Juno Chorus

[dmp]

Start with the regulator working (remover the components that connect to V) and then one by one add components until it starts failing. I'm remembering that the chorus mute section was a little weird with the current draw. That section might be the cause

 

[Midphase]

Start with the regulator working (remover the components that connect to V) and then one by one add components until it starts failing. I'm remembering that the chorus mute section was a little weird with the current draw. That section might be the cause

That is tricky unless I rebuild this entire circuit on a breadboard...not exactly the easiest thing to do. I also find it odd that the default state is that if the switch pins are not connected the chorus is working, and is the switch pins are shorted then the chorus is turned off. Seems like the other way around would make more logical sense.

I was referencing the original schematics and it seems like the switch section (minus the actual button section) are indeed part of the original circuit since I suppose the original Juno 6/60 had a chorus on/off switch. I am wondering that if I bypass that section, what should I actually bypass vs. what should I keep? Is the function of the SK30's strictly as an electrical ON/OFF switch or do they serve another function? Someone on Reddit said that they mix the wet and dry signals together, but looking at the schematic that doesn't seem to be the case at all, and rather the wet is mixed with a dry in what looks like a summing mixer right before it hits the final opamp? If so...would you recommend that I cut off the traces where I indicated with the red lines, and then run a bypass wire where I indicated with the green lines?




One of the other things I'm spotting is that if I wire the potentiometers as indicated on the schematic, they are all backwards (i.e. they operate counter-clockwise), assuming a 1,2,3 left to right pin numbering. Basically I need to reverse them in order for them to function in a proper clockwise lower to higher setting....strange.

P.S. My goal is to re-do the schematic once I've figured all of this stuff out and to get the PCB remade with a cleaner design.

 

[dmp]

That is tricky unless I rebuild this entire circuit on a breadboard...not exactly the easiest thing to do.

Do you know how to desolder components? I would remove R47 and R49, pull the FETs and bridge D to S. If you just pull R47 and R49 you can see if this is what is causing the PSU problems.

I was referencing the original schematics and it seems like the switch section (minus the actual button section) are indeed part of the original circuit since I suppose the original Juno 6/60 had a chorus on/off switch.

Yes, the Juno 6 has push buttons for I and II. If neither is pushed, the chorus is muted. The design is not the same as in the pcb you are using, but is essentially using the FETs the same way.
The FETs are not doing anything other than switching from ~0 ohms to inf ohms to turn the chorus on or off. Q13 is used to pull the gates of the FETs negative (or not).

 

[Midphase]

Yeah, I got a good Hakko desolderer that typically makes quick work of most of this stuff. Taking out R47 and R49 shouldn't be an issue.

Here's another question -- If I remove the entire on/off circuit, you suggested that I still need to send the +12v line to R11 and R12...however when I measure the voltage at both of those points, they're not receiving +12v but rather -9v IIRC, this is because the +12v rail is R55 and R56 first which I assume acts as a voltage divider which is bringing the voltage into the negative. So I just want to make sure that I'm actually feeding the correct voltage to the two NPN's Q5 and Q6...right?

 

[dmp]

Good catch, it is more complicated there. R55/R49/R47 are dominant in setting the voltage at R55/R56. Could either measure or do some back of the envelop math. Probably easiest to compare to the Juno schematic and simplify what is there for the always on config. I wanted to be able to mute the chorus, but I had to simplify / redesigned what was on the pcb.