The 18Wer's Tone controls
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The 18Wer's Tone controls
I'm very poor on theory, although I can follow most of the Marshall-style schematics I've looked at, but I can't work out what's going on with the 18Wer's Tone and Volume controls - esp that 100K between the two pots on the non-trem channel?
Can anyone here give me an idiot's guide to what they do? I was wondering why they aren't just wired up like a guitar's Volume and Tone pots? Must be a good reason...
Can anyone here give me an idiot's guide to what they do? I was wondering why they aren't just wired up like a guitar's Volume and Tone pots? Must be a good reason...
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It's been a long time since I did any real bench work, but I'll take a stab at it. Without the 100k resistor, if the tone and volume pots were both at
their minimums (i.e. 0 ohms) there would be no load to develop input to the next stage (V2). I don't have much experience with tubes, but that what I would say if there were transistors there instead. How did I do?
their minimums (i.e. 0 ohms) there would be no load to develop input to the next stage (V2). I don't have much experience with tubes, but that what I would say if there were transistors there instead. How did I do?
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- markh
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At the one extreme, the .01u is connected directly to ground, and all treble (and a bit of mid) frequencies will be shunted to ground at that point - "bassy" tone.
At the other extreme, there's 500K at the bottom, so virtually no treble is lost.
If this were the end of the story, the tone control would still work, but the second setting would be louder, because a significant portion of the signal is lost in the first (bassy) setting.
By connecting the 100k to the other end, there is a 100K paralleled with the volume pot in the second setting, attentuating the signal a bit, and evening out the end to end (tone setting) volume level.
That's my guess, anyway!
--mark
At the other extreme, there's 500K at the bottom, so virtually no treble is lost.
If this were the end of the story, the tone control would still work, but the second setting would be louder, because a significant portion of the signal is lost in the first (bassy) setting.
By connecting the 100k to the other end, there is a 100K paralleled with the volume pot in the second setting, attentuating the signal a bit, and evening out the end to end (tone setting) volume level.
That's my guess, anyway!
--mark
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Thanks chaps.
Roadking - I'm a bit confused (it's easily done!). With the Volume at minimum we don't want any signal into V2A, no?
markh - that makes sense, except I'm still confused about what that .005uF cap feeding the input to the Volume pot is up to?
It's all a bit academic at the moment, because I'll just copy the 18W circuit exactly to start with, but it'd be nice to understand what's going on for later tweaks/etc.
Roadking - I'm a bit confused (it's easily done!). With the Volume at minimum we don't want any signal into V2A, no?
markh - that makes sense, except I'm still confused about what that .005uF cap feeding the input to the Volume pot is up to?
It's all a bit academic at the moment, because I'll just copy the 18W circuit exactly to start with, but it'd be nice to understand what's going on for later tweaks/etc.
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- markh
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- markh
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- Senior Amp Tech
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