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Thread: Realistic 31-9081 EQ faders generate hum!

  1. #1
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    Realistic 31-9081 EQ faders generate hum!

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    Hi all,

    I have just bought a Realistic Equalizer, model 30-9081 new, never used!

    Plugging it into my Yamaha receiver with quality RCA cables I realize that a very audible amount of hum is coming out of my KEF speakers. If I play with the 31 to 250 Hz sliders, on both channels the hum gets more audible, but the other sliders (higher frequencies) don't add any noise to the sound...

    I have disconnected everything in my studio, having just the EQ and amp plugged in the same ac strip, and even tried with another amp and its the same.

    It must be the EQ... it is new but due to age maybe the sliders need a good clean with a proper contact cleaner?

    with the low frequency sliders at Zero the spectrum is already showing a lot of activity... while I am playing a pretty flat sounding acoustic song... thats the hum...!

    Any tips?

    thanks for your help!
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    Last edited by Floating Above; 09-17-2020 at 15:35.

  2. #2
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    Boulder, CO
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    That eq is pretty old. I believe it was sold under a variety of brand names, including perhaps BSR. I had one and I can't remember which brand it was (ADC?), but I'm pretty sure it wasn't Realistic. Most likely there's some fault in the circuit, a cracked solder joint or bad caps or something. It's not a high end unit, but it shouldn't be adding the kind of hum you're describing.

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  4. #3
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    northampton uk home of Dr Who and Blackstar Amps!
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    "Holy Printed Circuits Batman!" THOSE were the days when mnfctrs put schematics in user manuals, back then they did not assume we were all ripoff bastards or technically thick as shit!

    Filter caps, yes, a possibility but the power supply includes two discrete voltage regulators* and so even gross hum on the HT line would be removed to an extent. I would investigate ground loop issues first as there seems to have been two mains power versions, one earthed and another 'Classll' earth free. If it is not an external earthing problem then a good technician will be needed.

    Whilst leaving it running MIGHT sort the caps do not eff off and leave it unattended! Small chance it could burst into flames!

    *These can be a reet sod to fix and are never very rugged. Better to just bypass the whole lot and fit '78/79' regulators.
    VOLTAGE REGULATOR PCB for LM317 LM337 or 78xx 79xx IC - PS3.99 | PicClick UK

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