# Anyone built Sijosae's class AB amp ?



## ozshadow

How does it sound ?

 What opamp was used and how was it powered ?

 This one : http://69.36.189.159/usr_1034/audio/SimpleAB.gif


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## Blind Tree Frog

Power looks to be batteries or wall power. 2 9 volts would probably work well enough.


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## ozshadow

I either want to build this next, or a Pimeta. It'll take me a while for either, but I want to start one.


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## barkas

Looks nicely compact and easy to get components.


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## ATAT

Oz - pimeta will be easier because of the PCB, doing something on perfoboard isn't a very fun experience..


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## Tedro

Quote:


  Originally Posted by *ATAT* 
_Oz - pimeta will be easier because of the PCB, doing something on perfoboard isn't a very fun experience.._

 

edit: so MUCH fun!!


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## thedoctor

sounds much better than a CMOY, resembling a MINT, with a diamond buffer output stage. in fact, i like the diamond buffer used in the sijosae Class AB rather than the simplified diamond buffer used in the few new designs surfacing this few days.

 small enough to be fitted into a MINT tin, yet the donutboard might not be favorable to everyone.













 ^ with an integrated TREAD. the circuit is smaller if should you skip the TREAD implementation.


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## Polaris111688

The components are so densely packed.. I like it!


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## barkas

I'll probably build one.

 I already did eagle boards for power and amp, a lot less dense, but also a lot more clean, if somebody is interested, I'll post them.


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## ozshadow

I want to know how they sound compared to a Pimeta.


 I'll be using with Grados


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## thedoctor

Quote:


  Originally Posted by *ozshadow* 
_I want to know how they sound compared to a Pimeta.
 I'll be using with Grados_

 

different taste for different application. the Class AB is meant to be a portable solution. the PIMETA isn't. them 3 channels with BUF634s will suck the battery dry in a few hours.

 and good luck trying to fit a PIMETA into a MINT tin. SMD versions don't count.


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## ATAT

Quote:


  Originally Posted by *thedoctor* 
_different taste for different application. the Class AB is meant to be a portable solution. the PIMETA isn't. them 3 channels with BUF634s will suck the battery dry in a few hours.

 and good luck trying to fit a PIMETA into a MINT tin. SMD versions don't count._

 












 *grin*

 that grinning aside, Class AB is quite a nice way to get long battery life and that design looks nice.. Id probably say its better than a MINT, worse than PIMETA, or any of the buffered ground designs (i mean 3 channel). 

 But BUF634 running in low current mode will draw less than a class-AB IIRC...

 Also thedoctor, how is sijosae's a diamond buffer? its just a push pull current mirror .. I fail to see how this is a diamond buffer...


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## amb

Quote:


  Originally Posted by *ATAT* 
_Also thedoctor, how is sijosae's a diamond buffer? its just a push pull current mirror .. I fail to see how this is a diamond buffer..._

 

It's not a diamond buffer. It doesn't have any current mirrors, either. Don't let the schematic confuse you. If it had current mirrors the transistors' C and E junctions would have to be reversed... The two transistors on the input side are used merely as diodes (with the C-B junction shorted) to bias the output transistors, which are set up as a simple push-pull emitter follower.

 Btw, the virtual ground in this circuit is an open-loop buffer and has no opamp driving it and no negative feedback, so its output impedance is going to be a bit high. This means that the virtual ground potential will be modulated by the current it has to source and sink, and thus stereo crosstalk will be poor (built-in cross-feed!).


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## barkas

What if I drove the ground like the L/R channels using a uA741 and 2x220kOhm as rail divider as input for the uA741?
 That would probably get a lot lower ground impedance.


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## guzzler

Quote:


  Originally Posted by *barkas* 
_What if I drove the ground like the L/R channels using a uA741 and 2x220kOhm as rail divider as input for the uA741?
 That would probably get a lot lower ground impedance._

 

The rated output current for a 741 is only 25mA, ie, only 5mA greater than a TLE2426. You could use a OPA551 like amb used in his muting circuit: that's got a few hundred mA output


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## thedoctor

Quote:


  Originally Posted by *ATAT* 
_












 *grin*

 that grinning aside, Class AB is quite a nice way to get long battery life and that design looks nice.. Id probably say its better than a MINT, worse than PIMETA, or any of the buffered ground designs (i mean 3 channel). 

 But BUF634 running in low current mode will draw less than a class-AB IIRC...

 Also thedoctor, how is sijosae's a diamond buffer? its just a push pull current mirror .. I fail to see how this is a diamond buffer..._

 

ah, sorry for the mistake. it's a push pull config. though from testing (with my ears), i kindda prefer that more to this :


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## amb

Quote:


  Originally Posted by *barkas* 
_What if I drove the ground like the L/R channels using a uA741 and 2x220kOhm as rail divider as input for the uA741?
 That would probably get a lot lower ground impedance._

 

Yes, if you build the virtual ground to look just like the L & R channels, except wire the input to a resistor divider, then it would work well. However, the 741 is a nasty opamp for audio. If you're going to go through all that trouble, why not use something a little better?


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## barkas

Because I have 5 uA741 here 
	

	
	
		
		

		
		
	


	




 .

 However you are right. I should use a better opamp and I will have to mail order new photo boards for the new circuit so I may as well invest in another opa2132, or whatever good opamp I find that is not expensive.

 EDIT: I would have to wire the feedback loop not through a 10kOhm and a 5k to earth, but directly back into the opamp without any resistors, right?


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## Andrea

The OPA132 or OPA134 should be good for this purpose since they have good output current, and especially a very low output impedance. I'd look at the OPA227 too, and certainly the formerly suggested OPA551 that is powerful beyond necessity, if with unknown output impedance (I couldn't find it in the datasheet 
	

	
	
		
		

		
		
	


	




 )


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## ATAT

Whoops. My bad.. definately not a current mirror.

 Swapping the 3k resistor for a CRD will give better results IIRC.


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## barkas

If I use a push pull current amplifier behind the opamp, it does not matter one bit, what current the opamp can output, so I may as well use an opa2132.


