** 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

On Sep 29, 8:15*am, "Phil Allison" wrote:
** 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

Sneaky but smart!

" wrote:

On Sep 29, 8:15 am, "Phil Allison" wrote:
** 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

Sneaky but smart!


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.

"Michael A. Turd"


If the loads are equal.


** Not possible with paralleled secondaries.

Regulation is improved by doing that.



..... Phil

Phil Allison wrote:

"Michael A. Turd"

If the loads are equal.

** Not possible with paralleled secondaries.

Regulation is improved by doing that.

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.

On 29/09/2011 11:15 PM, Phil Allison wrote:

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

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

Sylvia.

"Sylvia Else is a IDIOT "


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

And if the customer uses that ability - how long will the unit last?


** 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

"Michael A. Turd"

If the loads are equal.

** Not possible with paralleled secondaries.

Regulation is improved by doing that.

Somewhat, but still not as solid as parallel primaries.


** With identical transformers - it is.


I've seen
two separate transformers with the primaries in series and the
secondaries connected as a center tapped full wave bridge,

** Bad idea.


and the voltage bounced all over the place.

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

it would have been even worse if
the transformers didn't saturate when the primary on that core went too
high.

** The only thing saving it.

It was done by some fly by night TV shop back in the '70s.


** 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

On 30/09/2011 4:59 PM, Phil Allison wrote:
"Sylvia Else is a IDIOT"


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

And if the customer uses that ability - how long will the unit last?


** 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.

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

So something's different.

Sylvia.

On Thu, 29 Sep 2011 23:15:51 +1000, Phil Allison wrote:

Customer brought in a Peavey CS800x4 four channel power amp he picked up
in eBay in near new condition.

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



--
Live Fast Die Young, Leave A Pretty Corpse