70v commercial speakers with home audio receiver

E

erik seel

Audiophyte
I have two JBL in wall commercial 70v speakers. Is there a way to rewire these to work with my regular home audio receiver? Thanks in advance for any help.
 
lovinthehd

lovinthehd

Audioholic Jedi
Curious what's involved myself, found this thread.

Makes me wonder what's involved in reverse, are transformers readily available for "normal" speakers if you have an amp capable of 70V use?
 
TLS Guy

TLS Guy

Seriously, I have no life.
Curious what's involved myself, found this thread.

Makes me wonder what's involved in reverse, are transformers readily available for "normal" speakers if you have an amp capable of 70V use?
Well that post on AVS was total bunk for a start.

The answer to your question is a may be.

Is the transformer with the power taps external to the speakers?

If it is, desolder the wires leading to the speaker from the transformer.

Now take your ohm meter and measure the DC resistance of the voice coil by putting the probes on the two wires that you desoldered from the transformer. If the reading you get is between 6 to 8 ohms you can theoretically use the speakers. If not you can't.

Now there is a further problem. 70 volt systems are usually wired with high gauge small conductor high resistance bell wire. This does not work well with 8 or 4 ohm loads. So you might have to rewire.

The next problem is that 70 volt systems are mono and not stereo. So you will find the transformers will be wired in parallel, daisy chained from one speaker to the other.

So on the speaker nearest to the receiver you would have to parallel the speakers at that point, unless you rewire. You would only be able to connect to the left or right out of the receiver, not both.

Now for background systems like that there is a lot to recommend a 70 volt system.

I would seriously consider buying a 70 volt amp and driving it from a zone preout. Connect left and right zone outs in parallel.

Now when you buy the new amp, you will almost certainly have to retap the transformers. The rule is that the sum of the connected wattage taps on all the transformers must equal the wattage of the driving amplifier.

That is all there is to it. Quite straightforward really.
 
L

larzman

Audiophyte
just a little clarification on the previous comment. The sum of the wattage of each speaker on the same run SHOULD NOT equal the wattage output of the amplifier. The general rule is DO NOT EXCEED 80% of the amplifier's output rating. This allows for adding speakers in the future or changing the tap level to make a specific speaker louder, usually because it's in an environment with a high ambient noise level, i.e. a wood shop in high school. 70V and 25V balanced (constant voltage) audio systems are typically used in institutional facilities, i.e. schools, and hospitals, and have multiple speakers connected in parallel on an amplifier's single speaker output . Unbalanced, 8 Ohm speakers are designed for consumer audio, where there is only 1 speaker on each amplifier output.
 
highfigh

highfigh

Seriously, I have no life.
Well that post on AVS was total bunk for a start.

The answer to your question is a may be.

Is the transformer with the power taps external to the speakers?

If it is, desolder the wires leading to the speaker from the transformer.

Now there is a further problem. 70 volt systems are usually wired with high gauge small conductor high resistance bell wire. This does not work well with 8 or 4 ohm loads. So you might have to rewire.

The next problem is that 70 volt systems are mono and not stereo. So you will find the transformers will be wired in parallel, daisy chained from one speaker to the other.

So on the speaker nearest to the receiver you would have to parallel the speakers at that point, unless you rewire. You would only be able to connect to the left or right out of the receiver, not both.

Now for background systems like that there is a lot to recommend a 70 volt system.

I would seriously consider buying a 70 volt amp and driving it from a zone preout. Connect left and right zone outs in parallel.


That is all there is to it. Quite straightforward really.
He didn't write that the speakers were still in the original installation, just that he has them.

The only part of the AVS thread that was bunk is the part where one person posted that the speakers could also be 4 Ohm- if they're marked 8 Ohms, they're 8 Ohms- there's no reason to mark them inaccurately. The rest is true- if the speaker is 8 Ohms, the transformer can be bypassed and if it has a rotary selector, that often has an 8 Ohm setting.
 
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highfigh

highfigh

Seriously, I have no life.
I have two JBL in wall commercial 70v speakers. Is there a way to rewire these to work with my regular home audio receiver? Thanks in advance for any help.
What is the model number? Google search that model (example, 'JBL C26S') and find the manual to read about their performance, power handling, etc. Most 70V speakers are rated for low to moderate power because they aren't generally used as the main speakers and the level used isn't as high as box speakers are called to produce. The transformer should be marked with power numbers near the wires or by color, at 1W, 2W, 4W, 8W, 15W and that's usually where they max out.
 

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