Simple DOD FX17 wah circuit spinoff.

[John Lyons]

Board arrived, thanks Ian!
Looking forward to playing with this.

John

[radio]

Mine arrived too. Thanks Ian!

Hope start building tonite.n

[Paul Marossy]

Hey Ronan, what did you use for a pot? Just a regular old 1/2 watt 10KB Alpha type pot?

[Ronan]

Yes, just a normal pot, nothing fancy. Don't forget to set the trimpots as described in this post. Otherwise, as happened to me, you might get no sound at first. There is also a risk of damaging the CA3080E's if the control voltage goes too high.

[Paul Marossy]

Yes, just a normal pot, nothing fancy. Don't forget to set the trimpots as described in this post. Otherwise, as happened to me, you might get no sound at first. There is also a risk of damaging the CA3080E's if the control voltage goes too high.

Cool, thanks. Already got those notes printed out for getting it set up. Just waiting on the CA3080s to arrive now...

[azrael]

Neat! Are there any spare PCBs left?

[Ronan]

Yes, there are 3 left, sent you a pm.

[Paul Marossy]

Got mine finished this evening. The voltages I measured weren't quite the same as what were listed in the voltage adjustment procedure for the pot & trimpots, but it works fine in any case. Now I just need to get used to it, it's got a different feel to it than a Crybaby type wah. I'm liking it so far.

[Ronan]

That's great Paul, I was beginning to think no-one was having any fun with this one. The lowpass setting is a lot warmer than the bandpass setting which is thinner sounding, I like a mix of the two. I prefer this wah to an inductor wah for clean sounds. With a dirt pedal, it is more radical than a crybaby, and is capable of a much larger sweep range, but it doesn't seem to achieve the sweet singing smoothness that an inductor wah often can with dirt. So the jury is still out (at my place) on which one I like the best with dirt. Just my thoughts on it.

[Electron Tornado]

I have some PCB's left over from a batch of 10, if anyone is interested pm me, $10 shipped to USA or wherever. They are better off going somewhere rather than sitting around here. Anyway, hope you enjoy.

Ronan, there's a new PM in your in box.

[Paul Marossy]

I like it because it doesn't get so "peaky" like an inductor wah does. I'll get to try it out in a band situation soon.

[Paul Marossy]

Here's a few pics of mine. I drilled two holes in the bottom plate so I could easily tweak stuff if I wanted to.

[Paul Marossy]

Just thought I'd add that I recommend using a 200K trimpot (or 220K if easier to find) for the resonance control. I put a 100K fixed resistor in there and it just didn't seem to have the kind of resonance I was looking for. I put a 200K trimpot in instead and tweaked it to taste. Now I can honestly say that it sounds very much like my Colorsound inductor wah pedal does.

I like this little circuit, it doesn't have the limitations of an inductor based wah pedal - like picking up EMI , being microphonic or picking up vibrations and sending it thru the your stuff (yes, I've had that happen on one of my original Maestro Boomerangs it was picking up the kick pedal of the drummer, we were all on a platform at the time).

[Ronan]

Sorry to see there are issues with the circuit Paul, and thanks for bringing it up here:

http://www.diystompboxes.com/smfforum/index.php?topic=98307.0

Seems there are latchup issues which I didn't detect in my build, but I can duplicate the latchup easily. So I apologise sincerely to all who have bought a pcb or attempted a breadboard. The problem is that no sound comes out after powering the circuit up because the TL072's go to their rails and stay there, preventing any sound coming through. I hate it myself when a circuit doesn't work, and I think its my fault, and keep pulling my hair out and wasting endless numbers of hours trying to get it going.

In this case there is a fairly easy fix, and that is to use LM1458 or TLC2252 or TLC2262 for IC1, that is the IC right next to the BP/LP mix trimpot. Paul has used LM1458, LT1013 and NE5532 with success in the other position, but the TL072 would not work for him there. I tried a TLC2262 for IC1 and left the TL072 in the other position and it works fine for me. That does not mean that will work for everyone else, its a bit unknown at this stage.

So again my apologies, this is supposed to be fun, not a trial, but I screwed up. If anyone wants a full refund on a purchased board just pm me and I'll do it right away (or as soon as I get home from work). Sorry guys, lesson learnt, I'll be more careful in future. Thems the breaks.

