# PPAS Build Thread.



## ATAT

I'll start this thread since Daniel's shipped off all the boards.. and some of you have already gotten them (
	

	
	
		
		

		
			





 Filbuuurrrttt)

 This thread is for any and all troubleshooting of PPAS, and to document compatibility with different parts and opamps.


 All standard SMD build procedures apply.. opamps and buffers first, then resistors, then build higher. 

 Also, the PPAS is VERY unfriendly to sloppy soldering.. DieInAFire's prototype failed twice because of sloppy soldering.. be careful and you should be fine.. 

 [size=medium]*Parts Availability*[/size]
*BUF634U* - this part is ALWAYS out of stock, but I have 23 or so left, ask me.

*LMH6321* - This part is stocked at digikey.

*TLE Railsplitter* - There are no alternate parts for this. 


*SST310* - Ive just been told the SST310 is out of stock.. Currently reccomended subtitute is the *BSR-57* from mouser electronics. If you know of any better substitutes, please PM me.

 [size=medium]*Build Warnings.*[/size]
*PLEASE make sure you buy the SST 310*.. the SST309 was marked in the old revisions of the BoM. The SST309 may be unable to supply enough current.. 

*Silkscreen may be missing at parts*.. due to gerber issues our manufactuerer may have left out sections of the silkscreen.. NB that you should use http://apuresound.com/ATAT/PPAS/PPAS...%20Artwork.htm as reference during the build.

*NB The tantalum capacitor direction*.. the Tantalum cap is polarized.. it is marked on the board artwork link, but NOT on the board (see warning above). 

*NB Opamp and buffer direction*.. Opamp and buffer pin 1 is indicated by the strip on the artwork above.. just for reference here's the directions.. Looking from the top down onto the board, OPA L/R pin 1 is left top, BUFL is right bottom, BUFR is left top.. on the bottom, looking down onto teh bottom of the board, both OPAG and BUFG have their pin 1s on the left top.. (the picture is mirrored)

 [size=medium]*Configurations/changes that *should* work*[/size]
 Using a larger ELNA sized cap on the rails (capacitor bending) should still fit in MINT tin.

 LM6172 / LM6171 / LMH6321.

*Warning for those using LMH6321* - The LMH6321 is a great buffer, can output nearly .7A of current and its ridiculously fast.. one problem. Pin 2 is used as current control. Before you solder the LMH6321, cut off Pin #2 (or bend it upwards). Pin 2 is connected to output on the schematic (so that opamps can be used as buffers) but this will prevent sane operation of the LMH6321.

*Warning for those using OPA551 or other Opamps.* - The PPAS can accomedate using running opamps in closed loop mode as buffer.. There's two things to watch out for. First, bandwith, make sure your opamp is fast, as well as being high power.. if a fast opamp feeds a slow buffer, you'll have some serious issues with the feedback loops (also stability) if using the OPA551, use a slow opamp like the OPA2227. Also, even though the L/R buffers wont have an issue running closed loop, the ground buffer is *finicky* and I'd suggest using the BUF634 or LMH6321 unless you're really feeling lucky.

 [size=medium]*Currently Tested Configurations - *[/size]
 (by ATAT)
 AD8620 / AD8610 / BUF634 (both bandwiths) (lots of detail on this one)
 AD8620 / THS4631 / BUF634 (both bandwiths) (similar to the above, but seems fater, and eats more battery)
 LM6172 / LM6171 / BUF634 <-- NOT RECOMMENDED, THROWS HIGH OFFSET AT LOW BATTERY
 AD8066 / LM6171 / BUF634 <-- See above
 AD8066 / OPA132 / BUF634 (bass beast.. nearly overpowering..)
 OPA2701 / LM6171 / LMH6321 (Amazing detail and midrange.. my rec, but KILLS battery)

 (by quicksilver )

 AD8610 / AD8620 / LMH6321 <-- LMH confirmed working.

 (by ozshadow)

 OPA2701 / OP627 / BUF634 <-- OPA627 confirmed

 [size=medium]*A List of Problems encountered*[/size]

 9v Offset on Channel





> (fixed)Prototype 1 - Routing problems





> (solved)Final Board (Proto 2) - Soldering issues(happened twice)


One Channel dead





> (solved)Proto 1 - Ground Mistakenly swapped with Left channel (whoops)


Current draw absurd 





> (solved)Proto 1 - Case shorted SST310.


Amp clips at all audible volumes





> (fixed)Proto 1 - SST309 Used instead of SST310.


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## NeilR

I'll start off the build discussion with this: Mouser's SST310 is out of stock, both RoHS and the good old stuff (actually 2 in stock of the leaded version- not enough for one amp).

 Any suggestions for alternatives? Maybe SST-109? That is 40ma, which kind a bit high, but I always thought the PPA ccs was mainly for noisy wall PSU's. Since this is battery powered (and should be very low noise power), does it really help?

 Edit: Digikey alternate would be fine....


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## NeilR

The schematic on the web site is a bit small- would it be possible to get a higher res version? My tired old eyes would appreciate it!


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## ATAT

NeilR - Ill try to get a higher res version, but the size is limited by photobucket I believe.. 

 Hmm the lack of SSTs are a problem.. I'll have to find alternatives.. 



 Possible altenratives -

 to be honest, the SST212 will likely work for most current conservative opamp setups.. since its designed as a N channel amp, its got a lower distortion figure than the others (*might* matter) while the others are N channel swtiches.. to be honest, it probably wont matter, so just pick the SST4392 if you dont know any better. (26 in stock) when that runs out, use the SST212 it should work for 90% of the people.. （EDIT- comment about SST109 removed. Was incorrect.. what was I thinking anyway? )

 *edit* found the BSR57, in stock for about 2000 units at mouser, and it looks like its about as good as the SST310 (maybe better)

 From Vishay Siliconix - (from most desireable to least)

 SST4392 - 25mA Idss, N Channel switch.
 SST212 - 15 mA Idss, N Channel amp
 SST109 - 40mA Idss, N Channel switch 

 Fairchild Semiconductors - 

 BSR57 (might be better than SST310) - 20mA Idss, N channel low noise amp
 MMBFJ310 - 24mA Idss N channel amp (same as SST310)
 MMBF4392 - 25mA Idss, N Channel switch.
 MMBFJ111 - 20mA Idss N channel switch.


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## NeilR

Atat- I was looking at the schematic on the top of the build notes page. The schematic on it's own link is fine. Thanks anyway- don't worry about it.

 Regarding the SST310... It appears you are running them in parallel, not as per the PPA schematic. Is that correct? What is the idea behind that?

 My understanding is that if I use an excessively high Idss jfets, it will not draw any additional current, it will just act like a constant current source that is configured for more current than will be drawn. It can't "push on the string" so to speak (won't draw more than the load demands). Is that not correct?

 Edit: Nevermind... I was thinking this was some sort of cascode setup, but after reading PPA V1, I'm not sure why you and Tangent used two in parallel (as opposed to PPA V2) but I see clearly they are in parallel and can deal with it.

 Regards,
 Neil


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## pddjsteve

Wow, really glad I put in an order in the beginning of the week - maybe I got the last ones 
	

	
	
		
		

		
		
	


	




 All I've got left to order is the buffers, and C3/C4. I found the dimensions for C1/C2 in the other thread, but I'm not sure the size for C3/C4 was. 5mm? 6mm?

 Edit: I can donate space for a high res version of the schematic if you need it.


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## ATAT

I didnt write down the dimentions for C1/2 C3/4? sorry! the originally spec'd part is 5x11mm. Voltage rating needs to be at least 9 volts. 

 The idea behind running the SSTs in parallel was to increase the max IDss, this way you could use some of the lower IDss chips.. the 

 NeilR- you're absolutely right 
	

	
	
		
		

		
		
	


	




 must be all that biology work clouding me.. a higher IDss will not affect battery draw.. but it will decrease the isolation between the two rails.. Tangent describes this in detail, but the closer you run your JFEts to max IDss, the better the isolation.. so you *could* use the SST309 in a conservative setup to ensure maximum isolation.. 

 Its entirely possible to get the SST309 working just make sure to use less than 8 mA / channel for each opamp.


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## pddjsteve

double post - mod please delete


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## pddjsteve

Quote:


  Originally Posted by *ATAT* 
_





 I didnt write down the dimentions for C1/2 C3/4? sorry! the originally spec'd part is 5x11mm. Voltage rating needs to be at least 9 volts._

 

Well, you mentioned C1/C2 were 8x10 25v but I couldn't find anything specific about C3/C4 (granted, it was a big thread).

 Looks like I can use a 10v 100uF Panasonic FM (digikey part number P12919-ND) and it will drop right in. I also accidentaly ordered a 470uF 25v FM that was 8x20 instead of 10x16, one number off from the part number for something meant for another project (P12389-ND), that turns out to fit for C1/C2 (the height isn't an issue as I plan to have mine on its side in a hammond J1201 case).

 Digikey shows the following (it says 3 because that was how many I added to my cart):

  Quote:


 Product Lead Time Estimates

 Part Number: BUF634U-ND
 Description: IC 250MA BUFFER 8-SOIC

 Ship dates are approximate and subject to change.

 Quantity ExpectedShip Date Estimate
 307/01/2006 
 

So it looks like everyone jonesing for the buffer might get a shot in a day or so. I'm going to try ordering it, I've also got some lm6321 on order from National Semi.


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## dhp

dont you mean LM*H*6321?


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## ATAT

absolutely right.. corrected in main post.



 Edit - You could also just not use JFETS altogether, shorting the pins will make for a unified rail. Your pick.


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## NeilR

One more question about the JFETs. You indicate that the SST309 was insufficient and resulted in clipping. That part has an Idss of 12ma. Assuming you used them in parallel, that would provide 24ma to the 3 opamps, or 8ma each channel. If you tested this with AD86x0, that is 2.5ma per channel, plus 0.5ma for the SST502 class A bias. It seems to me that that should have provided far more current than required for that particular Opamp. 

 (I built a PPA V2 using 13ma JFETS per channel and successfully ran it with OPA627/OPA637 with 1ma Class A bias, for about 8.5ma per channel. It works very well. I used 2n5486 hand picked for 13ma Idss).

 I just want to make sure I'm not missing something here as I pick my JFETs. At this point I will also probably use AD86x0.


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## ATAT

NeilR - you're correct, and that is the reason I originally reccomended the SST309 for the stock build of the PPAS, however I had issues with the prototype #1 which were resolved as soon as the SST309 was replaced with 310s. Although I havent the time to check again with the 309s, I felt the need to reccomend a configuration which is known to be working...

 In other words, it should work on paper, it didnt work once, so I'm suggesting a config that works. I'm hoping it was a defective SST309 and so each channel had 4mA =/... it'd be interesting if someone got it working with a 309 configuration.


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## NeilR

Atat- did you use the SST309 with a THS4631 in the ground channel? Your post#1 indicates you used that part and an AD8610 in the ground. That amp sucks up to 14ma, which would put the total draw on the opamp rails at 20.5ma, which is a little tight. Maybe that was the problem?

 (The JFET isolation is an interesting and tricky idea since, as you discovered, it is easy to totally hose the performance while chasing the last 1% performance 
	

	
	
		
		

		
		
	


	




 )


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## ATAT

SST309 was with the first prototype which used a AD8620 and 10 on ground.


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## NeilR

A minor correction to the web site BOM for the no compromise version- I think 3 ( not 2) SST502's are "required", including one for the ground channel, although certainly the ground channel class A could be left out since it is an optional feature.


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## pddjsteve

Got the boards! Man, that's really tiny. Now I'm just waiting for my mouser order (out for delivery, come on UPS guy get here) and then I can start assembly. I'll try to take pictures as I go.


 Boards:






 With Nano (dang they're small):





 AD8620 on, pot just sitting there for reference. PLEASE tell me I got the opamp on in the right direction.





 Same deal with AD8610. Is it on right?


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## rsabo

DOH! forgot to order buffers... well I guess we'll find out soon how well it runs bufferless... shorting out pins 2 & 3 should work, right?


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## ozshadow

Got mine too and above poster is right - thats damn tiny ! I am gonna have to order a clamp on magnifying glass for this job.

 Also to above poster - is it the pic, or have you solder bridged the opamp pins ?


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## pddjsteve

Quote:


  Originally Posted by *ozshadow* 
_Got mine too and above poster is right - thats damn tiny ! I am gonna have to order a clamp on magnifying glass for this job.

 Also to above poster - is it the pic, or have you solder bridged the opamp pins ?_

 


 Angle of the pic, those are actually pads for R6R, I got a little solder on them and didn't clean it up yet.


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## pddjsteve

Bottom populated with resistors, sst310s, caps:





 Top with caps and resistors:






 Yes, I am ugly at soldering SMD. 


 Questions:

 1) What is the purpose of the VGND pad?

 2) What is JP1 for? Buffer bandwidth?


 The only thing left is to wait for the buffers to arrive. Next thursday!


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## ATAT

Looks great so far. You probably want to take those pictures on teh macro mode on your camera, it'll turn out much nicer and you can make out the details.

 The opamps are oriented in the right direction, so are the tantalums =)

 VGND is for troubleshooting purposes. without that pad it makes life much much harder when something goes wrong. originally I was planning to take it out on the production run, but something told me it would be nice to keep that pad 
	

	
	
		
		

		
		
	


	




 yes, JP-1 is buffer bandwith for all buffers.. putting a resistance from 0-> open will change the bandwith, with shorted JP1 being wide bandwith mode. Apparently it makes a difference, though personallly neither I nor daniel can hear it..


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## pddjsteve

Excellent, looks like I did all that right, then. So far everthing is together nicely, with some temporary 100uF caps 'till I get my panasonic FM, and still waiting on the buffer. 

 I'm really tempted to just temporarily wire a socket to the pads and pop in a dip8 buffer, just to get the thing running.

 Edit: hmm, or jumper the buffers for now


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## rsabo

Anyone having trouble finding TLE2426's, try Jameco. As of now, they have them in stock, but unfortunatly they don't list how much is left.


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## rsabo

oh, and VGND would be useful in a amp-powered Alien DAC.


