Help Wiring Old 70 volt Amplifier to New Internet Radio (RCA type connector to screw terminals) - AVS Forum
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post #1 of 8 Old 01-16-2013, 07:12 PM - Thread Starter
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Sorry if this is in the wrong spot, but I need some help from the amplifier technical gurus.

Here is my situation. I've got an old Muzak sound system in my business, which I'm replacing with a SiriusXM TTR1D internet radio. I'd like to use the old existing amplifier which is already wired into the speakers, which is a 3M AT-30, 70 volt system. The audio output from the TTR1D radio is a simple 3.5 mm RCA, but all the input terminals on the back of the old amplifier are screw terminals. I guess what I'm asking is there a way to go from the 3.5 mm plug to 2 wire terminals on the back of the amplifier for the input signal?

Here is what the back of the amp looks like for the inputs. How to go from a 3.5 mm RCA plug to one of these connections, or is it possible?



Thanks!
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post #2 of 8 Old 01-16-2013, 07:20 PM
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I'd start with the "Music Hi-Z Unbal" connection. The shield would go to the screw with the ground symbol beneath it..

Problem is the radio is stereo so you need a mono summing adapter or if you can set the radio to operate in mono. A mono summing adapter can be built with a few resistors.



The two resistors drawn horizontal are 4.75K and the one drawn vertical is 200K. The exact values aren't particularly critical as long as the same approximate ratios are maintained and the two horizontal are the same as each other.

Instead of the phono plug on the right you'd just not have a plug there and connect the wires right to the amp.

Just because there is a knob doesn't mean you should turn it.
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post #3 of 8 Old 01-16-2013, 07:29 PM
 
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It would probably be easier just to replace with a newer 70 volt amp, that you can use a remote control or remote control pad, to adjust the volume. Plus it would have the proper inputs, so no hacking needing to create a special connector for it.
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post #4 of 8 Old 01-16-2013, 07:32 PM
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Hmmm...a new amp or $5 worth of parts and fifteen minutes?

It's not exactly a major hack job. It's a rather standard method.

Just because there is a knob doesn't mean you should turn it.
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post #5 of 8 Old 01-16-2013, 08:12 PM
 
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Quote:
Originally Posted by whoaru99 View Post

Hmmm...a new amp or $5 worth of parts and fifteen minutes?

It's not exactly a major hack job. It's a rather standard method.
If the person does not know what they are doing, they are going to have problems doing the "hack" job. Otherwise, newer amp, better features, and no having to home brew a cable to make it work.
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post #6 of 8 Old 01-16-2013, 09:45 PM
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What's not to know from post #2? It's only slightly harder than changing batteries in a flashlight.

Just because there is a knob doesn't mean you should turn it.
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post #7 of 8 Old 01-17-2013, 07:10 AM
 
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Quote:
Originally Posted by whoaru99 View Post

What's not to know from post #2? It's only slightly harder than changing batteries in a flashlight.
For a person that knows what they are doing, but you are talking about the possibility that the OP does not know enough about electronics, to make a test bench type adapter for their situation. Besides, with the Muzak amp being as old as it is, the capacitors are pretty much at their life expectancy, and bet if you cracked the case open, you can find signs of seepage from them.

Again, easier and best for the OP to just replace the old Muzak unit with a newer more modern 70v compatible amp or receiver, with the option of a aux input for external sound devices.
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post #8 of 8 Old 01-17-2013, 11:08 AM
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Give the fellow some credit. There is a picture and component values are given. It's drawn in a physical layout, you don't even need to understand a schematic.

I don't think the unit is as old as you think so the likelyhood of bad caps is pretty slim.

.

Just because there is a knob doesn't mean you should turn it.
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