[sdiy] OT: Bass Guitar Preamp

[Tim Daugard]

> On Tue, 19 Dec 2006, Tim Daugard wrote:
>
> > I haven't noticed or had complaints about noise with this preamp. I
> > redesigned it to better couple the bass with the preamp matching the
> > impediance of the bass and the new design resulted in more hum. That
> > design is not on my website.

>Reply from Antti Huovilainen

> A problem with the current design on the website is that the low input
> impedance will lower the resonance peak of passive pickups and thus reduce
> highs / otherwise affect tone.

The input impediance is more than sufficient for bass and guitars. This preamp has been
used with both active and passive instuments. It has been used with guitars, basses,
micropohnes and a balalika with a piezo pickup.

The redesign that I'm not happy with, adds a variable impediance matching network to allow
the instrument to be loaded heavier. I play bass, I wanted to be able to load the bass
down to reduce the high end. This is the circuit that adds noise.

> Decently wired unit should not be the source of any significant hum or
> noise. I've built a high gain tube guitar amp and it's pretty silent until
> you plug the guitar in (at which point the RF noise from pickups will
> dominate).

That's the purpose of C5 in the circuit. it reduces gain above audio frequencys. Other
than that, I agree with this statement. My greatest source of hum is the pickups on my
Fender Jazz. I can reduce hum by carefully balancing the feeds from the pickups. As soon
as I change the settings to change the tone, the hum is back.

Tim Daugard
AG4GZ 30.4078N 86.6227W Alt: 12 feet above MSL
http://home.sprintmail.com/~daugard/synth.htm