Feral Feline
Well-known member
Thanks for sharing this Dan.
Would love to know if this is a worthwhile build for Bass...
Would love to know if this is a worthwhile build for Bass...
Dunwich DA-120 on a breadboard
- Thread starter Dan M
- Start date
I know there are bass demos on youtube. For guitar, it works as expected. It sounds good on its own and it definitely stacks well. So far I've tried a Rat and a Muff in front of it with great results. I think I'm going to build a mini doom pedalboard with a compressor, parentheses, big muff, and this pedal. ("mini" pedal board with only 4 pedals, but 3 of them are 1590XX. . . ) Plug that into any power amp and it should shake the house down.
Feral Feline
Well-known member
That would be an awesome board: just a few, but BIG, pedals!
PS: Definitely worthy of a build for bass, but then ... most Dunwich stuff is.
PS: Definitely worthy of a build for bass, but then ... most Dunwich stuff is.
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Chuck D. Bones
Circuit Wizard
Looks good. How noisy is it? That's a whole lotta MOSFETs and they are noisier than JFETs.
It gets noisy. I did a check today. The Drive and Gain behave similarly, with the gain causing a bit more noise.
For some perspective, my Mojito is very quiet.
With drive and gain below 10 o’clock this DA120 is quiet.
At noon it’s noticeable but acceptable (similar to a maxed Mojito).
Maxed out it’s pretty noisy.
There’s a lot of fidelity in the gain and drive sweep. In the 9-12 o’clock range, there’s quite a bit of drive available while still being quiet. North of 12 o’clock, it’s well outside of “subtle overdrive tones”. At that point, the noise doesn’t bother me if I’m trying to vibrate the paint off the walls.
hello, could you share the layout schematic?
I never posted the layout because I can't say it's verified. I changed some things when building it because the layout is a mess and not easy to build (that was putting it lightly. The build is a nightmare. The traces are too tight, components to close together, the pots are a pain. Pretty much every step is a disaster waiting to happen).
The schematic posted above is good, so you could make your own layout. But here is the last drawing I made. The yellow wires go to the depth switch. The blue lines are jumpers on the component side of the board.
The schematic posted above is good, so you could make your own layout. But here is the last drawing I made. The yellow wires go to the depth switch. The blue lines are jumpers on the component side of the board.
Laundryroom David
Keyboard Cowboy 🤠
ooooooh this is my kind of build
finebyfine
Well-known member
Would it be feasible to replace the rotary switch S1 on this with the variable capacitance multiplier in Figure 21 on this article from Rod Elliot? https://sound-au.com/articles/gyrator-filters.htm#s12
Very interested in laying out a board for this but I always have such a hard time with laying out rotaries
Very interested in laying out a board for this but I always have such a hard time with laying out rotaries
I’m not sure if you really need all 6 choices. You could probably use a toggle switch for 1, 10, and 100nF. (Or whatever 3 seem the best)
benny_profane
Well-known member
Yeah, the six is a bit overkill given the footprint of the switch. Circuit sounds great, but that amount of nuance along with the bass/treble and active mid boost stage is a little redundant.
Also, it is very loud.
benny_profane
Well-known member
Also, the dunwich pedal alters the James stack from the typical orange values (not sure if that’s how the matamp is or not). That may be another place to alter the frequency filtering.
Chuck D. Bones
Circuit Wizard
That C-multiplier has the cap tied to GND, which is not want we want for the DA-120. We could build a "floating" C-multiplier with two opamps, but because the 1st stage has a low output impedance and the 2nd stage has a high input impedance, there is a much simpler solution.
1. If it isn't already, make the GAIN pot A1M.
2. Increase R6 to 4.7M.
3. We'll keep C3. Delete C4-C8 & the rotary switch. Change C3 to 6.8nF.
4. Connect pins 2 & 3 of an A500K pot to GND. This is the new FAC control. Connect pin 1 of the pot to a 10K resistor.
5. Connect the other end of the 10K resistor to the junction of C3 & R5.
That's it. The FAC pot has the same range the Orange 120 FAC switch. Turning FAC CCW decreases the bass content.
It's no coincidence that this new FAC control circuit is similar to the TIGHT control in the Friedman pedals.
BTW, D2 & D3 are unnecessary. Once the board is assembled, Q2 & Q3 do not need ESD protection.
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benny_profane
Well-known member
Did you bias Q4?i built a pcb using effects layouts 'ef120' schematic and it didnt work, so made another one using this one and having the exact same issue, first time im stuck on something i cant figure out
Chuck D. Bones
Circuit Wizard
I wanna know why Q4 needs an adjustable bias.
The 1st opamp's gain is too high and it will saturate before Q4 does. Unless one dials the bias way down. Why not just hard-wire the bias to the correct value?
The 1st opamp's gain is too high and it will saturate before Q4 does. Unless one dials the bias way down. Why not just hard-wire the bias to the correct value?
benny_profane
Well-known member
No clue. But if it’s not biased properly that would certainly cause problems.
Chuck D. Bones
Circuit Wizard
I just don't think we need a trimpot to get there. I'm guessing that designer intended Q4 and the IC to emulate a tube amp's push-pull output. Thing is, Q4 is single-ended and the opamp can't change that by sensing it differentially. The MOFETA & Brownout do it the right way with a differential transistor stage emulating the push-pull output. I have not breadboarded the MOFETA yet, but can tell you that the Brownout has some excellent tones.
Thanks Chuck. I’ve been away from pedals for a while. I’ve got a Mofeta board that’s half populated and I just looked at the build doc for the Brownout, I think I’ve got the five 2n5457’s on hand. I’ll queue that for the breadboard and check it out.
Chuck D. Bones
Circuit Wizard
Remember: JFETs are not plug-n-play. You'd better have more than 5 and they don't have to be 2N5457.
https://forum.pedalpcb.com/threads/a-tale-of-three-variacs.9697/
https://forum.pedalpcb.com/threads/a-tale-of-three-variacs.9697/
