Question about pedal power order

[skelts]

Hi guys,

I was putting together a new pedalboard with a new power brick (all isolated outputs) when I noticed my chorus pedal (an Arion SCH-1) was causing a lot of hiss when engaged, something it had never done before. So I got to work trying to troubleshoot the problem when I noticed it would only do so when place before another pedal.

On its own = fine
last in pedal chain = fine
with any other pedal after it = definitely not fine

Weird right?

I tried using the Arion with a seperate power supply, this didn't work. Then I tried powering the pedals after with seperate power supplys and the hiss was gone.

Now we're getting somewhere...so it's something to with the fact the arion doesnt like having any pedals after it in the chain that are powered by the same power supply. This had me pretty stumped, until I started playing around with the order of the how the pedals are powered. Where before I had it neatly setup so the first pedal in my chain was connected to power output 1 of the power brick and pedal 2 in my chain was connected to power output 2 ect....mixing them all up seemed to solve the problem.

Honestly have no idea why this worked, surely it should make no difference which power output on the power supply is used as they are all isolate...was wondering if anyone had any thoughts on this because i'm stumped?

Pedal chain goes: Tuner > Attack decay > Cry Baby > overdrive > overdrive > Arion Chorus > Superego > Oceans 11 reverb > Flashback delay

[Rob Strand]

Weird right?

Yes it's weird.

With power supply/grounding/noise issue you get some weird results because it's a complicated problem involving many components and many possible mechanisms.    When you find a solution you should be skeptical of any explanations from "hearsay" experts (that includes me) why it works because the reason might not be what you think.

So my 6th sense tells me it could be related to the new power brick combined with something peculiar about the Arion.  (and perhaps how the PCB or wiring is done in the Arion.)

So take a look at the SCH-1 schematic,

https://www.hobby-hour.com/electronics/s/schematics/arion-sch1-stereo-chorus-schematic.png

One thing that stands out is the Boss-like power supply configuration of R59 and D1.   Firstly these parts are usually present on pedals which require an unregulated supply.   A 9V unregulated supply often produces 12V DC and the voltage drops of R59 and D1 result in 9V DC at the circuit.  When you run these pedals from a 9V regulated supply, which most isolated outputs will be, the voltage at the circuit can be low and the pedal might not work correctly.     When you use a non-isolated supply with multiple pedals components like R59 and D1 get shorted out by the multiple ground connections between the pedals.

I tried using the Arion with a seperate power supply, this didn't work.

So that could be because the separate power supply is a regulated type.    To absolutely sure perhaps you need to try an unregulated supply on the Arion.

Then I tried powering the pedals after with seperate power supplys and the hiss was gone.

I can't quite get the exact picture here.    So in this case are you saying the Arion is powered from the (new) isolated supply but *each* of the following pedals are powered from their own separate supply?

Where before I had it neatly setup so the first pedal in my chain was connected to power output 1 of the power brick and pedal 2 in my chain was connected to power output 2 ect....mixing them all up seemed to solve the problem.

There's two options here:
- It's possible each isolated output has a separate switch-mode supply, perhaps using one of those small isolated PSU modules.   The switching frequency of these devices are not consistent.    So one of the outputs may be affecting the Arion.    It's possible one of the outputs is faulty.   You could go through the outputs one by and one and try to find a pattern.
- There could be noise between the outputs or grounds and re-ordering the supplies might be redistributing the noise currents in a way that could reduce or even cancel each other out.   That could happen with isolated modules or a single switch-mode with multiple outputs.

Like I said at the start take these theories with a grain of salt.   The bottom line is there is a problem lurking in there.

[skelts]

Hi Rob,

Thanks for the incredibly detailed reply, appreciate that it's a pretty hard problem to diagnose online 

That's a great point about the the power supply schematic of the Arion, I have an old Boss Od-1 that had the same thing but I modded to bypass this section. The new power brick has options for powering pedals at 12V so I might try this with the Arion and see if that helps. If so I'm sure I can perform the same mod. Fingers crossed for this one.

I can't quite get the exact picture here.    So in this case are you saying the Arion is powered from the (new) isolated supply but *each* of the following pedals are powered from their own separate supply?

Yes, exactly that. I had the Arion (and all the pedals before it) hooked up to the new power brick. Then I took 3 different power supplies I had and used them with the superego, oceans 11 and the flashback placed after the Arion in the chain. No more hiss.

There's two options here:
- It's possible each isolated output has a separate switch-mode supply, perhaps using one of those small isolated PSU modules.   The switching frequency of these devices are not consistent.    So one of the outputs may be affecting the Arion.    It's possible one of the outputs is faulty.   You could go through the outputs one by and one and try to find a pattern.
- There could be noise between the outputs or grounds and re-ordering the supplies might be redistributing the noise currents in a way that could reduce or even cancel each other out.   That could happen with isolated modules or a single switch-mode with multiple outputs.

Given that the Arion was 6th in the chain and plugged into output 6, I did try placing a single pedal after it and trying it with outputs 7-12 . This didn't solve the issue though and neither did moving the output around for the Arion. What seems to have worked is placing the Arion into one of the last outputs and moving the 3 pedals afterwards as far away as possible in terms of what outputs they are using. Bottom of my board now looks a mess!

The bottom line is there is a problem lurking in there.

Couldn't agree more, trying to get an understanding of what's going on because it's always good to know. Worst case scenario is a buy new chorus and arion goes back into the cupboard. Shame because it's a lovely sounding chorus.

[amptramp]

You might have to conduct an exorcism.  We used to refer to our electromagnetic compatibility experts as priests or gurus.  We got used to circuits behaving as they damn well pleased.  Stock up on holy water.

[Rob Strand]

Given that the Arion was 6th in the chain and plugged into output 6, I did try placing a single pedal after it and trying it with outputs 7-12 . This didn't solve the issue though and neither did moving the output around for the Arion. What seems to have worked is placing the Arion into one of the last outputs and moving the 3 pedals afterwards as far away as possible in terms of what outputs they are using. Bottom of my board now looks a mess!

How confident are you the power brick has isolated outputs?   Not all of those bricks have isolated outputs.   IIRC one of the Dunlops (not the Dunlop MXR) has a switchmode supply inside but does not have isolated outputs.

The noise is likely to be originate from a switch-mode supply.   The way the noise is getting in is switching currents passing though the grounds.  Either tracks or sockets.

A devious way noise can get into a pedal is when a noise current passes through the input jack switch contact.   The switch contact I'm talking about here is the one that switches the pedal off and on when you insert the input jack.   In your case where the a following pedal causes the noise the noise currents would flow from the Arion's DC input, through input jack the board then through to the Arion's output socket.  However, the pedal works off the power supply and with preceding pedals so you think those would be enough to trigger the problem if it were the input socket switch.

So the key point point has to be the output socket or tracks to the output socket.

When I checked the PCB the ground for the output socket doesn't have a solid path to the input socket.   Also, on the schematic there seems to be a wire link W5 linking the output socket ground.    Maybe what needs to be done is to solder a thick wire across the PCB between input socket ground and output socket ground.   Technically you probably should lift the wire link W5 but if the wire solves the problem I'd be more inclined to leave W5 in.

https://www.suonoelettronico.com/docimg/arion/arionsch1circuit_back.jpg

Another thought is one of the following pedals is promoting the problem.   However, if *any* single pedal following the arion cause the issue then it's a more general problem related to the grounds of the arion and the power supply.

The puzzling thing is if the power brick is isolated, how is the noise getting in!    See if you can find a PCB pic of your power brick it might give you a a better idea what you are dealing with.