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## pddjsteve

Quote:


  Originally Posted by *rsabo* 
_oh, and VGND would be useful in a amp-powered Alien DAC._

 

I was thinking that, too 
	

	
	
		
		

		
		
	


	




 I just wasn't sure if it served an explicit purpose in the amp.


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## ATAT

pddjsteve - just wait for the buffers.. probably not worth it to attempt it without the buffers, the opamp rails will proably clip and it'll sound horrible. 

 PDDJ - if you have any high current opamps, you can put them onto the buffer pads and run them as a unity gain buffer..


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## pddjsteve

Quote:


  Originally Posted by *ATAT* 
_pddjsteve - just wait for the buffers.. probably not worth it to attempt it without the buffers, the opamp rails will proably clip and it'll sound horrible. 

 PDDJ - if you have any high current opamps, you can put them onto the buffer pads and run them as a unity gain buffer.._

 

Well, I've got some intersil buffers (the kind in the full size ppa). I just gave it a shot without anything on the buffers and it sounded like ass (but it worked!). I don't know if I've got the patience tonight to play with wiring a dip8 socket to try out my intersils. Maybe I'll just wait for the lmh6321s and not play anymore


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## ATAT

Its not worth it to rush and perhaps mess something else up on the circuit.. and yes, without the buffers the circuit will sound *horrible* worse than any cmoy you've ever heard.


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## ozshadow

Newark has over 600 SST310's in stock.

 Part# 13C1768


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## ozshadow

n/m


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## Teerawit

Quote:


  Originally Posted by *ozshadow* 
_Jameco has BUF634P in stock which should work if you bend the lead tips flat and level._

 

Too big and mechanically unsound.


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## quicksilver96

Quote:


  Originally Posted by *ozshadow* 
_Jameco has BUF634P in stock which should work if you bend the lead tips flat and level._

 

Not gonna happen, don't do this.

 Here is a size comparison for anyone unfamiliar with the size of a DIP chip vs SOIC pads and available board space:
 Image Gone


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## motherone

They do have DIP to SOIC adapters, but you're going to be paying as much as you are for the buffers for them, IIRC.


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## ATAT

More like.. you'll be paying $20 for each 
	

	
	
		
		

		
			





 rsabo (i think) made some intersil DIP8 -> SOIC adaptors but I havent made em yet.


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## ozshadow

If you are very tight in your assembly, I *think* you can slide all this into a C1201 hammond case. Batteries need to go end to end on one side and the board needs to be inserted upside down, but it should fit, and definitely would with a light bit of sanding here and there. Should leave a tad bit of room for a trickle charger.


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## ozshadow

Tightly packed C1201 case to scale. There is no room for sloppiness here.






 Similar to this: http://www6.head-fi.org/forums/showp...&postcount=164

 I do not have this setup to play with, but I am guessing the board could be angled a bit for slightly more space


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## ozshadow

Also, for those of you with a built version, is there enough room to use 6x11 caps on the opamp rails instead of the 5x11 listed ? This must be absorbed in width of the board and not pushing the other caps outward.

 The reason for this is that I need 16v caps instead of 10v for the charging/power circuit which will be splitting approx. 27 volts.

 There is a Panasonic FM cap in 120uf 16v that is 6x11 - one extra mill in diameter.


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## pddjsteve

Quote:


  Originally Posted by *ozshadow* 
_Also, for those of you with a built version, is there enough room to use 6x11 caps on the opamp rails instead of the 5x11 listed ? This must be absorbed in width of the board and not pushing the other caps outward.

 The reason for this is that I need 16v caps instead of 10v for the charging/power circuit which will be splitting approx. 27 volts.

 There is a Panasonic FM cap in 120uf 16v that is 6x11 - one extra mill in diameter._

 

I'm out of town and don't have the board with me, but from memory it was a pretty tight fit just with the 5mm. You could probably mount the caps a little off-board and bend them out of the way, though.


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## quicksilver96

Any takers on using the LMH6321 in this project yet? 

 I was looking at the data sheets for this buffer and had a question about the GND pin (5). Does anyone think this needs to be connected to the ground plane if the current limiter and error flag pins are unused? Looking at the simplified schematic (fig 1) I would say that it doesn't. In the subsection "Single Supply Operation", the guide mentions only one way to attach the ground pin and does not specify conditions when this connection is necessary. Also, I see there is no way to implement the current limit without some degree of hackery and the trace to pin 2 should be cut, or the pin should be removed from the chip, as this is a feedback loop in the PPAS circuit. In unlimited configuration the chip (open CL pin) will be able to provide up to 700(!) mA of current, though this should be avoided and it would seem that the CL pin provided any means of short circuit protection. Lastly, mechanically disabling the EF is unnecessary but there should not be anything bridging the high bandwidth jumper. Correct?


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## ATAT

Built my PPAS today, LM6171, LM6172, cant give you good impressions yet since ive had a total of about 10 minutes listening time, but BUF634/LM6171/LM6172 is deemed stable. 

 LM6321 had issues yesterday, tried em first and they started dumping a ridiculous amount of current onto the output didn't realize the output jack was shorted via a thin wire 
	

	
	
		
		

		
		
	


	




 So I'll have to try again.

 Quicksilver - the GND pin does not need to be connected if current limiter is not connected. the buffer will operate fine as long as you have a split supply..

 As i said in post #1, pin #2 should not be soldered on for this to work.. 

 Lastly, there's no reason why I would implement current limiting.. of course there's the off chance that something like the aboe (a small wire short) may happen, but its not destructive to the amp in any way.. current limiting is pretty bad for many reasons and I'd rather not have it at all, which is why provisions for current limiting were not included.


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## dhp

sounds good? try grabbing some l3ks in japan and you'll be set


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## quicksilver96

Cool. I didn't think that current limiting was necessary given the load, just that it might deliver some type of short protection. Good to know about the ground pin, there was really nothing in the docs saying that it needed to be connected, and the only time it showed up on the schematic was for an internal opamp in the CL circuitry.

 Were you just running the BoM config or did you make some bandwidth adjustments (R5, R6) with that fast chip? BUF634 in wideband?


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## ATAT

Wideband mode is undocumented - jumper to the left of the right buffer and below the pot is the bandwith jumper.. jumpering that gives wide bandwith mode while keeping it open leaves it in low draw mode

 quicksilver - I havent got a LMH6321 config working yet so my post was speculation from the datasheet. the simplified schem shows ground being used only as a reference for the error pins (makes sense, since that error signal's gotta be referenced to something) and the rest looks just like a beefed up BUF634 (and therefore not needing a reference point midway the supplies.. 

 For the LM6171 and such, no adjustments were made I will put the appropriate resistors to match bandwiths but the amp is stable at stock configuration.


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## rsabo

Quote:


  Originally Posted by *ATAT* 
_Wideband mode is undocumented - jumper to the left of the right buffer and below the pot is the bandwith jumper.. jumpering that gives wide bandwith mode while keeping it open leaves it in low draw mode

 quicksilver - I havent got a LMH6321 config working yet so my post was speculation from the datasheet. the simplified schem shows ground being used only as a reference for the error pins (makes sense, since that error signal's gotta be referenced to something) and the rest looks just like a beefed up BUF634 (and therefore not needing a reference point midway the supplies.. 

 For the LM6171 and such, no adjustments were made I will put the appropriate resistors to match bandwiths but the amp is stable at stock configuration._

 

I might be missing something, but is there a similar jumper to the left & ground buffers? (I'm going by the pictures on the website, I've been away so I don't have my boards yet)


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## ozshadow

Are there no other similar buffer chips with output like a Buf634 ? I looked at the LM6171, 6172, and 7171 and while fast, their outputs are limited to arround 100mA compared to the 250mA of the hard to get Buf634.

 I'd enjoy hearing some feedback as to the sound when some of you finish.


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## quicksilver96

Oz - the other buffer we are discussing is the National LMH6321. Pretty much your only other option for a buffer is a DIY discrete arrangement. Cetoole and ATAT devised a compact arrangement in the PPAS development thread that I intend to implement on one of my PPAS boards. The discrete buffer will come later, just want to ensure correct operation with the IC buffers before I attempt discrete. I'm not a huge fan of the buf34 sound and they are impossible to get in SOIC format right now, so I will attempt an LMH6321 config when my parts all show up.

 Edit
 rsabo - the one jumper is connected to all three buffers' BW pins so that jumper will function to place all 3 buffers in high BW mode. If you are looking at the board or board artwork, it is the 2 oval shaped pads to the left of BUFR. I believe you could also place a resistor here like pimeta R11, but the drilled pads allow you to hook up wires for a switch to that high BW can be turned off to save battery life.


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## rsabo

Quote:


  Originally Posted by *quicksilver96* 
_Oz - the other buffer we are discussing is the National LMH6321. Pretty much your only other option for a buffer is a DIY discrete arrangement. Cetoole and ATAT devised a compact arrangement in the PPAS development thread that I intend to implement on one of my PPAS boards. The discrete buffer will come later, just want to ensure correct operation with the IC buffers before I attempt discrete. I'm not a huge fan of the buf34 sound and they are impossible to get in SOIC format right now, so I will attempt an LMH6321 config when my parts all show up._

 

Plus the HA3-5002 adapters, that yours truly designed.
 Speaking of, ATAT, are you planning on selling those? Just so I know.

 I also see how the jumpers work now, but what is the effect when a resistor is used instead of a jumper? In the PIMETA, where R11 is used to set the bandwidth, each buffer has it's own jumper. Using a resistor in place of a straight jumper allows you to control the amount of quiescent current, but what happens when three buffers share the same resistor?

 EDIT: Man it took me a while to write that out. Thanks anyway quicksilver.
 EDIT2: oops, credited wrong guy


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## quicksilver96

Looking at the schematic from the data sheets, it would appear that BW limiting is done by adjusting a current, I.1, to V- by interjecting a parallel resistance with a 4K resistor and the V- plane via the BW pin. Even by tying these BW pins together (J1 still open), the design has effectively put all 3 of the 4K resistors in parallel between the current source and V- so the bandwidth is increased even without a resistance or straight connection present in the J1 location! 

 On a Pimeta, the 220 ohm R11 will go in parallel with 1 internal 4K ohm resistance for an equivalent of 208ish ohms (there is a 150 ohm internal resistance in series with the 4K/BW resistance as well). With the PPAS we already have reduced the 4K/BW resistance to roughly 1333 ohms so to achieve the equivalent of the 208 ohms on the pimeta, a 247 ohm resistor can be placed across J1 to achieve this value.

 I'll post up my schematics in a sec so someone can double check me.


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## rsabo

Quote:


  Originally Posted by *quicksilver96* 
_Looking at the schematic from the data sheets, it would appear that BW limiting is done by adjusting a current, I.1, to V- by interjecting a parallel resistance with a 4K resistor and the V- plane via the BW pin. Even by tying these BW pins together (J1 still open), the design has effectively put all 3 of the 4K resistors in parallel between the current source and V- so the bandwidth is increased even without a resistance or straight connection present in the J1 location! 

 On a Pimeta, the 220 ohm R11 will go in parallel with 1 internal 4K ohm resistance for an equivalent of 208ish ohms (there is a 150 ohm internal resistance in series with the 4K/BW resistance as well). With the PPAS we already have reduced the 4K/BW resistance to roughly 1333 ohms so to achieve the equivalent of the 208 ohms on the pimeta, a 247 ohm resistor can be placed across J1 to achieve this value.

 I'll post up my schematics in a sec so someone can double check me.
_

 

So if I'm reading the graph correct, that means by default, with an open J1, the BUF is running at around 4mA. Also, putting just a jumper in J1 does nothing, because according to tangent's calculator (I don't know the formula for parallel resistors) adding 0 ohms to the 3x 4k does nothing.


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## quicksilver96

Incorrect, adding a jumper reduces the resistance to zero rather than 1333 which it is currently. Go to the calculator and put 1 ohm in rather than 0, tangent must have some code that prevents a nil entry from effecting the calculation. Anything in parallel with 0 ohm is 0 ohms.

 I'm not sure that just jumpering J1 is the best course of action as well. This is from tangent's site:
 According to tests by KurtW and others, distortion drops as bandwidth goes up, though once R11 falls below about 200 Ω, distortion starts rising again.


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## rsabo

Quote:


  Originally Posted by *quicksilver96* 
_Incorrect, adding a jumper reduces the resistance to zero rather than 1333 which it is currently. Go to the calculator and put 1 ohm in rather than 0, tangent must have some code that prevents a nil entry from effecting the calculation. Anything in parallel with 0 ohm is 0 ohms.

 I'm not sure that just jumpering J1 is the best course of action as well. This is from tangent's site:
 According to tests by KurtW and others, distortion drops as bandwidth goes up, though once R11 falls below about 200 Ω, distortion starts rising again._

 

Yeah I read that on the parts info page. I also saw my error when I looked up what the formula is and realized that I would have to divide 1 by zero. I'll get this "electronics" gig eventually.


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## ATAT

First things first..

 the discrete buffer board and HA3-5002 adaptors *will* be made, but its been put off for a while now, and that may continue for a bit.. I cant possibly see enough demand to justify a group buy (nor do i have the time at the moment to organize one.. if anyone would like to gather interest and start one, I'll help) but I will likely order a panel (2ft x 1ft) through one of the PCB sponsors and I'll include these boards as part of the panel. I'll have to depanelize manually (therefore it'll be a pain..) and I'm trying to decrease the time spent on my part 
	

	
	
		
		

		
		
	


	




 Cliff notes version of that - Yes, but not now.

 Secondly..

 Quicksilver - watch out with the LMH6321 for shorts.. if even a slight short happens on the output, the LMH may die .. (of course the datasheet sayd the LMH dies from thermal overload when shorted.. ) I've not yet had the time to try the LMH6321 config again, but I will this weekend.

 Thirdly .. 

 Bandwith - Quicksilver is correct, the bandwith is increased absent any resistor on jumper =p for the case where J1 is left open, its equivalent to having a 2k resistor on the pimeta. the bandwith there is *decent* and should allow high speed opamps to run without problem. If one really wanted to save up on battery, they could cut the bandwith traces.. but then why are you building a PPAS? 
	

