to any PCB foil's inductence.

 True the JFET isolation technique is more effective up to the point that Criss takes over however this is still farly high in frequency. My Battery operated reference trravaler that the PPA style isolation technique was first used on employed all three methods of isolation the two used on PPA v 1.1 in addition to a Capacitence multiplier. 
 

I almost never disagree with you but I do on this point. Adding that resistor will increase the output resistance of the opamp and what's worse, it would inject the signal into the rails at the opamp (as the variable current will modulate the rail voltage through that large resistor (10 Ohm is large in this case)). It may not make much difference in this case as they don't drive a low impedance load but still. True, it would insulate the big capacitor(s) (since on the schematics you have a big cap before the resistor, then "small" cap at the opamp after the resistor)from the possible parasitic RLC loop, but my understanding is that the big capacitor is never the problem anyway - it would create resonance at relatively low frequencies, and there the small capacitor (film, ceramic) would have much lower impedance anyway (big ones usually have comparatively large resistance), so the loop would close through the small one instead. That's one of the reasons two caps are used. Now if you add resistor BEFORE the bypass capacitors, then it all acts as a filter, just like what FET does but less efficient.


----------



## morsel

Team M³ seeks high end Grado and Sony 32 Ohm headphone lovers for listening tests. We are looking for people with outstanding hearing (hopefully still in your 20s) to visit us in Sunnyvale, California. Bring your headphones, favorite amplifiers, and music. Send amb or morsel an email if you are interested.


----------



## drewd

That almost makes me want to cry. My Grados and I are in cloudy southern Idaho 
	

	
	
		
		

		
		
	


	




 -Drew


----------



## pabbi1

Are there any interim updates, with potential decisions (P/s, casing, pseudo parts listing)?


----------



## morsel

We are busy testing various aspects of the prototype, conducting listening tests, and drawing draft layouts.

 I created a DACT CT2 part and discovered much to my dismay that when overlaid with an Alps Blue such that they are both flush with the panel, the Alps rear wiper pad overlaps the front DACT wiper pad, so only one of them can have mounting holes for board mounting without a shaft extender. It would be too wasteful of space to have them side by side.


----------



## amb

Quote:


  Originally Posted by *morsel* 
_I created a DACT CT2 part and discovered much to my dismay that when overlaid with an Alps Blue such that they are both flush with the panel, the Alps rear wiper pad overlaps the front DACT wiper pad, so only one of them can have mounting holes for board mounting without a shaft extender. It would be too wasteful of space to have them side by side._

 

My feeling is that the ALPS blue will probably be the more popular choice amongst builders simply because the DACT is several times its cost (~$16 rather than ~$65+). As such, we should lay out the PCB for direct-mounting of the ALPS and provide a second set of pin headers not far from where the rear of the DACT would be (for hand wiring to a DACT or other models of pots or stepped attenuators). A short run of wires is easier to deal with shaft extenders, and should not adversely impact performance. I'd like to hear what your opinions are about this.

 Moreover, the TKD 2CP2500 has large solder tabs which makes it incompatible for direct board-mounting (ExpressPCB does not allow flat slots, so we'd have to use some huge holes to clear those tabs, and soldering the tabs to such holes is not going to be pretty. I don't think Morsel has tried creating a part in ExpressPCB for the TKD yet, but my guess is that it might also conflict with the ALPS. Thus, having the pin headers will also allow the TKD to be hand-wired.


----------



## morsel

We are considering a smaller, cheaper heat sink, the Aavid 504222.


----------



## z2trillion

This might have been mentioned already, but would the smaller CP601 work in the place of the CP2500? It appears to have leads that would enable it be mounted to the pcb more easily. Is this a possibility, or is the CP601 inferior to the CP2500?


----------



## jamont

Quote:


  Originally Posted by *amb* 
_My feeling is that the ALPS blue will probably be the more popular choice amongst builders simply because the DACT is several times its cost (~$16 rather than ~$65+). As such, we should lay out the PCB for direct-mounting of the ALPS and provide a second set of pin headers not far from where the rear of the DACT would be (for hand wiring to a DACT or other models of pots or stepped attenuators). A short run of wires is easier to deal with shaft extenders, and should not adversely impact performance. I'd like to hear what your opinions are about this._

 

I think this would be an excellent choice.


----------



## amb

Quote:


  Originally Posted by *z2trillion* 
_This might have been mentioned already, but would the smaller CP601 work in the place of the CP2500? It appears to have leads that would enable it be mounted to the pcb more easily. Is this a possibility, or is the CP601 inferior to the CP2500?_

 

The 2CP-601 would work, but indeed it is quite inferior to the 2CP2500. The 601's channel matching is rated at +-2.0dB to -45dB, compared to the 2500 which is +-0.5dB to -50dB.


----------



## raif

If this is a no-compromise design wouldn't it make more sense to tailor it towards higher end components? Especially considering the phenominal price we are getting on the DACT attenuators.


----------



## morsel

It is simple enough to hand wire the DACT CT2. The board should be friendliest to the most popular parts, and the Alps Blue will probably remain the most popular volume control, don't you agree?


----------



## Nisbeth

Quote:


  Originally Posted by *morsel* 
_It is simple enough to hand wire the DACT CT2. The board should be friendliest to the most popular parts, and the Alps Blue will probably remain the most popular volume control, don't you agree?_

 

FWIW I agree with you. Even if this is a "high-end" amp, making the DACT the default volume control would probably scare many people away (and draw others in no doubt 
	

	
	
		
		

		
			





)


 /U.


----------



## morsel

Team M³ is working on opamp power issues. In the mean time, here are a couple of draft layouts to look at. There are no opamp power components yet. The main focus is choice of heat sinks and channel component arrangement. The parallel vertical lines are 2 inches apart.

 What is your opinion on ground planes on the bottom layer .vs. the top layer of the pcb? Putting the traces on the top layer and the ground plane on the bottom layer results in fewer traces through solder pads on the bottom layer, and thus easier soldering, but perhaps there are some compelling reasons to have the ground plane on the top layer. Kevin points out that a top layer ground plane sandwiches the traces between the ground plane and metal case bottom.


----------



## morsel

M³ v008a





 M³ v008b


----------



## Nisbeth

That looks very nice Morsel. I think I prefer the heatsinks on v008a. I think they look better and I like the fact that they're fixed firmly to the board 
	

	
	
		
		

		
		
	


	






 /U.


----------



## morsel

Aavid 531202 heat sinks in v008a are firmly attached to the board with screws.

 Aavid 504222 heat sinks in v008b only connect to the TO-220 cases, probably should be drilled since the existing holes are meant for horizontal mounting and result in the heat sink floating in mid air, and probably should be used with insulators since they are so close together.


----------



## Nisbeth

Quote:


  Originally Posted by *morsel* 
_Aavid 531202 heat sinks in v008a are firmly attached to the board with screws._

 

That's what I meant, v008a (mistake corrected in the above post
	

	
	
		
		

		
		
	


	




)


 /U.


----------



## amb

Quote:


  Originally Posted by *morsel* 
_Aavid 504222 heat sinks in v008b only connect to the TO-220 cases, probably should be drilled since the existing holes are meant for horizontal mounting and result in the heat sink floating in mid air, and probably should be used with insulators since they are so close together._

 

I should elaborate this with a picture. As you can see in the picture below, the 504222 heat sink comes pre-drilled with two holes. Using the "top" hole leaves not enough of the TO-220 device's leads to go through the board. Using the "bottom" hole causes the heat sink to sit unsupported about 0.25" above the board (assuming you insert the TO-220's leads into the PCB holes up to the point where it changes thickness). Since the heat sinks "face" each other in the layout, the direction of instability will likely cause the heat sinks to touch each other. If the TO-220 MOSFETs are mounted without insulators we'd get a short circuit from positive power rail to the negative power rail.






 If you want the 504222 heat sink to sit against the board in a stable manner, you will need to drill a third hole on the heat sink somewhere between the two existing holes, and not exactly in the center. This has to be measured fairly precisely to achieve the desired result. The bottom edge of the heat sink will probably also need to be insulated to prevent shorting to the ground plane or traces (in case the soldermask wears through).

 Another point that I'd also like to bring up is that the two 504222 heat sinks as oriented on the board form a semi-enclosed area. Even though there are slits on the heat sink's wings I think it may trap some heat.

 The benefit of the 504222 heat sinks and the the v008b layout is that it allows for very direct PCB traces to the MOSFETs, and saves some board space.

 My personal preference is v008a, but your opinions are welcome.


----------



## Lil_JV

Haven't been here for a while. Its lookin great! I prefer version a heatsinks as well.

 Can't wait to build one of these suckers.

 JV.


----------



## peranders

Morsel, your layout looks alright but I would make it a bit more tight and get shorter traces for the feedback. I think you should strive to get it as compact as possible. Can't you use only one heatsink for both mosfets? Check the most left heatsink below. I have two transistors plus a temp sensing transistor.

 Your holes in the groundplane are hardly necessary if you have fairly low values of your feedback parts. On the other hand it's making no harm either.


----------



## amb

Quote:


  Originally Posted by *peranders* 
_Can't you use only one heatsink for both mosfets? Check the most left heatsink below. I have two transistors plus a temp sensing transistor._

 

We considered putting both MOSFETs back-to-back on a single (bigger) heat sink like in your pic, but abandoned the idea because not only must insulators be used between the MOSFETs and the heat sink, the screw and hardware for fixing the MOSFETs to the heat sink will also have to be insulated or non-conductive or else you short out the power rails (The drain pins on the MOSFETs are connected internally to the TO-220 body). Also, it makes for a messy PCB layout, everything has to go around the heatsink.

 We don't need a temp sensing transistor in this amp. It is thermally stable without it.


----------



## morsel

Quote:


 Morsel, your layout looks alright but I would make it a bit more tight and get shorter traces for the feedback. I think you should strive to get it as compact as possible. 
 

Hi Peranders. We could shorten the feedback loop by swinging C6+ around to C6- and sliding R5 away from the bias circuit at the expense of not bypassing the opamp right at the supply pin. Alternatively, we could rotate the entire opamp section 90° clockwise and slide the bass boost section towards the MOSFETs at the expense of bringing the input resistors closer to high current areas.
  Quote:


 Can't you use only one heatsink for both mosfets? Check the most left heatsink below. I have two transistors plus a temp sensing transistor. 
 

AMB covered the bases, but I'll expound a bit on the messy layout issues. Since it is undesirable to thermally couple MOSFETs from different channels, complementary pairs would be mounted on the same heat sink. The similar pinout of N and P channel MOSFETs results in input and output resistors being positionally reversed since they face outward, so they must cross paths on the N channel side, also crossing the power trace for that MOSFET. The pairs of input and output resistors must lie outside the domain of the dumbbell profile of the heat sink, and then come together again on the far side. The Vbe bypass cap C2 no longer has a niche to sit in, which results in greater distance from the MOSFETs and a longer feedback loop.

 While we are on the subject, another advantage of v008b (besides the shortest possible signal paths with or without the suggested modifications) is the option for a longer C2.
  Quote:


 We don't need a temp sensing transistor in this amp. It is thermally stable without it. 
 

Not only is it thermally stable, AMB noted that switching to the smaller heat sinks actually lowered the bias current.


----------



## digi01

moresl,great work!
 as always logical and in order,especially mosfet parts.
 About the feedback loops,I agree with peranders.it maybe more short.
 like this,shorter feedback and shorter opamp power supply +/- rail tracks.







 sorry for my ugly pic 
	

	
	
		
		

		
		
	


	




 digi


----------



## amb

Hi digi01, thanks for your suggestion. I was going to say that the power rails are also available on the left side but you fixed the picture and beat me to it. At any rate, we left some space near the TLE2426 because there may be additional parts to go there. The power supply is an area where we are still working on (whether there should be a separate TLE2426 per channel, whether there should be capacitance multiplier, or FET isolation for the op amp power, or additional regulators, etc.).

 But you're right, unlike the PPA, the M³ has a bigger pcb so there is some "wiggle room" to allow us to move things around to tighten up the layout. There are "no fly zones" on the left and right sides, though (corresponding to the front and rear panel areas of the case), so that switches, RCA phono jacks, power connector, phone jacks, etc. won't interfere with parts on the board.


----------



## pabbi1

Speaking of power supply, is a Condor P/s (a la the Dynahi) a possibility, or is this topic still premature?


----------



## morsel

Like the PPA, the M³ is designed to use a single rail supply. It should work on anything from a wallwart to a STEPS as long as the outputs are isolated, not tied to AC ground. A dual rail supply would be overkill.


----------



## pabbi1

Any update on the board and heatsink approaches (a or b)? Current estimate on board dimensions? How are the listening tests progressing?


----------



## morsel

Quote:


 Any update on the board and heatsink approaches (a or b)? 
 

We will let you know. AMB has been busy at work, and I will be out of town from 10/11-10/25, so it may be a while.
  Quote:


 Current estimate on board dimensions? 
 

 8x6" is a rough maximum, and we may go smaller.
  Quote:


 How are the listening tests progressing? 
 

NeilPeart and Raif came over and did some listening. I don't want to put words in their mouths, but they were very helpful, and will be doing more listening after we make some progress with the power supply section. I missed Raif because I was at the annual Bay Area Carnivorous Plant Society plant show, but AMB told me he was able to distinguish 2 .vs. 3 channel operation in double blind tests. Pretty cool!


----------



## raif

It was quite an amazing listen, especially considering the whole thing was built on a protoboard.

 I am going to keep my mouth shut, considering how early it is in the game, but I am impressed already.

 Thanks alot to amb too, as I roughly doubled my amp engineering knowledge while at his house. I swear he built every piece of electronics I saw in there.


----------



## pabbi1

Raif: Did you a/b against AMB's (highly modded) SDS?

 Morsel: Thanks for the schedule update.


----------



## Megaptera

Quote:


 I was at the annual Bay Area Carnivorous Plant Society plant show 
 

You mean designing high-end headphone amplifiers wasn't an esoteric enough hobby? 
	

	
	
		
		

		
		
	


	



 If you don't mind a very brief thread-jack, what kind of carnivorous plants?


----------



## Qpedejo

Hi!
 Even though it feels like I´m somewhat banned here...I would like an answer anyway...
	

	
	
		
		

		
		
	


	



 Wy don´t u use multiloop in this configuration? Is because the use of AD8610 with it's nice buildup u don't feel it's important?
 (hope I haven't miss a explanation to this in the earlier posts)
 And I hope no one did get offended by my q...
	

	
	
		
		

		
		
	


	




 would be interesting to know the answer...

 /qpedejo


----------



## raif

Quote:


  Originally Posted by *pabbi1* 
_Raif: Did you a/b against AMB's (highly modded) SDS?_

 


 yep


----------



## pabbi1

And, is M³ vastly superior to the modded AMB SDS? Details, por favor?


----------



## morsel

Multiloop would increase DC offset in this circuit configuration.

 M³ will be better than a modded SDS Labs because it will not suffer from the SDS Labs power supply problem bleeding hum into the input stage and because it has 3 channels instead of 2. There are other reasons, but those are a couple of good ones.

 I'm going out of town for a couple of weeks starting Monday. I may be too busy to post again until I get back at the end of October. We will let you know when we have news to report.


----------



## amb

Quote:


  Originally Posted by *Qpedejo* 
_Hi!
 Wy don´t u use multiloop in this configuration? Is because the use of AD8610 with it's nice buildup u don't feel it's important?_

 

That's a perfectly reasonable question. If you study the topology of this circuit and understand it, you'll find that the op amp's output will "sit" at about +3.5 to +4V due to the biasing requirement for the output MOSFETs (i.e., the op amp is not driving the "center" of the bias voltage span). This means that if you were to connect a Jung-style inner feedback loop here, it will adversely affect the amp's total output DC offset voltage. Indeed I've experimented with exactly that on the breadboard prototype, and proved it to be true (the offset went from a fraction of a mV to ~30mV). Not a good thing. The purpose of multiloop is to reduce distortion, but as it turns out, the M³ prototype measured as well or better than a multiloop'ed PPA wrt. distortion.

 Hope that answers your question.


----------



## amb

Quote:


  Originally Posted by *pabbi1* 
_And, is M³ vastly superior to the modded AMB SDS? Details, por favor?_

 

Yes, due to M³'s 3-channel configuration, I have observed an improvement in the overall sound, particularly in the bass, which is taut and more controlled. This is also confirmed by NeilPeart and Raif during their listening tests. I was also able to observe actual elimination of ground pollution with my function generator and scope.

 Moreover, while my modded SDS Labs MOSFET amp is good, I found that with sensitive low-Z cans there is audible hum due to the proximity of the AC power transformer to the low-level circuits on Sheldon's pcb layout. In retrospect I wish that I had designed my own pcb for that amp, but it doesn't matter now. The M³ will fix that and be better for a number of other reasons too.


----------



## Qpedejo

Thnx Morsel and amb!
 Nice to see that u know what ur talking about....
	

	
	
		
		

		
			




 And, I ´ve to discovered ur findings about multiloop when simulating these circuits, but it's always nice to have it confirmed from the source..


 Keep up the good work!
 /qpedejo


----------



## pabbi1

AMB, thanks for the reinforcement. Please forgive my impetuous nature, but I'm still living with the original 1.0 SDS, so I am anxious to build the M³.

 Can you give a short list of the major unresolved issues, since it looks like there is a 2 week break in updates?


----------



## morsel

We don't have a list of specific issues yet, just a rough game plan subject to change at any time. After we do our opamp power tests, in which capacitance multipliers, FET current sources, and no rail isolation will be evaluated, we will have a clearer picture of the final circuit. Then we get to decide how big to make the board, whether to support board mount pots, power connections, LEDs, etc. We are leaning strongly towards the Aavid 531202 heat sinks, but even that is not set in stone yet. Breath normally and take tranquillizers as needed until we are done.


----------



## amb

Quote:


  Originally Posted by *pabbi1* 
_Can you give a short list of the major unresolved issues, since it looks like there is a 2 week break in updates?_

 

Morsel is leaving town for two weeks but I'm continuing to work on the amp.

 Currently the focus is on the power supply. The original schematic posted in this thread shows the use of a separate capacitance multiplier and TLE2426 rail splitter for each channel. We are testing to determine whether that is overkill. Perhaps a single TLE2426 is sufficient for all three opamps. We are also testing to determine whether capacitance multiplier or JFET isolation (a la PPA) is better, or maybe even none at all. 

 Even though this is a fairly "deluxe" amp, our philosophy for it is that every part has to earn its keep. This is to meet our goal of excellent sound, good price/performance and KISS. We do not want to throw extraneous circuitry into the amp when they drive up the cost, complicate the PCB layout while offering dubious benefits. Doing these tests require rebuilding portions of the prototype and doing various measurements, which takes time. I do this during my spare hours, so please bear with us.

 The other open issues are PCB layout/component placement (not only for optimum trace routing, but also to allow for standard parts as well as audiophile boutique-grade stuff -- e.g., fancy capacitors, where feasible), board size and orientation, case selection, and other sundry related details. This will be worked out as we make further progress.


----------



## pabbi1

Thanks both for the update... I've adjusted my Thorazine intake accordingly.


----------



## ppl

Quote:


  Originally Posted by *amb* 
_That's a perfectly reasonable question. If you study the topology of this circuit and understand it, you'll find that the op amp's output will "sit" at about +3.5 to +4V due to the biasing requirement for the output MOSFETs (i.e., the op amp is not driving the "center" of the bias voltage span). This means that if you were to connect a Jung-style inner feedback loop here, it will adversely affect the amp's total output DC offset voltage. Indeed I've experimented with exactly that on the breadboard prototype, and proved it to be true (the offset went from a fraction of a mV to ~30mV). Not a good thing. The purpose of multiloop is to reduce distortion, but as it turns out, the M³ prototype measured as well or better than a multiloop'ed PPA wrt. distortion.

 Hope that answers your question._

 


 was that over the complete audio range or just 1K as typicaly THD will rise with frequency and multiloop trades a over all higher THD for a constant THD over a wide frequency range.

 Its is true that with several volts to eliminate is asking alot fom a low overall feedback topology. I had that exact same problem when operating Loudspeaker amps output open loop (Kind of a trend at the time and a nice one) a typical trippele Darlington controlled by one Vbe Multiplier i have seen preduce 200 or so mv of DC and this is bad evean for a speaker amp it would be real bad for a headphone. 

 In closing as AMB pointed out there is no one perfect topology as every eliment must be considered as a system.


----------



## amb

Quote:


  Originally Posted by *ppl* 
_was that over the complete audio range or just 1K as typicaly THD will rise with frequency and multiloop trades a over all higher THD for a constant THD over a wide frequency range._

 

For THD, yep, it's just at 1KHz because that's what RMAA does, and doing THD measurements at high fundamental frequencies aren't too meaningful with computer sound cards, because of the sampling rate limitation means that we aren't measuring many of its harmonics. What I really need is a good 'ol wide-band distortion meter and a very low distortion function generator, but my budget currently doesn't allow for that. 
	

	
	
		
		

		
		
	


	




 For what its worth, RMAA 5.4 has a IMD vs. frequency plot, and the M³ prototype measured very well, producing a flat line across the whole audio spectrum (no rise in IMD at high frequencies). I don't really know how RMAA internally does this test, though, so that's the reason for the FWIW.

 The fact that this is a class A amp means that it should have good linearity at the output stage, which is good for keeping distortions low.


----------



## ppl

I did not imply that the M3 measures bad at all just clerifiying what the advantages of Multiloop or large open loop bandwdth. and AD-825 dose this all on its own as as sutch is a perfect OPA for conventionial Globial feedback applications.


----------



## jamont

Quote:


  Originally Posted by *ppl* 
_AD-825 dose this all on its own as as sutch is a perfect OPA for conventionial Globial feedback applications._

 

Could you elaborate on this? Thanks!


