# Acetylene



## ALK2MT (Oct 24, 2021)

Does anyone have a pic of their Acetylene build? I just ordered one and was hoping to get a parts list, doesn’t appear to be posted yet! 

Thank you!


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## Chuck D. Bones (Oct 24, 2021)

I bought one too.  Until the Build Docs are published, the silkscreen on the board IS the build doc.  Being the A/R person I am, I make a spreadsheet for each build that includes a parts list, which can double as a shopping list.  Haven't done that yet for this board.


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## Robert (Oct 24, 2021)

I'm working on docs right this minute.     Not sure if I'll make it to this one this afternoon, but I'll give it my best shot.


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## ALK2MT (Oct 24, 2021)

Awesome, I’m excited to build it. I have a spreadsheet going.


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## ALK2MT (Oct 24, 2021)

Chuck D. Bones said:


> I bought one too.  Until the Build Docs are published, the silkscreen on the board IS the build doc.  Being the A/R person I am, I make a spreadsheet for each build that includes a parts list, which can double as a shopping list.  Haven't done that yet for this board.


Good plan! Same here. Are you using a 1590BB enclosure? I had a question about subbing in footswitches with an embedded LED, has anyone tried this?


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## Chuck D. Bones (Oct 24, 2021)

Don't forget my favorite part... the schematic 

In the meantime...


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## Robert (Oct 24, 2021)

Parts list.


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## Chuck D. Bones (Oct 24, 2021)

ALK2MT said:


> I had a question about subbing in footswitches with an embedded LED, has anyone tried this?



A few of us have done it with PedalPCB boards.  You need to look at the board schematic to see how the LED is hooked up because they are not all the same.


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## Chuck D. Bones (Oct 24, 2021)

I just looked at the board.  The LED ballast resistor is between +9V and the LED anode, which is what works best for a stomp switch with an integrated LED.  You can either wire both LED leads to the board, or jumper the LED pads on the board, connect the LED anode to the SW pad on the board and run the cathode lead direct to the stomp switch.  I prefer the latter, it's cleaner.

[edited for an even better way to hook up LED that is integrated with the stompswitch]


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## peccary (Oct 24, 2021)

In the list of my top three things I love about PedalPCB builds is the component values being printed on the board.


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## Bucksears (Oct 26, 2021)

Board waiting here to be populated (other projects in line first).
I'm just curious to see if there's a way to tweak the boost section for a full-range boost instead of just treble. (Some of us just want a straight-up gain boost, not wanting to sound just like Brian May).


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## Chuck D. Bones (Oct 26, 2021)

If only we had a schematic...


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## Chuck D. Bones (Oct 28, 2021)

Acetylene board
I really want to build this
_Build docs coming soon..._


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## mattburnside (Oct 28, 2021)

Would love the drill template too, or let me know if the template for another project will work. Thanks!


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## Robert (Oct 28, 2021)

Acetylene Build Documentation



Chuck D. Bones said:


> _Build docs coming soon..._



See?   Told ya so.   😂


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## fig (Oct 28, 2021)

Robert said:


> Acetylene Build Documentation


I'm not even sure if I have this board or not, but thank you anyway for all your hard work.


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## thesmokingman (Oct 28, 2021)

Never let it be said I didn't say thank you as quickly as I complained about wanting something ... THANK YOU FOR THE SCHEMA


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## Bucksears (Oct 28, 2021)

Thank you!


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## Robert (Oct 28, 2021)

thesmokingman said:


> Never let it be said I didn't say thank you as quickly as I complained about wanting something ... THANK YOU FOR THE SCHEMA



Is this the one you were waiting for?

I would have posted it sooner but I was too busy playing around in Photoshop all night....   😂


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## Chuck D. Bones (Oct 28, 2021)

Bucksears said:


> Board waiting here to be populated (other projects in line first).
> I'm just curious to see if there's a way to tweak the boost section for a full-range boost instead of just treble. (Some of us just want a straight-up gain boost, not wanting to sound just like Brian May).


 Make C2 larger.  Try 47nF.  If that's still not fat enough, then try 220nF.


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## Bucksears (Oct 29, 2021)

Chuck D. Bones said:


> Make C2 larger.  Try 47nF.  If that's still not fat enough, then try 220nF.



I'll get that a shot.
Do we know what that booster is based on?


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## Chuck D. Bones (Oct 29, 2021)

It's a simple common-emitter amplifier.  Similar to an LPB or a Silicon Range Master.  C4 rolls-off the top-end above 2KHz.