	
	
		
		

		
		
	


	




 Basically the formula for determining the parallel resistor value is (1/2+1/R)^-1 which gives the equivalent resistor value in the pimeta.

 Ozshadow - those opamp you said will work on the LR channel in closed loop mode, but dont try em on ground. those are opamps, not buffers (key difference). High output buffers that I know of are LMH6321, some current feedback types from National, HA3-5002,BUF634. you can also use high current opamps like OPA551.


----------



## ozshadow

Got smd version of the 2107 coming, and already have my railsplitters. I do not yet know which buffer I'll use, but I am kinda worried about it being TOO smooth behind a buf634, but my next task is finding some of those.

 I'm doing both a 2107/227 combo and a 8610/8620 - probably both behind buf634's


----------



## ATAT

Update on 6172s.. Reverse the reccomendation on them.. found one one problem, they start to get unstable as the battery voltages drop.. Ran them for one night and offset went from a managable 20 mV -> 1 V 
	

	
	
		
		

		
		
	


	




 Since I've not isolated the problem, i'll put the opamp under nonworking

 The AD8066 config is working fine however. 

 But this is as far as I can go since I ran out of batteries.. I'll get some more tomorrow.


----------



## pddjsteve

My buffers are here!
	

	
	
		
		

		
		
	


	










 I'm going to put them in and then I'll be able to give an initial impression of AD8610/20 and LMH6321.



 Edit1: CRAP. Maybe it was just hooking up the wires, but I'm not getting left channel anymore. Right channel sounds REALLY nice, though.


 Edit2: YES!!!! Works.


----------



## quicksilver96

Damn it!! I need to order all the rest of my stuff. The only parts I have are the opamps and the buffers, both of which I already had


----------



## ATAT

Retraction of previous comments.. the 6172 seems okay the 6171 however is unstable under most configurations.. it just seems that the 6171 / 6172 combo is the worst.. it seems to thorw a large amount of offset..

 The 6171 / AD8066 throws nearly 150 mV of offset, unacceptable (to me) and a large amount of heat in the ground opamp (also unacceptable)

 The OPA132 / AD8066 combo is working very nicely so far.. I'll post how it goes.

 First 10 minutes impression - What the heck?! this thing is ridiculous in the bass department.. like completely over the top.. I checked my equalizer.. I'm sure the bass will become more tame as I listen to it (psychoacoustic burn-in) but this lays the smackdown on my PPA v2 in terms of bass. it is a little bit lacking in the mids though.. Will post more impressions =p.

 Hmm. Perhaps that was a mistaken impression. To be more specific, the OPA132 / AD8066 combo seems very source dependent.. the iHP-120 line out sounds far less bassy compared to the M-Audio transit output (well. I wasn't expecting *that* much out of the transit) more balanced and less missing mids. Or maybe I'm just getting used to the sound.


----------



## quicksilver96

ATAT, steve - how much total current are your amps pulling? Are you running class A?

 steve - what opamps are you running? Scanned the thread quick but I might have missed it.


----------



## pddjsteve

Quote:


  Originally Posted by *quicksilver96* 
_ATAT, steve - how much total current are your amps pulling? Are you running class A?

 steve - what opamps are you running? Scanned the thread quick but I might have missed it._

 

AD8620/AD8610, LMH6321 in all 3 buffer positions. No class A or bandwidth resistor. I measured about 41mA at full volume into ~100ohm load (ER4P+75ohm adaptor).


----------



## ATAT

AD8066 / OPA132 - BUF634 on quiescent, measures 20mA max, 15 typical, 10 minimum into RS-1s at max volume.


----------



## Filburt

Try the AD826 if you can find it there. I'm curious about the sound with it.

 Edit: ugh...8066


----------



## quicksilver96

Quote:


  Originally Posted by *Filburt* 
_Try the AD826 if you can find it there. I'm curious about the sound with it.

 Edit: ugh...8066 _

 

Isn't the AD826 a bipolar input?


----------



## ATAT

The AD826 is bipolar input.. so special care would be needed to run that in a default gain of 11.. Id probably use it for gains of somewhere around 2.

 Filburt - whats wrong with the AD8066?


----------



## rsabo

Quote:


  Originally Posted by *ATAT* 
_The AD826 is bipolar input.. so special care would be needed to run that in a default gain of 11.. Id probably use it for gains of somewhere around 2._

 

I thought that op-amps get _more_ stable as gain increases.


----------



## Filburt

Quote:


  Originally Posted by *quicksilver96* 
_Isn't the AD826 a bipolar input?_

 

...yes. So are some of the other chips we've been looking at. Bipolar input isn't some sort of unmanageable thing


----------



## NeilR

Quote:


  Originally Posted by *rsabo* 
_I thought that op-amps get more stable as gain increases._

 

I think the idea behind that is that bi-polars tend to generate DC offset and the more gain the more offset you have to deal with.


----------



## rsabo

Quote:


  Originally Posted by *Filburt* 
_...yes. So are some of the other chips we've been looking at. Bipolar input isn't some sort of unmanageable thing 
	

	
	
		
		

		
		
	


	


_

 

If I had one more board, I'd definitly try to get the AD8397 to work, just for fun.

 neilr: ok, thanks.


----------



## Filburt

Quote:


  Originally Posted by *NeilR* 
_I think the idea behind that is that bi-polars tend to generate DC offset and the more gain the more offset you have to deal with._

 

*shrug*...I haven't had too much trouble with offset on bipolars either in the PINTs I've made or in my test box (which has, at times, been running at gain 11). So, I think we may be OK


----------



## NeilR

Quote:


  Originally Posted by *Filburt* 
_*shrug*...I haven't had too much trouble with offset on bipolars either in the PINTs I've made or in my test box (which has, at times, been running at gain 11). So, I think we may be OK 
	

	
	
		
		

		
		
	


	


_

 

I was just referring to the general nature of bi-polars, not specifically any particular circuit. Although you didn't have a lot of trouble with your Pints (nor I with mine) the design of the circuits tends to optimize (minimize) input offsets as opposed to optimizing other things (such as noise) , and I think that is part of the reason why there was so much trouble with the Pint compared to other amps using jfet inputs. other than the fact 8397 likes to oscillate


----------



## Filburt

Quote:


  Originally Posted by *NeilR* 
_I was just referring to the general nature of bi-polars, not specifically any particular circuit. Although you didn't have a lot of trouble with your Pints (nor I with mine) the design of the circuits tends to optimize (minimize) input offsets as opposed to optimizing other things (such as noise) , and I think that is part of the reason why there was so much trouble with the Pint compared to other amps using jfet inputs. other than the fact 8397 likes to oscillate 
	

	
	
		
		

		
		
	


	


_

 

Well my test box just has a basic local feedback loop in it with not even a resistive divider at the moment. I may stick in a TLE2426 or something at some point. I just use it for testing various ideas. It does have some nice power decoupling in it at the moment, though. Anyhow, I am not having too much trouble with offset in general other than if something else is wrong in the circuit that would foil many other op-amps.


----------



## quicksilver96

Quote:


  Originally Posted by *Filburt* 
_...yes. So are some of the other chips we've been looking at. Bipolar input isn't some sort of unmanageable thing 
	

	
	
		
		

		
		
	


	


_

 

I wasn't saying that it was unmanageable, just that the circuit topology so far hasn't been promising with the other bipolar opamp that had been tried (LM617x). I enjoy the sound of the LM617x and once I get around to working on this project, I will try a few things to get that offset down. If I can't, well theres plenty of JFET input chips that I'd stick in there too. I've also got a dual 8397 pint that runs without any problems.


----------



## Filburt

Quote:


  Originally Posted by *quicksilver96* 
_I wasn't saying that it was unmanageable, just that the circuit topology so far hasn't been promising with the other bipolar opamp that had been tried (LM617x). I enjoy the sound of the LM617x and once I get around to working on this project, I will try a few things to get that offset down. If I can't, well theres plenty of JFET input chips that I'd stick in there too. I've also got a dual 8397 pint that runs without any problems. _

 

Well, the LM617x is also a ridiculously fast bipolar op-amp with a PSRR that may be less-than-friendly in some situations. The AD826 should be easier to stabilise, but I think if we bolster the 6171/72 with some additional power decoupling and maybe some lowpass filtering (ferrites) it may chill out.


----------



## ATAT

Regarding bipolar inputs - 

 I believe the problem is not bipolar inputs in an inherent sense, but the current stock configuration.. gain of 11 is pretty damn high for a portable amp.. running it at a lower gain of around 3? would probably minimize offset (1/4th) one could also decrease the input resistor values to good effect. I'd expect one to be able to drop offset values to around 30mV (just dividing right now =p) with the LM6172. I currently dont have the extra resistors to test this theory, so it'll have to go on the backburner.

 Also, the AD826 would be easier to implement since the LM6172 is pretty quirky..

 Also, unstable opamps are not reccomended on the ground channel (ie lm 6171) since they have a tendency to misbehave.


----------



## pddjsteve

So I was going through some old electronics crap I've got sitting around, and found that I've got a wall wart (probably unregulated?) that puts out 24V @ 100mA, and my PPAS is drawing about 40mA. Will this be ok to use with a pint-style trickle charge circuit (lm317, resistor, diodes) or should I be looking for something with a bit more current avaialble?


----------



## quicksilver96

Quote:


  Originally Posted by *pddjsteve* 
_So I was going through some old electronics crap I've got sitting around, and found that I've got a wall wart (probably unregulated?) that puts out 24V @ 100mA, and my PPAS is drawing about 40mA. Will this be ok to use with a pint-style trickle charge circuit (lm317, resistor, diodes) or should I be looking for something with a bit more current avaialble?_

 

steve - that is definitely enough current to charge even the longest lasting NiMH rechargeables that I have seen at the standard .1C trickle charge rate. Seeing as how it is unregulated, it may even put out enough voltage for the 8 cell (9.6v) series of batteries. It does put out enough current to charge the batteries and run the PPAS though you may have audible noise introduced into your circuit. The other thing to worry about if you plan to listen with the power supply plugged in is isolation. Many cheap power supplies tie V- to earth ground, this creates a problem as it will fight your TLE set virtual ground which is a few volts above earth ground. The TLE will not win this fight. This will not be a problem if you only use the wall wart to charge the batteries.


----------



## ATAT

Quicksilver nailed it.. also be sure to use a larger rail capacitance if you're going to power it off the wall.. 660 uF of capacitance wont smooth out 60Hz ripple from mains.


----------



## pddjsteve

Thanks, everyone. I actually found some specs on it here, it apparently is not regulated. I really don't know whether or not I'd run it off this or not, I've always just used batteries before - maybe I should just use it to charge.


----------



## ozshadow

Pop a Tread between them. You really only need about half a tread coming off most wallwarts.


----------



## ozshadow

When will some general build notes be posted ? I am about a week or two away from building two of these, and I'd really prefer not to make a mistake like putting something in backwards or in the wrong spot. 

 Thanks !


----------



## rsabo

Quote:


  Originally Posted by *ozshadow* 
_When will some general build notes be posted ? I am about a week or two away from building two of these, and I'd really prefer not to make a mistake like putting something in backwards or in the wrong spot. 

 Thanks !_

 

Go carefully, have a copy of the board layout printed out or otherwise handy. (just flip the "back" image around in an image manipulation program)

 Don't do something stupid, like invert one of the buffers. Like I did.


----------



## ATAT

Id say the notes on the front are pretty much final .. 

 note that 90% of failures for this comes from the JFET isolation parts. The advantage of them is that they blow before any other component, the disadvantage is that they die. 
	

	
	
		
		

		
			





 So when you get very strange behavior, first thing to check is your TLE voltage. if its not 18 volts, your JFETS are dead.


----------



## ozshadow

As for the jumper for wideband or not with the Buf634's - would a simple mini-switch be ok ? As in, would it be safe to work between positions of wideband not wideband while the amp is on. If so, I'll just imbed a tiny toggle on the back panel.


----------



## Secret Squirrel

Just Finished the "Normal" Configuration of the PPAS. It sounds nice.


----------



## quicksilver96

Looks great! Did you purchase or make that case?


----------



## Secret Squirrel

I built the case from an old iPod and a block of wood (Exacto knife & grinding wheel).


----------



## ozshadow

What opamps and buffers, etc. did you use ? How does the setup sound to your ears and with what cans ?


----------



## Secret Squirrel

*What opamps and buffers:*
 AD8620,8610, BUF634U, BSR57 (in place of the SST310 JFET)

*How does the setup sound to your ears:*

 I am now listening to Gorillaz (Demon Days) and the details are very clear and accurate. I typically prefer the “mellow” Burr Brown sound, but the AD8620/10 combination seems to quite acceptable. I tried the AD8620/10 combination on a Pimeta and didn’t like the results (too harsh). To contrast this, I have been listening to a Millet Hybrid. It is definitely a keeper.


*And with what cans ?;*

 HD580, ATH-A900,PX-200, Kraptastic earbuds


*Comment:*
 Drives the HD-580’s and the ATH-A900’s sound great.


----------



## pddjsteve

Has anyone run theirs off a single 9v battery? Most everyone seems to be using 2.


----------



## ozshadow

4.7k R4 resistor gives this a gain of about 5.7 correct ?


----------



## cetoole

Quote:


  Originally Posted by *ozshadow* 
_4.7k R4 resistor gives this a gain of about 5.7 correct ?_

 

Depends on the value of R3, but if R3 is 1k, then yes.


----------



## muckshot

Quote:


  Originally Posted by *Secret Squirrel* 
_Just Finished the "Normal" Configuration of the PPAS. It sounds nice. 



_

 

Wow, that's fantastic casework! How do these compare to the PINT in a similar config?


----------



## Secret Squirrel

I have not made or listened to a “Pint”. I have made several Mints, PPA, Pimeta, CMOY, Millet Hybrid, and various iterations of Sijosae’s tube designs. I like the PPAS as an overall portable amp.


----------



## pddjsteve

Ok, so I'm about to start putting together my 2nd one. I'm going to continue using the LMH6321 buffers. I've got 2x470uF panasonic FM rail capacitors. I've got an unregulated 24v 100mA wall-wart and as soon as they arrive, a battery pack made from 12xAAA solder tab nimh (700mAh). I'm probably going to put together a partial TREAD, I've already got a pint-style charging circuit. I listen through ER4P and a homemade 75ohm P->S adapter.