----------



## raif

Quote:


  Originally Posted by *pabbi1* 
_And, is M³ vastly superior to the modded AMB SDS? Details, por favor?_

 

I am sorry, I just caught this post. As I said earlier, I did prefer the m3, but I really would like to hold off on details until I can hear a more finalized version. I tend to talk in superlatives and I don't want to create a FOTM craze for something that is still sitting on a breadboard.

 Also, I think amb answered this a little, so hopefully you got what you wanted to know.


----------



## pabbi1

Thanks Raif... I'm trying to extrapolate where my SDS v1.1 is from the modded v1.2, and then up to the M³. I read the verbage, but was after the superlatives to describe the sound.... 
	

	
	
		
		

		
		
	


	




 I _love_ my SDS, and realize the improvements that can be made, and greatly appreciate that Ti, Morsel, and others have found this is a worthy project to spend their time on to push forward.


----------



## amb

Quote:


  Originally Posted by *jamont* 
_(About AD825) Could you elaborate on this? Thanks!_

 

Looking at the datasheet, the AD825 has relatively low open-loop gain (76dB) compared to most other opamps, which means it must use a good amount of internal local feedback. It also has fairly good output drive capability (50mA).


----------



## amb

While Morsel is out of town I did more work with the prototype and more testing.

 The prototype is now running in full three-channel mode. It also has a capacitance multiplier transistor on each supply rail, fed by a JFET current source to power the opamps (see schematic in the beginning of this thread). This in effect multiplies the 100uF capacitance by the DC current gain _hfe_ of the pass transistors. Note that the capacitor is bridged across the bases of the pass transistors without being referenced to ground. This provides a good degree of rail isolation without the use of another voltage regulator. Use of IC voltage regulators cause more voltage drop each rail, and they must be referenced to ground which I'd like to avoid.

 Note that this is a bit different than the parallel JFET rail isolation scheme found on the PPA. The BJT pass transistor fed by a JFET CCS here provides greater current capability, which allows me to power all three opamps. I am leaning with this approach rather than having one per channel, which leads to reduced parts count. The current draw in each opamp is quite steady and there is no advantage to having one capacitance multiplier per channel.

 Furthermore, the signal ground is now a virtual ground, derived via a TLE2426 rail splitter, which is fed by the clean and isolated rails after the capacitance multiplier as shown in the schematic. Having a single capacitance multiplier and rail splitter for all opamps removes any possibility that multiple TLE2426s might "fight each other" while driving a common virtual ground.

 I tested the amplifier running at maximum output into a 33 ohm dummy load, while watching for ripples on the op amp supply rails with an oscilloscope (across both rails, and from each rail to the virtual ground), before and after these modifications. The benefit of each of these changes was quite evident.

 I also ran RMAA tests using an M-Audio Transit, and generated a report that compares the latest results against two previous measurements, as well as of the M-Audio Transit in loopback mode as a baseline. To view the report, look at the link below. I added some remarks to clarify the tests and results.

http://www.amb.org/mmm/comparison_20041019.htm

 I am very happy with the outcome so far and am excited that the continuing work is producing excellent results. While these measurements alone do not tell you how the amp sounds, I am pleased to say that it's everything I've hoped for and more. I dislike using ethereal adjectives to describe the sound, but it is very, very good.

 I am going to wait for Morsel to return from her trip to discuss the results of these developments, and hopefully we'd be making some important headway soon.


----------



## Nisbeth

That looks very good AMB 
	

	
	
		
		

		
		
	


	




 Keep up the good work! 
	

	
	
		
		

		
		
	


	






 /U.


----------



## ppl

Sounds good i know the cap multiplier you speak of works quit well as i have used this configured as you did for quite awhile and this was going to be incorporated into the PPA as was a High speed fully ground plane PCB however the other PPA team members overruled me on these aspects.

 Another thing you might consider is that in my early tests with the PPA i found three isolation op amp rails gave more imaging i suspect this is due to some inter-capacitive effects and PCB Foil inductance.

 You don’t have to reference a voltage regulator to ground referencing to the opposite supply rail is fine as long as the maximum input voltage to the regulator is not exceeded also two complementary regulators can be referenced at there midpoint as in a Dual tracking arrangement, Just a thought.

 If the jfets are somewhat matched with regard to Idss the TLe’s will not fight each other as they are isolated by the Rds on of the fets . Since the M3 is not a portable amp any mismatch in Idss of the fets will only serve to raise the current drain of the amp and just might be of some benefit by serving as a preload or Bias for the capacitance multipliers.

 The above are just my thoughts on some things you might want to investigate prior to the final PCB layout.


----------



## Tyop

I just finished reading this entire thread and want to compliment team M*³ on their achievement so far and to cheer them on in their quest for yet another DIY fix for us with good credit! Veni Vidi Visa!

 (I don't know half of what's been discussed, but I do enjoy the "clash of the titans" as much as anyone else.)


----------



## gradofan

I can't help at all from a technical aspect, but if you folks at M3 need to borrow any headphones for testing, perhaps I can be of some assistance.


----------



## amb

Quote:


  Originally Posted by *gradofan* 
_I can't help at all from a technical aspect, but if you folks at M3 need to borrow any headphones for testing, perhaps I can be of some assistance._

 

That's very generous of you. Your sig says that you have a HD600, which I already have. Your handle says that you might have some Grados? We'd love to have one on hand for low-impendance testing. But, you're in OH, and Team M³ is located in "Silicon Valley" CA, so we're not exactly neighbors. 
	

	
	
		
		

		
		
	


	




 Fortunately, though, there are several other head-fi'ers nearby who also have a good collection of differerent cans (including Grados and similar) who we've been able to get help from; not only for the use of their headphones but also their ears.


----------



## mekanoplastik

would this design (in 2 channel conf.) work good as preamp? ..if it is the case, could you add some kind of jumper or switch and a "fake gound" to avoid the 3rd channel and use it as preamp?? ... it shouldnt add many extra component but it would add an extra funcionality some people may apreciate..... 

 about the pot....you could add pins (ala ppa diamond) and connect a daughterboard with all the different pots holes independen of size, this way it can be placed where is needed and it should not take much room..althou it would requiere a taller enclosure and the manufacture of the extra board...just an idea

 keep up the good job !!!, it is truly entertaining to see a real world engineering project step by step...


 m.


----------



## morsel

Any 3 channel amp such as the M³ or PPA can be used as a preamp as long as input ground, not output ground, is used for the preamp outputs. There is no need to alter the circuit in any way. Just remember that output ground is for the headphone jack only.
  Quote:


 it is truly entertaining to see a real world engineering project step by step... 
 

This is definitely not the real world.


----------



## pabbi1

Current updates?


----------



## morsel

We want to compare FET current source .vs. capacitance multiplier on the opamp power rails before we commit to one or the other. I will post a new layout once we have done this testing. There is no need to ask for updates, we will let you know when we have news for you.


----------



## superjohnny

Quote:


  Originally Posted by *morsel* 
_This is definitely not the real world. 
	

	
	
		
		

		
		
	


	


_

 

Which world is it?


----------



## morsel

Our initial comparison of cap multiplier .vs. FET current source .vs. no rail isolation was inconclusive. We were unable to duplicate the results of 2004/10/19, which suggests the improvements were due to the other circuit modifications. We will perform more specific tests and post a new layout as time permits.


----------



## amb

Quote:


  Originally Posted by *morsel* 
_We were unable to duplicate the results of 2004/10/19_

 

Actually we were able to reproduce the RMAA results of 10/19 almost exactly (with the exception that the crosstalk curve being _slightly_ worse this time, by about 1dB, but this could easily be variations in test setup layout, etc.).

 The part that we were not able to conclusively determine was whether the capacitance multiplier was better than simple JFET isolation, or for that matter, no rail isolation. This was not tested with RMAA but was done with a scope and function generator. The residual noise observed on the supply rails drowns out what we were looking for. Come to think of it, I may have had the scope set up with the wrong horizontal time scale, so we were not looking at the right thing.

  Quote:


 We will perform more specific tests and post a new layout as time permits. 
 

Yes, we will do more testing soon.


----------



## superjohnny

I don't mean to be a pain, but do you have any idea when you will be complete? How does it compare soundwise & pricewise to the PPA?

 I can't be the only person wondering


----------



## amb

superjohnny,

 Morsel is hard at work on the PCB layout and will post a first draft of a complete board for comment soon. We will be building an engineering prototype based on that board layout and verify its design and performance. Assuming that all is well, then we will finalize the M³ v1.0 circuit and layout, and proceed to order the first batch of PCBs. Since we're not working to a specific schedule it is difficult to predict when this will all happen, but rest assured we're pushing along as quickly as we could.

 As for cost, both the PPA and the M³ could vary greatly depending on the parts selection (the opamps and capacitors/resistors you use, the pot or stepped attenuator, jacks, power supply, the enclosure and whether you add customizations and options). I'd expect a PPA to be on par with the M³ if you were to build barebones versions of each. The PPA's output buffers are more expensive than the M³'s MOSFETs, but the M³ will have a bigger PCB and enclosure.


----------



## morsel

Morsel has been playing video games, seeing friends, and doing other lifely things this week, but will try to get back to the layout soon.

 There is no ETA on boards. (see post 1 of this thread)

 Comparisons between M³ and PPA will have to wait until we have a working pcb prototype.


----------



## morsel




----------



## morsel

board dimensions are currently 6 × 7 inches
 limited ground plane to input area
 guard traces for input traces (not sure if this really improves 
 separation, will be tested in a future PPA v2 prototype)
 added series diode for reverse polarity protection
 added LED and RLED
 added bass boost pot
 committed to a single capacitance multiplier for the opamp power rails
 removed 10 Ohm series resistors from opamp rails
 modified C6 from 1uF to .1uF
 modified capacitance multiplier to use NJFETs for both rails
 (2N5484 or 2N5457)
 choice of TLE locations
 choice of 12.5mm or 18mm rail caps

 We would like to lower the default gain from 11 to 5, but gain and bass 
 boost are intimately intertwined, so we are going to defer on that until 
 some of the concurrent issues are ironed out. Note the thin red lines 
 connecting the right channel bass boost circuit to the bass boost pot, 
 which are possible trace routings. Alternatively, the JbbR jumper could 
 be hand wired to SbbR, eliminating the need for traces from the right 
 channel passing through the left channel, an issue that may bother some 
 purists, and may have a small effect on channel separation. The JbbR 
 under the pot would have to run under the pcb, whereas the other JbbR 
 could be wired either way.

 We need to get a clear idea of the range of bass boost capacitors people 
 are likely to use for both high and low gain configurations, so we can 
 better gauge the requirements for Cbb lead spacing. Lower gain and lower 
 feedback resistors mean larger bass boost caps. Also, I am not convinced 
 we need 3 pairs of electrolytic caps on the opamp power rails. Dropping 
 down to one shared pair and moving it to the empty area below the right 
 channel would save a lot of space, allowing for more graceful routing of 
 the bass boost functions and reduction of board surface area.

 C6 is now a slimmer .1uF film cap, which will provide clearance between 
 the cap and the opamp, important if using BrownDog adapters. 1uF caps 
 can still be used, but it will be a tight squeeze on one edge.

 There is no rear "no fly zone" because this board is not intended to sit 
 flush with the rear panel. A 6 × 7" board needs a 6.25 × 8" case. There 
 are no cases we know of that are close to those dimensions, so custom or 
 oversized cases are the logical choices. If there are any compelling 
 case choices that would require a change in layout, please let us know 
 asap so we can take them into consideration.

 There is a tantalizing empty area at the front panel where board mount 
 headphone jacks might be located, however we did some research on this. 
 Every make and model of board mount headphone jack requires a different 
 pinout, many of them require slots, not holes, and the double sided 
 power distribution bus would have to be replaced by a complex matrix of 
 parallel traces and vias to allow the outputs and power rails to cross. 
 We decided that panel mounting and hand wiring the jack(s) is best.


----------



## Nisbeth

This looks great Morsel!

  Quote:


  Originally Posted by *morsel* 
_We need to get a clear idea of the range of bass boost capacitors people are likely to use for both high and low gain configurations, so we can better gauge the requirements for Cbb lead spacing. Lower gain and lower feedback resistors mean larger bass boost caps. Also, I am not convinced we need 3 pairs of electrolytic caps on the opamp power rails. Dropping down to one shared pair and moving it to the empty area below the right channel would save a lot of space, allowing for more graceful routing of the bass boost functions and reduction of board surface area._

 

If the calculations for the cap value is similar to the PPA, you need to fit caps in the 220-330 nF range IMO. This means 15 mm lead spacing for both Wima and Rifa MKP types.

  Quote:


  Originally Posted by *morsel* 
_Also, I am not convinced we need 3 pairs of electrolytic caps on the opamp power rails. Dropping down to one shared pair and moving it to the empty area below the right channel would save a lot of space, allowing for more graceful routing of the bass boost functions and reduction of board surface area._

 

 If you can make the PCB considerably smaller by going to a single pair of 18mm caps, I think it is worth it. 

  Quote:


  Originally Posted by *morsel* 
_We decided that panel mounting and hand wiring the jack(s) is best._

 

Sounds like it is the best decision in this case.

 Once again, kudos to you and AMB (and anybody else involved in this). I'm looking forward to seeing more 
	

	
	
		
		

		
			






 /U.


----------



## 00940

Great looking project 
	

	
	
		
		

		
		
	


	




 Just a little question : would you consider to put traces for smd opamps directly on the board ? Since there's not traces on the top layer, it should be rather easy.


----------



## morsel

I would consider putting so8 opamp traces on the board. They would have to go on the underside, not the top side, due to mirror image superimposition. (see PIMETA, PPA v1.0, etc.) The reason I have not done this is to encourage socketing the opamp for easy replacement. This same argument took place over PPA v1.1 and the so8 pads lost, so I defaulted to no so8 pads.


----------



## Earwax

Quote:


  Originally Posted by *Nisbeth* 
_If you can make the PCB considerably smaller by going to a single pair of 18mm caps, I think it is worth it. _

 

I'll have to take the other side on this one. If subjective or objective tests indicate that the added caps help, I'd say who cares about board size.


----------



## NOTHINGness

Looking at the PCB I see you have the left and right channels next to each other, where the PPA has the ground channel between the left and right channels. Just wondering what the reason for this is, since IMO the board would be more symmetrical if the ground channel is in the middle.


----------



## Wodgy

Just a simple suggestion: eliminate the hole-and-cross connections where some pads meet the ground plane. This prevents the short traces from radiating high frequency energy and just looks more professional. It's an easy change in Eagle (a property of the ground plane).


----------



## morsel

The PPA has the ground channel in the middle partially because it can't go on the right side due to space considerations. While it might superficially seem nicer to have the ground channel in the middle, having the right channel in the middle reduces the length of the input trace from the pot to the right channel, which is a more important consideration.

 The thermal pads are intentional. They facilitate soldering and reduce the chance components will be damaged by overheating during assembly.


----------



## pabbi1

What are the trade offs in using the shared caps on the opamp power rail? I'm for fewer parts. unless there is any sonic benefit.

 What are the bias parts? trim pots?


----------



## amb

Quote:


  Originally Posted by *pabbi1* 
_What are the bias parts? trim pots?_

 

The bias parts are everything after the output of the opamps up to the MOSFETs.


----------



## amb

I would like to hear more opinions about the bass boost pot wiring to the right channel block. As Morsel pointed out, note that the left channel has real PCB traces for this purpose but the right channel has a couple of thin red lines suggesting where such traces might go. Alternatively, we would also consider no traces, so that if you want bass boost you'd have to run a pair of wires from the right channel block to the pot. The advantage of having traces is no separate wires off-board, the disadvantage is that the traces must cross the left channel amp block and the space is tight. Let us know what you all think about this.

 There are two different TLE2426 rail splitters shown on the PCB. These are suggestions of the location for a single unit. In my opinion either is fine, but we'd like you to help convince us that one might be preferable over the other.

 As for Morsel's suggestion about going to one single pair of (possibly larger) C5 electrolytic caps for all three opamps rather than three separate pairs; the theory is that having three separate pairs each located close to the opamp should be better, but we are not sure there would actually be a measurable or audible difference. Going with just one pair would allow us to shorten the board size by approx. 0.4 inch vertically. This means that we could actually fit the board into a 6-inch wide (external dimension) case and have some space for clearance and case thickness. Otherwise the case will have to be at least 6.25 inches wide. This may not be a big issue unless you already have a 6" wide case, but it might be convenient to have nice round numbers for the case dimension (at the expense of a fractional board dimension).
 Alternatively, the space we save could be better used to route the right channel bass boost traces. We'd like to hear your opinions about this too.


----------



## ble0t

I guess my thought is use the extra space to get good routing. The board is already out of the 'mini' category at 6"x7" and there are a lot of chassis' out there with 8" dimensions. I dislike 'external' wiring, so I'd say keep as much on board as possible


----------



## SDA

I agree, I'd rather see better trace routing than a small reduction in size, and I'd definitely rather have the traces on the PCB than deal with wires. (So I'm lazy.) Also, I'm probably missing something here (I tend to miss things, heh), but wouldn't one of the big Hammond 1455s fit the board in its current size/shape? I thought the biggest one was eight point something by 6.3in, seems like it'd work for this to me..

 I'd also say that if the extra caps do turn out to help, then I'd rather see them in anyway. That's a pretty big "if," though.

 EDIT: Found it, sure is big compared to the rest of 'em: 1455T2201


----------



## tangent

Is there any reason you're not using the 8-pin version of the TLE2426? It looks like you have the room for it.


----------



## morsel

We could adapt the board to fit the 1455T22011 but the internal height of less than 2" means short heat sinks would have to be used, and the lack of ventilation would be a serious problem.

 The 8-pin TLE is a possibility. I took a quick look at the pdf and saw no info on proper use of Cnr, does anyone have a pointer on this?


----------



## ble0t

Perhaps a small cap from output back to CNR? Funny how the datasheet doesn't have anything


----------



## amb

Quote:


  Originally Posted by *morsel* 
_The 8-pin TLE is a possibility. I took a quick look at the pdf and saw no info on proper use of Cnr, does anyone have a pointer on this?_

 

Tangent's virtual ground writeup shows a schematic with a 1uF Cnr going to the negative rail:
http://www.tangentsoft.net/elec/vgrounds.html

  Quote:


  Originally Posted by *ble0t* 
_Perhaps a small cap from output back to CNR?_

 

You'll see from the datasheet that doing that basically wraps a positive feedback loop around the TLE2426's internal buffer. I think it would make the TLE2426 unstable.


----------



## ble0t

I stand corrected


----------



## amb

My hunch is that you could also connect Cnr to the positive rail and the effect would be the same.


----------



## eweitzman

Quote:


  Originally Posted by *Lil_JV* 
_Is it okay if we just write M3 in the future? It is even easier than MMM._

 

 Quote:


  Originally Posted by *morsel* 
_M3 is a model of BMW. Why not just copy and paste M³ from a previous post?_

 

 Because
 1) a google search on "site:head-fi.org m3" yields a lot of hits for a certain MP3 player
 2) Micro$oft's file systems don't care much for superscript

 - Eric


----------



## ble0t

Whoa...those posts are a blast from the past 
	

	
	
		
		

		
		
	


	




 More to the matter at hand, any updates/decisions?


----------



## amb

Quote:


  Originally Posted by *ble0t* 
_More to the matter at hand, any updates/decisions?_

 

No, we're still waiting for more responses to trickle in. If there are updates we'll post them.


----------



## digi01

Any updates?i'm looking forward to this design.
 and i'm very glad to help you to do something useful.


----------



## amb

Quote:


  Originally Posted by *digi01* 
_Any updates?i'm looking forward to this design.
 and i'm very glad to help you to do something useful._

 

Thanks digi01. Morsel has gone out of town for a few days and has no email/web access. As soon as she returns I'll meet with her to discuss the open issues and I hope to order a couple of first-cut engineering prototype PCBs to build and test. We'll keep you all posted on the progress.


----------



## digi01

OK,thank you.I am very interested in test it.

 cheers


----------



## koladd

I just finished building PPA. And I'm really impressed with its improvement over my previous setup (CMoy and Szekeres). Thanks guys for your contribution. I'm considering taking a course next spring in analog IC design so I might be able contribute later to the society.

 I was excited to find out this new M3 project coming up. Can't wait to build it.

 I wonder if you guys could include some solution for the pop when the amp starts up.

 It seems like the common solution now is either take them off the head or add another switch so that the headphone output could be turned on seperately to avoid the spike in the power rail. Some people used relays or digital ICs to add a time delay, which I figure might go against Morsel's "keep it simple" principle.

 I wired my PPA heaphone output to a DPDT switch which works pretty well. However, it would be better if there are holes on the PCB to wire the switch directly to the board in stead half way between the output jack and the OL, OR, OG holes.


----------



## JohnFerrier

Quote:


  Originally Posted by *koladd* 
_I wired my PPA heaphone output to a DPDT switch which works pretty well. However, it would be better if there are holes on the PCB to wire the switch directly to the board in stead half way between the output jack and the OL, OR, OG holes._

 

I used switches too. I couldn't think of a better way/higher quality means of preventing a on/off pop... Relays use power (which for a battery powered system is a negative) and may cause a small technical degradation...


 JF


----------



## amb

We didn't design any pop-elimination scheme into the PCB, but you could always do whatever you want when you build the amp. Relays, switches, whatever. I find, though, on the M³ prototype and listening through the HD600, there is virtually no turn-on pop, and only a faint hiss and click on turn-off. Nothing to be worried about as far as headphone safety is concerned.


----------



## koladd

Quote:


  Originally Posted by *amb* 
_We didn't design any pop-elimination scheme into the PCB, but you could always do whatever you want when you build the amp. Relays, switches, whatever. I find, though, on the M³ prototype and listening through the HD600, there is virtually no turn-on pop, and only a faint hiss and click on turn-off. Nothing to be worried about as far as headphone safety is concerned._

 

That sounds nice. I think I've been paranoid with my HD600 hooked up to PPA. I've never tried once to see how loud is the pop with HD600. Maybe it's not as loud as with HD280 due to its higher impedance. I may try it later.

