MXR EVH Phase 90 - easily overdriven

[Guitarist]

I called MXR and a tech said this may inherent in the design and upping the power/voltage would unbias a transistor. Any ideas on getting more headroom? I have to put it first in on the pedal board, but prefer the tone of it downstream.
Sure, I can try a 12 or 18 volt adapter. How about adding a small trim pot someplace to rebias. I guess we need a schematic...

Thanks, Guitarist in BC.

[Mark Hammer]

The rebias is easily done, but the change in supply voltage is not the issue: the JFETs used in the phaser, as control elements, are.

There are tweaks one can do to the JFET subcircuit, that raise the clipping threshold, to avoid the problem. In fact, that arrangement is used in the Phase 45, as well as a number of other commercial phasers made in past. Look at the schematic for the 45 and 90 to see the differences: http://www.generalguitargadgets.com/pdf/ggg_p90_sc.pdf http://www.generalguitargadgets.com/pdf/ggg_p45_sc.pdf

A friend who is superbly knowledgeable in the world of phase shifters has told me that while this arrangement of additional components does raise the point where clipping results, he describes the transition from non-clipping to clipping as rather ugly and unmusical. In contrast, the arrangement found in the P90 and so many other FET-based phasers, results in a gradual transition from clean to clipping, which he finds a bit of a nuisance, but less ugly. I have to qualify this by noting that he deals primarily in the area of synthesizers, so he is dealing with hotter signals to begin with, and the P45 arrangement may well keep the clipping threshold safely above whatever you are feeding it.

[Guitarist]

Hey thanks so much. I just started comparing those circuits, yikes, I'm much better with tubes. Also just now I was patching throughout my pedalboard and monitoring with headphones via my new Audient interface. There are some funky things going on that get masked via the power amp and speakers. I was getting near -12dB on the meters (crunch pedals preceding a CF tube buffer as clean channel, all equaled), lows farting an input downstream, some minor very high freq. sizzling, and the reverb/delays bringing up the levels when engaged. So I must spend more effort on this. Most items are true bypass save one DOD compressor and a Guyatone overdrive. So maybe things are fine at 9V, as you imply.
Comparatively, the Phase 90 is doing relatively fine in the pole position Still, I don't miss the digital rig that had so deceived me until a year ago.

[Jazz P Bass]

Here is a fine link that helps explain the goings on in a phaser circuit.
ElectroSmash - MXR Phase 90 Analysis.

[Swervage]

Thanks for the link with detail explanation

[oc disorder]

A very good post here by " Gordonjcp " re MXR PHASE 90 SCHEMATICS... which may be useful on this topic

https://www.circuitbenders.co.uk/for...?topic=1532.15