Best topology for no-feedback ClassAB buffer ?

Elvee · 2010-09-24 9:38 am

Bigun said:
So there's a bit of JLH going on here too with that phase splitter.

Have you or somebody else ever built this to try it out ?

I have used the regular, N-version in test amplifiers. I don't remember using the unity, P-version, but the difference is relatively minor.

The N-version works OK, it tends to have asymetric properties such as slew-rates, which is not surprising, considering the topology.
This may or may not be be to your taste: some people love symetry, some hate it.
Others may have also tried the topology, for example:
http://www.diyaudio.com/forums/soli...-gain-5v-output-stage-sought.html#post1935087

Note that Wavebourn's circuit almost certainly has a lower distortion, thanks to the total feedback and symetry. The choice is yours.

djk · 2010-09-24 10:11 am

http://www.audiodesignguide.com/my/Cool_Follower1.GIF

Wireless World, October 1976 Wireless World page 74 has a 10W version.

Edmond Stuart · 2010-09-24 10:47 am

Bigun said:
[snip]
I'd rather try and get SS not to sound like anything at all.
[snip]
but I figure that I would want a super-clean SS output, not one that makes for 'tubey' sounds.
[snip]

Hi Bigun,

If using feedback is not a problem, you also might consider a CFB-OPS as discussed here:
http://www.diyaudio.com/forums/soli...terview-error-correction-270.html#post1350062
The discussion is quite long and it ends about here: http://www.diyaudio.com/forums/soli...terview-error-correction-283.html#post1358518

Cheers,
E.

apexaudio · 2010-09-24 10:55 am

Output stage from Tube/Mosfet Amp

Bigun · 2010-09-24 2:24 pm

Elvee said:
I have used the regular, N-version in test amplifiers. I don't remember using the unity, P-version, but the difference is relatively minor.

The N-version works OK, it tends to have asymetric properties such as slew-rates, which is not surprising, considering the topology.
This may or may not be be to your taste: some people love symetry, some hate it.
Others may have also tried the topology, for example:
http://www.diyaudio.com/forums/soli...-gain-5v-output-stage-sought.html#post1935087

Note that Wavebourn's circuit almost certainly has a lower distortion, thanks to the total feedback and symetry. The choice is yours.

Thanks Elvee.

I'm not too worried about a bit of distortion if it's 'Hiraga-like', meaning a predominance of lower orders and rapid fall off of higher orders. This harmonic profile will result from the tube front-end, but avoiding nasty higher order harmonics will be a challenge with the SS buffer and in particular it will be difficult to avoid odd order harmonics if using a symmetric design. However, I like the soft-clipping potential of Wavebourn's output. I can see this being useful only if swing is limited by the output stage rather than the input stage.

The 'cool follower link' looks like a simple diamond buffer with paralleled output devices so not sure why it's labelled as new and never seen before ? Nevertheless, it looks simple to implement and I have a better chance of understanding how this works

Thanks Edmond - I remember trying to read that thread once. I did manage to read a good deal of it. It was quite fascinating. I wish it were possible to get a potted summary of some of these types of long threads as there's much to learn. I'll have to go back and look again, it's been several months.

Thanks Apex - what am I looking at here, it looks like source follower but with something going on in terms of bias - is this an auto-bias or error correction ?

jerluwoo · 2010-09-24 5:46 pm

i can vouch for the circuit elvee posted. i have used that buffer for a few years now. search for a thread "my simple class a approach". i never used an active current compensation, i used a ring of two current source with the sense transistor glued to hea

jerluwoo · 2010-09-24 6:02 pm

sorry i'm posting from my phone and it limits how i can post at once. i meant to say glued to the heatsink

Bigun · 2010-09-24 9:42 pm

Hi Jerluwoo,

It's good to hear that the circuit has been successfully employed in Class A. Did you try the circuit biassed at Class AB ? - I see a lot of options for Class A buffers which can yield excellent results, but this thread I'm raising the challenge of a no feedback Class AB buffer !

Anybody any thoughts about the Krill ? - the output stage that is.
http://www.diyaudio.com/forums/solid-state/134619-krill-little-amp-might.html#post1681384
http://www.diyaudio.com/forums/solid-state/151295-krill-next-generation.html

This options is also looking very attractive as many amplifiers have been built with positive results. A triode frontend looks quite feasible.

jerluwoo · 2010-09-25 11:24 pm

No this buffer can not be ran a/b. It works by dividing the current from ccs between the output transistors. Once one transistor reaches cutoff the other is at its max current output.

djk · 2010-09-26 1:05 am

The Cool Follower design is also know as a Diamond Buffer, and may be run in class A (Hot Follower), or class AB (Cool Follower).

