Building the Chopped OC2

[Taylor]

In this application it doesn't matter as far as I know. The FET is just used as a switch to flip the phase of the signal every other cycle.

[jeremypb]

ok thanks for clearing that up. now I have another problem: I have no octaving effect.
in audio probing i have mean square wave sound coming out of pin 8 and meaner out of pin 1 of the LM324 but I have nothing out of pin 7 or 14.
Is that my problem? I'm pretty novice so I'm not sure what I should be hearing out of those pins

[jeremypb]

upon further attempts I can hear noise from pin 14 of the 324 and I can hear the octave down out of the 4013 but both are only if I play very hard and they're extremely short. no sustain whatsoever.

[djaaz]

Hi everyone,

I tried to change the pots from front to back of the pcb. Doing so, i ruined the solder pads.

I'm trying to connect the pots lugs directly on the components on the pcb, using the schema and what i can see from the pcb traces.

CLean pot:

Lug 1: to right side of the 5k6 resistor at the bottom of the pcb near the led switch (should be Vref)
Lug2: to right side of the 100k resistor just below the octave pot. ?
Lug 3: to pin 1 of the TL074.


Octave Pot:
Lug 1: to the lug 1 of the clean pot
Lug 2: ?
Lug 3: to the pin 8 of the TL074.

I can't figure on what side of which 100k resistors i should connect the lug 2 of both pots.


Any help would be greatly appreciated.

[Taylor]

Hi there, if you can bump this thread one more time it will remind me to post back when I'm at my other computer - there I can look inside the circuit layout (since I don't have any more boards) and give you the answer.

[djaaz]

Sounds great!

Bump!

[Taylor]

All directions I mention are when looking at the silk-screened side of the board, with the text right side up so you can read it.

CLean pot:

Lug 1: to right side of the 5k6 resistor at the bottom of the pcb near the led switch (should be Vref)No, it should be the left side of this resistor
Lug2: to right side of the 100k resistor just below the octave pot. ?No, this connects to the left side of the 100k pot directly under the clean pot
Lug 3: to pin 1 of the TL074.correct


Octave Pot:
Lug 1: to the lug 1 of the clean potcorrect
Lug 2: This connects to the left side of the 100k resistor directly below the octave pot
Lug 3: to the pin 8 of the TL074.correct

[p_wats]

I finally got around to adding some mods to my board and am almost ready to box it up (have to forego the filter mod until I can get a dual 1M pot).

However, like others in the thread I can't seem to get rid of the fuzz in the signal (even without mods added). There's still a generous octave, but I would definitely not call it clean.

At this point, my board is unboxed and simply gator-clipped together (I've experimented with different grounding schemes), so I suppose that might be contributing to it? The fuzz doesn't go away with a buffered pedal in front though.

It's still pretty awesome with the synthy mod-tones, but I'd love to get a nice, fat, clean octave out of it too.

EDIT: I haven't tried scraping and grounding the 2 points suggested yet, so I'll do that tonight too.

[p_wats]

Scraped down to some copper both between the two pots and left of the ground pads on the top side and no progress.

It wouldn't be so annoying but the fuzziness is there between notes too, chortling and farting away.

Any one got any tips?

[djaaz]

All directions I mention are when looking at the silk-screened side of the board, with the text right side up so you can read it.

CLean pot:

Lug 1: to right side of the 5k6 resistor at the bottom of the pcb near the led switch (should be Vref)No, it should be the left side of this resistor
Lug2: to right side of the 100k resistor just below the octave pot. ?No, this connects to the left side of the 100k pot directly under the clean pot
Lug 3: to pin 1 of the TL074.correct


Octave Pot:
Lug 1: to the lug 1 of the clean potcorrect
Lug 2: This connects to the left side of the 100k resistor directly below the octave pot
Lug 3: to the pin 8 of the TL074.correct

Thank you Taylor. Fixed.

I have this light fuzz in the signal as well. I'm not sure i noticed it before this pot reversing adventure.

[p_wats]

Scraped down to some copper both between the two pots and left of the ground pads on the top side and no progress.

It wouldn't be so annoying but the fuzziness is there between notes too, chortling and farting away.

Any one got any tips?

I shouldn't say "between" notes, as much as easily agitated (ie. if I tap the strings). It sounds to me like the unison square wave (ie. the octave sounds clean, but my "clean" signal doesn't).

[p_wats]

Also, how possible do you think it would be to have a separate "wet only" out (ie, just the Octave down)?

[Taylor]

I think there were a few pages about the fuzz sound earlier in the thread. It seemed that some people had an impedance issue that seemed to be causing it and that it was solved by a better buffer. Check back over those pages and see if that helps.

A wet out would be easy, just take the output from the wiper of the octave pot IIRC. It may be quiet, so you may want to add a gain stage (opamp or transistor) on the end to get unity if it's too quiet.

[p_wats]

I think there were a few pages about the fuzz sound earlier in the thread. It seemed that some people had an impedance issue that seemed to be causing it and that it was solved by a better buffer. Check back over those pages and see if that helps.

A wet out would be easy, just take the output from the wiper of the octave pot IIRC. It may be quiet, so you may want to add a gain stage (opamp or transistor) on the end to get unity if it's too quiet.

Thanks for the info. I definitely read through and tried any suggestions I could find (scrapping solder mask and grounding, using a buffered pedal in front, etc.) to no avail. A few potentially interesting results though:

Taking the output from the wiper of the octave kills any fuzz whatsoever ( as well as my dry signal and the wet signal is nice and loud ) which leads me to think there must be a problem with something sneaking in to the dry output (?).

Also, maybe it's just late and I'm losing my mind, but I can't for the life of me find the 2n2 cap in the schematic. It also looks like there are 3 10uf caps and not just the one... Am I going nuts? Thanks for all the help...

[djaaz]

Hi guys,
I did it again & the input pad broke when i boxed the pcb.
Looking at the schema, i'm supposed to solder the input wire to a 1M resistor. I can't trace the pcb to this resistor.
I don't want to mess more with the pcb by trying my luck.
Can you tell me wich it is?

[djaaz]

Taylor?

[Taylor]

Looking at the silkscreen side, with the text the proper way up, the input goes to the left side of the lowest 1m on the left side of the board.

[djaaz]

Thanks Taylor!

Played a bit with it yesterday and the pedal bounce from octave to octave as soon as the note last more than 1 second. I did not use a 1n34 but a unknown germanium diode.
I replaced it yesterday with an 1n34 and tried another CD4013 yesterday just in case, without any change.

Any way i could improve this? What should i look for?

[Taylor]

To some extent that's the nature of all of these types of pedals. Rolling off treble, using the neck pickup, careful fingering etc. are key to getting good tracking in all analog octaves. You could play around with the the filtering in the circuit if you wanted to tweak it.

[djaaz]

I know i'm not supposed to expect a perfect thing. The weird thing is that i had better tracking when i was testing it before.