How do I reduce the gain of a mic preamp?

[MattP]

Hello all! I have a microphone preamp, but when I try reducing its gain by having lowish value resistor short the output to the ground (like volume control does, right?), the volume is reduced but so is the bass. This is no good at all!

Is there any other way that I can simply reduce the gain without affecting bass output?

Thanks!

 

[(*steve*)]

you need 2 resistors. Both in series are connected across the preamp output and the input to the next stage is taken across the "bottom" resistor. The resistors should probably add up to something like 10k to 50k. (you might have 51k and 3k9 for instance, or 33k and 18k

You can make this variable by the use of a device called a potentiometer

If you do this, get one with a logarithmic (or audio) taper.

 

[MattP]

Hi Steve!

So it should look a little like this?

output>--------33k------18k----------->next stage
ground>----------------------------------->ground

How come two resistors are necessary? I have a feeling that I'm misunderstanding your directions.

 

[(*steve*)]

No, the the 2 resistors go from the output to ground, in series.

then you take the attenuated output from the junction of the 2 resistors and ground.

 

[MattP]

Ohh, OK.

output>--------|
               R1
               |
               |-------->next stage
               |
               R2
ground>--------|--------->ground

Is that right? Sorry if I've got it wrong again; I'm a bit of a dunce when it comes to this kind of thing.

Thanks for your help so far Steve, I appreciate it!

 

[(*steve*)]

Yep, you've got it.

 

[MattP]

Cheers. I'll give it a go!

 

[MattP]

Thanks Steve, it works perfectly.