 JF, I'm gonna try using a 4P3T rotary switch to realize the power on/off sequency. 2 poles for power and 2 poles for the headphone output. Since there are 3 switchable positions, I'm gonna implement it this way.

 1st position: both power and headphone off
 2nd position: power on and headphone off
 3rd position: power on and headphone on

 With toggle or rocker switches this could be only done with two switches. Sometimes you forget which to turn on/off first. The rotary switch will totally eliminate this problem.


----------



## skyskraper

mm interesting. i think i will try this idea out on my next headamp.


----------



## JohnFerrier

Quote:


  Originally Posted by *koladd* 
_JF, I'm gonna try using a 4P3T rotary switch to realize the power on/off sequency. 2 poles for power and 2 poles for the headphone output. Since there are 3 switchable positions, I'm gonna implement it this way.

 1st position: both power and headphone off
 2nd position: power on and headphone off
 3rd position: power on and headphone on

 With toggle or rocker switches this could be only done with two switches. Sometimes you forget which to turn on/off first. The rotary switch will totally eliminate this problem._

 

Very interesting idea. You'll need to verify that between positions 2 and 3 that power doesn't turn off... Make before brake. (If it's not, then your idea probably will still work because the switching will be fast...the capacitor will probably hold the voltage up...)

 I've gotten used to a power on sequence. The headphone out switches is over the power switches. So, to turn on it's: (from bottom to top) up, up. Then for off it's: (from top to bottom) down, down. This is a smooth operation... I use totally seperate power for each channel. So, there are seperate switches for left and right. They are next to each other so, I do this with one hand... (Not that headphone listening has a problem with channel seperation... : ).


 JF


----------



## koladd

Quote:


  Originally Posted by *JohnFerrier* 
_You'll need to verify that between positions 2 and 3 that power doesn't turn off... Make before brake. 
 JF_

 

JF, thanks for the suggestion. There're several "shorting" rotary switches available at Mouser, e.g. 10WA367 and 10WR046. For my PPA, I'm even planning on putting the Linkwitz crossfeed and bass-boost all on another rotary switch (4P6T 6 position = 3 crossfeed levels X 2 bass-boost settings) . This way I will have one for the power and another for all the different effects. I think this idea could also be borrowed for M3 project, although I think it would be left to individual's preference.

 I'd like to know if having so many wires cramped together would have some issue with cross talk. That's my only concern.


----------



## JohnFerrier

Quote:


  Originally Posted by *koladd* 
_I'd like to know if having so many wires cramped together would have some issue with cross talk. That's my only concern._

 

It would be good to keep things seperate, especially power and signal. This will be less of a problem if you've got a good power source (with no ripple). Batteries are an excellent power source for audio (except for the need to recharge or replace...)

 You seem like a very thoughtful person. It's good to think all this out before you start building...

 Maybe you've seen the following link before. You can enter part numbers of all kinds of electronic parts that you are looking for (not just chips)...
http://www.findchips.com/
 Maybe you found your switch this way as Mouser is the only one that carries it. Anyway I like that link and using Digikey's website...


 JF


----------



## morsel

I suggest using a DPDT power switch, which connects the amp circuit either to the power source or a 1 Ohm resistor which rapidly discharges the onboard power caps, reducing or eliminating turn off noise.


----------



## JohnFerrier

Hi morsel,

 The other day, I went back through some of my original posts and noticed that you posted several answers for me. Thanks. How was I to know who you were? That was before I knew morsel was morsel (so to speak). You had a different avatar then--it was a potatoe, or a gear, a mushroom, or a flower, or something...I can't remember...


 JF


----------



## koladd

Quote:


  Originally Posted by *morsel* 
_I suggest using a DPDT power switch, which connects the amp circuit either to the power source or a 1 Ohm resistor which rapidly discharges the onboard power caps, reducing or eliminating turn off noise._

 

Sounds great, Morsel. This will totally eliminate the turn off noise. I don't have an idea about the power rating of the resistor. I don't want to use a chunky resistor in this case. But I doubt if 1/4 W resistor will be able to handle the peak current at the instance of turning off. Aside from that, this solution would work only for power off pop elimination, but not for power on, if I'm thinking right.

 JF, thanks for the link. I'm not aware of it before. I think I'll use it from now on whenever I need any parts. I happen to have a power supply with 0.25 mV RMS Ripple specified on the datasheet. I guess in this case it would not be a big issue with the crosstalk. You are right, shielding is almost impossible with these rotary swithces.


----------



## JohnFerrier

Quote:


  Originally Posted by *koladd* 
_But I doubt if 1/4 W resistor will be able to handle the peak current at the instance of turning off. Aside from that, this solution would work only for power off pop elimination, but not for power on, if I'm thinking right._

 

I = sqrt(P/R) = sqrt(0.25 W / 1 ohms) = 0.5A. This should work. It will only be a brief spike too...


 JF


----------



## koladd

Quote:


  Originally Posted by *JohnFerrier* 
_I = sqrt(P/R) = sqrt(0.25 W / 1 ohms) = 0.5A. This should work. It will only be a brief spike too...
 JF_

 

You're probably right. However, P_peak=U^2/R=24^2 V/1 ohm=576W. That's the peak power at the moment of switching. My concern is if this would be bad for the resistor.


----------



## JohnFerrier

Quote:


  Originally Posted by *koladd* 
_You're probably right. However, P_peak=U^2/R=24^2 V/1 ohm=576W. That's the peak power at the moment of switching. My concern is if this would be bad for the resistor._

 

Actually, I was thinking that this resistor was used to short the headphone output when powered off (to prevent a turn-off pop). In this case, a spike would likely not exceed 0.5A by much, if at all...

 I'm not sure. I guess I wouldn't do it this way...

 I like seperate power and signal switches. But, my amp is not a portable rig. It's easy for me (by design) to get into the habit of a power on/power off sequence.


 JF


----------



## koladd

I guess I was wrong. The resistor rating should be RMS, so a transient probabily won't matter at all. But since during the switch off, the capacitors and 1 Ohm resistor from a R-C loop with initial voltage 24V due to the charge in capacitor, the peak power calculation would still be correct, theoretically. 

 I was actually impressed by your design, in which the switch are laid out in such a way that it would be easy to form a habit. Nice discussion with you though. I have something in mind (some other idea) but I'll shut up for the moment until I test it out.


----------



## morsel

Alternatively, one could follow the time-honored practice of turning the volume all the way down before powering off.

 JF, your memory is better than mine. I was ready to deny having a different avatar but then I recalled that it was indeed a hot chile pepper.


----------



## eweitzman

A 4P3T switch between amp and hp jack will introduce it's own turn-on/turn-off clicks and noises. And it will be in the circuit when the amp's in use, so it has to be a high quality switch. If you're switching the AC along with the output, you'll have an AC field jus ta fraction of an inch away from the audio output.

 - Eric


----------



## JohnFerrier

Quote:


  Originally Posted by *morsel* 
_JF, your memory is better than mine. I was ready to deny having a different avatar but then I recalled that it was indeed a hot chile pepper. 
	

	
	
		
		

		
		
	


	


_

 

I was trying to surprise you and find it at the following site: http://web.archive.org/web/*/http://www.head-fi.org (Actually, I was going to try and trick you by posting it with the message "Is someone's firewall down?"...to test your steel...) Archive.org is great for finding info (and graphics sometimes) from past websites... Unfortunately, in head-fi's case, they link to the current avatars...

 Take care.


 JF


----------



## koladd

Quote:


  Originally Posted by *eweitzman* 
_A 4P3T switch between amp and hp jack will introduce it's own turn-on/turn-off clicks and noises. And it will be in the circuit when the amp's in use, so it has to be a high quality switch. If you're switching the AC along with the output, you'll have an AC field jus ta fraction of an inch away from the audio output.

 - Eric_

 

Eric, the hp jack is disconnected when the the power is switched on. The idea of using rotary switch is that you heaphone is not in a closed circuit when the power is switched on. The switch is for DC power source and it's a shorting type . If you short the position 2 and 3 (power is switched on from position 1 to 2) associated with the power poles on the rotary switch, the power will remain connected when the headphone is switched on (from position 2 to 3). I don't see where this would introduce clickes due to switching. I agree that a high quality swtich needs to be used. I'm going right now for Lorlin switches. The power rating should be good. I hope it works well.


----------



## eweitzman

koladd,

 I understood the purpose of the sequential switching. It's clever: I think I might use it in my next amp.

 When you use switch position 3, there will be clicks on turn-on and turn-off because of (1) contact bounce (2) load changes on the amp and (3) double load changes on the amp: the M³ has an active circuit on both hot and "ground" so you have two amps per channel being loaded and unloaded, and maybe not at precisely the same moment either because no switch is perfect. Two bounces/load changes per on, two per off. Per channel.

 I made a passive linestage. I thought I'd be clever, and wired the input selector to switch both hots and grounds to reduce crosstalk. (It's a milspec surplus Greyhills 4P6T switch.) Switching the grounds had the nasty side effect of permitting slight DC offsets in the disconnected components: some of them made little noises when switched on/off. I went back to a traditional approach.

 These noises would probably be no worse than what you'll get inserting and removing the headphone jack, though. But since your goal is to eliminate the noises ... nevermind ...

 - Eric


----------



## koladd

Quote:


  Originally Posted by *eweitzman* 
_koladd,
 there will be clicks on turn-on and turn-off because of (1) contact bounce (2) load changes on the amp and (3) double load changes on the amp: the M³ has an active circuit on both hot and "ground" so you have two amps per channel being loaded and unloaded, and maybe not at precisely the same moment either because no switch is perfect. Two bounces/load changes per on, two per off. Per channel_

 

This makes sense to me. I haven't thought about the load change as a factor. My current switch for headphone (since I haven't implemented the rotary switch idea yet) is DPST rocker switch for the headphone outputs. Frankly, I can't hear the pop when I switch them on, given that the power is already switched on. I believe they do exist, but the level must be much lower than the pop due to the power switch on. Would you think that connect some resistors (with lower resistance than the headphone) between poles for headphone output and position 2 will give a less dramatic change in load when the rotary switch goes from position 2 to 3, since the step change in load is smaller from a buffer's perspective?


----------



## eweitzman

Quote:


  Originally Posted by *koladd* 
_Frankly, I can't hear the pop when I switch them on, given that the power is already switched on. <snip> Would you think that connect some resistors (with lower resistance than the headphone) between poles for headphone output and position 2 will give a less dramatic change ... ?_

 

In retrospect, I don't think my experience with my passive is applicable and I probably should have kept my mouth shut. 
	

	
	
		
		

		
			





 As long as you're using a switch with good contacts, you should be alright. Adding a resistor will lower the sensitivity of the phones and make the noise less audible, but then you're just asking for more power from the amp, less headroom, more heat, and an extra resistor to muck up the sound.

 - Eric


----------



## jamont

Quote:


  Originally Posted by *morsel* 
_JF, your memory is better than mine. I was ready to deny having a different avatar but then I recalled that it was indeed a hot chile pepper. 
	

	
	
		
		

		
		
	


	


_

 

I don't remember it either, but I agree that morsel is hot stuff!


----------



## Voodoochile

Just a couple of thoughts on the layout thus far. It's looking pretty nice so far, I think.

 Regarding the TLE, I prefer the rear location, removing the front location. I also would think it would be desireable to utilize the DIP-8 TLE, the cost is negligible, and there can be performance improvements. I'm not so sure that those improvements could be notable in this application, but if the cost is essentially the same either way, why not have the option.

 As for the bass boost, I'm okay with either method of connecting the right channel. I'm more inclined to favor the wire, though. If you don't want boost, then you don't have the crossed traces in place.

 Main power caps: again, either way works... but I do think that you have more options with 18mm caps. Either many smaller caps or two-three big caps should offer similar performance. You can make the case shallower with many smaller caps, presuming the heatsinks are not taller than the 18mm caps anyway. If the minimal heatsink spec is 40mm or taller, then might as well stick with the 18mm caps.

 Regarding the gain, I'm glad to hear that you are trying to reduce it. If I had to pick one universal gain for any and all apps, it would be more like 6 or 6.5. I use 5 to 7 most often.

 As for the C5 caps. I definitely prefer a pair per channel. I think you have plenty of room for them, also.

 Finally, although you don't seem to have a maximum board size target or chassis in mind, it seems like a large amount of extra space to the right, especially considering that there are potential issues elsewhere (bass boost routing). I'd like to see one of two things-

 Either keep the big board, and add the pads in the rear for the Dact attenuator, keeping the Alps up front...

 or move both existing pots to the left by about half their width (heat from the sink should not be an issue, it's close already); move the front right mounting hole to where the version nomenclature is; drop the traces to the rear and have pads for some star-quad (including the shield) right at the back of the pot; move Q5+/- Q6+/- C4 group to the front a little bit, affording more clearance for a mounting hole at the right rear; slide the power cap bank a bit towards the front affording more clearance for the left rear mounting hole.
 This should allow you to take the width down to about 5" (maybe), or certainly 5.25", and you could also shave off 0.125" to 0.25" from the rear without too much trouble.

 It seems somewhat frivilous to have such a wide board only to accomodate traces to a front-mounted pot... you still need to cut and solder leads to run to the board either way. I have tried both locations on the PPA, and they both work very well if you are careful with your wiring. Don't run a long straight wire to the pot, hugging a power supply along the way, for example.

 But of course the extra board cost from having it as it is would not be huge, and I'm not complaining, mind you. It would offer some further flexibility in fitting the amp and/or psu to a chassis.

 Nice work, morsel and amb! Take your time and do it whichever way works the best.


----------



## morsel

Jamont: I love hot peppers and sometimes have a hot temper. 
	

	
	
		
		

		
		
	


	




 VC: Thanks for your thoughtful and detailed post. We will take some time to digest your proposals and get back to you. Its good you posted when you did as we were about to settle on a prototype.

 A few quickie replies:

 We discussed the DIP8 TLE and concluded it was not worth the trouble.

 We will probably include traces for bass boost in the prototype so we can test and see if they cause problems.

 Either 12.5 or 18mm power rail caps may be used as there are pads for both.

 At some point we will include alternate component values for a gain of 6.

 We plan to compare 1 .vs. 3 pairs of opamp rail caps.

 More after I talk to AMB.


----------



## morsel




----------



## amb

Hi folks, what morsel posted above are two alternatives of the M³ pcb layout for your comment.

 The first one is 6"W x 7"L and has the input pads at the right (which corresponds to the rear of the case). The input traces then run the length of the board under a ground plane and "protected" by ground guard traces to the volume control pot. This layout has the advantage that the length of hand-wiring from the RCA input jack to the board is minimized, and the board would provide optimum traces to the volume pot.

 The second one is 5"W x 7"L and includes some of Voodoochile's suggestion. It dispenses with the full length input traces on the board. The input pads are adjacent to the volume pot, which means that the hand-wiring from the RCA input jacks must be routed to this location. To minimize crosstalk and interference we recommend separate shielded coaxial wiring per channel be used here. The upside to this layout is the reduction of the board width by one full inch, which lowers the board cost a bit and potentially makes case selection easier. Note that there is less room over where the M³ logo is, and this is where the headphone output jack would normally be situated. If two jacks are desired and the LED is to be mounted here too, the space will be tight unless a wider case is used. Also note that the entire amplifier block has been moved up by 50 mils so that the big 18mm capacitors at the top are now closer to the edge of the board.

 We would like to hear your opinion about these two layouts and which one you prefer. We are going to base the first engineering prototype on one of these so speak up now or forever hold your peace 
	

	
	
		
		

		
		
	


	




.


----------



## skyskraper

i do like the fact the second one gives more options for enclosures. is it possible to not use or just jumper across the bass boost pot ?


----------



## tophu

I generally like to have bass-boost just to counteract the low frequency roll-off in the 'phones frequency response. This requires relatively large capacitors, to the point where I need to run wire to them since they don't fit on the board.

 Would it be possible to ask for some extra pads with larger holes within the capacitor footprint to allow running wires? On the PPA I had to drill out the holes to run my wires.


----------



## amb

Quote:


  Originally Posted by *skyskraper* 
_i do like the fact the second one gives more options for enclosures._

 

The difference is one inch. So the minimum width for the case is 6.25" for the first one vs. 5.25" for the second to allow for the enclosure wall thickness and a hair of tolerance.
  Quote:


 is it possible to not use or just jumper across the bass boost pot ? 
 

Yes, of course. The bass boost is entirely optional. You can jumper around it, use the pot for continuous adjustment, or use a switch for simple on/off.


----------



## amb

Quote:


  Originally Posted by *tophu* 
_Would it be possible to ask for some extra pads with larger holes within the capacitor footprint to allow running wires? On the PPA I had to drill out the holes to run my wires._

 

How big are the caps you plan to use? Note that our layouts have six holes for each of the Cbb capacitor so you could fit a variety of different sized cap in there.


----------



## skyskraper

thats cool. ive just been offered a 6.5" wide extruded case thats why i vote smaller


----------



## amb

Quote:


  Originally Posted by *skyskraper* 
_thats cool. ive just been offered a 6.5" wide extruded case thats why i vote smaller 
	

	
	
		
		

		
		
	


	


_

 

If the inside dimension of the case is a bit over 6" wide x 7" deep then both designs would fit. The case will have to be tall enough to clear the heat sinks and the tall capacitors. The minimum heat sink we spec'ed out is 1.5" tall, and you must add board thickness plus standoff height and give a little extra for breathing room (for a total minimum of 2" H). Also, the enclosure should have ventilation slots because this amp will run warm.

 Edit: BTW, we are targetting a Par Metal series 20 case, in a custom size; either 5.5"x8"x2" (WxLxH) or 6.5"x8"x2" depending on which design we go with. You are of course free to choose other cases as long as it all fits.


----------



## skyskraper

oh im fine on everything except ventilation. ah well may as well use it for ppa 2.0 and just get a nice 1ru rack enclosure for mmm


----------



## Lil_JV

Lookin good! I can't wait to build this now. I wanna use a black beauty pot for bassboost. Mmmmmm stepped bass boost.

 JV.


----------



## Voodoochile

That was fast. 
	

	
	
		
		

		
		
	


	




 Looks pretty nice to me. As for the mention of having the HP jack where the logo and revision nomenclature is located, consider that you could also shift the volume pads back to the right a bit, with the wiring pads behind it, and then place the mounting hole for the PCB in between the two pots, under the HP jack. The you could have two options for placement of the jack within the scope of the board's width.

 As for wiring from RCAs to the PCB, small coax would work; I think that star quad would also work well. With the star star quad, I'd use two center conductors to wire the + and - signals from one channel, and solder the shield only to the RCA end's - tab. As for coax, Canare GS6 is great stuff, and nice and limber. The usual video options like L5CFB are great also, but pretty stiff.

 Just to reaffirm, I didn't have problems with the long side traces, and would not mind spending an extra ~$4 on a bigger board, but it just seemed like overkill when you have to run wires from the RCAs to the PCB already. I could see running the traces if you wanted board-mounted RCA blocks for inputs, but thankfully that is not the case! Until someone makes a heavy-duty RCA block, that is a cheesy route for certain.

 Another tiny tweak- how about wiggling the three C5+ caps a whisker towards the rear, just so the clearance from the C5+ caps to the OPAs equals the clearance from the C5- caps to the C6 caps? Or vice-versa.


----------



## skyskraper

i dont want to steer this thread off topic. but i was wondering have many people bought parmetal cases who arent from the usa? i have yet to contact them, but is shipping/pricing/payment reasonable?


----------



## tophu

Quote:


  Originally Posted by *amb* 
_How big are the caps you plan to use? Note that our layouts have six holes for each of the Cbb capacitor so you could fit a variety of different sized cap in there._

 

Well, they're big Orange Drop ones, about .5x1.5 inches. They also have .8mm leads.

 Chris


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## morsel

Tophu: .8mm = 31mil. We can enlarge the auxillary bass boost cap holes, but there is no way we can make room for a .5×1.5" cap. 600mil lead spacing is as good as it gets. There are plenty of reasonable choices that are much smaller. Methinks your monsters will have to float.

 Skyskraper: There are many good case manufacturers all over the world. Use a case from your country, no need to order overseas.

 VC: My principal concern is that without the input traces across the board, people will do a terrible job of wiring which will result in inferior amps. Shield grounded coaxial cables for left and right channels are mandatory for this kind of run, yet the temptation to use ordinary wire is great and that is what lots of people will do, then complain about hum and noise, especially if they use an internal power supply. I know you will do a beautiful job, but what about the unwashed masses with no attention to detail? PCB input traces allow for the use of ordinary wire to the input jacks. Going from 6×7" to 5×7" saves 15% of the board cost. 
	

	
	
		
		

		
			





 The input pads don't fit behind the volume pot because of the way the pot traces need to route. As a result there is nothing to be gained by moving the mounting hole between the pots. I don't see why C5+ should be moved, they are plenty far from the opamps, align with their power traces, and are consistently placed relative to the other C5 and C6 caps.

 Many headphone jacks are narrow enough for 2 to fit side by side with the bass boost pot in a 5.5" wide case. If really fat bodied jacks are chosen, use a 6" case. I would rather not force a congested panel layout by putting the pots too close together. I haven't done detailed measurements on this since there are so many permutations of jack model and additional panel components such as LED, power switch, etc. but I'm guessing this should not be an issue. Just go with a case wide enough to accommodate your chosen components. The current placement allows for good feng shui and ergonomics in the smallest possible case width.


----------



## tophu

Quote:


  Originally Posted by *morsel* 
_Tophu: .8mm = 31mil. We can enlarge the auxillary bass boost cap holes, but there is no way we can make room for a .5×1.5" cap. 600mil lead spacing is as good as it gets. There are plenty of reasonable choices that are much smaller. Methinks your monsters will have to float._

 

Sure, floating is no problem. Larger holes is all I was after. I suspect I won't be the only one, as I've seen at least two other PPAs with similar monster bass boost caps.


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## pabbi1

Is STEP still a preferred solution, at 28v, or is this yet to be determined? 