 I haven't decided on opamps. My first one used AD8620/8610. I really like the way it sounds, except for a little bit of harshness on the highs. I'd like to try something else, though.

 I know that someone has tried ad8066 and someone else tried opa2107. What are your impressions of either of them? For ground, would an opa227 work in combination with either of those two?


----------



## quicksilver96

Finally built one of my PPAS boards and cased it up in an aluminum stomp box, pictures are in the big post pics thread. Here is my configuration for anyone curious:

 R1/R1G/R4G - 4.42kΩ
 R2 - 1MΩ
 R3 - 402Ω
 R4R/L - 2.21kΩ
 R5 - 4.02kΩ
 R6 - 1MΩ
 (I believe I managed to find .1% vishay in all these values at mouser)

 Gives the following specs-
 Outer Loop Gain - 6.47
 Inner Loop Gain - 249.76
 Total Gain - 6.322

 AD8620/10 GBP - 25Mhz
 Amp Bandwidth - 100kHz

 Full volume offset is around .1mV on the left .6mV on the right. The amp consumes right around 16.5 mA of current with the buffer bandwidth jumper position open.

 Build impression - Build is fairly simple for someone with building experience. Not the ideal intro to SMD with 0805 resistors but for someone who has worked with 1206, there shouldn't be much trouble. I don't know if there is a guide to building this, but I found it easier to solder on resistors, diodes, and jfets before the opamps and the smd capacitors. The soic parts are actually some of the taller components on this board and reaching over a 0805 or even 1206 resistor to get to the soic leads seemed less of a pain in my ass than having the ICs in the way of the resistor pads. Of course the through hole crap goes on last. 

 On a side note, I squeezed the 16V 180uF (6.3x15) Nichi UPWs in the spot for the 10v 100uF caps (5x11) so I could use a 24v steps to run the amp while charging if needed. This means that the 25v 120uF UPW will also fit and give an extra measure of safety should the rail splitter fail and hit those caps with full rail.

 Listening Impression - Well its AD86x0 through BB buf634s. If you've ever heard a Pimeta with the same setup, expect much the same. The buffers smooth out the 86x0 pleasantly. I could not tell any difference in sound with the buffers running in high bandwidth so I opened the jumper back up again. I ran it A/B next to my PINT and it would be cake to pick them out blind. The PINT has a fuller, though less precise, bass and a more forward midrange, the overall sound seems slightly blended together. The PPAS has a slightly thinner sound overall with much better instrument seperation, more sparkle on the highs, and a very precise, well defined bass through midrange. I am quite impressed by the last. The smearing/blending on the PINT may be caused by the input caps where the PPAS really doesn't have any caps directly in the signal path. Seeing as how these are portable amps, I would have to say the dealbreaker for the PINT is current consumption as it uses nearly 3x the current of the PPAS.

 Impressions are with K701s and my modded av710. Tomorrow I think I am going to pick up a pair of UE IEMs to give a try seeing as I can buy them locally and shouldn't have problems returning them if I hate them. If anyone can point me in the direction of some IEMs sub $300 that have a sound signature close to K701s...


----------



## ozshadow

Has anyone built using a 10k Alps pot and changed R2 to just 100k ? I do not know how noticeable it would be, but techinically it should reduce noise even if a minute amount. A 1M resistor would be advisable for 100k pot.


----------



## pddjsteve

Quote:


  Originally Posted by *ozshadow* 
_Has anyone built using a 10k Alps pot and changed R2 to just 100k ? I do not know how noticeable it would be, but techinically it should reduce noise even if a minute amount. A 1M resistor would be advisable for 100k pot._

 

I used 475k instead of 1M. Dunno what effect it might have had.


----------



## ozshadow

what has your total cost so far ? Mines gonna be way way more than $50. Like 150+


----------



## dhp

Quote:


  Originally Posted by *ozshadow* 
_what has your total cost so far ? Mines gonna be way way more than $50. Like 150+_


----------



## pddjsteve

Quote:


  Originally Posted by *ozshadow* 
_what has your total cost so far ? Mines gonna be way way more than $50. Like 150+_

 

I think I'll be around $100-120 for two of them by the time I order BUF634 for my 2nd.


----------



## ozshadow

I didn't see any decoupling caps. Do the buffers act in a similar manner to remove DC offset ? I am curious about whether I need to add caps in the signal path of my Alien DAC.


----------



## cetoole

Quote:


  Originally Posted by *ozshadow* 
_I didn't see any decoupling caps. Do the buffers act in a similar manner to remove DC offset ? I am curious about whether I need to add caps in the signal path of my Alien DAC._

 

I think you are confusing some terms here. I suspect you mean coupling caps, which are used to remove DC from the signal, and there are none of these, or any other method of removing DC offset in this amplifier. The buffers certainly dont help lower DC offset, and in fact, it is only the fact that they are being run closed loop that prevents them from exhibiting a small offset of their own. That said, you dont need to add coupling caps to your Alien DAC, but you must do something to block the DC it puts out, or fry your headphones, which is most easily solved by coupling caps, though could also be solved by playing games with a virtual ground on the DAC floating midway between ground and supply, equal to the voltage of the offset. This cant be implimented on the existing Alien DAC pcb, so you would have to either hack the board, do it offboard, or design a new pcb with that in mind. Or just add a pair of coupling caps, and dont worry too much about it.


----------



## ozshadow

This is for a PPAS in a tiny hammond case with charging circuit running right at 27 volts (want the tread to be able to power an AD8620/10 version too) I have several caps listed due to needing to make sure one set will squeeze in the case.

 Think this is all my parts for one of them:

 OPA2107
 OPA627 (seriously considering an AD8610 as well)
 Tread Kit
 30v AC/DC plug
 2 Accupower 9v 270mah
 Buf634u
 Silver Knob JD-50-1-6MM
 Alps RK097 pot

 Mouser:

 71-CRCW0805-4.32K
 Vishay/Dale 0805 Thick Film Chip Resistors
 1/8WATT 4.32KOHMS 1% 


 71-CRCW1206-1.0M
 Vishay/Dale 1206 Thick Film Chip Resistors
 1/4watt 1.0Mohms 1%


 71-CRCW0805-1.0K
 Vishay/Dale 0805 Thick Film Chip Resistors
 1/8WATT 1.0KOHMS 1%

 71-CRCW0805-10K-E3
 Vishay/Dale 0805 Thick Film Chip Resistors
 1/8watt 10Kohms 1%

 71-CRCW1206-100K
 Vishay/Dale 1206 Thick Film Chip Resistors
 1/4watt 100Kohms 1%

 581-TAJA105K020
 AVX SMD Tantalum Capacitors
 20V 1.0UF 10% 

 581-08055A100J
 AVX 0805 SMD Ceramic Capacitors
 50V 10pF 5% COG – 

 781-SST502-E3
 Vishay/Siliconix Diodes
 SOT-23 0.43mA Current Reg

 512-BSR57
 SOT-23-3 N-Ch Transistor Lo Freq/Lo Noise – 

 161-7300-EX
 Kobiconn Phone Jacks
 3.5MM STEREO 

 604-WP7104QBC/D
 Kingbright LED Blue
 T1 BLUE WATER CLEAR

 546-1455C1201BKHammond Instrument Enclosures
 4.72 X 2.125 X 0.91 Black Anodized – 

 512-LM317T
 TO-220 TO-220 1.5A ADJ VREG – 

 512-1N4001
 DO-41 Vr/50V Io/1A T/R 

 163-4303-EX
 Kobiconn DC Power Jacks
 PANEL MOUNT 2.5mm – 

 71-CRCW0805-3.32K-E3
 Vishay/Dale 0805 Thick Film Chip Resistors
 1/8watt 3.32Kohms 1% 

 647-UPW1C181MED
 Nichicon Low Impedance Radial Aluminum Electrolytic Capacitors - 105Degree
 16V 180uF 6.3x15 – 

 71-CRCW0805-4.7K-E3
 Vishay/Dale 0805 Thick Film Chip Resistors
 1/8watt 4.7Kohms 1% - 

 647-UPW1V331MPD6
 Nichicon Low Impedance Radial Aluminum Electrolytic Capacitors - 105Degree
 35V 330uF 8x20 

 647-UPW1V331MPD
 Nichicon Low Impedance Radial Aluminum Electrolytic Capacitors - 105Degree
 35V 330uF 10x16 

 647-UPW1V221MPD6
 Nichicon Low Impedance Radial Aluminum Electrolytic Capacitors - 105Degree
 35V 220uF 8x15


----------



## quicksilver96

Looking at your list, I would say you are running this:

 R1 = 4.32k
 R2 = 100k
 R3 = 1k
 R4 = 10k
 R5 = 3.32k
 R6 = 1M

 OLG = 11
 ILG = 302.2
 Total Gain = 10.556

 OPA2107 GBP = 4.5MHz
 Amplifier Bandwidth = 14.89 kHz

 Is there any reason that you don't optimize the multiloop values? With these resistances, your amplifier is going to suffer from rolled off high frequencies if you use a relatively slow opamp like the OPA2107. These values are from the Pimeta schematic and intended for use with an AD8620/8610 family of chips with a GBP of 25MHz where the OPA2107 only operates at 4.5Mhz. Generally, you want to adjust these values for a amplifier bandwidth at least twice the audible frequency band of 20kHz -- so minimum 40kHz bandwidth, though most shoot for 70-80kHz as this bandwidth limit is not a brick wall and opamps don't necessarily function at thier exact GBP rating. 

 Second, is there any reason that you chose such a high gain (10.5)? Weak source? Voltage loving phones? If you really want a gain this high, let me know and I will suggest some resistor values that will be more bandwidth friendly. 

 Another thing to look at is your chosen voltage, AD8620/8610 are specified a maximum +/- 13v supply (26v). The ABSOLUTE maximum is 27.3v, normal operation at 27v is not acceptable for this chip. If you go with these chips rather than the OPA2107/627 combo you have chosen, you will need to reduce the supply voltage. There is no performance benefit to outweigh the damage potential.

 Last, the 10mm caps will not fit with the 6mm caps in the normal position. You will have to bend the leads or topple the caps to use this configuration. With 8mm and 6mm, the capacitors will be pushing against each other and require minor lead adjustment. If you are planning on this, then you know the risks. Not that capacitors are very expensive anyway.


----------



## ozshadow

I am using the 4.7k resistor to set a gain of just under 6

 I do not understand the idea of optimizing the resistor values. What do you suggest and what differences would it make ?

 I will be running the tread at about 26.6 which by the time it comes out of the charging circuit, it should be about 26.0 flat.


----------



## quicksilver96

Quote:


  Originally Posted by *ozshadow* 
_I am using the 4.7k resistor to set a gain of just under 6

 I do not understand the idea of optimizing the resistor values. What do you suggest and what differences would it make ?

 I will be running the tread at about 26.6 which by the time it comes out of the charging circuit, it should be about 26.0 flat._

 

Alright, I'm going to try to summarize Walt Jung's article bluntly and quickly as I have to go to work in a while. If I butcher something, it is in haste and someone correct me.

 Bandwidth is the operating range of your amplifier, with the values chosen previously, you would be running a functional equivalent of a low pass filter. This happens because the amplifier effectively doesn't amplify frequencies as much above the bandwidth. The higher above the cutoff, the lower the amplification. Your cutoff would have been somewhere in the audible range, probably 12-16kHz somewhere, depending on the tolerances of the opamp.

 Basically, in a typical voltage feedback opamp circuit, gain and bandwidth share a generally linear relationship. I.E. if the gain is changed by a factor of 5, the bandwidth will change by a factor of 5. What we are doing in a multiloop is intentionally lower the overal bandwidth by using 2 loops. The inner loop sets the local gain and limits the bandwidth of the amp. The outer loop sets fairly close to the effective gain of the amplifier. The benefit of doing this is we can limit the frequencies outside of a preset range to gain stability, resistance to electrical noise, and improve phase margin. Basically you are going to set inner loop gain as (R5/R6)+1. This should be high such that GBP/ILG = somewhere from 60-100 kHz; this will be the operation bandwidth of the whole amplifier, the "cutoff" if you will. There are a couple guidelines in determining the whole set of values - general consensus is that R3 should be set somewhere above 220R, R5 should be 5-10x higher than R3, and lastly, you should avoid picking any of the values greater than 1M. Outer loop gain, which has a greater influence on the total gain of the amp is then adjusted using R4. Also, when picking values, remember the lower resistance will equal a lower noise floor and higher current use; the higher the resistance, the lower the current use but the higher the noise floor. From here, you want R1 = R3+R5. You are going to, of course, want to pick values that are available for purchase rather than arbitrary values. 

 Alright, I'm out of time. I can help you out or suggest some values for you in the morning if you want. PM me or respond here, I'll be around.

 Edit - Wow, that was in a rush, fixed a bunch of spelling/grammar errors


----------



## ozshadow

Hmmm, exactly how many SST502's are needed for Class A, because the BOM says ya need 2, but there are 3 pads for them. 


 And guess what, I ordered two.


----------



## ATAT

Class-a biasing ground has arguable benefit. 2 is the point of diminishing returns. Populate both L and R.


----------



## ozshadow

Just an FYI, but if you want to use the C1201 case with 2 9v batteries, you will need to grind the inside rails down a bit as it is an extremely snug fit otherwise, the middle rail primarily.

http://www6.head-fi.org/forums/showp...6&postcount=37

 I used a micro die grinder to give me an extra mill or two on each side, leaving just enough for the screw to thread into.


----------



## ATAT

Post some pictures, also where did you get the C1201? and do you have that charger running? I only see the 1202 available on the hammond site.

 ATAT.


----------



## ozshadow

It's this case:

http://www.mouser.com/search/Product...46-1455C1201BK

 I could take a picture, but nothings in the case yet, and I already recolored most of the insides black again. I still have to order the pot from Tangent to complete the amp, but everything listed in the diagram fits, I've already tried it.

