Lovepedal Champ Radio Interference

[katoptrizo]

I recently built a Lovepedal Champ using the layout on the blog but now am picking up radio stations when it is in the signal chain.

Do the instructions indicated on the recently posted Mictester Silicon Tonebender for alleviating this problem?

100pF from base of the 2N5088 to ground?

[Travis]

That's the easiest most typical solution (or small cap from input to ground). I'd give that a shot first. For me if the pedal is already "boxed up" it is usually easiest to add a cap between lug 5 & 6 on the bypass switch if you follow the wiring in the offboard wiring tab

[katoptrizo]

Thanks for the response. This is essentially a low-pass filter, yes? Filtering the signal above the useful range?

Any suggestions if I wanted to try and adapt the circuit for bass? Would that mean increasing the size of the 100n cap?

[Neil mcNasty]

Modding for Bass:
Yes, you can increase the 100nf (output) cap so that you get more low frequencies out of it, but you should also increase the input cap (the 22nf) so that it lets more of the low frequencies enter the circuit as well.
But be aware that sometimes you can end up with muddy lows, depending on the circuit design and how it reacts to low frequencies.
Not all circuits handles bass frequencies equally well, but it is absolutely worth a shot.
Low frequencies also sometimes distorts more than highs, so you might also get a sense of more gain when doing this.

Another idea would be to add caps to switches that run in parallel with the input/output caps, so that you can switch between guitar and bass use. Kind of a fat-mod that increases the lows.
Example: use two DPDT (on/on) switches, with a cap on one side and nothing on the other side for Bass-mode on/off.
Or: use DPDT (on/off/on) switches, with two different caps on each side for two different cap values/bass settings and a off position in the center.
If you have a 4PDT switch, you can get both the input and output caps on a single switch, instead of two DPDT switches (one for the input cap and one for the output cap)

John K has done a lot of mods on many circuits for bass use, so you should check out his site and see if you can pick up some good tips there regarding bass mods: http://johnkvintageguitars.homestead.com/Overdrive-Pedals.html

[katoptrizo]

Excellent explanation! Thanks! I'm going to breadboard the bass version first to see if it's even an effect I will use. My guitarist loves the champ apart from the radio interference and a sort of "swash" that is prevalent but I believe related to the high frequencies leaking into the transistor that I think the mod discussed originally will help alleviate. I, however, don't know if I'll end up liking the pedal for myself.

Anyway, thanks all for the insight. I'll post back with results.