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. 

D*A*M: FZ-676

So this looks like one of the D*A*M one-offs from back in the day - a MKI style fuzz, using a variation on a Zonk layout.  There are some departures from stock values, some of which are not entirely clear.

Here's the thread from an old FSB post.  Here's the thread on the D*A*M forum.

D*A*M  FZ-676  VERO LAYOUT

There are a few components that are not visible, but if you have any build experience, you can make some reasonable assumptions.  Pop it on a breadboard...  I know that's what I'm about to do.

One thing that throws me is this - the resistor next to the OC45 (the Q2 collector), is it brown green red gold, (1k5) or purple green red gold (7k5)?  I think 7k5, the schematic on FSB says 1k5.    

On the breadboard, 7k5 works just fine, so I'll stick with what I see and hear.  Can't always trust what you find online, including here ;-)   

JHS: Zonk Machine

Quick Zonk Machine layout to suit an enclosure that I just picked up from MW Pedal Parts - pretty much one row difference in terms of where the mounting holes are drilled compared to old layout that I have been using, and I decided to move a couple of components around while I was at it.  

MW are great by the way - no hesitation in recommending them based on my experience.  The ordering process is a little unusual, but they deliver on the goods.

ZONK MACHINE

Link to Zonk schematic and component values table or a MKI as the layout can be used for that too. 

and here's a link to the original tag board layout if that's more your thing.

DOD: 250

So by this stage, I think we can all assume that I'll be the only one making this.  I have a bunch of tin can LM741 opamps that I forgot about, so I thought why not...  

DOD 250 / DISTORTION + LAYOUT

DOD / MXR: 250, Distortion + component values table

This is probably where it all started in terms of opamp-driven distortion -  in one side of 741 opamp, out the other with some hard clippers.  

DOD 250 / MXR DISTORTION + SCHEMATIC

Direct link to Google Doc

741 SPECS

Numbers vary slightly by manufacturer and grade, but these headline specs are what give the 741 its “personality” in effects land:

• Supply voltage: works on dual or single supplies (it was designed with ± supplies in mind, but can be run single-supply with proper biasing).

• Gain-bandwidth product: around ~1 MHz class.

• Slew rate: about ~0.5 V/µs typical.

• Input bias current: tens of nA typical (bipolar input).

• Not rail-to-rail: inputs/outputs can’t swing anywhere near the rails, especially on a 9V battery. 

What that means in practice: a 741 can sound/feel a bit rounder and more easily pushed in simple dirt circuits, partly because it’s relatively slow and because it doesn’t have huge clean output swing on a 9V single supply.

LM741 PINOUTS

Note the little tab on the side of the opamp is pin 8.

OFFSET NULL

Offset null is a pair of pins on the 741 that lets you trim out its small DC offset so the output sits where you want it (often 0V on a dual-rail supply). 

In pedals it’s usually ignored because stompboxes are typically single-supply with a virtual ground and AC-coupled stages, so capacitors block DC and the tiny offset isn’t audible.

While the pins aren't used, be sure to isolate them anyway.

GEC: Germanium Signal Transistors (1971 Semicondcutor Handbook)

From the General Electric semiconductor handbook, 1971