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Realistic 31-9081 EQ faders generate hum!

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Realistic 31-9081 EQ faders generate hum!

Postby Floating Above » Thu Sep 17, 2020 9:58 pm

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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Re: Realistic 31-9081 EQ faders generate hum!

Postby blinddrew » Thu Sep 17, 2020 10:34 pm

It might be a grounding issue, worth reading this thread answer from Hugh and working through that: https://www.soundonsound.com/forum/view ... 35&t=74109
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Re: Realistic 31-9081 EQ faders generate hum!

Postby Martin Walker » Thu Sep 17, 2020 10:52 pm

I used to have one of those many, many years ago, mostly for using its spectrum analyser to inspect mixes:

Image

So, given that this a vintage item that could be over 20 years old, it might even be failing (or failed) capacitors that have resulted in this hum :(


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Re: Realistic 31-9081 EQ faders generate hum!

Postby James Perrett » Thu Sep 17, 2020 11:18 pm

If it has never been used then there's a good chance that the electrolytic capacitors are no longer at their best. With something that has lain unused for such a long time it is often necessary to reform the capacitors before use. You may find that things improve with use but it will probably be necessary to replace some of the capacitors to bring it back to top performance.
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Re: Realistic 31-9081 EQ faders generate hum!

Postby Floating Above » Fri Sep 18, 2020 12:36 am

Martin Walker wrote:I used to have one of those many, many years ago, mostly for using its spectrum analyser to inspect mixes:

Image

So, given that this a vintage item that could be over 20 years old, it might even be failing (or failed) capacitors that have resulted in this hum :(


Martin

Thank you so much! yep... I read elsewhere the same advice, that due to its age the caps may need to be replaced... and that i should leave it on for a log period of time and see if it gets better! thats what i will do, and if nothing changes, then I will take it to a pro. This thing as sentimental value... my father had one some 30 years ago and when I finally saw one for sale and it was new I didn't think twice... for €50.

thanks again!
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Re: Realistic 31-9081 EQ faders generate hum!

Postby Floating Above » Fri Sep 18, 2020 12:38 am

James Perrett wrote:If it has never been used then there's a good chance that the electrolytic capacitors are no longer at their best. With something that has lain unused for such a long time it is often necessary to reform the capacitors before use. You may find that things improve with use but it will probably be necessary to replace some of the capacitors to bring it back to top performance.

Thanks very much!

yes, the caps may well be gone bad. i don't know much about electronics so its good to know that several people in the know here and in other reputable forums are giving me the same tips...

Thanks again!
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Re: Realistic 31-9081 EQ faders generate hum!

Postby Floating Above » Fri Sep 18, 2020 12:49 am

Floating Above wrote:
Martin Walker wrote:I used to have one of those many, many years ago, mostly for using its spectrum analyser to inspect mixes:

Image

So, given that this a vintage item that could be over 20 years old, it might even be failing (or failed) capacitors that have resulted in this hum :(


Martin

Thank you so much! yep... I read elsewhere the same advice, that due to its age the caps may need to be replaced... and that i should leave it on for a log period of time and see if it gets better! thats what i will do, and if nothing changes, then I will take it to a pro. This thing as sentimental value... my father had one some 30 years ago and when I finally saw one for sale and it was new I didn't think twice... for €50.

thanks again!

also, by looking at your picture, I can see that with all the sliders at zero your spectrum display is showing quite a well formed frequency graph... in mine with all at zero I get some spikes but only at low frequencies... is it normal that with all at zero you get such a rich curve?
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Re: Realistic 31-9081 EQ faders generate hum!

Postby Tomás Mulcahy » Fri Sep 18, 2020 10:01 am

Floating Above wrote:is it normal that with all at zero you get such a rich curve?
Yes, when there's music running through it.
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Re: Realistic 31-9081 EQ faders generate hum!

Postby Tim Gillett » Fri Sep 18, 2020 11:49 am

Floating Above wrote:... is it normal that with all at zero you get such a rich curve?
Really there's no rule. The display just reflects the signals fed to it, or is supposed to.
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