Building the Chopped OC2

[Taylor]

The PCB and BOM are correct - the schematic has an error. The 10uf connected around U1A is the one that's really 10uf. The cap marked 10uf coming after the 2n3904 is actually a 1uf.

[Marcvv]

Hi Taylor,

These are the pics of my OC-2.
I still have a bleeding of the square wave on the dry signal.
I would be pleased if someone can come up with a suggestion

[Taylor]

Are you using a silicon diode where it should be germanium? I never tried that, but it might in fact induce a little discontinuity in the octave waveform. That diode's job is to create a DC offset on alternating phase flips, so I wonder if the different forward voltages of silicon vs. GE would create the wrong DC offset, and the disconinuity would be heard in the octave signal as a buzzing.

[Marcvv]

I used a 1n60 which is supposed to be a 1n34 workalike. So it is a germanium. 

I could see if i have another one and change it.

As you can see i did scrape some of the top coating to connect the top copper layer to the ground pad next to it. This is what you meant wasn't it?

Any other ideas?

[Taylor]

If it's germanium then it should be fine. It looked like a 914 or similar, but I guess not.

I don't know, I'm scratching my head. I guess the next step would be to probe through the circuit and see at what point the fuzz becomes audible.

You're using a J201 right?

[Marcvv]

I will start probing then. It would be great to have a pcb layout for that it would save me first tracing it.

And yes I am using a j201.

Marc

[Taylor]

My CAD software doesn't let me print PCB images easily.

The way I probe boards like this is to probe pins of the ICs. The pins are numbered on the schem so you can can trace through the major blocks and the FET to isolate the issue - it's rarely necessary to probe each individual passive component.

[MonkeyWrench32]

I had mine working fine until I tried adding the mods to it. I'm pretty sure I've damaged the "in" on the board beyond repair. Too much soldering and de-soldering.

I'm probably going to start over with a fresh board because the way I first designed the mod layout is a complete mess.

Here's my second try with DIYLC:



Does everything look correct? Also, could I use SIP sockets on all of the wire connectors for in/ledsw/led/out/gnd/9v? I'm pretty sure the holes at the top for the Clean and Octave pots are much too large, but that shouldn't be a problem.

EDIT: I just noticed that my two switches are off-center. Obviously I'll have those lined up properly when it's build time. 

[phector2004]

Ok so I'm 95% sure I can squeeze this thing into a 1590B, using prebond and blood caps, but I have a small worry... figured I won't start a thread to ask such a silly question:

Are there any good reasons for socketing CMOS chips? I haven't cooked any components since my first project and figure skipping the socket will give me an extra 2mm or so to work with - space that could be better used on PCB-bottom insulation. So is it wise to socket CMOS? They don't crap out after a while or anything, do they?

[Taylor]

CMOS is statically sensitive, so there's a very small chance that you could zap a chip - say, you just pet your cat vigorously before picking up the IC - and not know it. Troubleshooting would in this case be a nightmare and removing a 14 pin IC from a PCB is not fun if it's not socketed.

But, it's a pretty small chance. Neglect the feline and wait until after your pedal is working to ice skate across the carpet in socks, and you'll probably be fine. I have never confirmed that I killed a chip just by handling it, and that includes handling DSP chips by hand. But, I live in America's swampland. Dryer places will have more static danger.

[phector2004]

Alright! We've got tons of humidity here, surprisingly, and for once it'll work out in my favor 

I'll post as soon as my tantalum caps ship in, when I finish up. I'll confirm if the "vanilla" version fits in a 1590B, with appropriate changes

Cheers,

Phil

[Marcvv]

If it's germanium then it should be fine. It looked like a 914 or similar, but I guess not.

I don't know, I'm scratching my head. I guess the next step would be to probe through the circuit and see at what point the fuzz becomes audible.

Hi,

I probed through the circuit.
The fuzz is audible at the input already and certainly at pin 1 of U1a. Then it stays in the circuit.

Because of this I replaced the 0.1 uf filmcapacitor I already subbed for the 1uf at the input for another 1 uf elco.
No difference in the fuzz signal and I get the dc back on the pots. So that did not work.

Any suggestions?

Thanks, Marc

[Marcvv]

If it's germanium then it should be fine. It looked like a 914 or similar, but I guess not.

I don't know, I'm scratching my head. I guess the next step would be to probe through the circuit and see at what point the fuzz becomes audible.

Hi,

I probed through the circuit.
The fuzz is audible at the input already and certainly at pin 1 of U1a. Then it stays in the circuit.

Because of this I replaced the 0.1 uf filmcapacitor I already subbed for the 1uf at the input for another 1 uf elco.
No difference in the fuzz signal and I get the dc back on the pots. So that did not work.

Any suggestions?

Thanks, Marc

Bump.

Anybody any suggestions?

Thanks, Marc

[Taylor]

It's weird, these symptoms don't make much sense to me. Perhaps the noise is not coming from the 4013 at all? Try pulling it out of the socket and see how it sounds.

[Marcvv]

It's weird, these symptoms don't make much sense to me. Perhaps the noise is not coming from the 4013 at all? Try pulling it out of the socket and see how it sounds.

Hi Taylor,

I pulled the 4013. The fuzz changes into a lighter version but it is still there. I pulled the LM 324 and then it is gone.

The Lm324 itself should be ok as I changed it with another one that I know is working fine in another circuit with the same result. But then you never know....

Just to be sure: I am using a MC14013BCP and a LM324N.
(And to be even more sure: I am using 5x 1uf elco of which one is now nonpolar; 1x 10 uf elco and 1x 220uf and 100uf elco)

Thanks, Marc

[Taylor]

ok, this is interesting - so the issue is not the square wave logic signal bleeding at all.

Can you re-describe the problematic sound you're hearing? What ind of instrument and what other pedals if any are in front of it?

[Marcvv]

ok, this is interesting - so the issue is not the square wave logic signal bleeding at all.

Can you re-describe the problematic sound you're hearing? What ind of instrument and what other pedals if any are in front of it?

It sounds like there is a fuzzy/fuzzy sound running parallel to the sound of the guitar. If I remove the the 4013 it becomes high pitched and then changes to a lighter version. The high pitch is there only for a moment. If I remove the LM324 it is gone.

I am using a humbucker equiped guitar guitar, so no preamp or buffer in front either straight into a guitar tube amp (silvertone 1482) or first into my pedal board. No difference between the two different signal paths. I power the Chopped OC2 with either  a very well regulated power supply or from a battery. No difference between those two either.

Your description of square wave bleeding into it was closest but I guess now gets another point of vue as we still have something going with the 4013 removed.

Hmmm.... what now?

[Taylor]

It now seems like it's clipping of the normal sort. So I'd approach it as I would any unwanted clipping - turn down volume in front (guitar vol knob) and see what kind of effect it has.

[Marcvv]

It now seems like it's clipping of the normal sort. So I'd approach it as I would any unwanted clipping - turn down volume in front (guitar vol knob) and see what kind of effect it has.

Done that. No difference.
To me it does not appear as clipping at all.

[slacker]

The output of the LM324 is a squarewave, so it sounds like that's what you're hearing. Does the fuzz change or go away if you put a buffered pedal in front of it?