wonder why my 10k pot muffles the sound of my boost.

[acehobojoe]

10k pot placed at the beginning of the booster circuit I'm working on. It is basically just a booster much like this schem.

http://www.beavisaudio.com/techpages/blocksfragments/images/JFET_Booster_Schematic.gif

the pot is wired with the 1 to ground and 3 to in, 2 to beginning of transistor circuit. it baffles me. the circuit sounds great, I added a diode after the final output and that was it. don't know why the 10k pot would suck high end away.

[pupil]

You've lowered the input impedance a great deal by putting 10K in parallel with the 1M resistor?

[acehobojoe]

ah yes, maybe I'll test it after the 1m resistor. that makes sense.

[GibsonGM]

Yes, exactly Pupil.  You are changing the input impedance with the pot.   This is exactly the same 'phenomenon' that happens when you turn your guitar pot down a little and you lose the highs.  You just did the same thing, and with an even LOWER value pot, worsening the effect.

To do this the right way and keep (some) highs, you need to use a larger value pot (try values from 250k to 500k) and use a 'bypass capacitor'.   Google 'guitar pot bypass cap' for sites about it...usually a 'nanofarad' value cap is used to bypass, selected to taste).  Cap goes from the pot input to wiper, and allows the highs to take a 'shortcut' so they're not going thru the pot.  

Best place for a volume as at the end of the circuit to avoid this...

[GibsonGM]

PS - keep the 1M resistor...put the pot before all of it.  That resistor is for bias, you want it there.

[midwayfair]

ah yes, maybe I'll test it after the 1m resistor. that makes sense.

It will still be in parallel if you do that.

You could try GibsonGM's way of increasing the pot and putting in a high pass, but you'll be FAR better off just putting a buffer between the 10K pot and your guitar. (EDIT: A pot larger than 10K will still be best there, or you can make lugs 1 and 3 of the pot the emitter bias resistor for your buffer and take its output from the wiper; look at the Omega's output buffer for an example of what I'm talking about.)

If you use a 1M pot, it can be your bias resistor. See e.g. the first couple stages in one of the Runoff Groove circuits.

[acehobojoe]

I'll try a few of the things mentioned, and I'll update what happens. Thanks guys.

[PRR]

> why the 10k pot would suck high end away.

Guitar is 5K in bass but 100K in treble.

A 10K load has slight effect on bass but heavy effect on treble.

Impedances on the guitar side should generally be >100K.

(Exception is many fuzzes load-down guitar treble with a simple too-low input resistance. Excess distorted overtones can be too nasty on the ear. However simple loading works different on every guitar and may do nothing further up the signal chain.)

[GibsonGM]

ah yes, maybe I'll test it after the 1m resistor. that makes sense.

It will still be in parallel if you do that.

You could try GibsonGM's way of increasing the pot and putting in a high pass, but you'll be FAR better off just putting a buffer between the 10K pot and your guitar. (EDIT: A pot larger than 10K will still be best there, or you can make lugs 1 and 3 of the pot the emitter bias resistor for your buffer and take its output from the wiper; look at the Omega's output buffer for an example of what I'm talking about.)

If you use a 1M pot, it can be your bias resistor. See e.g. the first couple stages in one of the Runoff Groove circuits.

Good idea, Jon, if one really wants to tailor the input level to an effect.

I'd prefer to design so you don't need to do this, but for the few times it really *Is* required, a pre-buffer makes great sense!  Using different instruments/active vs. passive pickups etc. might make this necessary.

[acehobojoe]

This is exactly why the TS-9 is equipped with 2 buffers. There is tone loss on a little breadboard I'm doing of it.