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## Pars

Quote:


  Originally Posted by *ATAT* 
_Whoops. My bad.. definately not a current mirror.

 Swapping the 3k resistor for a CRD will give better results IIRC._

 

Do a search here for a BUF634 thread about 6 months ago where this was discussed quite a bit. Mono did a laout of a modified Sijosae buffer with FETs configured as current sources (IIRC). His layout was pin compatible with a BUF634... I've built some of these for a Pimeta and like them so far... better than the BUF634 with 221 ohm BW resistors to my ears.


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## amb

Quote:


  Originally Posted by *ATAT* 
_Swapping the 3k resistor for a CRD will give better results IIRC._

 

Yes. CRDs will make the bias current (mostly) independent of supply voltage, and increase the PSRR.


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## ozshadow

But is the sound quality very clean ?

 What I want is something portable, with tight, punchy and solid bass. Rich mids to go with my Grado's, and the highs just have to be accurate.

 Again, I'd like something very clean, but with the bass very present but not boomy, just with some tight impact.

 I've tried the 2227 and like the clean sound, but could be richer and the bass is a bit light. The 2132 was ok, but I felt the bass was more on the boomy side, but it was there, like a ported system in car audio, not a sealed box. It hurt the overall sound to me.

 I am trying a 2107 as soon as it gets here. I also have some single 627's on the way, but these will not work in anything I have to this point.

 So knowing that I want something clean, accurate, rich, with tight, punchy bass to use with Grados, I'd welcome any suggestions for the amp base and opamps to use.

 I really do not care about battery life, and size can be up to SR-71 size. If I had the money, I'd have me one of those !

 Thanks all !


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## ATAT

Quote:


  Originally Posted by *Pars* 
_Do a search here for a BUF634 thread about 6 months ago where this was discussed quite a bit. Mono did a laout of a modified Sijosae buffer with FETs configured as current sources (IIRC). His layout was pin compatible with a BUF634... I've built some of these for a Pimeta and like them so far... better than the BUF634 with 221 ohm BW resistors to my ears._

 


 Thats good, so the CRD biased buffer sounds good? I've been working on a discrete buffer using that design so that's good news =)


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## amb

ozshadow, before you get carried away with subjective descriptives, I believe sijosae conceived this circuit to be ultra-compact as a primary goal, not ultimate high-resolution hi-fi...


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## ozshadow

I do not have any ultra hi-fi recordings. I am just hoping for tips on a project. I described what I hoped to build as best I can. I am juggling something like this vs. a pimeta in a portable case vs. scrounging around for a pint board. I enjoy the building, even if a little at a time, but I do not have the cash to build lots of different amps and combos to find what I am looking for. I would prefer to enjoy the building, but have a result I am quite pleased to use as well.

 Thanks for the input.


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## mono

I could be mistaken but my general impression is that you have to consider the cans. You can choose lower current fast output transistors and lose some output current potential, or parallel them and lose a slight bit of treble definition with the current sharing resistors, or use larger die transitors that are slower. Then again I ended up putting output resistors on my reinvention of the Sijosae buffer after a defective 1/4-1/8" jack caused me to blow out one.

 Maybe this is all voodoo superstition, I can only tell you for sure that I have no desire to use BUF634 anymore, after coming up with even the simplistic discrete replacement. Kudos to Amb for the patience and help with it, people like him MAKE head-fi the great place it is!

 Anyway, I like Sijosae's AB and only wish he'd fit more capacitors into the designs so I don't have to alter them, as I like to throw in some 0.1uF ceramic and 1uF film where possible. BUT, you don't "HAVE" to built it like that, when i'd suggested it in a previous thread it was just an example of a step-up from a CMOY or A47, a very inexpensive way to get the next step up in performance. I'd think of the Sijosae AB as an unveiled MINT. Personally I would 3 channel this, do a ground channel too and then you have a simplified discrete Pimeta. It is a very high bang for buck, but will it synergize with your favorite cans and music? I can't know.

 I can tell you that I would give up a few percent overall accuracy for more treble definition and tight bass punch, but most of all I can't stand the "veiled" sound of BUF634, I can listen to a portable MP3 player or power amp directly if I wanted that.


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## ozshadow

Any guesses how it would affect the output if you doubled the amplification stage like this into an A47-type layout ?


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## ATAT

Oz, that's pointless since this already has a gain stage and buffer stage.. the A47 just uses an opamp for buffer stage instead of discrete transistors.


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## mono

Quote:


  Originally Posted by *ozshadow* 
_Any guesses how it would affect the output if you doubled the amplification stage like this into an A47-type layout ?_

 

This design is already capable of more current than the typical A47, ignoring variables like the supply voltage. If you meant doubling up the opamp (voltage gain stage), it wouldn't be a benefit for a headamp, AFAIK. You just raise the gain if you want, err, higher gain, or choose a different complimentary pair of transistors for more current handling. BC327/337 are just nice for a TO-92 package but something like 2N5087/2N5088 might be nice, or step up to TO-126 sized transitors, a couple common around here are BD139/BD140.

 I would suggest just building it in a basic version first, which can be done in short order and relatively inexpensively. If you had some 2N3904/2N3906 or whatever lying around it would give you an idea and you can take it from there. Just note the pinout of the transistors you choose, those Sijosae used (BC327/337) are CBE pinout (COllector, Base, Emitter), while many are instead EBC, so they'd be rotated 180' from the picture.


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## barkas

I have been playing with this design for the last few days.

 So far I have altered the design so it looks almost like a pimeta 
	

	
	
		
		

		
			





 .
 I replaced the output stage with sijosaes modular diamond buffer design.
 The virtual ground is now almost the same as in a pimeta, only without the jfet cascode, using a opa2132 with the diamond buffer, and a 220k voltage divider as input.
 I don't know if it works though 
	

	
	
		
		

		
		
	


	




 .
 I'll have to acquire some new platines for edging first and BC327/BC337s. I'm holding off mail order for now because I'm still working on the schematic and don't want to order twice.
 If this works, it would be a very nice portable amp.


