Fulltone - OCD  [traced]

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Postby bajaman » 06 Jul 2007, 14:06

Nick123 wrote:Is OCD just VoodooLab rippoff ( with MOSFET's instead of Si diodes) ?


I don't know - I have not seen one - but I have read that elsewhere on another forum/s - it may be true, but then it may be lies.
If you find out for sure, please let us know :wink:
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Postby markm » 07 Jul 2007, 02:19

I've read that same info and I myself cannont confirm this although, I had someone e-mail me that this is exactly what the OCD is.
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Re: OCD?

Postby Goop_buster » 23 Jul 2007, 16:04

Nick123 wrote:Is OCD just VoodooLab rippoff ( with MOSFET's instead of Si diodes) ?


I have tested the VL OD with mosfets as clippers but it did not sound very good to me.
However Jack Orman who de-gooped one said at Arons forum that the mosfets are NOT connected as clippers in the more common known ways.

Anyone know how the mosfets are connected in this one?
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Postby analogguru » 23 Jul 2007, 16:19

You don´t need the mosfet´s, take normal diodes. Have a look at the datasheet and you will find out, that every small signal mosfet (e.g. BS170) has protection diodes inside. If the polarity is reversed they start clipping. To overcome this problem the mosfet clippers had the germanium diodes in series. It was not or only sparely mentioned why. Now if you want to save money and don´t look at the datasheet, you cantend to ommit the ge-diodes.... You will believe in a mosfet-distortion but in reality it´s only a (protection)-diode distortion... that´s all....

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Postby Goop_buster » 23 Jul 2007, 16:31

analogguru wrote:You don´t need the mosfet´s, take normal diodes. Have a look at the datasheet and you will find out, that every small signal mosfet (e.g. BS170) has protection diodes inside. If the polarity is reversed they start clipping. To overcome this problem the mosfet clippers had the germanium diodes in series. It was not or only sparely mentioned why. Now if you want to save money and don´t look at the datasheet, you cantend to ommit the ge-diodes.... You will believe in a mosfet-distortion but in reality it´s only a (protection)-diode distortion... that´s all....

analogguru


Hi
I am aware of the internaldiodes :) . However according to Orman those OCD clippers are not conncted the usuall ways (examples):

http://www.muzique.com/lab/zenmos.htm

so still currious how they are used here.
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Postby analogguru » 23 Jul 2007, 16:44

You can use mosfets as clippers, but they will start clipping at a higher voltage and will have a different clipping characteristics than diodes. (rest see above). if you don´t use the additional diodes the effect will be lost since the protection diodes start clipping long before the mosfet itself does.

So you can use mosfets "not in a normal way" that the mosfet itself does the clipping, instead the clipping is done by the (mosfet internal) protection diodes.

In the pcb there are soldered mosfets but they are not working as mosfets - like the normal way - cause the protection diodes override them. The "usual way" would be to connect a diode in series to avoid this.

For more info about the "history" look here:
http://www.diystompboxes.com/pedals/schematics.html
and scroll down to "Shaka Braddah III".

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Postby Goop_buster » 23 Jul 2007, 17:38

analogguru wrote:You can use mosfets as clippers, but they will start clipping at a higher voltage and will have a different clipping characteristics than diodes. (rest see above). if you don´t use the additional diodes the effect will be lost since the protection diodes start clipping long before the mosfet itself does.

So you can use mosfets "not in a normal way" that the mosfet itself does the clipping, instead the clipping is done by the (mosfet internal) protection diodes.

In the pcb there are soldered mosfets but they are not working as mosfets - like the normal way - cause the protection diodes override them. The "usual way" would be to connect a diode in series to avoid this.

For more info about the "history" look here:
http://www.diystompboxes.com/pedals/schematics.html
and scroll down to "Shaka Braddah III".

analogguru


I hear you :D .
To clarify...my starting point was that Orman stated that they were not connected with serial diodes like in Shaka. So I tried this variant instead

http://www.muzique.com/images/mos5.gif

effectively using the internal diodes. That did not sound very good to me...just like regular diode clipping or in fact slightly worse.

If you know the actual connection for sure and want to share you could draw them in this VLOD schematic and I will try it out :) .

http://www.freeinfosociety.com/electron ... hp?id=1208
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Fulltone - OCD

Postby freedreamer » 08 Sep 2007, 09:13

on fulltone's site i found this:
http://www.fulltone.com/PDfFiles/OCD%20 ... _small.pdf

nobody has tried to remove goop from a fulltone OCD ? i hear this pedal and it plays a very good sound IMHO :)
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Postby JHS » 08 Sep 2007, 09:47

There's no need to remove the goop from an OCD, verified schems of all 3 versions, sound samples and detailed decriptions of the differencies are on the www.

IC is TL082, Mosfets are 2N7000, the rest is a slightly modded VL-OD.

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Postby freedreamer » 08 Sep 2007, 11:03

mmmh

"sound samples and detailed decriptions of the differencies are on the www. "

what site?
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Postby kagaxdx » 08 Sep 2007, 11:35

Would be too much asking for a schem? An OCD verified schem?

If possible, thank in advance! 8)
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Postby JHS » 08 Sep 2007, 12:00

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Postby freedreamer » 08 Sep 2007, 18:18

no schematic or layout ?
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Postby markm » 08 Sep 2007, 19:02

JHS wrote:There's no need to remove the goop from an OCD, verified schems of all 3 versions, sound samples and detailed decriptions of the differencies are on the www.


I see sound samples but, no schems? :?:
How about schem links??
Why are we talking in riddles with this circuit?
Join together with the "Banned"!
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Postby Goop_buster » 09 Sep 2007, 15:37

markm wrote:
JHS wrote:There's no need to remove the goop from an OCD, verified schems of all 3 versions, sound samples and detailed decriptions of the differencies are on the www.


I see sound samples but, no schems? :?:
How about schem links??
Why are we talking in riddles with this circuit?


+1

Although it has been rumored to be a Voodoo labs OD + tonectrl for a long time I have yet to see any verified complete schematic.
So just put the link(s) in this thread if it is out there :D
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Postby snail » 09 Sep 2007, 17:42

I'm quite curious about this one too, specially if there are any changes (from the VLOD) regarding the clipping section tied to the IC's input.

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Postby JHS » 09 Sep 2007, 19:33

http://i206.photobucket.com/albums/bb41 ... HS-mod.gif

It delivers V1, V2 V2 tone.

IMHO 250k for Drive is enough for this circuit.

I called it ++ 'cos it sounds better than the original, furthermore I replaced the 10uF O-cap w 2x470n MKT from ITT (the brown ones, Marshall uses in their amps) wired parallel for more natural highend response.
HP/LP Rs can be trimmed to taste.

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Postby freedreamer » 09 Sep 2007, 19:48

a volunteer to make PCB ;) ?
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Postby snail » 09 Sep 2007, 20:45

TKS :D
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Postby briggs » 10 Sep 2007, 08:31

markm already has one in his gallery...
Image

I am Klon.
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