# which diamond buffer to build for pimeta?



## Soymilk

i'm currently looking at which db to build for my pimeta that i'm planning, and i'm trying to figure out more about my options. through searching, i've found these:

 dDB - the millet hybrid db, is it a waste / too expensive to build in a pimeta?

 sijosae db - small

 monofied sijosae db - better than sijosae db?

 qrv05 - has a pcb available for sale, which is a plus i guess, also kinda big


 are there others? space isn't really an issue here, since this is going to be a home use pimeta. i'm putting db's in all 3 buffer positions. also, what does CCS stand for? i saw it used multiple times when talking about db's, but nothing ever said what it meant.


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## heatmizer

Have seen people use the qrvo5
 Tried the sijosae and the monofied stayed with the monofied
 ended up using a monofied with bd139 and bd140 on output and bc337 and bc327 on input biased to 20 ma. This is not portable. The sijosae and the monofied are both portable.
 Any reason you don't want to use the buf634p?


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## bhjazz

For ease of troubleshooting, you should start with the Buf634's, or at least borrow a set from another build. Get your Pimeta working correctly first, then do the upgrade. 

 The dDB does work. Search this forum for a thread by n_maher. As stated there, though, YMMV. He did say the sound was quite amazing.


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## n_maher

The Millett DB's, at about $35 to build (including the pcb), are a definite improvement over the single buf634's. I honestly didn't compare them to stacked buffers but some have and said that they're closer than single buffers if not indistinguishable. Also, there is the careful fact to consider that if you use the millett db boards you'll have to both cut them in half (carefully) and also off-board mount your pot to get it all to fit. Not the easiest bit of casework but doable. 







 EDIT - CCS stands for constant current source.

 EDIT2 - I would not use a DB in the ground channel, that position on the PIMETA pcb if very tight and you'll really be fighting yourself if you do this. If your desire is to have a discrete output stage on each channel just build a PPA V2 and be done with it.


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## Soymilk

Quote:


  Originally Posted by *heatmizer* /img/forum/go_quote.gif 
_Have seen people use the qrvo5
 Tried the sijosae and the monofied stayed with the monofied
 ended up using a monofied with bd139 and bd140 on output and bc337 and bc327 on input biased to 20 ma. This is not portable. The sijosae and the monofied are both portable.
 Any reason you don't want to use the buf634p?_

 

wait, so the monofied is portable, but your monified isn't? i want to build discrete buffers since it's around the same or cheaper than buf634 and should sound better.

  Quote:


  Originally Posted by *n_maher* /img/forum/go_quote.gif 
_The Millett DB's, at about $35 to build (including the pcb), are a definite improvement over the single buf634's. I honestly didn't compare them to stacked buffers but some have and said that they're closer than single buffers if not indistinguishable. Also, there is the careful fact to consider that if you use the millett db boards you'll have to both cut them in half (carefully) and also off-board mount your pot to get it all to fit. Not the easiest bit of casework but doable. 

 I would not use a DB in the ground channel, that position on the PIMETA pcb if very tight and you'll really be fighting yourself if you do this._

 

is it ~$35 to build populate one board, which you then cut in half and use as two buffers? also, would it be bad to have my buffers off board and have wires run between them and the board?



 i forgot to ask this in my original post, too: which would be better for wiring stuff with, 24 gauge stranded spc, or 30 gauge solid core spc? edit - both teflon insulated


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## n_maher

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_is it ~$35 to build populate one board, which you then cut in half and use as two buffers?_

 

Depending on where you are in the world (access to parts) and what parts you choose $35 should get it done pretty easily. However, if you don't already have a PCB finding one could be kind of tough. They went out of production about a year ago.

  Quote:


 also, would it be bad to have my buffers off board and have wires run between them and the board? 
 

Yes, in my opinion this would be a bad idea. It might work, it might cause problems, I tend to be a bit conservative with things that can cook themselves.

  Quote:


 i forgot to ask this in my original post, too: which would be better for wiring stuff with, 24 gauge stranded spc, or 30 gauge solid core spc? edit - both teflon insulated 
 

Either is find, if you can hear a difference between stranded and solid or different gages your ears are way better than mine.