 Are any components fairly well locked down, just in case friends & family want last minute Christmas gift ideas?


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## morsel

STEPS, Elpac WM080, or a homemade simple regulated supply will work.

  Quote:


 Are any components fairly well locked down, just in case friends & family want last minute Christmas gift ideas? 
 

We haven't made the first pcb prototype yet and you are asking if it will be ready for Christmas? Smoking tinsel again, I see.


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## pabbi1

Something has to keep the elves merry... and to keep them from getting in on the porta Corda group buy... 
	

	
	
		
		

		
		
	


	




 Good things come to those who wait. But, at Christmas, it seems to be use-it-or-lose-it...


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## silvervarg

It took a while to read this huge thread, but it was well worth it.
 I'm really exited about this project, and I hope to find more people locally that are interested.
 It looks like you got most things set, but I am a bit unclear about some things. It looks like the bass boost pot is sized for another alps pot, and it seems to be the Sbb switch in the schematics, right?
 Will there not be any need for a switch? Just turning the bass boost down will have allmost the same effect?
 I can't find any hole planned for mounting wires to an optional crossfeed. Was they forgotten or intentionally left out?
 Would it be usefull to have prepared holes for stealing power to something (like to an active crossfeed) ? Ofcourse it can be taken from the power supply directly, but that means less clean wireing.

 I put my wote on the smaller board (v016) since it gives more case options.

 Whats the chance that you can make the final product including mounting under the board to fit inside a case with internal height 48.63mm (1.915") ?

 I figured that ordering the case from over seas won't be a good idea, so
 I'm thinking specifically about a Hammond 1455 series case.
 Full measurements available here:
http://www.hammondmfg.com/pdf/1455T2201A.pdf

 I guess height is mostly a heat issue to keep heatsinks low, so it might matter a lot if we need to dump 1 or 2 watts on the hottest heatsink. I understand that this depends on how much idle current is needed to still stay in class A with 32ohm phones. Has this been tested?

 Having 2 headphone jacks has been mentioned. I hope we are not talking about driving 2*32ohm in parallell without tweaking the original setup.
 Can you just wire up 2 jacks in parallell without getting any other problems?


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## morsel

Use either a bass boost pot or Sbb and Rbb, no need for both. As you surmised, turning the pot all the way down = no bass boost.

 There are no pads for optional crossfeed because it tends to compromise the amp circuit and thus is frowned upon by most purists, however you have reminded me that we forgot to include mounting holes for Tangent's crossfeed daughterboard which can be wired to the amp inputs.

 2" case height means using short heat sinks, which in turn means your MOSFETs will run hotter. A Hammond 1455 case has no ventilation slots, not a good idea even with the full size heat sinks, but I'm sure someone will try it and report back once boards are available. Another option would be to drill some ventilation holes into the 1455 case.

 Our recommended idle current is 80mA per channel. We have tested with the breadboard prototype. We are suggesting 2 headphone jacks be wired in parallel. If headphones of different impedance and/or efficiency are used simultaneously, the volume level will not match.


----------



## morsel




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## morsel

M³ v018
 5×7" board dimensions
 1.5" pot shaft spacing
 retained cross board input traces
 rerouted right channel more directly from pot to opamp
 deleted guard traces (found useless in recent PPA v2 prototype tests)
 enlarged bass boost cap end holes (1mm/40mil ød, 600mil spacing)


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## silvervarg

Overall I do like the new changes. Cleaner as always good, especially the more direct routing of the right channel.

 It guess the intention is to use the inputs are the rear as they was on the v018 (just as they where on the v015, but not on v016).
 If the front hole for inputs on that track is unused, won't the tracks be very narrow? Could this affect sound?
 If this could be a problem the tracks could be made a bit wider around the front inputs?
 Is the input hole too close together (and perhaps to small holes) to mount thick input wires from the RCA jacks? Since the holes will be so close to the jacks this might not be a big thing, but some people might want to mount in a big box, and then really good cables might be nice.

 Any plans on when the first prototype PCB will be ordered?


----------



## morsel

Quote:


 If the front hole for inputs on that track is unused, won't the tracks be very narrow? Could this affect sound? 
 

No. The traces are plenty wide at 50mils, and the pads are through hole plated.

  Quote:


 Is the input hole too close together (and perhaps to small holes) to mount thick input wires from the RCA jacks? 
 

All IO pads are 75/40mils, that is a 1mm hole, plenty wide for #20 AWG hookup wire. Most people use #22 or #24 AWG hookup wire. No one has complained about the 100mil distance between pads yet. 100mil spacing allows Molex connectors to be used.

  Quote:


 Any plans on when the first prototype PCB will be ordered? 
 

No specific date is set. I just synched the layout to the schematic last night, but amb needs to verify the synch, and we have to be sure there are no more changes to implement. The process may seem slow, but remember we have lives outside of Team M³. Days or weeks sometimes pass without progress because other things compete for our attentions. Once the (2) pcb prototypes are ordered it will take some time to receive them, build them, test them, and invite our golden eared friends over for more listening tests. We will let you know when we have news.


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## skyskraper

i appreciate the effort you are putting in to this hugely 
	

	
	
		
		

		
		
	


	




 i can understand the time issue completely 
	

	
	
		
		

		
		
	


	




 and the fact that you are putting so much effort in is just so cool for all us diy'ers. i cant wait to build this amp, it looks gold. but my anxiety to get building may not be able to hold out until its ready for a pcb order, hehehehe. 

 thank you so much guys


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## z2trillion

I'm just wondering, if you only used the pot for the bass boost, wouldn't bad things happen if the wiper on the pot lifts?


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## doobooloo

Quote:


  Originally Posted by *z2trillion* 
_I'm just wondering, if you only used the pot for the bass boost, wouldn't bad things happen if the wiper on the pot lifts?_

 

With a semi-decent pot like the Alps Blue, how often does that happen?


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## z2trillion

I have no idea, but tangent mentions the possibility several times on his page. If it does lift, wouldn't it lead to a headphone frying dc offset?


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## morsel

Quote:


 I'm just wondering, if you only used the pot for the bass boost, wouldn't bad things happen if the wiper on the pot lifts? 
 

No. Look at the schematic, or the layout for that matter, and you will see that the pot is wired end to end with the wiper shorted to one end, so if the wiper should lose contact, the pot is still in series with the circuit, resulting in maximum bass boost, but no DC offset problems.


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## z2trillion

Indeed, I should pay more attention to such things. Thanks for your help.


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## doobooloo

Just wanted to say that it's looking really good! 
	

	
	
		
		

		
			





 One question - how hard is it to implement an additional treble boost option, just like the bass boost option? Will it be very difficult? Looks like there's enough space on the board for an extra Alps Blue.

 I feel like for some phones - in my case, the HD650s - would benefit greatly from some sort of a variable treble boost instead of bass boost. Simply boosting the treble by a bit on my PC with software EQ makes the cans really shine, so I was sort of missing that feature on my PPA with only an adjustable bass boost.

 I've been dreaming of someting like Meier Audio's implementation of treble and bass boost on their Prehead MKII for a while now... 
	

	
	
		
		

		
		
	


	




 (sorry if this has been asked before)


----------



## amb

Quote:


  Originally Posted by *doobooloo* 
_One question - how hard is it to implement an additional treble boost option, just like the bass boost option? Will it be very difficult? Looks like there's enough space on the board for an extra Alps Blue._

 

That would require more parts and traces in the amp's feedback loops. We can't fit that into the current pcb layout without major restructuring and increasing the board size. Moreover there isn't enough space for another Alps Blue. The "empty" area by the M³ logo is a "no-fly zone" to clear headphone jack(s). The bass boost option is very simple so we threw it in there, but I feel that adding treble boost would compromise the quality of the amp.

 I dunno, I have a pair of HD600s, and agree that they aren't as bright and sparkly as, say, the Grados; but I think the sonics of the Senns are actually very natural and fatigue-free to listen to for a long time.


----------



## doobooloo

Is it just possible then to just create optional pads to connect an Alps Blue externally (or just resistor pads like on the PPA) but be able to mount caps on board?


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## amb

Quote:


  Originally Posted by *doobooloo* 
_Is it just possible then to just create optional pads to connect an Alps Blue externally (or just resistor pads like on the PPA) but be able to mount caps on board?_

 

At this point we're not going to cram any more parts and traces onto the pcb for treble boost. I suggets waiting until this amp reaches "production" and listen to one before wanting treble boost. With AD8610 opamps it might be just right. If you still want more treble I think the best thing to do is to use a good preamp with tone controls.

 We are taking a "purist" and KISS approach with this amp, in that the focus is on quality rather than loading it up with features. The bass boost option is there only because it adds very few parts and some headphones do need a bit of help at the low end. If I were building this amp for my own use I'd actually skip the bass boost feature because I find it unnecessary with the HD600s.


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## doobooloo

OK. Thanks for the response amb!

 I can't wait to hear the amp!


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## morsel

We ordered prototype pcbs, they should arrive by the end of the week.


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## KurtW

Congraduations, very exciting!


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## morsel




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## morsel

M³ v022
 removed test pads
 enlarged output resistors to 200×600mils
 removed extra output pads
 moved D1 to make room for Molex power connector
 rearranged capacitance multiplier away from input pads
 reoriented labels

 The prototypes arrived. The only mechanical issue was output resistor fit, which has been addressed in v022. It will take us a while to assemble the prototypes and conduct electrical and listening tests. We will let you know when we have news to report.


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## silvervarg

Could you post a picture of how the physical PCB turned out?
 Was it 0.18 that you made for prototype?


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## peranders

Quote:


  Originally Posted by *morsel* 
_M³ v022

 reoriented labels_

 

I was just going to tell you that it's smart if you can see the labels when the parts are there. Don't forget to have polarity signs also visible. This will be a good help when checking the pcb and that parts are located right.

 Otherwise it looks good, Morsel.


 The picture below is just an example of what I mean. Check the LED, and the big caps for instance. I have also marked interesting nets like C, A, R in my case. This just for making it easier if an another refrence is used.


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## Edwood

At the very least, the positive leads for the caps are a square shape around the hole.

 -Ed


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## skyskraper

hrmm shame about the extra output pads going. i woulda quite liked that. no big deal tho really...


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## Earwax

I think the parts labels are a matter of taste. One could argue that it's better to have the label unambiguosly within the component outline rather than not be certain of which part is referred to by a label, especially when space is tight. 

 I'm looking forward to this project. So many amps to build, so little time.


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## morsel

Quote:


 Could you post a picture of how the physical PCB turned out?
 Was it 0.18 that you made for prototype? 
 

AMB has the boards and digital camera. I'm sure he will post some pictures at some point. The prototype (v021eng) pcb is translucent chartreuse and silver, with no solder mask or silk screen. The only difference from v022 is that the prototype has test pads and the old output resistor/pad configuration.

 Skyskraper: Why do you want extra output pads? When using 2 headphone jacks it is simpler to daisy chain them than run 2 sets of wires from the board. If there was a compelling reason, we could notch the power bus to make room for a second set of output pads.


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## skyskraper

as i said nbd, it was just for dual outs, i will just run one set of wires to a couple of pads on stripboard near the output jacks then wire the jacks to the stripboard.


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## morsel

Why not just go from the board to jack1, and from jack1 to jack2?


----------



## Syzygies

Quote:


  Originally Posted by *morsel* 
_Skyskraper: Why do you want extra output pads? When using 2 headphone jacks it is simpler to daisy chain them than run 2 sets of wires from the board. If there was a compelling reason, we could notch the power bus to make room for a second set of output pads._

 

The second output pads could include pads for output resistors, normally shorted but enabled by cutting traces. Then one could wire up two headphone jacks, one of which offered Etymotic 4p to 4s 75 ohm conversion with _no_ additional switching contacts in the signal path.

 This way, the two outputs can have different impedances, not as easy an option when daisy-chaining.

 Ety 4p's are my best headphones other than my electrostatic Stax. I have no idea how many other people are in my boat. I realize that the MMM is not intended for portable use, but I wish that shorted output resistor pads were a standard idea for anyone designing new amp boards. Wouldn't this help squish the "fried buffers" PPA debate, if this were also an option in PPA v2?

 Some people like to add impedance to other phones, but this makes a crucial difference in the sound for Etymotics; the 4p is a compromise for portable devices. Their conversion cable is $65 and introduces a new contact.


----------



## amb

Here are a couple of quick snapshots of the blank prototype pcbs. As Morsel stated, it doesn't have any silkscreen or soldermask to save cost (the production boards will have these).

 Top side:





 Bottom side:





 Syzygies, as for output resistors for a second jack, you can still use the daisy-chaining idea and just bridge the resistors between the jacks. I think that's better than cutting board traces.


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## Nisbeth

Nice! 
	

	
	
		
		

		
		
	


	





 /U.


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## skyskraper

Quote:


  Originally Posted by *morsel* 
_Why not just go from the board to jack1, and from jack1 to jack2?_

 

six of one really..... my jacks are board mount not solder lugged so i generally find it easier to only solder one wire to them.


----------



## silvervarg

Quote:


 my jacks are board mount not solder lugged so i generally find it easier to only solder one wire to them. 
 

If you will have them board mounted there should not be much problem to mount impedance resistors and connector wires on that small board, so you would still only need to have one set of wires to the M³ board.

*PSU questions*
 If you build your own PSU (I guess quite a few of us will do that), what would be the prefered way to build it?
 Opt1: Simplest possible: just transformer+rectifier bridge+caps
 Opt2: Use 7824 regulator (would 1.5A rated do fine?)
 Opt3: Something a bit more advanced. Preferably with link to schematics.

 What voltage would be best? 24V? 28V? or would anything 20-28V work fine?
 What VA is suggested? A continuous current draw of 300mA-500mA has been mentined in this project, so I guess around 12VA would be the absolute minimum. Usually a slight bit overkill is nice to have some margin, but any suggestion both on minimum and maximum that will make a practical difference would be nice.
 What capacitance is recommended in the PSU?

*Bias*
 So far all bias is regulated with trimpots, and that is fine at this point.
 For the finished board I guess that the need to adjust bias would be very little. I would guess that at least 95% of users will never want to adjust the OP-amp bias. Adjusting the output stage bias could be usefull depending on what kind of phones will be used vs if you like to reduce heat output a bit.
 So, I guess it would be convinient for most people to just use a plain resistor instead of pot. This can be done allready if mounted as standing resistor.
 In a layout this big and nice I would prefere if resistors did not have to stand.
 Would it be possible with small means to make room and holes to mount plain resistors flat (at least for opamp-bias)?
 Ofcourse this would only be usefull if you can figure out that appropriate value for fixed resistors during your testing with prototype PCB.


----------



## amb

Quote:


  Originally Posted by *silvervarg* 
_Opt1: Simplest possible: just transformer+rectifier bridge+caps_

 

This is *strongly discouraged* as the M³ pcb has no onboard voltage regulation. There is only a capacitance multiplier serving to stablize and isolate the opamp power rails.

  Quote:


 Opt2: Use 7824 regulator (would 1.5A rated do fine?) 
 

This is ok, but the LM317 or LT1085 adjustable regulators have better performance.

  Quote:


 Opt3: Something a bit more advanced. Preferably with link to schematics. 
 

I recommend something like the STEPS. You could of course use fancier designs if you wish. You could probably also get by with an Elpac WM080 regulated wallwart (available from Newark) but you'd be operating near its maximum rated current.

  Quote:


 What voltage would be best? 24V? 28V? or would anything 20-28V work fine? 
 

With the AD8610 opamps you should have no more than 27V. With OPA627s you could go up to 36V. These are absolute maximum ratings for the opamps but since the capacitance multiplier will drop about 1.6V, and if you use the D+ input on the M³ pcb, there will be an additional 0.6V drop, that will give us enough margin. I would not recommend anything less than 24V to maintain adequete voltage swing.

  Quote:


 What VA is suggested? A continuous current draw of 300mA-500mA has been mentined in this project, so I guess around 12VA would be the absolute minimum. Usually a slight bit overkill is nice to have some margin, but any suggestion both on minimum and maximum that will make a practical difference would be nice. 
 

If you're going to design your own PSU, I suggest the Amveco 700xx series PC-mount toroidal transformer, either 25VA or 35VA. These are available from Digikey.

  Quote:


 What capacitance is recommended in the PSU? 
 

It's up to you. I like to have ample amount of reservoir capacitance. Just be mindful that your power switch and rectifier diodes could handle the inrush current at turn-on.

  Quote:


 So far all bias is regulated with trimpots, and that is fine at this point.
 For the finished board I guess that the need to adjust bias would be very little. I would guess that at least 95% of users will never want to adjust the OP-amp bias... 
 

You _need_ to adjust this with a trimpot because there is no reliable way of knowing what resistor value will give you the desired CCS current. The Idss characteristics of the cascoded JFETs will influence the current. The only way that you'll be able to eliminate the pot is to use a CRD in place of the cascoded JFETs, with a slight loss in CCS performance. 

  Quote:


 Adjusting the output stage bias could be usefull depending on what kind of phones will be used vs if you like to reduce heat output a bit.
 So, I guess it would be convinient for most people to just use a plain resistor instead of pot. 
 

Here too a trimpot adjustment is necessary because MOSFET device variations will influence the outcome. If we put a fixed resistor there, on one amp it may cause too little quiescent current through the MOSFETs while on another amp, the same value resistor could cause too much current.

 I know that adjusting trimpots is inconvenient but there is just no way around this. I will set up a detailed web site for the M³, including an initial powerup adjustment procedure to help guide builders through all this. It won't be that bad, really; and you only need to do this once after building the amp.


----------



## amb

Just a little more eye-candy for all to see... 
	

	
	
		
		

		
		
	


	



 The prototype pcb being assembled.


----------



## ble0t

Lookin good 
	

	
	
		
		

		
		
	


	




 I'm anxious to hear how it sounds...


----------



## morsel

Someone was burning the midnight oil. 
	

	
	
		
		

		
		
	


	




 Silvervarg: It is interesting that you should bring up using resistors in place of trim pots. Team PPA was just discussing this recently. We have not seen anyone do this in real life, so we were considering abandoning resistor pads for the trim pots on PPA v2. But back to M³:

  Quote:


  Originally Posted by *silvervarg* 
_...I would guess that at least 95% of users will never want to adjust the OP-amp bias. Adjusting the output stage bias could be usefull depending on what kind of phones will be used vs if you like to reduce heat output a bit.
 So, I guess it would be convinient for most people to just use a plain resistor instead of pot. This can be done allready if mounted as standing resistor.
 In a layout this big and nice I would prefere if resistors did not have to stand.
 Would it be possible with small means to make room and holes to mount plain resistors flat (at least for opamp-bias)?
 Ofcourse this would only be usefull if you can figure out that appropriate value for fixed resistors during your testing with prototype PCB._

 

 Quote:


  Originally Posted by *amb* 
_You need to adjust this with a trimpot because there is no reliable way of knowing what resistor value will give you the desired CCS current. The Idss characteristics of the cascoded JFETs will influence the current. The only way that you'll be able to eliminate the pot is to use a CRD in place of the cascoded JFETs, with a slight loss in CCS performance.

 Here too a trimpot adjustment is necessary because MOSFET device variations will influence the outcome. If we put a fixed resistor there, on one amp it may cause too little quiescent current through the MOSFETs while on another amp, the same value resistor could cause too much current.

 I know that adjusting trimpots is inconvenient but there is just no way around this..._

 

The trim pots primarily facilitate initial bias adjustment rather than provide for periodic tweaking after the amp is built. Because the required resistance will vary according to FET Idss variations, one would have to use a pot, measure the resistance, and replace it with a resistor of that value, which is more work than installing and adjusting a trim pot to begin with. Since BC CT94W trim pots are only $1.68 from Digikey, it does not seem worth the trouble to replace them with resistors. Besides, adjusting them is easy.

 If the motivation is to cut costs to the bone, a few bucks could be saved by using hand selected resistors. It would require a significant stock of various 1% resistor values, or a separate parts order whose shipping charges would nullify the savings from not using trim pots. It would be easy for us to add the pads, but do we really want to encourage this practice? Let's hear your thoughts on this.


----------



## Nisbeth

Quote:


  Originally Posted by *morsel* 
_If the motivation is to cut costs to the bone, a few bucks could be saved by using hand selected resistors. It would require a significant stock of various 1% resistor values, or a separate parts order whose shipping charges would nullify the savings from not using trim pots. It would be easy for us to add the pads, but do we really want to encourage this practice? Let's hear your thoughts on this._

 

IMHO, you needn't bother with the resistor pads, the trimpot is much easier to work with 
	

	
	
		
		

		
			






 /U.


----------



## kasra

Quote:


  Originally Posted by *amb* 
_This is ok, but the LM317 or LT1085 adjustable regulators have better performance._

 


 amb: 

 You might want to try LM2937ET-15 & LM2990T-15. Mark Levinson replaced LM337&LM317 with those in their ML380S preamp.
 Also a friend of mine building SDS Labs exchanged LM for the above with positive results.

 /kasra


----------



## amb

Quote:


  Originally Posted by *kasra* 
_You might want to try LM2937ET-15 & LM2990T-15. Mark Levinson replaced LM337&LM317 with those in their ML380S preamp._

 

The LM2937 is a 500mA negative regulator which would be operating near its limit with this amp. The LM2990 is also a negative regulator with max output of 1A. Its "complement" is the LM2940 positive regulator.

 At any rate, this is a bit OT since the M³ pcb doesn't have any voltage regulators. If you want to design your own PSU for the M³, the LM2940 is probably ok, but I would feel a bit more comfortable with the LM317 which is rated at 1.5A or the LT1085 at 3A.


----------



## silvervarg

Thanks for the quick answers. My questions about the bias clearly showed my lack of knowledge in this area, so just disregard that. Btw the trimpots looks very neat on the board you made.

 With the answers about the power I should have no problem building a simplified version of the STEPS with localy available parts so I have it ready before I get hold of an M³ board and parts for that one.


