Missing AC adapter for preamp mixer - will this work?

[craigsmith]

Hello!

The AC Adapter went missing for my Gemini PMX-80 Preamp Mixer.

I found the service manual here: http://diagramas.diagramasde.com/audio/PMX-80.pdf

- The power source is "115V/15V AC 7.5W" *edited
- 7.5W divided by 15V = 500mA or higher (if i'm correct)
- the input jack is pin positive based on the schematic (if i'm correct)
- 2.5mm input jack

** I can't tell if the original AC adapter is linear or switching**

My question is: Will a cheaper, switching 15V AC-DC adapter be compatible, or would it result in hum / noise? I found one here for $9: http://www.amazon.com/gp/product/B00IX6DAK0

I found a "compatible replacement" here for $27 + shipping: http://www.amazon.com/gp/product/B00PQDGMIK
It appears to be a linear supply, based on the size and non-universal voltage input (if i'm correct).
I'd rather not spend 3x the price if a cheaper alternative could work.

Could anyone tell if the original supply is in fact linear or switching?

I realize I could simply "try and see", however I'd rather not be wasteful in cost/postage, any advice would be greatly appreciated, thank you!

 

[richie00boy]

I found the service manual here: http://diagramas.diagramasde.com/audio/PMX-80.pdf

- The power source is 115VAC - 15VAC 7.5W
- 7.5W divided by 15V = 500mA or higher

That tells you it is an ac output. So a switching or regulated supply is not suitable.

AC transformers are the simplest PSU you can buy, I would imagine you could pick one up for about 10 dollars.

 

[Spiny]

Hello!

- The power source is 115VAC - 15VAC 7.5W

This is simply a 115VAC -15VAC transformer, It is not a DC unit like the switcher, DC units will not work.

There is no polarity on the AC input, you could use a suitable AC transformer, like this for example 15VAC Wall Wart and add a suitable plug
Alan

 

[craigsmith]

Thank you richie00boy and Spiny for pointing this out. That was actually a typo; I meant to say "115VAC - 15VDC" but perhaps it is in fact AC-AC after all.

I'd like to clarify that, verbatim, the service manual says "115V/15V AC 7.5W" and the rear jack says "AC IN". Is this enough to safely conclude it is AC-AC?

 

[nigelwright7557]

AC wall warts are useful for providing 2 rails and zero volts from 2 wires.
I have used them in USB mixers and active cross over filters.

 

[Enzo]

If it says AC IN, then count on it needing AC. As others have said, it is nothing more than a transformer, nothing special.




And while this is AC, in other applications that need a DC supply, it doesn't matter if it is SMPS or linear, all that matters is the output is smooth DC of the appropriate voltage and sufficient current.

 

[arnyk]

Thank you richie00boy and Spiny for pointing this out. That was actually a typo; I meant to say "115VAC - 15VDC" but perhaps it is in fact AC-AC after all.

I'd like to clarify that, verbatim, the service manual says "115V/15V AC 7.5W" and the rear jack says "AC IN". Is this enough to safely conclude it is AC-AC?

As others have pointed out, the answer is yes.

There is a specific kind of wall wart that I've used repeatedly for gear like this. Its original purpose was providing AC power for alarm systems and it is typically rated at 16-18 volts @ 1 amp or so.

Example:

New 16 5V AC 2 4A Wall Transformer Power Adapter Screw Terminals 16 5VAC 40VA | eBay

It is used exactly as others have pointed out - both the plus and minus DC supplies are internally created from a single pair of wires.

The manufacturer obtains instant UL compliance and puts the hum-radiating transformer well outside the piece of gear.

The specific gear I have used these with were made by Symmetrix and Rane, but this sort of a power system is commonly used by other manufacturers as well.