Avoiding Amp Hiss

[thrangster]

So I’ve been reading a fair amount here and joined today… I’m looking to change my home theater amplification setup, but am unsure of direction. A bit of background:

- processor is an SDP-75 (trinnov) 24 channel
- LCR, LW AND RW are JBL M2 speakers (92 db sensitivity)
- side and rears are in-wall JBL SCL-4 (91 db sensitivity)
- Top front and rears JBL SCS-12’s, top middles SCS-8’s (96 and 94 db sensitivity accordingly)
- amps are Crown DCI/N’s, 2/1200 bi-amp center, 2/600 bi-amp LR, LW and RW, 2/300 for others. They are connected via Blulink connection (SDP to BSS Blulink converter to amps. The stated SNR is 108 db via blulink.
- Crowns are sstupid at 28 db input sensitivity; only other option is 24.
- SDP does the active crossover work; no DSP settings in the Crowns, though techncially, I dont think you can bypass the DSP section so my chain has an extra d/a conversion

Everything connected to a dedicated sub-panel

I am bothered by some hiss from the setup, which implies some amp noise or perhaps a gain structure issue . Any single amp is not bad, but in a multichannel setup, its noticeable enough in quiet passages.

So I am wondering what to look for an consider here. Is it purely the SNR ratings? Is it a gain consideration? Both? Something else (there is no ground noise, just the compressed air hiss sound)

The issue is most pronounced with the M2’s. I have tried lowering the channel sliders in the Crown’s down about 8 db, and that’s a small improvement, but after that, no change so its seems an inherent noise floor issue.

On Trinnov’s site, they describe their wildly expensive Amplitiude (NCore, built by ATI I think) as being perfectly gain-matched (19db I believe) to the Altitude/SDP to eliminate the very issue I’m dealing with:

”We perfectly matched the input level of the Amplitude8 to the output level of the Altitude32, optimizing the system’s dynamic range. By doing this, we are able to decrease the background noise of the system by a highly significant 6 to 8 dB, a benefit unavailable when using other amplifiers.​

Why is this so important? Immersive audio systems have a large number of speakers, and each is a potential source of background noise, especially when the system has high-sensitivity speakers. A silent background ensures that low-level sounds critical to a soundtrack will not be obscured.”​

• Input Sensitivity: 6.15V (+18dBu) RMS balanced in = 225W into 8Ω out

Full specs: https://www.trinnov.com/en/products/amplitude8/#Specifications

Of course, I dont want to spend that kind of money on amps, but if the issue is more gain matched amplification than going from 108 to 125db SNR, I think I am having a difficult time find amps that match the Trinnov/SDP in this way. Even ATI amps are more like 28 db gain

So any conversation around this will be helpful, including if there are ways to better optimize the Crowns than I’ve thought of.

Thanks in advance

 

[Eurasian]

Maybe sell the Crowns and buy a bunch of Benchmark AHB2s?

 

[thrangster]

Well, I am looking to sell, the question is what is/are the causes of hiss so I can avoid the issue. Is it the gain? Or SNR?

The Benchmarks are also very expensive and might be as much or more as the Amplitude for 8 channels… There seems to be a number of great amps discussed here for far less, but without knowing what in my chain are the causes of hiss, i could end up not improving things

Thanks

 

[Eurasian]

The Benchmark amps are extremely quiet overall but also offer 3 gain settings, the lower ones probably more appropriate for the JBLs you use.

 

[AdamG]

Well, I am looking to sell, the question is what is/are the causes of hiss so I can avoid the issue. Is it the gain? Or SNR?

The Benchmarks are also very expensive and might be as much or more as the Amplitude for 8 channels… There seems to be a number of great amps discussed here for far less, but without knowing what in my chain are the causes of hiss, i could end up not improving things

Thanks

Welcome Aboard @thrangster.