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## FallenAngel

Hey guys, just wanted to find out, which one should sound better, Class-AB I or Class-AB II.

 Also, I noticed there are no input caps, would the sound quality benefit from having these or not, I've got a few Orange Drops lying around.

 Thanks


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## Eokboy

Never built a Class AB II. Interesting.

 I left out input caps since I have no problem with offset. Based on tangent's article, it should sound better without caps.

 My Class ABs:


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## FallenAngel

Thanks Eokboy, i'll be getting parts for the Class-AB II today/tomorrow and building it as soon as I get them.

 I've read tangent's article, I was just wandering how much the sound would get worse by having 0.1uF or 0.47uF input caps.

 Plus, in that article it has the f=1/2(pi) RC formula, but this amp doesn't have an R. To add input caps would I need to add this one too?

 I'll have to measure how high the offset is on my crappy soundcard at work is and hopefully woun't need to add input caps, but just in case, I'd love to know this.

 Thanks


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## Eokboy

You could try with 100K input resistors and 0.47uF caps. I just followed the original schematic.


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## amb

Quote:


  Originally Posted by *FallenAngel* 
_Plus, in that article it has the f=1/2(pi) RC formula, but this amp doesn't have an R. To add input caps would I need to add this one too?_

 

If you add a coupling capacitor between the volume pot and the input to the opamp, you will also need to add a resistor from the input of the opamp to ground. Without it, there won't be any bias path for the opamp and it won't function properly. The value of the resistor should be at least 10x that of the volume pot. Without the coupling cap, the volume pot itself serves as the bias path, but I prefer to add a resistor anyway in case the pot wiper contact fails (which may lead to high DC offset).


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## FallenAngel

Just built one of these, getting a big problem with DC offset. Exactly 2.6V on both channels. Took me a bit to find out that the discrete rail splitter only works when you close the loop between V+ and V- before you get a good even split. After that I added all the components and I think I hooked up everything correctly.

 I measured DC offset between Right/Left Out to Ground without any source connected with an AD823 as the chip. Only finished putting this thing at 1:00am before getting called into work *GRRR!*. Will play with it later today to see if something changes, but with a config like this, I'm not sure of what there is to do except scan over all the soldering to make sure nothing that shouldn't be is connected.


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## thedoctor

Quote:


  Originally Posted by *barkas* 
_I have been playing with this design for the last few days.

 So far I have altered the design so it looks almost like a pimeta 
	

	
	
		
		

		
		
	


	




 .
 I replaced the output stage with sijosaes modular diamond buffer design.
 The virtual ground is now almost the same as in a pimeta, only without the jfet cascode, using a opa2132 with the diamond buffer, and a 220k voltage divider as input.
 I don't know if it works though 
	

	
	
		
		

		
		
	


	




 .
 I'll have to acquire some new platines for edging first and BC327/BC337s. I'm holding off mail order for now because I'm still working on the schematic and don't want to order twice.
 If this works, it would be a very nice portable amp._

 

if you're adding this as ground channel:



 then it'll work just fine. and look something like this once finished :






 or look something like this if you're running it in Jung MultiLoop configuration :






 but still even after all of that, it still falls short compared to these which uses a completely different discreet buffer implementation :




, improved layout : 





 also running in MultiLoop, with around *27-29mA* of current drain and a much better sound. all of the circuits shown above uses 2 dual channel Opamp to with one dedicated channel to split the voltage and buffer it like in the PINT/Mini3. a good sounding portable amp indeed, especially for people that has a particular fetish with through-holes and donutboards.


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## ozshadow

thedoctor, do you have teh schmatic for the best layout in the bottom right ? I might try to build one, but probably will try to etch a board for it.


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## thedoctor

Quote:


  Originally Posted by *ozshadow* 
_thedoctor, do you have teh schmatic for the best layout in the bottom right ? I might try to build one, but probably will try to etch a board for it._

 

i'm not exactly educated in Eagle, but here's a sketch. trying to learn how to use it to draw schemtics, but free time is running low.


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## FallenAngel

Just wanted to ask, how important is it to match the BC337/BC327 transistors? I don't exactly know how this is done so I just took the first pair of each and installed them.


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## thedoctor

Quote:


  Originally Posted by *FallenAngel* 
_Just wanted to ask, how important is it to match the BC337/BC327 transistors? I don't exactly know how this is done so I just took the first pair of each and installed them._

 

if the pair is working in an open loop (hope i got that right) like in the sijosae discreet rail splitter, then unmatched pairs could cause voltage imbalance to happen. but if the pair is working in a closed/feedback loop of an Opamp, then the Opamp will keep the offset at near ground levels.

 to match the transistors, the easiest way is to use a multimeter that could measure HFE.


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## FallenAngel

Uhm... and in the Sijosae Class-AB II amp, are they working in open or closed loop?


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## cetoole

Quote:


  Originally Posted by *FallenAngel* 
_Uhm... and in the Sijosae Class-AB II amp, are they working in open or closed loop?_

 

The L/R are closed loop, while the discrete rail splitter is open loop, although in the schematic posted above by thedoctor, which he feels is the best configuration, all is closed loop.


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## FallenAngel

Thanks, but now that makes me wander. I simply put a resistor and an LED between V+ and V- which kinda closed the loop and got a completly stable (and very accurate) ground split when I was making the rail splitter. I'll check if that changed since attaching the amp, but if it hasn't then I'm pretty confused why I'm getting such an offset, guess I'll be looking for other problems.


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## thedoctor

Quote:


  Originally Posted by *FallenAngel* 
_Thanks, but now that makes me wander. I simply put a resistor and an LED between V+ and V- which kinda closed the loop and got a completly stable (and very accurate) ground split when I was making the rail splitter. I'll check if that changed since attaching the amp, but if it hasn't then I'm pretty confused why I'm getting such an offset, guess I'll be looking for other problems._

 

try feeding it with 24V and you'll see what i'm talking about.
	

	
	
		
		

		
			




 you're having DC offset problem with your unit? are you using input capacitors? if yes, then try bypassing them. or you could ground the Opamp input with a high value resistor. amb already mentioned about this.


