# Acetylene Overdrive ?



## Mike McLane (Mar 3, 2022)

The Acetylene OD has two internal trim pots (Input & Bias).  I looked and the Wampler manual to see what those were about, but there's no indication that they exist.  I assume Bias mimics altering the output tube bias.  Input.  .  . an input pad?  Can anybody clarify?


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## jimilee (Mar 3, 2022)

Yeah, the bias is to bias the J201, and the other manages the input signal, obviously a louder signal will history more. Hope this helps.


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## Mike McLane (Mar 3, 2022)

Great. .  .Thx!  I play a Deluxe Reverb and would like a simple "Vox in the box" pedal.  Would love a 125B unit . . . . deep-six the Boost, even the headroom switch if necessary.  I just want clean chime to moderate grit, don't need Brian May.  I don't know if there's enough demand on this model to warrant such a mod, but who knows.  Maybe we'll get some surprising response.


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## G.G. (Mar 4, 2022)

for folks who have built the Acetylene, how much breakup are you getting from the main channel's Gain? My build stays very clean even with the Gain all the way up. The Boost adds a little dirt but it has to be up pretty high to get even a mid-level breakup and at the point the pedal is extremely loud even with the output volume way down. The controls seem to be working correctly and bias voltages look correct, just getting mainly volume and only a little dirt. Maybe that's how it's supposed to work?


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## Mike McLane (Mar 4, 2022)

Just curious. . . do you happen to have the Input trimmer turned down, thus reducing the strength of the input signal?


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## G.G. (Mar 4, 2022)

I played around with the internal input trimmer a bit. It's possible to push it into more dirt territory that way but the pedal gets really, really loud to the point where I had the output volume almost all the way down. The distortion seemed kind of harsh at that point and I was wondering if that's really the intended use for the internal Input volume.


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## zgrav (Mar 4, 2022)

usually the input trimmer is there to cut down the incoming signal and maybe give you a more useful range for the output level.  I have no clue how much dirt you should be getting along the way without hot-rodding the incoming signal level.  you can use the* bias trimmers* to lower the voltage on the transistors to get more distortion if you want to give that a try.


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## Chuck D. Bones (Mar 4, 2022)

Check the source voltage on Q3 & Q6.  I suspect that not all J113s will bias properly.  While you're poking around on the board, verify that Q2-D and Q4-D are between 4V and 6V.


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## G.G. (Mar 7, 2022)

I set the J201 to 4v
Q3 & Q6 say 1.28
Q2 & Q4 are at 4.99

thanks for the help everybody!


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## Chuck D. Bones (Mar 7, 2022)

That all looks ok.  I'd like to see Q3-S & Q6-S higher, but that's personal preference and I don't know what the voltage is in a stock 30-Something.  If those tansistors are socketed, try J112 if you have them.


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## G.G. (Mar 7, 2022)

I'll see if I can swap out Q3 & 6, thanks for the advice!


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## Chuck D. Bones (Mar 7, 2022)

Ideally you want 4 to 5V on the source for maximum headroom.  Changing the JFETs may or may not help.


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## music6000 (Mar 7, 2022)

G.G. said:


> for folks who have built the Acetylene, how much breakup are you getting from the main channel's Gain? My build stays very clean even with the Gain all the way up. The Boost adds a little dirt but it has to be up pretty high to get even a mid-level breakup and at the point the pedal is extremely loud even with the output volume way down. The controls seem to be working correctly and bias voltages look correct, just getting mainly volume and only a little dirt. Maybe that's how it's supposed to work?


This will help understand the pedal!
Brian Wampler himself, Go to 4.00 minutes:


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## zgrav (Mar 7, 2022)

I vaguely recalled the conversation about this being an underdrive more than an overdrive.


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## music6000 (Mar 7, 2022)

Yep, switching to the ''15'' setting will get you into the Gain territory.


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## G.G. (Mar 7, 2022)

hmm, yeah my 15 side sounds about as clean as his 30 side, I don't get nearly that much breakup. Thanks for the video, I hadn't seen that one.


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## music6000 (Mar 7, 2022)

G.G. said:


> hmm, yeah my 15 side sounds about as clean as his 30 side, I don't get nearly that much breakup. Thanks for the video, I hadn't seen that one.


I would recheck your resistor values
Number 1 mistake on this Forum for Builds ie 470r, 4K7, 47K, 470K ---- 100r, 1K, 10K, 100K, 1M --- 3K3, 33K, 330K!
That 3rd Band can Make or Break a circuit!!!!


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## Gt6371 (Jun 11, 2022)

Hey guys, sorry I am a newbie. Why is there 5 conductor spots on the ace but the trim pots I bought have 3 leads?  Did I buy the wrong pots?  Thanks for any help!


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## Barry (Jun 11, 2022)

Gt6371 said:


> Hey guys, sorry I am a newbie. Why is there 5 conductor spots on the ace but the trim pots I bought have 3 leads?  Did I buy the wrong pots?  Thanks for any help!


Those are to accomadate trimmers with different spacing


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