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[Conrad Muzoora]

Hi All,
I Purchased 2 QSCs, a used qsc rmx 5050 made in 2005 and a new rmx 4050 made in 2010. My target was to convert both of these from 120v to 240v. The old 5050 had 2 primary coils on the transformers and was easily modified to work well on 240v but the newer 4050 had only one primary coil on each torroid although the schematic shows that it should have 2 coils in parallel for 120v operation.
Now am tired of feeding my 4050 with 120v from a big and heavy transformer and was hoping someone here has an old broken 4050 preferrably the version made before 2006 and could sell this to me to put me out of my misery! (Think the non CE Models). All i need is a pair of torriod transformers, not the whole amp
All help greatly appreciated.

Conrad
NB: I want these shipped to MA01863 USA

[John Roberts {JR}]

If you have two amps you could always just wire the two 120V primaries in series, with a single line cord and power switch.

It would be a good idea when using them that way, to carefully balance the loads, so they play together nicely, and one heavily loaded one doesn't fry the lightly loaded one with too much mains voltage.

While more involved, you could connect the secondary sides together to force them to share the load equally.

Note: the UL does not approve this message.

JR

[Jeff Robinson]

If you have two amps you could always just wire the two 120V primaries in series, with a single line cord and power switch.

It would be a good idea when using them that way, to carefully balance the loads, so they play together nicely, and one heavily loaded one doesn't fry the lightly loaded one with too much mains voltage.

While more involved, you could connect the secondary sides together to force them to share the load equally.

Note: the UL does not approve this message.

JR

Wow, JR, series connection means the same current flows through both toroids so he better set it up to share the secondary load too. That way the secondaries' parallel connection can balance the current draw so the primary windings aren't fighting each other.

I believe the 4050 is a 'dual-mono' construction in one chassis.

HTH

Jeff Robinson

[Bob Leonard]

Conrad,
I remember the threads some time ago prior to your modifying these amps. Your best bet will be to contact QSC. Both amps are still in production so parts will be available.

[John Roberts {JR}]

Wow, JR, series connection means the same current flows through both toroids so he better set it up to share the secondary load too. That way the secondaries' parallel connection can balance the current draw so the primary windings aren't fighting each other.

I believe the 4050 is a 'dual-mono' construction in one chassis.

HTH

Jeff Robinson

Yup, while even I do not advocate doing this, it seems tying the tops of the PS reservoir caps together should force sharing close enough.

A bit of a kluge, and I am not very comfortable with consumers messing with primary wiring.

JR

[duane massey]

JR, I call that "thinning the herd".

[Conrad Muzoora]

Thanks all for very useful input.
Yes the 4050 is a dual mono power supply with two torroidal transformers. I did try connecting the two torroids in series and it worked only that the "protect" light kept coming on i guess due to the imbalance on the loads. Thats why i was hoping that someone might have a broken old amp that might have two primaries per torroid. But it looks like these amps never really totally break down!
Will probably attempt connecting the secondaries together but would very much like it if i got the replacement torroids.
Conrad
www.kooleventug.com

[John Roberts {JR}]

Using the correct transformers is always the best solution.

I am not familiar with the 4050 schematic so my suggestions are based on my ASSumption that the two channel power supplies are both grounded center tap, not driven rails, like a different old QSC amp discussed recently.

If the two power supplies are operating at roughly the same DC voltage, tying the rail voltages together should help the two power transformers share the load evenly. By definition, if they are tied together they can't be at different voltages, and similar turns ratios will reflect back to the primaries equally.   

I would not expect QSC service to approve this modification, so you will be on your own for warranty claims.

JR

[Conrad Muzoora]

I dont expect QSC to approve of this either and i dont think they can sell to me the UK version transformers in the US. Bob Lee already affirmed that, all mods are to be done at the QSC factory, period.
One thing though JR, I was hoping to connect "Jumper" cables between simmilarly coded secondaries from the two transformers just before the rectifier assembly. Would this work too?
Conrad

[Tim Weaver]

I dont expect QSC to approve of this either and i dont think they can sell to me the UK version transformers in the US. Bob Lee already affirmed that, all mods are to be done at the QSC factory, period.
One thing though JR, I was hoping to connect "Jumper" cables between simmilarly coded secondaries from the two transformers just before the rectifier assembly. Would this work too?
Conrad

Wouldn't the Toroid from the 5050 work? If it fits....

[John Roberts {JR}]

I dont expect QSC to approve of this either and i dont think they can sell to me the UK version transformers in the US. Bob Lee already affirmed that, all mods are to be done at the QSC factory, period.
One thing though JR, I was hoping to connect "Jumper" cables between simmilarly coded secondaries from the two transformers just before the rectifier assembly. Would this work too?
Conrad

In theory connecting the windings before the rectifier should work, since the windings should have exactly the same number of turns, and the transformers have exactly the same output.

However should one winding differ from the other even slightly, then the two windings would fight each other.

Since i don't feel lucky, connecting the two rails together after the rectifiers allows the diodes to help force the current sharing and ignores any small differences between winding voltages.

JR

[Conrad Muzoora]

I Just checked the QSC website and seems they are available as parts

XF-000233-gp (Left Torroid) $143.88
XF-000232-gp (Right Torroid) $143.88

The price looks prohibitive. Comes close to buying a used amp (RMX2450). Anyone willing to get for me dealer pricing on these parts? I Have a budget for about 150$ for the pair
Need them shipped to MA01863.

Conrad
www.kooleventug.com

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