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[Conrad Muzoora]

Hey Labsters,

Going back to good ol Heavy iron! I have made a purchase of the above amps, the qsc is replacing a plx 3602 on subs in my "B" rig (Mainly because the plx was very unforgiving on "Iffy" Power) and the CA 18 will replace my Crown MA9000i on my "A" rig because of recurrent breakdown of the crown. Now my problem is that these are american 120v models and i will be operating them on 240v. I therefore need advise on how i can convert these to run on 240v. The QSC has 2 transformers, and am considering connecting them in series if i do not find a 240v tap, but the crest has one transformer. Anyone ever attempted what am about to do? And would this reduce the performance if i did the mods?

Conrad
www.kooleventug.com

[Todd Black]

Hey Labsters,

Going back to good ol Heavy iron! I have made a purchase of the above amps, the qsc is replacing a plx 3602 on subs in my "B" rig (Mainly because the plx was very unforgiving on "Iffy" Power) and the CA 18 will replace my Crown MA9000i on my "A" rig because of recurrent breakdown of the crown. Now my problem is that these are american 120v models and i will be operating them on 240v. I therefore need advise on how i can convert these to run on 240v. The QSC has 2 transformers, and am considering connecting them in series if i do not find a 240v tap, but the crest has one transformer. Anyone ever attempted what am about to do? And would this reduce the performance if i did the mods?

Conrad
www.kooleventug.com

dont know about the crest, but it looks to be possible on the QSC. There are different taps for the transformers, but 240v operation calls for a couple resistors to be changed. There is also a line filter shown for 240v operation. And the circuit breaker is smaller. The schematic is here, look at page 4 for the power input section. http://www.qscaudio.com/support/library/schems/Current/RMX%20Series/RMX4050HD.pdf  maybe qsc will sell you the parts you need. I would not just wire the transformers in series.

[Conrad Muzoora]

Thanks Todd,

Looking at the schematics, it appears the transformers are different for the 120 and 240 units (XF 00201 GP for 120v and xf 00232 GP for 240v model), but it appears each 120v transformer has 2 primary coils for 120v input, could i just connect those in series at each transformer level? Also i dont think i will be able to get parts from QSC since am located in Africa and the amps are already on the ship, do you think the line filter is very critical? Or could i just do without it.

Conrad
www.kooleventug.com

[Bob Leonard]

Conrad,
Some years ago I posted a rant about how unforgiving the 3602 became when used to power subs. There have been many posts since then with most people agreeing with my opinions. I replaced mine with 4050HDs and moved the 3602s to power my SRX725s. I run my 4050s using 115v, and to this day have not had a problem and am more than satisfied with the performance under any conditions.

I would suggest that before you make any changes to those QSC amps that you call QSC, tell them what you want to do, and let them make the decision for you. It's very possible there may be a conversion kit available as well.

In the end unless you're in a position where you must change the amps to suite your needs I see no reason to alter the circuit of this very capable amplifier, probably eliminating any chance QSC would be willing to help in the event of a failure or future issues.

[Conrad Muzoora]

Dear Bob,

Thank you so much. I have indeed read many of your posts on the topic and, having had a good reputation with the qsc plx (SQ and reliability-but not good low power tolerance) i decided to go with the RMX 4050HD. Now, i am located in Africa and therefore a qsc warranty means very little to me (And thus the need for super reliability). The plxs i have i run on heavy step down transformers negating the benefit of the light weight. Now the 4050 is not light by any standards, add a 70 pound step down transformer (they cost some) and you get the feeling!.
I have been to the qsc forum and they dont give any advise on the conversion and insist that these must be shipped to QSC to do that. Am hoping some "weekend worriors" here have attempted this and are willing to share the wisdom. The crest too would be less trouble if i can do the conversion.

Conrad
www.kooleventug.com

[Todd Black]

Dear Bob,

Thank you so much. I have indeed read many of your posts on the topic and, having had a good reputation with the qsc plx (SQ and reliability-but not good low power tolerance) i decided to go with the RMX 4050HD. Now, i am located in Africa and therefore a qsc warranty means very little to me (And thus the need for super reliability). The plxs i have i run on heavy step down transformers negating the benefit of the light weight. Now the 4050 is not light by any standards, add a 70 pound step down transformer (they cost some) and you get the feeling!.
I have been to the qsc forum and they dont give any advise on the conversion and insist that these must be shipped to QSC to do that. Am hoping some "weekend worriors" here have attempted this and are willing to share the wisdom. The crest too would be less trouble if i can do the conversion.

Conrad
www.kooleventug.com

if you look at the chart at the top of that page on the qsc schematic it shows different terminals to connect the transformer wires to depending on input voltage. In 120v mode the split primaries on the transformers are connected in parallel, in 240v mode they are connected in series. Follow the chart and look at the schematic and you will see this. I dont know about the line filter, but it looks like those power resistors do need to be changed out though. I am guessing the 240v transformer p/n is 240v only and doesnt have the split primary winding. If doing any mod such as this first connect power with the transformer secondaries disconnected and measure voltage to make sure you didnt make a mistake and blow your amp up.

[Conrad Muzoora]

if you look at the chart at the top of that page on the qsc schematic it shows different terminals to connect the transformer wires to depending on input voltage. In 120v mode the split primaries on the transformers are connected in parallel, in 240v mode they are connected in series. Follow the chart and look at the schematic and you will see this. I dont know about the line filter, but it looks like those power resistors do need to be changed out though. I am guessing the 240v transformer p/n is 240v only and doesnt have the split primary winding. If doing any mod such as this first connect power with the transformer secondaries disconnected and measure voltage to make sure you didnt make a mistake and blow your amp up.

Thanks Todd,
This is so helpful. Now forthe crest, nobody seems to have any ideas, if i find no taps on the transformer, i will go on a hunt for a broken 240 volt Ca 18 and get a 240v transformer out to replace the 120v one on my new amp. I will have to be lucky because the original Ca18 seems to live for ever. There have been a lot of Ca 18 clones here that seem to die more often but am not sure if the power transformers would match. Well i guess i have to wait.
Conrad
www.kooleventug.com

[Marty McCann]

Hey Labsters,

Going back to good ol Heavy iron! I have made a purchase of the above amps, the qsc is replacing a plx 3602 on subs in my "B" rig (Mainly because the plx was very unforgiving on "Iffy" Power) and the CA 18 will replace my Crown MA9000i on my "A" rig because of recurrent breakdown of the crown. Now my problem is that these are american 120v models and i will be operating them on 240v. I therefore need advise on how i can convert these to run on 240v. The QSC has 2 transformers, and am considering connecting them in series if i do not find a 240v tap, but the crest has one transformer. Anyone ever attempted what am about to do? And would this reduce the performance if i did the mods?

Conrad
www.kooleventug.com

What you are not considering is that 60 Hz transformers will run hotter than a pistol when used at 50 Hz.  Also the charging rate at 50 Hz is 80% of that @ 60 Hz.

[Conrad Muzoora]

What you are not considering is that 60 Hz transformers will run hotter than a pistol when used at 50 Hz.  Also the charging rate at 50 Hz is 80% of that @ 60 Hz.

Hi Marty,

I have run the 120/60hz gear on 120/50hz line (After stepping down the voltage from 240v/50hz to 120) with no issues at all. Do you think this will become an issue when i convert the 120v models to 240v?
Conrad
www.kooleventug.com

[Todd Black]

What you are not considering is that 60 Hz transformers will run hotter than a pistol when used at 50 Hz.  Also the charging rate at 50 Hz is 80% of that @ 60 Hz.

the qsc amp is rated for use at 50/60hz -look at the specs

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