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previous: JMF I just finished soldering the board... -- 10/13/2000 6:50 AM View Thread

Re: EPFM Ring Modulator

10/13/2000 7:57 PM
Mark Hammer
Re: EPFM Ring Modulator
What he means is that you should not run it on more than +/-9v (e.g., at +/-15vdc), since a number of parameters are set based on the assumption that it is running off +/-9v. It DOES require a bipolar supply. I've made the one from EPFM1 and EPFM2. The second one is better with respect to nulling and timbral control. I would recommend a decent 10-turn trimpot for the nulling pot. Trust me, you'll appreciate it.  
The project article/chapter points out a cap that can be used to alter the modulator frequency range. DO play with it. Bear in mind that very low audio frequency modulation gets you sum and difference frequencies that are fairly close to the actual note. If you would like to play with your RM *as if* you were playing in tune, you probably want to keep the modulation freq down around 80-200hz.  
The other thing to consider is that the VCO tone is going to be pretty ornery, so consider aggressive use of the tone-cap switching option. You might also consider increasing the gain of the final mixer stage so you can use a master volume control instead of adjusting volume by dickering with the straight and effect levels.  
Finally, he uses two diodes to clip the signal going to the PLL chip. You might want to play with that, and maybe stick a cap in parallel with them to tame the harmonics going into the PLL.  
It's a lotta fun. Just try to avoid chords unless there is someone you want to hurt.

JMF Thanks for the help. Just plugged i... -- 10/13/2000 10:03 PM