Help with Arion SCH-1 Chorus/Vibe Mod

[clarisso11]

Hi everyone,

I've been working on an Arion SCH-1 chorus pedal from the 80s. It had a sketchy footswitch, so I decided to convert the whole thing to 3pdt true bypass.

I followed instructions online to do the conversion, and it works well. While I was at it, I also tried to change the functionality of the Direct/Stereo switch to a Chorus/Vibe switch. The idea is that the switch cuts the dry signal, leading to vibrato-like sounds.

These are the instructions I followed: https://www.diystompboxes.com/smffor...topic=105620.0

At the moment, the Chorus/Vibe switch works on one setting, but kills the signal completely when engaged. I have attached the schematic, with all the changes I have made. I thought I followed the instructions exactly, but I must have done something wrong..

Any help would be greatly appreciated!

[clarisso11]

To clarify my question:

Looking at the schematic, I'm struggling to understand why disconnecting pin 1 of IC1 from the R30/R31 junction would kill the audio signal completely.
I used an audio probe to confirm that there is dry signal on pin 1 of IC1 when the Chorus/Vibe switch is not engaged, and wet signal at IC2 pin 6.

Shouldn't the wet signal still reach IC2 pin 6, even with IC1 pin 1 and R30/R31 disconnected?

[Helmholtz]

I guess disconnecting IC1 pin 1 from R30 changes the DC bias for IC2.

See how the DCV at IC2 pin 7 changes.

[clarisso11]

I guess disconnecting IC1 pin 1 from R30 changes the DC bias for IC2.

See how the DCV at IC2 pin 7 changes.

I've just did the measurements, DC voltage changes consistently at IC2 pin 7 when the switch is engaged, but by very little: 4.11V to 4.14V.

[Helmholtz]

So no problem here.

Do you have effect signal before Q4?

[clarisso11]

So no problem here.

Do you have effect signal before Q4?

The effect signal is present before Q4 (at R32), but is cut when the Chorus/Vibe switch is engaged.

[Helmholtz]

Same with original wiring?

[clarisso11]

Same with original wiring?

Do you mean, with the switch still functioning as Direct/Stereo switch? I'm getting another (unmodded) unit in this week, and should be able to check.

Signal before Q4 is also cut when the footswitch is pressed, if that helps at all.

[g1]

Your drawing of the direct switch changes do not seem right. You should draw it out in proper schematic form.

[clarisso11]

Good point, that would probably help.. I will look into that.

As far as I know, the direct switch is now completely isolated from where it was originally connected, and all it does now is make or break the connection between IC1 pin 1 and R30/R31 junction. I will confirm again using a continuity tester.

[clarisso11]

I have just double-checked, the direct switch is completely removed from the circuit, all it does is connect/disconnect IC 1 pin 1 and R30/R31.

Once the unmodded SCH1 pedal arrives, I will try disconnecting IC 1 pin 1 and R30/R31 on that unit, with everything else untouched. If that doesn't cut the signal, I will know that the issue lies somewhere else.

Thanks everyone for now, I will report back once I have done the tests.

[g1]

As far as I know, the direct switch is now completely isolated from where it was originally connected, and all it does now is make or break the connection between IC1 pin 1 and R30/R31 junction.

Then you would have had to restore the connection made when direct switch in 'effect' position.

[clarisso11]

Then you would have had to restore the connection made when direct switch in 'effect' position.

I'm not sure I understand, what connection on the schematic is that?

[g1]

Never mind, I see from the description of the mod that it completely disables 'out B' jack.

edit: ignore and see post #15 below

[g1]

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.