 

[Dimifoot]

https://www.analogueseduction.net/x...othwell-balanced-xlr-in-line-attenuators.html

 

[levimax]

So I’ve been reading a fair amount here and joined today… I’m looking to change my home theater amplification setup, but am unsure of direction. A bit of background:

- processor is an SDP-75 (trinnov) 24 channel
- LCR, LW AND RW are JBL M2 speakers (92 db sensitivity)
- side and rears are in-wall JBL SCL-4 (91 db sensitivity)
- Top front and rears JBL SCS-12’s, top middles SCS-8’s (96 and 94 db sensitivity accordingly)
- amps are Crown DCI/N’s, 2/1200 bi-amp center, 2/600 bi-amp LR, LW and RW, 2/300 for others. They are connected via Blulink connection (SDP to BSS Blulink converter to amps. The stated SNR is 108 db via blulink.
- Crowns are sstupid at 28 db input sensitivity; only other option is 24.
- SDP does the active crossover work; no DSP settings in the Crowns, though techncially, I dont think you can bypass the DSP section so my chain has an extra d/a conversion

Everything connected to a dedicated sub-panel

I am bothered by some hiss from the setup, which implies some amp noise or perhaps a gain structure issue . Any single amp is not bad, but in a multichannel setup, its noticeable enough in quiet passages.

So I am wondering what to look for an consider here. Is it purely the SNR ratings? Is it a gain consideration? Both? Something else (there is no ground noise, just the compressed air hiss sound)

The issue is most pronounced with the M2’s. I have tried lowering the channel sliders in the Crown’s down about 8 db, and that’s a small improvement, but after that, no change so its seems an inherent noise floor issue.

On Trinnov’s site, they describe their wildly expensive Amplitiude (NCore, built by ATI I think) as being perfectly gain-matched (19db I believe) to the Altitude/SDP to eliminate the very issue I’m dealing with:

”We perfectly matched the input level of the Amplitude8 to the output level of the Altitude32, optimizing the system’s dynamic range. By doing this, we are able to decrease the background noise of the system by a highly significant 6 to 8 dB, a benefit unavailable when using other amplifiers.​

Why is this so important? Immersive audio systems have a large number of speakers, and each is a potential source of background noise, especially when the system has high-sensitivity speakers. A silent background ensures that low-level sounds critical to a soundtrack will not be obscured.”​

• Input Sensitivity: 6.15V (+18dBu) RMS balanced in = 225W into 8Ω out

Full specs: https://www.trinnov.com/en/products/amplitude8/#Specifications

Of course, I dont want to spend that kind of money on amps, but if the issue is more gain matched amplification than going from 108 to 125db SNR, I think I am having a difficult time find amps that match the Trinnov/SDP in this way. Even ATI amps are more like 28 db gain

So any conversation around this will be helpful, including if there are ways to better optimize the Crowns than I’ve thought of.

Thanks in advance

For hiss noise when music is not playing or playing very low SINAD is not the best indicator as it is a ratio. You want to look for very low "Total Integrated Noise and Residual Mains Hum"

You might take a look at the Neurochrome amps https://neurochrome.com/products/modulus-686 , they can be configured for between 20 dB and 26 dB of gain. They are also very quiet with good specs and low residual noise i.e. 20.0 µV RMS20 Hz - 20 kHz A-weighted, and not too expensive (although they are DIY assembled modules, Tom may be able to hook you up with someone that can assemble them in a case).

 

[thrangster]

Thanks - is the gain setting though more about matching the processor output than the sensitivity of the speakers?

I also came accross an Appollon multichannel that has gain settings…

 

[Dimifoot]

Appollon multichannel that has gain settings…

Which one?

 

[thrangster]

https://www.analogueseduction.net/x...othwell-balanced-xlr-in-line-attenuators.html

Thanks - I though about this for a moment, but perhaps I dismissed because I was thinking about it backwards…I guess this means the output voltage of the SDP/Trinnov is high, and, in conjunction with the 28 db Crown gain, enhancing signal path noise floor? And these will help achieve a better balance/reduced hiss?

 

[thrangster]

Which one?

https://www.apollonaudio.com/apollon-audio-purifi-premium-multichannel-amplifier/

 

[DonH56]

What matters is the level of noise at the MLP, which in turn depends upon speaker sensitivity and frequency response as well as amplifier gain, power output capability, and SNR. If you have an amplifier that can deliver way more power than you need, then you'll be operating near its noise floor, and may hear hiss. A significantly under-powered amp will have less gain but may distort on loud passages. Optimizing the chain for noise and distortion is a trade that can be tricky. Fortunately, for consumer audio systems, gains tend to be roughly the same so I would focus on SNR.

