Tym Red Army Overdrive Mk II

After making the first version of this great BM circuit I have completely run out of the original Russian NOS "green and white dot" transistors but it's such a great fuzz I decided I needed to work out how to make this one using more common components.

As I said in the original post and in other Big Mud posts, the actual transistors have little, or no, influence on the tone of a BM circuit. The only real exception I've found with this "rule" is, in the right circuits, the old "tin can" BC108's have a really nice "crackle" to them if you keep the components around the transistors within specs to make the gain "right".

As for most of the other transistors available as long as the gain is "about" right, there seems to be very little difference in tone between equivalent (silicon/NPN) transistors when driving the four stages of this circuit.
Component values and types make more difference to the tone than the transistors so with that in mind, I started testing and measuring.

 

The important part of this pedal as far as components go is those NOS Russian diodes, the ones they actually used in all the early S0vt*k BM's. My original Red Army Overdrive used not only the original NOS Russian transistors, but the original NOS Russian diodes and after messing around them in other BM circuits, and other distortion circuits, they have a really unique quality. 

The original "green and white dots" are a standard silicon NPN transistor with a fairly high gain (hFE) and have many "replacements" listed including a few of the original, earlier and later transistors used in the originals. Specs are very similar to many commonly available transistors and would have been used in these Russian BM's (or OD's) simply because they were there.
There are original KT3102 transistors available, and I have packets of them but all of the non "green and white" ones are far too low in hFE to use in this circuit with these diodes. There are also "tin can" versions available, that were used in the original RAO's but they are far too expensive to use in productions like this where four transistors are needed for each pedal and, like most NOS parts available online, approx 40-60% can be unsuitable after testing. These higher gain NPN's work really well and if I get more high gain 3102's down the track, I'll use them in these again just to be nerdy.

 

So, after measuring a bunch of transistors I use in other BM's I came up with a suitable alternative. I built a circuit exactly the same except for high gain 2N5088 transistors and the tone was intact. After changing some capacitor values and types slightly to make it compatible with parts I already use in Big Muds, it was still VERY much there, and also importantly, consistently reproducible.

Those all important diodes really make this pedal different from other later versions of the Russian BM's. Component value changes make the Civil War different from the Red Mud although all three of these pedals are very close circuit wise but all have their own unique flavour.

So, to differentiate these from the 15 original RAO's I made using all original parts, the artwork has been changed and these will NOT be limited edition as I have HEAPS of the NOS Russian diodes and everything else is common components I use in other Big Muds. 

This is a really nice BM circuit with slightly nicer harmonic edge to the distortion and slightly more open gain. It has more bottom end than my standard Civil War but not as much as my standard Red Mud, but keeps a clarity and focus the Red Mud doesn't have. All in all, it was a great experiment. 

The Mk III is available HERE.

 

Feb 18 2016 Written By: Tim Brennan