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[John Roberts {JR}]

Maybe I am missing something.  QSC CX series 70v amp 400w is $1770 MAP.  QSC RMX series 400-500w (depending on preferred rating) @ 8 ohm is only $750 MAP.
Granted, as the number of speakers added increases, the 70v amp's cost per speaker goes down.  If using many low wattage ceiling speakers the 70v can work out really cheap.  If using 100w taps on larger format speakers the 70v is really expensive.

400W is relatively large for a 70V amp... I think the largest install amp I recall was 300W (and mono). A 100W tap on a 70V line sounds a little loud to me. For larger than a few hundred watts we would just use a conventional amp.

FWIW the RMX series is a value (cheap) amp series.  I looked at the CX series and did not see a 400W 70V model... in fact most of the CX amps were stereo low Z, and the 70V amps had hooks for computer control (not-cheap amps).

Maybe look at basic install amps from an install manufacturer, while it appears QSC has models intended for that market. 

JR 

[David Allred]

400W is relatively large for a 70V amp... I think the largest install amp I recall was 300W (and mono). A 100W tap on a 70V line sounds a little loud to me. For larger than a few hundred watts we would just use a conventional amp.

FWIW the RMX series is a value (cheap) amp series.  I looked at the CX series and did not see a 400W 70V model... in fact most of the CX amps were stereo low Z, and the 70V amps had hooks for computer control (not-cheap amps).

Maybe look at basic install amps from an install manufacturer, while it appears QSC has models intended for that market. 

JR

CX602V is the amp.  I was basing the power needed on larger speakers covering larger areas in a foreground music situation.  85-95 db required

[Luke Robinson]

CX602V is the amp.  I was basing the power needed on larger speakers covering larger areas in a foreground music situation.  85-95 db required

Look at the CMX series from QSC it is a much more affordable 70v amp

[Mark Wilkinson]

To expand on Ivan's comment, just make sure you have an amp capable of 600W into an 8Ω load. When you have close to 600W of 70V speakers on the amp you can start worrying about more amps.

Mac

I recently tried a 400W into 8ohm amp, on some 70V speakers with taps that added to about 220watts.
I was wanting to see if less than 70^2 / 8 would work...
It didn't, too under powered....by more than i expected

[Robert Healey]

Maybe I am missing something.  QSC CX series 70v amp 400w is $1770 MAP.  QSC RMX series 400-500w (depending on preferred rating) @ 8 ohm is only $750 MAP.
Granted, as the number of speakers added increases, the 70v amp's cost per speaker goes down.  If using many low wattage ceiling speakers the 70v can work out really cheap.  If using 100w taps on larger format speakers the 70v is really expensive.

In QSC world, CX install series = PLX and PL3 portable series. CMX install series = RMX portable series. The ISA series is also cost effective 70V amps.

[Mac Kerr]

Maybe I am missing something.  QSC CX series 70v amp 400w is $1770 MAP.  QSC RMX series 400-500w (depending on preferred rating) @ 8 ohm is only $750 MAP.
Granted, as the number of speakers added increases, the 70v amp's cost per speaker goes down.  If using many low wattage ceiling speakers the 70v can work out really cheap.  If using 100w taps on larger format speakers the 70v is really expensive.

If you're using 100W taps you probably don't want to use a 70V system. If you want that much power to each speaker you are better off will regular 8Ω speakers. You can use any amp, and you don't have that extra transformer to cut the low end.

If you want a lot of low power speakers all paralleled together 70V is the way to go, but you don't need a special 70V amp, a 600W into 8Ω amp will be fine.

Mac

[Stephen Kirby]

CX602V is the amp.  I was basing the power needed on larger speakers covering larger areas in a foreground music situation.  85-95 db required

That's not a job for a 70v system.  Those are mainly used for distributed background music and paging.  If you need 95dB somewhere with music playing then you are talking about a fairly decent normal PA or the sort of thing used in loud restaurants.  That might be an application for medium sized powered speakers depending on distance from an amplifier closet.  You can also use a companion 70v system to pipe sound into halls and auxiliary rooms as required.

[John Roberts {JR}]

If you're using 100W taps you probably don't want to use a 70V system. If you want that much power to each speaker you are better off will regular 8Ω speakers. You can use any amp, and you don't have that extra transformer to cut the low end.

If you want a lot of low power speakers all paralleled together 70V is the way to go, but you don't need a special 70V amp, a 600W into 8Ω amp will be fine.

Mac

like button?

[David Allred]

 but you don't need a special 70V amp, a 600W into 8Ω amp will be fine.

Mac

But the amp has to push 70V for the system to be "stable".  In other word, the volume HAS to be controlled post amp?  Not by a mixer or by the amp?

Are there any problems (for the 70V speaker system) if the amp is driven beyond 70V?  Thereby allowing a min-max by the system controller for volume adjustments.

[Ivan Beaver]

But the amp has to push 70V for the system to be "stable".  In other word, the volume HAS to be controlled post amp?  Not by a mixer or by the amp?

Are there any problems (for the 70V speaker system) if the amp is driven beyond 70V?  Thereby allowing a min-max by the system controller for volume adjustments.

NO.

The voltage is not "constant" as in you will read 70V if nothing is going on.\

You can turn it up or down as needed up stream.

It is simply a typical musical signal that when the voltage is at 70V (70.7V to be exact) the loudspeaker will be delivering the rated tap wattage (give or take a bunch for impedance) to the loudspeaker.

If you drive it to more than 70V, you risk having the amp clip or saturating the transformers on the speaker end.

What really surprises me is that a system that is sooooo simple (70V) causes so much confusion.

All it is is a high impedance transfer system.

Just like the high voltage lines coming to outside your house.

If the impedance is higher-there is less loss across the lines-just like regular loudspeakers.  And since the impedance is high-you can hook up a lot of speakers by simply adding the wattages (and allowing 10% for "fluff") and have them run at different levels easily if you want by changing the taps.

There is a transformer at your house that steps it down for the house to use.

The speaker is "your house".

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