Hoffman Amplifiers Tube Amplifier Forum
Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: 12AX7 on November 15, 2016, 09:06:48 am
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I have a effects loop that is fed from the cathode follower in a marshall style amp, so the tone stack feed is AC. When i inserted a signal, at the TS input and check the signal level at the input of the TS then at the treble wiper output, i get about 45% of the input signal at the output with the tone controls all on 10. Doesn't that sound about right? I'm just trying to eliminate all possibilities to find a issue i'm having so i just want to confirm that this is typical. Thanks.
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Use the Duncan Tonestack Calculator. Also without a schematic your question requires too many assumptions to answer. BTW all tones tacks are always fed with AC. All signal is AC.
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Use the Duncan Tonestack Calculator. Also without a schematic your question requires too many assumptions to answer. BTW all tones tacks are always fed with AC. All signal is AC.
I have the TSC.
As to DC vs AC....if a cathode follower is AC, what could cause mine to output DC? Because thats what i reads stable.
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As to DC vs AC....if a cathode follower is AC, what could cause mine to output DC? Because thats what i reads stable.
D.C. is always present at the output of a tube stage (before any coupling capacitance) to allow the tube to function. A.C. is present at the output when a signal is applied, and transferred from input to output.
The output of any tube feeding a tone control circuit often has no extra coupling cap to block d.c., because the tone circuit contains caps already which can then serve double-duty to block d.c.
... When i inserted a signal, at the TS input ... i get about 45% of the input signal at the output with the tone controls all on 10. ...
PRR's plot shows 45% output happens at 3 frequencies. One of those is very-near 1kHz.
I'm guessing you used a 1kHz test tone...
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The output *at the cathode* will be several volts AC/Audio riding on maybe 150V of DC.
The output *after the tone stack* should be AC/Audio and zero DC.
Say what your real concern is.
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As to DC vs AC....if a cathode follower is AC, what could cause mine to output DC? Because thats what i reads stable.
D.C. is always present at the output of a tube stage (before any coupling capacitance) to allow the tube to function. A.C. is present at the output when a signal is applied, and transferred from input to output.
The output of any tube feeding a tone control circuit often has no extra coupling cap to block d.c., because the tone circuit contains caps already which can then serve double-duty to block d.c.
... When i inserted a signal, at the TS input ... i get about 45% of the input signal at the output with the tone controls all on 10. ...
PRR's plot shows 45% output happens at 3 frequencies. One of those is very-near 1kHz.
I'm guessing you used a 1kHz test tone...
I see. And yes, a 1khz tone.
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Say what your real concern is.
I already posted about it but got no responses so i deleted it because i figured no one had any advice on it. So i decided just to ask questions about ideas i had to try and troubleshoot it myself. So no reason to post about it. I just wanted to get this question answered and it was, thanks.
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All the resistors and capacitors in a circuit present an AC-load (to the signal). The more resistors (and/or caps) there are in parallel, the higher the AC load (and the more signal attenuation there otherwise is).