Help with Arion SCH-1 Chorus/Vibe Mod

[clarisso11]

Never mind 2:
The description about out2 jack being disabled was for an sch-Z, and maybe only a certain interpretation of the mod.

Here is a true bypass schematic, check if yours matches. And the connection I mentioned in post #12, that needs to be restored would be from R38/R40 junction to W3.

Thanks for sharing this.

I've come across this before but didn't think it would work. Isn't the input always connected to the circuit in this configuration? And would I still be able to do the Chorus/Vibe mod? It looks like the switch still needs to be used as Direct/Stereo with that wiring.

With the footswitch engaged, I'm pretty sure the R38/R40 junction to W3 connection is restored in either wiring, unless I'm missing something.

[g1]

Thanks for sharing this.

I've come across this before but didn't think it would work. Isn't the input always connected to the circuit in this configuration?

How about on that drawing, show what is different about your true bypass with 3PDT.

[Mick Bailey]

I've changed a few of these to true bypass for a number of customers, but in the manner that the OP has used (one output then is disabled) to disconnect the input stage. The second method shown is used to retain the stereo output. I've also worked on a few Analogman re-boxed units that use a 4PDT switch and retains stereo output.

[clarisso11]

I've changed a few of these to true bypass for a number of customers, but in the manner that the OP has used (one output then is disabled) to disconnect the input stage. The second method shown is used to retain the stereo output. I've also worked on a few Analogman re-boxed units that use a 4PDT switch and retains stereo output.

Thanks, that would make sense! I bet the 4PDT wiring just expands on the wiring shown in post #15, by disconnecting the input completely.

[g1]

Going back and re-reading the linked thread from post #1, I see that 'Output B' will be the only working output with the mod.
I still don't understand your drawing from post #1. It shows 'cut' at output B, but nothing gets re-connected there, so the drawing is incomplete.

[clarisso11]

Going back and re-reading the linked thread from post #1, I see that 'Output B' will be the only working output with the mod.
I still don't understand your drawing from post #1. It shows 'cut' at output B, but nothing gets re-connected there, so the drawing is incomplete.

The way I understand it is this:

The goal is to completely isolate the Direct/Stereo switch from the circuit, so it can be repurposed to make or break the IC1 pin1 - R30/R31 connection.

It is connected to the circuit in three places.
1. Removing the W3 jumper disconnects it from the Output B jack.
2. Cutting the track going upwards from the switch disconnects it from R6/C4, which is the dry signal (when switch in "Direct" position). I've seen instructions for this mod for the Arion SCH-Z that suggest to remove that resistor and capacitor to isolate the switch, the result is the same.
3. Cutting the track going to the left from the switch disconnects it from R38/R40, which is the dry with wet added signal (when switch in "Stereo" position).

The track that used to go up from the switch remains disconnected, since this was just the dry signal, it's no longer needed.
The track that used to go to R38/R40 is now wired as the effect return, going straight to the 3PDT. And the track that used to go to Out B is wired as the output, also going to the 3PDT.

At this point, the switch is isolated, and the 3PDT footswitch should function as a standard true bypass switch, adding or removing the wet signal from the output. I might have gotten some of this wrong, but I think that's the overall idea.

Removing the dry signal from the effect return, by cutting it between IC1 pin1 and R30/R31, should in theory give the vibrato effect, but my signal is cut completely here, even before Q4.

[Mark Hammer]

This drawing, and circuit, makes no sense to me. The feed off C4 - indicated by my added blue line - is used for a "buffered bypass", providing an untampered clean/dry signal. The clean signal then receives treble pre-emphasis in IC1, before sending it's output, along the violet line, to the tone circuit. The tone circuit simultaneously feed the wet/delay path, shown in violet, as well as R30 and R31 to the mixing stages. Q5 provides a phase-splitter, giving opposite-phase wet outputs, which are then fed, via the orange lines, to the mixing stages. One of the mixing stages provides dry plus wet and the other provides dry minus wet. In effect, the tone control simultaneously darkens or brightens and thins out BOTH the wet and dry, as opposed to only affecting the wet signal, which several other chorus designs prefer to do. Call me crazy, but this arrangement makes no sense to me. Why would you want to dull both wet AND dry?

As for the problem to be solved by the OP, I'm guessing that somehow the output from pin 1 of IC1 was unintentionally cut completely, such that no IC1 output is continuing along the violet pathway, and not just lifting the dry signal feeding R30/31.

[clarisso11]

As for the problem to be solved by the OP, I'm guessing that somehow the output from pin 1 of IC1 was unintentionally cut completely, such that no IC1 output is continuing along the violet pathway, and not just lifting the dry signal feeding R30/31.

I can't believe it, it's working now! Thank you Mark, your hunch was right - it turned out that one of the violet lines in your drawing was disconnected by mistake, the one leading to IC1 pin 1.

Thank you also for the analysis of the circuit, I find these things incredibly helpful for learning more about circuits! Hoping this will help people attempting this mod, and others.

[Mark Hammer]

Another one sold!

Congrats. I love it when a hunch proves right.

And, while pretty much any chorus or phaser CAN be converted into providing vibrato, by cancelling the dry signal, bear in mind that the LFO is not always optimum for the purpose. Indeed, the venerable Boss CE-1 used a different LFO waveshape for its vibrato function than for its chorus function. For me, that was the standout feature of the unit.


That said, squeezing one more trick from a pedal is always a satisfying achievement.

[Mick Bailey]

Hey, Mark, that's an excellent and well-reasoned deduction. Nice work.