ilovefuzz.com

i was plonking around on the internet looking for information about the LM-2 limiter i bought to use at the end of the looper chain, and i came across this on an old Gear Page thread where someone was wondering why a pedal would work on a 9V battery and off a 12V power supply:

Those old ACA boss pedals have a Zener diode that drops 12v down to 9v, when powered with an adapter. With a 9v battery, the pedal gets the whole 9v. Daisy chaining with a 9v adapter and another 9v pedal will also bypass the Zener diode, and give the pedal full 9v.

n.b. this won't work by chaining two Boss/ACA circuits.

i'm not sure exactly what to do with this information because i already researched power supplies for the looping board that include a 12V output, but if you have a 12V Boss unit that's problematic to power it looks like there's a relatively simple--and i say "relatively" because i hate reorganizing boards after the layout has been settled--workaround. i wonder if it would work connected to one of other boxes on the board, maybe the isolated summing box that sits next to it on the board. anyway, i thought it was worth sending to the hive mind. i can't help but wonder why the fuck they designed it that way so everybody has to use a Special Power Supply.

I believe 12v power supplies were simply more common then. Can't explain you the physics but if you simply daisy chain it with any other 9v pedal it works.

The old ACA power supplies weren't regulated. So they deliver on average more, then there is a limiting diode to make sure the pedal only sees 9V.

These days pedal specific power supplies are more common and they are regulated, so they deliver 9V (or most deliver slightly over 9V). So the purpose of the diode was to make sure that it was consistent with a battery.

Daisy chaining bypasses the diode because a daisy chain has a common ground. If you use an isolated output on a modern power supply of course this doesn't happen.

goroth wrote:The old ACA power supplies weren't regulated. So they deliver on average more, then there is a limiting diode to make sure the pedal only sees 9V.

These days pedal specific power supplies are more common and they are regulated, so they deliver 9V (or most deliver slightly over 9V). So the purpose of the diode was to make sure that it was consistent with a battery.

Daisy chaining bypasses the diode because a daisy chain has a common ground. If you use an isolated output on a modern power supply of course this doesn't happen.

I assume from that it would be possible to remove the diode or connect the adapter socket the other side of it and just use a 9v power supply then.

Or replace the diode with one that just protects the circuit from the use of an incorrect adapter (9v centre +ve for example).

I just chain mine to another pedal on the board, no issues with a One-Spot and the venerable HM-2 etc.

i got out of OneSpots because my total setup is so large now (see "What's on your PEDALBOARD" for details) that i have to do everything in my power not to introduce any kind of noise or interference.

Paul_C wrote:

goroth wrote:The old ACA power supplies weren't regulated. So they deliver on average more, then there is a limiting diode to make sure the pedal only sees 9V.

These days pedal specific power supplies are more common and they are regulated, so they deliver 9V (or most deliver slightly over 9V). So the purpose of the diode was to make sure that it was consistent with a battery.

Daisy chaining bypasses the diode because a daisy chain has a common ground. If you use an isolated output on a modern power supply of course this doesn't happen.

I assume from that it would be possible to remove the diode or connect the adapter socket the other side of it and just use a 9v power supply then.

Or replace the diode with one that just protects the circuit from the use of an incorrect adapter (9v centre +ve for example).

Yep. There is a resistor you've gotta get rid of too. If you're not super awesome at reading schematics this should help:

https://stinkfoot.se/archives/1019

I don't think this will work on all pedals...
I have an old HM-2, which asks for an ACA power supply (it's the Swedish Chainsaw model in my day job product). I looked at the schematic and the circuit board. I was able to do an extremely inelegant, highly unprofessional "blob of solder" mod, where I connect two discreet solder points with one big blob of solder. This bypasses the diode and resistor voltage dropping circuit.
https://www.hobby-hour.com/electronics/ ... -metal.php
There's a schematic on that page. You can see that D1 and R2 are connected to pads 4 and 5. Connect those and one can use 9v from a battery or a power supply. Want to restore it? Just wick that excess solder away.

Cheers!

Heyo, it's Kowloon Walled Benadrian!