ECN Forum Forums General Topics of the Trade Voice - Data - Video Discussion 70v speakers

I have a 70v speaker system. It is fed with a speco PA amplifer 120w. Can I connect a standard stereo receiver with a 100 c changer to this?

It depends on what you mean.

A standard reciver will not drive these speakers directly, at least not well or for long.

If you mean you already have a working system yes you could patch in standard componants.

Your PA amp should have some aux inputs that take phono plugs.

Go from 'tape out' (or any low level outputs the reciver has) on your standard stereo receiver to the AUX input of the PA amp.

You may want to buy a 'Y' adapter so you can feed both left and right chanels into the mono PA amp.

If I understand your question you want to disconnect the PA amp (I HOPE you want to disconnect the amp) and try to drive the speaker system with the speaker outputs of a receiver that is designed for 4 to 8 ohm speakers.

A 70 volt system is intended to be driven by an amplifier with a 70 volt output which is what that PA amp has. You can use the receiver but I doubt you will be able to get sufficient volume before it starts clipping and other nasty things. You also have the problem of combining the two output channels into mono. If there is a stereo/mono switch use it, but I haven't seen one in 30 years. I don't think there is any consumer amplifier that would take kindly to the outputs being tied together so if you are going to try it use only the left or the right, NOT both!

As Iwire says, the proper way to do this is to take a line level output from the receiver and input it to the PA amp.

You are still going to have the problem of combining the two channels into mono. Using a "Y" cable may actually cause damage to the output devices feeding the jacks. Proper way is to combine each channel through something like 1K resistors.

-Hal

I guess I should clarify:
The application is to provide back ground music in a "medi-spa", which does laser hair removal etc.
We installed speco 70v speakers. We ran all the wiring, installed volume contols etc. An audio guy was to install and provide the equipment (amp, tuner,cd etc). The owner wants me to supply the equipment.

I purchased a PBM-120 Speco Technologies PA Background Sound Amplifier. It can have 3 microphone inputs or 3 inputs which look like RCA jacks. I know I can connect the cd player, but am unsure of the receiver. Maybe I should have gotten a tuner instead of the receiver to get the low level input?
ps. I am an electrical contractor in central NJ. The owner is my wife's boss and though I am being well paid for the job I am being "forced' to do the audio.

Yes, a tuner would be better for the purpose than a receiver. However, some receivers have line-level outputs in addition to the speaker outputs; if yours has these, then you can use these to connect to the PA amplifier. The receiver's amplifier isn't used, so it's kind of "wasteful" in the sense that you're throwing away the most expensive part of the receiver. Production volumes being what they are, though, it could be that a suitable receiver is less costly than a tuner. (That is, tuners tend to be a high-end "niche" item, and that is reflected in the price tag.)

I agree that you shouldn't use a "Y" to connect the line-level outputs together. 1K in series with each side is about the right range.

[This message has been edited by SolarPowered (edited 01-18-2005).]

I looked at the manual for your PBM-120 and you won't have to worry about "Y" cables or combining the inputs. Each aux. input has two jacks for a stereo input so combining the inputs has been taken care of. Just make sure that you move the input selector slide switch on the back next to the inputs you are using to the left for "AUX". This activates the RCA jacks and the line level input for that channel.

Just connect the outputs from your CD player to the aux-1 inputs. No problem there.

As to the receiver, yes you should have gotten a tuner if all you want is FM reception. Can you return it? Since you are using Speco consider the P-FA tuner.

What receiver is it that you have? If I can have a look at it I could see if there is a way to use it.

-Hal

By the way, since the subject of this thread is "70 volt speakers" I'm going to throw this information in here for anybody that is interested in learning what constant voltage and distributed sound is about.
http://www.rane.com/note136.html

-Hal

Keep in mind that the receiver may have line-level outputs which are not specifically labeled as such. See if it has TAPE OUT or TAPE RECORD jacks.

Thanks for all the info!
I don't know what receiver he purchased. It will be delivered tommorrow.

I'd often wondered why the U.S. used 70V lines instead of the 100V systems we use in this part of the world.

You learn something every day.

radio is not royalty free you must be an ascap member to rebroadcast radio!!!

Good point PBXtech. Most people don't know this and even as a contractor for the customer they put themselves or their company at risk for legal action from the music industry that we all know is on a witch hunt lately.