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## Soymilk

hmm... well, as long as there isn't one that's vastly superior or inferior to the rest, i think i'll just go for the one that's easiest to acquire parts for / build. currently looks like the qrv05 is the easiest since it has a pcb available for purchase; i'll have to look at the parts lists for the sijosae, modified sijosae, and qrv05 to see if any of them have hard to find parts.

 also, the sijosae and monofied sijosae db's just have a schematic available, and you use that to build it on a perf board, right?


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## slowpogo

Soymilk, check out this thread where I posted a ton of info about using the QRV05 in PIMETA:

http://www.head-fi.org/forums/showth...ighlight=qrv05

 Maybe you'd have better luck finding the specified resistors, but I ended up ordering my parts from ELFA, a European company--and paid about $20 shipping. The parts themselves cost around $25. Good luck if you go with these, they sound great, a definite improvement over stacked 634Ps (in my opinion).


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## Pars

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_hmm... well, as long as there isn't one that's vastly superior or inferior to the rest, i think i'll just go for the one that's easiest to acquire parts for / build. currently looks like the qrv05 is the easiest since it has a pcb available for purchase; i'll have to look at the parts lists for the sijosae, modified sijosae, and qrv05 to see if any of them have hard to find parts.

 also, the sijosae and monofied sijosae db's just have a schematic available, and you use that to build it on a perf board, right?_

 

You could build it on perfboard. Mono has a board pattern available to home etch boards for his. I've used these and prefer them to BUF634s in WB mode, including stacked. I probably have the board pattern around if you can't find it from Mono. These boards are small (around 1/2" or 12mm square) and fit the Pimeta quite nicely. I have a Browndog single opamp 8-pin DIP to dual opamp DIP adapter for a pair of AD744s and this will fit with the mono buffers.


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## heatmizer

This one i believe:


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## Soymilk

thanks for the responses. wow, that looks really straight forward (monofied image heatmizer provided), should be easy enough to perf board it. making sure though: the ones labeled JFET in that image are the 2N5486, right? also, with discrete buffers, i dont need the resistors for biasing the buffers anymore, but i still want the JFETs for class-A biasing of the opamps, right?

 just curious, has anyone compared a triple diamond buffer pimeta with a ppa? either way i'll probably still build the pimeta so that i have a longer upgrade path to follow and keep me busy if i continue with this hobby 
	

	
	
		
		

		
		
	


	




 edit - the qrv05 db looks like it's a lot bigger / more complicated than the monofied sijosae buffer. why is that? here's the image i'm talking about (slowpogo's pimeta, qrv05 for l/r, buf634 ground)

 note: the electrolytic caps aren't called for by the original bom, but slowpogo says it sounds much better with those instead of the smd's called for.






 the monofied can fit on a 6x6 square of perf board. compared to that, the qrv05 is huge! does it offer anything extra?


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## tomb

Discrete buffers are like little amplifiers all their own. Amb/Steinchen's Jisbos buffer is one such case, literally. Most are made to work as an output stage in conjunction with a signal gain stage. Since they are tasked with directly driving the load, they sometimes need to handle prodigious amounts of current or slew wide swings in voltage. Often, their size and complexity is directly related to how much of either of those quantities they can manage.


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## Zigis

I can't find 2N5486 on elfa.se and distrelrc.com, are there replacement JFETs ?


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## balou

Zigis: yes, just use a JFET which has Idss current of about 2.7mA. A bit higher Idss should not be a problem (except if you want to battery power it, then the battery just won't hold as long)


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## Soymilk

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_Discrete buffers are like little amplifiers all their own. Amb/Steinchen's Jisbos buffer is one such case, literally. Most are made to work as an output stage in conjunction with a signal gain stage. Since they are tasked with directly driving the load, they sometimes need to handle prodigious amounts of current or slew wide swings in voltage. Often, their size and complexity is directly related to how much of either of those quantities they can manage._

 

i still don't quite understand the difference. would that make the more complex ones better overall, or would they just be able to handle a worst case scenario better?


