Extending the Roland Double Beat

[Mark Hammer]

As some of you may know, I have been slowly but surely putting together a rack unit with a dozen different fuzzes on tap, and available via rotary switch.  I recently asked for suggestions of what to fill the 12th slot with and the winner was the Roland Double Beat.  I was very impressed with the sound.

I figured that if I was going to use a rotary switch to select the 3 voices of the stock Double Beat fuzz, I might as well use a 6-position switch and add a few more voices that provided a contrast to what  was already in there.  So here is what I did:


Outputs A, B, and C are the stock circuit.  I added D, E, and F.  D is a 2-pole lowpass filter that provides a sharper cutoff.  It gives a nice vocal tone with all the growl but a lot of the edge taken off.

E iis essentially the same as A, but introduces some crossover distortion.  I used Germanium diodes, but I'll probably switch to silicon to provide a bit more contrast.  Bridge pickups LOVE crossover distortion.

F is an adaptation of the classic Superfuzz mid-scoop.  Apart from B, the levels are within spitting distance from each other.

Sounds decent, and offers some nice variety to suit your mood.  I didn't have three 2SC1000s, so I used the spare one I had for the input, a 2N3391 for Q2 and a BC546 for Q3.  All had hfes inthe mid to high 200's.  Apart from that everything is as shown.  I'll see if I can get some samples together.  For the moment, the thing is held together with hopes and dreams, so I'll need to mount it somehow.

That said, if you were going to make yourself one, I recommend it, and recommend the 3 additional voices.

[glops]

Thanks, Mark for the additions. I had a friend visiting from out of town a few months ago and he wanted a pedal so I did a comparison of what I had laying around which included a Buzzaround, Bee Baa, FY2, Acetone Fuzzmaster and the Double Beat. It was nice to hear someone else play these with a different guitar.

Hands down, the Double Beat sounded the best. It stood out. Definitely one of my favorites.

[jrod]

Very cool, Mark!

What do you mean by "crossover" distortion for switch E? I've not heard of this before.

[Mark Hammer]

The usual way we implement diodes is as a means to limit the positive and negative excursions of the wave.  The signal rises, or descends, and hits a limit set by the diodes.  Placing the diodes in series with the signal forces the signal to reach some threshold to initiate conduction.  That is, no signal passes unless it is a high-enough amplitude.  This results in the "sides" of the waveform being squared, rather than the top or bottom.  The Boss HM-2 uses a combination of series diodes for crossover distortion and clipping diodes to produce its particular sound.

It's not a hugely different tone, as I have it set up, though using diodes with a higher forward voltage would increase the audible difference.  One of the side-effects of imposing such a threshold is that when the signal is not high enough to pass, nothing passes, and that includes any noise.    Obviously you wouldn't normally use this as a noise gate because it changes the tone, but if you're going to be producing a fuzz anyway, may as well keep the hiss down, eh?

[jrod]

Right on! Thanks for the explanation!