Morley PFA phaser. suggestion needed!

[MarcoMike]

Hi, I was "inspecting" my PFA and saw that the bypass switch is actually a DPDT but wired as SPDT, with the input always connected to a buffer.
schematic HERE

a difference from the schematic is the 68K resistor wired on the output jack instead of before the switch. anyway...

I couldn't help to use the second pole of the switch to make it true bypass and (good or bad luck?!?) actually I can hear the difference:
the pedal now is louder in bypass mode!! 

so... what shoud I do? turn back to non-true-bypass or tweak some components to balance the output of bypass and effect? any suggestion?

thanks

[Mark Hammer]

Back in the day, when SPDT stompswitches were the way pedals were bypassed, the circuits were essentially designed in anticipation of maintaining signal-level balance between effect and bypass mode.

The question you need to ask yourself is whether any potential advantages to be obtained from imposing full TB on the pedal are counterbalanced by disadvantages, or whether you gain more from the mod (after remedying the volume imbalance) than you lose.

What would full TB add here?  Well, if your battery dies, you don't have to worry about switching-FET nonfunctionality.  Oops!  No switching FETs involved, plus there's an AC power supply, so TB doesn't really add anything.  Okay, it could prevent the tone-sucking.  Well, the input impedance looks pretty dang high, and people tend to use phasers after other pedals anyways, so a low output impedance from an earlier pedal, going to a high input impedance on this one, tends to step around tone-sucking.  The signal also doesn't pass through any buffers or anything in bypass mode, so scratch another reason for going full TB.  On the other hand, while there isn't any tone-sucking, the hard-wiring to the circuit clearly provides "level-sucking".  If you were sticking the phaser ahead of other devices that needed a hot signal, the insertion loss from the PFA would be slightly problematic.  So, do you do that?  That is, do you stick the PFA ahead of other pedals that need a hot output, or is it near the end of your signal path?

My gut says to leave the SPDT switching in place and move the 68K resistor to the output of the circuit, rather than leave it on the switch, simply because, as shown in the schem, it provides no pop-protection while switching.  Other than that, I'm not seeing any bona fide reasons to need to convert to full TB.

[MarcoMike]

Mark, I blind-trust your opinion! the pedal is going back to non-true-bypass!  I swear! 

The pedal at present has only true bypass pedals before it, but this may be the right time to put a buffer somewhere on my pedalboard... just to be "safe".

Thanks

Marco

[Mark Hammer]

Thank you for your trust in my opinion.  Seriously.  I guess all those years of listening to others paid off.

The "master buffer" sounds like an excellent idea.  As I'm fond of saying, manufacturers design pedals the way they do because they have no idea how and where you will be using it.  So, they design as if it were the only pedal on your board....for the most part.  Those of us on the purchasing side end up with either loads of superfluous buffering and DC-coupling caps, or else not enough buffering, or buffering in the wrong spot.  The nice thing about DIY is that you can plan out your own signal path, stick a buffer where it will be known to do the most good, and work/adapt everything else around that. 

There is nothing intrinsically wrong about TB, and there is nothing intrinsically wrong about buffered FET switching either.  There IS something wrong, however, in viewing every pedal in complete isolation from its context of use.  Took me decades to learn that lesson, but it was one well worth learning.