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Discussion Starter · #1 ·
My house was previously wired up with an older 70v system (speaker in each room in the ceiling with a volume control in the wall). Each rooms wiring comes back to a panel with plug-jacks in a closet in the main area. I attached an image below.


I was wanting to get a basic amp that I could just plugin the output of it into whichever room I wanted sound. (i.e. something to convert my stereo output to a 70v system signal) The system is all mono, so its just for background music, really.


Anyone have any ideas? (I am not an audiophile by any means, just a guy trying to make it work
)

 

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One way is to get a large capacity 70 volt matching transformer and hook it up backward s to your existing amp. In other words, the 8 ohm output taps (common and hot leg) from the transformer output is connected to the small amp output. The 70 volt INPUT taps to the transformer are connected to you existing 70 inputs in each room.


These transformers come with multiple taps on the output. They will be marked in watts. This is the determining factor for your hookup. Whatever the output rating of your amp is, connect it to the closest wattage taps on the transformer. All the unused taps should be individually taped if they are wires or covered with tape if they are solder lugs.


These transformers are available up to about 50 watts output in their original design configuration. It is always a good idea when doing this to use a larger than necessary transformer as the "output". You will not get quite the same output power doing this as when the original amp actually has a 70 transformer output.


These transformers are available from Digikey, Allied, Mouser and many other electronic suppliers.
 

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Heck, a big modern amplifier could drive a 70V system pretty loud without a matching output transformer. After all 70V RMS into 16 Ohm's is 300 Watts.
 

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If there's a gain control in each room, are you sure this is a passive system? IE, are you sure that each speaker is not already powered? If the patch panel accepts line level inputs, you don't need an amp at all, just feed the output from the stereo directly to whichever room you want.
 

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Discussion Starter · #7 ·
That's a good question!



The volume controls are older model "Soundolier" (now Atlas) AT10 's, which according to their tech support are a 10 watt, mono, 70 volt model. The speakers also have a transformer on them, but I don't have the details...though they look like these:

Atlas Speakers


I can get more information on them tonight, as I have 2 that are not connected anymore from the basement.


Unfortunately, this does not mean a whole lot to me



The patch panel is just a homemade cabinet dor with some connectors in it, and the wires to the back of the connectors. I am pretty sure nothing is "powered" already, but I could be wrong.
 

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Discussion Starter · #9 ·
OK, I will try, but this is what I got from tech support at Atlas a little while ago, which is why I was asking about the Amp:


"I assume your Stereo only has 8 or 4 Ohm output . .. and therefore NOT compatible with a 70 volt system. Our AT10 volume controls are intended for a 70 volt system. Let's determine if your speakers actually HAVE a transformer on them. If they DO .. your Stereo will NOT be compatible. You'll need an amp with a 70 volt speaker output"
 

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Quote:
Originally Posted by netmatt /forum/post/16909271


OK, I will try, but this is what I got from tech support at Atlas a little while ago, which is why I was asking about the Amp:


"I assume your Stereo only has 8 or 4 Ohm output . .. and therefore NOT compatible with a 70 volt system. Our AT10 volume controls are intended for a 70 volt system. Let's determine if your speakers actually HAVE a transformer on them. If they DO .. your Stereo will NOT be compatible. You'll need an amp with a 70 volt speaker output"

Yeah, so what they're telling you is that the attenuator is designed to be used with a line level input upstream and a 70v transformer downstream. Also, the pro line level is different from a consumer line level (-4db vs -10db).
 

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Discussion Starter · #12 ·
OK, so I think I am back to my original questions on this, but now based on using a step-up transformer in the diagram below:


1) If I use a Step-up transformer between stereo and the volume controls (AT10), does my Stereo amp output need to be a certain "power"?


2) Are any of the links below the right type of "part" for this application (i.e. step-up transformer) If not, is there an example part you can point me to?


Link 1: Parts Express Transformer

Link 2: MCM Transformer

Link 3: Frye's Transformer


3) (sorry for the dumb question) Once I get it, I assume I connect an "audio out" from the stereo, and not a "speaker out"? Is that right?

 

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1) It doesn't matter as long as you can output 10watts from the stereo amp. The attenuators can't take any more power than that. You will, however, need an amp or an AVR. Line level outs from a pre/pro will not work.


2) I'd probably go for the cheapest one you can find. This is basically a multi-speaker mono PA system. You're simply not going to get any kind of high fidelity sound, so no reason no go breaking the bank for a fancy transformer with a large frequency response.


3) You would need to splice the speaker wire from the stereo amp into the transformer. So you would be using the "speaker out" or binding posts.
 

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Just get a 70 volt amp and be done with it instead of worrying about transformers, etc. Crown, QSC, Bogen all make commercial 70v distribution amps. Don't expect anything but Muzak quality but it will give you background sound.
 
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