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Audio and Video Talk
Valves / Vacuum Tubes
100 watt push-pull fixed bias amplifier
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<blockquote data-quote="Ampdog" data-source="post: 859803" data-attributes="member: 144"><p>A few thoughts from me:</p><p></p><p>One needs to be careful here. C11, C12, C13 (in connection with R22, R23) form supersonic phase correction, from about 40 KHz to over 120 KHz. Likewise C7 curtails open-loop frequency response above 26 KHz in order to keep NFB stable. Making C7 = 220pF starts roll-off at some 9 KHz.</p><p></p><p>Point: One needs to rather check operation involving these capacitors with an oscilloscope and a say 5 - 10 Khz square wave to watch for over/undershoots/instability. By the time you can hear a difference with music, case might be that the 'poor sounding' side is already suffering from instability, as all of the above except C7 has effect only well above the audio band (guesstimate some 40 Khz to 120 KHz, also directly dependant on OPT h.f. characteristics.).</p><p></p><p>This in connection with the OPT internal capacitance and leakage inductance; unknown(?) in Dr Gillespie's case. It can be simulated; sadly my SPICE programme does not work at present (seems to age even faster than its owner!)</p></blockquote><p></p>
[QUOTE="Ampdog, post: 859803, member: 144"] A few thoughts from me: One needs to be careful here. C11, C12, C13 (in connection with R22, R23) form supersonic phase correction, from about 40 KHz to over 120 KHz. Likewise C7 curtails open-loop frequency response above 26 KHz in order to keep NFB stable. Making C7 = 220pF starts roll-off at some 9 KHz. Point: One needs to rather check operation involving these capacitors with an oscilloscope and a say 5 - 10 Khz square wave to watch for over/undershoots/instability. By the time you can hear a difference with music, case might be that the 'poor sounding' side is already suffering from instability, as all of the above except C7 has effect only well above the audio band (guesstimate some 40 Khz to 120 KHz, also directly dependant on OPT h.f. characteristics.). This in connection with the OPT internal capacitance and leakage inductance; unknown(?) in Dr Gillespie's case. It can be simulated; sadly my SPICE programme does not work at present (seems to age even faster than its owner!) [/QUOTE]
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Audio and Video Talk
Valves / Vacuum Tubes
100 watt push-pull fixed bias amplifier
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