Fulltone - OCD  [traced]

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Torchy

Post by Torchy »

Already done one - just getting verification from another forum member then we'll post it.

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Post by Beedoola »

sweet

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Post by Valoosj »

I just read most of this topic, and I have only one question. Is the OSeeD Markm schematic verified?
Image

Or do I need to add something? I read some stuff about a diode.

If it's verified I can start drawing a pcb for this one, which I'll post off course.
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Post by tuemmueh »

I corrected my version today, just added the original led-switching. I did NOT build it up allready (maybe I will do. Maybe even this year ;))
This schem should include all versions that are floating around and have been verified by different members. Maybe this can help you ...
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Fulltone OCD rev.1-3 tuemmueh SCHEM.gif

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Post by briggs »

Nice work tuemmueh, I built up a OCD/Voodoo labs OD type circuit the other day - tried loads if different diode combinations, this is definately where the secret is in my opinion. A change in diodes imediately changes the whole character of the pedal. I'll be drawing up a scheme of what I tried soon. You can do some great mods to this circuit "structure" and get a completely different sound, in many ways just like the standard TS circuit....
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I am Klon.

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Post by erikm5150 »

tuemmueh, thanks for that copmrehensive schem.

Also, this might help with some more info about the different versions:

http://www.fulltone.com/PDfFiles/OCD%20 ... _small.pdf

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Post by Valoosj »

Thanks men, this helps a lot. Temmueh, that thing in the right hand top corner, that's a millenium bypass I assume?
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Post by erikm5150 »

To those you have built the circuit:

Would it be useful to replace the 22k and 33k switchable parallel resistors
with something like 10K and 25k pot in series.

I'm wondering if there are any useful tones in between.

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Post by bestegw »

erikm5150 wrote:To those you have built the circuit:

Would it be useful to replace the 22k and 33k switchable parallel resistors
with something like 10K and 25k pot in series.

I'm wondering if there are any useful tones in between.
I've thought about the same thing and I'll be building that soon (will order the parts tonight), so I'll let you know. I'll be adding it as a trimpot though, since it doesn't appear useful to me to have it "on the box".

Anybody have any thoughts on the bass response of this pedal?? Lack of bass is the part I really dislike in TS-circuit and I'm hoping that this will be better. One can always mod it for more bass, but I'm curious about the standard bass response.

Anybody tried to add clippers to the feedback loop of the opamp???

Seems like a great schematic for modding to me!!!!

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Post by MKB »

bestegw wrote:
erikm5150 wrote:To those you have built the circuit:

Would it be useful to replace the 22k and 33k switchable parallel resistors
with something like 10K and 25k pot in series.

I'm wondering if there are any useful tones in between.
I've thought about the same thing and I'll be building that soon (will order the parts tonight), so I'll let you know. I'll be adding it as a trimpot though, since it doesn't appear useful to me to have it "on the box".

Anybody have any thoughts on the bass response of this pedal?? Lack of bass is the part I really dislike in TS-circuit and I'm hoping that this will be better. One can always mod it for more bass, but I'm curious about the standard bass response.

Anybody tried to add clippers to the feedback loop of the opamp???

Seems like a great schematic for modding to me!!!!
The bass response on this pedal is very good being used as a distortion pedal into a clean amp channel (no overdrive on the amp). I've not felt the need to add any, and have used the pedal now for almost a year. I didn't try clippers on the feedback loop either, as the circuit in the schematic hit exactly what I was looking for, so I stopped messing with it. FWIW, the HP setting sounds a lot better, it really "cleans" up the midrange and makes a big difference. If I built another I would wire it in the HP position permanently.

Be very careful to use the same capacitor types as the original as there is where a lot of the magic lies. It's a simple circuit so those things make a lot of difference. You should be able to determine the cap types by looking at the pics of the PCB.

If the circuit has any flaws it is that it doesn't sound good at all with the gain above half. If you keep the gain below that and hit the input with a big signal, it's pretty amazing. One mod I'd add is to change VR1 to 250k and R5 to 250k to lock the max gain, and add another switchable gain stage to the pedal input. It works really well with the standard Marshall type boost pedals like a Boss SD-1 set with gain at min and output at max. It might also be pretty sweet with a Rangemaster type treble booster, but I haven't tried that yet.

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Post by bestegw »

The bass response on this pedal is very good being used as a distortion pedal into a clean amp channel (no overdrive on the amp). I've not felt the need to add any, and have used the pedal now for almost a year. I didn't try clippers on the feedback loop either, as the circuit in the schematic hit exactly what I was looking for, so I stopped messing with it. FWIW, the HP setting sounds a lot better, it really "cleans" up the midrange and makes a big difference. If I built another I would wire it in the HP position permanently.
OK, now I'll definetely build it with a trimpot to make it "set-and-forget"
Be very careful to use the same capacitor types as the original as there is where a lot of the magic lies. It's a simple circuit so those things make a lot of difference. You should be able to determine the cap types by looking at the pics of the PCB.
What kind did you use? Probably film, right??? I mostly use the box-versions and am pretty pleased with the results.
If the circuit has any flaws it is that it doesn't sound good at all with the gain above half. If you keep the gain below that and hit the input with a big signal, it's pretty amazing. One mod I'd add is to change VR1 to 250k and R5 to 250k to lock the max gain, and add another switchable gain stage to the pedal input. It works really well with the standard Marshall type boost pedals like a Boss SD-1 set with gain at min and output at max. It might also be pretty sweet with a Rangemaster type treble booster, but I haven't tried that yet.
Is it just me or would you achieve just the opposite by doin that?? Doing that would mean that you couldn't get the resistance anly lower than 250k, which is exactly what you wouldn't want to do. I think I'm gonna order three pots and see what I like best: 250kA, 500kA and 1MA. Perhaps I'll lower R5 even further to 10K, but my guess is that won't do all that much.