If a business uses ANY music they must pay royalties to BMI, ASCAP and SESAC. Yes ALL three and they do monitor using "mystery shoppers".

The only way around this is to use a music service such as Muzak and DMX that incorporate the fees into what you pay. XM and Sirius also have commercial rates that work the same way.

-Hal

IBM got in a different kind of trouble because of this. The ROLM tech was playing with the radio in his gear while he was installing the PBX and went off leaving it running. Well it turns out that was being ported to "music on hold".

As is their custom, 96 K-Rock in Ft Myers plays Jimmy Buffett - "Why don't we get drunk ..." every friday at 5 PM. A customer, who was trying to reach his rep, was not happy with the choice of music.

If a business uses ANY music they must pay royalties to BMI, ASCAP and SESAC. Yes ALL three and they do monitor using "mystery shoppers".

Out of curiosity, where does the line of what "uses" is get drawn?
If the wholesale house has a radio on in the morning when customers are getting their orders is that a violation?

If a crew shows up on a rough wire and turns on the DeWalt job radio is that a no-no.

For that matter if I'm on job by myself listening to a broadcast an I doing wrong because I'm there in a commercial capacity? What if other trades are there and can hear it?

It seems a bit silly since anyone I've mentioned can simply tune in for free providing they brought their radio.
The real problem is getting everyone to agree on a station.

Out of curiosity, where does the line of what "uses" is get drawn?

That determination as well as the cost depends on several factors. Whether or not the venue is a business and it's type, how the music is distributed and who's control is it under.

For instance, if a radio or CD player is located on a shelf in a restaurant kitchen for the kitchen help to listen to it would not be subject to royalty fees. It's considered to be under the control of the people in the kitchen for their enjoyment. However, a CD player connected to speakers in the dining areas would be subject because the music is for the enjoyment of the customers and enhances the business. Fees are based on the square footage and number of speakers.

So, you have nothing to worry about with your boombox on the job site.

-Hal

The Rolm guys had their rack radio on in the telco room and it turned out, also "music on hold" on the switch. It was always on 96 K-ROCK (the Ft Myers version) There was some concerns about the ASCAP issue and the station format for a couple days but it all went away when a whizzed off customer got "why don't we get drunk and screw" at 5PM on Friday (the station's custom).
The radio got removed from the rack.

For future reference, all that PA amp is doing is sending it's output into an impedance matching transformer before sending it to the terminals on the outside of the box.

The actual amplifier inside is the same as a normal PA amp plus this transformer.

Add a transformer to the receiver, and suddenly it too can be a 70V line amplifier. Most cheap receivers these days are MUCH happier with 8 ohm loads (4 ohms may damage them or cause a shutdown), so be sure to get a transformer with an 8 ohm primary.

Stereo mixes are odd, most of the information is on the left channel for some reason. If you have a mono system, connect it to the left output. DO NOT attempt to bridge the output of a receiver, catastrophic damage to the output section may result. This is essentially a short and the protection circuit on most receivers will be blind to this type of fault. Most are only good for same channel lead to lead or lead to chassis ground shorts. Some sort of isolation is required and even then, with anything above line level (1-4V p-p), I wouldn't push your luck.

Radio Shack used to sell a 100W 70V line matching transformer for this purpose, but that was 10 years ago when the still sold replacement speakers during my grade school ultra cheap project days.... I miss the old RS.

Wait I take that back....who am I kidding.... I live 13 miles from the Mouser Electronics warehouse and I have a business account with them so I can do will call.... makes even RS in its heyday look silly and ridiculously expensive.

Radio Shack had stores in Britain too, although over here they went under the Tandy name. They might have been considered acceptable by the average consumer who just wanted to buy an RCA lead or something and didn't really know the true costs, but in "proper" electronics circles everybody knew that the prices were ridiculous.

They'd charge something stupid like 40 pence for two little 1/4-watt carbon resistors all done up in a plastic package, when you could buy the same resistors anywhere else loose out of the bin for about 2 pence each.

I've never seen a receiever that didn't have a TAPE OUT or TAPE REC. jack.

Of course, if it doesn't you could always get a line output converter (as used for car stereo amplifier installations) and connect that to the speaker level outputs to get a line level output.