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Building a massively parallel op amp power amplifier
Building a massively parallel op amp power amplifier
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Old 30th November 2017, 01:22 AM   #41
xrk971 is offline xrk971  United States
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Building a massively parallel op amp power amplifier
Nice work Idiosyncrasy!


The “choir” comment was aimed at discrete output transistors. It’s a real effect - that’s why we have load sharing resistors to take up the small differences. If totally unmatched, even load sharing resistors can’t help.

With opamps in a buffer config, each one has local feedback to make it match its neighbors. But one thing to consider is that a feedback free amp sounds better from an imaging standpoint - phase is very flat and with great margin. Listen to a single opamp based amp and then 40 in parallel - with tracks that rely on stereo imaging. Now you have 40 feedback loops going on. See in your minds eye which is better or more clear.
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Old 4th December 2017, 01:52 PM   #42
jcx is offline jcx  United States
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Default listening with your imagination does give 'different' results from 'ears only'

Quote:
Listen to a single opamp based amp and then 40 in parallel - with tracks that rely on stereo imaging. Now you have 40 feedback loops going on. See in your minds eye which is better or more clear.
of course you can inform your imagination

try comparing unity gain vs 2x gain with fast opamps for difference in group delay, essentailly the same as batch GBW variation of 2:1

result: ~ 130 ps @ 20 KHz - yes that's picoseconds
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Old 5th December 2017, 07:00 PM   #43
xrk971 is offline xrk971  United States
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JCX,
That’s cool if you don’t believe ZGF amps make a difference in imaging. It makes a difference for live recorded minimally produced ambient music. I don’t want to clog up this thread with that debate. It’s in a way similar to people who argue that speakers without transient perfect response crossovers are indistinguishable from those that are because they think LR2 XO’s sound fine with a tweeter signal that’s 180deg out of phase. It’s the most popular XO in multi ways.
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Last edited by xrk971; 5th December 2017 at 07:03 PM.
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Old 8th December 2017, 05:15 PM   #44
70s Veteran is offline 70s Veteran
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Utter nonsense. Doug Self is not The guru of Audio design nor is Nelson Pass. But I must admit his Camp Amp with lateral MOSFETS is very good indeed. Especially when driven by a EF86 pentode configured as a triode with an MJE340 buffer transistor for 0.003% distortion. Maybe you like Opamp sound I don't. In my opinion the best web site I have found is Elliot Sound Products.
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Old 8th December 2017, 05:25 PM   #45
scottjoplin is offline scottjoplin  Wales
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Quote:
Originally Posted by xrk971 View Post
The “choir” comment was aimed at discrete output transistors. It’s a real effect - that’s why we have load sharing resistors to take up the small differences. If totally unmatched, even load sharing resistors can’t help.
Any literature on this? I can't find any
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Old 8th December 2017, 06:14 PM   #46
Decker is offline Decker  United States
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Hey 70s Veteran, can you post a schematic of the triode/MJE340 circuit? I have a couple of Amp Camp boards that I haven't used yet. Been thinking of a project with them and would love to see your ideas.
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Old 8th December 2017, 07:52 PM   #47
traderbam is offline traderbam  Europe
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Each of the 80 op-amps in a channel is different. If they were all exactly the same then there would still be variance in resistor values, connection trace resistances and reactances, and noise. Any individual op-amp output target voltage that's different from the average (sort of average) of the herd will be driven into a 1 ohm resistor. How large are these differential currents likely to be when playing music?
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Old 9th December 2017, 08:07 AM   #48
palstanturhin is offline palstanturhin  Finland
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Quote:
Originally Posted by traderbam View Post
Any individual op-amp output target voltage that's different from the average (sort of average) of the herd will be driven into a 1 ohm resistor. How large are these differential currents likely to be when playing music?
Each opamp will also sink the error voltage any opamp produces, so paralleling a million should create quite good average. Starting from 80 for example.
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