Ross R70 Phase Distortion

Some like 'em and some don't, but I bet everyone has at least a couple — Analog Delay, Digital Delay, Reverb, Chorus, Flanger, Phaser, Tube Overdrive, Transistor Overdrive, Fuzz, Octave Fuzz, Tremolo, Vibrato, Compressor and the list goes on!

Ross R70 Phase Distortion

Postby PeterS on Fri Feb 20, 2015 5:08 pm

For the last couple of years I've been using the Ross Phase Distortion, which is a phaser and a distortion in one box. The phaser is great. The distortion is too trebly for my ears. The Ross distortion is very similar to the MXR Distortion Plus and the DOD 250. Funny thing is, although they're all very similar, internet comments on sound quality seem to be that the DOD is awesome and the Ross is not so great. There's been slight variations in components over the years but the general schematic looks like this:

Image

The clipping diodes are Ge but some versions have silicon.

When I first got the pedal I made two changes -- increased the 0.047 cap that sets the low end roll off of the opamp to 0.1, and increased the 0.001 cap across the clipping diodes to 0.002. Those changes helped but it's still harsh.

I went looking on the net - there's millions of words about modding the mxr Distortion Plus. There are discussions of changing the opamp --- mine is a 4558 (it's a dual opamp but only 1 half is used), which people seem to love in tube screamers. Some discussions suggest high end Burr-Brown opamps, which have very low noise etc. But the better-loved variations of the pedal have a 741 op amp, which is a 1960's design which has a very low slew rate (i.e. it has poor high frequency response). So I put in a socket for easy swapping, and put in a 1458 opamp (dual version of 741, same crappy frequency response). I didn't have a lot of confidence that changing the opamp would make much difference but it really does --- the high end is much smoother and less harsh.
PeterS
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