[sdiy] low level

Mon Sep 30 18:16:23 CEST 2002

Hi Toby:

The Chapman stick is probably similar to guitars in impedance...
(25-50K) so the preamp should be at least 10x that (500K-1M is a good
target).

If you have modified an opamp circuit for more gain, you may be
running into a gain bandwidth product (GBP) problem. As you increase
the gain, the full signal bandwidth must drop (its a constant)...
so you can lose highs.

What you want to do, is take gain in several stages... maybe a
high impedance preamp with low gain (maybe 5x or so) that has a low
impedance output, then follow with a higher gain, low impedance input
stage. Maybe a TL071 for a first stage (or a FET preamp) and an opamp
following.

If you send me some schems offlist of what you are doing I could
give specific advise

H^) harry

--------Original Message--------  

From: carpet8 at mac.com
To: <synth-diy at dropmix.xs4all.nl>
Sent: Sep 29 2002 22:36
Subject: [sdiy] low level

>Hey folks.
>I've never built a mixer before, but I'm having trouble that I can't
>resolve.  I built a mixer intended for chapman stick, and I modified Craig
>Anderton's 8-in mixer by adding a high impedance preamp.  I'm able to get
>more highs out of my signal but not enough, it seems.  I don't know the
>output impedance of a stick, but I assume it's in the 250-500k range.  If
>anybody could give me a general idea of a signal path, or basically any
>other help, since I've never worked on things where I had to worry much
>about impedance, that would be muchly appreciated.  One thing that really
>helped was using a tube mp-1 by itself, but I need to mix before that.
>thanks
>toby
>p.s. I live in Seattle, if there's anybody--especially drummers--interested
>in jamming, please contact me.