6
The bypass on this one is quite unusual. Not the typical Boss buffered dry path and effect path that is alternated with FET switches. In this one, the dry is always on (provided nothing is plugged into the ‘direct out’), and Q8 mutes the delay sound going to the level and regen pots. Muting the regen in bypass is nice. So is the FET switching because it fades in over a few ms and doesn’t pop and send pops through the regen when you turn it on.
If a plug is plugged into the ‘direct out’, Q5 mutes the dry in the dry/wet mixer at IC1a, but unmutes the dry when in bypass, opposite Q8.
The bypass signal does go through a lot of stuff, not just the buffer, but a pre-emphasis (IC1b) and de-emphasis (IC1a) that I didn’t notice sounding terrible on my DD2, but, I don’t think it is crazy that guitarists might object to having to run through all that stuff in bypass.
There’s a bunch of functionality that is lost by true bypassing by disabling the FET switching and BA634 flip flop- you lose muting the regen, you lose the popless transition when the delay gets switched on, I’m pretty sure the hold won’t work right because the there is no input to the delay buffer before you hit the switch, and the relay doesn’t know to switch momentary in hold mode.
A ‘truer to the original design’ way to do a relay bypass would be to do the classic “tone sucking” bypass, where you are always feeding the effect input, and switch the output jack from pedal input jack to effect out, with one SPDT switch. Don’t worry about tone sucking because the input impedance is nice and high, 1M. Control the relay with the 0/+9v logic at wire connection #1 on the SW BOARD (the common of S1 Mode switch, top throw on the schematic).
That logic has the bypass to go with the LED, and does the momentary thing when in Hold mode. Also in this configuration the direct out works as intended, making the effect output wet only, when a cable is plugged in. Hold mode should work right because you are always feeding the buffer.
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