#123 has a 500K resistor wired as a variable resistor, one of the outer lugs connects to the junction of the 150K and Ratio control the other to a .022uF cap leading to ground. Gil uses the same control but with different values: 250K and .001uF.
It is my understanding that the corner frequency is then 14.5Hz for HAD's and 636.9Hz for Gil's. What's interesting to note about HAD's is that the corner frequency changes very little over the range of the pot. For HAD's filter to have approximately the same corner frequency as Gil's, a 10K pot with a .022uF cap might as well be used.
Also, interesting is the fact that when the HF pot is open a hard wired low-pass filter forms between the 150K resistor and the .022uF cap with a cutoff frequency of 48.3Hz. I guess HAD designed it to be imperceptible whereas Gil's corner frequency will be 1061.6Hz with an open HF pot.
Question:
1. Is the control designed to cut highs when turned CW or CCW? Gil, you've posted before that you set this control at about 30%. On the 250K pot, do you connect lugs 1 & 2 together or 3 & 2?
2. I've never seen an amp with the HF taper inside. Does anyone know if HAD mounts it on a board like Gil or on the back of the Ratio pot?
OK, to summarize:
Judging by the values alone, HAD's taper is quite ineffective. Yes, it does it's job but the only usable range is a small fraction of the pots rotation. Gil's has a much more usable range, this is probably the one I'll use in my non-HRM amp. The only downer with the 250K/.001 is that there is
cutoff when HF pot is open, whatever!
If you want to play around with the values of these HF taper controls, go to: www.muzique.com/schem/filter.htm
Or if you want to expand on the HF Taper concept check this out (written in the context of pedals): www.muzique.com/lab/swtc.htm
I have a feeling that I've overlooked or misinterpreted something. Can someone give me a clue?
Anyone? Thoughts, speculation, feelings of rage?
P.S. Have a HAPPY NEW YEAR Everyone!!!! D.S.
