Build Your Own Clone Message Board

Just finished it. Works fine in bypass. When activating foot switch all I get is a high pitched oscillation. The chorus itself seems to work on the oscillation. Rate and depth seems to work. LED flashes with the rate. So, the chorus circuit seems to be working, its just instead of my guitar coming thru I get the oscillation. Adjusting the trim pot somewhat affects the tone of the oscillation (it goes from a high pitched noise to a low pitched noise at both extremes of the taper). Does the same thing on both battery and adapter.

I replaced all the opamps with no change. I tried running the pedal without the mn3007 ic and without the cd4047 ic to see if it would kill the oscillation, but it didn't (it just killed the chorus sound)

Built almost stock, 2 knobs, no extras. Except that I forgot to order a .033 cap (input cap), so I ran a .022 and a .01 cap in parallel to get there. Also, I replaced the 1uf and the 10uf caps with tantalums, could that be the issue?

Any ideas? I'll post pics tonight if an answer doesn't present itself to me. I did a search and found that a few different people have had the same problem, but never really saw that the issue was resolved.

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Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis

ok, fixed one problem, now i got a new one. While examining the board, I noticed that the 2.2 cap had a crack in it, so I pulled it and replaced it. That killed the oscillation. But now I have no chorus effect, only the guitar with a small volume decrease. Adjusting the trimmer had no effect. Any ideas? I'll keep hacking at it.

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Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis

never mind my last post, I went back in and turned it back on and the oscillation was back. Weird. So, the original problem remains.

Just a note: the oscillation does not change whether I'm using my guitar or just a chord plugged into nothing

_________________
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis

A low battery can do this behavior in some circuits. Measure the voltage of your battery and if it is below 8VDC measure the voltage of a fresh one and plug it in, or plug it into a 9VDC supply and see if that helps.

I had this exact issue with my BYOC delay. The battery I tried it with was from another pedal and was probably old. It presented barely over 6VDC. A fresh battery fixed the issue.


Barry

Thanks for the reply. It happens using both battery and AC, so no luck there.

I took a break to get a milkshake with my wife and am now looking at this again. Here are a few other notes of interest:
If I plug the the cable from the input into my amp, I get the same oscillation. So I'm getting it on both sides of the circuit
With no power attached at all, I get sound through the circuit. It doesn't chorus, but it passes the guitar signal through (actually, I'm thinking this is probably what I did before I posted the second time here). It's a tad quieter, and while messing with the depth and rate knobs do nothing, the trimmer inside effects the volume.

_________________
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis

Alright, I got it to work, sorta.

After poking around with a audio probe, I removed the .033uf parallel cap configuration and added a jumper in that slot. Bingo. Very nice chorus sound. I tried adding in the cap again but it just brought back the squeal. In fact, a cap of any size would cause the effect to oscillate. I tried about ten different sizes, from .1uf to 100pf, and the result every time was oscillation. So, I just did what probably any of us would do, said screw it, and left the jumper in. Anyone know what the .033 cap does? (c1)

Now, there are still a few issues. I loose quite a bit of volume when I engage the effect. This isn't actually too bad, but it forces me to turn up my amp. And at the louder volume I start to hear the clock noise. Is the clock noise normal? It sounds like my amp has a heart beat.

Theres also the problem of the insanely loud pop. Probably wouldn't be so bad if I can get a level equalization between the effect and bypass. This pedal sounds so good I might be willing to sacrifice true bypass if I can get the pop down to a manageable level.

_________________
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis

C1 is just the input cap. Blocks DC coming down the line, cuts some low end while doing it. If C1 causes oscillation, there's something seriously wrong; probably a short somewhere. Go over your board and make sure there's no solder bridges or dead solder points anywhere. You should have C1 in there, but you can try adding it outside the board.

Losing volume: Can be due to component tolerances, or if the difference is big, more likely a wrong component somewhere. Go over your resistor values at R1, 2, 4, 22, 26 to 29.

Clock noise is not normal. The post filtering of the chip should remove it. Make sure the wiring to your speed and depth pots does not cross or travel along with the rest of your wiring - Keep those wires separated from the others. May be worth trying shielded wiring for the audio path to and from board to switch and switch to jacks. (Ground shielding in one end only).

Tantalums may not be a good idea here. I would replace them with regular electro's, apart from C10. If you still hear clock noise after this, post good picts so we can have a look.

Popping; may actually be due to the lack of C1 again, so try placing it at the main bypass switch between the wire going to the input lug on the board and the switch. Usually you will have that wired to lug 5 on the switch. So, just insert a .033uf cap between lug 5 and the board input. If that doesn't help, add a 2M2 resistor to the switch going from lug 5 down to lug 6. If that doesn't help, it may be the led circuit popping. Try lifting your led limiting resistor and see if it stops the pop (R34a or b, and your led will stop working while you test this).

K

So basically, what you're saying is that everything about my build is wrong.
Thanks K, gives me something to do today while my wife is cleaning house (and asking me to help)

_________________
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis

Well... why do you think I'm here writing long-winded comments on a saturday...?

K

Ok, some success.

Replaced the tants and I can now put c1 back in the circuit without it going crazy.

Now, if I use .033uf for c1, it completely kills the pop, which is good, but it also lowers the effect volume so low that I have to really boost the amp to hear. Any value higher than .01 controls the pop to a usable level, but also drags down the volume. Its a pretty dramatic change in volume, and the larger the cap, the larger the drop. All the values of my resistors seem to be correct...and I'm using 1% and 2% vishay and xicon resistors. I'll start pulling the ones you suggested and see what happens.

Interestingly, the smaller cap I use at C1 makes the clock noise less apparent.

_________________
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis

lol. Well, one step forward, two steps back.

So, I figured since it wasn't oscillating anymore, I could move the input cap back to the board instead of inline with the switch. I even installed sockets so I could mess with it a bit. Fired it up and the high pitched oscillation was back. Socketed a few other components around there, replaced a few others I felt might be suspect. Still, nothing.

But wait, adding the jumper back at c1 kills the noise and gives me a working pedal. I noticed that changing the value of the cap changes the pitch of the oscillation tone. Lower value = higher pitch, and vice versa. A 1uf cap gave me a low rumble tone, a .01 cap gave me a higher tone, and so forth. A jumper gives me a chorused guitar sound with volume issues and clock noise. So, is what I'm hearing the cap releasing its charge to create a tone?

Anyways, I'm out of ideas for now. I won't touch this again for a few days, so here's some pics. Please excuse the poor wire dressing on the board. It didn't start poor, but after lifting it up and down so ofter things have started to go bad (its the solid core wire I accidentally bought the other day, it pulls up pretty bad). I figured it would be the last thing I fix before sealing it up. This was one of the best looking things I had created until troubleshooting started.

click to enlarge

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Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis

Sorry Teddy, these picts are of no use. Maybe step further away, use a flatter lightning. I cannot help you with these.

K

Did you figure this one out? I was playing with the chorus pedal ,thinking about doing the new mix mod. While I was noodling away, I gave the trim pot a turn to see what was happening. When I turned the trim pot full clockwise I got the high pitched oscillation. So where's your trim pot set?

I never did figure this one out. Adjusted trim pot several times, no change. The oscillation was coming from the input cap, or something connected to the input cap more likely. Lower value cap, higher pitched noise. Higher value cap, lower pitched noise. Anyway, I finally threw it in my "work on it later" box. I have since built 4 choruses for customers that have worked just fine first time.

_________________
Christianity, if false, is of no importance, and if true, of infinite importance. The only thing it cannot be is moderately important - C.S. Lewis