[Paul Marossy]

Sorry to see there are issues with the circuit Paul, and thanks for bringing it up here:

http://www.diystompboxes.com/smfforum/index.php?topic=98307.0

Seems there are latchup issues which I didn't detect in my build, but I can duplicate the latchup easily. So I apologise sincerely to all who have bought a pcb or attempted a breadboard. The problem is that no sound comes out after powering the circuit up because the TL072's go to their rails and stay there, preventing any sound coming through.

I didn't think to mention it here earlier because it was kind of a minor issue at the time, but when I wanted to try and get it quieter I had to start the other thread because it was bugging me why the TL072s were giving me a hassle (although a JRC4558, JRC4580 and a couple other types would not work either). My being annoyed with it has more to do with a very simple build I did previously where the TL072's  Input Common Mode Range was an issue, not this little wah circuit - I still like it a lot. I have concluded that the hiss must be coming from the CA3080s, not the other opamps. Not sure what can be done about that other than maybe trying a different brand of OTAs or something.  

In any case, I'm not going to use a TL072 in anything I build from now on.

[Ronan]

Paul, regarding the voltages when setting the unit up, if the voltage won't go low enough or high enough, its probably due to the actual physical position of the 10K pot mounted in the wah shell. It can be rotated a little, or shift the rack by one tooth, to get the right voltages. But, if you are happy with the sound of the sweep going low enough, and high enough, then that's all that matters, and best to leave it alone. The setup procedure is just to get you in the ball park in the first place.

If the TLC2272 works in this unit, it is probably one of the quietest IC's I can think of.

[Paul Marossy]

Paul, regarding the voltages when setting the unit up, if the voltage won't go low enough or high enough, its probably due to the actual physical position of the 10K pot mounted in the wah shell. It can be rotated a little, or shift the rack by one tooth, to get the right voltages. But, if you are happy with the sound of the sweep going low enough, and high enough, then that's all that matters, and best to leave it alone. The setup procedure is just to get you in the ball park in the first place.

If the TLC2272 works in this unit, it is probably one of the quietest IC's I can think of.

Yeah, I figured out that the physical position of the pot in the shell was a factor in that. And I did monkey around with where the pot gear was on the pinion gear. It's OK, because in my case, if the low side went any lower the sound would cut out completely. I'm using an off-brand wah pedal and it's a little different than a crybaby shell in terms of the travel at the heel down position (there's some "squish" at the very end because of soft rubber pads).

I still think the noise (hiss) in my case is coming from the CA3080s themselves since putting in "quieter" opamps barely made a difference. Like I said before, it's not too bad, it's just not silent with no signal going thru it when using a high gain pedal. This is with the wah before the distortion, so it's picking up hiss from the wah and amplifying it.

[Ronan]

I thought about it for a few days, and although no-one has asked for a refund, I decided to refund all pcb buyers. I cannot take money from fellow hobbyists if the pcb is not up to scratch, which it isn't, because it has latch up issues with TL072, which is due to my lack of understanding the details of the CA3080. TLC2262 however works fine (in my torture experiments). Now I understand why other designs like the LM13700 running on 9V use the inbuilt darlington buffers, since a discrete buffer cannot latch up! It will hit the rails, just like this circuit, but bounce back again. A rail to rail opamp, or more specifically, one that will accept an input that goes to 0V and can output a voltage that goes to 0V, like the TLC2262, will do the same as the discrete buffer. With only 2 build reports, mine and Paul's, the degree of the circuit's instability is still unknown, and could be worse than what I think. I'm really sorry guys that I probably caused cursing/pulling out of hair/WTF's?/stress/etc. I will try to do better in future.

[Paul Marossy]

Live and learn.  

Thanks for the refund although I am happy with it. I've been using it when I practice in the morning. Anyway, if it makes you feel better...  

[pinkjimiphoton]

no worries mate...

i still am awaiting my build, so i'll send a report when i get to it. now that i'm a working musician again, it's harder to get the time to get anything done.

but don't feel bad bro...here's the thing. even when we build something problematic, it means we all learn more.

ya don't learn from doing things right, somebody said.... i think. ....maybe it's me.

looking forward to a positive report for ya...after how buggy my last few builds have been, it's about time i get one right, so i hope it's yours!!