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Old 21st June 2002, 03:02 PM   #11
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Default The original version

Dubbed the "Universal Tiger", Popular Electronics, Oct. 1970.

Jocko
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Old 15th July 2002, 08:15 PM   #12
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Location: Germany
Quote:
Originally posted by Nelson Pass

The output coil and resistor are similarly hangovers from the
old days. They were in the original RCA manual, and most
designers use them because monkey-see-monkey-do.

I have never seen a case where they stabilized an unstable
amp, nor where their absence caused instability, and so I
don't use them.
Well, I found they can be quite useful, but only when using nasty loads. I tried to remove the coils or only replace them with lower values on several commercial designs - sometimes made the amps oscillate heavily when driving a square wave into a 3 R resistive load!

I try to make my own designs stable with all kinds of loads, including 100 pF - 10 uF stacked film capacitors on the output. Found I could not eliminate the coil completely if I did not want to limit the bandwidth but was able to do with 1/100 of what is commonly used.

Eric
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Old 15th July 2002, 11:55 PM   #13
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Location: Orleans, France
Use of output coil is very dependent of what kind of load is connected, but also of phase margin and gain in the overall feedback loop. In fact, this is the same thing because at very high frequencies the amp becomes a current generator, and the reactance of the load is the essential part of the current/voltage converter at the output.

The major problem is that one cannot divine what kind of load can be connected by the artless user... which always reads the carefully prepared "user manual" after the disaster.

Regards, P.Lacombe.
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