 This is not my pic, but it fits very similar to this pic, which uses the same case:

http://www6.head-fi.org/forums/showp...&postcount=164

 As for the micro die grinder, I used one at work. It's just like this one:
http://www.harborfreight.com/cpi/cta...emnumber=47869

 Like I said, I only needed an extra 2 mills or so.

 During final assembly, I'll take pics along the way. Prolly order my pot next week.


----------



## ozshadow

Oh, I am pulling a flat 17.0 mA current draw with opa2107/627/buf634 on low/SST502 class A


 How long should Two 9v 270 mah batteries last in that ?


----------



## abcheng

Does anyone have completed pictures of the PPAS? I'm currently building one but don't know which direction some of these chips should be soldered onto the board.


----------



## ATAT

default boardart is shown

http://apuresound.com/ATAT/PPAS/PPAS...%20Artwork.htm

 The line shows where pin #1 should go. 

 The ground is mirrored so be careful.


 Ozshadow - if its 17 mA and you have the two 9V in series, then you have 

 270mAH / 17mA = 15.8 hours.


----------



## ATAT

Anyone still interested in Diamond buffer boards?

 I'll be making a proto run sometime soon.


----------



## abcheng

I'm interested depending on price.


----------



## Tedro

Quote:


  Originally Posted by *ATAT* 
_Anyone still interested in Diamond buffer boards?

 I'll be making a proto run sometime soon._

 

All SMD? SOT-23 NPN/PNP with 805 resisters?


----------



## cetoole

Quote:


  Originally Posted by *Tedro* 
_All SMD? SOT-23 NPN/PNP with 805 resisters?_

 

TO-92 input and output transistors, 1206 emitter resistors on the output pair, and 0805 emitter resistors on the input pair, for class AB biasing. CCS is provided by a pair of SST50x precision jfet crds, in SOT-23.


----------



## ATAT

Finished LM6171 / OPA2107 amp (LM6172 had .5 v offset, probably still impedance balancing issues.. will sort that out later) 

 Sounds absolutely fantastic, the OPA2107 just fits really well with this amp.

 Oh and the buffers are LMH6321, really has that nice slam to it =)

 will o


----------



## ozshadow

Might want to edit the original post before people start asking where you and I got those magical 2701 chips (the 2107's) 
	

	
	
		
		

		
			







 I think I could now solder this board with my eyes closed. Freakin buffer ! I think I soldered/removed/resoldered everything but the caps on mine multiple times just to find out one buffer had issues.


 But I completely agree, the 2107 is a beautiful chip in this amp.


----------



## pddjsteve

Well, I'm convinced that I'm just going to need to find some funding and get more boards, because I want to try 8620/8610/buf634, 2107/something/buf634, and 2107/something/lmh6321 and I only have 1 board left. 

 Right now I'm thinking 2107/something/lmh6321 - you've said it was very detailed and had a nice slam, would you say it was less bright than the 8620?

 Battery drain isn't a problem because I made a pack out of AAAs. I'm not sure if I wanna go with the lm6171.


----------



## ozshadow

Finally posted a full review found here:

http://www6.head-fi.org/forums/showthread.php?t=203099


----------



## alfie

Wow, yesterday I got the PCB for this little amp. I am so happy, because of I was never able to get a PINT PCB and I truly need a portable amp. Now I have a couple of questions. Could someone list multiple opamps combinations to be used on the PPAS? Also, it seems really impossible to find a SST310 online here in Italy; which else could be used?


----------



## ozshadow

The original thread lists many combos of opamps and buffers. The ones that say 2701 are actually opa2107, which I prefer with opa627 ground and buf634u buffers.


 As for the SST310, you can use BSR57 just fine and is probably more available.


----------



## alfie

Quote:


  Originally Posted by *ozshadow* 
_The original thread lists many combos of opamps and buffers. The ones that say 2701 are actually opa2107, which I prefer with opa627 ground and buf634u buffers._

 

Come on, just 2-3 items, like
 x1, y1, z1 : laid back
 x2, y2, z2 : details
 x3, y3, z3 : fantastic!







  Quote:


  Originally Posted by *ozshadow* 
_As for the SST310, you can use BSR57 just fine and is probably more available._

 

Thanks, but it seems hard too.


----------



## ATAT

http://www6.head-fi.org/forums/showp...75&postcount=1

 Thats the first post of this thread, I tried to compile my impressions on working opamps.

 NB that LM6171s are confirmed working, so the AD8066/LM6171 combo should work

 By next week I should be able to get LM6172 working (i have an idea in my head, just havent had time to get to iron) so i'll give impressions on that and the AD8057

 TBH, I reccomend the AD8066 for low draw, OPA2107 for high draw use, the AD8620 when compared to the others is too shrilly.

 And the LMH6321s are better all around, but just has a higher draw.

 As for the JFETs

http://www6.head-fi.org/forums/showp...37&postcount=4

 is a list of alternatives


----------



## ozshadow

I think a key part of what setup you get depends on what headphones you use.

 Like for Grados, I find the 2107/627/buf634 is a very nice combo
 For darker Senns, I'd say 2107 or 8620/8610/buf634 or possibly 6321 if you can handle battery drain
 For K701's and many IEMS, it basically depends on your personal tastes and what you listen to.


----------



## pddjsteve

Quote:


  Originally Posted by *ozshadow* 
_or darker Senns, I'd say 2107 or 8620/8610/buf634 or possibly 6321 if you can handle battery drain_

 

My 8620/8610/6321 combo uses about 43mA, which will kill a 170mAh 9V in a little over 4 hours or a 250mAh in a little over 6. I use it with a 15xAAA 700mAh
 battery pack and it lasts quite a while.

 That being said, with Ety ER4 this combination is almost too harsh in the highs. Dunno how that compares to the headphones he has, but it is something to watch out for. 

 Based on your and ATAT's comments, I'm thinking about trying 2107/???/6321.


----------



## ATAT

Opamp / buffer selection table--

 ---- Buffers ----

 Purpose - Home mainly, occasional portable use
 LMH6321, Class-A biasing, Trickle charging, larger hammond case.

 Purpose - Mainly portable use.
 BUF634, Small case.

 ----- Opamps ----

 Sound wanted - 

 Bassy sound (good with IEMs, K501 .etc)
 AD8066 / OPA132 

 Midrange / Dynamics / Detail (generally good all around, but esp with Grados, some IEMs)
 OPA2107 / LM6171 (for highend detail)
 OPA2107 / OPA627 (for more soundstage / midrange)
 --- NOTE -- the OPA2107 requires 2x9v for low offset use.

 Treblehead / "ER-4 type detail" (HD650? dont own any dark cans do dont know)
 AD8620/AD8610 (too shrilly on cans with emphasized high ends, but could be good with HD650 types..)
 -- Note -- AD8620 is extremely low draw, BUF634 + AD8620 can last an ungodly amount of time.



 I'll refine this as time goes on.. anyone have anything to add?


----------



## ATAT

Quote:


  Originally Posted by *pddjsteve* 
_My 8620/8610/6321 combo uses about 43mA, which will kill a 170mAh 9V in a little over 4 hours or a 250mAh in a little over 6. I use it with a 15xAAA 700mAh
 battery pack and it lasts quite a while.

 That being said, with Ety ER4 this combination is almost too harsh in the highs. Dunno how that compares to the headphones he has, but it is something to watch out for. 

 Based on your and ATAT's comments, I'm thinking about trying 2107/???/6321._

 

my 270 mAH Accupowers go down pretty quick with this config (OPA2107/LM6171/LMH6321) I measured around 7 hours. 

 Also, 15x AAA? what case are you using and how do you recharge it?! dear lord.


----------



## pddjsteve

Quote:


  Originally Posted by *ATAT* 
_Also, 15x AAA? what case are you using and how do you recharge it?! dear lord._

 

It actually is 2 packs I made from AAA solder tab cells. I threw it into my hammond J1201 that had previously housed a cmoy and 2x9V. One pack is 12xAAA and it fits in behind the amp, in a 6x2 config. I ran it like that for a while, with 14.4V, then got the idea to add the other (3xAAA) which is just kind of crammed in around the jacks. I made a lm317 trickle charger but changed the resistor so it would charge the 700mAh instead of whatever the pint value would do. I charge it overnight off a 24V wallwart.


----------



## ozshadow

For non rechargeable people, a regular 9v is about 540 mah, so thats like 30 something hours typical.


----------



## alfie

Quote:


  Originally Posted by *ATAT* 
_Opamp / buffer selection table_

 

Thanks.


----------



## sidewinder

What the actual difference between an A47 and PPAS? As far as I recognize, the're both opamp + buffers designs, so where lies this big gap in soundquality?

 edit: never mind, I found an answer:

  Quote:


 _In the A47, you'll notice that the opamps aren't in series, they're actually in parallel. The output from the first half is driven in the input of the second half (this is how the gain is set), and then the two opamps are paralleled at the output. The resistors are there to stop large currents flowing between the opamps due to slight intrinsic differences.

 In series, no benefit. In parallel, more current _ 
 

So to rephrase my question, how does the PPAS compare to other opamp + buffer designs? What does it make so 'special'?


----------



## ATAT

The PPAS is 3 channel buffered.

 CMoy- Passive 2 channel
 A47 - Parallel no-buffer 2 channel
 PINT - 3 Channel no buffer
 MINT - 2 Channel buffered

 ..

 Also there is changes in the power supply
 JFET isolation prevents ripples in the high current (buffer) supply from affecting the opamp supply.


----------



## MikeNAS

ATAT are you selling me any PCB's?


----------



## ATAT

MikeNAS, send me your address and number of boards.


----------



## Teerawit

Does anyone have extra C5/C7 caps that I could buy? I need a pair of the 20V tantalum caps.


----------



## ATAT

Bipolar and unstable opamps are now confirmed working.

 on a fully charged NiMH, I'm getting about 1.3 mV offset from the combination AD8058 / LM6171... sounds great.

 Now the amp can use the LM6171, LM6172, AD8058, AD8057, ICs.

 Revised BoM and bypassing mod instructions will be posted in a bit.


----------



## ATAT

AD8058 has issues with high gain.. not sure why I'll figgure this out later. (up to 70mV on a gain of 5)

 For now, I've completed this..
 LM6172/LM6171/LMH6321.. impressions later.. 
 Runtime 5xAAA NIMH - 7.5~6 V at 24 hours- with charger.
 Size.. see pic.











 Sorry about cameraphone..
 Also, DC jack not yet soldered.


----------



## ozshadow

Thats a lil one. Someone needs to make Hornet sized knobs for 6mm shafts.


----------



## pddjsteve

Did you cut down a C801? That's teeny.


----------



## ATAT

Yearp.. in a C801.. with LMH6321s.. now my RS-1s can sound good on the go 
	

	
	
		
		

		
		
	


	




 Scary thing is.. the batteries can charge using a 9v battery...


----------



## Teerawit

Can anyone with the OPA2107/LM6171/LMH6321 combo measure the voltage drop across each SST310 (Q1/Q2/Q3/Q4)?


----------



## dhp

Quote:


  Originally Posted by *Teerawit* 
_Can anyone with the OPA2107/LM6171/LMH6321 combo measure the voltage drop across each SST310 (Q1/Q2/Q3/Q4)?_

 

Don't have mine on me... but I'll be able to measure it after the weekend.


----------



## Teerawit

Or OPA2107 + LMH6321 + any ground...

 please


----------



## ATAT

Across the SSTs? should be zero (or close to it).


----------



## Filburt

The PPAS I have with me at the moment is running OPA2107/AD825/BUF634. Sounds pretty good, lot of soundstage and detail. I still like my AD8058/AD8397 PINT better at the moment, though. I blame the BUF634s to some degree, though. I hope we can get an AD8058 configuration working on the PPAS. I need to get parts to try it myself.


----------



## Teerawit

Quote:


  Originally Posted by *ATAT* 
_Across the SSTs? should be zero (or close to it)._

 

Um, no?


----------



## ATAT

Wait. which pins.. 1 and 3 should be zero (since they're shorted.. duh) 
 The others should be around 4.5 volts (at least thats what I measured on non-new 9vs)


----------



## Teerawit

Quote:


  Originally Posted by *ATAT* 
_Wait. which pins.. 1 and 3 should be zero (since they're shorted.. duh) 
 The others should be around 4.5 volts (at least thats what I measured on non-new 9vs)_

 

Interesting, thanks!

 BTW, what voltages are your opamps seeing? (with an ~18V supply)


----------



## ATAT

AD8058s confirmed working, culprit was BUF634s, oscillating.

 LMH buffers fix the problem.


----------



## Filburt

Yay! I'm glad at least someone listens to my op-amp recommendations...and that it works out >_>

 I'm also glad the 8058 is working in the PPAS, as that's what I plan to use with mine. I may go all out and use the AD9631 for ground ^_^


----------



## ozshadow

Seems the 2107 is fast becoming the chip of choice for this amp. And tweaking it becomes selecting the ground opamp and buffer of your choice. The 8610 in ground sure did make the 2107 bright, I'd hate to hear it with a 8620 main.


----------



## jbloudg20

What is the deal with the Jfets? Do the four of them go in Q1 and Q2?


----------



## ozshadow

Takes 4 - go in Q1, Q2, Q3, and Q4


----------



## jbloudg20

Quote:


  Originally Posted by *ozshadow* /img/forum/go_quote.gif 
_Takes 4 - go in Q1, Q2, Q3, and Q4_

 

Thought so.

 ATAT... maybe put that designator on your BOM?


----------



## ATAT

Good point,, I've been working on modifying the BoM to work with bipolars. I'll upload the new BoM in a week or two.


----------



## pddjsteve

Quote:


  Originally Posted by *ATAT* /img/forum/go_quote.gif 
_Good point,, I've been working on modifying the BoM to work with bipolars. I'll upload the new BoM in a week or two._

 

Any updates on this? I've got all the parts for my 2nd board ready to go, and I'm thinking of giving the AD8058/????/LMH6321 a try and doing something like you did with the 5AAA and the C801. I need to order a case for my pimeta anyways, so I thought I'd pick up anything else I might need to try this out.