I keep thinking of adapting my old RF system gain optimization notes for audio, since it is the same procedure, but it's a lot of work and I am lazy...

 

[thrangster]

What matters is the level of noise at the MLP, which in turn depends upon speaker sensitivity and frequency response as well as amplifier gain, power output capability, and SNR. If you have an amplifier that can deliver way more power than you need, then you'll be operating near its noise floor, and may hear hiss. A significantly under-powered amp will have less gain but may distort on loud passages. Optimizing the chain for noise and distortion is a trade that can be tricky. Fortunately, for consumer audio systems, gains tend to be roughly the same so I would focus on SNR.

I keep thinking of adapting my old RF system gain optimization notes for audio, since it is the same procedure, but it's a lot of work and I am lazy...

Thanks - the reason I focused on gain a bit is the Trinnov amps are at 19 db as opposed to the more standard 27-29, with those comments about noise and amp gain from their site… I am supposing this means the output from the Altitude / SDP is higher than most other processors…

 

[DonH56]

Thanks - the reason I focused on gain a bit is the Trinnov amps are at 19 db as opposed to the more standard 27-29, with those comments about noise and amp gain from their site… I am supposing this means the output from the Altitude / SDP is higher than most other processors…

I believe so although it is hard to find much in the way of specs for the Trinnov (or my SDP-75, a rebadged Altitude 32). My understanding is they use a pro sound card that does have higher output levels. But the speakers also matter a great deal... I have no audible hiss from my SDP-75 driving Emotiva amps and Revel Salon2 speakers. Driving something like M2's or high-sensitivity horn (compression) drivers is a different situation and has more potential for hiss.

 

[thrangster]

Anyone familiar with these?

https://www.amazon.com/Whirlwind-IM...ild=1&keywords=xlr+10db&qid=1619375059&sr=8-8

the link posted above was for a UK supplier and I’m in US.

 

[thrangster]

I guess I am also ignoring a very obvious and simple test - power the amps with the Trinnov off and evaulate the base noise floor of the amp alone.

Sometimes, I think I’ve been in this hobby too long…

 

[MakeMineVinyl]

Thanks - is the gain setting though more about matching the processor output than the sensitivity of the speakers?

I also came accross an Appollon multichannel that has gain settings…

Start with disconnecting the inputs to your power amps and see if they still hiss. If they do the problem is the power amps.

 

[thrangster]

Start with disconnecting the inputs to your power amps and see if they still hiss. If they do the problem is the power amps.

Thanks - yes, I had just posted before your note, I was being quite stupid here.

So I did this and the hiss is unchanged.

Crowns are rated at 108db SNR, but who knows how accurate this is (other Crown amps here test lower I think, but no DCI’s tested…)

So I’m left with wondering if this is an inherent gain circuitry and amplification issue (600 watts each per horn and woofer for all five M2’s, (which is really more than I need for my setup I think) in conjunction with the 92 db sensitivity of the speakers, or more that a truly better SNR-rated amp is required for the sensivity of these speakers (though 92 isn’t THAT high, is it?)

Thanks

 

[MakeMineVinyl]

Thanks - yes, I had just posted before your note, I was being quite stupid here.

So I did this and the hiss is unchanged.

Crowns are rated at 108db SNR, but who knows how accurate this is (other Crown amps here test lower I think, but no DCI’s tested…)

So I’m left with wondering if this is an inherent gain circuitry and amplification issue (600 watts each per horn and woofer for all five M2’s, (which is really more than I need for my setup I think) in conjunction with the 92 db sensitivity of the speakers, or more that a truly better SNR-rated amp is required for the sensivity of these speakers (though 92 isn’t THAT high, is it?)

Thanks

Crown amps are primarily for industrial/commercial/pro sound reinforcement use and as such, noise is not an overriding concern in their specs. Ruggedness is what is important in these uses, so its no surprise that the amp is hissy. If it does have a gain adjustment, try turning it down. I have horns too, and it is extremely difficult to achieve low hiss with very efficient speakers - it comes with the territory. If turning down the gain (if you can) does not reduce the hiss, time for another amp.

 

[DonH56]

ATI amplifiers have a reputation for low noise. You could look into their 6000 series if you want class AB.