Full disclosure
You might as well tell us what pass transistor you are using. I wonder if some low capacitance types would work better for the CCS and driver for the pass transistor driver like say the 2SA970 and 2SC2240 or 2SA872 and 2SC1775. These parts have very high Hfe in the low mA range also The Zetex parts are great transistors also though, and I am going to try one of thier devices for the pass transistor. Maybe the Zetex ZTX795A and ZTX694B would be good choices also. I really like your PCB layout the more I look at it........
H.H.
You might as well tell us what pass transistor you are using. I wonder if some low capacitance types would work better for the CCS and driver for the pass transistor driver like say the 2SA970 and 2SC2240 or 2SA872 and 2SC1775. These parts have very high Hfe in the low mA range also The Zetex parts are great transistors also though, and I am going to try one of thier devices for the pass transistor. Maybe the Zetex ZTX795A and ZTX694B would be good choices also. I really like your PCB layout the more I look at it........
H.H.
Same as it ever was
The pass device is D44 / 45H series, OnSemi as per originals.
I couldn't be bothered to try anything else and they are cheap and robust. The modelling didn't show any huge gains to be had here, performance being dominated by other factors, AFAICT.
I've built prototypes using BD135's I had lying around.
A.
The pass device is D44 / 45H series, OnSemi as per originals.
I couldn't be bothered to try anything else and they are cheap and robust. The modelling didn't show any huge gains to be had here, performance being dominated by other factors, AFAICT.
I've built prototypes using BD135's I had lying around.
A.
You may ask yourself
This is not my beautiful pass transistor! Try a 2SC3298. Better Hfe linearity and Ft. The D44/D45 are an old design and optimized for higher currents than this circuit will be typically used for. Walt Jung is an op amp guy and never seems to use really good transistors in his designs Some of the Zetex 2 amp SMTs look great also and I have some on order to try. Did you model those better sound capacitors also?
H.H.
This is not my beautiful pass transistor! Try a 2SC3298. Better Hfe linearity and Ft. The D44/D45 are an old design and optimized for higher currents than this circuit will be typically used for. Walt Jung is an op amp guy and never seems to use really good transistors in his designs Some of the Zetex 2 amp SMTs look great also and I have some on order to try. Did you model those better sound capacitors also?
H.H.
Attachments
I am impressed Harry
Many would have missed that one - album cover too, very good
Will investigate other options, but they have to be PCB compatible now
One thing I found actually was that comparing discretes is bloody hard work - op-amps are quite easy these days with parametric searches, but I got bored poring over transistor data sheets and decided to take the easy route.
I seem to remember the OnSemi part being an 'improved' choice over whatever was used originally. I've not found the reasons for it's choice though.
A.
Many would have missed that one - album cover too, very good
Will investigate other options, but they have to be PCB compatible now
One thing I found actually was that comparing discretes is bloody hard work - op-amps are quite easy these days with parametric searches, but I got bored poring over transistor data sheets and decided to take the easy route.
I seem to remember the OnSemi part being an 'improved' choice over whatever was used originally. I've not found the reasons for it's choice though.
A.
Re: You may ask yourself
Harry,
I have to take it up for Walt here, the '44 and '45 types were as much my choice as his. It was the best we could find at the time, as far as Ft and beta-linearity with the anticipated load current was concerned. I'm sure, 6 or more years later, that someone can come up with an even better alternative (if that is what it is).
Personally, I have also used BD137/138 types in dedicated regulators where the load current is moderate, with good results.
But, don't forget, the original *very high* performance is with the given types. I have yet to see a (documented) improvement. (Maybe Andy will raise the bar this time?)
Cheers, Jan Didden
HarryHaller said:
Harry,
I have to take it up for Walt here, the '44 and '45 types were as much my choice as his. It was the best we could find at the time, as far as Ft and beta-linearity with the anticipated load current was concerned. I'm sure, 6 or more years later, that someone can come up with an even better alternative (if that is what it is).
Personally, I have also used BD137/138 types in dedicated regulators where the load current is moderate, with good results.
But, don't forget, the original *very high* performance is with the given types. I have yet to see a (documented) improvement. (Maybe Andy will raise the bar this time?)