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## FallenAngel

Well, I'm running off 14V and it splits to exactly 7V/7V within 0.01V but I'll double check with higher Volts.


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## Eokboy

Quote:


  Originally Posted by *thedoctor* 
_i'm not exactly educated in Eagle, but here's a sketch. trying to learn how to use it to draw schemtics, but free time is running low.




_

 

A schematic woot! I'll try drawing this back in TinyCAD.

 So this thing would work well with alkalines/rechargeables? I've been using BC327/BC337, no -25/-40 at the back.


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## thedoctor

Quote:


  Originally Posted by *Eokboy* 
_A schematic woot! I'll try drawing this back in TinyCAD.

 So this thing would work well with alkalines/rechargeables? I've been using BC327/BC337, no -25/-40 at the back._

 

it'll work fine. tested and splits exactly till 32V without problem. since all the discreet parts are inside the feedback loop of the Opamp, transistor matching are not needed.


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## FallenAngel

Quote:


  Originally Posted by *thedoctor* 
_try feeding it with 24V and you'll see what i'm talking about.
	

	
	
		
		

		
		
	


	



 you're having DC offset problem with your unit? are you using input capacitors? if yes, then try bypassing them. or you could ground the Opamp input with a high value resistor. amb already mentioned about this._

 

Alright, found out the railsplitter gives me around 8V / -6V split which is causing a very bad DC offset in the amp. I'll probably just abandon the discrete rail splitter for this amp and just use a good old TLE2426.

 I am planning to build another one of these if it works and in that one I'll want to use a more stable rail splitter and ground channel design and the schematic in thedoctor's post #41 looks pretty good with a ground channel so I'll try that one out.

 A little question about the opamp choices for that, what kind of things would I be looking for in an opamp for that position? I've got a couple AD823's, OPA2227, OPA2134's and 2 left over OPA2137's.

 Thanks!


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## Eokboy

I'm using it with OPA2107AP.


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## FallenAngel

I was talking about the ground channel opamp, not Left/Right. I think I'll use the AD823 for L/R and give the OPA2227 a try. But for ground, I'm just not sure what would work best.


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## Eokboy

Yep, the OPA2107AP is unity gain stable and suitable for ground channel as well. OPA2227PA/OPA2134PA would be the cheaper alternative.


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## FallenAngel

Thanks, I'll give it a try as soon as I get some free time.


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## FallenAngel

Wow, noticed something very weird after completing this amp. When I was testing, I was getting a HUGE amount of DC offset, almost the full V+/V- voltages on the output. Then I tried connecting a source to the amp, and all of a sudden, no more DC offset, this is very weird. Hopefully this doesn't happen when just a POT is connected to it, otherwise, it's pretty dangerous having that many volts going to the headphones when no source is connected, but the amp is on.


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## ijan

as theDoctor said, true, the original sijosae AB is in open loop and u putting a resistor/led wont close the loop (its a whole different thing). I haf been having problem with the rail splitter beforehand and implemented a unity gain opamp to close the loop and control the feed, then saw this thread which theDoctor gave a better layout.


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## FallenAngel

Quote:


  Originally Posted by *thedoctor* 
_i'm not exactly educated in Eagle, but here's a sketch. trying to learn how to use it to draw schemtics, but free time is running low.




_

 

Hey guys,

 After building like 5 different Sijosae Class-AB amps, I'll finally try to build this one (and another modified version of it but that's later), and I've got a couple of quick questions.

*This version*
 I don't see the power caps in the schematic, I'll be using something like a TREAD to power this thing and I usually put them power caps right after the rail splitter, but here I don't see that at all. Should I just put in a big cap across the V+/V- rails, but I see 2 caps and I'm not positive no how they're wired. From what I've always seen, the caps should be going between V+ to Ground and V- to Ground, is that the case here, and if yes, where on the ground is it going, I'm thinking Input Ground.

*My Upcoming modification*
 Since this amp uses a dual-opamp for the ground channel and rail splitter, If space is not an issue, wouldn't it be benefitial and more cost efficient to use a good opamp for the ground channel and a cheap one for the rail splitter or just use a TLE2426 with a few caps following it like the Pimeta power supply?

 Thanks in advance!


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## cetoole

Quote:


  Originally Posted by *FallenAngel* 
_Hey guys,

 After building like 5 different Sijosae Class-AB amps, I'll finally try to build this one (and another modified version of it but that's later), and I've got a couple of quick questions.

*This version*
 I don't see the power caps in the schematic, I'll be using something like a TREAD to power this thing and I usually put them power caps right after the rail splitter, but here I don't see that at all. Should I just put in a big cap across the V+/V- rails, but I see 2 caps and I'm not positive no how they're wired. From what I've always seen, the caps should be going between V+ to Ground and V- to Ground, is that the case here, and if yes, where on the ground is it going, I'm thinking Input Ground._

 

Personally, I would just put ps caps from v+ to v-, though you could, and there are arguements for and against this, put caps from v+ to v- and also some from v+ to input gnd and v- to input gnd. Dont put any on the output gnd.
  Quote:


 *My Upcoming modification*
 Since this amp uses a dual-opamp for the ground channel and rail splitter, If space is not an issue, wouldn't it be benefitial and more cost efficient to use a good opamp for the ground channel and a cheap one for the rail splitter or just use a TLE2426 with a few caps following it like the Pimeta power supply?

 Thanks in advance! 
 

Beneficial, maybe, probably. Cost effective, probably not. Dual opamps tend not to cost much more than single ones. I can see a few changes to that schematic that I am pretty sure would make a bigger difference than what you suggested. First, add resistors in series with the emitters of each of the input transistors in the buffer greater than or equal to the value of the resistors in series with the emitters of the output transistors (>=4.7r), for Class A-AB biasing, and second, replace the 3k biasing resistor for the input transistors of the buffer with a ccs, whether it be a CRD, lone jfet, jfet cascode, or something else. The following is an example of what I mean, though without any parts values. I just happened to have this made up and uploaded to my photobucket account for the Pimeta BUF634 replacement diamond buffer boards I was working on a while ago. To make it a bit easier, you could swap CRDs for the two 2N5484 jfets. It would also remove the need to match the jfets.


