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In Reply to: RE: Behaviour in overload of PP EL84M cathode bias amp? How to examine for that? posted by Timbo in Oz on September 04, 2014 at 16:27:15
If by "examine" you mean measurements based on a controlled test, you'll need a test setup specifically for this. The easiest way to see what's happening is probably to drive the amplifier with an arbitrary waveform generator. Generally speaking, I would input several cycles of an "overload-level" sine wave and immediately follow that with a few hundred milliseconds of low-level signal. Analysis of the recovering signal probably must be done visually with a scope, as the short lifespan of the "recovery-in-process" condition probably prevents use of a distortion analyzer or other test gear. A simpler test might be to drive the stage into overload, then kill the input and monitor the DC drift on the grid with the scope, then repeat the test while looking at the cathode (if self-biased).
This issue might produce less obvious audible artifacts in a biamped system such as yours. The higher levels of THD and IM that I would expect to be generated during recovery are most likely to occur in the low frequency amplifier. That amplifier, however, is cutoff at a fairly low frequency, so much of the distortion won't be heard.
As for simply not worrying about this, I think it's worth noting that a number of respected designs from the '60s, including the Heath W6M and McIntosh MC60, used cathode followers to drive the final stage. Regardless of how modern audiophiles rate amplifiers like these, it's clear that driver impedance and overload recovery were on the minds of those earlier designers.
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Buy Chinese. Bury freedom.
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On the AA website under 'reviews,' yes or no?
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Tim Bailey
Skeptical Measurer & Audio Scrounger
No, do you have a link?
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Buy Chinese. Bury freedom.
"can read it up over in reviews.' First line of my OP!? :-)!
Not that hard to find, really.
Warmest
Tim Bailey
Skeptical Measurer & Audio Scrounger
I don't see anything in that post related to this thread. Is there a connection?
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