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## tomb

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_i still don't quite understand the difference. would that make the more complex ones better overall, or would they just be able to handle a worst case scenario better?_

 

"Prodigious amounts of current and slewing wide swings in voltage" does not refer to a worst case. The comparison among buffers is analogous to comparing a Yugo that may still be able to get you to and from work - but not much more vs. the finest-tuned, highest performance Ferrari - that will run fast, turn fast, and respond to every single touch, while cruising effortlessly at speeds that would make the Yugo croak.

 One is obviously more complex than the other. Which would you want - given a choice, of course?


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## Soymilk

ah, that makes more sense now. so you would recommend the qrv05 over the monofied sijosae?

 hmm... i think what i'll end up doing is first building the monofied sijosae, and then if i feel the need to upgrade around winter break i'll upgrade to the qrv05 to have something to do over break 
	

	
	
		
		

		
			





 for now though the monofied sijosae is looking much more appealing due to how easy it looks to make.


 still wondering: has anyone compared a triple db'd pimeta with a ppav2?


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## tomb

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_ah, that makes more sense now. so you would recommend the qrv05 over the monofied sijosae?

 hmm... i think what i'll end up doing is first building the monofied sijosae, and then if i feel the need to upgrade around winter break i'll upgrade to the qrv05 to have something to do over break 
	

	
	
		
		

		
		
	


	




 for now though the monofied sijosae is looking much more appealing due to how easy it looks to make._

 

That sounds like a sensible strategy. The "Monofied Sijosae" is like any successful item: it was designed to meet certain goals and constraints - not the least of which was to fit in the same footprint as a DIP-8 socket. However, it can't compete on an equivalent basis with a DB such as those shown in N_Maher's post. Those are paralleled output power transistors that can withstand quite a bit of current, plus a lot more if given a rudimentary form of heat sinks. Further, the DB's have a trimmer, which means you can fine tune them for the very best in performance, regardless of parts variances or other conditions.

 I am not personally familiar with the qrv05, but with that many chips and those caps, it's bound to handle more than the monofied. That said, the monofied is probably fairly easy to build by comparison, is cheap, and there won't be any worries about fitting it on the board - or even making it work, period. Plus, it probably still sounds better than the basic BUF634. So again, there are certain design conditions that are met much better with the monofied.


  Quote:


 still wondering: has anyone compared a triple db'd pimeta with a ppav2? 
 

I understand your question, but at some point it becomes like asking whether anyone has built a B22'd M3. You've passed the point of diminishing returns long before reaching that point and you should just go ahead and build the more sophisticated amp.


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## n_maher

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_still wondering: has anyone compared a triple db'd pimeta with a ppav2?_

 

Similarly equipped they'll be close, but then again they'd cost about the same to build with the PPA actually probably being easier to manage and offering more future flexibility. The PPA circuit has additional advantages over the PIMETA, even if you add a discrete output to the PIMETA. And again, I'd remind you that DB'ing the ground channel of the PIMETA will be even more work than the L/R channels given the extreme space constraints of that area of the PCB. Floating buffers are not attractive to me at all.

 It is also worth noting, since this sounds like you haven't build all that many projects, that both the PPA and anything with a discrete buffer are going to be seriously difficult to trouble shoot if something goes wrong. Not trying to be a downer, only guard against major disappointments. Finally you should remember that just because you're replacing an IC with some discrete components doesn't mean that it's going to sound better. The BUF634 run in wide bandwidth mode and also paralleled is more than decent sounding.


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## Soymilk

i wanted to build discrete buffers since they should be cheaper than the buf634. the monofied sijosae buffer can be dropped into the socket, so there shouldn't be any floating buffers.

 i have considered building a ppa instead of the pimeta though, still kind of debating whether or not i should do it. the ppav2 already has discrete buffers, right? tomb, would the jameco wall wart that you recommend be enough to power a ppa as well?


