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Author Topic: 70V system amp recommendation  (Read 4958 times)

Lee Buckalew

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Re: 70V system amp recommendation
« Reply #10 on: September 04, 2015, 09:08:31 pm »

It does not go into protect mode without the load. At first I assumed that it was a short in the system. To check that, I hooked up a single JBL cabinet. It went into protect mode right away.

I'm looking at the QSC CMX500va

http://qsc.com/products/Power_Amplifiers/Cmxa_Series/CMX_500Va/

Think that would work out well for me?

As long as you only need 1 channel.

You said earlier that the CE1000 was driven as 2 channels into 2 transformers.  The CMX500VA will only give you 1 - 70 volt output of 1200 watts. 
If you need the two channels at 70 volts you could use two amps (either the CMX300VA or the CMX500VA) that need to be bridged to drive 70 volt loads or step up to a single CMX800VA or CMX2000VA since they will each drive 2 channels at 70 volts.

Lee
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Mac Kerr

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Re: 70V system amp recommendation
« Reply #11 on: September 04, 2015, 09:39:35 pm »

As long as you only need 1 channel.

You said earlier that the CE1000 was driven as 2 channels into 2 transformers.  The CMX500VA will only give you 1 - 70 volt output of 1200 watts. 
If you need the two channels at 70 volts you could use two amps (either the CMX300VA or the CMX500VA) that need to be bridged to drive 70 volt loads or step up to a single CMX800VA or CMX2000VA since they will each drive 2 channels at 70 volts.

Lee

He has the transformers, he doesn't need to make the amp transformerless on the output, although if the total power is high, getting rid of the transformers may be a good idea as they will saturate just like the ones on the speakers.

Knowing how many speakers are on each channel, and what they are tapped at would help make this an informed recommendation.

Mac
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Lee Buckalew

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Re: 70V system amp recommendation
« Reply #12 on: September 04, 2015, 10:04:51 pm »

He has the transformers, he doesn't need to make the amp transformerless on the output, although if the total power is high, getting rid of the transformers may be a good idea as they will saturate just like the ones on the speakers.

Knowing how many speakers are on each channel, and what they are tapped at would help make this an informed recommendation.

Mac

True.  He does not need to use the amp in a 70 volt mode if he uses the existing transformers.  In that case the CMX500VA is slightly smaller than the CE1000.  The CMX500VA may not be large enough if the CE1000 was borderline.

Check all taps if they are accessible and add them up.  Industry best practices is to size the amp at 1.5x the total of all the tap ratings.  At a bare minimum the amp should be sized at 1.1x the tap rating.

Lee
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John L Nobile

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Re: 70V system amp recommendation
« Reply #13 on: September 05, 2015, 12:09:31 am »

There's a lot of speakers on the system. The system was professionally installed years ago. I had nothing to do with it and there's no paperwork. I can count speakers but since it's worked for probably over 10 years, I'm going to assume that an amp with the same specs as the CE1000 will do the job. I'll spec out the larger QSC amp.
Or I might look at Ashley as suggested above. Istill have a bunch of 25 year old FET 2000 and 1000 amps that worked flawlessly until I retired them last year. Hopefully the new ones have kept that quality. 
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Lee Buckalew

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Re: 70V system amp recommendation
« Reply #14 on: September 05, 2015, 07:03:27 am »

There's a lot of speakers on the system. The system was professionally installed years ago. I had nothing to do with it and there's no paperwork. I can count speakers but since it's worked for probably over 10 years, I'm going to assume that an amp with the same specs as the CE1000 will do the job. I'll spec out the larger QSC amp.
Or I might look at Ashley as suggested above. Istill have a bunch of 25 year old FET 2000 and 1000 amps that worked flawlessly until I retired them last year. Hopefully the new ones have kept that quality.

If you don't check the speakers to see how they are tapped then use an amp that is the same size or larger than the CE1000 it is replacing.  That's the simplest way to know your not too small.

Lee
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John Roberts {JR}

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Re: 70V system amp recommendation
« Reply #15 on: September 05, 2015, 11:23:51 am »

While lots of good general advice for engineering a constant voltage system, if it ain't broke don't fix it.

The general advice to throw a higher power amp at it makes sense for upgrading a 70V amp with another 70V amp since they make the same output voltage and the higher power version just provides more current. but... when swapping a 4/8 ohm amp with a higher power 4/8 ohm amp you get more voltage and more current, so the old step up transformer interface may no longer deliver the correct normalized 70v.

As I already posted, replace the CE1000 with a modern amp that makes similar output voltage. If you are dying to re-engineer this, try to get a spec sheet for the 70v transformer to confirm input side drive voltage expectation.

JR
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John L Nobile

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Re: 70V system amp recommendation
« Reply #16 on: September 05, 2015, 05:20:59 pm »

While lots of good general advice for engineering a constant voltage system, if it ain't broke don't fix it.

The general advice to throw a higher power amp at it makes sense for upgrading a 70V amp with another 70V amp since they make the same output voltage and the higher power version just provides more current. but... when swapping a 4/8 ohm amp with a higher power 4/8 ohm amp you get more voltage and more current, so the old step up transformer interface may no longer deliver the correct normalized 70v.

As I already posted, replace the CE1000 with a modern amp that makes similar output voltage. If you are dying to re-engineer this, try to get a spec sheet for the 70v transformer to confirm input side drive voltage expectation.

JR

I'm going for the easiest solution. I'll look up the specs on the CE1000 and get a similar QSC or Ashley amp. The CE1000 that was repaired is chugging along just fine. I don't trust it though and it was a backup amp for the show. I think I'll leave the CE1000 in there and use whatever we buy as a backup.
Thanks for the help guys. I know 70 volt systems aren't that complicated but it's an area I've never dealt with. And I would have preferred to keep it that way. I've got so much on my plate lately and I don't want a bigger one.
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Hal Bissinger/COMSYSTEC

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Re: 70V system amp recommendation
« Reply #17 on: September 05, 2015, 07:59:43 pm »

It does not go into protect mode without the load. At first I assumed that it was a short in the system. To check that, I hooked up a single JBL cabinet. It went into protect mode right away.

I'm looking at the QSC CMX500va

http://qsc.com/products/Power_Amplifiers/Cmxa_Series/CMX_500Va/

Think that would work out well for me?

I would really like to see you do an analysis of the existing speakers first to determine what the actual load is and if there are any problems. The fact that there were five amps makes me wonder- were they there for zoning or was the power needed?

-Hal
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John L Nobile

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Re: 70V system amp recommendation
« Reply #18 on: September 05, 2015, 10:28:29 pm »

I would really like to see you do an analysis of the existing speakers first to determine what the actual load is and if there are any problems. The fact that there were five amps makes me wonder- were they there for zoning or was the power needed?

-Hal

The 5 amps were leftovers from the old system. The main ballroom got new amps for PA ceiling system. It's horrible and less than useless. I've turned the amps off to  save power.  I'm guessing that the installers figured the 2 working CE1000s were good enough for background music.
I'm not qualified or have the time to do a system analysis. And now that it's working, I doubt management would want to spend the money to get someone up to do that. But that is a great idea. If it does fail again though, I will be calling in the pros. If I can find one.
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Re: 70V system amp recommendation
« Reply #18 on: September 05, 2015, 10:28:29 pm »


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