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#159730 - 01/18/05 07:40 PM 70v speakers  
John in Jersey  Offline
Junior Member
Joined: Aug 2002
Posts: 7
somerset county, NJ,USA
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?


john

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#159731 - 01/18/05 08:00 PM Re: 70v speakers  
iwire  Offline
Moderator
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
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.


Bob Badger
Construction & Maintenance Electrician
Massachusetts

#159732 - 01/18/05 09:37 PM Re: 70v speakers  
hbiss  Offline
Member
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
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


#159733 - 01/18/05 11:10 PM Re: 70v speakers  
John in Jersey  Offline
Junior Member
Joined: Aug 2002
Posts: 7
somerset county, NJ,USA
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.


john

#159734 - 01/19/05 12:08 AM Re: 70v speakers  
SolarPowered  Offline
Member
Joined: Jul 2004
Posts: 625
Palo Alto, CA, USA
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).]


#159735 - 01/19/05 03:15 PM Re: 70v speakers  
hbiss  Offline
Member
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
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


#159736 - 01/19/05 03:26 PM Re: 70v speakers  
hbiss  Offline
Member
Joined: Dec 2003
Posts: 886
Hawthorne, NY USA
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


#159737 - 01/19/05 05:33 PM Re: 70v speakers  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
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.


#159738 - 01/19/05 06:11 PM Re: 70v speakers  
John in Jersey  Offline
Junior Member
Joined: Aug 2002
Posts: 7
somerset county, NJ,USA
Thanks for all the info!
I don't know what receiver he purchased. It will be delivered tommorrow.


john

#159739 - 01/22/05 05:28 PM Re: 70v speakers  
pauluk  Offline
Member
Joined: Aug 2001
Posts: 7,520
Norfolk, England
I'd often wondered why the U.S. used 70V lines instead of the 100V systems we use in this part of the world.
Quote
Back in the late '40s, UL safety code specified that all voltages above 100 volts peak ("max open-circuit value") created a "shock hazard," and subsequently must be placed in conduit -- expensive -- bad.


You learn something every day. [Linked Image]


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