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## tomb

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_i wanted to build discrete buffers since they should be cheaper than the buf634. the monofied sijosae buffer can be dropped into the socket, so there shouldn't be any floating buffers.

 i have considered building a ppa instead of the pimeta though, still kind of debating whether or not i should do it. the ppav2 already has discrete buffers, right?_

 

A fully-discrete output stage is the differentiating component of _V2_. 
  Quote:


 tomb, would the jameco wall wart that you recommend be enough to power a ppa as well? 
 

No, the PPAV2 is much too detailed and more powerful than the PIMETA. You wouldn't be doing it justice to not use at least a TREAD or perhaps a STEPS. Note that the TREAD is one of the best deals going - cheap, super easy to build, and only requires the most basic AC-AC walwart - highly recommended.

 IMHO, the PIMETA is about the limit for the packaged, linear regulated Jameco walwart.


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## NelsonVandal

I finally added CCS (single JFET's) to my "somewhat monofied" buffers. The bias is set to 2 mA because of need for portability. Input transistors = BC327/337 and output transistors = BD137/138. I've come to the same conclusion as Heatmizer. CCS's make them sound better - deeper, wider, better soundstage. BD's sound more neutral than BC's and have a better bass impact. BC's are a little too bright as output transistors for my taste. It's a bit trickier to make the buffers small using TO220 transistors like the BD's. Even though there are 6 transistors and 6 resistors (I use emitter/output resistors), I can make them 5x5 "holes".

 LMH6321 is a strong contender if you don't want all this fiddling. I just finished my PPAS with LME49710/20's as input opamps and LMH's as buffers. The ground buffer was fried from earlier experiments, so it's only the LME in ground at the moment. Sounds great. Detailed and powerful. Not as neutral as the discrete buffers, but very nice.


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## Soymilk

Quote:


  Originally Posted by *tomb* /img/forum/go_quote.gif 
_A fully-discrete output stage is the differentiating component of V2. 
 No, the PPAV2 is much too detailed and more powerful than the PIMETA. You wouldn't be doing it justice to not use at least a TREAD or perhaps a STEPS. Note that the TREAD is one of the best deals going - cheap, super easy to build, and only requires the most basic AC-AC walwart - highly recommended.

 IMHO, the PIMETA is about the limit for the packaged, linear regulated Jameco walwart._

 

that's what i thought (from reading on tangent's site), just wanted to make sure. i guess i'll make a TREAD, too. just checking: did you mean AC-DC walwart, or does the TREAD take care of converting from AC to DC? i thought it was the regulator for making sure it puts out even power. also, what wall wart would be good to use with the TREAD?

 i decided i'm just going to bite the bullet and go with the ppav2 instead of the pimeta. my boss also expressed some interest, since he'd seen the designs before, so he wants me to build it and bring it in to see how it does with better testing equipment (audio precision stations up to 120dB sensitivity, i think tangent's benchmarks only go up to 100). i'll be sure to post the results whenever i get done with it (expect at least two weeks 
	

	
	
		
		

		
		
	


	




)


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## FallenAngel

Hey guys,

 I'm thinking of building another Pimeta with some discrete buffers and wanted to double check the schematics and layouts by you guys.

 I don't have an input resistor like heatmizer showed at the beginning, I can probably add one if it's necessary so the opamp doesn't drive the buffer directly.

 Sijosae Class-AB 








 Class-A








 This Class-A buffer would run 22mA of current as per the formula. Output current = CCS * (Input resistors / Output resistors).


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## amb

FallenAngel, in the first circuit, the two input biasing transistors are wired as diodes. The original Sijosae circuit used identical transistors for the output devices to take advantage of the same Vbe characteristics between the biasing devices and output transistors. Since you are using different output devices then that advantage is lost, and you may experience crossover distortion because there is nothing to allow you to trim the bias.


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## FallenAngel

Thanks _amb_, I'll stick with BC327/BC337 for the first circuit. Is there anything that seems off about the second schematic and layout? Would I need to use an input resistor so that the opamp doesn't drive the buffer directly?

