Thinking of trying an OCD build. I'm curious if anyone can recommend something other than 2N7000 (or BS170) transistors to use as clippers. I have played a few OCDs and found the sound a bit tiring on the ears after a short time of playing, something I have found with a few Mosfet ODs. As the OCD is using the Mosfets as diodes rather than transistors I was wondering if (a) the Mosfets are causing the ear-fatigue or whether it's just the knowledge that Mike Fuller is behind the design, or (b) anyone has had fabulous results with something else?
Anyone tried diodes instead of Mosfets in an OCD?
- Thread starter HamishR
- Start date
Laundryroom David
Keyboard Cowboy 🤠
The key to best OCD tone is to melt at least a bit of the box caps.
I breadboarded a Voodoo Labs OD and used BAS33 diodes for clipping. Sounded good to me. That’s the closest (and quite at that!) I’ve come to building an actual OCD. Which is (no offence to Mike) QUITE SIMILAR.
I think the OCD has some op amp clipping (before the mosfet clipping). That can sound kinda thick. Upping to 18V or maybe adding some blue led soft clipping leds would reduce or remove the op amp clipping.
No idea if the TL op amp clipping is part of your “fatigue”, just a thought to try. Let us know what you find out with diodes.
No idea if the TL op amp clipping is part of your “fatigue”, just a thought to try. Let us know what you find out with diodes.
cdwillis
Well-known member
I think using the Mosfets body diodes for clipping is usually a little smoother because they have some capacitance vs something like a 1n4148 silicon diode. I've found that is definitely the case when I've used them in a noninverting tube screamer or zen drive type overdrive circuit. If they're not in the loop and used as hard clippers to ground you're clipping the op amp before it hits the Mosfets like phi1 said. Besides running it at 18v you could try another dual op like a 4558 or 5532 and see if it takes away some of the harshness.
Barry
Well-known member
Chuck D. Bones did some comparison
forum.pedalpcb.com
MOSFET body diode
We see MOSFETs used as clipping diodes and 99% of the time, they're wired so that the body diode is doing the clipping. I got to wondering... what's the big deal with MOSFET body diodes? I ran a curve on a 2N7000 and compared it with two popular clipping diodes: 1N4004 & 1N4148. The MOSFET...
forum.pedalpcb.com
jesuscrisp
Well-known member
TBH the mosfets are basically the only thing that make it stand out, otherwise it's a rather straightforward hard clipping distortion circuit. You could maybe also try implementing a different tone control to smooth out the high treble better.
Chuck D. Bones
Circuit Wizard
The OCD has a 1nF cap in parallel with the MOSFET clippers. That should swamp any capacitance difference between 2N7000 & 1N4148. The 2N7000 body diode has a sharper knee and lower resistance than 1N4148 or 1N400x. Above 1mA, the 1N4148 has a higher Vf than the 2N7000.
Some versions of the OCD have a Ge diode in series with one of the 2N7000s. There is also a version with Ge diodes in series with both 2N7000s.
I too recommend trying different opamps. At low gain settings, the diodes do all of the clipping and the opamp doesn't matter much. At higher gain settings, the opamps does most of the clipping and different opamps will make different tones.
Some versions of the OCD have a Ge diode in series with one of the 2N7000s. There is also a version with Ge diodes in series with both 2N7000s.
I too recommend trying different opamps. At low gain settings, the diodes do all of the clipping and the opamp doesn't matter much. At higher gain settings, the opamps does most of the clipping and different opamps will make different tones.
Well Chuck as you know I prefer lower gain sounds, so that is encouraging. I always intended to try different opamps because even though the differences can often be so subtle as to be hard to hear I imagine that if the IC is clipping then it becomes a little more obvious when different types are used.
I've never actually enjoyed the OCD but figure it's worth a try to mod because you never know!
I'm getting sidetracked right now by an old modded circuit you might be familiar with - my modded Honey Beest. I have some NOS tin can LM308Ns which might be fun to try in that circuit!
I've never actually enjoyed the OCD but figure it's worth a try to mod because you never know!
I'm getting sidetracked right now by an old modded circuit you might be familiar with - my modded Honey Beest. I have some NOS tin can LM308Ns which might be fun to try in that circuit!
Chuck D. Bones
Circuit Wizard
At the gain levels you like, I doubt the opamp will saturate.
If you haven't checked out the Roger Mayer Voodoo-1, you might want to try that. Sounds very nice with GAIN below 10:00. You can fiddle R7 to put the GAIN sweet spot at noon.
If you haven't checked out the Roger Mayer Voodoo-1, you might want to try that. Sounds very nice with GAIN below 10:00. You can fiddle R7 to put the GAIN sweet spot at noon.
