[sdiy] reamp?

[Don Tillman]

   Date: Fri, 24 Aug 2001 15:21:19 +0200
   From: Ingo Debus <debus at cityweb.de>

   Paul Perry wrote:
   > Some guitar fx boxes assume that they are being fed from 500k impedance,
   > otherwise the tone is a bit different.

   But isn't the output impedance of an electric guitar often much lower? A
   magnetic guitar pickup is a coil after all, and the guitar's volume pot
   won't make the impedance higher if set to max.

The typicial guitar pickup has a DC resistance of around 3000 to 5000
ohms.  There's a lot of inductance, somewhere around 1 Henry or so,
and some capacitance, so the impedance can get pretty high near the
resonant frequency, which might be around 3000 to 8000 Hz or
thereabouts. 

The load impedance affects the sound quality of guitar pickups, and in
general you don't want to run a guitar into less than 1M ohm.  There
are some stomp boxes that violate that rule, chalk it up to
quirkiness.  The worst offender is probably the wah-wah pedal (Vox,
Cry Baby, Maestro, whatever, they're all the same circuit).

   If the fx box needs a high source impedance, why not put just a
   resistor in series with the input?

A transformer is much closer to a guitar pickup impedancewise.

  -- Don

-- 
Don Tillman
Palo Alto, California, USA
don at till.com
http://www.till.com