Cheers, Jan Didden
It was the best we could find at the time
I am sure you are right, but there are a lot on new really good BJT transistors out there now, that I think would work fine and perhaps even sound better. A higher Ft would allow improved loop stability by moving the pass transistors pole out further. Higher Hfe types will allow the op amps to work less hard. Tosihba and Zetex are making some excellent transistors that have proved themselves in many high end audio designs. This high Hfe advantage is surely along the lines researched by Mr. Jung. I know he has advocated buffers within the feedback loop of an op amp. I also wonder if there are not some other op amps that would work well are better than the AD825 with this circuit. Maybe the OPA627 or AD8610 for example. A higher gain bandwith is should give better measured results, assuming the high frequency stability is acheived. Better voltage references have also been discussed in this forum.
Many improvements may be only arrived at through subjective listening test as is often the case in audio design. Mr. Jung and yourself did a great job and I applaud your efforts. I meant no serious criticism but merely that there are stiil probably some advances to be made. I hope that I have not offended you on your fine work. It was really not my intention to do so.
H.H.
P.S. Maybe AWL is not the only one working on this circuit......
I am sure you are right, but there are a lot on new really good BJT transistors out there now, that I think would work fine and perhaps even sound better. A higher Ft would allow improved loop stability by moving the pass transistors pole out further. Higher Hfe types will allow the op amps to work less hard. Tosihba and Zetex are making some excellent transistors that have proved themselves in many high end audio designs. This high Hfe advantage is surely along the lines researched by Mr. Jung. I know he has advocated buffers within the feedback loop of an op amp. I also wonder if there are not some other op amps that would work well are better than the AD825 with this circuit. Maybe the OPA627 or AD8610 for example. A higher gain bandwith is should give better measured results, assuming the high frequency stability is acheived. Better voltage references have also been discussed in this forum.
Many improvements may be only arrived at through subjective listening test as is often the case in audio design. Mr. Jung and yourself did a great job and I applaud your efforts. I meant no serious criticism but merely that there are stiil probably some advances to be made. I hope that I have not offended you on your fine work. It was really not my intention to do so.
H.H.
P.S. Maybe AWL is not the only one working on this circuit......
Useful ap notes for low noise voltge references
Performance Verification of Low Noise, Low Dropout Regulators
http://www.linear-tech.com/pub/document.html?
pub_type=app&document=84
Understanding and Applying Voltage References
http://www.linear-tech.com/pub/document.html?pub_type=app&document=83
Voltage Reference Circuit Collection
http://www.linear-tech.com/pub/document.html?pub_type=app&document=45
REFERENCES AND LOW DROPOUT LINEAR REGULATORS
http://www.analog.com/technology/powerSupervisoryHotSwap/training/pdf/fsect2.pdf
H.H.
Performance Verification of Low Noise, Low Dropout Regulators
http://www.linear-tech.com/pub/document.html?
pub_type=app&document=84
Understanding and Applying Voltage References
http://www.linear-tech.com/pub/document.html?pub_type=app&document=83
Voltage Reference Circuit Collection
http://www.linear-tech.com/pub/document.html?pub_type=app&document=45
REFERENCES AND LOW DROPOUT LINEAR REGULATORS
http://www.analog.com/technology/powerSupervisoryHotSwap/training/pdf/fsect2.pdf
H.H.
Gee, thanks
Thanks for the kind comments UrSv, they are appreciated.
HH, with regard to opamps modelling of the AD8610 looks VERY promising, but getting hold of any in the UK is difficult. AD have not supplied any samples, despite my request. I have a very strong gut feeling that it will be marvellous though, based on my opinion of what is important in a PSU, and my brief modelling.
I will pursue this soon through my 'real' work, since it may lend a greater air of credibility, I've had lots of success with this route in the past.
Time is the biggest problem to me at present, I've a number of applications to demonstrate having got this far, further development is not so important right now, but like all of us affected by audiophile nervosa I will want to go further, later
Still seeking the elusive device for 5V bootstrapped operation though, the AD825 doesn't seem to work here, despite my hopes.
There must be some suitable low V devices for this application - Harry, how's your search engine...
A.
Thanks for the kind comments UrSv, they are appreciated.
HH, with regard to opamps modelling of the AD8610 looks VERY promising, but getting hold of any in the UK is difficult. AD have not supplied any samples, despite my request. I have a very strong gut feeling that it will be marvellous though, based on my opinion of what is important in a PSU, and my brief modelling.
I will pursue this soon through my 'real' work, since it may lend a greater air of credibility, I've had lots of success with this route in the past.
