Question for anyone who has built Tim Escobedo's PWM

[Top Top]

I built this and all seems to be working, including the LFO.

However, it seems that it requires a lot of volume at the input to work well. If I just plug the guitar straight in, the signal dies out pretty quickly and I have to pick kind of hard to get a note to sustain at all. It sounds pretty cool when I put a nice loud preamp before it though!

I notice that the schematic doesn't show an input cap, but the layout I used does... could increasing the input cap size help this out? I notice more sustain on fuzzes when it has a larger value input cap, but I don't know if this circuit is operating in the same way.

[bluesdevil]

Definitely increase the input cap. It made a big difference in my build. I can't remember what I used, but try a 2.2uf at least. I made a pcb layout w/LFO that had everything to my taste.... gotta dig it up.

[Top Top]

Hmmm... I tried increasing it, but the more capacitance, the more it cut out on high frequencies. With .15uF, I can't even get the high E and B to get a note through. When I decrease it, I am getting a little more, but still it is cutting out pretty quick. I have it down to .015uF right now.

[bluesdevil]

I'll have to dig around for my layout.... maybe I changed more than the input cap. Something's gotta be wrong 'cause my sounds HUGE.

[bluesdevil]

Oh yeah, forgot to mention this thing does decay abruptly, like a gate but the bigger input cap did improve the sound for me as far as a bit more sustain and bass response.

[Top Top]

Ok, I did a highly illogical thing... I went out on a whim and followed the design, which calls for no input cap. What do you know? It works perfectly! 

Ok, actually it is a little glitchy. Maybe a very low value input cap would fix it, but I can live with it the way it is.

If I wanted the LFO to be able to go slower, I would need a larger value pot, right?

[bluesdevil]

Sorry Top Top, I must have confused this with another build! I probably stuck with the schematic. I think the 386 chip already has a cap at the input from what I read on another thread. As far as glitchy sound, try rolling your tone knob all the way down and use neck pick up.

[Solidhex]

Yeah

  You can also put a cap connected to ground at the input to roll off highs. Start with like a .01 and go bigger until you get the sound you like. Put it on a switch though for when you want the glitchy sound. Its good to have built into the pedal so you don't have to roll off your guitar tone everytime you engage the effect.

--Brad

[Top Top]

Thanks for the suggestions guys. The tone knob and neck pickup thing definitely tames it, though that is a good idea about a switch to tame it without having to use the tone knob.

The PWM sound is actually a lot better this way (no cap) than it was with the cap and a lot of volume coming in - more raw and synth-like, better sustain.

Great sound from such a simple circuit... I am going to try a 1M pot on the LFO rate to see if I can get really long sweep times, which would be the only thing I would improve about this circuit.

Tim Escobedo has provided so much fun, simple stuff for us to work with. Does he ever post around here anymore?

[mr.adambeck]

Top Top, did you try the 1Meg pot?  I'm messing around with the PWM, and was hoping to play around with some things to get a slower LFO.  I seem to only like it really, really fast or really really slow.  Also, I'm putting a boost with a passive Low Pass Filter on it at the start of the circuit - This way I can control the amount of "glitchiness" that it gets.