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## FallenAngel

Quote:


  Originally Posted by *cetoole* 
_Personally, I would just put ps caps from v+ to v-, though you could, and there are arguements for and against this, put caps from v+ to v- and also some from v+ to input gnd and v- to input gnd. Dont put any on the output gnd._

 

For this amp, since size is a HUGE issue, I'll stick with a single cap between the rails.

  Quote:


  Originally Posted by *cetoole* 
_Beneficial, maybe, probably. Cost effective, probably not. Dual opamps tend not to cost much more than single ones. I can see a few changes to that schematic that I am pretty sure would make a bigger difference than what you suggested. First, add resistors in series with the emitters of each of the input transistors in the buffer greater than or equal to the value of the resistors in series with the emitters of the output transistors (>=4.7r), for Class A-AB biasing, and second, replace the 3k biasing resistor for the input transistors of the buffer with a ccs, whether it be a CRD, lone jfet, jfet cascode, or something else. The following is an example of what I mean, though without any parts values. I just happened to have this made up and uploaded to my photobucket account for the Pimeta BUF634 replacement diamond buffer boards I was working on a while ago. To make it a bit easier, you could swap CRDs for the two 2N5484 jfets. It would also remove the need to match the jfets.



_

 

As for Dual vs Single, the only main reason is that I have a couple of OPA627s I'm dying to use for this and have tons of TLE2426s lying around.

 For the CSS, I'm also building a SOHA so I have ordered a few J113 which I would use for this position.


 Thanks for the reply! Since I've got a layout that I hope will work, I'll go start building the original version and see if I can fit it into a Hammond 1455C802 with a DIY tread and a 9V


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## FallenAngel

After looking over Sijosae's CCS comparison, I'm not sure which CCS to use. It says the 2N5484 CCS isn't good but recommends the LM317 CCS as very good and I used it in a Sijosae Class-AB II amp before. Would it be a good idea to use the it in this application as well?

 This is what I'm thinking for the buffer using this modified LM317 CCS: *Please take note, that I have absolutly no EE background and have totally no clue if I'm breaking any (or all) basic rules here, but I am fairly creative with mixing and matching different schematics in hopes of making something work*





 I have read over this tread (Page 3 and 4 are the most important ones) to find some more information on the CCS to use in diamond buffers and now I'm more confused than ever.

 Unfortunatly I cannot get 2N5484 jfets, only 2N5486 which have a much higher current rating. After looking over at mono's design of a modified Sijosae Class-AB buffer, I've merged them into this (again, I'm hoping it makes sense 
	

	
	
		
		

		
			





 ):





 Please let me know if you guys think either of these buffers would work well - as in better than the original design in the LM317 case and just as well in the 2N2586 case.

 Thanks!


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## steinchen

Sijosae's ccs comparison only compares how the supply voltage affects the ccs current, imo there are several specs that are far more important: PSRR, impedance, noise and capacitance. As long as you don't need high currents (of more than 20mA or so) or run the ccs at high voltages cascoded jfets are superior. Even a lone jfet or a CRD is a good choice as a ccs.


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## FallenAngel

Thanks steinchen, I'll get my thoughts back to the 2N5486 version.

 cetoole: I just did a search on threads you started and came up with so much great info! 
	

	
	
		
		

		
		
	


	




 After checking out these buffers, it seems I have very little if any originality in the above schematics so I'll just ask, how is the second from the bottom which is VERY similar to the 2N2586 I had. I added the inline input resistor of 4.7Ohms to match the output resistor.

 I'm actually very surprised at myself for even coming up with something similar (but of course somewhat worse) than the great looking design here. So I will (shamefully 
	

	
	
		
		

		
		
	


	




 since I was thinking of coming up with something a little new) be turning my thoughts to breadboarding a slightly modified version of that design since I can't get any 2N5484's and I'll be probably using 2N5486's.

 Something interesting. From what I know, those jfets are used to run the buffers in Class-A. By adding them to the output of the amp, before the buffer, I'm thinking makes the opamp run in Class-A as well. So for using the 2N5486, would the 1K resistor be alright for current limiting, I saw mono having a 1K in his, so I'm hoping it'll be alright.

 After reading the schematic, I've taken guesses for a lot of the parts, but I can't figure all of them out. I'll post my guessed values tonight, but the main ones that I'm not sure about are: 

*Caps around the OPA627*: I'm guessing as per datasheet they're 0.1uF ceramics, but I'm not positive.

*R10 (R / L / G)*: As per Pimeta it's 1K, but since I'm using 2N5486 instead of 2N5484, will it be different and will I need to add another resistor for current limiting, but I'm guesing those are *R19, R20 & R21*. So, obviously, my next question is what's the recommended value for those 3?

 Thanks!!!


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## cetoole

FallenAngel, there is more useful information for what you are looking for available on Headwize, so you may wanna check there. For example, in this thread on discrete buffers, AMB does a great job explaining what does what, and how it works, as well as how to calculate some of the data. I dont have any of these PCBs, due to the difficulty in getting small quantities manufactured for a reasonable cost, so unfortunatly, I have not been able to try it. The jfets seen in the buffer are not for class A biasing, they just set the quiescent current of the input stage of the buffer, which affects that of the output stage. It is actually the emitter resistors on the input stage which pushes it towards class a, and the ratio of input transistor emitter resistors to output transistor emitter resistors along with the idss of the jfets sets the quiescent current of the output stage (how deep into class A). AMB does a much better job explaining it in that thread I linked above, so check it out. 1k source resistors on the 2N5486 works, but you really should calculate the values to get the current you want.

 In that dDBed pimetaesque amp thread of mine, yes, the bypass caps default value would be 0.1uf ceramics. X7R is just fine here. Sounds like your amp will end up pretty close to the one I have done here.