Time is the biggest problem to me at present, I've a number of applications to demonstrate having got this far, further development is not so important right now, but like all of us affected by audiophile nervosa I will want to go further, later
Still seeking the elusive device for 5V bootstrapped operation though, the AD825 doesn't seem to work here, despite my hopes.
There must be some suitable low V devices for this application - Harry, how's your search engine...
A.
5 volt part
The AD 823 is supposed to be a quite good sounding op amp and the specs are still good at +5 volts. Its a dual though and needs a buffer follower before the pass transistor, which I believe you have in your design. It would be on the top of my list. You could solder a SMT part on a component header to translate dual SMT to single DIP for testing. I bet you wish I had brought all this up before you started! I will email you on where to send my consulting fees. I am getting samples for everything I ask for in about 3 or 4 days including some $30 voltage references. I had to buy some LT parts but they were not too bad. If you only knew the stuff I am holding back........ Sure hope I am not helping any of your competitors for the ultimate regulator board design.........
H.H.
The AD 823 is supposed to be a quite good sounding op amp and the specs are still good at +5 volts. Its a dual though and needs a buffer follower before the pass transistor, which I believe you have in your design. It would be on the top of my list. You could solder a SMT part on a component header to translate dual SMT to single DIP for testing. I bet you wish I had brought all this up before you started! I will email you on where to send my consulting fees. I am getting samples for everything I ask for in about 3 or 4 days including some $30 voltage references. I had to buy some LT parts but they were not too bad. If you only knew the stuff I am holding back........ Sure hope I am not helping any of your competitors for the ultimate regulator board design.........
H.H.
Road to somewhere
> Its a dual though and needs a buffer follower before the pass transistor, which I believe you have in your design.
Yep, the board can be used without it for some small price reduction, but I like the isolation it provides to the op-amp o/p stage and it allows some serious high current versions to be built.
An important point to note is the inefficiency of this circuit at low o/p currents - the op-amp / buffer transistor has to sink all the unwanted drive current from the base of the pass device, some care in operating criteria needs to be observed. I have some cooked looking 2N2907's on some early boards where I'd got a bit excited with the source current!
>I bet you wish I had brought all this up before you started!
One can spend so long designing that you never get to an end result though, I'm so pleased with the sonic results I'm getting, I'm not overtly bothered. I am wondering though whether to make the next PCB, originally intended to be a negative version, dual purpose - some careful thought and one board may be able to fulfil both roles with some different stuffing and a couple of simple links (damn - there's another good idea for the competition!)
>I will email you on where to send my consulting fees.
Likewise
>I am getting samples for everything I ask for in about 3 or 4 days including some $30 voltage references.
Hmm, location or identity I wonder - will have to try again, different ID...
>If you only knew the stuff I am holding back........
I took the decision that this was a fairly easy option to a big improvement, at sensible cost, for all areas of my system. My next design would almost definitely be discrete, since op-amps are just too limiting (CF possibly being an exception). That design has somehow morphed into a headphone amp now though, whilst I learn more about discrete amp design
>Sure hope I am not helping any of your competitors for the ultimate regulator board design.........
I don't really consider myself to be in competition, I'm too much of a philanthropist for that, but do intend to make a small sum to cover investment and future releases I wouldn't post here if I had any business sense.
If you want to make money from this, you have to sell complete products - I'm too busy for that at present (damn again - more good advice for others to capitalise on). See what I mean, all the business acumen of goldfish...
A.
> Its a dual though and needs a buffer follower before the pass transistor, which I believe you have in your design.
Yep, the board can be used without it for some small price reduction, but I like the isolation it provides to the op-amp o/p stage and it allows some serious high current versions to be built.
An important point to note is the inefficiency of this circuit at low o/p currents - the op-amp / buffer transistor has to sink all the unwanted drive current from the base of the pass device, some care in operating criteria needs to be observed. I have some cooked looking 2N2907's on some early boards where I'd got a bit excited with the source current!
>I bet you wish I had brought all this up before you started!
One can spend so long designing that you never get to an end result though, I'm so pleased with the sonic results I'm getting, I'm not overtly bothered. I am wondering though whether to make the next PCB, originally intended to be a negative version, dual purpose - some careful thought and one board may be able to fulfil both roles with some different stuffing and a couple of simple links (damn - there's another good idea for the competition!)
>I will email you on where to send my consulting fees.
Likewise
>I am getting samples for everything I ask for in about 3 or 4 days including some $30 voltage references.