 One more question. Is there any reason why I shouldn't use 2N5087/2N5088 for this? I have 100' of those around and will be needing to order the BC327/BC337.


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## amb

An input resistor is a good idea (to avoid parasitic oscillations).

 There is nothing magical about BC327/337 in these circuits. You can substitute with 2N5087/5088 or many other types and they will work fine. In the first circuit, the choice of transistor will ultimately limit the amount of output current.


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## Negatron

Quote:


  Originally Posted by *Soymilk* /img/forum/go_quote.gif 
_i wanted to build discrete buffers since they should be cheaper than the buf634. the monofied sijosae buffer can be dropped into the socket, so there shouldn't be any floating buffers.

 i have considered building a ppa instead of the pimeta though, still kind of debating whether or not i should do it. the ppav2 already has discrete buffers, right? tomb, would the jameco wall wart that you recommend be enough to power a ppa as well?_

 

I realize the question re: the wallwart was addressed to tomB but I seem to have missed his post so excuse my presumption, but the Jameco 174845 24v 1A may serve.
Jameco Electronics Power Supplies & Wall Adapters: JAMECO RELIAPRO: HTD24-1000

 It has a substantial transformer and the trans is held captive by the case & thick rubber sticky tape and can be moved back far enough to fir in a TREAD with a good size Panasonic FC cap. With that simple mod it becomes a very respectable wallwart. I'm very pleased with one I use with the Fubar DAC.

 Edit: It also runs an Millett revMH very well indeed.
 ..saw tomb's post, going screen blind.


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## peranders

A way to make the footprint smaller is to have one or more standing very thin pcb's soldered into a main pcb. The volume of a TO92 is huge compared to a SOT23.


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## mono

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Thanks amb, I'll stick with BC327/BC337 for the first circuit. 

 One more question. Is there any reason why I shouldn't use 2N5087/2N5088 for this? I have 100' of those around and will be needing to order the BC327/BC337._

 

When I made more of mine I found the general trend was higher current capable transistors drifted from bright to balanced. 2N5087/5088 significantly too bright, BC327/337 a little bright (depends on the cans), BD139/140 more balanced but sometimes it seemed a little uninteresting. I also ended up biasing the BD139/140 buffers a bit more, might've been around 6mA CCS. It was handy that I'd used 2N5486 with it's higher IDSS in that case rather than 2N5484. I think I finally settled for around 4mA CCS with BC327/337 as sounding a little better than 2.7mA, but of course at the cost of runtime on battery power.

 My choice to stick with BC327/337 was due to higher than average current capability for a TO92 sized transistor. BD139/140 was too tall if I wanted it to fit in a Serpac H65 case. Come to think of it, I never did end up putting my Pimeta with monofied Sijosae buffers into an H65 but I _assume_ I had measured and determined that with the TO-92 transistor leads bent enough to get them far enough down into the PCB, it would fit.

 It should be noted that after I put those into a Pimeta I ended up putting current limiting resistors in the L & R "R8" positions. They might've been 4.7Ohm or thereabouts.


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## joneeboi

What would be the bit opposite the BC337 and BC327? I'm guessing it's another BC337 and BC327, respectively, but I just want to make sure.


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## Pars

Yes, 337 on the top and 327 bottom.


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## joneeboi

Since I have some 2N5087 and 2N5088 lying around, I'm thinking of building of with those instead of the BC327 and BC337. Anything I should know before I fry my dad's PIMETA?


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## Pars

check the pinout...


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## joneeboi

I just built it with the 2N5087 and 2N5088. I didn't have exact resistors though, but I think they were close; 6.5R and 3.32K. The first one I made didn't drop in, so I built a second to make sure. The layout is the same, with compensation for the reverse pinout of the 2N5087 relative the BC327 and the 2N5088 the BC337. It's not playing anything, so maybe you guys can help me out a bit. Is there some kind of balancing act I need to perform with the hfe to get things to work?

 edit: If it helps, checking the offset on the discrete buffered channel shows that the DC level grows in magnitude, where the output is negative relative the input ground.


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## heatmizer

Pictures please. Where is it plugged into the socket?


