120V to 240V conversion

Sep 29, 2011 9 Replies

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Phil Allison 14 years ago

** Hi

Customer brought in a Peavey CS800x4 four channel power amp he picked up in eBay in near new condition. Unfortunately he forgot about the AC supply voltage difference in the USA and the model is not dual voltage.

Very luckily, the amp uses two identical 120V toroidal transformers - one for each pair of channels.

Soooo, I realised it was possible to connect the two primaries in series and parallel the main secondaries to ensure the primary voltages always stay equal.

While running the amp on my variac at 120 V, I checked the secondary AC voltages were identical to within a few mV.

Took me only minutes to do to the needed rewiring and it works like a charm.

A bonus is there is now 20% to 30% more power available on a one or two channel basis.

... Phil

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hrhofmann 14 years ago

one

and

rm.

Sneaky but smart!

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Michael A. Terrell 14 years ago

If the loads are equal. If not, the regulation will be crap.

You can't have a sense of humor, if you have no sense.

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Phil Allison 14 years ago

"Michael A. Turd"

** Not possible with paralleled secondaries.

Regulation is improved by doing that.

.... Phil

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Michael A. Terrell 14 years ago

Somewhat, but still not as solid as parallel primaries. :) I've seen two separate transformers with the primaries in series and the secondaries connected as a center tapped full wave bridge, and the voltage bounced all over the place. it would have been even worse if the transformers didn't saturate when the primary on that core went too high. It was done by some fly by night TV shop back in the '70s. :( An OEM replacement took care of multiple problems.

You can't have a sense of humor, if you have no sense.

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Sylvia Else 14 years ago

And if the customer uses that ability - how long will the unit last? Who will be liable for the failure?

Sylvia.

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Phil Allison 14 years ago

"Sylvia Else is a IDIOT "

** All internal DC supply voltages are the same at idle as it was before.

If all four channels are driven, their combined power is also to same as before.

All channels share the same heatsink.

So there is no issue.

Idiot.

... Phil

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Phil Allison 14 years ago

** With identical transformers - it is.

** Bad idea.

** It would, since each transformer is loaded on alternate half cycles.

it would have been even worse if

** The only thing saving it.

** I know of one *commercially made* stereo power amp ( 600 watt per channel ) that had twin transformers, 120 volt primaries in wired series and 70 volt secondaries feeding separate bridge rectifiers and filter electros. There was a permanent 10 volt difference in the + and - supplies.

When driven with low frequencies ( < 20Hz ) the DC rails went berserk.

Insane.

... Phil

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Sylvia Else 14 years ago

You said that there is "20% to 30% more power available on a one or two channel basis"

So something's different.

Sylvia.

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Meat Plow 14 years ago

I anchor my fishing boat with one of those. Very effective.

Live Fast Die Young, Leave A Pretty Corpse

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