Author Topic: Phase 90 distortion  (Read 2051 times)

Offline james

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Phase 90 distortion
« on: January 08, 2015, 07:10:50 PM »
Is it normal to get distortion from the MXR Phase 90 when you're playing harmonically complex chords? This is the first time I've ever had the chance to use one, and the results seem pretty dirty...
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Offline Tim W

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Re: Phase 90 distortion
« Reply #1 on: January 08, 2015, 07:43:52 PM »
Yes this is normal for a stock Phase 90.  It needs to be modded to handle a Rhodes without distorting.

Tim
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Offline james

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Re: Phase 90 distortion
« Reply #2 on: January 09, 2015, 11:44:20 AM »
Is the R28 mod the one I want?

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« Last Edit: January 09, 2015, 12:34:18 PM by james »
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Offline Tim W

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Re: Phase 90 distortion
« Reply #3 on: January 09, 2015, 03:45:22 PM »
You can do the R28 mod as a simple place to start and see if it helps.  We have had to sometimes modify the overall gain of the preamp stage in the pedal by changing some resistors to handle a higher input signal without clipping the phasing stages.

There are several different versions of MXR Phase 90s with different amounts of ICs (single/dual opamps, etc.) and components (some are even now surface mount) so we generally figure out what to do on the fly based on what is in front of us.  All versions of the P90 circuits are basically or mostly the same (except mainly for R28 as you pointed out, LEDs, and DC power jacks), but they changed how they built them over the years.

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Offline pianotuner steveo

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Re: Phase 90 distortion
« Reply #4 on: January 09, 2015, 04:55:48 PM »
Tim,

slightly off topic, but I have a similar problem with my old surround sound unit for my stereo. (1970's Sony) I think I need to add resistors to the audio input- my Blu Ray player audio seems to be too hot for the input. The rear channels distort. The front channels are fine( more modern front amp)

Any suggestions for what value resistors to try? 10k? 20k? Less?

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