Hmm, location or identity I wonder - will have to try again, different ID...
>If you only knew the stuff I am holding back........
I took the decision that this was a fairly easy option to a big improvement, at sensible cost, for all areas of my system. My next design would almost definitely be discrete, since op-amps are just too limiting (CF possibly being an exception). That design has somehow morphed into a headphone amp now though, whilst I learn more about discrete amp design
>Sure hope I am not helping any of your competitors for the ultimate regulator board design.........
I don't really consider myself to be in competition, I'm too much of a philanthropist for that, but do intend to make a small sum to cover investment and future releases
I wouldn't post here if I had any business sense.If you want to make money from this, you have to sell complete products - I'm too busy for that at present (damn again - more good advice for others to capitalise on). See what I mean, all the business acumen of goldfish...
A.
Hmm, location or identity I wonder
I like to think it is my personel charm.........
"since op-amps are just too limiting"
Half the circuit is discrete now. It takes some pretty serious design to get the PSRR, Gain bandwidth product, and distortion with a discreet design. You had better be a top notch PCB designer too, since the board parasitics will eat you alive for high speed analog design. Plus there is the issue of building and testing. The guys designing op amps are more talented than the majority of high end designers out there. Maybe an op amp is and pretty good choice for the error amp after all. With a buffer
it is not swinging much current and as an error amp it isn't swinging much voltage. A pretty sweet job for any amplifier.
H.H.
I like to think it is my personel charm.........
"since op-amps are just too limiting"
Half the circuit is discrete now. It takes some pretty serious design to get the PSRR, Gain bandwidth product, and distortion with a discreet design. You had better be a top notch PCB designer too, since the board parasitics will eat you alive for high speed analog design. Plus there is the issue of building and testing. The guys designing op amps are more talented than the majority of high end designers out there. Maybe an op amp is and pretty good choice for the error amp after all. With a buffer
it is not swinging much current and as an error amp it isn't swinging much voltage. A pretty sweet job for any amplifier.
H.H.
Attachments
AD825
NO
A 5 volt version has been just discussed in this thread.
Which schematic are you refering to?
Go to http://products.analog.com/products/info.asp?product=AD825 and read the data sheet.
Everyone , please read the whole thread and provide enough information in your question to answer it in one shot. People are less likely to answer if they have go back and forth for 5 or 6 post to figure out what you are asking.
Art
NO
A 5 volt version has been just discussed in this thread.
Which schematic are you refering to?
Go to http://products.analog.com/products/info.asp?product=AD825 and read the data sheet.
Everyone , please read the whole thread and provide enough information in your question to answer it in one shot. People are less likely to answer if they have go back and forth for 5 or 6 post to figure out what you are asking.
Art
Push pull
Since the load is almost pulling (in every application I can think of) , I don't see the point. Tthe addition of emmiter resistors for bias stability wound degrade the output impedance. Preloading or a more Class A bias with a resistor load would make more sense for improvements in Ft, Hfe, and Zout.
Art
Since the load is almost pulling (in every application I can think of) , I don't see the point. Tthe addition of emmiter resistors for bias stability wound degrade the output impedance. Preloading or a more Class A bias with a resistor load would make more sense for improvements in Ft, Hfe, and Zout.
Art
Well, I've done a rather similar vreg circuit in the past, and when I changed to a P-P output, I felt that the sound was more cohesive and retained a given level of resolution better when reproducing densely orchestrated music. Your experience, of course, may be different.
regards, jonathan carr
regards, jonathan carr
Push Pull
There is more than one path up the mountain. Emitter resistors can add high frequency stability. The possible increased bias for a push pull verses non preloaded single ended follower can lower output Z. They are many variables. The circuit is complicated enough as it is now; and more parts complicate stability, lengthen signal paths (and complicate ground current return paths which are critical) and make PCB layout more difficult. One would have to get down to particular circuit details to really compare theory and results. Why not post a schematic if interest is high.
Art
There is more than one path up the mountain. Emitter resistors can add high frequency stability. The possible increased bias for a push pull verses non preloaded single ended follower can lower output Z. They are many variables. The circuit is complicated enough as it is now; and more parts complicate stability, lengthen signal paths (and complicate ground current return paths which are critical) and make PCB layout more difficult. One would have to get down to particular circuit details to really compare theory and results. Why not post a schematic if interest is high.
Art
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