----------



## morsel

Thanks for your kind words. With AD8610 opamps and 80mA MOSFET bias, the total current draw will be around 250mA, well within 24V wallwart range if you wish to use one. The classic Elpac WM080 is a good choice. A STEPS and OPA627 or OPA132 opamps will allow you to choose a higher operating voltage from 30-36V suitable for the most demanding applications such as driving small speakers or the AKG K1000.


----------



## amb

An update: The prototype pcb has been assembled and is now working well. We will be doing measurements and conducting listening tests on this rig.

 One minor thing that occurred to me as I was building this rig is that the input pads at the rear of the pcb, as viewed from the front (the side with the pots) are oriented as G-R-G-L-G. In other words, the right channel trace is on the left side and the left channel trace is on the right. If the amp will have its RCA input jacks on the rear panel arranged in a side-by-side manner, then the most "direct" wiring will be R L when viewed from the front. From the rear it would be L R, of course. I wonder if this might be counter-intuitive for some people, and note that on many commercial stereo gears with horizontal jack arrangements the left channel jack is assigned to the left side when viewed from the front of the case. It's not a big deal to simply cross the wiring, of course, but just want to ask your opinion about this. If this bothers you then we could simply re-label the left channel as the right and vice-versa (without changing any actual pcb components or traces).

 Here is a picture of the test rig.


----------



## n_maher

Very cool! I've been following the thread (not reading every post...) and was just wondering what you expect the fully populated board to run? The original thread mentioned that one of the design goals was a better bang for your buck over the PPA. I don't know if this meant that it would be an overall cheaper build, better performance at a similar price, or more $$$ but way better performance.

 I'm hoping that the M³ will be my first project of 06!

 Keep up the great work.

 Nate


----------



## doobooloo

Quote:


 One minor thing that occurred to me as I was building this rig is that the input pads at the rear of the pcb, as viewed from the front (the side with the pots) are oriented as G-R-G-L-G. In other words, the right channel trace is on the left side and the left channel trace is on the right. If the amp will have its RCA input jacks on the rear panel arranged in a side-by-side manner, then the most "direct" wiring will be R L when viewed from the front. From the rear it would be L R, of course. I wonder if this might be counter-intuitive for some people, and note that on many commercial stereo gears with horizontal jack arrangements the left channel jack is assigned to the left side when viewed from the front of the case. It's not a big deal to simply cross the wiring, of course, but just want to ask your opinion about this. If this bothers you then we could simply re-label the left channel as the right and vice-versa (without changing any actual pcb components or traces). 
 

IIRC the PPA has its L/R input pads placed so that the most direct wiring would lead to L-R from the rear (R-L from the front) which seems to be the case here. Personally I've made all my amps that way, but then I don't own any commercial stereo gear at this point, so I can't say what the real standard is.

 Honestly I would like it to remain the way it is just because all other "standard" DIY projects are made that way but it probably won't make a big difference to most people either way. 
	

	
	
		
		

		
		
	


	




 As long as it sounds good!


----------



## stadams

Quote:


  Originally Posted by *n_maher* 
_The original thread mentioned that one of the design goals was a better bang for your buck over the PPA. I don't know if this meant that it would be an overall cheaper build, better performance at a similar price, or more $$$ but way better performance.

 Nate_

 

Hey Nate,

 It did some estimating, and it looks like the entire output stage not including the cascoded current source or the 1 uF cap, which are used in the PPA anyway, will cost right at $10.00 per channel. Compare this to $24.40 per channel when you max out the buffer arrangement with BUF634's and you can start to see the benefits already. Not to mentioned the simplified output stage from an electronic standpoint. I'm not sure about the prices on the different diamond buffer versions. The simpler the better.

 Now if we could get away from these IC op-amps altogether and design a completely discrete front end to go with a similar output stage.

 I really like what has been done so far, its rather inspiring. Maybe I'll get back on the horse.

 Later,

 Todd


----------



## morsel

I think having the jacks L R as viewed from the rear, which is how you look at them when you hook them up, is the intuitive way to do it. Of course anyone is free to orient their jacks vertically or in reverse order, and color coded input jacks should be the primary method of identification, but my vote is to leave the amp channels in the order L R G rather than change them to R L G.

 The initial choice to go L R G was made with deliberation, not chosen at random. The work required to swap channels would be extensive. The swap would mean those people who wire input jacks R L would no longer have to cross input wires 200mils, while those who wire input jacks L R would now have to cross input wires 200mils, and the channel layout would be bass-ackwards from a left right perspective.


----------



## morsel

Another solution for those who want R L G order is to wire both headphone jacks and input jacks with left and right channels reversed. You get to have your alternate order and don't have to cross your input leads, but, ohmygod, the labels inside the amp will be wrong!


----------



## morsel

NeilPeart and Raif joined us for listening tests of the M³ pcb prototype this evening. It sounds great. There were no technical problems. Thanks so much for helping out, you guys. It was a lot of fun.

 We are going to wrap up development soon, so now is the time to bring up any last requests, or reiterate old ones we let slip by the wayside.


----------



## amb

My thanks also to NeilPeart, Raif and Morsel for visiting. It was a fun evening listening to the M³ prototype with various headphones and other equipment, as well as having great conversations. While I know that the M³ measured well and sounded good to my ears, it's reassuring to be confirmed by all in this micro-meet.


----------



## NeilPeart

I met with Morsel, AMB and Raif today to conduct some listening tests to aid the development of the M3 (M Cubed) amplifier project. The evening was rife with passionate discussions regarding the merits of happy hardcore, the obligatory Rush vs. Yes debate and the casual reference to Nakamichi addictions. I had a blast discussing audio and life with Morsel and AMB, and Raif is always in the enviable position of being cooler than me. I brought over Ayt999’s Audio-Technica ATH-L3000; Raif brought his DAC1, Audio-Technica ATH-900 and Grado PS-1 Pro, while Morsel and AMB supplied their DT990-600, HD600, PPA and M3 amplifiers. I’d already been introduced to the pleasure of proper tape listening, but this was re-affirmed tonight with renewed vigor. AMB’s homebuilt turntable and DIY speakers are nothing short of amazing. The M3 sounds very similar to the PPA, but if pressed I would say the M3’s bass is just slightly superior in terms of decay and impact. I also prefer the M3’s design to the PPA’s but my limited knowledge of EE obviously renders my opinions in this regard basically valueless. 
	

	
	
		
		

		
		
	


	




 I can’t wait for the next meet!


----------



## morsel

M³ v024 changes

 restored the second set of output pads
 (they are in line down the cap/heat sink canyon)
 notched the power rails for the output pads
 modified the TO-220 part to fit better
 (pads moved 25mils to the front)


----------



## doobooloo

Wow! Looks great. Can't wait for the production boards to be released!


----------



## doobooloo

Same comment as for the PPA v2:

 I just noticed something...

 Shouldn't the bass boost pot area also have the twelve little square silkscreen areas on the volume pot area to protect the board when mounting an Alps Blue?

 Or, that's what I always thought those twelve silkscreen squares are for...

 Anyway, I thought it'd just make more sense, howmuchever difference it'll make, to have the same sort of silkscreening for both pots.


----------



## Dreamslacker

Quote:


  Originally Posted by *NeilPeart* 
_






_

 

Looks like the power was supplied using the crocodile clips to the tabs of the transistors?


----------



## morsel

doobooloo: I'm on it, thanks!

  Quote:


 Good catch, doobooloo! While the little silkscreen squares mostly cover the unsightly windows in the ground plane put there to prevent the sharp landing points on the pot legs from puncturing the soldermask and shorting to ground, the fact remains that the bass boost pot could theoretically short itself. I'll probably just move the traces so they don't cross the landing zone. 
	

	
	
		
		

		
		
	


	



 

Dreamslacker: Yes, the MOSFETs are not electrically insulated from the heat sinks.


----------



## amb

Quote:


  Originally Posted by *Dreamslacker* 
_Looks like the power was supplied using the crocodile clips to the tabs of the transistors?_

 

Yeah, I happened to be using an adjustable bench power supply in those photos, which came with banana-to-alligator-clips wires. It was convenient to simply clip them onto the heat sinks (which are tied to the drain pins of the MOSFETs) rather than make another cable.
  Quote:


  Originally Posted by *doobooloo* 
_Shouldn't the bass boost pot area also have the twelve little square silkscreen areas on the volume pot area to protect the board when mounting an Alps Blue?_

 

As Morsel states, those little squares under the volume pot are actually cutouts on the ground plane to keep the sharp points around the Alps Blue pot pins from touching the ground plane. There are matching squares on the silkscreen layer to serve as markers. Since there is no ground plane under the bass boost pot the extra insulation is not necessary. I didn't have any problems with the layout as it was on the prototype, but I guess Morsel will move the traces slightly to make extra sure that no contact between pads (via the pot pins) would occur.


----------



## ppl

Quote:


  Originally Posted by *amb* 
_The LM2937 is a 500mA negative regulator which would be operating near its limit with this amp. The LM2990 is also a negative regulator with max output of 1A. Its "complement" is the LM2940 positive regulator.

 At any rate, this is a bit OT since the M³ pcb doesn't have any voltage regulators. If you want to design your own PSU for the M³, the LM2940 is probably ok, but I would feel a bit more comfortable with the LM317 which is rated at 1.5A or the LT1085 at 3A._

 

A frendly 
	

	
	
		
		

		
		
	


	




 Correction the LM2990 is the Negitive complement to the LM2937 Both are fixed with 15 volts being the max output voltage Both are low dropout devices with 500mA for the 2937 and 1 amp for the 2990. These are might fine devices as far as Fixed voltage regulators go
 Data Sheets> 
http://cache.national.com/ds/LM/LM2990.pdf and http://cache.national.com/ds/LM/LM2937.pdf

 My favorite IC voltage regulators are fromn LTC and the Best devices from them is The LT1185 for Negitive adj at 3 amps 
http://www.linear.com/pc/downloadDoc...19,P1465,D2875

 and the positive matching one is the LT1764
http://www.linear.com/pc/downloadDoc...55,P1820,D1316

 also see the LT1085
http://www.linear.com/pc/downloadDoc...55,P1283,D3741

 I also recomend reading this app not from LTC on Performance enhancements of three term Reg's AN2
http://www.linear.com/pc/downloadDoc...55,P1283,D4099


----------



## amb

Thanks ppl. The info would be useful for those who want to design and build their own PSUs.


----------



## morsel

M³ v025

  Quote:


 Since there is no ground plane under the bass boost pot the extra insulation is not necessary. 
 

Although the chance of it happening was remote, it was possible that the sharp pot landing leg could have pierced the left bass boost trace, shorting it to the center tap, thus disabling bass boost for that channel, which is why I moved the trace.


----------



## doobooloo

Is it possible to make the board 5.28" wide instead of 5"? Perhaps the extra 2 x 0.14" can go on both sides to allow for the board to slide in even with larger caps installed, and to make sure that the railings don't cover the input pads.

 The Lansing MicroPak style cases can accommodate 5.28" x 5/6/7/8.5" PCBs.

 I think the closest Hammond alternative is 6.319" x 8.661", a bit too big.

 The Lansing enclosures look much nicer anyway...


----------



## amb

doobooloo, the Lansing MicroPak series do not have any ventilation holes or slots, neither do the Hammond 1455 series. This makes the cases unsuitable for use with this amp. The MOSFET heatsinks get warm, and the heat need to escape.

 I am working on enclosure solutions. Watch this thread for more info when I have more to share.


----------



## silvervarg

Quote:


 Lansing MicroPak series do not have any ventilation holes or slots, neither do the Hammond 1455 series 
 

That what you got the dremmel for...

 During the test, how hot did the warmest heatsink become?
 I guess it would be the heatsinks in the ground channel. An aproximate temperature would be enough. Just want it to base decision of using 1" or 2" heatsinks. I guess you never put the prototype in a box, but it might still be good as a guide.
 Also would any other component on the board be over 1" high (counting from the PCB)?

 It just came to my mind that in a chassi it will be easier to get air circulation near the edge of the board to cool the heatsink, and the warmest heatsinks happens to be the ones closest to the edge. Was it just luck that made it turn out like that?


----------



## morsel

doobooloo: I think the issue of enlarging the board to fit one of those cases is worth exploring. Let's look at the thermal issues more closely. I think it is worth evaluating just how hot a closed box will get with all 3 channels biased at 80mA. 

 silvervarg: If you have a Dremel you can drill 4 mounting holes for pcb standoffs, however, it would be nice if there were an off the shelf case that fits M³.

 I'm going to be out much of the next two days, and plan to wrap up PPA v2 tonight, so things will be a bit hectic until Thursday.


----------



## Earwax

Quote:


  Originally Posted by *morsel* 
_doobooloo: I think the issue of enlarging the board to fit one of those cases is worth exploring. Let's look at the thermal issues more closely. I think it is worth evaluating just how hot a closed box will get with all 3 channels biased at 80mA. 
_

 

Don't the Hammond and Lansing cases both have slide-off tops? If so, it might be interesting to replace those lids with something "airier" -- or just go topless


----------



## doobooloo

Quote:


  Originally Posted by *Earwax* 
_Don't the Hammond and Lansing cases both have slide-off tops? If so, it might be interesting to replace those lids with something "airier" -- or just go topless 
	

	
	
		
		

		
		
	


	


_

 

My thoughts exactly. Those panels should be easy to machine, and it should also be pretty easy to make some substitute top cover as well.

 Or Head-Fi can do a group buy on custom Lansing enclosures - or at least just a custom top panel?


----------



## Akku

How about this?

http://www.audiokit.it/ITAENG/Cabine...000-Galaxy.htm

 For european builders, off course (but I guess they ship to US).

 Ciao


----------



## kasra

Quote:


  Originally Posted by *Akku* 
_How about this?

http://www.audiokit.it/ITAENG/Cabine...000-Galaxy.htm

 For european builders, off course (but I guess they ship to US).

 Ciao_

 

I was also going to recommend those, beware they present the measures: [Width x Length x Height]

 Depending on the final card size and the internals size of the GX187 which measures externally: WxLxH(124x170x80)(4.9"x6.7"x3.15") 

 It might be a good choice, that is ofcourse if the powersupply is external.


----------



## amb

Let's say that we have 3 channels all running at 80mA quiescent, with a 36V power supply. This roughly translates into 9W of total power dissipation. I'll do some experiments, but you could probably calculate how much heat there would be in a totally-enclosed case... My guess is that it's going to be uncomfortable.

 Akku and kasra, the audiokit.it GX187 looks nice, but just a bit too small for the current pcb size.

 While Lansing will do custom work, I wonder how much it would add to the cost in small-ish quantities? I have a feeling that to the Lansing people, anything less than thousands would be considered "small". Personally I am not too enamored by the looks or the standard color on the Micropak line. It would be fine for an industrial gizmo, but it's missing that "high end audio" aura. 
	

	
	
		
		

		
			





 I do like to set up some kind of group buy for enclosures if we could nail down a vendor and style, but it will be unreasonable to make everyone dremel their cases for ventilation or go topless.

 I have initiated a conversation with Larry at LaroccoAudio, and he is open to the idea of making custom M³ cases. As many of you know, his cases are gorgeous (see the examples on Laroccoaudio.net). We haven't drilled down any specifics or costs yet, but if it turns out to be feasible, then that's a possibility.

 Of course, a custom Par Metals 20-series enclosure is still something I am looking at. I will be talking to them within a few days about this.


----------



## silvervarg

Quote:


 Depending on the final card size and the internals size of the GX187 which measures externally: WxLxH(124x170x80)(4.9"x6.7"x3.15") 
 

I believe that the board is currently exactly 5"x7" so it would have to be squeezed a bit to fit in that case.

 There is already lots of case options popping up, so it is time to decide what is important.

 I guess there will be lots of different cases used for the board so I don't think it would be right to optimize for a specific case unless lots of people will go for that case. We are already talking about wented vs closed cases, with or without PSU, tall to take 2" heatsinks or low for 1" heatsinks. The PSU could be compact or large and could be placed close to the board or further away.
 With these options alone we have 20 good cases even if they are custom made for this board (4 without PSU and 16 with PSU).

 Seeing all these options I think we need to make the choise really simple:
 1. No changes on board (go to production ASAP).
 2. Decide on one specific case that we optimize for, preferably one that is available both in US and Europe and that is really close to fit the board anyway.
 3. Custom made case that will fit the board perfectly with custom made fron panel. Just one version will be made for simplicity. For shipping reasons this will probably be economically interesting for US only.

 If you don't go for a custom made case with custome made front panel you will need to drill holes for the pots in the front panel, so the step of drilling holes for PCB standoffs should not be a problem. Drilling 2 or 6 holes should not make much difference.

 Personally I am leaning towards an oversized case where I can fit the PSU in the same box.


----------



## pabbi1

Well, my Sun 911 has served me so well for so long, I'm considering this solution:

http://home.swbell.net/pabbi/case1.jpg

 This case (fancied up with a $4 can of vinyl dye) is 9.25"(w), 10"(l) and 5"(h). One possible configuration:

http://home.swbell.net/pabbi/case6.jpg

 The board is mounted horizontally, and the STEPS vertically in the former P/s cage (with some of the existing teflon shielding, supplemented by some of Tangents also). I am certainly open to suggestions about attaching the STEPS, given the recent tales of woe about shorting (and toasting) the LM317. Or, the STEPS can be mounted horizontally, higher, with some metal shielding underneath (with little or no cage modification):

http://home.swbell.net/pabbi/case7.jpg

 In addition to the high heat tolerance plastic case, it is also internally metal shielded, yet vented to the gills, even with the fan removed.

http://home.swbell.net/pabbi/case4.jpg

http://home.swbell.net/pabbi/case2.jpg
http://home.swbell.net/pabbi/case3a.jpg
http://home.swbell.net/pabbi/case5.jpg

 Just a thought...


----------



## amb

Pabbi, that's cute. Try to keep the power transformer as far away from the amp as you could.

 For those of you looking to build the M³ with the PSU in the same case as the amp, you can use the off-the-shelf Par Metal 20-series case in the 12"W x 8"D x 2"H size. This allows you to put the PSU board on the left side (as viewed from the front panel), a good distance away from the main board. You could even order the case with an internal divider plate, for a bit of extra shielding.


----------



## doobooloo

If the board width is slightly increased to be accommodated in the Lansing cases with removable tops, I am willing to initially produce some quantity (maybe 100-ish?) of laser-cut acrylic (clear or black) slide-in panels that will have proper ventilation and supply them to either whoever's going to distribute the boards (Tangent?) or distribute them myself.

 Or we can do a group buy on nicer ventilated FPE panels as well. But I feel that for a large number of us the Lansing option will be a very cost effective, easy, compact, and decent-looking way to house the M3.


----------



## BradJudy

Quote:


  Originally Posted by *amb* 
_For those of you looking to build the M³ with the PSU in the same case as the amp, you can use the off-the-shelf Par Metal 20-series case in the 12"W x 8"D x 2"H size. This allows you to put the PSU board on the left side (as viewed from the front panel), a good distance away from the main board. You could even order the case with an internal divider plate, for a bit of extra shielding._

 

Here's a pic of my PPA built in a series 20 case with a STEPS PSU as amb described. I used a 16" wide case so that it matched with standard sized components. 

http://forum.av123.com/photopost/dat...Small_-med.JPG


----------



## amb

I will be distributing the M³ boards when it goes to production. I am also entertaining the idea of offering some other related parts like tangent does for his amps, for example the AD8610 opamps pre-mounted on Browndog adapters, the Alps blue velvet pots, and maybe the heat sinks, JFETs and MOSFETs too. This might helps builders reduce the number of vendors to order from, and help some non-USA builders who might have difficulty locating some of the parts.

 Whether I offer these extra parts depend on the level of interest. I am not looking to make a profit on these. Just enough to cover my expenses, effort, and shipping; as a service to the community. Let me know if you think this is a good idea, and what parts you would like me to offer along with the blank boards.


----------



## steinchen

some of the jfets/mosfets are diffcult to get in Europe, same with tle2426clp. Alps pot is not necessary, since it's easy to get (at least in Germany) and due to its size expensive in transatlantic shipping. OrangeDrop and BC416 caps could be taken into consideration, too.

 It's a big advantage if you can put the components in an envelope and declare it as a gift with minor value (<< $60), saves very much shipping cost and customs duty


----------



## Magsy

It is not looking too bad here, RS seem to have everything on the schematic!


----------



## kasra

Quote:


  Originally Posted by *amb* 
_I ...idea of offering some other related parts ...help some non-USA builders...._

 


 amb: A very good idea 
	

	
	
		
		

		
		
	


	




 Jfets, AD8610!, (MOSfets) perhaps heatsinks, I now have 1.5"ones and perhaps they might be enough..


----------



## __redruM

Is there an official M³ page? Like http://elvencraft.com/ppav2?


----------



## silvervarg

Quote:


 Amb, might sell: ...AD8610 opamps pre-mounted on Browndog adapters, the Alps blue velvet pots, and maybe the heat sinks, JFETs and MOSFETs... 
 

It would be great if you could sell the hard to get parts so all the other stuff can be found locally.
 Could you add TLE2426 and the trimpots to that list.

 I am sure I could get the heatsinks and alps blue locally, but probably at twice the cost.

 Could you put together a parts list with Digikey numbers, preferably with the componets you might sell marked.

 Pabbi1, that Sun 911 case looks great for an amp! 
 But I do like when things fit together, so BradJudy idea with a full-width stereo case looks like a more convenient way to go.


----------



## BradJudy

My take is that it sound be similar to what Tangent has done. It's useful for you to sell items that are not readily available via Digikey/Mouser/Newark. I haven't tried shopping for the MMM parts yet, so I'm not sure what availability is like, but the Alps and the 8610 on Browndogs are a good start.


----------



## morsel

http://elvencraft.com/mmm/ has some skeletal content. Once things settle down with Team PPA I'll put more effort into the M³ website. AMB will have a more detailed site, similar to Tangent's. It's not ready yet, either, and I don't know what the address is.


