Reducing noise in voltage regulators

[HarryHaller]

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.

[ALW]

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.

[HarryHaller]

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.

[ALW]

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.

[janneman]

Originally posted by HarryHaller
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.

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]

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......

[UrSv]

Please let me thank you, especially ALW, HH and Jan, for the quality of this thread. I really appreciate your efforts and rest assured that I will learn from you in one way or another.

Thanks/UrSv

[HarryHaller]

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/docum...pp&document=83


Voltage Reference Circuit Collection

http://www.linear-tech.com/pub/docum...pp&document=45



REFERENCES AND LOW DROPOUT LINEAR REGULATORS

http://www.analog.com/technology/pow...pdf/fsect2.pdf

H.H.

[ALW]

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.

[janneman]

Originally posted by HarryHaller
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......

Harry, no offense taken at all. And I am the first to admit should I do this project today, I would different devices for sure. This is an exiting field to be part of!

Jan Didden