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Axelvilhelm 13th March 2011 03:16 PM

Where shall I place the potentiometer?
This might seem like a dumb question, but I'm a total newb in electronics. I built this preamp to amplify the signal from a small speaker that i use as a pick-up element in a DIY spring reverb. The preamp works fine but i would like to be able to adjust the gain, because often the level of the output signal is too high, so the signal distorts in the line input. So, i shuold probably add a potentiometer to the circuit, but exactly where in the circuit should i put it? Here are the schematics:

Thanks in advance!

Zen Mod 13th March 2011 03:24 PM

at output

Axelvilhelm 13th March 2011 05:17 PM

Thanks for answering! Then, another question: What value should the pot be?

Arty 13th March 2011 06:14 PM

good question, if i was you i would try 50K linear one.
but that's just me, and i em not expert.
I prefer linear pots over log.

Zen Mod 13th March 2011 08:51 PM

question :

line inputs usually have pots right after selector ;

how's the case that this one is clipping line stage that way ?

give us more data , something is fishy there

knutn 13th March 2011 09:10 PM

Too high gain?
If the signal distorts in the line input, then your gain is to high. You have made yourself a common base amplifier with high gain; so you will have to reduce the collector resistance, i.e. place a pot in parallel with R2 (you will need a capacitor too).

Axelvilhelm 13th March 2011 09:51 PM

Yes, that's just the problem, as I see it, too much gain. It's not a problem if I connect it to a line input with a pot following it. But, if I, for instance, connect it to a line input of a A/D audio interface with no input level pot, then clipping will occur.

So, a pot parallel with R2, right? And what about the cap? Should that also be parallel to R2 and what about it's capacitance and should it be a polarized one? Sorry all this question, but this is all really new to me...

knutn 14th March 2011 08:44 AM

1 Attachment(s)
My first thought was this (C= 1000u ? and Pot=5k ?)

Zen Mod 14th March 2011 11:06 AM

if you need less sensitivity from circuit - do like this

if you need to maintain sensitivity - place pot on output

Axelvilhelm 16th March 2011 11:06 PM

I tried both, and realised that placing a pot in the circuit resulted in noise in all potentiometer positions but full throttle, so I'll just go without the pot. Maybe the circuit is generally sensitive to noise, or perhaps the power supply is poorly filtered. Anyway, I think I'll be fine just adjusting the volume before the pick-up. Thanks to everyone for helping, my deepest appreciation!!

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