Bigun · 2010-09-26 3:14 am

Thanks jerlwoo.

djk - yes, I am leaning towards the Diamond buffer. I am looking at the Krill implementation, it offers an interesting bias scheme (assuming I may refer to the Krill as a form of Diamond Buffer).

Edmond Stuart · 2010-09-26 10:07 pm

Bigun said:
.................
Anybody any thoughts about the Krill ? - the output stage that is.
http://www.diyaudio.com/forums/solid-state/134619-krill-little-amp-might.html#post1681384
http://www.diyaudio.com/forums/solid-state/151295-krill-next-generation.html
..........

Yes, I have: :rofl:

Bigun · 2010-09-27 3:35 am

Edmond Stuart said:
Yes, I have:

did you build one (I thought you said you don't usually build, mostly simulate) ?

Edmond Stuart · 2010-09-27 10:42 am

Hi Gareth,

You have a PM.

Cheers,
E.

tiefbassuebertr · 2010-09-27 2:25 pm

Elvee said:
Here is an unconventional suggestion:

It is a half-diamond circlo buffer.

It has a full NPN output, low-Z, good linearity, no crossover distortion, a servoed Iq control, and a decent bandwidth, even with 2N3055s.

this circuit is based on the circlomos circuit - go to
http://www.diyaudio.com/forums/solid-state/154388-its-cheap-its-n-its-dirty-its-circlomos.html
are here additional threads about this topology?
I don't find suggestions about circlobjt, circlomos with bjt's and circlobuffer

Bigun · 2010-09-27 6:16 pm

my memory is coming back now. I've seen some of this before.

http://www.diyaudio.com/forums/soli...llower-diamond-buffer-power-output-stage.html

and some further thoughts on biassing:
http://www.diyaudio.com/forums/soli...put-stage-vertical-fets-thermally-stable.html
Re: New error correction amp - diyAudio.

Bigun · 2010-10-07 2:10 am

Thank you everyone for contributing so eagerly, I almost feel obliged to build all of these and give them a fair listen !!!!

Well I'm going to start with the Diamond Buffer, the Krill version of it. I've started a new thread over in the tubes section to get some input on that aspect of the design.
http://www.diyaudio.com/forums/tubes-valves/174889-cellini-2-hybrid.html

Once I have that up and running I will know a lot more about where to go next, but I am a closet fan of the Sziklai and it would seem relatively easy to put one of these at the output of the Krill Diamond. At that point I can look at some of the cool features contained within Wavebourn's circuit and the search goes on.....

tiefbassuebertr · 2010-10-18 6:43 pm

Elvee said:
Here is an unconventional suggestion:

It is a half-diamond circlo buffer.

It has a full NPN output, low-Z, good linearity, no crossover distortion, a servoed Iq control, and a decent bandwidth, even with 2N3055s.

In the attachement the DC conditions in my simulation for that circuit (between 2N3773 and 2N3055 no difference to observe).
The p-spice modell of 2N3773 I have download from
ON Semiconductor

Bigun · 2010-10-19 2:53 am

It has a very JLH kind of look to the topology and I think this bodes well.

tiefbassuebertr · 2010-10-19 11:17 am

Bigun said:
It has a very JLH kind of look to the topology and I think this bodes well.

at first look it seems to be right - also by the DOZ
http://www.diyaudio.com/forums/solid-state/165660-i-build-my-jlh-amplifier.html
http://www.diyaudio.com/forums/pass-labs/28494-doz-death-zen-amp-rod-elliot.html
But the greatest similarity concerning the output is to Olsson's circuit about
http://www.amplimos.it/images/N-CH1.JPG
Original article: Better Audio from non complements? from Bengt Olsson (B. Olson?)
Electronics World + Wireless World, December 1994 page 988
and additional the Creek Circuit from X-pro
http://www.diyaudio.com/forums/soli...50-mk2-circuit-descr-arround-q12a-wanted.html
so as this circuit:
http://www.diyaudio.com/forums/solid-state/160285-class-b-w-o-crossover-distortion-1975-a.html (post #6)

Best topology for no-feedback ClassAB buffer ?

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