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Author Topic: home stereo in-wall volume controls  (Read 6370 times)

Craig Hauber

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home stereo in-wall volume controls
« on: April 15, 2008, 01:44:12 am »

I just "inherited" this mess of a restaurant job.  Apparently the GC did a turnkey build and handled all systems install under his umbrella.  Well that means the electrician wired in this fairly large BGM system in a rather screwed-up way.

There are 8 "Russound" transformer-type volume controls in the wall next to the bar.  They have a "L" & "R" input and a "L" and "R" output.  There is one ceiling speaker wired to each individual output on each volume control (16 total).  All the inputs are parallelled for each R & L input (8 "R" inputs on one channel of the amp and 8 "L" inputs on the other side of the amp)  The system just keeps killing amps and the only adjustment I can find is a "2x 4x 8x" switch on each volume control.  

Coming from a 70V mindset I am confused as to how these are meant to be used -and I am not getting alot of technical backup from the sales and installation literature.  Where should I set that switch and how many "watts" is the system (there are no transformers on the speakers) and I have no idea how to size an amp for this system.  (such as accidentally putting 200W worth of speakers on a 100W amp in a 70V type system.
The ceiling is mostly hard-lid and decorative wood so getting to the speakers is not easy.  Climbing through the t-grid in the kitchen I can get near one speaker and see that they have no back-boxes or transformers (just crossover circuit-board and cheesy gold-plated binding posts so they must be a consumer product.

The last amp to perish was a QSC RMX-2450, before that it was a peavey.  There are no shorts in the lines, yet at clip it is not very loud in the room (I've had louder with 4W tap Quams running on a 60W TOA)  It seemed to work fine when I test-fitted it with a PLX-3402, but at 1100W-per-ch I thought that was ridiculous for a BGM system

So I need to fix this for my client -any recommendations (I was considering retro-fitting the system with 70V transformers and attenuators and using a QSC CX-series amp) -They do want to add more zones and more speakers and are fed-up with having to adjust 4 volume controls just to turn down the dining room!

Any home installers with advice would be appreciated.

Thanks
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Craig Hauber
CSA Productions Inc.
Ventura-Santa Barbara CA
www.csaproductionsinc.com

Karl P(eterson)

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Re: home stereo in-wall volume controls
« Reply #1 on: April 15, 2008, 11:17:24 am »

I have dealt with inherited systems like these. The problem you have is ultra low ohm-age on the amps that are killing them.

Go pickup a QSC CX168 - http://www.qscaudio.com/products/amps/cx/cx8/cx8.htm

Put two (2) speakers on each channel (take 4 channels for the L and 4 for the R)

Parallel the inputs, and ride off to happiness.

Karl P
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Hal Bissinger/COMSYSTEC

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Re: home stereo in-wall volume controls
« Reply #2 on: April 15, 2008, 12:57:58 pm »

Maybe that's why I saw over 8000 watts used in a dentist's office for BGM once.

You can tell when a BGM system was installed by a hack or DIY when you have ceiling speakers arranged for stereo. How many speakers are we talking about is it 16 or 32? I won't even bother wasting my time. You can usually find a JBL or other 70v speaker that will fit in the same size hole and the wiring is already there. Get something like an 80W Crown 180MA and it will be done right.

-Hal

Jason Lavoie

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Re: home stereo in-wall volume controls
« Reply #3 on: April 15, 2008, 10:48:24 pm »

if there is even a HINT of wanting to add more speakers in the future, then you really have to convert it to 70V


Jason
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Jerry Turnbow

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Re: home stereo in-wall volume controls
« Reply #4 on: April 15, 2008, 11:52:51 pm »

Craig -

I'm like you;  When I worked for a systems contractor, we dealt with 25 volt lines for schools, healthcare, 70.7 volt lines for other stuff, and even 200 volt line for large industrial facilities, where there was a speaker tapped for the wattage of the device.

I just stumbled across the same type of thing you describe while working on a system at a local church.  Different brands, but same concept, where the transformer is in the volume control (or two for stereo operation), and there's a ratio setting that basically mulitiplies the speaker impedance by a factor of 1, 2, 4, or 8.  It's a different way of thinking about it, requiring you to "do the math" using Ohm's law to get to the total load and ensure it doesn't drop below the amplifiers minimum rating.