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## Pars

Do you have V+ and V- on the right pins (7 and 4 in the socket)? Does it measure OK?


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## joneeboi

Quote:


  Originally Posted by *heatmizer* /img/forum/go_quote.gif 
_Pictures please. Where is it plugged into the socket?_

 

Yes, I plugged them into the wrong socket positions. Always check the datasheet. u_u Oh well, now I'm enjoying the PIMETA without making a $30 order to Digikey that wouldn't happen because of the stock issue. Huzzah!


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## FallenAngel

Hey guys,

 I'm building one of these buffers with a 2N5486 + 1K Trimpot CCS and was wandering how do I set the current flow through the CCS? I want 3mA through it. What voltage through the resistor am I looking for for it to be so?


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## TzeYang

you cant calculate it this way.

 Think of the idss spread like the hfe spread in bipolar transistors. They vary alot. So the thing is to measure the current flow and tune it with the trimpot. Normally it's very hard to do so, which is why we alternatively, tune the bias using the trimpots of each half of the circuit respectively. (you must get equal bias for each of the output transistors).


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## Spacehead

Quote:


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

 I'm thinking of building another Pimeta with some discrete buffers and wanted to double check the schematics and layouts by you guys.

 I don't have an input resistor like heatmizer showed at the beginning, I can probably add one if it's necessary so the opamp doesn't drive the buffer directly.

 Class-A








 This Class-A buffer would run 22mA of current as per the formula. Output current = CCS * (Input resistors / Output resistors)._

 

Your Class-A buffer seems to be working. I used 1K constant current resistors, or even smaller, I should check it out and do another. I only have one yet. I used 2SK117 JFETs so I had to improvise a little. Thanks!!


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## FallenAngel

Nice, glad you got it working. I never managed to complete this one unfortunately.


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## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Nice, glad you got it working. I never managed to complete this one unfortunately._

 

I used 300 ohm resistors instead of 1K trimpot, 75 ohm resistors input, 2SK117, and 2.8 ohm emitter resistors on BD139 and BD140. 

 But now I hear distortions, like it would be running out of current. Class AB Buffer works flawlessly in the same spot. I buffer left and right channels on a cmoy core. 

 What resistor value would you suggest changing? I could try if I need 200 ohm resistor in between buffer and op amp. Now I have only bare wire. Buffers are not warm so I guess they are not oscillating, though distortion means there is a problem. 





 protoboard fun


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## Spacehead

I tried 620 ohm resistors instead of 1K trimpot which I don't have, then I tried 200 ohm, 

 then instead of 75 ohm I tried 29 ohm, I also tried 2.9 ohm emitter resistors

 But NO GO! I just cannot get that distortion free.

 I have 2SK117 JFET which is rated for 6 mA IDSS , that should be enough for biasing...

 I don't understand how I could make that circuit working like it should. Now it gives bad distortions into bass. 

 I got mad to that and abandonded it, I put single ended BJT BD139 instead with 82 ohm emitter resistor (91 mA bias). Now I have bass but somehow boring sound and too easy.


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## hiker101

That buffer is meant to be wrapped in a global feedback loop- that's why it's suggested as an option for the PiMeta. It's not clear how your circuit is set up in that regard.

 It's also not clear what you're doing about the ground, maybe that's the part of the circuit that's current starved. You said you had another class AB buffer working in the same circuit- was it a discrete buffer, or something else?


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## Spacehead

Quote:


  Originally Posted by *hiker101* /img/forum/go_quote.gif 
_That buffer is meant to be wrapped in a global feedback loop- that's why it's suggested as an option for the PiMeta. It's not clear how your circuit is set up in that regard.

