Fulltone - OCD  [traced]

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Manfred
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Post by Manfred »

gsb wrote:Hi,
Here some pictures ,all SMD.Q1 transistor is marked with MX. I have played one more time -pedal works fine all controls are fine ,no led .I have check voltages on q1 . Measured voltage about 9,06v pin2 -S,8,6v on pin 3 -D and 9,06 on pin 1 G. Voltages are equal in off and on mode!! I think it must be Q1 ?
gsb
Or perhaps the connection to the switch.
Could you please trace the switching circuit?

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gsb
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Post by gsb »

hi,
I dont work usualy with SMD ,Friend need the drive ,i have disabled q1 and put bs250 in and shorted the legs .Now led is working .I hate fu....g SMD.Sorry i cant trace this build.Pedal is working very good .
thanks for help
gsb

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Manfred
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Post by Manfred »

gsb wrote:hi,
I dont work usualy with SMD ,Friend need the drive ,i have disabled q1 and put bs250 in and shorted the legs .Now led is working .I hate fu....g SMD.Sorry i cant trace this build.Pedal is working very good .
thanks for help
gsb
The main thing is, the LED is working again.
I agree with you in SMDs.

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x-tn
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Post by x-tn »

https://www.fulltone.com/products/custom-shop-cs-ocd-ge

"The earliest OCDs used 2 x Mosfets plus 1 x Germanium diode, but very quickly these diodes became harder and harder to find, and they became expensive.

Recently I stumbled across a reasonably large stash of the right kind of Germanium diodes so I ponied-up and bought all of them. I then decided to do a small run of the ultimate OCD: a Custom Shop offering with a few circuit tweaks, 2 x Mosfets plus 2 x Germanium diodes...

The sound? Great definition, more tube-like feel, a bit wider dynamic range, more sustain, and a more focused single-note tone."

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caspercody
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Post by caspercody »

So do they have a GE per MOSFET for the clipping? With orientation opposite of each other?

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Cigla tel.
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Post by Cigla tel. »

x-tn wrote:https://www.fulltone.com/products/custom-shop-cs-ocd-ge

"The earliest OCDs used 2 x Mosfets plus 1 x Germanium diode, ....................
.........................

The sound? Great definition, more tube-like feel, a bit wider dynamic range, more sustain, and a more focused single-note tone."
Do you believe in these fairy tales? :lol:

The title talks everything: "COMING SOON!.. The Fulltone Custom Shop CS-OCD-Ge."!

IN TRANSLATION: "It's time to fooling the fool"!!!

:lol:

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Post by rpc66 »

caspercody wrote:So do they have a GE per MOSFET for the clipping? With orientation opposite of each other?
Ditto
Is the OCD-GE the same as the original but with an added diode? And is it in-line with the first MOSFET?

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Post by Bernardduur »

OCD V2 LED sw.JPG
OCD V2 LED sw.JPG (11.85 KiB) Viewed 5309 times
Here's the LED switching part of the OCD V2.0

I don't know the value of D4 and C19

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Post by plush »

Bernardduur wrote:
OCD V2 LED sw.JPG
Here's the LED switching part of the OCD V2.0

I don't know the value of D4 and C19

Greetings!!

D4 is a schottky diode, 3v3, 5v6 or so. Must be much lower than supply voltage to operate correctly.
C19 together with R23 controls the speed of switching, I beleive, it's something in between 1n and 22n.

The whole point of this circuit is to smooth led switching (and possibly mitigate popping nose which is not the case here). Seems more like a remnant, than a feature.

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Post by mictester »

plush wrote:
D4 is a schottky diode, 3v3, 5v6 or so.
Nope. You mean ZENER diode. A Schottky diode is a completely different beast - low forward voltage drop and low reverse leakage.

A zener diode is designed to be used reverse biased, and when the marked threshold voltage is reached, it starts to conduct.
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Post by plush »

mictester wrote:
plush wrote:
D4 is a schottky diode, 3v3, 5v6 or so.
Nope. You mean ZENER diode. A Schottky diode is a completely different beast - low forward voltage drop and low reverse leakage.

A zener diode is designed to be used reverse biased, and when the marked threshold voltage is reached, it starts to conduct.
Yeah, zener, of course.

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Post by bluesky636 »

Anybody have a schematic of the OCD "V2.01" that was introduced in 2020. Supposedly less compressed than the V2.0.

https://www.fulltone.com/products/obses ... sive-drive

Bill
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mediy
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Post by mediy »

I haven't seen a schematic, but I am willing to bet that it goes back to using a single diode in series with one of the clipping transistors.

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Post by bluesky636 »

Ok. Thanks.
Bill, "The Piranha"

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Post by caspercody »

I was going to suggest Pedal PCB but realized it was V2.0

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Post by bluesky636 »

Thanks. I found that schematic earlier in this thread.

It's not clear what the difference is between V2 and V2.01 other than the claim that V2.01 is "less compressed". The manual that came with my V2.01 is labeled V2 and dated 2017. The date could be wrong.
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Post by Gila_Crisis »

A friend gave me an Abominable Electronics Oppressive Cult Destroyer to fix. This is a clone of the OCD, tuned for bass, and with a boost circuit, footswitchable clipping diodes.
The problem was the pedal squealing as hell... my solution was to swamp the opamp with a LM358 and higher the cap between lugs 1 and 2 of the opamp from 220p to 330p/470p.
Zwischen Ordnung und Chaos fangt die Musik an

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Post by Gila_Crisis »

For all who are interested these are some guts of the Abominable Electronics Oppressive Cult Destroyer I had for repair last week. These are the pictures prior repair.
Top right under that spongy thing there is a charge pump to convert 9VDC to 18VDC (a classic one based on the MAX1044 or 7660/2).
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Post by smear »

Looking over all the schematics available, it seems like only a couple things really matter to the "tone" between versions V1.1-V1.7

The drive knob and tone knob values only affect the overall range of those controls. They usually affect the frequency response in a noticeable way. The 25k tone pot can hit all the same values as the 10k. They sound different with the knobs at noon, but the switch to 10k only limited the overall range.

And if you have a buffer after the pedal, the value of the volume knob is basically irrelevant too (since even a 1uF output cap is high enough that hardly any volume knob settings settings cut bass).

The 220k bias resistor adds less than 1dB of gain, hardly significant.

Obviously the 1N34 diode affects the dynamic response, and perhaps the tone in how it appears to allow through more bass because it clips less, but that's easy to stick on a toggle switch.

So what matters for the "tone" of the different versions? Seems like it's just three capacitors: the the tone knob cap and the two feedback caps. The tone cap has a major impact on the low mids, and the feedback caps have a big affect on the overall emphasis.

With a With a 1M drive knob and a 25k tone knob (for maximum range of each), you can get any of the sounds of V1.1 to V1.4 just by adding a couple switches for those capacitors (or a single 3PDT).

Maybe someone did this already, but I haven't seen it in this thread. I guess that's understandable, as folks seem to be using speculation rather than simulation software in the early posts.

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Post by smear »

Screen Shot 2023-01-07 at 12.30.45 AM.png
someone asked about my last past, so here's a schematic. all versions of the pedal in one schematic. short the labeled pins to access the alternate versions. in the real world just sub 100pF for the ideal 110pF.

for the 3PDT pins, see the image below. 1 refers to the first row (leftmost SPDT), 2 refers to the second row, etc. the letter is the pin within each SPDT. or alternatively, you can use three spst switches, since all you need to do is short pins together.
Image

EDIT: fixed value of R17
Last edited by smear on 08 Jan 2023, 00:23, edited 1 time in total.

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