----------



## pabbi1

Second the BradJudy solution, especially since I'm in for multiple units.

 The 12" x 8" footprint, with a nice front panel (& countersink holes, dividing interior metal, with black annodize), seems like an excellent choice. At the least, a (more or less) standard set of attributes to order from, and we might get some break on a minimum run, though shipped individually.



 Above all else...

 AMB/Morsel: Could not appreciate more what you guys have done - honestly.


----------



## halman

Im sorry if this have been adressed before but...

 Why not make an effort to make the board 4x6 as the older ppa board to me the posted layout contains quite much empty space.

 / Micke


----------



## SHLim

Quote:


  Originally Posted by *amb* 
_Whether I offer these extra parts depend on the level of interest. I am not looking to make a profit on these. Just enough to cover my expenses, effort, and shipping; as a service to the community. Let me know if you think this is a good idea, and what parts you would like me to offer along with the blank boards._

 

This is a very good idea.


----------



## morsel

Quote:


 If the board width is slightly increased to be accommodated in the Lansing cases with removable tops... 
 

doobie: After researching the Lansing MicroPak cases a bit more carefully, it seems that 2.5" high cases and 8.5" long cases are only available as C Style, not D or E Styles, which are the ones with the board grooves. The largest size D and E Styles are 1.5" high and 7" long, which is too small to reasonably accommodate the M³, so it does not make sense to enlarge the board.

 The largest Hammond 1455 case is 8.6" long, 6.3" wide, and 2.1" high, a better choice, although it will require installing standoffs to mount the board. I think operating with a 24V power supply and 40-50mA bias should allow for an M³ in a sealed case as an alternative to using the full blown configuration of 36V/80mA in a vented case. We will play around with this and get back to you.


----------



## amb

Quote:


  Originally Posted by *halman* 
_Why not make an effort to make the board 4x6 as the older ppa board to me the posted layout contains quite much empty space._

 

You might think that there is a lot of "empty" space, but one of the nice things about the M³ board is the fact that parts are arranged optimally for best performance without being crammed as on the PPA. Also, the spacious board gives us the ability to provide builders with more parts options. For example, we use 400-mil lead spacing for resistors (compared to 300-mil on PPA), and we put in holes for 18mm capacitors on the MOSFET power rails, so that you could use larger, boutique-grade parts if you wish.

 In fact there isn't too much extra wiggle room for components without compromises. We had already slimmed down the width from 6" to 5" and there isn't latitude for further reduction in that direction. We can't squeeze the 7" length down without having the 3-channels encroach into each others' space. On the PPA, the ground channel has to fit in the middle instead of the far back, because that's the only way it would fit. But that means the bass boost pot traces cannot be routed to the front for the right channel and has to be hand-wired. The heat sinks take up a lion's share of the space on the M³, and they cannot be made any closer because there are parts between them.

 From the beginning we have not intended this to be a portable amp, therefore making it as small as possible is not a requirement. We would rather optimize the board layout for maximum function and performance, rather than for minimum size.


----------



## Syzygies

Quote:


  Originally Posted by *amb* 
_For example, we use 400-mil lead spacing for resistors (compared to 300-mil on PPA)_

 

Yes! Thank you. This is datasheet spec for Welwyn resistors, or what appears to be nearly the same, IRC RC Precision Metal Film Resistors from Mouser.


----------



## doobooloo

Quote:


  Originally Posted by *morsel* 
_doobie: After researching the Lansing MicroPak cases a bit more carefully, it seems that 2.5" high cases and 8.5" long cases are only available as C Style, not D or E Styles, which are the ones with the board grooves. The largest size D and E Styles are 1.5" high and 7" long, which is too small to reasonably accommodate the M³, so it does not make sense to enlarge the board.

 The largest Hammond 1455 case is 8.6" long, 6.3" wide, and 2.1" high, a better choice, although it will require installing standoffs to mount the board. I think operating with a 24V power supply and 40-50mA bias should allow for an M³ in a sealed case as an alternative to using the full blown configuration of 36V/80mA in a vented case. We will play around with this and get back to you._

 

Hmm, I didn't realize that the D and E didn't come in 2.5" heights. Oh well. 
	

	
	
		
		

		
			





 Anyway, if something could be worked out with the Hammond option, that would be great. Looking forward to your solution to this!


----------



## morsel

Here are two power input configurations for your perusal. Either can be used with a 100mil Molex KK, SIP header, or terminal block. #1 is the original configuration. #2 sacrifices convenient bypassing of the series diode in exchange for 200mil terminal block compatibility.

 The traces are rated at 2A and the diode at 1A, so there is little point in sacrificing the V+ pad for compatibility with 15A 200mil terminal blocks other than the desire to use larger terminal blocks for appearance's sake. Molex or SIP headers are more convenient than terminal blocks for disconnectability.

 Bypassing the series diode saves .7V, which might be desirable with a 24V supply, but risks damaging the amp with accidental application of reverse polarity unless the power supply is internal and the power connection is polarized or hand wired and soldered.

 While more complex power pad arrangements are possible, KISS philosophy (Keep It Simple, Stupid) applies. Between the caps, mounting screw, heat sink, and edge of the board, there is not much room to place the diode and pads such that a terminal block has adequate clearance. We would rather not enlarge the board. This is the last issue to resolve before we call for the end of development. Sitting on the matter for a week did not help us come to an agreement, so let's hear your opinions.


----------



## Syzygies

Quote:


  Originally Posted by *morsel* 
_Bypassing the series diode saves .7V, which might be desirable with a 24V supply, but risks damaging the amp_

 

Are there no Schottky diodes that could be used here, for those who care about the .7V? I know there's a litany of caveats with Schottky diodes, but satisfy them one is down to .35V.

 That said, I'm indifferent, I _wouldn't_ bypass the series diode _or_ use terminal blocks.


----------



## amb

I was the one who suggested to Morsel that we consider supporting the use of 200-mil lead-spacing terminal blocks for the power input, because they seem to be favored by the Gilmore amp designs, and has a much higher current rating than the 100-mil Molex KK connectors. It's true that the diode is only rated at 1A and the connector need not be rated higher, but perhaps a beefier connector would provide more reliable contact over the long run, even though we will typically operate at well less than 0.5A.

 The second solution does not preclude bypassing the diode, you just have to install a jumper in the place the the diode. But I would strongly discourage this for external PSUs. If someone plugs in the wrong PSU with reversed polarity, lack of the diode would mean some fried parts.

 Anyway, I am not dead set one way or another, so your comments would be appreciated.


----------



## morsel

relevant current ratings:

 200mil terminal blocks = 10-15A
 100mil terminal blocks = 4-6A
 100mil Molex KK connectors = 2.5-4A
 50mil traces on the board = 2A
 D1 1N4001 diode = 1A
 M³ Iq < 300mA

 Assuming you don't fuse the amp and use an overkill power supply, which (needless to say) is a bad idea, and then have a short on the board, the diode is going to pop like a Christmas cracker before the traces melt or the power connector fails.


----------



## Earwax

I'd rather use a 200mil terminal block than a molex. No good reason for that, it just feels more solid to me.

 [edit] Now that I fully undersatand the layout, I also agree with the point Voodoo makes below. Option 1 could be confusing for people assembling the amp. I can see how someone would not read the instructions and end up using v+ & v- for power and install the diode, but un-intentionally leave it disabled.


----------



## silvervarg

Why is there 3 connections to connect V+ and V-? (I guess D+ and V+ both be connected to possitive on the PSU.)
 I would prefere just 2 connections labled V+ and V- and made with the diode (or jumper if you don't want the diode).

 I think 100mil connections would be fine, but it doesn't matter what types will be used.


----------



## amb

silverarg,

 In option 1, the three pads have the V- in the middle, and you would use a 2-pin 100-mil Molex header either between V+ and V- (no diode protection) or between D+ and V- (with diode protection).

 In option 2, the three pads have V- on one end, and D+ for the other two. This is to allow either a 2-pin 100mil Molex header between the middle D+ and V-, or a 2-pin 200-mil connector between outer D+ and V-. Both are diode protected unless you jumper the diode.

 Hope this clears up the confusion. So, which do you prefer?


----------



## steinchen

since there is no need for a 15A 200mil terminal block /me votes for option 1

 the only advantage I see in option 2 is that you have to "explicitly" jumper the protection diode, maybe giving a little more security for novices


----------



## Voodoochile

If your amp and PSU are going to be hard-wired together, then you can simply jumper the polarity protection diode, saving the .7v drop and saving the Schottky.

 Thus, my vote is to leave it (diode) enabled by default. Those who wish to skip it can jump it instead. My concern is that some trusting new DIYer will install the diode, thinking they are covered... then wire their plug incorrectly, and do some damage.

 Will the silkscreen have a plug polarity tab indication on it like the PPA?

 Finally, if you do go with #2, possibly consider having the center pin be negative, giving two negatives and one positive. No reason given for this idea. 
	

	
	
		
		

		
			





 ~editorial rhetoric segment below~

 Either way works fine by me, and regardless of how much you try to appy KISS, there will never be any guarantees that someone's build won't go south due to something being done wrong. So I would not loose too much sleep over it. The board is very thoroughly labelled, so it's not as though getting a functioning amp will be a crapshoot.

 There are so many pitfalls that board layout and labelling will never address. I think you've done a fine job, and as always, DIYer beware. Not to try and scare anyone off, but just realize that you are buying a few hundred dollars worth of components and you can destroy them in an instant. It's not that hard to assemble an amp from a PCB, but likewise, it's not that hard to build one that does nothing at all. Fortunately there are people to help out on here, but rework is always more difficult.


----------



## silvervarg

Thanks for the clarification Amb then I did understand things correctly.
 Having an extra connection to bypass the diode seems like a waste to me. It would look kind of ugly to not have anything connected to V+ IMHO.
 I agree with Voodoochile's reasoning and put my vote for option 2. But I would still prefere the silkscreen to say V+ instead of D+.

 Giving the option to use 100 och 200 mil connector is not important, but since you done similar things to the caps it seems reasonable to give the option here as well.


----------



## morsel

Quote:


  Originally Posted by *Earwax* 
_I'd rather use a 200mil terminal block than a molex. No good reason for that, it just feels more solid to me._

 

Testosterone at work. 
	

	
	
		
		

		
		
	


	




  Quote:


  Originally Posted by *silvervarg* 
_ It would look kind of ugly to not have anything connected to V+ IMHO... But I would still prefer the silkscreen to say V+ instead of D+._

 

There will always be unconnected pads. For example, there is no way all those electrolytic cap pads will ever be used. In any case, a Molex or other connector will cover the unused power pads. Rest assured we will rename D+ to V+ *if we get rid of V+*.

  Quote:


  Originally Posted by *Voodoochile* 
_If your amp and PSU are going to be hard-wired together, then you can simply jumper the polarity protection diode, saving the .7v drop and saving the Schottky... Will the silkscreen have a plug polarity tab indication on it like the PPA? Finally, if you do go with #2, possibly consider having the center pin be negative, giving two negatives and one positive. No reason given for this idea. 
	

	
	
		
		

		
		
	


	


_

 

We will use both silkscreen labels and square/round pads to indicate polarity. You inspired me with your two negative pads suggestion. The point of #1 is to allow omitting the diode without having to jumper it. With that in mind, check out #3. This lets us have 100mil and 200mil spacing for both V+ and D+. At the moment it seems like #2 is in the lead, so that's what we will probably go with if the true concern is not letting people accidentally bypass the diode.






 (edit: the attachment poofed, had to upload it again)


----------



## ub312g0d

Quote:


  Originally Posted by *morsel* 
_There will always be unconnected pads. For example, there is no way all those electrolytic cap pads will ever be used. _

 

Anybody else have a strange urge to use all of the electrolytic cap pads now just for the sake of it?


----------



## amb

Quote:


  Originally Posted by *ub312g0d* 
_Anybody else have a strange urge to use all of the electrolytic cap pads now just for the sake of it?_

 

You can do that with smaller value caps. There is no measurable or audible benefit in more than 3000uF or so of total capacitance in this amp.

 Too much capacitance has drawbacks. The turn-on inrush current will be large and could damage your power supply and degrade the power connector contacts over time. Also, after poweroff, the amp might output undesirable noise as the supply voltage discharge too slowly.

 The reason we provided many cap positions in alternate sizes is to allow for "boutique" caps that have small capacitance for their physical size. It is not for filling up with nine 1000uF+ capacitors!


----------



## morsel

#3 went over like a lead zeppelin, possibly because the attachment poofed and no one saw it. We will be going with #2 unless by some miracle people speak up before the end of the day.

 There is no joy in Mudville, mighty V+ has struck out.


----------



## Voodoochile

I meant to make note, but work got in the way. 
	

	
	
		
		

		
		
	


	




 #3 is pretty creative, I do like it. But I'd still pick #2.
 Thanks for demonstrating all the gyrations though!


----------



## Earwax

Quote:


  Originally Posted by *morsel* 
_#3 went over like a lead zeppelin, possibly because the attachment poofed and no one saw it._

 

Right, I couldn't see the picture last night. #3 is a very creative solution which satisfies everyone technically, but I think it still leaves an open ambiguity for the casual board stuffer to stumble into.


----------



## morsel

v026

 removed old V+
 renamed D+ to V+
 V+ now routes through series diode D1

 Last call for comments.
 The deadline is 2005/2/3,Thursday night.
 Barring unexpected issues, we are going with v026.


----------



## z2trillion

Would it be possible to to delete one of the sets of silkscreens for the top bank of capacitors? imho i think it looks pretty strange the way it is right now.


----------



## doobooloo

Quote:


  Originally Posted by *z2trillion* 
_Would it be possible to to delete one of the sets of silkscreens for the top bank of capacitors? imho i think it looks pretty strange the way it is right now._

 

I thought the same ever since but was afraid to voice my opinions... 
	

	
	
		
		

		
		
	


	




 Perhaps the larger cap silkscreen should go away. I feel more people will use the smaller cap just because they'll have more of those from building other amps such as PPA and PIMETA.

 Also, using the smaller cap also conveniently and neatly exposes a positive pad and a negative pad per channel if one wishes to connect outboard caps... so, could the larger cap silkscreen be removed? It should be fairly clear anyway how to connect the larger caps if one wishes to do so.


----------



## morsel

The 18mm cap outlines are not hurting anything, and their absence will make it less convenient for those who wish to use 18mm caps. After all, the entire purpose of part outlines is to show where the parts go.

 Since using many smaller value caps will probably provide lower ESR than fewer larger value caps, I don't recommend using 18mm caps at all, but it seems like a bad idea to get rid of the 18mm outlines just because you think they are unsightly. Keep in mind the silkscreen lines are only 8mils thick. I doubt you will notice them once you have a row of 12.5mm electrolytics in place.

 We are recommending 2000-3000µF total rail capacitance. There is no reason to use outboard caps. Excessive capacitance may damage your power supply.

 edit: Forgot to ask, what do other people think about this?


----------



## steinchen

I don't mind the 18mm cap outlines, although I'm gonna use 6*680uF caps


----------



## aeriyn

Morsel,

 Would ~2000uF be too much?

 I would like to use 9 Elna SILMIC II or Cerafine (if I can find them) capacitors, which will likely be 220uF @ 35V, and I believe they are 12.5mm in diameter. Nine of those would be around 2000uF of total rail capacitance, perhaps a bit less.

 Edit: Oops, you recommended 2000-3000uF. -.-'

 Also, the extra silkscreening does not bother me. =P


----------



## morsel

35V 12.5mm: 9×220µF = 1980µF is fine.
 50V 16mm: 6×470µF = 2820µF is also good and supports the full supply voltage.
 16mm caps fit in the 18mm positions.

 BTW, the reason I don't recommend 18mm caps is because I don't recommend boutique caps - Panasonic FC or Nichicon PW are just fine.


----------



## pabbi1

Quote:


  Originally Posted by *morsel* 
_35V 12.5mm: 9×220µF = 1980µF is fine.
 50V 16mm: 6×470µF = 2820µF is also good and supports the full supply voltage.
 16mm caps fit in the 18mm positions.

 BTW, the reason I don't recommend 18mm caps is because I don't recommend boutique caps - Panasonic FC or Nichicon PW are just fine._

 

Given the choice of 470µF, 35v vs 63v, which is preferrable?


----------



## SDA

Pardon my ignorance, but would there be any measurable difference between, say, 2000µF and 3000µF of rail capacitance? I know that too much is a bad thing, just wondering if there's anything to be gained by going nearer to 3000µF.

 Can't say I'm really bothered by the big cap outlines, myself. I wouldn't use them, but they could be useful for those who would, and they're not really distracting (to me, at least).


----------



## amb

Quote:


  Originally Posted by *pabbi1* 
_Given the choice of 470µF, 35v vs 63v, which is preferrable?_

 

If you will never run a PSU higher than 30V or so, then the 35V capacitor is sufficient. However with some opamps you could go up to 36V, and in such cases I would recommend 50V capacitors which is the next step up.

  Quote:


  Originally Posted by *SDA* 
_Pardon my ignorance, but would there be any measurable difference between, say, 2000µF and 3000µF of rail capacitance? I know that too much is a bad thing, just wondering if there's anything to be gained by going nearer to 3000µF._

 

The 2000-3000uF is just a ballpark recommendation. Other factors influence whether a certain amount of capacitance is too little or too much. For example, if you're using a PSU that already has a copious amount of capacitance at its output, then you won't need as much in the amplifier. I wouldn't recommend less than 1000uF onboard, but that's yet another ad hoc number I drew out of a hat. You should have some capacitance near the MOSFETs for the lowest impedance, and I would recommend using at least one capacitor adjacent to each amplifier channel (rather than just one or two capacitors at one end).


----------



## shiggins

Excuse my ignorance, but is there any reason why most of the pads connected to the ground pland are connected with a cross, unlike the IG pads which are fully connected?


----------



## peranders

1 They may have made this on purpose or simply forgot.

 2 Diodes can take a bit more heat than plastic caps.

 These crosses are for making it easier to solder "heat relief pads".


----------



## morsel

A large area of copper surrounding a pad acts as a heat sink, forcing the use of more heat to solder the pad and increasing cool down time, which in turn may damage components, especially capacitors. The cross shaped thermal pad conducts less heat into the surrounding copper, which facilitates quick soldering. Since the IG pads are for wires, not components, there is no need for thermal pads.


----------



## morsel

Only 1 day left until the close of development. Any more thoughts on the request to remove the 18mm cap outlines?


----------



## NOTHINGness

Would it be possible to add mounting holes for tangent's crossfeed? I remember that this was mentioned once earlier in the thread. 

 Also amb, would it be possible to carry the DACT stepped attenuators and TDK pots along with the boards?


----------



## morsel

I believe we agreed that with the shrinking of the M³ board there was no longer a specific good spot to put the daughterboard mounting holes, but since the amp will be going into a case larger than the board, it will be no problem to add extra standoffs to mount the daughterboard separately.

 I think I can safely answer for amb that the added investment of stocking stepped attenuators and another brand of pots is prohibitive.


----------



## SDA

Quote:


 The 2000-3000uF is just a ballpark recommendation. Other factors influence whether a certain amount of capacitance is too little or too much. For example, if you're using a PSU that already has a copious amount of capacitance at its output, then you won't need as much in the amplifier. I wouldn't recommend less than 1000uF onboard, but that's yet another ad hoc number I drew out of a hat. You should have some capacitance near the MOSFETs for the lowest impedance, and I would recommend using at least one capacitor adjacent to each amplifier channel (rather than just one or two capacitors at one end). 
 

Great, thanks. If I understand what you and morsel have said about this, the best solution (with respect to performance, not convenience) for C7 would probably be nine low-value caps, then..?


----------



## morsel

Yes, but perhaps the most important point we can make is not to obsess about caps. I defy anyone to hear a difference between Elna, Nichicon, and Panasonic. You can use configurations that are theoretically better, but probably will not result in a real world improvement. The "stock" configuration is more than good enough.


----------



## SDA

Quote:


  Originally Posted by *morsel* 
_Yes, but perhaps the most important point we can make is not to obsess about caps. I defy anyone to hear a difference between Elna, Nichicon, and Panasonic. You can use configurations that are theoretically better, but probably will not result in a real world improvement. The "stock" configuration is more than good enough._

 

Thanks! I wasn't planning on using anything exotic... I'm not really a believer in the value of overly expensive passive components (no offense to those who feel otherwise, of course), I was just wondering what would theoretically be the best configuration. It's not really that I believe that C7 is all that important so much as that I'm cheap and already have an awful lot of (relatively) low-capacitance Panasonic FCs sitting around


----------



## amb

Quote:


  Originally Posted by *morsel* 
_I think I can safely answer for amb that the added investment of stocking stepped attenuators and another brand of pots is prohibitive._

 

Indeed.


----------



## silvervarg

Amb, have you decided on what parts you will sell?
 Do you have an estimate on the cost of the board and parts you will sell?


----------



## amb

Quote:


  Originally Posted by *silvervarg* 
_Amb, have you decided on what parts you will sell?
 Do you have an estimate on the cost of the board and parts you will sell?_

 

I am still working on that. Watch this space for news.


----------



## morsel

M³ development is closed. Thanks to everyone who participated. 
	

	
	
		
		

		
			





 It is a few hours early, but there have not been any new issues since yesterday, so the time feels right. We will let you know when boards are available.


----------



## amb

An update: The M³ boards are in the queue to be manufactured. The ETA is about 2 to 3 weeks. I will announce the web site where you can get the boards and some related parts when it is ready.


----------



## BradJudy

Good news. I may have to build this one for giggles and then sell it or my PPA.


----------



## z2trillion

yay!!! this is going to be so much fun. [edit] what color are the boards? [/edit].


----------



## amb

Quote:


  Originally Posted by *z2trillion* 
_what color are the boards?_

 

It's going to be the ubiquitous green soldermask with white silkscreen.


----------



## n_maher

oh no... just what I needed... another project...