----------



## ATAT

pddj - Yes, I got it working, but I havent typed up the part #s for those, its just tweaking the feedback resistor values.. I'm working on my oversampling usb dac right now so I havent the time to finish the Bom

 I'm sure I can find my old mouser BoM and send it to you if you'd like


----------



## pddjsteve

Quote:


  Originally Posted by *ATAT* /img/forum/go_quote.gif 
_pddj - Yes, I got it working, but I havent typed up the part #s for those, its just tweaking the feedback resistor values.. I'm working on my oversampling usb dac right now so I havent the time to finish the Bom

 I'm sure I can find my old mouser BoM and send it to you if you'd like_

 


 Ah, ok. So nothing really drastic then? I've got pretty much everything ordered from back when I made my original (ordered enough to make both), I followed the high-end configuration from the site/thread BOM except stayed with 1% resistors instead of .1%. 

 So essentially, you made changes to R3, R4, R5, and R6? I read Tangent's cranky opamp article, and his suggestions seemed to be lower the bandwidth and balance R3/R4 with R2 and the pot.

 I'm not really interested so much in part numbers as just some guidelines or rough values. If you'd like, I could even work on taking the old BOM and looking up part numbers and adding to it.


----------



## ATAT

R1, R2, R3, R6, R5 are changed, R4 is held constant.

 buffers must be LMH6321s for very cranky opamps, there is also need for bypassing capacitors. (basically put tiny 0603 capacitor underneath the big electrolytic caps 100uF ones)


----------



## pddjsteve

Quote:


  Originally Posted by *ATAT* /img/forum/go_quote.gif 
_R1, R2, R3, R6, R5 are changed, R4 is held constant.

 buffers must be LMH6321s for very cranky opamps, there is also need for bypassing capacitors. (basically put tiny 0603 capacitor underneath the big electrolytic caps 100uF ones)_

 

Things I have on hand:
 LMH6321
 R2 = 100K
 R4 = 10K
 R6 = 475K

 Calculated based on my limited understanding on Tangent's cranky opamp article and electronics calculator page:
 R1 = 33k
 R3 = 3.32K
 R5 = 30k

 Need to get:
 ~.1uF 0603 bypass (NP0?)

 Am I way off base here? You said you lessened the values, did you drop them all? I tried following the equations and it seems like raising R3 lessened offset but led to bigger R5 and R1


----------



## ATAT

Are you balancing for halfway in between the pot value? thats what you'd ideally do.. also smaller resistor values would allow you to fine tune your values...


----------



## pddjsteve

Ah, you replied before my edit went through. Hmm. Base my calculations on the pot being 5K, since that is half of its 10k value? Lemme go through this again.


 POT = 5k (half of the 10k rating)
 R1 = 4k
 R2 = 100k
 R3 = 500
 R4 = 1.5k
 R5 = 3.32k
 R6 = 330k

 Plugging those into the calculators on Tangent's site, that gives me a gain of 3.87 and an estimated offset of 8.77mV when I plug in the values from the AD8058.

 I probably should go a little lower in the values, though. Am I on the right track? I'm pretty much in between projects at work and have the time tomorrow to sit and crunch numbers all day.

 Edit: In addition to Tangent's multiloop gain calculator and DC offset calculator, I used the following equations from the pimeta and cranky opamp writeups:

 R1 ~= R3 + R5
 R5 ~= [5 to 10] * R3
 R6 ~= 100 * R5


----------



## ATAT

Looks good at least on back of the napkin check... (R6 does look tad high though.. are you sure that one's right?)

 I think my values were
 R1 - 1k
 R2 - 100k
 R3 - 1k 
 R4 - 10k
 R5 - 220
 R6 - 6.2k


----------



## pddjsteve

Ok, so I'm on the right track with the calculations. I'm going to play with this and see if I can come up with some good values for a range of gains, and then find part numbers.


----------



## pddjsteve

Yeah, my R6 above way way out of wack. I just reduced it based on what I had on hand. Bad idea. 

 My goal is to keep my gain around 4 and minimize my DC offset. I'm not sure, but I am going to choose either AD8058 or LM6172 for OPALR. I haven't selected OPAG yet. I'll be using LMH6321 as my buffer.

 How do these look?

 R1 = 3.8K
 R2 = 100K
 R3 = 400
 R4 = 2.43K
 R5 = 3.32K
 R6 = 35K

 The cap I picked out for doing the additional power supply bypassing:

 CBypass: 80-C0603C104J3R (0603 .1uF 25V 5% X7R)

 I could try going .01 and a COG/NPO 

 EDIT

 Here is a work-in-progress BOM based on the original, with R4 values for various gains, a start on a bipolar version (pending me playing some more with the numbers) and a very little section on the opamps and buffers.

Excel Spreadsheet
Zipped Excel Spreadsheet


----------



## pddjsteve

So I picked up a couple of the AD8058 and AD9631 from digikey, and I was too impatient to wait to figure out proper resistor values, so I put one of each on a browndog and threw them in my Pimeta (ran off a single 9V to better match what I'll be running my PPAS off). I'd previously gotten LMH6321 on browndogs for my Pimeta with good results.

 Holy crap. Blows everything else I've tried out of the water. I can't decide if I like the AD8058/AD9631/LMH6321 or the AD8058/LM6171/LMH6321 combinations better, but right now I'm running the 9631 in ground.

 DC offset is managable (4mV to 18mV at the volume range I was listening at, mid 30's when cranked to full volume) even without bypassing or resistor optimizing. I'm optimistic about what it will give with the right treatment. 

 This just sounds amazing. Detail, punch, not lacking but not overpowering in bass, highs are not harsh.

 I think I've settled on these values:

 R1 4.32K
 R2 100K
 R3 3.32K
 R4 14K
 R5 698
 R6 42.2K
 Cbypass = .1uF X7R (or would .01uF NPO be better?)
 ----------------------------------------------------
 New version of the BOM is done... I made the opalr/opag/buf selectable from among the list of what people have confirmed working. I think I'm going to do the same for the gain resistor R4 for the normal config. End-of-year boredom was getting to me at work, and playing with exeel makes it look like I'm busy 

Excel Spreadsheet
Zipped Excel Spreadsheet


----------



## abcheng

I have a few questions regarding parts for the PPAS

 1. Mouser is currently out of 647-UPW1A101MDD, but they have UPW1A101MDH and the only difference I can see is that the MDH caps aren't RoHS compliant. The MDH caps will replace the MDD caps without any problems correct?

 2. Mouser and Digikey both don't stock the TLE railsplitter. Does anyone have a spare one they could sell me?

 3. I'm going to use the OPA2107 / some ground opamp / BUF634 combo on my PPAS. First of all, what ground opamp do you guys recommend that is currently available at digikey? Do I need to change any resistor values or is what is in the original BOM fine?


----------



## ATAT

1. RoHS is irrelavent for the functionality

 2. Sorry, I'm beginning to run low too, but if you're running 18 volts, you can leave TLE not populated and put the midway point of the 18 volts soldered to the VGND pad

 3. BoM is fine for that config. I would suggest something easy to handle like the OPA132? I'm not familiar with easy to work with single channels... I'd go with the AD6171, but that's a bit cranky to work with.


----------



## blueworm

opa2134 L/R, opa134 G, BUF634 all around.
 Sounds nice.


----------



## blueworm

Qsilver2001 has asked me what is pin #1 on the IC. 
 I agree it is a bit unclear.
 Here is a modified picture that should clear it up








 Pink dot is pin #1.


----------



## Qsilver2001

Hi blueworm,

 Thanks for the pics. Hope other new builders will benefit from this clearer diagrams like myself.


----------



## OtterMarc

Blueworm. 
 Nice amp! I like your connectors in the picture above. They seem like plastic body, meaning isolated GND from chassis. Old parts or still available? I've just spent 1-1/2hours digging through Digikey Newark and Mouser with no joy finding something similar.

 I may use miniQ XLR instead.

 Thanks

 Anyone have one or two PPAS boards they'd consider selling? Puhleez?

 Else, count me in for the _NEXT_ round! Hehehehe.


----------



## Qsilver2001

Quote:


  Originally Posted by *OtterMarc* /img/forum/go_quote.gif 
_Blueworm. 
 Nice amp! I like your connectors in the picture above. They seem like plastic body, meaning isolated GND from chassis._

 

Those are Kobiconn 161-7300-EX from Mouser.


----------



## blueworm

Quote:


  Originally Posted by *Qsilver2001* /img/forum/go_quote.gif 
_Those are Kobiconn 161-7300-EX from Mouser._

 

Correct.


----------



## OtterMarc

Thanks QSilver1. Noted and added to my list.

 Now if only I could tempt someone with an extra PPAS PCB (hint hint) to part with theirs. Chocolate? Beer? Magic head-phone mojo juice? Hopefully progress will bring about a Ver.2! 
	

	
	
		
		

		
		
	


	




 You guys have made a nice little and rather desirable project amp a reality. Nice going.

 Marc

 Seeking PPAS PCB...


----------



## threepointone

I'm going to do more investigation myself on this, but I'm just wondering if anyone had any good pointers for where to look first:

 My PPAS has been pretty darn cranky from the start. First, I had a huge DC offset issue which I found out was somehow related to the fact that I'd lifted one of its pins.
 Now that got fixed for the night, but a couple of days later I started getting something like 100-200mV on both channels. I was debugging everything with the meter, and managed to short out two pins of the TLE for a moment (I think it's ground and one of the rails) Guess what? The offset disappeared, and it suddenly started working again. I suspected it was some bad solder joint, so I reflowed everything. Still working a couple of days after that.

 I haven't been using the amp for a while, and today, just to retest it, I discovered that there was about 40something/30somethingmV offset on both channels. Actually, now that I check again, it's at 38mV/28mV. It's _just_ within the range in which I'd call the offset unreasonably dangerous for 64ohm headphones. I'm most worried that this might be some weird intermittent/drifting problem. Any ideas on where this problem might be? I've already un-glue-gunned this thing and desoldered the jacks like ten times, and I'd rather not do it again unless I have a good idea of what to look out for.

 My configuration is the one recommended in the first post, LMH6321 buffers, OPA2107 OPAR/L, and LM6171 in the ground channel. The isolation JFETs are in there, the CRDs are installed; pretty much everything's maxed out. The main nonstandard features in my PPAS are a homemade SOIC->DIP adapter, since I don't have any SOIC OPA2107's on hand, 12V TREAD power supply (no batteries), trimpots for volume adjustment, RCA outputs + 1/8" inputs. Weird, I know, but these are just a couple of needed modifications for a little project I'm working on.

 **EDIT: 
 this is really weird now. I just plugged it in and tested again, and it measures 11mv/22mv offset. Bad component? weird solder joint? I'm really not sure what kind of problem this might be.

 **EDIT AGAIN:
 I just remembered, I bumped the voltage of my TREAD to 13V from 12.5V. Maybe the opamps just need voltage? I heard the OPA2107 likes lots of voltage. But then again, this looks a lot like something weird going on with the ground channel, and the OPA2107 is in L/R. I'll play around with the supply voltage a bit more. . .

 --> It seems that it is a LR channel problem; all the offset in the L/R channels also appears as offset from input to output. Is this just a problem with the OPA2107 wanting more voltage, or is it a more serious problem? Anyone with experience with this confgiuration?


----------



## OtterMarc

Threepoint one,

 Any progress? Answers to your questions have been slower than usual.
	

	
	
		
		

		
		
	


	




 Marc


----------



## daggerlee

I'm thinking of using a LM4562/OPA132/BUF634 combination. I'm not too familiar with opamp characteristics, does anybody know under which BoM this would fall under (FET, Bipolar, ??)?


----------



## Filburt

Bipolar. LM4562 is bipolar, and 10nA is still 2000 times the Ib of something like an OPA134. So even though it's a low Ib for a bipolar input op-amp it's still high such that you need to observe the same sort of build rules.


----------



## daggerlee

Cool, thanks for the info Filburt.

 Ran into another problem today - remembered that Mouser was OOS on the SST502 part, and they won't be getting stock in for at least another 2 months. Same with digikey/newark. 

 Anybody know of any alternative part for this position, or better yet have a spare one to lend me? Thanks!


----------



## daggerlee

Hmm looking at ATAT's original BoM it looks like the SST502 is just for biasing into class A. I'll leave em out. 

 Ordered 2 too few of the SST310 though so will have to order some more of those. Oh well.


----------



## daggerlee

Got my SST310s today, soldered everything up. Works great! Getting around 8-11 mV of offset per channel, nothing serious. I guess I will leave it running overnight to see how it responds when the battery voltages dip. The LM4562/OPA132 sounds pretty great. More impressions later.


----------



## vixr

cool... Please post pictures!


----------



## daggerlee

Here's one 
	

	
	
		
		

		
			










 Just cased it up, looks very good so far. I am measuring around 9 mA per channel, if that's the correct way of measuring output then I guess it's using 20 around mA total, which seems a bit low to me...maybe it's because I haven't biased it to class A yet. 

 DC offset is stabilizing at 9mV per channel...pictures to come of it cased up.


----------



## vixr

ah... jumped the gun on the phone jack soldering... It has to go thru the case first...been there done that... I love those jacks though. very nice job Dan... looking forward to seeing it finished.


----------



## daggerlee

Quote:


  Originally Posted by *vixr* /img/forum/go_quote.gif 
_ah... jumped the gun on the phone jack soldering... It has to go thru the case first...been there done that... I love those jacks though. very nice job Dan... looking forward to seeing it finished._

 

Yeah, I forgot about that in my hurry to get it working 
	

	
	
		
		

		
		
	


	




 no matter though unsoldering/resoldering was a breeze. Here's the finished product..






 I put in .1% 75 ohm resistors in line with the output since I will be using them mainly with Ety ER4Ps, for an instant P-S conversion. Unfortunately one of the resistor legs broke off when I was soldering, so right now it's being held on to the jack by a gob of solder. I hope it'll be enough to hold up through my trip abroad this summer.

 As for sonic characteristics, it's not as warm as my Heed, which I think is because of the naturally 'clinical' characteristic of the PPA, and it's a little slow. Perhaps changing to the LMH buffers might be worthwhile...