 It's also not clear what you're doing about the ground, maybe that's the part of the circuit that's current starved. You said you had another class AB buffer working in the same circuit- was it a discrete buffer, or something else?_

 

ground is buffered with OPA633, it has plenty of current capability. Sijosae Class AB discrete buffer (bc337&bc327) works very well in this circuit, which is Cmoy style, and buffers are inside feedback loop (wire is as short as possible)

 I am trying to study Walt Jungs Diamond buffer article http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_2.pdf

 My "input" resistors are now 10.9 ohm , emitter resistors 3.8 ohm, constant current resistors 620 ohm 
 between op amp and buffers there is 200 ohm resistor. I have decoupled buffers with 100 uF capacitor rail-to-rail. 
 I tried and added red leds to BD139 and BD140 base and another end to output, it didn't help. 
 What disturbs me most, is that BD139 and BD140 don't get warm at all. They are actually cold. I wonder if it would help to lower that current source resistor again to 200 ohm. But ?! hmm, could the JFETS (I used 2SK117) limit the current ?! If removing them would release the circuit so that there would be enough current for 32 ohm headphones (40-100 mA)?


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## FallenAngel

Not sure why you want to limit current there, you're essentially just setting CSS ("constant current" for Class-A operation), more will be drawn if needed in Class-AB.


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## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Not sure why you want to limit current there, you're essentially just setting CSS ("constant current" for Class-A operation), more will be drawn if needed in Class-AB._

 

I just wonder why at 7.5V rail voltage the buffer doesn't work properly, gives distortions to bass. Then at 10V one of the smaller chips, usually BC337 goes to thermal runaway and heats up until burn out. 
 It isn't stable then?


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## FallenAngel

Hmm... could be an issue with implementation?


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## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Hmm... could be an issue with implementation?_

 

have you checked in simulation its frequency response?


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## FallenAngel

Unfortunately, no, that's too techie for me.


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## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Hmm... could be an issue with implementation?_

 

I couldn't find any problems. 






 Then I built that. It works, but isn't as strong as Sijosae Class AB buffer. 

 All these lose to single Class A BJT or Mosfet. 

 I am trying to learn what controls the bias of transistor, but very little has come clear to me.


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## cobaltmute

To my understanding, the bias of the output stage is controlled by the CCS (JFET + resistor).


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## Spacehead

Quote:


  Originally Posted by *cobaltmute* /img/forum/go_quote.gif 
_To my understanding, the bias of the output stage is controlled by the CCS (JFET + resistor)._

 

I just cannot get output transistors warm. I have tried many source resistors, 3K, which was worse than 620 ohm, 200 ohm, 80 ohm, 50 ohm, 470 ohm. None worked without distortions in bass. Transistors got hot when I connected gate directly to source on 2SK117 JFET but it also gave out distortions. 

 I cannot get it working. You try it!


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## Spacehead

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_



_

 

I did two of those for stereo. I used smaller resistors R2, R5 = 100 ohm, R3,R4 = 4.7 ohm, R6,R7= 3.3 ohm and changed Q3,Q4 to BD139,BD140

 It took 2.5 hours. 

 First I had input and output shorted on other, and one BC327 burnt out. No more problems after changing that and clearing the short. 






 Those look cool and they run (too) cool





 In Walt Jung´s article http://waltjung.org/PDFs/WTnT_Op_Amp_Audio_2.pdf
 R4 and R7 ratio is 2X , mine is now 1.42X
 I don't know if want to bother with that, I don't have 2 ohm resistors and there isn't room for two, except underside. 

 These sound good and they are almost identical, transistors are matched.


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## FallenAngel

Very cool, congrats.

 So... which buffer do you like most?


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## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_Very cool, congrats.

 So... which buffer do you like most?_

 

Thanks
 This new one is absolutely best. Best bang for the buck is for sure basic Sijosae Class AB BUF634, it has clear sound and can deliver good currents for proper bass. Soundstage is definitely best on this diamond buffer. Sijosae BUF634 Diamond Buffer is third of these, it is slightly weaker. Then I have tried single mosfet and single bjt (Poor Man's Class A BUF634 - ÒôÏìDIYÂÛÌ³ - HIFIDIYÂÛÌ³ - Powered by Discuz! They are strong but lifeless. OPA633 is a diamond buffer too, but sounds too much like op amp, and like OPA2132 which I don't like. I couldn't yet get your diamond buffer working, maybe 75 ohm resistor needs to be 20 ohm, cool idea though using those CCS JFETs. 
 These buffers don't color sound that much as op amps so it is difficult to distinguish differences. Now I have AD8022 on my X-FI and AD8620 on this amplifier. That means very neutral sound. 
 I haven't tried Monofied Sijosae BUF634 yet, if I would get your thing working it would be it.

