OCD

[aziltz]

I built (what i think) is an OCD, not sure what version, and WOW.  Just a great mid-gain overdrive.

Aside from the tone control, its working great on the breadboard (wrong taper)

And of all things, i used 741s!  It can only get better from here right?

[tehfunk]

I built (what i think) is an OCD, not sure what version, and WOW.  Just a great mid-gain overdrive.

Aside from the tone control, its working great on the breadboard (wrong taper)

And of all things, i used 741s!  It can only get better from here right?

I just built one too, yeah it sounds pretty good. what schematic/layout did you use?

[aziltz]

i found a schematic on this site: http://revolutiondeux.blogspot.com/2008/07/fullclone-vlod-fulltone-ocd-by.html

[oldrocker]

Can BS170's be used instead of the 2N7000's?

[WGTP]

I have found the 2N7000 has a lower clipping threshold than the BS170.  The 2N7000 was slightly less than 2v and the BS170 slightly higher.  I use the 2N7000.  YMMV.

Below is a nice mod to allow the Mosfet to be used both ways, or not at all.   

http://www.aronnelson.com/gallery/main.php/v/WGTP/Mosfet_Switching.jpg.html?g2_imageViewsIndex=1

[aziltz]

i'm using bs170s and lm741s for the opamp until i get some more to try.

[earthtonesaudio]

The MOSFETs in the OCD are just connected as regular Si diodes.  The capacitance and some other subtle factors may be different from "normal diodes," but the clipping threshold is the same 0.5-0.7 Volts.

You could connect them as "MOSFET threshold" diodes of course, but that would require some rearrangement of the circuit.

[WGTP]

I noticed that for both the OCD and Zen Drive the body diode was used.  It is sort of false advertising to say your using Mosfets and then use the body diode, IMHO.  That is why I included the switching diagram.  If the other diodes are are reversed, it forces the signal thru the Mosfet and the clipping threshold will rise to around 2.4v.  The volume also increases and the signal cleans up and distortions softens.  Of course when the op amp starts distorting, it's sort of like other similar distortions.   A CMOS rail to rail op amp might be a good tweak for this.  TLC2262 etc.   

[aziltz]

I noticed that for both the OCD and Zen Drive the body diode was used.  It is sort of false advertising to say your using Mosfets and then use the body diode, IMHO.  That is why I included the switching diagram.  If the other diodes are are reversed, it forces the signal thru the Mosfet and the clipping threshold will rise to around 2.4v.  The volume also increases and the signal cleans up and distortions softens.  Of course when the op amp starts distorting, it's sort of like other similar distortions.   A CMOS rail to rail op amp might be a good tweak for this.  TLC2262 etc.   

Excuse my ignorance, but whats a body diode?  I didnt understand what your wiring diagram does.

[earthtonesaudio]

http://www.muzique.com/news/mosfet-body-diodes/

[WGTP]

http://www.diystompboxes.com/smfforum/index.php?topic=38581.0

It's sort of confusing, but remember you asked.   

You could probably substitute a std. 1N914 or 1N4814 diode for the Mosfet with only a subtle, if noticable difference in the distortion, as earthtonesaudio has indicaed.  The real mosfet clipping is noticably different.   

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

Another good one from Jack.  I use the second method in feedback loops.   

[twangquack]

Yeah, this one is a winner ... I built the same one (layout) and used BS170's instead of 2N7000 ... sounds great! Also, I tried tons of op amps until I came back around to the first couple tried; in fact, I ended up stacking (parallel) a TL082 and NE5532 and I really like this combo, although either of these alone also sounds good. I think, as usual, op amp choice is very gear-dependent (YMMV). I tried a TLC2272 and although I liked the quality of distortion, this op amp resulted in tone that was just a little too dark, but with substantially brighter amps this may be a great choice. TLC2272: not wooly, certainly (not muddy) but certainly not as spanky as I prefer an OCD to be. Rather than make adjustments to the circuit, I tried the standard OCD op amp (TL082) and it sounded like it should ... and stacking with the NE5532 gave a hint more girth -- it took away just enough slight crispiness (some of which is a must for this circuit, but you don't want TOO much) -- the overall tone is now very well-balanced. Also, a 3-way switch with various MOSFET/Ge diode combos is a big plus; I tried LEDs and that wasn't a success ... but the various MOSFETs and Ge clipping combos sound wonderful. Experimenting with various cap values in parallel with the clippers is also a nice way to further tune this pedal.

As an aside, the TLC2272 I tried and removed from this OCD clone ended up in my COT50/Zendrive clone -- a "2-fer pedal": COT-into-Zen, combined (series) or each alone. It sounds really good, better than both the AD712 and OPA2604 I tried (but not by a huge degree), but of course this is probably gear-dependent.