 Steinchen got it dead on with regards to what is important in the CCS for this purpose. What Sijosae was measuring has little relevance to this, as our supplies will remain almost constant. This is why buffers like those used on the PPAv2 work great, even with the inaccuracy of the standard current mirror, and the simple jfet+source (adjustable) resistor. The bias current may not be dead on, but it tracks between the positive and negative supplies evenly. If I was to use a different CCS besides jfets or crds, I would definitly go for the LED based one, which, IIRC, is what Mr. Walt Jung used in his origional diamond buffer that started all of this. Also, for the LM317 CCS, which I would not recommend for use here, you should have the wire from Adj to the base of the input transistors go instead to the junction between the 620ohm and >4.7ohm resistors. The 2N5486 CCSed diamond buffer looks good though, and I would expect very nice results using this. I say this however without running the numbers to determine quiescent current. It will definitly be easier to build than my drop in buffer for the pimeta, due to your addition of source resistors on the ccs jfets.

 Keep up the good work though, I cant wait to see this built.


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## FallenAngel

Oh great, after reading the latest schematic on this amp, I realized my amp will be almost EXACTLY like it 
	

	
	
		
		

		
		
	


	




, call me a little theif, but I totally love that DB design *which someone should have told me already existed 
	

	
	
		
		

		
		
	


	




* with a jfet cascode.

 So that more or less seals my fate at this buffer design:





 Also, since I think i'll be moving much more in the direction of cetoole's design, further discussion on this should be moved to his tread.


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## sphinxllama

Hi,

 this amp looks great and I plan on building it. most of the parts I got at my local electronic dealer. but I have difficulty to get one of this opamps I listed below:
 AD823 / OPA2134PA / OPA132 / OPA134 / OPA2107AP / OPA2227PA / OPA2132PA

 does anybody have experience with other opamps besides the above or knows any good one I can use with this amp and that are easy to get?
 I have two opamps from other projects:
 NE5532
 TDA2822m
 can I use one of these?

 I have to more questions about the layout. I drawed the battery supply in the shematic is it right like this:




 and @thedoctor why do you use this parts i marked at the picture:



 cant find it one sijosaes shematic.

 thanks for your help hopefully 
	

	
	
		
		

		
		
	


	



 sphinxllama


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## heatmizer

You can use the ne5532 but it is a bipolar opamp you need to be aware of your resistors they have to match on the input and feedback. Maybe add a 1K between pot and input of opamp and a 100K to ground. Use 6K and 1.2 K in feedback loop for a gain of 6. No input cap so watch your offset. As far as the railsplitter goes good luck getting it balanced. Look at The Doctor's schematic on his ground channel with a opamp in the ground channel the the railsplitter will balance itself. The 2 things you circled are small box caps bypassing the electrolytics


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## Nordic

You still got to love that guy.

 I just finished a minor mod now to get his Poor Man's Zen working.... I was naughty and didn't follow his layout, and paid the price in hours wasted.... copying him more closely this headphone amp certainly is amongst the best I built.... top 2.


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## sphinxllama

hi,

 thanks for your quick answers! i do not understand a thing you wrote. mybe some of it but i am a newbe in diy and my english is not that good eather 
	

	
	
		
		

		
		
	


	




 just finished my first cmoy. it worked great and now i want to step up.

 so the easiest way would be to buy the opa2134 and just build as shown on sijosaes shematic. should i use the electrolytics 100nF (right???) and put both between the +4.5 and GND and the other one between -4.5 and GND and connect both GNDs?
 is the connection from the battery correct? sorry but i am confused because on the pictures from thedoctor the battery power goes straight to the opamp. or do i look wrong 
	

	
	
		
		

		
		
	


	




 thanks
 sphinxllama


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## heatmizer

build the amplifier part as shown but you will have problems with the power section. sijosae's amp sound really nice but the Railsplitter (read power section is not very accurate i could never get it within 1/2 volt from positive to negative. if you really want to build the power section as is protoboard the thing 1st and switch out bc327 and bc337 until you have an even split 1/10 of a volt is good so say 1, 9 volt battery +4 and -5 volts would be bad +4.5 and -4.6 volts would be good. my solution was a buf634 for my railsplitter/power section.


 the yellow things are small film capacitors bypassing the electrolytics which are on their side


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## TzeYang

^alternatively, just match the transistors using a HFE capable DMM. (which is cheap)


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## .:tuxianer:.

Hi,is there anywhere a part list? An i want to build this amp for my Grado sr325. Can I use the standard parts or should i change they to optimize them for my Grado?Thanks


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## FallenAngel

Quote:


  Originally Posted by *.:tuxianer:.* /img/forum/go_quote.gif 
_Hi,is there anywhere a part list? An i want to build this amp for my Grado sr325. Can I use the standard parts or should i change they to optimize them for my Grado?Thanks_

 

All the parts are in the schematics.

 Customize all you want 
	

	
	
		
		

		
		
	


	




, you can lower the gain if it'll only be for Grados, but I didn't see any real reason to with mine.


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## .:tuxianer:.

Ok. Ithink I will take the standard parts. Is ther any final schematic? And wich version sounds better? I or II?

 And what's this: 
	

	
	
		
		

		
		
	


	




?


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## TzeYang

it's a small intergrated TREAD regulator.


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## Seaside

Quote:


  Originally Posted by *.:tuxianer:.* /img/forum/go_quote.gif 
_Ok. I think I will take the standard parts. Is ther any final schematic? And wich version sounds better? I or II?

 And what's this: IMG_

 

The red circled section of that image is TREAD like power supply. I think this is thedoctor's board, and the section is optional. He did it that way because that is simply better in terms of stability.

 I think you should start with standard parts and standard layout just as the way sijosae did. It is not like I do not want you to be creative, but I think his layout is very carefully designed one, vey clever layout that did not take up whole lot of space. He is not only an expert at electonics but also at miniaturation too. 

 Which is better I or II... that is good question.
 They are basically similiar things with different idea. 
 I do not think one is better than the other though, I found I like "I" more than "II".

 Just for your Information, one comment on the power section of his layout, as you can see, there are 4 transitors. 1 pair of transitor close to the power source are... not really working like transistors, since their leads are connected. They are working just like diodes. So, you can replace it with diodes, 1N917 or 1N4148 type. In fact I highly recommend you do that, because in that way you don't have to worry about things like TR hfe matching. Sijosae himself once stated that he originally designed it with diodes but used TRs as alternative because he did not have diodes at hand when he made his.


