Guitars of Love

Waveforms of the preamp in action ...


At right are screen grabs the of the new simpler GuitFET preamp captured on an GWInstek GDS1022 oscilloscope with a frequency close to an A440Hz sine wave. The signals greatly increase in complexity with complex harmonics. The top trace is the input signal; the bottom trace the preamp output. These were done with the volume out at maximum so there is a  large overall gain.

Note: Since doing these tests on my breadboard prototype I have limited the frequency response to be within 3dB from about 35Hz to 50KHz. This is pretty much the spec on a typical good sounding Hi Fi amp such as a NAD or Rega, and is more than adequate for it's purpose. Going up into RF frequencies is not desirable!

Low drive with little change in the sound:

Slight OD with rounding when the FETs kick in with rich even order harmonics:

More signal combines the clipping of the buffer transistor driving the OD FET and the FET itself:

Winding up the drive resulting in a sharpened wave form, but still with slight rounding from the FETs:

Maximum drive with hi input giving sharp square clipping:

400 Hz square wave response with clean signal and tone controls at neutral position:

Frequency response measurements taken with clean signal and tone controls in the neutral position at 20Hz / 200Hz / 2KHz / 20KHz / 200KHz: