Seeking advice on 100V systems

[dcp]

I am currently doing an install at a health club and am having great difficulty with adding a volume control to an existing 100v system.

The system is driven by a DSPPA MP-610P 250W Mixer/Amplifier. It has six 100V outputs of which five are currently used. Four of the five outputs each feed a pair of 10w JBL wall mounted speakers. (Not sure on model number)

Two of these feeds just run off the mixers volume outputs. Two of them need seperate wall mounted volume controls so the clients using those areas can adjust the volume if needed.

Now one area already had a volume control (made by Redback couldn't find a model number. Has four connectors: amp+, amp-, spk+, spk-). It only worked on full, that is to say that sound only came out of the speakers when the volume control was turned to it's maximum setting. I thought maybe it wasn't being fed enough signal from the amp so I turn up that channels output volume but this didn't make any difference.

Interestingly I detached this volume control and connected to the other pair that needed a volume control and it seems to work fine. When the volume is OFF there is no sound and gradually the volume increases as you click up through the 11 settings. There is quite a jump in volume going from just below max to max though.

Basically I do not understand why this is or why this volume control seems to work on one channel and not on the other. Both are coming from the same amp and the speakers and wiring are identical.

Is the volume control the correct kind?

Is it as simple as connecting the amp and speakers to the volume control or am I missing something?

Any advice or help is appreciated.

Also does anyone know of any good publications or sites that provide detailed information and instruction on 100V systems. I have done some searching but I can only find small teasing pieces here and there.

Thank you in advance.

Craig

[David Duffy]

Was it like this one?

 

It sounds like the original speaker it was hooked up to was not 100V, but an 8 Ohm type. That would explain the no sound until full on. Actually, there should have been a small amount of sound on the lower settings but you may not have heard it over the room noise?

 

You need to make sure you use 100V attenuators only on 100V lines. Same goes for 8 Ohm attenuators and low impedance lines.

[AndyL]

Was it like this one?

 

It sounds like the original speaker it was hooked up to was not 100V, but an 8 Ohm type.

 

Or may be a switchable type set to Low Z (i.e. 8ohm) or 'bypass' instead of the appropriate 100V tapping.

[dcp]

I have now discovered that your belief that the speakers are not 100V. They are in fact a pair of 8ohm JBL Control One speakers. The attenuator is a 40W 100v model. It is a Redback like your picture.

Is there something I can put in to the signal chain, either between the attenuator and the speakers or the amp and the attenuator, that will allow the attenuator to work properly?

Thank you for you help so far,

Craig

[david.elsbury]

You should be able to get a transformer that takes the 100v output, after the auttenuator, and drops down to 8R for the speakers.

[David Duffy]

Yes, a off-the-shelf 100V step down transformer will do the job. Here's a 40W one.