CUNNINGHAM AMPS: Zonk / MKI

I came across a series of photos of this build on the PedalPCB forum, and there seemed to be a bit of confusion around the schematic.  Thought it was worth documenting some of the observed values here for reference.

The board shown below is from the wedge enclosure.  There’s also a more pedalboard friendly version, which includes an internal tone control.  It looks to be implemented with a trimmer and a capacitor in series at the output of the circuit — not unlike the approach used in a Marshall Supafuzz MKI.  I tried a 4n7 in series with a A1M pot on the breadboard - worked just fine.  There also appears to be a resistor and a small value capacitor in parallel to ground on the input of the circuit - kind of hard to see that bit, but it looks like 2M and 1300pf.

A few of the capacitor values are non-standard, and there are some variations in the resistor values as well — clearly some biasing tweaks and tuning by ear going on here.

The Zonk / MKI switch is a nice touch.  It adds a 2n7 capacitor in series with a 10n capacitor at the input. It’s a clever implementation too - mounting the 2n7 directly on the switch reduces the number of connections back to the board and keeps everything neat and tidy.

They're all impeccably built - amazing work.

CUNNINGHAM AMPS ZONK / MKI

As always with these circuits, while the passive component values are easy enough to document, the real story is in the transistors - their gain, leakage, and how they interact in-circuit. That’s the part you can’t see on a schematic, and it’s what makes or breaks a MKI style circuit.

Q1: TI 2N1307
Q2: OC45 
Q3: TI 2G308

BE: MKI Tone Bender - Shorty

Yes, it's another MKI.   I designed this layout based on a Zonk to fit a specific enclosure width.  So nothing remarkable, just one for me to use later.

MKI TONE BENDER - SHORTY

It's missing the 33k resistor that normally sits across the 50k pot, cause I like to use an A25k instead.   I sometimes make a few other taste related changes, depending on the transistors, etc. 

 

RUSH: Pep Box

One that I've probably overlooked a little, given its place in the early history of English fuzz pedals - which was likely inspired by the Maestro...  

There was a three-transistor version prior to this called "Fuzzy" which by all accounts is a Maestro.   The later versions dropped the input buffer and made the jump from 3 to 9 volts.

These are gated nasty wonders of the fuzz world.

RUSH PEP BOX - GE VERSION

The 56k resistor is sitting across the 500k volume pot, so you could just drop the pot down to 50k and lose the extra part.  

RUSH PEP BOX - SI VERSION

Later versions transitioned to silicon devices and became more widely recognised in their large red WEM enclosures.  Rush had originally manufactured these units for WEM, before the company reportedly parted ways with him while continuing to use his circuit design.  

Further reading:  

Link to Stompboxes UK

Link to FSB

Reverb

MENATONE: Red Snapper Overdrive

I'd never heard of these until this morning - and I could not believe the second-hand prices of the original...   especially considering the new price of a hand-made pedal from the builder.

It's kind of a Timmy x boutique Tubescreamer type thing - can find the schematic here.   Dual tin can opamp is required - hope this is the layout you were looking for.  

  

MENATONE RED SNAPPER OVERDRIVE

BE: MKII Tone Bender

One of my projects - just a MKII layout built to suit a particular enclosure and layout style that I've been working with lately. 

The board is just the right size for this enclosure.  Most of the assembly is done on a wiring jig first, before transferring it into the enclosure - would be a nightmare to do it any other way.  

Sounds pretty good.  The OC75 adds some texture without the need to go all out and use three of them.  They're a little expensive for that these days.  The OC84 are pretty decent.    

BE MKII TONE BENDER

Q1: OC84   Q2: OC75  Q3:  OC84

  

D*A*M: 1965 Vintage Tone Distorter

I’m surprised I had not covered this one before, but I suppose it is a MKI, so it should feel fairly familiar.

There seem to have been a few different iterations — essentially just different flavours of the MKI, so keep that in mind when choosing transistors and biasing the circuit. Some versions also used the more familiar point-to-point MKI style board. 

I found on the D*A*M forum that the Super Zee switch boosts the output.   D*A*M uses a rotary for this, but I just put a regular switch on the layout.  

Quotes from Dave Main re the side switch:   

Basically it cuts the output limiting resistor in half, from the stock 2.2 Meg down to 1 Meg. The first batch of the new 2015 1965's that went to Joe all had approx 1.5 Meg limiting as stock and the Super Zee bypassed it entirely.

Also worth noting from another post:  What no side switch? This is correct. It was making my tuning of the pedal a little erratic at times.

I have not listed transistor types, because they varied, and the chances of you having the exact same transistors D*A*M used — and for them to sound great in a MKI anyway are fairly small.  Even from reading posts on the D*A*M forum, Dave appears to have moved away from using 2 x OC75s in this circuit because they were less stable than other options - and you can be pretty sure that D*A*M has a larger selection of transistors to choose from than you or I.

D*A*M 1965 VINTAGE TONE DISTORTER

Further reading can be found here, on the archive for the1965.