question regarding using mismatched PSU with DSP

I have a old digital effects processor for which i don't have the proper wall wart. Lost it i guess, but i tried another with lower specs and it worked. But i'm having a issue that i think may be due to the PSU and i don't want to spend 20 or 30 bucks on the proper one unless i'm sure it's the reason for the problem. The unit is a old boss VF-1 that i use in the effects loop of a tube amp thats designed to accept +4 line levels which this Boss is also designed for. I have the switch set to +4 and have tried every imaginable gain staging scenario but the problem persists. The issue is that when i use it in the amp's loop it adds a slight distortion/compression that i do not get if i play the amp without the boss in the loop and just patch the send and return together. So it;s not the loop, it;s happening in the boss.

So the obvious question is, can the wall wart be the cause even tho besides this slight distortion everything else works fine? The unit is spec'd for 14VAC (yes, AC....rectifier is in the unit) 800mA supply. The one i am using is 12VAC/500mA. Can you say w/o reservation that is the reason for this ? If no one is sure please state that. I just want to know if it can be said it;s definately the reason. Seems like 500 vs 800 mA probably would be an issue, but i don't know enough about these things to be sure and don't want to spend the money only to find i still can't use the boss. Thanks in advance.

dazco said:

The unit is spec'd for 14VAC (yes, AC....rectifier is in the unit) 800mA supply. The one i am using is 12VAC/500mA. Can you say w/o reservation that is the reason for this ?

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Raw math yields 11.2 Watts for the original. 6W for yours. It's likely your supply voltage droops below a threshold at times, causing distortion.

A unit does not necessarily need all the power specified on the label. It may not absolutely need that level of voltage, or that level of current. This makes it hard to be sure which approach you should take to boost your supply, whether adding 2V amplitude, or 300 mA.

The easiest way to proceed depends on what equipment you have at hand.
Conceivably your could take a 2VAC/500mA transformer and add it in series.
Or, take a 12VAC/300mA transformer and add it in parallel.
(Take care to keep waveforms in phase, of course.)

When internal circuitry rectifies AC, it implies it can also handle DC unchanged. So, do you have a 14VDC 800mA supply? Two 7VDC 800mA (in series)?
Etc.

You might test with one of the above arrangements, just to find out if greater voltage helps, or greater current.

There are converter circuits that turn 12VAC/500mA into a higher V at less A, or smaller V at greater A, but none that get more Watts than you start out with.

Thanks, but no, don't have any supplies like that. In fact i only have one other thats a 9vDC@300mA i believe.

dazco said:

Thanks, but no, don't have any supplies like that. In fact i only have one other thats a 9vDC@300mA i believe.

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There's no easy way to add the two supplies together into one power source.

Are you confident enough that you could open up the unit to see what supply voltage reaches the circuit board? Or to read a meter telling whether the supply droops at the times of poor sound quality?

If you visit a computer repair shop, you might find a suitable power supply in the 'bargain box'. (Example, some computer peripherals take an AC supply.) I imagine it only consists of a transformer. Maybe a fuse or thermal fuse too. Avoid telling the guy what you're looking for right away, because he's liable to charge you a high price. Rummage in the box first, and be casual when you ask 'How much?'.