Re: Using Batteries For Odd Voltages

From: Roger Johansson (no-email_at_no.invalid)
Date: 03/26/05 

Date: 26 Mar 2005 14:51:58 +0100

"phaeton" <blahbleh666@hotmail.com> wrote:

> I was going to use this small practice
> amp as a "disposable amp" project for testing homemade effects pedals
> and such. I would hate to mis-wire something in a stompbox and damage
> my Reverend :-(

To protect the input of a power amp you can put two diodes in
antiparallel over its input. That ensures that the input voltage can
never get higher than plus minus 0.6Volt. Add a series resistor 1k too to
protect against very low impedance sources which could blow up the
diodes.

> It would also be useful to have a small portable amp

For headphones you can probably use common op-amps, like the TL071
series. A TL072 for stereo.

Or no amp at all. You probably use some guitar effects boxes before the
amp, and most of them have output power enough to drive earphones
directly. There are schematics for thousands of guitar effects on the
web, and they are suitable as beginner projects in electronics. Check out
geofex.com, for example.

> Futurlec is awesome but they take forever to ship.

That is interesting.
Have you tried them or do you base that on some information? 

-- 
Roger J.

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