dangers of running a synth on LESS voltage than its rated?

[rjd2]

hey guys, hoping this is an easy one to answer. i've got a moog rogue synth-its rated for 24VAC. i have a variable wall-wart PSU that's 18/24VAC. is there any danger in operating this at 18VAC on a regular basis? i tried it, and it powered up fine. my thinking is that if a variac sends a LOWER voltage to a unit, then in THEORY, it must be safe.

thoughts? (reason i would do this is that the synth exhibits a bizarre phenomenon occasionally, and i want to see if running it at 18VAC would NOT bring on this phenomenon. been over it, and i cant determine anything wrong with it.) thanks!

[RefD]

analogue synths that don't have some kind of microprocessor in them (so this excludes things like the Prophet 5 and OB-Xa, etcetera) won't be hurt by that.

will probly affect timbre and tuning, however.

[rjd2]

great-just as i suspected. thanks for confirming RefD!

i A/B'ed 18 vs 24 V with the filter set to test the extremes of the lower and upper ranges, and i cannot hear any difference in timbre/freq response/tone. tuning seems to be spot on at 18V. and so far, 2 hrs with no bizarre phenomenon. problem solved, i believe!

[Andy Peters]

hey guys, hoping this is an easy one to answer. i've got a moog rogue synth-its rated for 24VAC. i have a variable wall-wart PSU that's 18/24VAC. is there any danger in operating this at 18VAC on a regular basis? i tried it, and it powered up fine. my thinking is that if a variac sends a LOWER voltage to a unit, then in THEORY, it must be safe.

thoughts? (reason i would do this is that the synth exhibits a bizarre phenomenon occasionally, and i want to see if running it at 18VAC would NOT bring on this phenomenon. been over it, and i cant determine anything wrong with it.) thanks!

The synth undoubtedly has an internal power supply that rectifies the AC in and regulates it.

If the incoming AC goes too low, the regulators in that power supply will drop out of regulation. One symptom of this is low-frequency (120 Hz) hum.

They specify a 24VAC transformer so that under worst case low-line (mains) conditions, the power supply still works. If you replace that transformer with a lower voltage type, then your margin for low line voltage degrades. If your mains is a steady 120VAC all the time, you might just get away with it. If it varies due to loads switching on and off, then you could be hosed.

Just use the right voltage. I don't understand why you wouldn't.

=-a

[???????]

reason i would do this is that the synth exhibits a bizarre phenomenon occasionally, and i want to see if running it at 18VAC would NOT bring on this phenomenon. been over it, and i cant determine anything wrong with it.

[earl parameter]

yeah what andy ( and refd said about tuning ) basically.

but the rouge regulators are rated at 12V so with an 18VAC supply you are fine. you are still feeding them the minimum +3V over so there should be no ill effects and tuning should be fine as well. just make sure you have the right amperage.



steven

[stevedood]

The synth undoubtedly has an internal power supply that rectifies the AC in and regulates it.

=-a

Not correct - The Rogue has an external power supply

I would suspect running it at 18 VDC from a switching power supply wouldn't be too bad but I would test it with both waveforms & volume maxed-out, try to load it up and see if you can hear the PSU switching stages. I recall hearing somewhere that a linear power supply might be a better choice for running Moog's...not sure if this true?

BTW, Did you ever track down the noise issue with your Rogue that you had awhile back? I'm guessing you must have if you've swapped in a new power supply?

[earl parameter]

the scheme didn't say the entire supply was external?

if your new supply doesn't provide a regulated +/-12VDC when all is said and done then what i said doesn't apply. and the only thing that matters then is that you don't use less then the chips will need to run. there could then be tuning issues but you said there were not so...


steven

[Andy Peters]

The synth undoubtedly has an internal power supply that rectifies the AC in and regulates it.

=-a

Not correct - The Rogue has an external power supply

Umm, lemme rephrase.

rjd2 said that the Rogue uses an external 24VAC "power supply," which is simply a step-down transformer in a box.

Inside the synth is an internal power supply that rectifies the 24VAC input and regulates it.

In fact, this link (the very first result when googling for "Moog Rogue Power Supply") has a description and a schematic of this internal power supply.

Thank you, drive through.

For rjd2: the schematic shows 12V and -12V linear regulators fed by simple rectifier and smoothing caps. Using an 18VAC transformer should be fine and it'll certainly keep the regulators cooler.

-a

[The Scum]

It should be mentioned that the current rating of the wall-wart will play a factor here, too. As the load demands more current, the output voltage of the transformer will drop.

That link says it wants 200 mA from the secondary, which is often how those wall warts are rated (ie: "200mA @ 24V").

If the 24V wall wart couldn't supply 200 mA, then it's output would have dropped, and the regulators could have shut down...or led to shutdown in a brownout.

If the 18V transformer is more capable of driving the load, then it's output won't sag as much, and the regulators keep working.