There's a good tech sheet on Atlas-Soundolier's version of this approach here:

http://www.atlassound.com/support/SLSheets/SL4.1570.PDF

Good luck!

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Hal Bissinger/COMSYSTEC

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Re: home stereo in-wall volume controls
« Reply #5 on: April 16, 2008, 03:53:12 pm »

In my opinion such "speaker matching devices" are amateur and have no place in a commercial venue. Their only application is with consumer equipment to allow the connection of a limited mumber of speakers beyond what the equipment was designed for. Since most incorporate transformers they offer no advantage over a system that locates the transformer at the speaker and an amplifier designed to work with a constant voltage system. As a matter of fact there is usually a considerable cost savings over high markup home stereo equipment.

-Hal

Charlie Zureki

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Re: home stereo in-wall volume controls
« Reply #6 on: April 17, 2008, 08:52:15 am »

  The Problem is probably mis-matching of Equipment.  The Volume controls you speak of are for speakers that are rated 4/8/or 16 ohns.  Check the speakers and be certain they do not have transformers (70/100) volt.

 If the Outputs of the Amp are 4/8/16 ohm and the speakers are 4/8/16 ohm (no transformers), then you are using one amp to Power 8 speakers per channel! which, loads the amp down and brings the  Speaker Impedance too low for the Amp. (using the quantity of Volume control you're using)

 Using the Equipment you already have. The Pin jumpers must be set properly. Based on the Information Given All jumpers must be set to 8x on All Volume Controls.

 Make Certain that all Volume control INPUTS are wired in Parallel from the Amps Output
 The Speaker wiring should be of atleast 16 gauge. Make Certain the Amp has enough power for all of the speakers. Add the wattages of each speaker leg eg. ( 8 x 60= 480 watts)

 Disconnect and check each speaker direct run with an ohm meter
to varifiy each speaker is still good, before proceeding.
 
 Hammer
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Craig Hauber

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Re: home stereo in-wall volume controls
« Reply #7 on: April 17, 2008, 01:58:35 pm »

Since every speaker has an individual 12ga home-run to the cabinet with the volume controls, could I just put 70V speaker transformers in that cabinet instead of at the speaker itself?  and then use 100W attenuators per zone instead of the 8-ohm units

Changing the speakers is out of the question.  Custom Faux-painting of the ceiling plus the need for scaffold over booths would make it almost impossible

70V would allow me to add the future speakers without needing additional amplifiers as well as being able to compensate for ceiling height by tapping some of the speakers quieter within the same zone.

So is this at all possible?  does 75' of 12ga between the transformer and the speaker effect 70V calculations enough to matter?

Thanks for the advice.




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Craig Hauber
CSA Productions Inc.
Ventura-Santa Barbara CA
www.csaproductionsinc.com

Karl P(eterson)

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Re: home stereo in-wall volume controls
« Reply #8 on: April 17, 2008, 03:01:41 pm »

If you have home run 12ga, why not just continue to use the volume attenuators as-is with a multichannel amp? I understand it isn't the "ideal system" but it should work just fine.

Alternatively you could pull the attenuators out altogether and use something like an ashly vcm module and controller to do the attenuation on the line level side with a multichannel amp driving the speakers direct.

While it isn't the most ideal solution, it is a valid one and small non-70v BGM systems are done this way all the time. I would certainly (personally) avoid filling a cabinet full of 70v transformers just because I could.

Karl P
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Craig Hauber

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Re: home stereo in-wall volume controls
« Reply #9 on: April 17, 2008, 07:00:47 pm »

They already have around $600 invested in the amplifier.  They don't have any budget for the 1000+ it would take for a new amp (CX-series 8ch) AND it won't solve thier 4-knob to-turn-down-1-zone problem, AND I would still have to buy another 70V amp for the 8 more speakers I'm adding for a new bar and cabana patio outside.

I'm thinking of a 200 dollar soulution (70V xfrms and attenuators) instead of another $2000 -which I would rather they spend on the projector I'm installing.

My plan was to do an even trade, thier most recent-replaced RMX-2450 for a new EV PA2400T.  I'm doing a private-dining conference room install for them so I want to keep them going on thier audio-needs as well but without digging into my own pockets.

Thanks
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Craig Hauber
CSA Productions Inc.
Ventura-Santa Barbara CA
www.csaproductionsinc.com
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