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Old 27th November 2012, 06:57 PM   #2231
benb is offline benb  United States
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Quote:
Originally Posted by kgrlee View Post
It's still not too late to put forward your criteria for consideration.

I think Scott & I share very clear common criteria; eg low THD, sensible stability adjustment for different loads & gains. no funnies on overload or startup, no Unobtainium, robust to component variations ...
I don't see the point of those last four words, unless this is to be manufactured for the lowest price. One percent resistors are common and cheap, and transistors are cheap enough to buy a handful and measure beta with a $20 DMM to get several pairs matching within two percent or so. It would of course be nice if a design works out to be "robust" but is it really needed?
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Old 27th November 2012, 08:30 PM   #2232
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.. robust to component variations.
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Originally Posted by benb View Post
I don't see the point of those last four words, unless this is to be manufactured for the lowest price. One percent resistors are common and cheap, and transistors are cheap enough to buy a handful and measure beta with a $20 DMM to get several pairs matching within two percent or so. It would of course be nice if a design works out to be "robust" but is it really needed?
IMHO, (and this is borne out by one of the few sim results I actually believe 100%) even with 1% resistors and 2% BJTs (and 2% FETs from the Unobtainium FET Shop) you will still need a twiddle pot for 'acceptable' DC offset and output stage quiescent current.

You can put the tweak pot(s) in various places but even in the 'best' positions, some circuits are MUCH more fussy than others. The pot range can be insufficient to allow for your 1% resistors, 2% BJTs etc and at the same time still be too twitchy to adjust accurately.

'.. robust to component variations' usually implies good thermal stability too.
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Old 27th November 2012, 08:47 PM   #2233
RNMarsh is online now RNMarsh  United States
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Default Robust design- Try this in SIM -

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Originally Posted by kgrlee View Post
IMHO, (and this is borne out by one of the few sim results I actually believe 100%) even with 1% resistors and 2% BJTs (and 2% FETs from the Unobtainium FET Shop) you will still need a twiddle pot for 'acceptable' DC offset and output stage quiescent current.

You can put the tweak pot(s) in various places but even in the 'best' positions, some circuits are MUCH more fussy than others. The pot range can be insufficient to allow for your 1% resistors, 2% BJTs etc and at the same time still be too twitchy to adjust accurately.

'.. robust to component variations' usually implies good thermal stability too.
Take a look at sim of the circuit I did last year and is in Linear Audio for something different. Did you see it -- I put it up here, at DIYAudio forum, too. Seems to fit your description of what you are looking for. TotalHD+Noise at 1-2 vrms out into >600 Ohm is under (measured as built - not sim) .0005% no dc offset and no thermal drift. No servo. Moderate gnfb. wide open loop BW. Will drive down to 30 Ohms with low distortion -- about 1W. Bias for more, if you like more class A into low Z. Just have to match the cheap devices. Not developed to compete here as a universal OPA but you can play with it's circuit to suit your needs and curiousity and compare results. THx-RNM

Last edited by RNMarsh; 27th November 2012 at 08:54 PM. Reason: No tweaks used
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Old 27th November 2012, 09:00 PM   #2234
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Originally Posted by RNMarsh View Post
Take a look at sim of the circuit I did last year and is in Linear Audio for something different. Did you see it -- I put it up here, at DIYAudio forum, too. ... Not developed to compete here as a universal OPA but you can play with it's circuit to suit your needs and curiousity and compare results.
I'd love to have a look, Mr. Marsh. Got a more precise link to the circuit? Beach bums don't buy magazines cos kunt reed en rite.

If it sims in the same ball-park as SW-OPA, you're still ahead cos Scott hasn't finished his breadboard.
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Old 28th November 2012, 01:51 AM   #2235
RNMarsh is online now RNMarsh  United States
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Default Affects of dynamicly varying open-loop BW on music-

Reflected load Z artifacts etal from output to Av stage is not unknown. Output 'buffer' circuits vary in their isolation ability to minimize the affects.
But it clearly can affect performance, especially with reactive and changing loads with freq.... such as, power amp and loudspeaker reflecting back any nonelinear Z.
SO. and BUT -->

Can we make a circuit that can modulate just the open-loop bandwidth of the opamp/pwr amplifier and while this is going on, measure IM and other distortions. Especially interesting would be any phase modulation distortion caused by this.... PIM?
Such as via switched C or an injected square wave somewhere that we can control the speed of change in open-loop BW.

