WTF Master Volume

Frequently asked question regarding resistors, potentiometers, types, requirements, ratings etc.
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TV-Set
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Post by TV-Set »

Hullo.
I've been putting together my own od circuit when I noticed something a bit odd: when I added the master pot (I tried 22K, 100K, 500K and 1M) it actually acts as a volume pot of a tube amp (meaning that u have to crank it to get overdrive). Well, I know this is a common thing and in most analog fxs I used or built it is so. But in this particular case the impact on the sound is huge! I get little to no overdrive with the master at low levels even when the circuit's gain is at max. Then, when I bring the master level to 10/10 I get the full ammount of distortion... yes, that's ok, but the volume gets too high and basicly makes the thing unusable in an fx chain.

Is there a way to make a proper master controll without it acting as a gain pot at the same time?

PS: just screwing around I measured my amp's input impedence, it' 1M. And then I realized that by putting any master pot at the fx's output the impedence is 0 ohm at min level and would go as high as 500K if I used a 1M pot for instance. The circuit is at it's best when there is no master pot at all and the signal is fed to the amp straight from the output cap... hmmm hmmm

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juanro
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Post by juanro »

That probably means that the overdrive sound you're getting is because, well, *ejem*, you're over-driving your amp input.
So your circuit is really working as a booster (mainly amplifying the guitar signal without overdriving it much by itself) but as the output of the circuit is really hot, it makes the preamp in the amplifier to distort.

Can you post a schematic? Regards

Juanro
La única verdad es la realidad.

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TV-Set
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Post by TV-Set »

Image
  • Q1 2N5088
    Q2 2N5088

    R1 33K
    R2 2M2
    R3 470R
    R4 100K trim
    R5 100K
    R6 2M2
    R7 470R
    R8 1M
    R9 100K trim

    C1 10n
    C2 22u
    C3 100n
    C4 47u
    C5 100n
Collector voltage set at 4.5V. Trims should be substituted with pots and the Vc range would be from 2 to 7V (low Vc = high gain)

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