ADHD : Soft Clipping + Hard Clipping = Tighter Bass

[phi1]

Title sounds strange but hear me out on this one.

I built an OCD circuit (on vero) and when you reach a certain point on the gain knob, the bass gets kinda heavy and mushy. This is a cool sound in it's own way, but I was curious if there was a way to tighten it up. I used to own an EHX OD GLOVE (OCD clone) and IIRC it had the same behavior.

I believe what's happening is that when the gain hits a certain point the op amp is overloaded (saturated, op amp clipping), and that is what's generating that heavy bass sound. The mosfet clipping removes the harsh op amp clipping, but the eq change (heavy bass) remains. One suggestion is to run the pedal at 18V, which does reduce this significantly (op amp rails are higher, so it doesn't saturate until later).

My idea was to put RED LED's in a soft clipping configuration across that first op amp. This clipping will prevent the op amp from being saturated, but you don't necessarily hear this soft clipping. The mosfet clippers should hard clip the signal below the threshold of the red led soft clipping. The difference is you don't have that heavy bass since the op amp wasn't saturated.

I applied this mod to my OCD build and it works quite well for tightening up the bass at higher gain levels. The sound is somewhat similar (not exactly the same though) as running the unmodded circuit at 18V. I recommend putting this mod on a switch since the bassy sound at 9V is still cool.

Let me know if anyone tests this out, or has any comments (or corrections) about the theory here. At some point I may revisit this on a bread board to be able to test and verify more thoroughly the behavior of the op amp clipping in this circuit.

 

[DGWVI]

I've done this to my Blue Waffle (Alpha Drive/ OCD). It does work well to tame the bass from overloading the op-amp, and gives it a more immediate and aggressive attack. I used a 1n4739 and a white LED

 

[Chuck D. Bones]

Lotta pedals do both soft and hard clipping, some have switches or pots to dial them in and out. Check out the Wampler MDMA.

 

[DGWVI]

The Dingo (VFE Apha Dog) does this amazingly. So do a lot of the BJFE/ Mad Professor/ Bearfoot overdrives. Their Sweet Honey is everything I want to like about Tube Screamer (I hate the clean bleed) derived pedals with the aggression of a low-mid gain Rat. The Superlead by GuitarPCB is another that I'm fond of

 

[phi1]

Lotta pedals do both soft and hard clipping, some have switches or pots to dial them in and out. Check out the Wampler MDMA.

Yes mixing soft and hard clipping is not uncommon, but I think the purpose is often different than mine. The MDMA, King of Tone/Pantheon have a switch to select soft OR hard clipping, not both at the same time. So the purpose is for the user to have the option, not to clean up op amp clipping bass. Looks like the Alpha Dog's blending could be set up for both soft and hard, but I'd still guess their main purpose is user choice.

The Honey Bee / Sweet Honey / Dyna Red are very interesting circuits with their "feed forward"(?) loops, which tame the high end but I've read also contribute to the touch sensitivity (hard transition from hard to soft clipping). I'm not sure about this. In any case, the Honey Bee and Sweet Honey are lower gain than the OCD, so I would guess the op amp bassy-ness wasn't as much of an issue. I've built the Honey Bee is definitely in my top 2-3 favorite dirt pedals. I like the Sweet Honey too, but I wish it had more control over the highs and high mids than the focus knob offers (could easily be modded).

The LEDs probably have this effect in the Plim Soul when the hard clipping diodes are brought in. To be honest, what got me thinking down this track and led me to start thinking about this and experiment with the OCD was our thread about the Plim Soul, even though the topic was slightly different.

 

[phi1]

Anyway, not saying it’s a brand new innovation, but I wanted to share the idea since I like what it does to the OCD and could be applied to clean up other pedals like DGWVI said.

 

[Chuck D. Bones]

I did a similar thing to a DS-1 (actually a Chinese clone of one). I put a 10K resistor in series with the feedback diodes. It softens their clipping action, allowing more signal to drive the hard clippers and if you really crank your guitar, you can drive the opamp into overload.