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## Bucksears (Oct 29, 2021)

Chuck D. Bones said:


> It's a simple common-emitter amplifier.  Similar to an LPB or a Silicon Range Master.  C4 rolls-off the top-end above 2KHz.



Thanks - I'm basically trying to avoid that BM/cocked-wah midrange when I hit the boost. 
I just want a gain boost.


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## Coda (Oct 29, 2021)

Chuck D. Bones said:


> Acetylene board
> I really want to build this
> _Build docs coming soon..._


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## Chuck D. Bones (Oct 29, 2021)

Build docs were uploaded last night.



Bucksears said:


> Thanks - I'm basically trying to avoid that BM/cocked-wah midrange when I hit the boost.
> I just want a gain boost.



If you want the full top-end, then make C4 1nF or leave it out altogether.  Wampler knows what he's doing and it may well be to your liking as-designed.


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## benny_profane (Oct 29, 2021)

Chuck D. Bones said:


> The LED ballast resistor is between +9V and the LED anode, which is what works best for a stomp switch with an integrated LED.


What is the impact of the order here?


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## Chuck D. Bones (Oct 30, 2021)

The order only matters if you want to wire up the LED differently from just soldering it directly to the board in accordance with the Build Docs.  On the few PedalPCB boards that have the LED's anode tied directly to Vcc, you have to make sure that there is a ballast resistor between the LED cathode and the stomp switch because your LED wiring might bypass the on-board ballast resistor and blow the LED.  Been there, done that.


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## Chuck D. Bones (Oct 31, 2021)

I've spent some time studying the Acetylene before I build mine.  It is my opinion that the J113 FETs (Q3 & Q6) should have a high Vp so that they do not clip.  I recommend using whatever JFETs you have whose Vp is greater than 2V, ideally 4.5V.  J112 would be a good option.  I have some mods in mind, including deleting Q3 & Q6, but I'll wait until I breadboard them before sharing the details.


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## MAO (Nov 12, 2021)

Do we know if the J201 50k trimmer was in the original, or was there a fixed drain resistor? 

And if there was a drain resistor rather than a trimmer, what was the value?


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## Mentaltossflycoon (Nov 12, 2021)

peccary said:


> In the list of my top three things I love about PedalPCB builds is the component values being printed on the board.


It's extra satisfying to pull one together with no paperwork.


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## Chuck D. Bones (Nov 12, 2021)

Until you need to troubleshoot.  😖


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## mdc (Nov 12, 2021)

Just looking at the schematic a bit this am, and this is a very cool-looking circuit. The mosfet/JFET/npn stages and interstitial filtering all make sense to me, but I'm not familiar enough w/ opamp circuit topology to know what the heck is going on in the final stage(s). Is it simulating a power amp section?


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## Chuck D. Bones (Nov 12, 2021)

mdc said:


> Just looking at the schematic a bit this am, and this is a very cool-looking circuit. The mosfet/JFET/npn stages and interstitial filtering all make sense to me, but I'm not familiar enough w/ opamp circuit topology to know what the heck is going on in the final stage(s). Is it simulating a power amp section?



My thought was that the last section (IC1 & IC2) is a cab sim.  The two gyrators create a pair of overlapping mid humps: one at 400Hz and a smaller one at 800Hz.



MAO said:


> Do we know if the J201 50k trimmer was in the original, or was there a fixed drain resistor?
> 
> And if there was a drain resistor rather than a trimmer, what was the value?


There appears to be only one trimpot in the production model and that is the INPUT trimmer.  Wampler most likely hand-picks their J201s.  Would be interesting to know what value drain resistor they use.

Here's a link to the manual.


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## Robert (Nov 12, 2021)

Chuck D. Bones said:


> Would be interesting to know what value drain resistor they use.



14K


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## mdc (Nov 12, 2021)

Ah! The cab sim is an interesting idea - it's sort of a final EQ/output buffer stage I guess.


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## jubal81 (Nov 12, 2021)

mdc said:


> Ah! The cab sim is an interesting idea - it's sort of a final EQ/output buffer stage I guess.


Runoffgroove introduced a design in 2012 called the Azabache that's sorely overlooked. It's a great OD that broke some conventions at the time by using JFETs as 'clean' amplifiers, diodes for clipping and tacking on a primitive cab sim at the end.
Subsequent designs from them built on this, but IMHO, the Azabache is the real gem of the bunch.


