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Spa/Retail Install - Distortion as I add speakers?

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Gordon Brinton:
Are you certain you have things hooked up correctly?

You are using the 70V terminal on the amp as (+) and the Com as (-). Since it is a 500 W amp, (we're probably talking 50 to 150 rms,) you can use the 5 W lead from each speaker transformer for (+) and the Com lead for (-). All 8 speakers together should then draw 40 W total. I wouldn't think that should be too much for that amp. All speakers should be wired parallel from that one 70V out terminal.

See if you can find a Denon DN-333XAB.
Now discontinued...but perfect


--- Quote from: MikeHarris on February 28, 2020, 01:57:08 am ---See if you can find a Denon DN-333XAB.
Now discontinued...but perfect   Built in Bluetooth

--- End quote ---

Paul Shearer:

--- Quote from: Brian Jojade on February 27, 2020, 07:22:53 pm ---The specs on that unit are even uglier.  Advertised THD at 1%  Yikes! Most amps you'll see listed at .05% or less distortion.  But you're dealing with a $65 amp.  Don't have any expectations of quality out of that.  Yeah, they say that it's a 500 watt amp, but they say 'MAX' That's a far cry from the RMS rating that any reputable manufacturer would use.  Peak power is what you get when all hell freezes over. Real RMS power can be a fraction of that.

Do you have a realistic budget to work with on this? If you're driving 8 speakers tapped at 15 watts per speaker, that means you need an amp capable of 120 watts or more.  For ceiling speakers in an office setting, 15 watts is pretty high, actually.  You could probably roll them back to 10 watt or even 5 watt taps and have them do the job.

A nice matching amp that I'd consider is the JBL CSA 1120Z. 120 watt amp, designed to give you years of reliable service without the gimicky crap on the toy amps.  However, the MAP on this unit is $419.  That's pretty much at the lowest end of what would be considered decent quality.  Quality 70v amps are designed to give you decades of reliable service, so over the life of it, it's not that expensive.

Alternatively, you can use standard amps and use your own matching transformer which I linked earlier. Note that just the matching transformer costs nearly what your amp does.  That should be an indicator of what you're working with....

--- End quote ---

Thanks, Brian and everyone else for your replies. I will get on replacing the amp ASAP, and report back if the distortion still persists.


Jim Thorn:

--- Quote from: Paul Shearer on February 28, 2020, 10:19:29 am ---Thanks, Brian and everyone else for your replies. I will get on replacing the amp ASAP, and report back if the distortion still persists.


--- End quote ---

Take a look at the ceiling speakers.  If they were installed by somebody who is not familiar with 70 volt systems, unused transformer taps at the speakers may be shorted together.  A short between taps of a transformer is reflected back to the amp as a NEARLY shorted feed line.  I have seen inexperienced installers tape the stripped ends of unused speaker taps together to tidy things up, unintentionally creating a mess of shorts.  Perhaps the single speaker you are using has no shorts, but others in the ceiling might have them.  The solution is to clip off the bare ends of the unused tap wires before taping them together, preferably with the cut ends staggered so that they can't possibly make contact with each other.

And don't feel that you have to tap the speakers high to use all available power from the school intercoms, the single speaker in the middle of a classroom that carries morning announcements is usually tapped at 1/2 watt or 1 watt!!  As others have mentioned, the actual reliable power from the Pyle amp is probably a tenth of the advertised power, but even 50 watts can make a lot of noise if the wiring and speakers are okay.

I hope this is helpful.

Wishing you well,
Jim Thorn


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