 Now I am afraid that again one BC327 would get burn out, when I was having a nap other buffer had gone dark, fortunately there was no DC offset. I fixed that again and changed both input transistors, I hope it stays good now. It is PITA changing transistors and trying to figure out where there is a short if there even is. Transistors can come bad from factory, too? BTW. when transistors are pretty closely matched, DC offset is 00.00 mV under op amp feedback loop 
	

	
	
		
		

		
		
	


	




 Edit:
 I had forgotten to isolate the dip8 socket from the protoboard so I guess it was shorting that transistor. I noticed that when I had trouble getting a good connection, leds didn't light up even I pressed it hard. I hope that electricity tape solves that problem and I would have a reliable and powerful diamond buffer.

 Edit2:
 As Suggested by Walt Jung I bypassed the buffers with 470 uF capacitors. Now leds are even colored and bass response is like it should be. I am quite happy to those buffers.


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## Spacehead

Quote:


  Originally Posted by *joneeboi* /img/forum/go_quote.gif 
_



_

 

Then I tried that, but with diodes and BD139/BD140, 2SK117, 620 ohm source resistors, and emitter 4.7 ohm. I omitted 220 ohm resistor as that is in my circuit already. Didn't work, distorted. Maybe some problems with shorts as I used old piece of protoboard (the one with FallenAngel's diamond buffer). I hate to do things that don't work. It feels bad.


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## FallenAngel

Want to try to build one of these?
discrete Diamond Buffer - Design


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## Spacehead

Quote:


  Originally Posted by *FallenAngel* /img/forum/go_quote.gif 
_





 Want to try to build one of these?
discrete Diamond Buffer - Design_

 

I would love to try it, but I am missing all those transistors. I am getting 2N5486 next week though and maybe I order 2N5088/87. MJE243/MJE253 can be replaced with BD139/BD140 I guess. 

 That Walt Jung buffer ran out of current with my 32 ohm Sennheiser HD438. It distorted at high volume much easier than pure class A BD139. 
 That is kind of weird because it has BD140 driving the load too. Again I don't understand enough to calculate maximum safe resistors values. Optimal would be if BD139/BD140 would dissipate about 1W in free air, then bias would be right. 
 Now these class A BD139 Poor Man's Class A BUF634 - ÒôÏìDIYÂÛÌ³ - HIFIDIYÂÛÌ³ - Powered by Discuz! have 82 ohm emitter resistor, which means (ohm's law&power) 1.21W dissipation. And they don't yet need heatsink. 

 I am getting PPA V.2 PCB next week too. It has a nice diamond buffer. But largest task is getting all the parts for it. Do you have any spares you could share? It is my first PCB project


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## FallenAngel

2N5486 you'll need, but any with similar Idss will work.
 2N5087/2N5088 can be replaced with BC327/BC337 and MJE243/MJE253 with BD139/BD140, but remember different pinout.

 The PPAv2 actually has basically the same buffer as the one I just linked. 
	

	
	
		
		

		
			




 As for parts, they should all available from one common distributor, such as Newark.


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## Spacehead

Spacehead;6469608
 R4 and R7 ratio is 2X  said:
			
		

> Oh I fixed that, added 4.7 ohm parallel with 3.3 ohm, got 2.35 ohm which is exactly 1:2 of 4.7 ohm.
> That fixed the strength of this buffer, now there is no distortions in bass even at higher volumes. Sounds better than single BD139.
> 
> Little silly that I have biased my op amp so hard, that it gets warm to touch. But no worries, I have a fan directed towards my amplifier. Now listening to AD8066 which is excellent op amp. Smooth strong bass with almost BB-style "lazyness" with accurate AD soundstage imaging.
> ...


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