WEM, Watkins, Rush - Pepbox, Rush Pep Box  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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peps1
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Post by peps1 »

123-2.png
Can someone confirm what the missing pads on the solder side are connected to?
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peps1
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Post by peps1 »

Looking at the schematic posted be EW......looks like this is about right, but please let me know of you spot a mistake!
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Post by danr »

This vero is unverified. I put it together using ElectricWarrior's schematic on page 2, and phibes' schematic of the Studio Two on page 3. Top-to-bottom the pinout of the transistors is CBE. It is designed for use with Alpha 9mm pots, but could just as easily be used for with regular pot wiring. If anyone notices any problems/mistakes, please let me know!
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Post by skumberg »

Musicground gave me the cap values of the GE version WEM fuzz. It's 25uf 25V. They could not read the pot values. However It think it just a matter of tuning the bias/gain pot to the transistors. Anything from 20k-100k depending on leakage.

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Electric Warrior
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Post by Electric Warrior »

Thanks a lot, here's the updated schematic:
germaniumpepbox.png

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Post by Steven_M »

Electric Warrior wrote:Thanks a lot, here's the updated schematic:
germaniumpepbox.png
I'm a little confused about that 56k resistor before the volume control. Is that part lowering the volume of the circuit or is it affecting the tone as part of high/low pass filter? (I can never remember which is which)

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Post by RnFR »

it's going to do both. it's a HPF combined with the output cap, but having that resistor to ground is also going to affect the output volume. you would usually just combine the output cap and the volume pot as a HPF, so it is probably there to knock the volume down. they didn't like loud effects back in the day. :block:
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Post by royaltoots »

Wow - thanks guys! I feel ridiculously like it's xmas in March, as I only just saw the Music Ground guts pics yesterday, on their ridiculous £2K Pep Box auction - so much fun to have a 'new' circuit to build - and I do love ye olde 60s fuzz. I don't have much time at the moment, but will be on it soon.

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Post by royaltoots »

Anyone tried this yet? I've built it but it has very low power, tried it with various Germs, no fuzz or fun.

Is there something special about these transistors that other Ge PNPs can't match, or did I just do my layout wrong? It's been a while since I did one... I'm using a 50k pot for Pep/Attack and 100K for Vol

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kaycee
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Post by kaycee »

Try a track cut between the two emitters - they both go to ground, but as you have them they are connected to each other as well.

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Post by Electric Warrior »

Don't!
The layout seems to be alright. What transistors did you use? Maybe they don't leak enough? :scratch:

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Post by skumberg »

The layout look alright. Check you collector voltages for misbias, effect pot maxed

This box should produce a healthy output. Because of low input impedance it reacts similar to a fuzz face when lowering guitar volume, cleans up well. The output filter gives it a very beatle like treble sound. Like it very much.

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Post by royaltoots »

Thanks for confirmations - I thought the layout was ok, but tried 2N270, OC71, 2G381 and didn't get far.
It's simple enough so I was dismayed at lack of success - will try again! Maybe i've got a short or something...

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Post by kaycee »

royaltoots wrote:Thanks for confirmations - I thought the layout was ok, but tried 2N270, OC71, 2G381 and didn't get far.
It's simple enough so I was dismayed at lack of success - will try again! Maybe i've got a short or something...

Tell you what, if your going to scrap it anyway why not try the track cut between emitters? Just to satisfy my curiosity, otherwise I'll have to build one from your layout to see for myself - and its not as if I haven't enough of my own dead builds laying around the place :lol:

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Post by alnico »

Because the emitters are meant to be connected? :idea:

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Post by RnFR »

yes, all grounded connections should be together. no track cut needed.
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Post by kaycee »

alnico wrote:Because the emitters are meant to be connected? :idea:
Well, I don't really see the need for the sarcasm - I do understand that two components connected to the same thing are also connected to each other. I looked over the layout and schematic and that was the only part that looked odd to me, so I just made a suggestion. I know that you can get an output from the emitter as well as the collector, and also that 'signal' can carrry bothways so I just wondered if something was going on there?

Take a little time to explain, and I'll be very happy to have learnt something.

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Post by alnico »

OK, I apologise, that wasn't helpful.

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Post by alnico »

I've just built this with a pair of nondescript transistors, ~100hfe and 200uA leakage. I used 47K for the fuzz pot and 470K for the volume.

It works and has plenty of output. The tone is a bit thin for me and it needs some mods to make it more usable. It cuts out with the fuzz at minimum and gets glitchy with the fuzz at maximum. I'm thinking of changing the 16K to something like 33K to hit the second transistor harder, larger limiting resistor on the fuzz pot, smaller collector resistor on the second transistor and a bigger output capacitor.

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Post by kaycee »

Appreciated, Alnico - and thanks for the build report and suggested mods, very useful :thumbsup

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