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Discussion Starter · #1 ·
I have JBL 4722n's ([email protected]@1m) for LCR and recently bought some Peavey IPR3000DSP's to power them. After connecting the 4722's to the amps and powering the amps on there is quite a loud (can hear clearly from listening position) speaker hiss shhhhh noise coming out the horns. This is with no input connected to the amp and changing the amp gain/volume does not effect it.


Before I exchange these amps for another brand/type of pro amp I'm wondering if this is just an inherent issue with using a high powered pro amp with high sensitivity speakers. Do others running this kind of system have these issues? Any other amp recommendations in the IPR price range? I did a quick test and connected one of the 4722's to my Denon 4520 and there was a slight hiss but it could only be heard by sticking your head pretty much inside the horn.
 

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Quote:
Originally Posted by rob4321  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps#post_23195480


Before I exchange these amps for another brand/type of pro amp I'm wondering if this is just an inherent issue with using a high powered pro amp with high sensitivity speakers.
It's an inherent issue with amps that have a poor S/N ratio, be they pro or otherwise. You hear it with a high sensitivity HF driver because that idle noise is up to 20dB louder than with a typical dome tweeter. Peavey claims the hum/noise is -92dB, and that's about 10dB less than I'd want.
 

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Yep, it could be either a grounding issue or inherent to the amp in question. Do you have any other amps to try temporarily? I've not used any of the integrated DSP pro amps but I've heard complaints that they tend be a bit noisy. Of course, those complaints might have been due to something outside of the amp itself (ground loops, poor gain structure, faulty amp etc).
 

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Discussion Starter · #5 ·
Thanks. I'll see if I can find a cheater plug to test. The amps are plugged into 2 dedicated 20 amp lines with nothing else on the line. There's a 15amp line nearby I could test running from that.


I actually didn't even order the DSP versions. They were out of stock so upgraded me to them for free. I see that the non DSP has a signal to noise ratio of -101.5db and the IPR1600 has -105db. Maybe I could exchange for that since I'm not using the DSP.
 

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signal to noise is a little tricky because of the different ways that it can be measured and reported.


peavey states -92db a weighted at rated power @ 4 ohms.


at 4 ohms, the amp is producing 815 watts.


so adjusting that down to 1 watt requires a 29.1 db add (log (815/1)*10).


that leaves roughly a 1w signal to noise rating of -63db. in my estimation that is a defective product.


the 4722n is 101db 1w1m, so 63db off that is about 38db of noise. that is much too high unless you sit about 50 back from the speakers. :)


if you have a good clean signal going to the amp, most pro amps should be unheard even with high sensitivity speakers unless perhaps you put your ear right next to the driver.
 

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Any piece of pro audio gear with an A-weighted noise spec should be approached with caution. An A-weighted spec is a less-rigorous standard than the unweighted specmost pro audio manufacturers adhere to (i.e. typically designated as xx dBu) . As you can see in the graph below, an A-weighted curve rolls out the upper and lower frequencies. By comparison, an unweighted spec is a flat-response reference with no roll-out of the bottom or top end.



The problem with using an A-weighted curve to obtain a signal-to-noise spec, obviously, is that it “ignores” upper- or lower-frequency noise that may be present. So if a component happens to generate a bit more hum or hiss than it should, and this problematic component can only muster an unweighted spec of 88 dB, A-weighting would allow the manufacturer to “honestly” bump the figure up to a more respectable 94 dB. This is merely a hypothetical example of a component that’s only a bit worse than it should be; in reality A-weighting can “improve” a noise spec as much as 10 dB.


Regards,

Wayne A. Pflughaupt
 

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Discussion Starter · #8 ·
Thanks for the tips on calculating SNR. Should help when I have to pick out another amp. Any suggestions of one to look at? Maybe the non DSP versions since they have 10 - 13db better ratings. Lots of people on the Peavey forum claim the IPR's are dead silent for background noise so perhaps mine are just defective.


I tried a cheater plug and it made no difference. Also tried the 15 amp circuit also with no difference. I'm going to drop them off at the store on Monday for them to test.
 

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I was using an inuke3000dsp with my ewave style speakers using the de250 cd but it had quite a bit of hiss as well so it has been replaced. Even a cheater plug and/or external ground wire couldn't quiet it down. It's a great amp for subs but not so much for high efficiency speakers.
 

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Quote:
Originally Posted by LTD02  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps#post_23197606


tsloms, was that stand alone or with other equipment plugged in?

I tried several ways to eliminate the hiss. With all inputs disconnected from the amp and with or without a separate ground wire to the receiver the hiss was still present.
 

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All speakers hiss.


Some causes of unacceptable hiss: bad balanced cable(s), bad jacks and a poor gain structure, which creates a poor SNR.


If the hiss is that annoying and all of the above causes are investigated with no satisfactory result, I would use a gate. IMO, any dead silent home audio components use a gate circuit. Without it, you'll always have some hiss.


2 and 4 channel gates run $120 to $1200 from all of the usual suspects (Sweetwater, Musician's Friend, Guitar Center, etc).


2 cents, FWIW.
 

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Quote:
Originally Posted by bossobass  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps#post_23197868


All speakers hiss.
No speakers hiss. Electronics hiss, speakers reproduce it. If you've got an amp that produces high levels of hiss a gate won't help, as the gate only stops noise that's sourced prior to the amp, not in the amp. The cure is an amp with better S/N.
 
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Discussion Starter · #15 ·

Quote:
Originally Posted by auburnu008  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps#post_23197634


What about the Crown DSI amps?
Those would be great but at more than double the IPR price. I'll keep them in mind though.

Quote:
Originally Posted by tsloms  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps#post_23197745


I tried several ways to eliminate the hiss. With all inputs disconnected from the amp and with or without a separate ground wire to the receiver the hiss was still present.
Did you find an amp that worked?
 

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Discussion Starter · #16 ·

Quote:
Originally Posted by Bill Fitzmaurice  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps#post_23197935


No speakers hiss. Electronics hiss, speakers reproduce it. If you've got an amp that produces high levels of hiss a gate won't help, as the gate only stops noise that's sourced prior to the amp, not in the amp. The cure is an amp with better S/N.

Thanks, yes there is no input connected to the amp and they are hissing big time. I guess a gate wouldn't help.
 

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Quote:
Originally Posted by rob4321  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps/0_100#post_23197943


Those would be great but at more than double the IPR price. I'll keep them in mind though.

Did you find an amp that worked?

You can get the DSI1000 on ebay for about $350. They are refurbs but the still carry the full Crown warranty.
 

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Discussion Starter · #18 ·

Quote:
Originally Posted by auburnu008  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps#post_23198021


You can get the DSI1000 on ebay for about $350. They are refurbs but the still carry the full Crown warranty.

I'll keep an eye out. I see one for $450. I'm in Canada so the shipping may kill the deal.
 

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Quote:
Originally Posted by rob4321  /t/1467939/jbl-cinema-and-other-high-sensitivity-speakers-hissing-with-pro-amps#post_23198041


I'll keep an eye out. I see one for $450. I'm in Canada so the shipping may kill the deal.
Plenty of good old heavy iron amps are out there, as their owners are looking to replace them with compact lightweight amps.
 

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Check out Axe music for decent prices on amps in Canada. I find amps to be a pain to find for a good price here. Ill probably buy one next time I'm down in the states. Maybe next weekend. If I can find a good deal. Where in Canada do you live
 
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