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previous: Corwin Is it possible to modify the circui... -- 9/9/2000 2:39 PM

Re: Harmonic Tremolo in a pedal?

9/9/2000 6:38 PM
jon	Re: Harmonic Tremolo in a pedal? Corwin, With the the cap and resistor values in the Fender Brownface oscillator circuit, dropping the pot values to lower ranges will cut down on the speed range. You can tweak the R + C values up or down, to try and recover some of the slow or fast speed,but ultimately you'll be affecting the width of speed ranges available by using the lower value pot. You'll ultimately come to a point that the circuit won't oscillate at all if you go too low with the pot value. I'm using 4+ meg pots that I pulled from old audio gear; a lot of the old Magnavox stuff used CTS audio pots in the 3-5 meg range. Not RA, but they'll work. As for the 10 meg pot, see KOC's mods in TUT2; he has it set up so you can use a 1 meg pot for the depth control. Use a lower value resistor off the CF, though. I believe he indicates using a 10 meg prior to the .02 blocking cap to the pot. I found 1 meg here makes the circuit come alive; the other value damps the LFO signal too much. You might also try subbing other oscillator networks, like from the Ampegs or Magnatones. They use lower value pots and different value caps and resistors in the oscillator circuit. I haven't actually checked the available low frequency spread in any of these circuits, just seems by ear that the Fender will allow dialing in slightly faster or slower speeds than the others. For a very complete discussion, I believe Randall A. has an exhaustive discussion on design parameters. let me know if you need the link. cya. Jon

9/9/2000 6:38 PM

jon

Re: Harmonic Tremolo in a pedal?

Corwin,
With the the cap and resistor values in the Fender Brownface oscillator circuit, dropping the pot values to lower ranges will cut down on the speed range. You can tweak the R + C values up or down, to try and recover some of the slow or fast speed,but ultimately you'll be affecting the width of speed ranges available by using the lower value pot. You'll ultimately come to a point that the circuit won't oscillate at all if you go too low with the pot value.

I'm using 4+ meg pots that I pulled from old audio gear; a lot of the old Magnavox stuff used CTS audio pots in the 3-5 meg range. Not RA, but they'll work.

As for the 10 meg pot, see KOC's mods in TUT2; he has it set up so you can use a 1 meg pot for the depth control. Use a lower value resistor off the CF, though. I believe he indicates using a 10 meg prior to the .02 blocking cap to the pot. I found 1 meg here makes the circuit come alive; the other value damps the LFO signal too much.

You might also try subbing other oscillator networks, like from the Ampegs or Magnatones. They use lower value pots and different value caps and resistors in the oscillator circuit. I haven't actually checked the available low frequency spread in any of these circuits, just seems by ear that the Fender will allow dialing in slightly faster or slower speeds than the others.

For a very complete discussion, I believe Randall A. has an exhaustive discussion on design parameters. let me know if you need the link.
cya.
Jon