[sdiy] OT: Bass Guitar Preamp

[Antti Huovilainen]

On Wed, 20 Dec 2006, Tim Daugard wrote:

> Some effects boxes are reported to create some of the sound quality by 
> loading the instrument. The claim is that even when bypassed (not a true 
> bypass) the effect changes the sound.

This was often the case with older cheap pedals where the input buffer had 
too low impedance and was always left connected. It is generally 
considered to be something to avoid. A related case are some distortion 
pedals which depend on the low input impedance to remove excess highs 
before the distortion. An example is the Fuzz Face where it was a happy 
byproduct of the cheap design (only two transistors!).

> A question for you other geniuses: Does a microphone have to be loaded 
> with 600 ohms? I use the same circuit, with more gain, for microphones 
> with apparently acceptable (for rock and roll) results. My mic preamp 
> creates a 2- 300K load (I'd have to check to see if the fixed resistor 
> is 100k or 180K).

No. Matched load is only needed when maximum power transfer is required or 
extremely long lines are used. Neither are the case in audio normally, so 
the load impedance should be much higher than the source (for mic inputs a 
few kohms or more).

Antti

"No boom today. Boom tomorrow. There's always a boom tomorrow"
  -- Lt. Cmdr. Ivanova