Build report: Multi Rat

[Stu]

JUst boxed a multi rat, a rat design with mods by Tonda and some mods by me. Instead of using a 2/3's of a 3 to 4 rotary, i used a full 2 to 6 rotary to select clipping diodes in the feedback path of the op amp and the normal after op amp clipping section. The pairs were LED's, silicon diodes or nothing. I mounted all the LED's on the face so they can be seen and had the millenium bypass as well.

The only real drama in the building it was putting the electrolytic cap after the opamp the wrong way round (easy to see as one of the LED's came on indicating a non zero DC voltage) and my laziness of not double checking what the connections were on the rotary switch - had to re solder the lot. It's a tight squeeze in the box (using a box from Jaycar similar to the Hammond somethingBB) with 3 pots, gain, filter, volume, the rotary switch, 5 LEDs, a footswitch and a battery (power jack coming soon)

i'm happy with the sound. The best combo to my ears is when nothing is clipping(nice chunky sound) then the LED feedback clipping and diode post op amp clipping  for some smooth lead work.

The only mod i would do if i started again would be to test the different combo's b4 hand (don't have my breadboard at the mom so i couldn't) and use a 3 to 4 rotary and change the some cap somewhere with every switch so that i could use it for my bass or to accentuate different frequencies.

Stu

[Khas Evets]

I'm working on a similar design. In addition to the diode selection you've built, I also want to add asymmetrical clipping. I've had good results experimenting with 1 diode in one direction and two or none in the opposite direction. It would also be interesting to hear the positive swing clipped in the feedback loop and the negative swing clipped after the op amp. I may use internal dip switches to handle this.

I've read that most of the distortion from the rat is op amp clipping rather than diode clipping. What has your experience been?

[Stu]

There is a fair bit of op amp clipping (enough that you don't have to worry about diodes if you don't want) it sounds beefier without diodes but sort of smoother with them in, i haven't really like the sound of assymetrically clipping about a year ago when i played round with it, i'll have a bit of an experiment with them again soon.

The idea of the clipping one side in one and one in the other sounds like an awesome one, i think i'll try that as well. If i get anything that sounds awesome i'll post back


Stu