Phase 90

[kurtlives]

I would like to mod a Phase 90 to deal with the following issues...

When the effect is engaged there is a volume boost.

Could I add a wet/dry option?

I have a few ideas, but I am curious to what you guys have to say.

Thanks

[Papa_lazerous]

An original or a clone?

[kurtlives]

Sorry original

[mac]

You could try using a 180k or 220k instead of the 150k going from output transistor base to collector. That may give you more boost.

mac

[kurtlives]

I want to get rid of the boost.

[Papa_lazerous]

go the other way with the resistor value then

[kurtlives]

Ya thats what I figured...

Any ideas one the wet/dry control?

[Jaicen_solo]

The Phase90, like many true bypass phase/modulation effects incorporates a volume boost on the output to raise the apparent volume to match the unbypassed signal. That's especially important for phase type effects, because the filtering reduces harmonics, making the sound less perceptible, hence the need to boost gain. Originally, when the P90 was non-true bypass, the volume boost brought the signal level in line with the bypassed level. With the recent addition of the true-bypass (Dunlop jumping on the bandwagon and getting it half-right), the volume boost is excessive. As Mac say's, the 150K resistor from between the Collector and Base of the ouptup transistor can be replaced with a smaller value, or ideally, a trim-pot. Alternatively, keep it stock and add a simple voltage divider volume control on the ouput of the circuit. That way you can choose to have a boost, which might be useful for some solos (Eruption anyone..   ).

EDIT: Check out this page for the schem of the P90, if you're comptetent enough to do the mod, you can figure it out from this

http://www.geofex.com/FX_images/p180.gif

[bumblebee]

the phase 90 isnt true bypass. ive never seen one that is.
mines non TB and has an awful god damn boost.

[mac]

I want to get rid of the boost.

Sorry, a lower value resistor then.

mac

[Mugshot]

upping this thread guys 


i have a Phase 90 clone built for me by a good friend based on Tonepad's layout. it plays well really. but like most builds, there is a perceivable volume boost when this pedal engages, becoming more pronounced when i kick this in after fuzzes, but before other dirt pedals (VLSD clone and Rat) no problems.

so quick question: to control the overall volume, is it okay to add a pot on the output to control the volume, 250K perhaps? i dont want to mess with the PCB anymore, the build is top notch, i'd dare not meddle with the 150K resistor between the Base and Collector of the output transistor.

[petemoore]

  Since the Jfet phaser may distort with high input levels, perhaps tame the input instead?
  If you have space for a knob and related circuit, a signal split / clean bypass / mixer could be added.
  See 'Buff 'n Blend', there are others, also see GEO parallelyzer.