DSE/Jaycar PreChamp kit mod ideas

[evilpaul]

I picked up one of these kits ($4!) recently with a view to modding it for guitar purposes .I'm hoping to achieve something fairly fuzzy-sounding, but as long as it sounds good, anything along the overdrive-distortion-fuzz spectrum will be satisfactory.

I've socketed the trannies (of course), so any interesting ideas for alternatives would be nice.

Here's the original schematic, and my basic mod ideas.





I swapped the 100k pulldown resistor at the output with a pot, to act as a volume control.

Instead of changing the gain from 23 to 101 by changing the 2.2k resistor to 10k, I could substitute a 10k pot. The potential problem with that is that it will effect the 48kHz low-pass filter and at 10k, it will be rolling off frequencies above 10.6kHz. This might not necessarily be a bad thing, since I'm assuming there will be more distortion along with the higher gain, rolling off some of the top end might smooth it out a bit.

The 22k collector load resistor is described in the documentation like this "... although not strictly necessary, it helps to linearise the output and significantly reduces distortion.", so I figured I'd sub it with a pot and see how it sounds. I'm not 100% on the theory behind how it works though, so if anyone could expand on it, it would be appreciated.

Other ideas:

The 22uf electrolytic cap in series with the 100ohm resistor at the emitter of Q1 sets the lower frequency response to 72Hz. That's low enough for a guitar tuned to drop-D, but not low enough for bass. What kind of bass attenuation usually gets used to prevent 'farty' sounding bass?

[Caferacernoc]

Actually, 72hz is practically full range. Many pedals cut bass off much higher than that for a "tighter" sound. You might also put some clipping diodes to ground right before the volume knob for some extra distortion.