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## cetoole

Quote:


  Originally Posted by *Seaside* /img/forum/go_quote.gif 
_Just for your Information, one comment on the power section of his layout, as you can see, there are 4 transitors. 1 pair of transitor close to the power source are... not really working like transistors, since their leads are connected. They are working just like diodes. So, you can replace it with diodes, 1N917 or 1N4148 type. In fact I highly recommend you do that, because in that way you don't have to worry about things like TR hfe matching. Sijosae himself once stated that he originally designed it with diodes but used TRs as alternative because he did not have diodes at hand when he made his._

 

I dont see why the beta of the transistor plays a factor when it is diode connected. When used like this, the transistor IS a diode, and one which better matches the characteristics of the output transistors; a benefit in my mind.


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## Seaside

You're right cetoole. My point is to avoid tedious job like TR matching. You may able to find schematic by sijosae, that uses diodes in place of those transtors. Any of both will work fine, becasue they basically are the same thing. I happened to use diodes because I had them in my drawer.


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## .:tuxianer:.

Ok but can anyone post the latest layout? And what function have the Diamond puferr and where should i put th buffer? The Railsplitter makes a virtual Ground right?


 edit: ok the buffer strengthens the signal again! Is this right? What of the shown Buffer layouts is the best?


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## FallenAngel

Quote:


  Originally Posted by *thedoctor* /img/forum/go_quote.gif 
_i'm not exactly educated in Eagle, but here's a sketch. trying to learn how to use it to draw schemtics, but free time is running low.




_

 

Thread revival from quite a bit ago, but I think I'm allowed for one reason... I built this amp, and in a Hammond 1455C802@ 
	

	
	
		
		

		
			





 I threw in a nicer PSU, similar to PPAS:
 TLE2426
 2x 470uF V+ to V-
 100uF & 1uF V+ to ground
 100uF & 1uF V- to ground

 No rail isolating JFETs but there is a trickle charger for the 9V battery hard-wired to the DC jack; as you'll see in the photos, there was just absolutely no room.

 After some testing, I settled on OPA2107 on Left/Right and AD744 compensation pin output on Ground because I really like the sound of OPA2107 and the current draw is nice and low. Full amp current draw is 22mA, so the 270mAh AccuPower 9V lasts over 12 hours. Now what kind of diamond buffered portable amp can say that! 
	

	
	
		
		

		
		
	


	




 Yes, it sounds very good, I'll just say that. I don't have many portable amps (only PPAS) and I don't trust to compare something I built and worked on hard to other amps on pure memory so I'll have to get somebody else to compare for me.

 Without further ado, pics!


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## TzeYang

Nice!

 The only issue i have is the OPAMPs. Both chips don't seem to love low voltages.


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## FallenAngel

While both chips perform better at higher voltages, according to the datasheet and while listening, they run perfectly well off 9V.

 I unfortunately burned the AD8066 I had in there before and didn't like the AD823 that much.

 The opamps driving buffers does make it a lot easier on them instead of driving headphones directly so they should never clip.


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## Spacehead

I am sorry for digging up old thread. But today I made this amp, but with active ground. I think Sijosae's discrete rail splitter sounds really bad. It just ruins good stereo image and bass. 
 I did left and right channels exactly following Sijosae's picture. It took some hours, I dunno what took so long, but maybe it is just so precise work. I made sure that I didn't get any cold joints. 




 The ground is very very simple dual op amp buffered TLE2426. The dual op amp is fed TLE2426 output and bridged with 5 ohm resistor for double current, and unity voltage gain. It is stable and high current TLE2082AI, for now. 




 Voltage to the 4700 uF capacitor comes from a regulated (adjustable LM7805) 15V supply. 

 To the input I added 0.1 uF plastic capacitors


 It sounds excellent! Should be superb for battery operation and portable too! 
 I can hear the mixture of Class A and Class B operation. It isn't as smooth as pure Class A amplifier but for the size of it, it still is very good. And it is very accurate with the OPA2107 op amp. I could try other op amps there too. I think the transistors don't have any sound of their own, which of course is a good thing. I am just afraid that they burn up, they run hot. 
 I am using 47 ohm output resistors, because I am afraid that possible short circuits when plugging the headphones would burn the transistors. I would just hate to do the amplifier again. Now enjoying this amp.


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## diditmyself

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_ I think Sijosae's discrete rail splitter sounds really bad._

 

Indeed it does. The output impedance is far to high to serve as a ground for low impedance returns like phones. The crosstalk will be bad unless large capacitors from rails to ground are used.


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## Fred_fred2004

I might as well chip in 
	

	
	
		
		

		
		
	


	




 I used a TLE2426 rail splitter, and an OPA2227, Sijosae's excellent plans made the layout very easy, and it sounded very respectable, battery life was good as well












 cheers
 FRED


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## Spacehead

I checked DC offset and I get plenty of it if I use other op amp than OPA2132. But I don't like OPA2132s sound and wished to use OPA2107. Could I get DC offset because I added capacitors in series to input rca connectors?
 I also built a ground channel which has parallel op amps for higher current capability:









 The resistor in ground channel are
 op amp bridging 12, 6 and 5 ohm
 feedback 27k / 5.56k to ground
 first op amp to buffer op amps -> 47 ohm

 With OPA2132 I get -30 mV of DC offset, with OPA2107 1100 mV


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## ericj

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_I checked DC offset and I get plenty of it if I use other op amp than OPA2132. But I don't like OPA2132s sound and wished to use OPA2107. Could I get DC offset because I added capacitors in series to input rca connectors?
 I also built a ground channel which has parallel op amps for higher current capability:

 The resistor in ground channel are
 op amp bridging 12, 6 and 5 ohm
 feedback 27k / 5.56k to ground
 first op amp to buffer op amps -> 47 ohm

 With OPA2132 I get -30 mV of DC offset, with OPA2107 1100 mV_

 

Are you getting these offsets with or without the ground channel? 

