Not an auto wah in a normal sense, more like an inductorless wah circuit driven by an LFO.
This must be one of the earliest modulation pedals and IMO it is a hidden gem. Lots of murky psychedelic madness can be found in this circuit, especially with a dirt box upfront.
Rate and Depth controls is self explanatory but the Tone control really widens the ranges of tones. Clockwise you'll get normal wah wah sweeps, roll it back and you can dial in vowel and yuo-yuo sweeps.
With the Depth control CCW, the LFO is disengaged and the unit acts as a eq / filter circuit.
Layout has some mods; power supply mod since original units was positive ground, CBE pinout for the transistors, power filer cap and protection diiode. As for the transistors, most low gain NPN silicons should work, I ended up with PN2222s in the 150Hfe ballpark.
This is soon to be boxed but need to figure out how to add a rate LED first...
*Edit* Rate LED added with help from Radu. Thanks!
Schematic is avaiable HERE
I built it and I like it, weird (in a good way) and not what I was expecting xD. I might experiment different values for Speed pot - B50k pans between slow and slower (unless I have a mistake in my build and something is wrong, but I don't think so). Thanks for the layout!
ReplyDeleteHmmm, the Speed pot has a wide range in my build, goes from quite slow to really fast, almost "ringmodish... You might need to check the values of the 22k 4,7k resistors and 2,2uf caps on the right side of the board?
DeleteBTW, here is a demo which illustrates how the controls work.
Deletehttps://youtu.be/_-c9ACDds7E
You were right, and you made troubleshooting quick xD one of the 4.7K wasn't connected - now it sounds like the demo. Very nice! Thanks
DeleteYou can get slower speeds using a 100kB pot without sacrificing top speed, and 500k gives some weird cool stuff on the first half of the turn (it’s hard to explain).
DeleteHey man, any chances of a Pal 800 layout?
ReplyDeleteThere is a layout that needs to be verified.;-)
Deletehttps://dirtboxlayouts.blogspot.com/2020/07/marshall-800-jcm-emulator.html
Whoa! I missed that! Will verify it this weekend
DeleteI built the peavy decade and jcm800 emulator this month . Verified!for the jcm800 the tranny i used is2sk117
Deletewhat does N.C. mean? (for depth 3, tone 1, speed 1)
ReplyDeleteIt just means No Connection.
DeleteThanks, looking forward to building this!
DeleteBuilt this, sounds great... used 3904s.the layout says 5 links but there are actually 6
Deletegot it to work but am getting some crazy lfo Ticking from it. I am using PN2222's for Q1&2 and 2n3904's for 3,4, and 5 - could that be whats causing the tick?
ReplyDeleteQ3 to Q5 is the LFO section and the 2N3904s might be too hot. I would try PN2222s or other lower gains trannies in there instead.
DeleteI've been messing around with the values for the 2.2uf caps. The best combo I've landed on for speed range and LFO curve is 4.7uf for C9 and C10 and 10uf for C11. The only problem with this is that when the speed knob (I'm using 250k) is in the lower half of its range depth seems to decrease as well. I've tried a higher value Depth pot with no luck. I'd really like to get a long, deep, slow moving wah out of this thing. Any info on how?
ReplyDeleteOkay now 47uf for C9/C10 and 100uf for C11 gives me the speed and depth I want, but only because even at maximum speed is pretty slow. The same problem is occurring where low speed also results in lower depth.
DeleteI just discovered this circuit : thank you!
ReplyDeleteIs there any way to tweak the resonance (I'm thinking maybe a capacitor on a switch)?
I'm no wah expert by any means but maybe tweaking one or both of the 10nF caps?
DeleteHello,
ReplyDeleteI built it today : easy build, thanks to a very nice layout!
- The effect sounds good, very "liquid" sound, resonant but not harsh... I think i don't need to fine tune the resonance at all, it's great stock!
- The only changes i made : I used 10k pot (instead of 5k) for TONE and DEPTH, and 4.7µF electro caps (instead of 2.2µF), in order to reach slower LFO speed as advised above : the LFO range is quite good (it doesn't go very slow, but it's a very acceptable range imho).
- I used BC547B transistors (turned 180°) : I get no LFO ticking, but the overal volume is below unity gain. Any advice to get more gain/volume out of it? Would 2N5088 be more gainy? Or should I get 2N3904?
I got a volume boost in my build so you might have a small bug in your build. I doubt higher gain transistors will help raising output in this type of circuit. But you could try to decrease the 100k resistor connecting to Output.
DeleteThank you, I will try that.
ReplyDeleteI also noticed that i get the loud wet signal on the rows D and F from the left side of the veroboard layout (which correspond to the Q2 Emittor , and the 10k resistor going to Q2's Collector).
Would it be safe to wire the output to either row D or F, and thus skipping the last portion of the circuit?
Hi, tweaks made, pedal improved!
ReplyDelete- The 100k resistor at row 12 was responsible for the volume loss. I used a 10k instead, and now i am running the pedal at unity gain.
- I tried to tweak the 10 nF cap (row2), hoping to change the resonance : increasing it lowers the cutoff point, making the sound "darker". 22nF sounds good, 33nF starts to be quite dark, but the stock value sounds fine as it is :)
- I tried to use a 47µF electro cap (instead of the 2.2µF row 19) : the LFO can go much slower, but (maybe because i changed only 1 cap) I found the modulation shape to be quite assymetric (more a saw than a triangle), thus creating a strange modulation effect. I think I will keep the stock value here, too.
Excellent! Glad you sorted the volume issue.
DeleteBuilt this last night, works like a charm! I read through all the comments and socketed stuff that people were tweaking. I used a 100k for the Speed, but, all said and done, seems like Colorsound and Fuzzhead knew exactly what they were doing and building this thing just as the layout shows is the way to go!
ReplyDeleteI slapped the simple yet brutal Ritual Fuzz in front of it on a toggle and boxed it up. Makes for a real unique pedal and allows you to push this thing well above unity. Thanks fuzzhead!
For anyone trying to build it : I tried with both BC547 and 2N222 : 2N222 gave more output volume, better sweep and normal LFO speed.
ReplyDeleteQ1 & Q2 changed the volume
Q3 gave better sweeping
Q4 & 5 changed LFO time.
https://drive.google.com/file/d/1ejaZ4i-qnxdJb4PuuLOMXupyYEnnoA56/view?usp=drivesdk
ReplyDeleteBuild this one with 2N3903. Works great!
ReplyDeleteThanks for another great layout!
Boxed one of these up today and I love it. It has a lot of cool sounds in it and is really fun. I just made the stock layout and everything works great. I used 2n2222's that were all 215hfe.
ReplyDeleteI didn't know about this...it's on the list!
DeleteHow would I set it up for the Rate LED to be the bypass LED. Right now on my test box if power is hooked up to it the Rate led goes whether its bypassed or not. Getting ready to box this, but don't want the blinking light going constantly on my pedal board.
ReplyDeleteDid you finally find a way to do it?
DeleteThank you!!!
This comment has been removed by the author.
ReplyDeleteIt works perfectly. I used five C547B because I had a bunch of these lying around and their pinout is CBE, hFe about 300.
ReplyDeleteThis comment has been removed by the author.
ReplyDeleteWhat tranny you are using for this?
DeleteI have built it and it has not been complicated... in fact, and with my zero knowledge of electronics, it has been surprising to me, and it sounds very good.
ReplyDeleteThe only problem I find is that it makes like a Tack Tack at the same rate as the LED and I don't know what the solution could be.
Thank you very much for sharing all this knowledge and best regards