Acetylene
- Thread starter ALK2MT
- Start date
Chuck D. Bones
Circuit Wizard
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.
Coda
Well-known member
Attachments
Chuck D. Bones
Circuit Wizard
Build docs were uploaded last night.
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.
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.
benny_profane
Well-known member
What is the impact of the order here?
Chuck D. Bones
Circuit Wizard
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.
Chuck D. Bones
Circuit Wizard
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.
Mentaltossflycoon
Well-known member
It's extra satisfying to pull one together with no paperwork.
Chuck D. Bones
Circuit Wizard
Until you need to troubleshoot. 
mdc
Well-known member
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?
Chuck D. Bones
Circuit Wizard
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.
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.
Robert
Reverse Engineer
jubal81
Well-known member
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.
Chuck D. Bones
Circuit Wizard
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?
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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