HM-2 Mutant

[WGTP]

http://aronnelson.com/gallery/WGTP/Mutant_Metal

If anyone is interested.  An emulation of the HM-2 clipping section using a dual op amp.  The diodes, resistors, caps, etc. are straight from the schematic.  The first op amp replaces the real buffer/boosters in the original.  Let me know what you think.   

[Processaurus]

HM-2s are funky.     

Wouldn't the Ge diodes in line with the output of U1B cause a gating kind of action, where something would have to be over .6v peak to peak to get through?

[brad]

crossover distortion!

[MartyMart]

Nice WGTP, how does it sound ?
My HM-2 needs some tweaking, its gain seems "flat out" with the pot
at 10% rotation !! the rest is just "a bit more dirt"  !!   .... and more "FIZZZZ" ..
I was thinking of pulling the Ge diodes completely and replacing a pair of Si's with some
LED's ...... & a bit more roll off would help
Cheers,
Marty.

[Steben]

The Ge diodes let signal through around 0.2-0.3V, not 0.6. This beast is used for high gain, so the signal coming to the Ge pair is about (0.6+0.2) 0.8 on one side, and about (1.2+0.2) 1.4 on the other.
My major question is why it is interesting to clip assymetrical, followed by clip symmetrical. You loose all second order harmonics this way!

[MartyMart]

The Ge diodes let signal through around 0.2-0.3V, not 0.6. This beast is used for high gain, so the signal coming to the Ge pair is about (0.6+0.2) 0.8 on one side, and about (1.2+0.2) 1.4 on the other.
My major question is why it is interesting to clip assymetrical, followed by clip symmetrical. You loose all second order harmonics this way!

Wouldn't the two "flavours" add up to a more harmonicly rich output ?
Or, are you saying that the symmetrical stage cancels all that out ?

Marty.

[Steben]

In a way, yes.

First you have 0.8 and 1.2, than 0.6 and 0.6 volts cut off. I wonder what rests of the assymetry (responsable for even harmonics). I would put in a resistor in series with the second clipping diodes. Or make them assymetric too (the same polarity of course!).

[WGTP]

Thanks for the comments.  I just put it together like the factory schematic.  The GE's in line do have a certain sound to them that can be used in most other distortions, or left out if desired.  SI's sort of over do it to me, but others may like it.  The .001uf cap next to the diodes to ground can be increased if it is too bright and fizzey.  It will depend on how/if the notch filter is used.  The 220K resistort in the feedback loop can be increased or decreased for gain control.   It is not my preferred dual op amp distortion set up, but I thought some folks might like to try a simplified version of the HM-2.  Plus I have gotten way into drawing these things in Paint.   

I HIGHLY recommend anyone into this sort of op amp based distortion get a small bread board and loose their grip on reality by trying the zillion variations possible.  You were warned.