70V volume control on non 70v system

[Nic J]

Ok, I was attempting to install a volume control for a boat that I work on to control 2 zones, zone A: outer deck, zone B: dining deck

Both zones have 4 speakers attached to them and are essentially daisy chained together and each zone connected to 1 channel of a 2 channel 600w amp.

money is a little tight around the company and the only volume control knobs I have laying around came off of a boat that is running a 70V system, so the control knobs are ATLAS-35 brand/model. and they have 3 leads, a=com b=speaker in c=speaker out.

My question is, if I were to just hook this inline with my speaker system, leaving COM lead d/c and connecting the (+) lead from my amp, to speaker in on the volume control, then the speaker out on the volume control to 1 side of the (+) side of the speaker chain, and the (-) lead from amp directly to the (-) lead on the speaker chain. will this work for me?

What are the risks and any suggestions on a good course of action with nearly no funds to work with?

I'm VERY green when it comes to audio systems like this. any help is greatly appreciated. thank you in advance

 

[teqniqal]

This should work fine as long as the total speaker load for each zone does not exceed 35 Watts (the power limit of the autotransformer - you can also get 100 watt rated autotransformer type volume controls). If you know how the speakers are wired (series, parallel, both, etc.), and the impedance of each, you can calculate the net load impedance that each speaker run presents to the amplifier, and from that you can make a good approximation of the power draw. The amplifier you describe puts out about 50 volts. Basic Ohms' Law will get you there. Speakers in series / parallel are just like light bulbs in series / parallel.

Amplifiers are almost as cheap as autotransformer type volume controls, consider just buying another amplifier.

 

[David Ashton]

why do you want to fit this control?
why not control the input level with a $1 pot?
what is the output impedance of the amp?
what is the power rating and impedance of the speakers?
we need more information.

 

[FMEng]

I agree with David, control the level on the input side. What you propose might work, but if the speaker system is made up of 4, 8, or 16 ohm speakers, instead of ones with 70 V transformers, the volume control's autoformer is going to saturate from being loaded by the low impedance. That will increase distortion and reduce the low frequency response. If the application is paging, it might be good enough. Music could sound ugly.