 Anyway, thanks again Rob for the board 
	

	
	
		
		

		
		
	


	




 Good luck in building yours!


----------



## vixr

Dan,
 Awesome! looks great. I hope you enjoy it, I hope to get around to building a couple of these soon. I would like to give one as a gift to my daughter, although she uses all my amps anyway...( and phones, cables, interconnects, battery chargers, i pod, laptop...) She says the CMoy type amps are a guy magnet...they all want to know "what _is_ that thing?"


----------



## el_matt0

hey im just trying to order parts for my PPA, need a bit of help though, ive never done surface mount stuff before so im a little unsure. from the sounds of what people have said in this thread, as well as whast AVAILABLE to order online, i think im going to go with the LMH6321 buffers (of which i need 3 right), which do i want from digi key, they have 2 available. 
LMH6321MR-ND

 OR 

LMH6321TS-ND

 also, i wanted to go w/ the ad8066 as i hear it has good bass, for my opamp, bug again, several available through digi. could someone link me to the correct P/N for the one i should order, as well as a suitable ground channel opamp to use with it? preferably stuff thats available through digi key, if its not, a different opamp would probably suffice. THANKS guys, and sorry for being clueless


----------



## el_matt0

http://www.digikey.com/scripts/DkSea...428317&Site=CA

 is that the one i want, if i wana go w/ the ad8066? 
 with something like
http://www.digikey.com/scripts/DkSea...871802&Site=CA
 as a ground ompamp? 

 and then like i said in my last post, using 3 lmh6321 wiht those 2 would work well? am i on the right track?


----------



## hellomai

Quote:


  Originally Posted by *el_matt0* /img/forum/go_quote.gif 
_hey im just trying to order parts for my PPA, need a bit of help though, ive never done surface mount stuff before so im a little unsure. from the sounds of what people have said in this thread, as well as whast AVAILABLE to order online, i think im going to go with the LMH6321 buffers (of which i need 3 right), which do i want from digi key, they have 2 available. 
LMH6321MR-ND

 OR 

LMH6321TS-ND_

 


 Use the MR
 here is a link: http://www.national.com/pf/LM/LMH6321.html


----------



## el_matt0

alright, what about my second to last post about the opamps. would the ones i have in mind be an appropriate choice? and if so, which of the various different ones should i get? tx i appreciate the help guys


----------



## NelsonVandal

Please help me choose opamps! I have 3 LMH6321's which seem to sound amazing (tried them without opamps, but they started to oscillate), and I don't want crap in front of them. Since the LMH's are 12 V max, and since I'm planning on using 7 x AAA = 8,4 V and fit everything in a Hammond C801, my choices are limited. At first I was aiming at AD744's but I don't think they'll sound good at that voltage (I haven't heard them, only AD746, and it doesn't sound good at 9 V). Neither will OPA2701. AD8058 lacks "body". OPA2132 and AD823 are just not good enough.

 Maybe I'll go for LM4562 or AD8066, but what opamp will sound good in the ground position? I'm not fond of AD8610 (too harsh). Maybe I should remove the ground LMH6321 and use LMH6654 or AD8045 or some other high current opamp alone?


----------



## hellomai

Quote:


  Originally Posted by *el_matt0* /img/forum/go_quote.gif 
_alright, what about my second to last post about the opamps. would the ones i have in mind be an appropriate choice? and if so, which of the various different ones should i get? tx i appreciate the help guys 
	

	
	
		
		

		
			






_

 


  Quote:


  Originally Posted by *el_matt0* /img/forum/go_quote.gif 
_http://www.digikey.com/scripts/DkSea...428317&Site=CA

http://www.digikey.com/scripts/DkSea...871802&Site=CA
 as a ground ompamp? _

 

Can't see the link. I don't have much experience with different opamp sound, so i can't comment on the that. but you can check this.


----------



## el_matt0

Quote:


  Originally Posted by *NelsonVandal* /img/forum/go_quote.gif 
_Please help me choose opamps! I have 3 LMH6321's which seem to sound amazing (tried them without opamps, but they started to oscillate), and I don't want crap in front of them. Since the LMH's are 12 V max, and since I'm planning on using 7 x AAA = 8,4 V and fit everything in a Hammond C801, my choices are limited. At first I was aiming at AD744's but I don't think they'll sound good at that voltage (I haven't heard them, only AD746, and it doesn't sound good at 9 V). Neither will OPA2701. AD8058 lacks "body". OPA2132 and AD823 are just not good enough.

 Maybe I'll go for LM4562 or AD8066, but what opamp will sound good in the ground position? I'm not fond of AD8610 (too harsh). Maybe I should remove the ground LMH6321 and use LMH6654 or AD8045 or some other high current opamp alone?_

 

aalmost IDENTICAL situation!! 3 lmh6321 and i want to use the AD8066...two things, can someone link me to the corect p/n via digikey for that, theres several versions and im a little unsure. and secondly, which opamp should i go for in the ground position?? thanks!


----------



## el_matt0

^^ anyone??


----------



## NelsonVandal

One of the members here claims that LT1363/64 are very good opamps, spec'd for 5 - 30 V and unity gain stable. They're quite expensive, and PPAS is very small so it will be hell to desolder them and roll in a new opamp if they aren't to my taste. I'm thinking that one of those high current/high speed opamps will be the best choice - AD9631, AD8045, OPA690, LMH6654 etc (all unity gain stable), and drop the ground channel LMH6321.


----------



## el_matt0

arent the LMH6321s the 3 buffers? from my current limited understanding, i need 3 buffers (my 3 lmh6321s) and 2 opamps, one OPALR and one OPAG right? would the ad8066 not be a great choice for my OPALR, with something like the LM6171 as my OPAG? please clarify!!


----------



## balou

hi el_matt0
 what nelsonvandal is suggesting is that you drop the lmh6321 for the ground channel, and use a high current opamp instead. kind of like a chip with both features built in.


----------



## NelsonVandal

Quote:


  Originally Posted by *balou* /img/forum/go_quote.gif 
_hi el_matt0
 what nelsonvandal is suggesting is that you drop the lmh6321 for the ground channel, and use a high current opamp instead. kind of like a chip with both features built in._

 

Yes.

 Of the high current opamps I've only heard LMH6642 and LMH6654. The 6654 sounds very good, better than most of the "normal" opamps. AD9631 is claimed to be even better. OPA690 is probably very good as well, since it's going to be used in the Mini3. The problem is DC-offset, which isn't a problem in the ground position. And since it has enough output current, why use a buffer.

 This will take some tweaking, to bypass the buffer and get the feedback loop and output right. Because of the size, PPAS isn't easily tweaked. It would be easier to just put it in front of the LMH6321, but then you have two amps adding to coloration.

 I have used LMH6654 "stand-alone" in Xenos, and I liked it more than AD8620, AD8058, OPA2134, LM4562, AD823 (DC-offset was as far as I remember about 15mV). I've used it as ground channel amp in a PINT configuration and my buffer-only amps with great result. I've never used it in front of a buffer though, so I'm not sure how that would work out.


----------



## el_matt0

so what hes saying is use a high current opamp like lmh6654 in the OPAG position, and it wont need a buffer in the BUGF position (BUFG is empty?, or is it the other way around, chip goes in BUFG, OPAG is empty?) and then with whatever opamp i decided on, id have two LMH6321s in my BUFL and BUFR positions? 
 1) is LMH6654MA the one i want?
 2) will AD8066ARZ be suitable for my OPALR position, or can someone suggest something that might be a better option?

 **im looking at P/N's via digi-key btw


----------



## balou

BUFG will be empty with this config

 1.) depends if you want a single opamp or a buffered opamp in your ground
 2.) yup, this will be an option. after some listening to the ad8066 (in a cmoy driving grado phones), I must say it has nice bass. not boomy, not to much, but well defined and nice. but I was quite used to agressive highs, the ad8066 is almost a bit to less agressive there in comparison. overall detail is good, much better than opa2132, a bit better than ad823
 I wonder how the lm4562 sounds, it should arrive soon


----------



## gates_2

any way to get those discrete buffer boards for this? I may have snagged a ppas board, and I'd be interesting in building it


----------



## amb

LMH6654 has relative high output current (asymmetrical 80mA source, 120mA sink), but not in the same league as OPA690, AD8010 (200mA) or BUF634 (250mA). Also, the max voltage rating of the LMH6654, OPA690 and AD8010 are all +-6V, so can't use two 9V batteries.

 Btw, DC offset _does_ matter in the ground channel, just as it does with the other two channels.


----------



## el_matt0

k so, can someone take a quick look at the parts im about to order and just double check im not doing something silly. 
 1) AD8066ARZ for my OPALR
 2) LMH6654MA in the OPAG (maybe someone can suggest an alternative, if i want to use 3 buffers)
 3) LMH6321MR x3 in all the buffer positions
 or should i stick with what ive got planned and just drop off one of the buffers for the BUFG and use the LMH6654 un buffered? im planning to power this with a single NiMh 9V, if that changes anything.


----------



## NelsonVandal

Quote:


  Originally Posted by *amb* /img/forum/go_quote.gif 
_Btw, DC offset does matter in the ground channel, just as it does with the other two channels._

 

In my PINT-clone using LMH6654 as ground channel, I have 2/3 mV DC-offset at max volume. With LM4562 as LR there's only 0.4/0.7 mV. It doesn't add more offset than using passive ground. In what way does it matter?

 What do you say about this, using just e.g. OPA690 and not the LMH6321 buffer in the ground channel? Is there anything to gain using the buffer as well?

 Our "problem" is we are going for 9 V since we're using LMH6321, otherwise AD744 would have been an easy choice for me.


----------



## amb

Quote:


  Originally Posted by *NelsonVandal* /img/forum/go_quote.gif 
_In my PINT-clone using LMH6654 as ground channel, I have 2/3 mV DC-offset at max volume. With LM4562 as LR there's only 0.4/0.7 mV. It doesn't add more offset than using passive ground. In what way does it matter?_

 

Your DC offset figures are good. When I say "it does matter" it's simply to point out that DC offset is as important on the ground channel as it is on the left and right channels.

  Quote:


 What do you say about this, using just e.g. OPA690 and not the LMH6321 buffer in the ground channel? Is there anything to gain using the buffer as well? 
 

Since those two have only 50mA difference in output current, and both are high, then the difference isn't big. There are advantages to either scheme. A separate buffer eliminates thermal coupling between the output and input stages. But a separate buffer may give rise to instability when the buffer is wrapped in the feedback loop (depends largely on the characteristics of the opamp and the buffer). On the other hand taking the buffer outside the feedback loop loses the DC offset control and low output impedance characteristics. I have not tested a OPA690 + LMH6321 combo so I couldn't tell you if it would work well.


----------



## el_matt0

Quote:


  Originally Posted by *el_matt0* /img/forum/go_quote.gif 
_k so, can someone take a quick look at the parts im about to order and just double check im not doing something silly. 
 1) AD8066ARZ for my OPALR
 2) LMH6654MA in the OPAG (maybe someone can suggest an alternative, if i want to use 3 buffers)
 3) LMH6321MR x3 in all the buffer positions
 or should i stick with what ive got planned and just drop off one of the buffers for the BUFG and use the LMH6654 un buffered? im planning to power this with a single NiMh 9V, if that changes anything._

 

 anyone please? confirm this for me so i can order?


----------



## NelsonVandal

Maybe you should go for OPA690, since it's used in Mini3, it's probably even better than LMH6654. Those people know what they're doing. It's very cheap, and hopefully it's as stable as the 6654.

 I simply can't come up with a known good opamp to use in front of LMH6321.


----------



## amb

Quote:


  Originally Posted by *NelsonVandal* /img/forum/go_quote.gif 
_Maybe you should go for OPA690, since it's used in Mini3, it's probably even better than LMH6654. Those people know what they're doing. It's very cheap, and hopefully it's as stable as the 6654._

 

Actually, the OPA690 choice was based on KurtW's amp (he used AD8397s for left and right and OPA690 for ground, except that his amp's "ground" is a OPA690 acting as a rail-splitter, and no separate output ground channel). Kurt reported good sound and lower battery comsumption as compared to AD8010. I have yet to test any of this, pending the arrival of prototype PCBs. So, I am just operating on blind-faith here, and won't know whether the OPA690 would be the final recommendation until I build several prototypes with different chips and test them all.


----------



## el_matt0

should the OPA690 be used with a buffer like the lmh6321 or is it bufferless?


----------



## balou

the purpose of the mini³ is to be bufferless, that's why it uses the high output ad8397 and the opa690. 

 so the opa690 is bufferless


----------



## el_matt0

k, well i ordered a 3rd lmh6321 ANYways just incase i end up needing it at some point. i should leave opa690 bufferless though, so leave BUFG just completely open?


----------



## el_matt0

or since i have one, should i put an lmh6321 in that spot?


----------



## balou

no, that would just add unnecessary current draw and it'll degrade sound quality - it would be the distortion of the opamp plus distortion of the buffer.

 you can jumper across the buffer with a short wire. I don't have the exact pinout in mind, just look at the datasheet and jumper from input to output


----------



## el_matt0

ok balou, thanks thats exactly what ill do then. on a different note, has anyone heard the ad8066 / opa690 / lmh6321 combo?? any thoughts?


----------



## NelsonVandal

Now I've listened to AD8066 in my Sijosae amp. I compared it to LM4562. I'm quite sure what opamps to use in my PPAS - LME49720/LME49710 (it's supposed to be the same as LM4562). AD8066 wasn't to my liking, too rough and sibilant. I liked the energy though, especially in the lower registers. I hope the slam of the LMH6321's compensate for the slightly sterile sound in the LM/LME's.

 There will be some serious current draw. A single 9V is out of the question. It's going to be a tight fit to squeeze in 7 AAA's and a charger in a C801.

 I forgot to order resistors, and I'm up to some other projects (and work, and family, and house, and garden...) so it will take some time I'm afraid.


----------



## Filburt

amb, would you mind trying the ADA4899-1 on the Mini3. I'm curious as to how well it works for you. I wonder about the AD9631 as well, though the PSRR may be a bit too low.

