Here's a cool vintage fuzz circuit from the mid 60s–the WEM Pep Box. It's probably best known its use by John Lennon during the Revolver sessions. There are two versions of this effect, the first using germanium transistors and the later using silicon. I've drawn up layouts for both iterations of the circuit, as there are slight variations between the two. The originals used a 500k Level pot with a 56k resistor in parallel. This equates to a 50k pot, so the layouts reflect that. Also, if the effect is to thick for your tastes, try reducing the 2 electro caps down to 10µ. It seems both values were used.
If you're building the germanium version, the layout shows positive ground on the perf side (original transistors were PNP), and the PCB side shows negative ground (for use with NPN germaniums). Since the original ACY41 transistors are pretty scarce now (especially outside the UK), socket and experiment.
Hi, I'm newby yet, so it can be to easy question but, when I make the fuzz with germanium, is it okay to use AC 128 for both of TR? or, they should be different for them?
Yes those should work well. Just remember those are PNP transistors, so make sure to use a positive ground power supply, and orient any polarized components like the ones on the perf side of the drawing. Good luck with your build!
I finally built this pedal with germanium TR AC 128, and it sounds great! I recommend germanium for this layout, it is good. And I used 7660 for the negative 9V, and it needs only two more line from the original layout. I built this with 1590B case, but it is possible to built this pedal with 1590A also.
Hello. I've tried this circuit twice but it just doesn't seem to work at all. I seem to be getting true bypass, but when I switch the 3pdt switch to run through the effect circuit it just sounds like the bypass with a loud hum over the top. I've tried it again with fresh components, but still no joy.
I ask because I think the 22uf cap on from the in on the silicon one is backwards. On another schematic I found it had the positive side connected to the B pin of the transistor. I made that change on mine and get the exact sound from "What is life" by george harrison on the beginning lead line (which is rumored to be a pep box.)
built the silicon version.. sounds awesome. used a 2n4400 (hfe ~80) for Q1 and a c945 (hfe ~350) for Q2. it's definitely more gain and fuzzier than the original. I am skeptical of the 100k trim pot value with my choice of transistors because the biasing seems a bit off and i have to max out the trim to get it to stop gating but i enjoy the sound now so i am going to leave it as is. thanks for the drawing! confirmed!
ACY41 is UK code for AC128, AC153, AC188. I built one using ACY41 and tested with AC128 it have the same sound.
ReplyDeleteThanks for the info. Did you build the effect using this layout?
DeleteHi, I'm newby yet, so it can be to easy question but, when I make the fuzz with germanium, is it okay to use AC 128 for both of TR? or, they should be different for them?
ReplyDeleteYes those should work well. Just remember those are PNP transistors, so make sure to use a positive ground power supply, and orient any polarized components like the ones on the perf side of the drawing. Good luck with your build!
DeleteI finally built this pedal with germanium TR AC 128, and it sounds great!
ReplyDeleteI recommend germanium for this layout, it is good.
And I used 7660 for the negative 9V, and it needs only two more line from the original layout. I built this with 1590B case, but it is possible to built this pedal with 1590A also.
Awesome! Thanks for verifying
DeleteWhat 'two more line' does this need? I can't get this pedal to work at all as per the layout above.
DeleteHello. I've tried this circuit twice but it just doesn't seem to work at all. I seem to be getting true bypass, but when I switch the 3pdt switch to run through the effect circuit it just sounds like the bypass with a loud hum over the top. I've tried it again with fresh components, but still no joy.
ReplyDeleteAny germanium pnp transistors with hfe=50+ should be working here. I ended up using (gain-leakage) 44-225 for Q1 and 82-325 for Q2 in my build.
ReplyDeleteDo you happen to have the schematic for the Silicon Version? I am having some issues and would love to work through it. Thanks!
ReplyDeleteI ask because I think the 22uf cap on from the in on the silicon one is backwards. On another schematic I found it had the positive side connected to the B pin of the transistor. I made that change on mine and get the exact sound from "What is life" by george harrison on the beginning lead line (which is rumored to be a pep box.)
DeleteGOD I'd love a PCB of this
ReplyDeletewhat should i get with the trimpot?
ReplyDeletebuilt the silicon version.. sounds awesome. used a 2n4400 (hfe ~80) for Q1 and a c945 (hfe ~350) for Q2. it's definitely more gain and fuzzier than the original. I am skeptical of the 100k trim pot value with my choice of transistors because the biasing seems a bit off and i have to max out the trim to get it to stop gating but i enjoy the sound now so i am going to leave it as is. thanks for the drawing! confirmed!
ReplyDelete