# Phase ii (w Blend Knob)



## phi1 (Dec 29, 2019)

The 1590B enclosures from Small Bear are slightly roomier on the inside than the ones from Tayda (because of the thinner walls).  So, the 2.2" wide board just fits.  Plus, this is a really cool blue color.  The knobs are from Small Bear too.  I meant to take a pic of the solder side of the board to show how the pots are oriented, but I forgot.  The Rate and Depth pots are rotated 180deg from how they would normally be mounted so that they are inside the perimeter of the board instead of hanging outside the perimeter like the board is designed.  I had to use solder lugs and short wires to reverse lugs 1 and 3 in an 'X' shape for both pots.  The Feedback pot also uses solder lugs and wire to move it over to the side. 

For the blend knob, I just put a simple BJT buffer on the dry side and a 50kB blend pot.  You can kind of see the buffer vero board, which is superglued to some doublesided tape down next to the footswitch.  I experimented with a buffer on the wet side (before the phase circuit), since the input impedance is only about 390k(?), but it didn't seem to make a noticeable difference. 

I set the trimmers by ear, but ended up similar to what some others have suggested, the 10k trimmer at noon, and the 1k trimmer (sets the led brightness) slightly high at about 1:30.  With the brightness trimmer lower, you get some wonky glub glub sounds at high depth settings, and bringing the brightness up smooths it out.

I don't have much experience playing with phasors, but I really love the sound.  I think the blend knob is really nice, allows some textures I can't get just by changing the depth and feedback knobs.  Hopefully there's a blend pcb available on here soon so it's easier for people to access this mod.


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## Chuck D. Bones (Dec 29, 2019)

Nice build, tight fit.  

Another way to implement a Blend function is to replace R31 with a 10K pot.  Dialing the pot down removes some or all of the dry signal.  If you want to dial down the wet signal instead, Replace R5 with a 5K pot.  In either case, you will want to tweak R30 to get maximum phase effect when the BLEND pot is maxed.


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## phi1 (Dec 29, 2019)

Huh interesting, I see what you mean but I wouldn’t have thought to do that. Thanks for sharing. 

I have a question, in both those cases you mentioned (using a pot to boost or attenuate either the dry or wet signal), would the pot be able to keep constant volume through the sweep?  For example if you put a 5k pot in for R5, you could dial less wet, but I’d think the overall volume would go down too.  Is there a simple way around this?  Maybe a dual pot which affects the wet and dry side simultaneously, but it seems this might be tricky to tune for consistent overall volume through the sweep. 

The way I did (basically like a tagboard split n blend) keeps pretty consistent volume through the sweep, since you’re just planning between the two signals.


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## Chuck D. Bones (Dec 29, 2019)

The mod I described will make a <2dB variation when you dial the Blend from from one end to the other.  It will barely be noticeable.  The end-to-end dry signal gain is 0.82 or -1.7dB.  The end-to-end wet signal gain (with feedback set to zero) is also -1.7dB.  

The wet signal's phase varies with frequency.  At frequencies where the wet and dry signals are exactly (or nearly) in phase, they reinforce each other and the signal is 6dB stronger.  At frequencies where they are exactly (or nearly) out of phase, they cancel each other out.  At most frequencies, they are somewhere in between.  Because of this, phase shifters will alter the perceived volume a little bit.  Feedback can accentuate the volume change.  The Phase II design deliberately tries to compensate for the volume change by reducing the wet and dry signals by 1.7dB.  The Phase 90, by comparison, does not compensate for the volume change; the wet and dry gains are 0dB.  A few phase shifters, like the Abyss, have a volume knob so you can make your own adjustment.


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## phi1 (Dec 29, 2019)

Gotcha. I know what you mean about the perceived volume... hard to nail down if it’s unity or louder, since it’s frequency dependent. 

As a test (with my blend pot all the way wet) I shorted out R5 (just touched some leads to pins 1 and 2 of the op amp). With A/B testing you can hear a volume drop from the bypassed signal compared to the signal through the pedal with R5 shorted, basically dry, just slightly less volume. But it’s not a huge drop, which aligns with what you said. So there’s prospect for it being a much simpler way to implement a blend pot.


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## Mourguitars (Dec 30, 2019)

Awesome build phi1 !

Congrats !

Mike


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