----------



## steinchen

on http://elvencraft.com/mmm you recommend the Aavid Thermalloy 531202b00000 2" heatsinks, I'd prefer 531202b02500 with pins. Do they fit ? The pcb seems to have the holes drilled for pin mounting.

 Is there a benefit in taking silver mica caps for C1 and C3 instead of generic NP0 / C0G ceramic caps ?


----------



## amb

Quote:


  Originally Posted by *steinchen* 
_on http://elvencraft.com/mmm you recommend the Aavid Thermalloy 531202b00000 2" heatsinks, I'd prefer 531202b02500 with pins. Do they fit ? The pcb seems to have the holes drilled for pin mounting._

 

You can use either style. The pin-style means that you'd solder the pin
 to the pad below to secure it, however it will be a lot harder to remove. The style that we recommend has holes in the heat sink which you can use with screws. I run a #4-40 tap for about 3/8" deep into the holes and use #4-40 machine screws. You could also use self-tapping screws if you wish.

 I now recommend 1.5" high versions of these heat sinks (Aavid Thermalloy 531102b00000) which are comfortable with 80mA of bias. 2" is of course fine if your case has enough clearance inside.

  Quote:


 Is there a benefit in taking silver mica caps for C1 and C3 instead of generic NP0 / C0G ceramic caps ? 
 

The pin spacing on the board for these are on 0.1" centers, and the Kemet Golden-max C315 series multilayer ceramic NP0/C0G fits well. If you could find silver mica caps that fit, they will also work.


----------



## tingj

Would someone here be willing to build one of these for me? I would pay the cost of parts plus a build fee -- whatever is considered reasonable.
 Thanks. Hopefully this is not a violation of etiquette.
 Jess
 handsurgeon at gmail dot com


----------



## steinchen

just two more questions: 

 what are the requirements for the power supply ? With 3x 80mA + 3x 14mA (ad843) + 3x 2mA (OpAmp classA bias) + LED + ... the amp will draw about 300mA quiscent current in idle mode. How much will I have to put approximately on top of that for the dynamic load into a K1000 ? How much current should the psu at least provide ? 

 Are bigger values than 1uF for C2 reasonable ? Since they are for stabilizing the voltage drop and lowering impedance bigger should be better.


----------



## amb

Quote:


  Originally Posted by *steinchen* 
_what are the requirements for the power supply ? With 3x 80mA + 3x 14mA (ad843) + 3x 2mA (OpAmp classA bias) + LED + ... the amp will draw about 300mA quiscent current in idle mode. How much will I have to put approximately on top of that for the dynamic load into a K1000 ? How much current should the psu at least provide ?_

 

The K1000 is a medium impedance (120 ohms) headphone and will not cause the amp to drop out of class A at max voltage swing, so the amp will not be drawing any more current than quiescent at max output. So, a power supply capable of of 0.5A should be sufficient, although I'd be happier with 1A. The K1000's low efficiency means that you will need a lot of voltage swing capability to get loud. I suggest using a 36V power supply and opamps that could handle that and swing close to rail-to-rail.

 Unfortunately, the AD843 is a poor choice for the K1000 because it can't swing very close to the supply rails before clipping. In fact, the AD8065 can swing a smidge more voltage with a 24V supply than an AD843 on a 36V supply. The AD823 may be a good candidate here, with rail-to-rail swing and able to handle a 36V supply.

  Quote:


 Are bigger values than 1uF for C2 reasonable ? Since they are for stabilizing the voltage drop and lowering impedance bigger should be better. 
 

I have done all sorts of measurements and listening with different values of C2 and concluded that a larger capacitance provides no benefit. Even a 0.1uF cap works just great.


----------



## jamont

Quote:


  Originally Posted by *amb* 
_doobooloo, the Lansing MicroPak series do not have any ventilation holes or slots, neither do the Hammond 1455 series. This makes the cases unsuitable for use with this amp. The MOSFET heatsinks get warm, and the heat need to escape.

 I am working on enclosure solutions. Watch this thread for more info when I have more to share._

 

Any progress to report here?


----------



## Syzygies

I understand that the M³ was never intended to be portable, yet I see people on planes all the time who think that 8 lb laptops _(the 90's are calling! they want their laptop back!)_ are portable.

 Can anyone imagine using a 20 AA cell travel power supply with the M³? I'd in fact prefer to outboard the battery pack, as a modular alternative to an outboard AC power supply. The M³ just gets hot, it's not a fire hazard, right?

 (I know I should consider a PPA, that will in fact be next once the new boards are out and I finish my PIMETAs and MINTs. The M³ just looks very, very cool. I'm faithful to one woman, why should I be faithful to one amp?)


----------



## Voodoochile

Quote:


  Originally Posted by *Syzygies* 
_I'm faithful to one woman, why should I be faithful to one amp?_

 

Uh-oh... that one is just screaming 'custom title'. 
	

	
	
		
		

		
		
	


	



 [size=xx-small](no, I don't deal with custom titles... just an observation)[/size]


----------



## amb

jamont, as far as Hammond 1455 series goes, the 1455T2201 or 1455T2202 can be used if you run with a lowered quiescent current (set to <= 50mA per channel), but this is in my opinion less than optimal as the MOSFETs do like to run with more bias. However if you must use this case then you'd have to make some compromises. Maybe make a custom top plate with ventilation holes...

 As for Lansing, the Micropaks are out because none are big enough, but there are some Graybox B series cases that could be used and they can be ordered with ventilation panels.

 Par Metal 20 series still looks to be the best bet, and maybe someone here could spearhead a group buy after the board comes out. I have gotten some quotes from Par Metal. Single orders of a custom sized case is going to cost about $70 but in quantities of 10 or more it drops to less than $40 each. Quite reasonable.

 Larry ar Larocco Audio is still working on a quote for a beautiful custom case for this amp. I'll report when I hear more from him.

 Syzygies, the temperature gets warm, but not dynahi-hot. The MOSFETs have a beautiful tendency to self-regulate in this respect. But You will need a pretty hefty battery pack to supply 0.3A for a prolonged period of time. You can do your own calculations and see how long would 20 AA cells last.


----------



## jamont

Thanks for the update! I think you and morsel have done a great job on this, and I'm looking forward to building it. The case is the only aspect that troubles me...


----------



## Jazper

Quote:


  Originally Posted by *Syzygies* 
_Can anyone imagine using a 20 AA cell travel power supply with the M³? I'd in fact prefer to outboard the battery pack, as a modular alternative to an outboard AC power supply. The M³ just gets hot, it's not a fire hazard, right?
 )_

 

why limit yourself to AA?

http://www.thomas-distributing.com/c...-batteries.php 

 (links to D size 12,000mAh batteries)


----------



## Magsy

I have read this thread countless times but I'd appreciate it if someone could clarify a few things for me (I'm building a parts list)


 Can I substitute BF245A (Idss min 2 / max 5) inplace of 2n5484?

 Trimpots are rated '5k' ?

 What is Cbb pin spacing? (Would these fit? - 15mm lead spacing)

 R9 is on the schematic as '1', is that 1M?

 Thanks!


----------



## amb

Quote:


  Originally Posted by *Magsy* 
_I have read this thread countless times but I'd appreciate it if someone could clarify a few things for me (I'm building a parts list)_

 

Before you rush into that, I am setting up a very detailed web site that should have all the info you need. It will offer specific parts recommendations and alternatives. So please wait until I'm done and I'll announce the URL to the site here.

 But anyway, here are the answers to your questions...

  Quote:


 Can I substitute BF245A (Idss min 2 / max 5) inplace of 2n5484? 
 

Yes, you could use a BF245A or BF244A (the A-suffix is important). Unlike the rail isolation JFETs on the PPA, for this amp the capacitance multiplier actually needs small-Idss devices. Note that the pin orientation of the BF devices are reversed, so you'd have to put them on the board backwards than what the silkscreen indicates.

  Quote:


 Trimpots are rated '5k' ? 
 

The BIAS trimpots are 5K ohms, the BIOSOP trimpots are 1K ohms. Both should be 3/8" multi-turn cermet type.

  Quote:


 What is Cbb pin spacing? (Would these fit? - 15mm lead spacing) 
 

There are multiple holes for Cbb, giving you the choice of 0.2", 0.3", 0.4", 0.5" and 0.6" lead spacings (5mm, 7.5mm, 10mm, 12.5mm and 15mm).

  Quote:


 R9 is on the schematic as '1', is that 1M? 
 

That's 1 ohm, 2 watt rated metal film or metal composition type. The hole spacing on the board is 0.6" for these, so make sure you use something that would fit. If you must, you could also use 1 watt rated resistors for these, but I suggest you stay with the 2 watt units.


----------



## Magsy

Thanks Amb!

 I got impatient and used the current WIP webpage you have...I'll wait now


----------



## morsel

tingj: The boards are not available yet, but should be arriving in a few days. We will post when all is ready. You will then be able to choose from a list of builders.

 steinchen: Try the OPA227, OPA132, or OPA627 with 36V rails for driving the K1000. I think a .33 or .5A power supply will be just fine.

 Magsy: Even 1mA Idss FETs should be OK.


----------



## steinchen

thanks for the info, I'm curious how much difference the voltage swing will make, I'll give most of my opamps a try

 a 36V .8A psu is in the works, my present 30V .3A may be a bit weak

 since ad823 is only available in dual package I'll have to build an adapter for it to fit, what shall I do with the second amp on each chip, simply leave all connections disconnected ?

 I'm going to isolate the transistors from the heatsinks for safety reasons, I found "High Performance Kapton, TO-220, 0,07 K/W" parts. With about 1.5W heat dissipation from each transistor this should be overkill I guess, but I don't mind spending 3 bucks for safety.


----------



## Magsy

What psu are you building mate?

 All this talk of 36v has got me wondering, do I need that much? I was going to build the Velleman kit but that is ~25v max

 I really like the OPA637 from my Pimeta and I do plan to use them, but I don't really want to limit myself psu wise, because it may well sound different in this amp.


----------



## morsel

steinchen: Forget the AD823, it is not worth adapting a dual channel opamp.

 Magsy: 36V is overkill unless you are driving AKG K1000 headphones or small studio monitors.


----------



## steinchen

36V are only needed for AKG K1000 which are a very inefficient cans, for most cans 25V should be fine

 I'm building tangent's STEPS psu, using a 2x21V 730mA 30VA transformer, LM317*A* regulator, the line filter on a separate board (for 240V creepage safety distance min 8mm)


----------



## amb

Quote:


  Originally Posted by *steinchen* 
_since ad823 is only available in dual package I'll have to build an adapter for it to fit, what shall I do with the second amp on each chip, simply leave all connections disconnected ?_

 

Oops, my bad for mentioning this chip, I had forgotten that it's a dual. Morsel is right about it not worth the trouble. It's too bad there aren't any really good rail-to-rail opamps that could handle a 36V power supply for something like the K1000.


----------



## myhui

Quote:


  Originally Posted by *morsel* 
_36V is overkill unless you are driving AKG K1000 headphones or small studio monitors._

 

I have been considering using the PPA v1.* to drive the AKG K1000 headphones.

 I don't know what its AC impedence is though.

 Has anyone tried it with a headphone amp instead of speaker amp?


----------



## steinchen

it's not a question of impedance (K1000 120 Ohms) than of very low efficiency

headphone tech letter from Lehmann Audio

 a maxed out pimeta or ppa at 30V doesn't drive the K1000 to high volumes, sound is very good, but won't get loud :/


----------



## morsel

K1000 Efficiency = 74dB SPL/mW. Impedance = 120 Ohms.

 To achieve 90dB SPL, 2.2Vrms pushes 18mA to deliver 40mW of power.
 To achieve 100dB SPL, 7Vrms pushes 58mA to deliver 400mW of power.
 To achieve 104dB SPL, 11Vrms pushes 91mA to deliver 1W of power.
 (1W is the maximum input power of the K1000)

 2.2Vrms = 6.2Vpp. 7Vrms = 20Vpp. 11Vrms = 30Vpp.

 This gives some idea of the output swing and current required to drive the K1000. Note that while 100dB SPL is hazardously loud, it may not be loud enough for some soon to be if not already deaf headbangers.


----------



## n_maher

Quote:


  Originally Posted by *morsel* 
_(1W is the maximum input power of the K1000)_

 

Not saying you're wrong or that I necessarily know anything but do you have any reason why Headroom makes the claim that they require at least 7 watss of power? 

 Just trying to figure out what's going on here...

 N


----------



## steinchen

say what ? did somebody say anything ? 
	

	
	
		
		

		
			





 hm, with a 30V psu you'll never get 30Vpp, you loose Volts with the reverse protection diode, isolation jfets, output capability of the opamp, buffers, ...

 anyway, I'm curious how loud I let the music play usually, I should find out


----------



## tkam

I'll continue this slightly off-topic jaunt, the K1000 are not that hard to drive. My dynahi and melos drive them to louder levels than my ears can take. Even my old ppa w/ diamond buffers drives them pretty decently. 

 I just thought of this but I also remember someone I think it might have been hirsch was able to drive the K1000s to listenable levels using one of xin's supermacro or supermini amps.


----------



## PeterR

Quote:


  Originally Posted by *n_maher* 
_Not saying you're wrong or that I necessarily know anything but do you have any reason why Headroom makes the claim that they require at least 7 watss of power? 

 Just trying to figure out what's going on here...

 N_

 

Although I wouldn't necessarily expect the guys at headroom to fall into that trap, I believe many of the claims about the power levels required for the K1000 result from people using loudspeaker amps with these headphones. These will of course produce a lot less power into the 130 Ohm AKG than into a speaker load for which they're rated. FWIW, headroom also reports they were _"pleased—no, AMAZED—at how good the Grace Model 901 sounds with the K 1000!"_, which IIRC is capable of a little less than 1W into a K1000 (someone correct me if I'm wrong, but in any case it's well below 7W).


----------



## morsel

Quote:


 do you have any reason why Headroom makes the claim that they require at least 7 watts of power? 
 

I am merely quoting specifications for the K1000 from the AKG website:

 Max. input power 1000mW (measured with test noise to DIN 45582), equivalent to approx. 100dB

 According to the Grace 901 manual, maximum output level is 10.9Vrms, 30.8Vpp.

 I have no idea how accurate the specs from AKG are or how HeadRoom arrived at their conclusion. We are getting off topic, perhaps this should be taken to a K1000 thread so we can get back to M³ issues.


----------



## amb

I am happy to announce my new M³ web site. Check it out:

http://www.amb.org/audio/mmm/

 Boards are not yet ready, but I am letting this cat out of the bag a few days ahead of time to give propective builders some time to read and digest the information. Have fun!


----------



## z2trillion

w00t!!!


----------



## doobooloo

Very nice!


----------



## n_maher

[pumps fist in air] NICE! 

 Again, thanks to the team for putting together this project for those of us to unedjumakated to figure stuff like this out. 

 N


----------



## morsel

amb's M³ web site is detailed, thorough, and completely over the top. Did you notice his bass boost calculator dynamically generates a custom graph?






 (Trumpet Fanfare)


----------



## SnoopyRocks

Quote:


  Originally Posted by *amb* 
_





 I am happy to announce my new M³ web site. Check it out:

http://www.amb.org/audio/mmm/

 Boards are not yet ready, but I am letting this cat out of the bag a few days ahead of time to give propective builders some time to read and digest the information. Have fun!_

 

The site looks good. It's well documented and thurough. Nice job team M³ 
	

	
	
		
		

		
		
	


	




 One of the stated project goals was to attain a "better price/performance ratio than the PPA." Could you elaborate a bit on this please. Does this mean
 1) same price (roughly) with better performance?
 2) cheaper than PPA with equivalent performance?
 3) much cheaper with almost as good performance?
 4) more expensive with even better performance?
 5)something else?
 I realize that this is a subjective assesment, opinions vary and that few have heard an M³, let alone AB'd one with a PPA. If it's premature to answer that now, what was the design object in this regard?

 Speaking of money, what is the projected cost to build the project? This information would be nice to see on the website for 3 cases: 
 1) barebone
 2) typical
 3) true audiophile $$$

 your (team M³) effort is appreciated


----------



## stadams

I hope you don't mind if I call you Snoop, do you?

 I went back and checked another post, and found the cost per channel for the M³ will probably be about $10.00 compared to ~$25.00 a channel for a maxed out PPA V1.X. I don't know about the V2.0 though. With the board purchase and various other components I would hazard a guess of $150.00 less a power supply and using a case of your own construction. With the M³ website now in operation and the list of components just available, I'm sure someone will generate BOM's from the least expensive to the most extravagant of configurations.

 In this thread I have read favorable reviews concerning the M³ in comparison to a PPA, although I cannot remember if the exact configuration of the PPA was given.

 Somewhere around post #350, probably later.

[size=medium]*Kudos to Team M³*[/size] and to those who helped in any small way. amb, the website looks good and is much appreciated.

 Later,


----------



## morsel

Hi SnoopyRocks and Todd, thanks for your kind words. I'm not sure that M³ will be much cheaper than PPA v2, and may even be more expensive depending upon your choice of case, but a basic M³ should be comparable in price. The jury is out until people build them and report back.

 As far as I know, the only people to have A-B compared the M³ and PPA v1.1 are Raif, NeilPeart, amb, and me. None of us could hear a significant difference. amb and I will be at the Head-Fi Meet in San Mateo this Saturday with both M³ and PPA v1.1 for folks to listen to. Sorry, only Tangent and PPL have a PPA v2 at this time.


----------



## SnoopyRocks

send me an email

  Quote:


  Originally Posted by *stadams* 
_I hope you don't mind if I call you Snoop, do you?

 I went back and checked another post, and found the cost per channel for the M³ will probably be about $10.00 compared to ~$25.00 a channel for a maxed out PPA V1.X. I don't know about the V2.0 though. With the board purchase and various other components I would hazard a guess of $150.00 less a power supply and using a case of your own construction. With the M³ website now in operation and the list of components just available, I'm sure someone will generate BOM's from the least expensive to the most extravagant of configurations.

 In this thread I have read favorable reviews concerning the M³ in comparison to a PPA, although I cannot remember if the exact configuration of the PPA was given.

 Somewhere around post #350, probably later.

[size=medium]*Kudos to Team M³*[/size] and to those who helped in any small way. amb, the website looks good and is much appreciated.

 Later,_

 

Thanks. I didn't want to dig through the entire thread for this information. $10 vs $25 refers to the output buffers right? $150 seems reasonable. I'm too lazy to try and source all the parts to verify it myself. Maybe later...


----------



## Magsy

Wow that has taken some effort! 
	

	
	
		
		

		
		
	


	




 A job well done Amb/Morsel, hopefully it should make the whole process of building the M³ nice and easy.

 Thanks!


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## steinchen

excellent site

 can't wait to get the pcb (got all parts allready at home :X )

 just found one little thing: in the parts list, the qty for Cbb, shouldn't it be 2 instead of 9 ? typo or did I overlook something ?


----------



## amb

Quote:


  Originally Posted by *steinchen* 
_in the parts list, the qty for Cbb, shouldn't it be 2 instead of 9 ? typo or did I overlook something ?_

 

Good catch! It was a copy-and-paste mistake, now fixed. Thanks.


----------



## Magsy

Quote:


  Originally Posted by *amb* 
_Good catch! It was a copy-and-paste mistake, now fixed. Thanks._

 

Almost had 9 there for a minute, lucky ordering parts takes agggggggeees! 
	

	
	
		
		

		
			





 $130 lighter and I think I'm all set, bring on the boards!!

 Will you have the h/s in stock from the start AMB? Cannot find the exact model here..


----------



## guzzler

Magsy; Rapid sell the right heatsinks

http://www.rapidelectronics.co.uk/rk...0146&XPAGENO=2

 g


----------



## Magsy

Quote:


  Originally Posted by *guzzler* 
_Magsy; Rapid sell the right heatsinks

http://www.rapidelectronics.co.uk/rk...0146&XPAGENO=2

 g_

 


 Are you sure? Same one on RS I think, they have a different model number to the Amb recommended ones. I mean they look like they fit but because Amb is going to sell the right ones, I thought I would hang on..

 My order has already gone at Rapid I think, too late now


----------



## guzzler

The pitch for large TO-220 heatsinks is standard (25.4mm), and so any heatsink with reasonable size will fit okay. Just watch out for the fins being too wide is all...

 Nice work on the MMM, probably won't build one for a while, but looks good 
	

	
	
		
		

		
		
	


	




 g


----------



## individual6891

Quote:


  Originally Posted by *steinchen* 
_36V are only needed for AKG K1000 which are a very inefficient cans, for most cans 25V should be fine

 I'm building tangent's STEPS psu, using a 2x21V 730mA 30VA transformer, LM317*A* regulator, the line filter on a separate board (for 240V creepage safety distance min 8mm)_

 

Won't the 2x21V secondary outputs blow the rated 40V input of the LM317?


----------



## morsel

The LM317 has a 40V maximum input-output voltage differential, which implies you can use a supply voltage up to 40V higher than your output voltage.


----------



## steinchen

I made up my mind and realized that a 2x18V 2x800mA transformer should be sufficient, with aprox 1.5V dropout voltage at 300mA for the LM317 and 50% load on the transformer the 36V output voltage shouldn't be a problem

 thanks to brokenenglish for the hint 
	

	
	
		
		

		
		
	


	




 I must admit I tend to oversize from time to time 
	

	
	
		
		

		
		
	


	






 much helps much, more helps even more


----------



## Magsy

I built one of the Velleman kits today, all went well and I have a nice 20-26v DC output! Used a 30VA 2x12v toroidal which reads about 30v AC.

 It made a good difference with my Pimeta, bass is much better, I was getting some bass distortion on a handful of songs but thats gone now!

 Unfortunately while pulling the spade connectors off the switch (tight) I pulled out both of the switch contacts too, oops


----------



## z2trillion

Does anyone know if the RN60 lines of Vishay Dale resistors will fit on the board? They look like they will, but I'd like to be sure before I place an order. Thanks.


