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Author Topic: 70V system amp recommendation  (Read 4966 times)

John L Nobile

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70V system amp recommendation
« on: September 04, 2015, 12:02:53 pm »

Our Crown CE1000 has gone into constant protect mode. I had a spare that was repaired a while back but I'd like to order something a little newer for a more permanent solution. It drives a 70V system with speakers all over the hotel and has been working fine for years.

I have absolutely zero experience with 70V systems and after figuring out where all the wiring was ending up, I was surprised to find only 1 amp driving all those speakers. 4 zones covering a large restaurant, a bar, 2 hallways and the main lobby.

What amps have you had good results from? I'd like something with terminal strips for inputs and I have some terminal strip to Speakon adapters from the current system.

Thanks
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Lee Buckalew

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Re: 70V system amp recommendation
« Reply #1 on: September 04, 2015, 12:09:50 pm »

Our Crown CE1000 has gone into constant protect mode. I had a spare that was repaired a while back but I'd like to order something a little newer for a more permanent solution. It drives a 70V system with speakers all over the hotel and has been working fine for years.

I have absolutely zero experience with 70V systems and after figuring out where all the wiring was ending up, I was surprised to find only 1 amp driving all those speakers. 4 zones covering a large restaurant, a bar, 2 hallways and the main lobby.

What amps have you had good results from? I'd like something with terminal strips for inputs and I have some terminal strip to Speakon adapters from the current system.

Thanks

John,
I have had great results from QSC CMX series.  Very cost effective and have been bulletproof.
Look at the series carefully as the smaller models must be operated in bridged mode for 70 volt operation (meaning they are also single channel at that point).

There are many other very solid choices, these have just become my go to, no frills amps that are cost effective and do what they claim.

Lee
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John Roberts {JR}

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Re: 70V system amp recommendation
« Reply #2 on: September 04, 2015, 01:02:26 pm »

Literally anything but a CE1000...   ;D

There are a number of serious companies making professional 70V amps.

Did the CE1000 have an external step up transformer? Or drive output bridged?

JR
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John L Nobile

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Re: 70V system amp recommendation
« Reply #3 on: September 04, 2015, 01:10:24 pm »

Literally anything but a CE1000...   ;D

There are a number of serious companies making professional 70V amps.

Did the CE1000 have an external step up transformer? Or drive output bridged?

JR

It was driven stereo into 2 external transformers.

I see why you said anything but. There used to be 5 CE1000's in the rack. I gave 3 to a buddy and he got them repaired and the one left as backup didn't work wither. 5 out of 5 went down.  The one I have working now is one that my buddy had repaired.
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John L Nobile

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Re: 70V system amp recommendation
« Reply #4 on: September 04, 2015, 01:11:43 pm »

John,
I have had great results from QSC CMX series.  Very cost effective and have been bulletproof.
Look at the series carefully as the smaller models must be operated in bridged mode for 70 volt operation (meaning they are also single channel at that point).

There are many other very solid choices, these have just become my go to, no frills amps that are cost effective and do what they claim.

Lee

Thanks Lee. I'm going to look at those right now.
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Scott Carneval

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Re: 70V system amp recommendation
« Reply #5 on: September 04, 2015, 03:19:33 pm »

Our Crown CE1000 has gone into constant protect mode. I had a spare that was repaired a while back but I'd like to order something a little newer for a more permanent solution. It drives a 70V system with speakers all over the hotel and has been working fine for years.

I have absolutely zero experience with 70V systems and after figuring out where all the wiring was ending up, I was surprised to find only 1 amp driving all those speakers. 4 zones covering a large restaurant, a bar, 2 hallways and the main lobby.

What amps have you had good results from? I'd like something with terminal strips for inputs and I have some terminal strip to Speakon adapters from the current system.

Thanks

QSC makes a great amp.  So does Ashly Audio.  Unless you have an impedance meter (different than a multimeter) you won't be able to calculate the load that this amp is currently driving.  So just make sure you get something as big or bigger than the current amp.
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Lee Buckalew

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Re: 70V system amp recommendation
« Reply #6 on: September 04, 2015, 03:37:40 pm »

QSC makes a great amp.  So does Ashly Audio.  Unless you have an impedance meter (different than a multimeter) you won't be able to calculate the load that this amp is currently driving.  So just make sure you get something as big or bigger than the current amp.

I'll also second Scott's comments on Ashly.  Great amps and a very responsive company especially regarding tech questions.  Ashly has become an entry price go to with built in DSP (they offer non-DSP versions as well).  Very capable. 

Lee

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David Buckley

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Re: 70V system amp recommendation
« Reply #7 on: September 04, 2015, 03:49:10 pm »

There is essentially three ways of doing 70V systems, buying an old-school "public address" style amplifier that says "70V out",  usually from a manufacturer that rock and roll and theatre types wouldn't recognise as a mainstream name.  Then there is a "normal" amplifier with a common name in these parts, with an external transformer to convert 4 ohm to 70V.  Thirdly, a "normal" amplifier that can deliver a bit over 1200W into 4 ohms is producing an output of 70V directly, and this can drive a 70V line directly.

To decide, figure out how much power you need, which is the sum of the selected output of all the speakers.  Most 70V speakers are settable as to their power output, with "taps" usually something like 0.5W, 1W, 2W, 4W.  Add it up.

Then determine the costs of each of the options.  As the power goes up, the third option usually becomes cost very effective. 

Note that if one chooses the third way, the actual output power of the amp is determined by the load; the signal lamps on the amp might be showing full output just under clip, but the power is determine by the load.  If there is only 100W of speaker load connected, then that is what the amp is delivering, even though the blinkienlitz look like that 1500W amp is running at full tilt.

As a final note, some 70V systems are part of a fire alerting systems; do not tool with these, they need specialist equipment which is monitoring the integrity of the system.

For non-USA folks, exactly the same applies to 100V systems, only the third option needs an amp of about 2500W into 4 ohms.
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John Roberts {JR}

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Re: 70V system amp recommendation
« Reply #8 on: September 04, 2015, 04:34:35 pm »

I forgot the obvious question.. does the CE1000 stay in protect mode, when the load is removed?

It sounds like the CE1000 was working for years (remarkable enough), and he already has 70V transformers, so I would just look for a new general purpose amp that doesn't suck.

I would look for something with similar power to the CE1000 (at the impedance tap it is driving the 70V transformer), and better yet with a built-in HPF (70V systems don't like bass).

JR
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John L Nobile

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Re: 70V system amp recommendation
« Reply #9 on: September 04, 2015, 07:01:29 pm »

I forgot the obvious question.. does the CE1000 stay in protect mode, when the load is removed?

It sounds like the CE1000 was working for years (remarkable enough), and he already has 70V transformers, so I would just look for a new general purpose amp that doesn't suck.

I would look for something with similar power to the CE1000 (at the impedance tap it is driving the 70V transformer), and better yet with a built-in HPF (70V systems don't like bass).

JR

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?
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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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