Pre-Amp output levels

[HW_Hack]

So after a few weeks of getting parts and pieces ordered and assembled I've got my first circuits breadboarded and am seeing some results. I've set up two circuits:

- The classic FET J201 Tillman Pre-Amp circuit which most folks here should know
- A simple BJT ElectroHarmonix
http://www.beavisaudio.com/schematics/Electro-Harmonix-LPB-1-Schematic.htm

I'm using a PC and Audacity to generate a 440Hz sine wave to drive the circuits. I'm fortunate to have a scope borrowed from work so I'm able to get waveform data. My guitar produces a 900mV p-p signal across a 1M ohm load so that is the input amplitude I'm driving into the circuits. Both circuits are powered at 9V.

The Tillman circuit is very clean and produces an output of 1.5V pk-pk from the 900mV input. The ElectroHarmonix produces a slightly clipped signal with a max of 9v pk-pk. The clipping is there I'm guessing to produce an over driven sound (I'm guessing).

So here is my quandary as a newb at this pre-amp stuff. I've not plugged either of these into my Marshall Amp yet --- I want to make sure I don't overdrive or blow the input on the Maarshall. So the Tillman seems pretty safe as its only at 1.5V pk-pk, but I have concerns about driving 9V pk-pk into my amp. Of course I could use the 100K pot to dial it down to a lower level. And of course these output levels are no load present.

Are there some rules of thumb on max voltages to drive into a basic guitar amp like a Marshall or Fender ? And BTW my Marshall is a solid state G30R

Your feed back is highly appreciated --- thanks

[PRR]

> Are there some rules of thumb on max voltages to drive into a basic guitar amp

"Anything can happen!!" Most guitar amp inputs are protected against absurd inputs. Certainly anything you can get out of a 9V battery.

It is also known that the LPB is one of the oldest pedals, has been used for 4 decades with EVERY amp.

Do what most musicians do. Just try it.

BTW: while you can get 9V p-p out of the LPB, you probably will turn it down for a more reasonable nasty racket.