 I wish there had been some way to fit single channel for the L/R on the PPAS. Would be neat to try something like the OPA655.


----------



## NelsonVandal

Filburt, I've just built a platform to try AD8099 LR and AD8045 ground. I forgot to order resistors for this as well, and I don't know when I have time to finish it. ADA4899 sure looks more interesting. Specwise it seems to be _the_ opamp for headphones. I wish I've heard about it before I ordered AD8099. If there are problems with AD8099/45, I'll go for ADA4899 (I'll probably go for it anyway sometime). Thanks for sharing the information. Have you tried it yourself?


----------



## el_matt0

if im using opa690 as my OPAG, i understand this is an un-buffered opamp, so i dont need a buffer in the BUFG position right next to it right. do i need to jumped across that pad somehow, or can it just be left empty? the jumper needs to go from pin 1 to the pin directly opposite it?


----------



## amb

Quote:


  Originally Posted by *el_matt0* /img/forum/go_quote.gif 
_if im using opa690 as my OPAG, i understand this is an un-buffered opamp, so i dont need a buffer in the BUFG position right next to it right. do i need to jumped across that pad somehow, or can it just be left empty? the jumper needs to go from pin 1 to the pin directly opposite it?_

 

I'd warn against using OPA690 in a circuit not designed to use it. This is a very wideband, fast opamp, and sensitive to capacitive loads. At the minimum you'll need a ferrite bead at its output to isolate such capacitance or the opamp could become unstable. Without proper instrumentation you may never know if it's not performing well.


----------



## el_matt0

OH.. i actually only went with it on someones recommendation here. bummer. k so ill need to buy a ferrite bead somewhere, although i have no idea where? back to the bufg, do i just run a jumper from pin 1 to the pin directly opposite it?


----------



## el_matt0

in addition to my jumper question...this concept of the ferrite bead is totally new to me. what rating should i be looking for when i buy one? and i assume since i need to put it on the opa690s output, i would have to wire each of the 8 pins with a wire rather than have the opamp directly soldered to my board (and in which case the ferrite bead goes between pin 8 and the board?)? thanks guys...darn i wish someone coulda advised me against opa690 earlier


----------



## amb

The ferrite bead would have to go in series with OPA690's output pin (pin 6), and there is no provision on the PCB for it. I can't tell you what ferrite to use because that has to be tested with appropriate instrumentation, and could vary from design to design. As I said, OPA690 is a wideband, high-speed opamps and the board and amp has to be designed for it. If you do anything but solder the opamp directly on the board, then even a short 5mm piece of wire could have enough inductance to render it unstable.

 Just give up on the OPA690 idea and use an opamp that is known to work in that circuit. If you must try OPA690, build a Mini³ v2.

 Different opamps are not as "plug and play" as many people make them out to be!


----------



## el_matt0

anyone care to suggest a good replacement for my opa690 then? using ad8066 as OPALR, and ive got 3 lmh6321 for my buffers. thanks


----------



## amb

Since you have buffers on all three channels, the opamp choice becomes less critical, especially for the ground channel. What's wrong with using a tried and true, well-behaved and excellent chip like AD8610?


----------



## el_matt0

sounds good. i ran into a bit of an ugly problem with jumpering BUFG, the pad of pin 8 (i THINK pin8, opposite pin 1), the silver contact on the PCB peeled up and off of the board. from looking at the schematic with what limited knowledge i have IM NOT sure that specific pin is necessary so its not the end of the world..but i could very well be horribly wrong..anyways whats the best course of action now..glue the pad back on or something, to solder onto? or go without...?


----------



## amb

Heed MisterX's advice and _read_ the LMH6321 datasheet... it will show you plainly what pin 8 is, and whether it matters that its pad had delaminated.


----------



## el_matt0

hm i was mistaken it was actually pin 5 that became delaminated. seeing as this is the ground...whats the best course of action i should take?


----------



## amb

You should use a small piece of (very thin gauge) jumper wire to connect the chip's pin 5 to ground. The buffer's internal current limiting circuitry would probably misbehave without the ground connection.


----------



## el_matt0

whichever ground i connect to should be fine? ie, could i just attach that pin 5 to the GOUT since thats the closest in location, or do i wanna go to VGND?


----------



## amb

Technically VGND is more correct, but I don't think it really matters. All that is required of that pin is that it be tied to a point where the voltage is halfway between V+ and V-, and GOUT is just as good.


----------



## hellomai

Quote:


  Originally Posted by *el_matt0* /img/forum/go_quote.gif 
_whichever ground i connect to should be fine? ie, could i just attach that pin 5 to the GOUT since thats the closest in location, or do i wanna go to VGND?_

 

GOUT is active ground, you need the "ground" that is relative to the V+ and V-, so you connect it to VGND.

 EDIT 1: AMB is correct, as long as the ground is 1/2 of the voltage, it should be good.

 EDIT 2: this post seems already covered the LMH6321 ground connection question. In quick summary: the GND pin does not need to be connected if current limiter is not connected.


----------



## Filburt

Quote:


  Originally Posted by *NelsonVandal* /img/forum/go_quote.gif 
_Filburt, I've just built a platform to try AD8099 LR and AD8045 ground. I forgot to order resistors for this as well, and I don't know when I have time to finish it. ADA4899 sure looks more interesting. Specwise it seems to be the opamp for headphones. I wish I've heard about it before I ordered AD8099. If there are problems with AD8099/45, I'll go for ADA4899 (I'll probably go for it anyway sometime). Thanks for sharing the information. Have you tried it yourself?_

 

Haven't tried it myself, but I'm curious as to why you think it's preferable to the AD8099; I'd have said the opposite, though the AD8099 *is* more difficult to work with. One of these days I'll get around to using both.


----------



## NelsonVandal

Quote:


  Originally Posted by *Filburt* /img/forum/go_quote.gif 
_Haven't tried it myself, but I'm curious as to why you think it's preferable to the AD8099; I'd have said the opposite, though the AD8099 *is* more difficult to work with. One of these days I'll get around to using both._

 

Even lower distortion, unity gain stability (you can use the same opamp in the ground channel), higher output current, no need for external compensation - less fiddly, claimed to drive low impedance loads, no paddle that needs to be connected to ground, less DC-offset.


----------



## NelsonVandal

Now I've finally got my shipment from Digi-Key, and I've finished my PPAS with LME49710/20 and LMH6321. Seems stable. Slightly more noise than Mini3. Only -0.7/-1.7 V DC offset. Even without burning in it sounds very sweet and very very airy. I'm going to burn in this and the Mini3 I just finished. I'll report after some burning in and listening. First impressions are really the impressions of the opamps. PPAS a bit distant smooth and airy just like LM4562 (=LME49720). Mini3 very forward and a bit harsh and grainy like AD8397.

 I've put it in a black Hammond C801 (same size as the Mini3), so it's quite small and nice looking. There's 6 AAA's and a trickle charger, and the run time should be good. It's a very tight fit and it's heavy because of the batteries.

 Oh, and I forgot I use panasonic FC before and Sanyo OS-CON after the JFET's. I wonder if it would improve by adding a larger cap. I think I could squeeze in a 1000 uF.

 I couldn't find SST502, so I use SST505 instead.


----------



## hellomai

picture here
 TLE is from Tangent's ADAPTLE kit. BUFs are LMH6321. 

 just listen to it for a while and have to pull of all the wire for casing. initial impression: definitely sound better than my X-Fi LM4562 mod. and it can be really loud!


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## NelsonVandal

Some impressions of my (not fully burnt in) PPAS with LME49720/10/LMH6321.

 What really strikes you at first are details, refinement and width. Extends very well in both directions. Very smooth, no sibilance but a tiny bit on the bright side, and the treble isn't totally neutral (more energetic than LM4562 used with discrete buffers). Overall it has more slam than LM4562/discrete buffers. My major complaint is lack of mid, a bit hollow sound. Not the same warmth, intimacy and fullness as in the best Analog or TI opamps. I think this has to do with the LME4972/10 (=LM4562) and nothing else. This is how this opamp sound in all the amps I've tried it in. I've never heard it sound better than in this amp.

 All in all this is a very good amp, easy to listen to and non-fatiguing.

 I'm going to ground the box. LM4562 is the most sensitive opamp to pick up external noise I've ever used (not only in this amp). I think I'll add a 1000 uF electrolytic. Maybe I'll add some ceramic decoupling caps too.


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## el_matt0

using the stock parts from the PPAS bom, what is the default gain of a PPAS?


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## pinkfloyd4ever

hmm good question as I'll be building one sometime too. I looked on the PPAS site & tangent's PPA site and couldn't find it either. This may help? Btw, anyone know if those discrete buffer boards ever got made?


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## dbfreak

Quote:


  Originally Posted by *el_matt0* /img/forum/go_quote.gif 
_using the stock parts from the PPAS bom, what is the default gain of a PPAS?_

 


 Don't quote me on this but I believe it's around 10. Too much for my Grados but you should check it out with Tangent's calculator.


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## FallenAngel

Hey guys,

 I just wanted to revive this thread. I'm about to build one (got my hands on a board) with AD8066 and AD825 opamps with LMH6321 buffers. I'm not one to optimize the resistors for bipolar opamps. I ordered from DigiKey so no Class-A (no SST502) but they did have MMBFJ310 (SST310 substitute).

 I will be running this off 8x AAA in a Hammond 1455C1202 case along with a trickle charger (too bad I couldn't fit it into the C802. If only the board was just a little shorter with the POT facing to the side, it would be possible to put it into the C802 with 8x AAA easily (hint hint for next revision of the board 
	

	
	
		
		

		
			





).

 Any suggestions, experience to share about this amp would be appreciated.

 Thanks


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## 04BluMach

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Hey guys,

 I just wanted to revive this thread. I'm about to build one (got my hands on a board) with AD8066 and AD825 opamps with LMH6321 buffers. I'm not one to optimize the resistors for bipolar opamps. I ordered from DigiKey so no Class-A (no SST502) but they did have MMBFJ310 (SST310 substitute).

 I will be running this off 8x AAA in a Hammond 1455C1202 case along with a trickle charger (too bad I couldn't fit it into the C802. If only the board was just a little shorter with the POT facing to the side, it would be possible to put it into the C802 with 8x AAA easily (hint hint for next revision of the board 
	

	
	
		
		

		
		
	


	




).

 Any suggestions, experience to share about this amp would be appreciated.

 Thanks_

 

The PPAS is a great performer - you will be well pleased with your build. 

 My on hand SOIC AD8620/8610 and BUF634 chips dropped into my build along with a SST502 for Class A Op. It uses the basic BOM resistor values since it is uses the baseline 8620/8610. Two 9V rechargeables Batteries really wake this portable Amp up. 
	

	
	
		
		

		
		
	


	




 For the build - follow the instructions for the order of the parts to be installed. Standard build fare lowest to highest, etc. Be patient with the SMD component installs making sure that you have each properly oriented before soldering. You really don't want to rework these if at all possible. Check your solder job on each SMD component with a Magnifier as you proceed - it will help to eliminate a lot of debug work later by maintaining quality as you build.

 Recommend you go to TANGENT's site for his SMD soldering techniques instructional videos unless you have done a lot of SMD work. Even if you have done some experience - he has very good tips (real hands on experience base) that are very useful and worth some review time.

 Enjoy....!


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## pinkfloyd4ever

.....


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## FallenAngel

Quote:


  Originally Posted by *pinkfloyd4ever* /img/forum/go_quote.gif 
_(from the first post of original PPAS build thread)

 does this still apply?_

 

Why would it not? You might be asking about the new boards by _error401_ in which case, I'm not sure


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## JCD

Kind of a mini bump..

 After 2 years (!?!) I'm FINALLY getting ready to build this thing. I'm putting my BOM from pddjsteve's list (page 12, post 169). There are a couple of parts that seem to be no longer available at Mouser: 
 JFET, Mouser part #781-SST310-E3
 CRD, Mouser part #781-SST502-E3

 I'm sure I could plow through the catalog and find something that might work, but I'm not technical enough to know what would work for sure. Can someone point me in the right direction?

 Also, Digi-Key is out of the buf634, but mouser did have it in stock -- mouser part #595-BUF634U. 

 And one final question -- is there someplace I didn't see where the merits of the different gain values of R4L and R4R are explained?

 Thanks for any help/guidance.

 JCD


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## Mullet

I'm going to have to dig this one up again... scored a PPA-S board and I'd like to find a replacement for SST502. Are there any viable replacements? or am I SOL at this point?


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## tcpoint

www.trendsetter.com has them.  Budget price of $4.73 each and if I remember correctly they kill you on shipping charges.


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## Mullet

Oooff... hehe. To run the PPA-S in Class A... that is the question. It looks like I only need two anyways and not a third for the GND channel.


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## Mullet

Just about to hit the buy button in Mouser. I was able to find 99% of the parts there with the exception of the SST502. I decided to go with the OPA2107/LM6171/LMH6321 config. Is there any reason I should choose the OPA627 instead of the LM6171? I tempted to go with the OPA627. Other than that, I've chosen to lower the R4 value to 2K in order to get a gain of 3. Also as an alt. went with 5.11K for a gain of close to 6. Is there any reason I should be changing my other values? I read up on balancing the values, but in the end Tangent mentions in his parts selection guide for the PPA to change the value for R4 to adjust gain.
  
 Finally, I'm considering adding in a PINT type trickle charger -- if I plan on using two 9v NiMH batteries what would be the most ideal AC/DC adapter to get voltage-wise that would let me keep default values for C1 and C2 -- 330uF? Or would I have no choice and have to up the values here in order to add in the charger?


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## tcpoint

I'd go with the AD8620 and AD8610 combo.  I was hesitant to try it with my Pimeta but I really liked it.  It will be hard to get the opa627 to work.  There's no opa2627 that I know of.


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## Mullet

The reason I'm swaying towards the OPA2107/LM6171 instead of the AD8620/AD8610 is because people have complained that the 8620 combo to be a bit more harsh in the highs. Other than that if the OPA2107/LM6171 combo is for the most part a drop in replacement I'd go with that. The only reason I brought up the OP627 is because a few people mentioned they used it with success and they thought it sounded better than the LM6171 for the GND channel position.


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