Can anybody explain what's the purpose of this array of capacitors and resistors between the plate of the pentode and the volume control? definitely looks like some kind of equalization and it is more or less like a resulting 333k in parallel with the volume pot and a 1nF capacitor.
Or is it something else ? I know I've seen this before.
this is part of one of the inputs of:
http://i67.tinypic.com/2hs466e.jpg
also
Or is it something else ? I know I've seen this before.
An externally hosted image should be here but it was not working when we last tested it.
this is part of one of the inputs of:
http://i67.tinypic.com/2hs466e.jpg
also
An externally hosted image should be here but it was not working when we last tested it.
Easy.
It´s a 4 stage 32Hz highpass filter to stop the vibrato modulation signal from going on through the amplifier.
It´s roughly 24dB down at 32 Hz and falls like a brick below that.
Since vibrato frequency is a few Hz frequency, it gets attenuated.
It´s a 4 stage 32Hz highpass filter to stop the vibrato modulation signal from going on through the amplifier.
It´s roughly 24dB down at 32 Hz and falls like a brick below that.
Since vibrato frequency is a few Hz frequency, it gets attenuated.
Thank you never thought it was related to the vibrato, now that you mentioned I see the coincidence with these two circuits.
What was said above.
This type of tremolo works by bias modulation; a low frequency AC signal component, which is superimposed to the audio signal, slowly alters grid-to-cathode voltage of the gain stage and therefore its gain. Trick is that the low frequency signal from the LFO is in a frequency range that is easily below human hearing threshold but the amplitude modulation it causes is easy and distinct to hear as change of loudness in the "generic" signal content.
-BUT- one does not wish to pass that modulation signal component to subsequent stages: It is generally much higher in amplitude than the "generic" modulated signal and could therefore easily overdrive the following stages in very obtrusive way, and even when that does not happen one often hears "wobbling" artefacts that are higher harmonics of the modulation signal, or intermodulation distortion of the audio and modulation signals.
An x-order hi-pass filter (here 4 or 5 generic first order filter circuits in series) will remove the low frequency signal component after the gain-modulation has been introduced.
This type of tremolo works by bias modulation; a low frequency AC signal component, which is superimposed to the audio signal, slowly alters grid-to-cathode voltage of the gain stage and therefore its gain. Trick is that the low frequency signal from the LFO is in a frequency range that is easily below human hearing threshold but the amplitude modulation it causes is easy and distinct to hear as change of loudness in the "generic" signal content.
-BUT- one does not wish to pass that modulation signal component to subsequent stages: It is generally much higher in amplitude than the "generic" modulated signal and could therefore easily overdrive the following stages in very obtrusive way, and even when that does not happen one often hears "wobbling" artefacts that are higher harmonics of the modulation signal, or intermodulation distortion of the audio and modulation signals.
An x-order hi-pass filter (here 4 or 5 generic first order filter circuits in series) will remove the low frequency signal component after the gain-modulation has been introduced.
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