Quiet power amp SNR

Discussion in 'Amps [BG]' started by Dippitydip, Nov 14, 2012.


  1. Dippitydip

    Dippitydip

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    Hey guys

    Do you have any suggestions for a super quiet power amp that will be near silent when I'm not playing? My current Crown amp has a hiss that is quite irritating. It's rated at 100db SNR but I doubt that..

    Cheers
     
  2. dincz

    dincz

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    Does it hiss with nothing connected to the input?
     
  3. BassmanPaul

    BassmanPaul Gold Supporting Member

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    +1 Any modern power amp will be pretty much silent with no signal applied. The hiss will be coming from whatever you have plugged into the amps inputs.
     
  4. Jeff Scott

    Jeff Scott Don't just TalkBASS - PlayBASS! Supporting Member

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    +2. My first thought (actually, only thought! :D) when seeing the OP.
     
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  6. will33

    will33

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    Ya, I doubt it's the amp, but rather open mics, bass needs better shielding, treble boosted......somethin'. My XLS 402 is quiet, and that's a budget model Crown. My QSC and Peavey are quiet too.
     
  7. Dippitydip

    Dippitydip

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    With no instrument plugged in, and the Eden Navigator preamp turned off and unplugged, and still hisses. The hissing is louder when it's all plugged in and turned on from the pre side, but it kind of introduces another spectrum of hiss. FYI the power amp is a XTi series. I'm thinking its because of all of its DSP shenanigans built it, which is all disabled, but might still be a generally noisy signal path. I think what I would like is a very conventional amplifier that's designed to be quiet and perfect. I can read all of the specs I like, but firsts hand knowledge would give me a better idea. So who's found a a super quiet power amp for their rig?
     
  8. will33

    will33

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    If it does it with nothing plugged in the input, then yes, it might be the DSP stuff, or other problem. When you say it gets quieter, or different with something plugged in the input, could be a grounding thing, or who knows what.

    If you don't need the DSP, the XLS Crowns are an option. My old QSC MX700 is dead quiet. And my older CS 800X Peavey is too aside from fan noise. Most any half-decent power amp is quiet that I've seen.
     
  9. Jeff Scott

    Jeff Scott Don't just TalkBASS - PlayBASS! Supporting Member

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    The only power amp I own these days is an Aragon 2004 which is velvety quiet.
     
  10. 1958Bassman

    1958Bassman

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    Does the spec sheet show the S/N of the DSP? Have you tried setting everything to factory defaults? My guess is that your settings are such that you're no longer working at unity gain or at least one EQ band is set for more level than the rest and those are already at +/- 0dB or higher. Also, the output impedance of the piece in front of the power amp matters WRT noise/output levels. What's the setting for the input sensitivity- that usually tells a large part of the noise story.
     
  11. Interceptor

    Interceptor Supporting Member

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    What are you running for a speaker, how loud is the tweeter set and what sort of room are you hearing the hiss in?

    Where I'm going here is piezo tweeters are very efficient, and even a pretty quiet power amplifier does make some noise.
     
  12. Dippitydip

    Dippitydip

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    The SNR is stated to be 100db. The DSP is disabled entirely. Speaker is an Eden 410 XLT, with horn setting at 12 o'clock. Room is a carpeted spare bedroom with partial sound tile covering on walls.

    Jeff, not surprised to hear a Mondial amp mentioned. I run an Acurus a200x3 which is SNR 110db and absolutely dead silent unless you put your ear right up to a tweeter in a very quiet room. Amazing. Not expecting that from a rugged prosound amp, but I'd need a big improvement on current noise levels.

    Thanks for suggestions thus far guys. I also found the EV and a Yamaha rated at 105-106db. Not bad at all.
     
  13. Jeff Scott

    Jeff Scott Don't just TalkBASS - PlayBASS! Supporting Member

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    I love the amp; I run a 24K preamp into the 2004 and out to Magneplanar MG-Ic and Definitive Technologies Super Cube II speakers.
     
  14. fdeck

    fdeck Supporting Member

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    What's the rated output power of the amp?
     
  15. Interceptor

    Interceptor Supporting Member

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    Keep in mind, that 100 dB down is in reference to full power out of the amplifier.

    The way Crown specs the amplifier noise floor is in reference to full power output.

    The output of that thing (bridged) is in the neighborhood of 1,000 Watts. That is +30dBW.
    100 dB down from there is -70 dBw.

    Given the speaker you are using, which is has an output level of 100 dB for a Watt (0dBW)of input, the noise floor is on the order of 70 dB down from the level you'd have with a Watt of power going in.

    That level of noise will be audible in a small room with an efficient speaker such as yours.
     
  16. seamonkey

    seamonkey

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    Crown XTi are good amps.
    Your hiss is likely coming from your pre-amp.
    Short the amp input and it is going to be quiet.

    Turn the DSP back on and EQ out the hiss.
     
  17. chucko58

    chucko58

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    Is the power amp's attenuator control (often misunderstood to be "volume" or "gain") all the way up? If so, that's part of the problem. Ideally you should be feeding the power amp a good hot signal, and you shouldn't need to crank the attenuator on the power amp to drive it to full power.

    Do a web search on the phrase "gain staging" for more info. Here's one good article on the topic.

    You are unlikely to find a power amp in that power range with a S/N ratio much better than 100 dB.
     
  18. Jerrold Tiers

    Jerrold Tiers

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    And, depending on your speakers and environment, even 100 dB s/n can be annoying. Hiss noise is relatively OK, but any trace of hum really stands out. the higher power the amp, the louder the noise will be with same s/n, as pointed out.

    As for turning input controls..... the maximum noise is probably with the control at half, if there is no active stage in the amp before the control. In that condition, the resistance "looking back out of" the amp is the highest, with the actual input shorted.

    Every value of resistance has a noise level associated with it just due to its resistance. This comes up mainly in mic preamps, but can affect other amps as well.

    100dB is about as good as it gets...... so you likely shouldn't complain too much.
     
  19. fdeck

    fdeck Supporting Member

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    Back of envelope...

    1000 W amp is 30 dBW.

    100 dB SNR means that noise is at -70 dBW

    If the speaker tweeter has a sensitivity of 100 dB SPL/W @ 1m, then...

    Noise is at a level of 30 dB SPL @ 1m. One link says that 30 dB SPL is like being in an empty movie house. That's pretty quiet. But like Jerrold says, there are operating conditions that could degrade the SNR of the amp.

    Is the hiss the same coming out of both channels? If it was different, it could indicate a dodgy component in one channel.
     
  20. Dippitydip

    Dippitydip

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    The amp is 275W into 8ohms, 100db SNR. That is an A-weighted measurement though. Noise comes from both channels with both attenuators at zero, with no input. With no source plugged in, I can turn both attenuators to full with no change in noise. It is always there, and always at the same level. The noise doubles in bridged mode, as you would expect. To lower the noise floor I now run only off the L channel. I lift the attenuators to the point at which preamp noise equals the amp noise, so the result is I only hear that constant noise level, as the preamp doesn't raise the noise floor.

    I have found a tonne of amps rated at 105, 106, 107. Most likely I will end up with one of the high-end Yamaha or EV models that I've come across. The EV CP3000S is 450W into 8ohms at 107db A-weighted. Could be a good option. This current Crown XTi was very, very inexpensive. This EV is 7X the price.
     
  21. chucko58

    chucko58

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    What are you using for speakers? They must have a pretty aggressive high end for the hiss to be such an issue.
     

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