Ross Analog Delay

[Marlowe]

First, let me thank you for allowing me to post here!

I have been given a Ross Analog Delay. It's the Taiwanese model, black with the yellow writing. It's AC powered like the old MXR green delay.

The Ross works very well, except that the delayed signal has an odd harmonic on top of the delayed sound. It's like a harmonizer is being used on the delayed signal. The clean side of the signal is beautiful. There's no AC hum, but the delayed signal is a bit dull. The noise is not clock noise as far as I can discern. The pedal appears unmodified.

Would any of you with more experience with these than I have any idea what might be occurring?

Thank you, Marlowe.

[Mark Hammer]

The MXR, and Ross, were somewhat forward thinking for their time, in using a tracking lowpass filter.  That is, instead of a fixed cutoff, as used in just about every other delay pedal of that era, the cutoff frequency of the lowpass filter changed with the delay-time setting, so as to get the most bandwidth possible.

How did they do that?  Well, the delay time depends on a clock pulse to shift the BBD through its paces.  MXR harnessed the clock, and divided it down, to also controlseveral CMOS switch chips (4066 or 4016, if memory serves).   Those chips, in turn, were used to make switched-resistor filters.  (If a resistor is switched on and off at high speeds, the circuit acquires the characteristics of an "average resistance" that varies with the switching rate).  So, you should see a couple of 4013 flip-flop chips to divide down the master clock.  As the master clock was set faster, the switches also worked faster, and the cutoff frequency was set higher.

So the question is: does the "harmonic" vary with the delay time?

[Morocotopo]

Interesting. The idea of a tracking filter should be applicable to the many PT2399 delays... maybe with a double gang pot for the delay time, one controls time, the other controls the filter(s) cutoff...

[mth5044]

^Check out rring's delay on this board and at his site, circuit salad. It uses a MAX7401 which could work very well for a tracking filter.

[Marlowe]

Thanks, fellows for the comments!

And thank you, Mr Hammer. I've read your comments in searches of this site.

No, the harmonic does not change with time. The sound is best described as if you were using a harmonizer set to a high, odd out-of-tune harmonic which rides on top of the delayed signal. The sound is rather like the sound old analog delays get when you set the delay VERY close so that you get that "sproing in an empty room" bounce back. But the "boink" stays whether the delay is long or short. I'm reasonably sure it's not clock noise. The clock null trim pot has that silenced pretty well. The pedal is functioning perfectly otherwise. The delayed signal is a bit dull, but I supposed that goes hand in hand with BBD...

One thing I will say about this Ross: I have an EP-3 preamp I built years ago, and I thought that sounded great, but the preamp in this pedal- with the delay set to 0- gives the guitar a really great punch!

Thanks again, Marlowe