Diamond Cascode, a Diamond-like buffer/current booster - Page 2 - diyAudio
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Old 16th August 2013, 10:22 PM   #11
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well there is a benefit to the circuit if it ads nil harmonics to the basic opamp and manages to boost the current!
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Old 16th August 2013, 10:35 PM   #12
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Hi Guys

That's essentially my point. The EF is just one stage - not a diamond - so it does give the benefit of current boosting. An open-loop single-ended EF produces mostly 2nd harmonic THD. One would expect some canceling of evens with a push-pull EF but this is not always the case. So, there may in fact be some harmonic enhancement with the EF on its own basis.

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Old 17th August 2013, 10:03 AM   #13
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FWIW, I added the base-to-base capacitor for the EFs and redid the layout, squeezing it in the same area as before - however, only a 0603 will fit for now, which is fine for small X7Rs. There's an added bonus - a zero-ohm resistor can be optionally fitted there to allow modifying the assembly (with the nJFET CCS installed, but the rest of the discretes omitted) for opamp + CCS Class-A operation alone.
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Old 18th August 2013, 02:03 AM   #14
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Originally Posted by linuxguru View Post
Thanks - I haven't specifically measured the DC offset, except at the output of a MyRef Rev C with an LM318M installed as U1. In that case, it was negligible - 0.6 and 1.4 mV respectively in the two channels at the main speaker output.

...

The existing prototypes use LM318M (~6 qty) and LME49990 (1st unit assembled this morning, tested working - will do another one and audition shortly).
Hi Siva, may I know what do you expected with your prototype installed as 'LM318' in MyRef Rev C?
Does it give better sound?
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Old 18th August 2013, 04:10 AM   #15
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Originally Posted by clarkynoel View Post
Hi Siva, may I know what do you expected with your prototype installed as 'LM318' in MyRef Rev C?
Does it give better sound?
I certainly prefer it to the plain LM318 for the kind of music I listen to - the audible sonics of the LF07 are distinctly Class-A in a MyRef Rev C: better definition, resolution, micro-detail, air, smoothness, etc.

However, for the differences to be audible, the other components in the MyRef also have to be of sufficiently high quality - C13, C9, C12, C7, R12, C10, C32, C30, C34, C6, C11, etc. have an impact on sound quality in a MyRef.
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Old 18th August 2013, 05:05 PM   #16
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So have you tried the newer "super-ultra low distortion" opamps at all?
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Old 18th August 2013, 07:15 PM   #17
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I've tried the LME49990, which works - but it needs a reference DAC/CD player to be able to tell the audible difference with and without the buffer. Perhaps a better test would be in a CMoy, driving low-Z headphones.
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Old 19th August 2013, 02:45 PM   #18
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Have you compared it to the Chris Paul/Bob Cordell cross coupled output buffer? (Cordell uses that connection, but Chris Paul published it I think earlier... still trying to get to the bottom of that... like where that circuit came from)

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Old 20th August 2013, 02:26 PM   #19
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Have you compared it to the Chris Paul/Bob Cordell cross coupled output buffer? (Cordell uses that connection, but Chris Paul published it I think earlier... still trying to get to the bottom of that... like where that circuit came from)
Is there a link that shows or discusses this topology? Bob has posted a lot of stuff here, so it's daunting to wade through a zillion posts.

Meanwhile, the base-to-base capacitor for the EFs suggested by Kevin does not appear to hurt audible sonics, and it sims with lower H2 and THD20 as I mentioned earlier. I kludged a 100nF Panasonic ECHU stacked PPS film cap into a couple of LF07 modules and auditioned them in a MyRef Rev C. The sonics are the same as before, except that the definition and resolution of the highs seem enhanced. I'll listen to it for a while, but it already looks like a worthwhile enhancement.
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Old 20th August 2013, 03:42 PM   #20
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Yeah... ummm... it's used in the output stage of his power amps, iirc... in his book. I mentioned it some years ago in a thread about output buffers, and suggested the connection instead of having the drivers collectors going to the rails, go to the junction of the output's emitter + emitter resistors on the opposite side.
So instead of going to the + rail, the lower driving transistor would connect to junction of the output run off the + rail and its emitter resistor...

dunno if that makes any sense...

I'll try to find an example I can link or upload.
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