Greetings,
I am facing a usual problem - lack of specific value potentiometer (500kC with knurled shaft) to build a Ross Phaser clone. I do have several 100kC pots that fit the bill, but the LFO speed doesn't decrease to it's slowest, naturally. I wonder, is there a timing capacitor in this particular LFO, or is it purely current-driven? Can anyone perhaps advise on the topology of this particular LFO and formulas to calculate it?
Thanks so much in advance!
Link: http://tonepad.com/project.asp?id=25
File: tonepad_rossphaser.pdf 255.1 KB-- Ross Phaser, Rev.1.Nov.29.2005
I believe the 3.3uF cap (at pins 10 and 12 of IC4b) is the timing cap. Probably best to socket it and try some higher values. Personally, I'd whack a 10uF in there and see what happens.
Personally, I've never found the rate control on the Ross pleasing, even with the "correct" taper pot. Absolutely nothing wrong with having a fast/slow range switch that introduces either a fixed resistance in series with the 100k pot, or else a parallel resistance along with a larger-value (e.g., 1meg) pot.
FWIW, when I converted a Ropez to a Uni-Vibe format, a 50k pot was really all I needed to cover the complete range of usable speeds.
So, no real need to change the cap value.
Gentlemen, you have my gratitude. :) Will try this tonight! :)
Constantin,
It just clicked. I haven't seen you here in a long time. Are you still in Toronto?
Hi Mark,
Yes, although now my stomping grounds are the business area of Mississauga. How are you? Still in Ottawa?