Anyway, thanks alot for your answers!

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Post by Greg »

bestegw wrote:Is it just me or would you achieve just the opposite by doin that?? Doing that would mean that you couldn't get the resistance anly lower than 250k, which is exactly what you wouldn't want to do. I
No... More resistance in the loop = more gain.
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Post by bestegw »

Greg_G wrote:
bestegw wrote:Is it just me or would you achieve just the opposite by doin that?? Doing that would mean that you couldn't get the resistance anly lower than 250k, which is exactly what you wouldn't want to do. I
No... More resistance in the loop = more gain.
Yes, but he said he didn't like the "second half of the pot", which would be 250K, so changing R5 with a 250K and replacing the POT with a 250K-pot would never give you less than 250K in the feedback loop and would therefore make it impossible to get the pedal in the desired low-gain mode.

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Post by Greg »

bestegw wrote:
Greg_G wrote:
bestegw wrote:Is it just me or would you achieve just the opposite by doin that?? Doing that would mean that you couldn't get the resistance anly lower than 250k, which is exactly what you wouldn't want to do. I
No... More resistance in the loop = more gain.
Yes, but he said he didn't like the "second half of the pot", which would be 250K, so changing R5 with a 250K and replacing the POT with a 250K-pot would never give you less than 250K in the feedback loop and would therefore make it impossible to get the pedal in the desired low-gain mode.
Oh, OK.
Then you're right. Changing R5 in the schematic above by "tuemmueh" to 250K would lock the minimum gain to a high value.
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Post by nooneknows »

hi,
I'd like to build this pedal but I've not 2N7000, I've only BS170 around, do you think - as I think - they would however work?
Using them as clippers I don't see much difference but I could be wrong.
Thank you,
Marcello

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Post by erikm5150 »

BS170's should work -- just remember that they usually have opposite pinouts.
I'm not sure about any sound differences, if any, though...
nooneknows wrote:hi,
I'd like to build this pedal but I've not 2N7000, I've only BS170 around, do you think - as I think - they would however work?
Using them as clippers I don't see much difference but I could be wrong.
Thank you,
Marcello

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Post by MKB »

bestegw wrote:
If the circuit has any flaws it is that it doesn't sound good at all with the gain above half. If you keep the gain below that and hit the input with a big signal, it's pretty amazing. One mod I'd add is to change VR1 to 250k and R5 to 250k to lock the max gain, and add another switchable gain stage to the pedal input. It works really well with the standard Marshall type boost pedals like a Boss SD-1 set with gain at min and output at max. It might also be pretty sweet with a Rangemaster type treble booster, but I haven't tried that yet.
Is it just me or would you achieve just the opposite by doin that?? Doing that would mean that you couldn't get the resistance anly lower than 250k, which is exactly what you wouldn't want to do. I think I'm gonna order three pots and see what I like best: 250kA, 500kA and 1MA. Perhaps I'll lower R5 even further to 10K, but my guess is that won't do all that much.

Anyway, thanks alot for your answers!
You guys are absolutely right, that suggestion of mine was WRONG. I'm so embarrassed... :oops: Not enough coffee yet perhaps.

You'd keep R5 at its 18k value and reduce the value of the pot to 250k, that's what I meant.

And FWIW, I used BS170's in mine. They sound very good so I haven't seen a reason to replace them with 2N7000's.

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Post by blanik »

hi, i finished mine on a Torchy Vero, i just need to get the pots (i didn't have them at hand), so far the vero seems alright, based on the Oscarr77 schematic, i also borrowed a real OCD to compare and it's indeed the Version 4 (well, V1.4 actually) all OCD with a serial number higher than 16061 are version 4, the one i have has the 1N34 on the 2N7000

the only mods i did from the original are two 10nF in parallel cause i didn't have the 20n and i've set the LP/HP switch to HP only after testing the real OCD i found out LP to be useless for me (the actual value of 33k and 22k in parallel is 13K2... one could put a 50k trimpot in place of those 22/33k and fine tune the pedal to their taste

i should get the pots this week (SBE sent them today), i'll keep you posted

i did notice the upper range of the drive to be a little too "driven" and the first 50% could use a little "cleaning up" so once the layout is checked i might try a 500k drive like on the V1.2 (so far the most natural one i've heard)

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Post by gtrwrks »

Thanks, Blanik; nice to be able to test a build directly against the store-bought model.

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Post by Beedoola »

Am I just stupid? I don't see a Torchy vero layout.... :slap:

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