----------



## Syzygies

The RN60 datasheet gives two dimensions:

 A = 0.344 +- 0.031
 C (max) = 0.425

 A is the shortest length one could describe them as being, how much of their body is "cylindrical". C is the longest length one could describe them as being, beyond this they are clearly just leads.

 Anyone's call how to interpret this.


----------



## amb

Seems like the RN60 is just on the edge of being oversized for the 0.400" resistor hole centers of the M³ board. To be safe, why not just use the RN55?


----------



## amb

Here's a pic of my newly "dressed" M³. For more pics go to My M³ site and look under "M³ gallery".


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## BradJudy

Very nice - I dig the thick panels.


----------



## Magsy

Sweet! Good job Amb, it looks bulletproof


----------



## Excalibur

Very attractive enclosure.


----------



## art633

What can one say? Superb does not seem correct but, I think you all get the sentiment.

 AMB and MORSEL have done a very professional job of this design. 

 AMB – how did you cut the acrylic? By hand, router or LaserCNC?

 M


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## BrokenEnglish

amb... can't believe, what i'm seeing. your m³-page is marvelous! so much comprehended information, even for people not involved in building the m³. thanks for that!


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## morsel

Tap Plastics does custom work for reasonable prices. I'm guessing they did the machining.


----------



## ble0t

I've ordered some stuff from Tap before...they do very good work, and they are not that expensive at all. Just put together some decent CAD drawings for them, and you're all set...


----------



## amb

Yeah, I had Tap Plastics do the basic cutting for me, but I drilled all the holes myself (except the routed one on the top cover). They charge for everything, so if you want them to do a lot then the cost would quickly add up.


----------



## primer

How about the Hammond case L220 series with holes drilled on the top panel?


----------



## amb

Quote:


  Originally Posted by *primer* 
_How about the Hammond case L220 series with holes drilled on the top panel?_

 

The L220 is not wide enough at only 4". You can use the T220. The parts list page on my M³ site has all this info.


----------



## primer

Sorry, I meant to say T220. Would holes in the top panel be sufficient? Pars-metal etc. would be hard for us aussies but the Hammond case can be sourced.


----------



## amb

Quote:


  Originally Posted by *primer* 
_Sorry, I meant to say T220. Would holes in the top panel be sufficient? Pars-metal etc. would be hard for us aussies but the Hammond case can be sourced._

 

Yes, although cutting the holes (or preferably, slots) neatly would be a challenge.


----------



## amb

OK, while we're on the subject of enclosures, and since the boards are expected within days now, I think it's fine time to check for interest in a Par Metal 20-series custom-sized case group buy. As I mentioned in a previous post, Par Metal can make any custom size you want, but it's pricey in single quantities. I asked them about a 6" wide x 2" high x 8" deep case, and the quote was something like $70. However, that price drops to the mid-$30 range for a quantity of ten or more, which is quite reasonable.

 If there is enough interest, and people could agree to a common specification (size, color, finish, etc), then I suggest someone should step up and coordinate this. I am too busy to conduct this myself, so I am asking for a volunteer. Maybe a separate thread for this is appropriate?


----------



## morsel

SF bay area folks can hear M³ at the San Mateo Head-Fi Meet today.

 Saturday, February 26, 1pm

 Rays Tea Time
 138 East 3rd Ave.
 San Mateo, CA 94401
 650-348-7233

Google Maps - Rays Tea Time


----------



## amb

Great San Mateo California meet!

 M³ has now had its first real public showing and it's garnering praises. 
	

	
	
		
		

		
		
	


	




 Check out  this post-meet impressions thread.


----------



## MisterX

Put me down as a maybe on running the group buy on the cases..... I will have to see what the girlfriend has to say when she wakes up. 
	

	
	
		
		

		
		
	


	




 BTW.... nice showing. The impressions posted in that thread look/sound very promising.


----------



## individual6891

Any chance of shipping to the UK for the par metal cases? Maybe a new thread should be started if/when? MisterX gets the green light


----------



## Magsy

I'm possibly in, depends on the style. I don't much like the one depicted on the site, maybe in black with less holes cut in it...


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## BrokenEnglish

europeans might consider those marvelous galaxy cases of audiokit.it... at least... i would do so..


----------



## BradJudy

For reference, here's a pic of a larger (16x8x2) ParMetals series 20 in anodized black (note that the faceplate is a custom FPE one, not the stock one):






 It looks pretty nice, but the anodizing doesn't seem that durable. It scratches more easily than other anodized aluminum items I own. 

 Some venting holes will be required since the MMM puts out some heat.


----------



## Nisbeth

Quote:


  Originally Posted by *BrokenEnglish* 
_europeans might consider those marvelous galaxy cases of audiokit.it... at least... i would do so.. 
	

	
	
		
		

		
		
	


	




[/IMG]_

 

Those a good cases, but it's quite annoying that there's only two heights 40 and 80 mm. 40 mm is a bit to thin and 80 mm is much more than necessary. If they were to make a 60 mm high version I would have about 10 different projects for them in various sizes 
	

	
	
		
		

		
		
	


	





 /U.


----------



## z2trillion

I'd definately be interested in at least 3 of the par metals cases. Hopefully, we can all decide on dimensions. I would prefer it to be wider than it is deep, but I guess we'll have to see what other people want.


----------



## uzziah

Quote:


  Originally Posted by *amb* 
_OK, while we're on the subject of enclosures, and since the boards are expected within days now, I think it's fine time to check for interest in a Par Metal 20-series custom-sized case group buy. As I mentioned in a previous post, Par Metal can make any custom size you want, but it's pricey in single quantities. I asked them about a 6" wide x 2" high x 8" deep case, and the quote was something like $70. However, that price drops to the mid-$30 range for a quantity of ten or more, which is quite reasonable.

 If there is enough interest, and people could agree to a common specification (size, color, finish, etc), then I suggest someone should step up and coordinate this. I am too busy to conduct this myself, so I am asking for a volunteer. Maybe a separate thread for this is appropriate?_

 

so the par-metal idea would be that we would decide on a CUSTOM size case for the m3 and then groupbuy that custom size. yes?


----------



## amb

Quote:


  Originally Posted by *uzziah* 
_so the par-metal idea would be that we would decide on a CUSTOM size case for the m3 and then groupbuy that custom size. yes?_

 

Yes. The idea is to make the price of the custom sized cases reasonable with the group buy. Since only ten is enough to get the price down, I guess it's possible to have a couple of (size/color/finish) combinations if we could get enough quantity together for each one.

 By the way, the 2" high case has an available internal height of 1.85" after subtracting the thickness of the top and bottom panels. It will fit a board with the 1.5" heat sinks, but just barely. See diagram:






 You'd have to use short (0.125") spacers to mount the board and put an insulating plastic sheet below the board to safeguard the heat sink screws and parts pins from touching the bottom, and that gives only 0.145" clearance above the heatsink to the top cover. Also, the volume/bassboost pots will have their centers below the centerline of the front panel by 0.205". There isn't enough pin length on the Alps blue velvet to raise them to the center. But then my home-built case also has the pots below the centerline and it looks fine...


----------



## primer

0.145" doesn't leave much room for miscalculation.


----------



## BradJudy

As long as it would be a custom size, does increasing the height really add much cost? It seems like another 0.25-0.5 inch would make it easier to work with.


----------



## uzziah

Quote:


  Originally Posted by *amb* 
_Yes. The idea is to make the price of the custom sized cases reasonable with the group buy. Since only ten is enough to get the price down, I guess it's possible to have a couple of (size/color/finish) combinations if we could get enough quantity together for each one.

 By the way, the 2" high case has an available internal height of 1.85" after subtracting the thickness of the top and bottom panels. It will fit a board with the 1.5" heat sinks, but just barely. See diagram:






 You'd have to use short (0.125") spacers to mount the board and put an insulating plastic sheet below the board to safeguard the heat sink screws and parts pins from touching the bottom, and that gives only 0.145" clearance above the heatsink to the top cover. Also, the volume/bassboost pots will have their centers below the centerline of the front panel by 0.205". There isn't enough pin length on the Alps blue velvet to raise them to the center. But then my home-built case also has the pots below the centerline and it looks fine..._

 

in my mind, the thermal dynamics of the heatsink being closer to the lid would actually be a good thing. conduct the heat more directly from the hs to the case and thus radiating to outside air. does that makes sense? though i understand the concern for a tight fit, it seems good to me.


----------



## morsel

Or you could use 1" heat sinks, which is OK as long as you don't jack up the bias too high.


----------



## amb

Quote:


  Originally Posted by *morsel* 
_Or you could use 1" heat sinks, which is OK as long as you don't jack up the bias too high._

 

For performance reasons I would advise against 1" heat sinks unless there is absolutely no alternative. Such a small heat sink would necessitate operating with reduced bias. The MOSFETs will not be operating in its most linear region with too little bias. The global negative feedback will correct this, but it's best to rely on negative feedback to fix things as little as possible.


----------



## silvervarg

Quote:


 the heatsink being closer to the lid would actually be a good thing. conduct the heat more directly from the hs to the case and thus radiating to outside air. 
 

The major concern is if heatsinks touch the case (e.g. when case is pressed down). Unless you use insulation the heatsinks are live, so if they touch the case we can have a major shortcircuit.

 In general you want to have air slots so air can escape through the chassi, preferable just above the heatsinks. The distance from heatsink to top of case is not very important.


----------



## uzziah

Quote:


  Originally Posted by *silvervarg* 
_The major concern is if heatsinks touch the case (e.g. when case is pressed down). Unless you use insulation the heatsinks are live, so if they touch the case we can have a major shortcircuit.

 In general you want to have air slots so air can escape through the chassi, preferable just above the heatsinks. The distance from heatsink to top of case is not very important._

 

good point. thanks for the clarification. i suppose using a plastic lid, whether full, or cut out such as amb's would negate the possibility of short circuit? of course, it would be more $, especially if it's cut, and if it's not, it wouldn't conduct heat well AT ALL, and i think that would be very bad. i like amb's lid, except i'd be concerned with lots of dust getting in over time. no fans, but i'd imagine it could start looking pretty dirty inside. yes? exagerating?


----------



## amb

If the tops of the heat sinks are close to the (metal) top cover, you should use TO-220 heat sink mounting kits for the MOSFETs, that will isolate them.

 Yes, a cutout like mine will cause dust accumulation inside. I built the case primarily with "show" in mind, hence the clear acrylic top, but it's not the most practical solution. I cover the amp with a piece of cloth when not in use to keep the dust out.


----------



## silvervarg

I happened to notice nother product called M³ (with the superscript and everything) on TV today. It is the new model manual razor (with battery!) from Gillette.
 It is way to late to change name for this amp now anyway, and I believe the name was used long before any of us knew about this product, but it might still be a bit funny as you choose not to call it M3 since there was another product with that name...


----------



## z2trillion

Once the dust gets in, is there any easy way to get it out, or is that something I'll just have to live with? I'm sort of compulsive about keeping all my things dust free, but I guess everything has a price.


----------



## amb

silvervarg, it's too late to change the name. Bte, the Gillette razor is called M3 here in the US, not M³. I always thought that was a bit funny, because there is a competing product from Schick called "Quattro" (with reference to cars).

 z2trillion, you can blow out the dust with compressed air.


----------



## uzziah

i think we're all getting a bit dust-crazy 
	

	
	
		
		

		
			





 point made.


----------



## kasra

What kind of bias increase can one expect if 2" heatsinks are used compared to 1,5"?


----------



## uzziah

btw: this is a bit late in coming, but you guys deserve a big round of applause for all this. very exciting. if your ever in the denver area, glad to offer you a brew


----------



## amb

kasra, the recommended bias is 80mA per channel, but you can pump it up some more if you want, as long as your power supply has the capacity. Of course the 2" heat sink will allow you to do this more than the 1.5" version, but it all depends on how well ventilated the case is. If the heat sink gets uncomfortable to touch for more than a few seconds, then you know it's too hot! 
	

	
	
		
		

		
		
	


	




 I had experimented with 250mA per channel in an open-air environment (uncased) on 2" heat sinks and 24V supply. It got hot, but was still safe. However that's likely too much within a case even with good venting slots.

 uzziah, thanks for the compliments. We're having a lot of fun with this too.


----------



## kasra

amb: 
 Thank you for the clarification, the reason is im going with a 80mm (external) chassie. I also found that the heatsink model in question is available in 2.5" height, which might be fun to play around with 
	

	
	
		
		

		
		
	


	




 Ive also read through your homepage, and it is magnificent and great information source for builders!

 Which of the options is prefred for the compensation of N-channel´s less capacitance? (C3 vs. adj. R8+-)


----------



## amb

Quote:


  Originally Posted by *kasra* 
_Which of the options is prefred for the compensation of N-channel´s less capacitance? (C3 vs. adj. R8+-)_

 

No preference... it's up to you.


----------



## morsel

Kasra: I prefer using C3 to compensate the N channel MOSFET as this results in symmetrical impedance for both halves of the output stage, but both methods work.

 M³ boards are now available at amb's audio shop. Woohoo!


----------



## amb




----------



## skyskraper

*sigh* just as the iron is cooling from my dynalo and i start to look forward to a break, morsel answers my eternal question 
	

	
	
		
		

		
		
	


	







 off to buy i go!


----------



## uzziah

hows about that pars-metal groupbuy about now? 
	

	
	
		
		

		
		
	


	




 now that us folks can buy ourselves the goods, we're probably going to want to get to building. wasn't someone going to arrange that?

 we should start a seperate thread, get the dimensions we want down quickly, and get er done, eh?

 i hope whoever offered to do that could, but if that falls through i can do it.

 (i'd much rather have them do it, though 
	

	
	
		
		

		
		
	


	




 )


----------



## MisterX

Quote:


 i hope whoever offered to do that could, but if that falls through i can do it. 
 

Have at it.
 I have to many other things going on right now to take on the group buy anyhow.


----------



## Nisbeth

AMB: Could you perhaps update the documentation on your website with the max. physical dimensions of the capacitors (especially for C6 and Cbb)? Thanks! 
	

	
	
		
		

		
		
	


	





 /U.


----------



## uzziah

Quote:


  Originally Posted by *amb* 
_Yes. The idea is to make the price of the custom sized cases reasonable with the group buy. Since only ten is enough to get the price down, I guess it's possible to have a couple of (size/color/finish) combinations if we could get enough quantity together for each one.

 By the way, the 2" high case has an available internal height of 1.85" after subtracting the thickness of the top and bottom panels. It will fit a board with the 1.5" heat sinks, but just barely. See diagram:







 You'd have to use short (0.125") spacers to mount the board and put an insulating plastic sheet below the board to safeguard the heat sink screws and parts pins from touching the bottom, and that gives only 0.145" clearance above the heatsink to the top cover. Also, the volume/bassboost pots will have their centers below the centerline of the front panel by 0.205". There isn't enough pin length on the Alps blue velvet to raise them to the center. But then my home-built case also has the pots below the centerline and it looks fine..._

 

ok, i'll have at the groupbuy. i have the time right now, so i can arrange it. i've not organized one before however, so i could use input from others who have. i understand the basic premise. assuming we cannot get a larger-discount by buying over 10 cases (has this been verified?), we could probably do with different size/color/finish combos as amb states. but if we can get an increased discount for buying over 10 cases; and certainly if there is not enough interest (less than 10 cases) for a specific size/color/finish combo, perhaps we should consider one design only. either way, but i'd like to know if $30 per case (was that it?) is the lowest price we can get. i'll get on the phone and try to negotiate the lowest price possible once we have a definite idea of what we want. i'll post a seperate thread shortly.


----------



## Magsy

Woohoo! Order placed, cant wait


----------



## amb

Quote:


  Originally Posted by *Nisbeth* 
_AMB: Could you perhaps update the documentation on your website with the max. physical dimensions of the capacitors (especially for C6 and Cbb)?_

 

Hi nisbeth, download and print this M³ pcb silkscreen layer pdf. It should print in actual size, and you could see how much space there is for everything. The hole spacings are listed under the "Parts list" section of my M³ web site.


----------



## morsel

Sawing off 1/8" from the 1.5" heat sinks would allow for 1/4" standoffs for the pcb, eliminating the need for the plastic sheet under the board, and resulting in centered alignment of the pot, without significantly reducing the effectiveness of the heat sinks. An orbital sander with coarse grit could remove 1/8". Thoughts?


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## n_maher

Any reason someone doesn't design a standoff for the pot? It would seem to me that one of the more gifted folks on this site would have no problem designing a Brown-Dog like adapter to lift the pot(s) 1/4", rather than mess with grinding all the heat sinks. 

 Just a thought.

 Nate


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## morsel

such a pot standoff would be more trouble than shortening the heat sinks, and would not solve the problem of the pcb standoffs being too short, thus requiring a plastic sheet to insulate the case bottom from the standoff screw heads.


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## doobooloo

Quote:


  Originally Posted by *morsel* 
_Sawing off 1/8" from the 1.5" heat sinks would allow for 1/4" standoffs for the pcb, eliminating the need for the plastic sheet under the board, and resulting in centered alignment of the pot, without significantly reducing the effectiveness of the heat sinks. An orbital sander with coarse grit could remove 1/8". Thoughts?_

 

But then the heatsinks would be ugglllyy...


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## morsel

The sanded side could face the pcb if it was not uniform. Alternatively, go to a shop and cut them down with a table saw. The cuts should be cheap.


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## doobooloo

What about having the heatsinks just stick out a bit (a la tube amps) from the top? The top panel can be cut out like amb's amps, if the top is made of clear acrylic there is no danger of shorting so the heatsink holes can even be made tighter (but then heat dissipation would be worse)...?

 I think it'll look quite cool. I may even install 2"~2.5" heatsinks and make them extrude out more. If I can't have tubes, gotta have my second best alternative, right? 
	

	
	
		
		

		
		
	


	




 Then jack up the bias...


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## Nisbeth

Quote:


  Originally Posted by *morsel* 
_The sanded side could face the pcb if it was not uniform._

 

Doesn't these heat sinks have solder pins?


 /U.


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## morsel

They have screw holes: Aavid Thermalloy 531102b00000


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## amb

Quote:


  Originally Posted by *morsel* 
_Sawing off 1/8" from the 1.5" heat sinks would allow for 1/4" standoffs for the pcb, eliminating the need for the plastic sheet under the board, and resulting in centered alignment of the pot, without significantly reducing the effectiveness of the heat sinks. An orbital sander with coarse grit could remove 1/8". Thoughts?_

 

The board side and the top side of the heat sinks are not the same... There is a cutout towards the board side and the screw hole for the TO-220 mount is not exactly in the vertical center. I suppose there is a little bit of tolerance for you to grind off on the bottom side but not much. Grind off too much and the MOSFET's pins won't insert far enough into the board to allow the screw hole in the TO-220 tab to line up with the hole in the heat sink.


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## morsel

An internal bar could be bolted across the tops of 1" heat sinks, adding mass without requiring unsightly holes through the case top. If the bar were of the right thickness and had recessed bolt head cavities, it could maintain contact with the case top over a wide surface area, thus conducting heat into the case top, eliminating the need for ventilation and allowing even higher bias currents than would be possible with the standard 1.5" heat sinks. Since this would be a simple rectangular aluminum bar with a few holes, it should not cost much to have it made at a machine shop.


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## BradJudy

Quote:


  Originally Posted by *morsel* 
_without requiring unsightly holes through the case top._

 

I think an MMM with extra tall heatsinks poking up through the top of the case would look pretty nice.


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## uzziah

Quote:


  Originally Posted by *BradJudy* 
_I think an MMM with extra tall heatsinks poking up through the top of the case would look pretty nice._

 

only issue being the same with the issue of slits on the top of par-metal case: dust


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## BradJudy

Quote:


  Originally Posted by *uzziah* 
_only issue being the same with the issue of slits on the top of par-metal case: dust_

 

All of my regular stereo amps (and my PPA) have vents in the top - I'm not worried about dust.


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## uzziah

Quote:


  Originally Posted by *BradJudy* 
_All of my regular stereo amps (and my PPA) have vents in the top - I'm not worried about dust._

 

i'm not particularly either. it's more of an ascetic question. let's discuss this in par-metal groupbuy thread if we are specifically referring to par-metal cases


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## uzziah

Quote:


  Originally Posted by *BradJudy* 
_All of my regular stereo amps (and my PPA) have vents in the top - I'm not worried about dust._

 

i'm not particularly either. it's more of an Aesthetic question. let's discuss this in par-metal groupbuy thread if we are specifically referring to par-metal cases


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## Syzygies

Quote:


  Originally Posted by *morsel* 
_M³ boards are now available at amb's audio shop. Woohoo!_

 

This link is neither on the first page, last page, or amb's home page. I can put it on the last page by bumping it like this.


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## mirlo

I received my package today from amb's audio shop. The boards and parts look terrific, and I'll be ordering the rest of the parts shortly from Digikey and Mouser. 

 Kudos to amb for setting up the shop. I don't think I've ever quite received such great fast service even from the big guys like those mentioned above. 






 -- Mirlo


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## pabbi1

Got my boards today as well, and will start work on them tomorrow. Ti, thanks for being flexible, and great follow through.

 Should we start a m³ build thread for specific build and configuration issues?


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## amb

Quote:


  Originally Posted by *pabbi1* 
_Got my boards today as well, and will start work on them tomorrow. Ti, thanks for being flexible, and great follow through._

 

You're very welcome 
	

	
	
		
		

		
		
	


	




 . 

  Quote:


 Should we start a m³ build thread for specific build and configuration issues? 
 

Yeah, sure. It seems that this thread is getting too long and we're no longer in the "project announcement" mode. I'll start the new thread and all build-related discussions can continue there.

 Update: the new thread is here:
http://www6.head-fi.org/forums/showthread.php?t=109760


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## algar_emi

Hi...


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## d-cee

Quote:


  Originally Posted by *algar_emi* /img/forum/go_quote.gif 
_Hi..._

 

hello

 also wow at this being your first and only post on head-fi in 3 years


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## amb

The current M³ build discussion thread is on headwize:
HeadWize: DIY Workshop > M³ Build Discussion


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