Boss ACA and PSA - Arion clones

[spacecadetcharlie]

My understanding: older Boss pedals using ACA had a diode and resistor in series between the input jack sleeve (ground) and the power supply negative; this pair did not exist between the input jack sleeve and battery negative. This accounts for the ACA 12v supply vs. the 9v battery supply.

When Boss changed to PSA (9v) supplies, they modified existing pedal designs by removing this diode and resistor pair. Thus the connection between input jack sleeve and power supply negative was now the same (electrically) as the connection between the input jack sleeve and battery negative. Correct? Or is this not true?

THE QUESTION:
Now, I have an Arion (Boss pseudo-clone) SFL-1 that claims to need a 9v power supply (on the sticker on the back). However, the input jack sleeve --> power supply ground looks A LOT like a Boss ACA and not PSA. I.E. this pedal has a diode and resistor in series between the input jack sleeve and power supply negative, but that pair does not exist between the input jack sleeve and the battery negative.

Here's a schematic that is nearly identical to my pedal (D1 and R59, to the left of the image, are the ones in question):
Arion SCH-1 schematic from Hobby Hour

Am I reading this correctly, that the pedal is actually designed to use a Boss ACA style supply, despite what the sticker says on the back? And that I can use the common ACA to PSA mod shown here:
Stinkfoot ACA to PSA mod

Thanks very much for the help!

 

[giovanni]

I think that schematic is stating 9V pretty clearly. Keep in mind that even with a protection diode in series, you get about 0.6V drop, not even close to the 3V that make up the difference between 12 and 9, so I’m not convinced by your explanation of the switch to 9V. Moreover I’m also not convinced that Boss pedals don’t have a protection diode, but I have seen crazier things.

 

[mnemonic]

I have an arion tubulator (ts clone) I got back in college when I was poor, it has the same ACA thing going on. Easy way to tell, plug it into a 9v regulated supply buy itself, then daisy-chain another pedal (non-aca) using the same power supply. If the indicator LED suddenly gets brighter when the other pedal gets plugged into power, it’s ACA.

I never bothered to mod it since any time I use it, it’s daisy chained power with other pedals anyway.

 

[giovanni]

Wait why is that?

 

[spacecadetcharlie]

Wait why is that?

Older (the original) Boss pedals were designed to use an unregulated 12v power supply, instead of the regulated 9v power supply most modern pedals use.

So even though Boss pedals were designed to be run off a 9v battery, the circuits also included a voltage dropping diode-resistor pair that was only in circuit when a 12v power supply was plugged in. Hence my question to start this thread, I believe that even though the Arion schematic says 9v, it is copied from Boss ACA and actually requires a 12v supply.

In any case, the pedal ran and sounded different when I used a 9v battery, vs when I used a 9v power supply. Like mnemonic said, when switching between those types of power, the led would change its luminescence and get brighter on battery.

I went ahead and modded the pedal:
I don't use a daisy chain power supply, so I modded my pedal and added a small jumper on the back of the pcb to bypass that voltage dropping resistor... an easily removable mod. Now the power supply and battery use the exact same circuit, sound the same, and the led is the same.

 

[spacecadetcharlie]

Here's an example of an ACA Boss schematic vs a PSA Boss schematic:

ACA 12v: Boss CE-2 Chorus
In this circuit, D5 and R53 provide voltage dropping from the 12v ACA power supply this pedal was designed to use. Thus the rest of the pedal runs either on 9v battery; or 9v power supply plus the voltage dropping resistor/diode = 12v.

PSA 9v: Boss Metal Zone
We're looking at the Input Jack > Battery > AC Adaptor parts of the circuit - you can see there is no voltage dropping resistor in circuit between the input jack sleeve and the power supply negative. The battery and power supply use the same circuitry, as they should. They are both 9v.

 

[giovanni]

I’m gonna have to study all that. TIL!

 

[spacecadetcharlie]

I’m gonna have to study all that. TIL!

To be fair, I have a tenuous grasp on it myself. That’s really why I was asking the question; I was confused by the apparent disconnect between the 9v on the schematic/pedal and what I saw in the power supply section of the schematic itself.