Secondarily, which topology in the output stage has the greatest isolation from output to Av stage. [What about no output buffer stage - just off the Av stage.] Thx- RNMarsh

Last edited by RNMarsh; 28th November 2012 at 01:59 AM.
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Old 28th November 2012, 02:15 AM   #2236
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Quote:
Originally Posted by RNMarsh View Post
Take a look at sim of the circuit I did last year and is in Linear Audio for something different. Did you see it -- I put it up here, at DIYAudio forum, too. Seems to fit your description of what you are looking for. TotalHD+Noise at 1-2 vrms out into >600 Ohm is under (measured as built - not sim) .0005% no dc offset and no thermal drift. No servo. Moderate gnfb. wide open loop BW. Will drive down to 30 Ohms with low distortion -- about 1W. Bias for more, if you like more class A into low Z. Just have to match the cheap devices. Not developed to compete here as a universal OPA but you can play with it's circuit to suit your needs and curiousity and compare results. THx-RNM
If you guys have axes to grind, take it elsewhere.
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"The question of who is right and who is wrong has seemed to me always too small to be worth a moment's thought, while the question of what is right and what is wrong has seemed all-important."
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Old 28th November 2012, 03:08 AM   #2237
RNMarsh is online now RNMarsh  United States
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Default WTF ??!!

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Originally Posted by scott wurcer View Post
If you guys have axes to grind, take it elsewhere.
What axe would that be?
It appeared to me, kgrlee was pointing himself in a direction I had gone before so informed him of the design. Its for him to study and play with and as I said isnt a competitor here.
So, take it easy. Handle it.
I, myself and me.... have zero axe to grind. I am here to participate and contribute and learn from all view points. -R. Marsh

Last edited by RNMarsh; 28th November 2012 at 03:28 AM.
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Old 28th November 2012, 04:06 AM   #2238
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Quote:
Originally Posted by scott wurcer View Post
If you guys have axes to grind, take it elsewhere.
No axes, Scott. This is a civilised thread.

Several interesting topologies have been suggested and I've tried to apply the same criteria to the more interesting ones in SPICE land. So far SW-OPA is one of the front runners.

Also unlike certain pseudo Messiah's that shall remain nameless, Marshy has tested his circuit so it has credibility that wannabe SPICE gurus like me lack. But the race is hotting up cos you're about to test the complete SW-OPA.
____________________

Mr. Marsh, any idea when you posted that circuit in diyaudio? I'm looking through your 1000 odd posts but its slow.

Last edited by kgrlee; 28th November 2012 at 04:21 AM.
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Old 28th November 2012, 05:59 AM   #2239
RNMarsh is online now RNMarsh  United States
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Default What does it all add up to?

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Originally Posted by EUVL View Post
Gentlemen,

You have a once-in-a-lifetime chance to learn from professionals like Mr. Wurcer, Mr. Marsh, Mr. Curl, maybe even Mr. Jung, .....
on how to design opamps for audio without worrying about cost of production and what not.

Why would one want to miss it ?

Anyway, if it is not your cup of tea, I am sure there are other more entertaining threads on the forum.
Why not just let those interested have some fun ?

Cheers,
Patrick
I have 45 years of intense learning about something. Scott has 40 years of doing something else. That right there is 95 years of continuous hard work on something. Here we have a common interest that overlaps. Ditto for JC, WJ. More than three centuries doing something which we all overlap here in our common interest areas. I dont begin to assume that I can know what another knows. That knowledge and experience ought to be respected by each and all. More than 200 years of expertise in just the 4 people mentioned above plus the many others who comment here and in other forums (N.Pass) means what is brought up is not to be taken lightly or quickly dismissed. There are a lot of years work behind my sometimes simple sounding statements/style presented as I am just as sure from the others. Thx- R.N.Marsh

Last edited by RNMarsh; 28th November 2012 at 06:29 AM.
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Old 28th November 2012, 06:26 AM   #2240
RNMarsh is online now RNMarsh  United States
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Default Where is it?

Quote:
Originally Posted by kgrlee View Post
Mr. Marsh, any idea when you posted that circuit in diyaudio? I'm looking through your 1000 odd posts but its slow.
gads. Did I write all that? And, I only came here in May this year. I just wanted to help DIY headphone amp builders make the headphone amp and enjoy it. Now here I am spilling my life's guts out to a bunch of strangers on this social medium! Am I that desperate!? [not really]. Wasnt I breast fed?

Kgrlee--- I'll see if I have any better luck finding it. -RNM
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