Ambient Hiss Issue

Discussion in 'Hi-Fi Stereo Systems & Separates' started by bluedroog, Jan 11, 2012.

  1. bluedroog

    bluedroog
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    Hi Guys, I was hoping someone could offer some advice on this issue. The problem is my tweeters in both left and right channel give off a quiet hiss, in between tracks or during pauses between notes it's fairly prominent and during general music it's harder to pinpoint but definitely having an adverse effect on the overall sound.

    I've not had to issue in the past but am still struggling to identify the source of the problem. My system is a Laptop running Squeezebox server, Squeezebox Touch > Beresford Caiman > Quad 909 power amp > B&W 602 S2 / BK XXLS400. The issue is a new one and I have recently got rid of my old Arcam integrated amp and replaced it with the Quad. The Quad is a brand new amp though.

    I had thought it may be the DAC causing a problem so last night tried the Touch direct to the 909, the hiss definitely got quieter but is still there. I've checked that all the cables are secure, doesn't appear to be anything wrong there.

    I have thought the lack of a dedicated pre-amp might be an issue, is this plausible?

    Could my electricity supply be to blame?

    Could it be cables crossing behind my cabinet? (Never been an issue before)

    Could it be the Quad? (brand spanking new though).
     
  2. Alan Mac

    Alan Mac
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    I would suspect the Quad 909 power amplifier.

    This has a voltage gain of 43 (32.7 dB) which is about 6 dB higher gain than most power amplifiers.

    The B&W 602 S2 loudspeakers have a relatively high sensitivity of 90 dB above 20 μPa rms at 1 m for 2.83 V rms input.

    The combination of high power amplifier gain and high loudspeaker sensitivity may lead to audible hiss from the loudspeakers.


    Alan
     
  3. formbypc

    formbypc
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    What does it sound like if you disconnect all components from the Quad, and power it up with nothing connected?

    If the tweets go silent, that implicates one or more other components, and excuses the Quad.

    Do you have any other components you could try through the Beresford, such as CD player?

    How are you accessing the music on the laptop? Is the SB Touch connecting wirelessly or via ethernet?

    So, you're saying that you connected the analogue outs from the SB Touch direct to inputs on the Quad, and that resulted in less hiss than going digitally from the SB to the Beresford, but didn't eliminate it altogether?

    What's the source material? Ripped CDs? Downloaded tracks? Something else?

    If you press Pause on the SB, does the hiss stop, and resume when you press Play?
     
  4. bluedroog

    bluedroog
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    Thanks for your thoughts guys. Frombypc I will try out your suggestions when I get home, off the top of my head I'm pretty sure this hiss is still there when I pause. The music is a mixture of downloaded and ripped from various sources, the problem doesn't seem to be Exclusive to any particular source material within my library. I'll dig out my old CD player and play that via the DAC.

    Alan - If your theory is correct do you think a pre-amp (was thinking of a Croft Micro 25 which is a tube pre) would help? Or a DAC with a better pre stage such as the new Audiolab M-DAC.
     
    Last edited: Jan 11, 2012
  5. Alan Mac

    Alan Mac
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    If the tweeters go silent when there is no input to the Quad 909 then an attenuator at the input to the Quad may help. This assumes there is additional amplification after the “volume” control but before the input to the Quad 909.

    The attenuator will reduce the noise produced by this additional amplification stage. The gain control will then be altered to restore the wanted signal level.

    These attenuators (one for each channel) will reduce the hiss during quiet passages (assuming it is not present in the source signal).


    Alan
     
    Last edited: Jan 11, 2012
  6. bluedroog

    bluedroog
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    Ok so last night I tired a couple of things to see if causes could be isolated. I switched the Touch into stand-by and the noise was still there, any one with a Touch will know that stand-by really just disables the screen so I pulled the power cable out. Now this was interesting, it certainly improved things but has lead me tot suspect there could be more than one source to my problems. The noise reduced obviously, however it also changed. The hiss became more of a buzz but far quieter which leads me to believe a faint buzz is also always there but the hiss is more audible and covering things up. This is by the way all still with the DAC out of the equation.

    I didn't get round to trying another source via the DAC yet.

    Do you think an upgraded power supply for the Touch could help?

    Do you think a main conditioner could help?
     
  7. Alan Mac

    Alan Mac
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    I don’t think that a pre-amplifier would help in this case.

    If you turn the volume control to its minimum position, the hiss should disappear. If it does not, and assuming there is not an actual fault, the audible hiss would appear to be caused by too high a voltage-gain following the volume control.

    This gain needs to be reduced; ideally by reducing the internal gain of the Quad 909 power amplifier but this is not possible without invalidating the guarantee.

    Using external attenuators on the Quad 909 inputs (about 10 dB attenuation in each channel) seems a more practical solution.


    Alan
     
  8. bluedroog

    bluedroog
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    Well thought I'd come back to this thread as I've on the whole got to the bottom of this issue, the colprit actually turned out to the the Squeezebox Touch, I feel guilty on my amp and DAC now!

    I haven't got a pre-amp yet but was missing my 5.1 for films so instead of using the DAC as a pre and using the digital volume on the Touch I sent the DAC in to my AVR used the pre-outs to my power amp and used in 'pure direct' mode.

    I now set the volume on the Touch to fixed at 100% and used the remote of the AVR for volume. Hey-presto, hiss has gone.

    As I mentioned on another post above I think there is actually two issues and there is a very slight buzz at times. The hiss was the real issue but would like to try and fixed the buzz too. Perhaps a group loop issue, I have read something about the Quad noting being earthed?!
     

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