 If with, start by removing the ground channel. Which, fwiw, should be at unity gain. 

 Capacitors in-line with the inputs would remove rather than add offset. 

 If your opa2107 is showing a DC offset, it's fake. The opa2107 is a precision laser-trimmed jfet-input opamp. That's why it costs so much.


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## Spacehead

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_Are you getting these offsets with or without the ground channel? 

 If with, start by removing the ground channel. Which, fwiw, should be at unity gain. 

 Capacitors in-line with the inputs would remove rather than add offset. 

 If your opa2107 is showing a DC offset, it's fake. The opa2107 is a precision laser-trimmed jfet-input opamp. That's why it costs so much._

 

I recall reading something like that if I add capacitors to this amps input I need to add resistors to ground too. This doesn't have input resistors like Cmoy, could that cause op amp to malfunction on certain situations? 
 Now I have the ground channel in place. Can I use feedback resistor with unity gain? I am trying to get my ground channel working too, because I need high current capability and I don't have BUF634 and I want to use lot of op amps. At least I want to try if I can make it work. 

 I have ordered those OPA2107s from TI as samples. They should be working, yeah, I tried another one and same results. 

 I had this working before with another ground channel. But I tried to recreate another with NJM4556S, TLE2426 and Capacitor and it didn't work, I didn't use resistors, and NJM4556S was in unity gain. 

 I was pretty disappointed today, but now I am listening to the device with OPA2132 x 4 and it works, has bass too.

 I am doing this because my Sennheiser HD-201s need a LOT of current (24 ohm).


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## Spacehead

Yeah! I solved it. It was the fact that I didn't have 10k volume pot like Sijosae's drawings suggest! That caused my main op amp to malfunction as it's input bias currents had no place to flow. I added 27K resistors to RCA connector 




 and adjusted the feedback on ground channel, used 3K feedback resistor and didn't ground it so it is at unity gain. DC Offset is now with OPA2107 very low, 0.6 mV for both channels. 
 I power it with 7805 adjusted to +15V


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## ericj

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_I recall reading something like that if I add capacitors to this amps input I need to add resistors to ground too. This doesn't have input resistors like Cmoy, could that cause op amp to malfunction on certain situations? 
 Now I have the ground channel in place. Can I use feedback resistor with unity gain? I am trying to get my ground channel working too, because I need high current capability and I don't have BUF634 and I want to use lot of op amps. At least I want to try if I can make it work. _

 

Yeah, you need a resistor from +input to ground if you add the caps. 

 I still don't understand what you're on about wrt the feedback resistor on the ground channel.


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## Spacehead

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_I still don't understand what you're on about wrt the feedback resistor on the ground channel._

 

TLE2426 output=virtual ground

 virtual ground -> op amp -> buffer -> output ground

 this time I ditched the three op amps and used sijosae's class ab "buf634" buffer instead. It needs to be kept in op amp control, in feedback loop or there will be dc offset. 

 But now I understood, I don't need a resistor, I need only bare wire, right? hmm, I think I should start practicing using some schematic and simulation program (know any good and easy for Windows?), because I sometimes do things more complicated than is necessary.


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## ericj

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_TLE2426 output=virtual ground

 virtual ground -> op amp -> buffer -> output ground

 this time I ditched the three op amps and used sijosae's class ab "buf634" buffer instead. It needs to be kept in op amp control, in feedback loop or there will be dc offset. 

 But now I understood, I don't need a resistor, I need only bare wire, right? hmm, I think I should start practicing using some schematic and simulation program (know any good and easy for Windows?), because I sometimes do things more complicated than is necessary._

 

I suggest examining the schematic of any amp already designed to have a buffered ground channel - like a pimeta, or an M3. Or even a mini3, though that doesn't have a buffer.


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## diditmyself

Quote:


  Originally Posted by *Spacehead* /img/forum/go_quote.gif 
_TLE2426 output=virtual ground

 virtual ground -> op amp -> buffer -> output ground

 this time I ditched the three op amps and used sijosae's class ab "buf634" buffer instead. It needs to be kept in op amp control, in feedback loop or there will be dc offset. 

 But now I understood, I don't need a resistor, I need only bare wire, right? hmm, I think I should start practicing using some schematic and simulation program (know any good and easy for Windows?), because I sometimes do things more complicated than is necessary._

 

The problem with BUF634 as ground channel buffer is not DC-offset. It's the high output impedance = bad crosstalk = unnatural soundstage.

 For simulation most of us use LTSpice. Since there are many users it's easier to get support from fellow DIY'ers. It's free, and the simulations correlate well with reality.


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## amb

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_I suggest examining the schematic of any amp already designed to have a buffered ground channel - like a pimeta, or an M3. Or even a mini3, though that doesn't have a buffer._

 

Or rather -- the Mini³'s opamps have the "buffer" built-in.


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## Spacehead

Quote:


  Originally Posted by *ericj* /img/forum/go_quote.gif 
_I suggest examining the schematic of any amp already designed to have a buffered ground channel - like a pimeta, or an M3. Or even a mini3, though that doesn't have a buffer._

 

I see that my ground channel is almost like PPA ground channel except my JFET cascode is in front of buffer op amps. Shouldn't that pull all of them to class A? I don't know how to calculate the bias , I am using 2SK246 JFETs and 1K resistor.


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## Spacehead

Is it possible to further bias this amplifier into class a? I added 78L05 regulators to outputs configured as current source with 3K resistors. Seems to be working.

 here is the link: http://www.headphoneamp.co.kr/bbs/zb...desc=asc&no=58


 edit: now with 1K resistors, even smoother sound, no distortions anymore at all. I see that in original config 2K resistors are the current sources. But they set transistor bias, not op amp. 

 Could this be modified to Class A? I wonder will those BC337/BC327 work in class a too long, if they heat up too much.


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## buzz2086

I know this is a really old thread. But I have some questions on this headphone amp. There are few versions of BC337 and BC327. They have BC337-25 and BC337-40. Which one is suitable for this amp ?


----------