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## mdc (Nov 12, 2021)

I'd not seen that one before - definitely looks to be worth a breadboardin'.


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## MAO (Nov 12, 2021)

Does anyone have the drain voltages for the BS170s? (Q2 & Q4) Thx


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## Chuck D. Bones (Nov 12, 2021)

Those are easy to predict.  They'll be close to 5V.  The Vt on a MOSFET has a much smaller spec range than Vp on a JFET.

Why do you ask?


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## MAO (Nov 12, 2021)

Chuck D. Bones said:


> Those are easy to predict.  They'll be close to 5V.  The Vt on a MOSFET has a much smaller spec range than Vp on a JFET.
> 
> Why do you ask?


Just curious, I've had a few BS170s in the past with drain voltage readings way out of expectations. 
My vero layout build of the Acetylene is working, but I'm getting a ton of hiss. Very similar issue I had with my Azabache builds, which I was never able to resolve.


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## MAO (Nov 12, 2021)

MAO said:


> Just curious, I've had a few BS170s with drain voltage readings way out of expectations in the past.
> My vero layout build of the Acetylene is working, but I'm getting a ton of hiss. Very similar issue I had with my Azabache builds, which I was never able to resolve.


Getting 4.74v on Q4 and 5.06v for Q2. Thanks for the info.

And false alarm, must have been an impedance mismatch causing the noise/hiss as it sounds correct feeding the input on the amp. (Was originally testing it plugged directly into the power amp, found that adding a buffer between the two solved the noise as well with this setup)


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## Chuck D. Bones (Nov 18, 2021)

jubal81 said:


> Runoffgroove introduced a design in 2012 called the Azabache that's sorely overlooked. It's a great OD that broke some conventions at the time by using JFETs as 'clean' amplifiers, diodes for clipping and tacking on a primitive cab sim at the end.
> Subsequent designs from them built on this, but IMHO, the Azabache is the real gem of the bunch.


Another pedal design goes into the breadboard queue.


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## MAO (Nov 18, 2021)

Chuck D. Bones said:


> Another pedal design goes into the breadboard queue.


If you do build the Azabache, please let me know how you make out. My 2 builds had way to much hiss. Only noticeable when not playing, but it was crazy loud.  Pedal did sound great...until I stopped playing.


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## Chuck D. Bones (Nov 18, 2021)

Hmmmm.  I ran some sims and the gain is not that high.  I would not expect it to be noisy.  
How clean is your power and did you use any carbon comp resistors or disk ceramic caps?

Trimpots can be noisy.  ROG recommends replacing the trimpots with fixed resistors once you find the desired value.


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## MAO (Nov 20, 2021)

Chuck D. Bones said:


> Hmmmm.  I ran some sims and the gain is not that high.  I would not expect it to be noisy.
> How clean is your power and did you use any carbon comp resistors or disk ceramic caps?
> 
> Trimpots can be noisy.  ROG recommends replacing the trimpots with fixed resistors once you find the desired value.


Hey Chuck, thanks for checking into this. All metal film and mylar or monolithic caps. Also used fixed resistors. When probing the circuit, the hiss increased through each gain stage.  This is where I was at troubleshooting when finally throwing in the towel:

"I built a 2nd one with all new components except the pots. Same issue with hiss!!!

Anything above 7 on the volume control and the hiss is very apparent (when not playing). Not an issue with higher gain settings and moderate volume, but with lower gain settings and higher volume, way to much hiss.

I find it strange no one else has mentioned this, which leads me to believe there is something wrong with my builds, but I can't figure it out.

So I ended up adding a 3-way "hiss reduction" toggle switch. The center position is the original unmodded circuit, which sounds great as long as I keep the volume below 7. Switch up adds in a 1n from the gate of Q2 to ground, this removes a good bit of the hiss. Switch down also increases a low pass filter I have at the output.

Been using it for a few days now, the added switch seems like a good countermeasure when the hiss becomes annoying."


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## ALK2MT (Jan 8, 2022)

Chuck D. Bones said:


> I bought one too.  Until the Build Docs are published, the silkscreen on the board IS the build doc.  Being the A/R person I am, I make a spreadsheet for each build that includes a parts list, which can double as a shopping list.  Haven't done that yet for this board.


How’s it going??


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## Chuck D. Bones (Jan 8, 2022)

No progress yet.

Build docs were posted a couple of months ago.


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