PETE CORNISH: CC-1 Crunch

The Pete Cornish CC-1 is an interesting one -  two stages of soft clipping and a three-band active tone stack.

I initially built and tested the CC-1 using the larger of the two layouts below, and I can't say that I immediately loved it at the time.  Regarding others in the Cornish line-up, I preferred the SS-2 or SS-3.  It's not bad at all; in fact, it's very good at what it does.  I found that it took some time to dial in tones that I liked, and perhaps I was put off by the number of tones I didn't like along the way to finding the sweet spots.  

What I didn’t realise at the time with the first build I did, was that two resistor values on the schematic were wrong, which affected the bass response.

So after I saw the updated schematic, I decided to do a new layout and rebuild it (partially because I wasn’t happy with the size of my first layout, and I also couldn’t find the circuit that I previously  built anywhere.)

PETE CORNISH CC-1 CRUNCH - VERO LAYOUT

Note that while the layout above is smaller than the one below, the power supply has been simplified.  Filtering for every IC, transistor and bias voltage seemed a bit much to me.

It all fits on the board pretty well - a couple of resistors still missing, as I’m going to try a few different values for the resistors going to the diodes, and I ran out of 200k resistors and need one for the buffer.

The layout works, and I’ve taken the 22k and 51k resistors that are in series with the clipping diodes off the board - I have a dual B50k pot, with a 50k resistor across one side to reduce it down to closer to the original value of 22k.   It provides more control over the clipping - more clipping happens by reducing the resistance.  It already has five knobs; one more won’t hurt.

One thing I have noticed, and this happened on the LTspice simulations as well - the output op-amp clips with some of the tone controls on full.  While this isn’t necessarily always going to happen, depending on how the circuit is used, it did annoy me a little.  Easy fix - run it at 12v.  Problem solved.

OLDER CC-1 LAYOUT

updated November 2021.  Two resistors had an incorrect value on the original trace.  Thread on FSB can be found here. 

There's a smaller layout that includes the buffer over on Dirt Box Layouts - well worth a look compared to mine.

 

ON THE SCOPE / FFT

Signal:  440hs sine wave, approx 130mv TRMS

 

Gain 100%, signal taken from the 1uf cap after the two clipping stages.

 

 

This is the diode clipping mod I mention in action

LTSPICE

Mid-range & Treble response - bass on 50%

Bass and middle response - treble on 50%

Mid-range response - bass and treble on 50%

Frequency response varies with gain

Opamp output traces, gain on 100%, EQ all on 50%

Pedal output, various gain levels

PETE CORNISH CC-1 - DIODE MOD

Being a two-stage soft clipper, there are a few options available - the most obvious and usually everyone's go-to would be changing the diodes.  It might be worth testing some LEDs or different combinations of diodes in series etc - all the usual diode mods.

What does get some pretty immediate results is reducing R17 and R12, which are the two resistors in series with the diodes acting as soft clippers.  Reducing the diodes increases clipping, which looks like this when R17 is set to 1ohm, 10k and 22k (22k is stock).  Of course anything involving changing the value of a resistor could be an external pot, which is what I've gone for, as mentioned above.

Then there's always the option to play with the gain of the opamps, but I'm not sure if this would be a good way to go with a circuit based around two soft clipping stages - introducing opamp clipping may not be nice.