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Lmaloney
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Last seen: 1 year 9 months ago
Joined: Mar 17 2013 - 1:09pm
Troubleshooting help

It's been a few years since I posted on here, so long I couldn't remember my username and had to create a new one.  With the help from people on this website, I put together a little starter system back when I just got out of college.  After a few years of moving around for work, the stereo got left in boxes waiting for me to find a more permanent dwelling.  Well this weekend I unpacked the stereo and was going to listen to some albums.  Unfortunately I am having some problems

 

i have: denon dp500m turntable, connected to pro-ject phono box 2, connected to jolida jd202. PSB image b25 speakers. Ortofon 2m blue mm cartridge.

 

when I turn the amp to the channel the turntable is hooked to, I get a fairly loud humming sound?  If I select a different source like iPod, the sound is fine.  So I am getting some feedback from either the turntable or the pre-amp right?  I made sure the project is on the moving magnet setting.  If I play an album, I hear the music but the humming is still very noticeable. I checked the RCA connections, they are tight.  Any ideas on what else I could be checking? Do I need to take it to a repair shop? Has one of my components bit the dust?

 

thanks in advance for your help!

luke

Kal Rubinson
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Joined: Sep 1 2005 - 9:34am
Sounds like a ground loop. 

Sounds like a ground loop.  Assuming all the components are connected to the same AC, I would start by disconnecting the TT from the pro-ject phono box 2.  If there is still hum, try grounding the pro-ject phono box chassis to the amp chassis to see if it goes away.  If so, good.  If there is no hum, reconnect the TT and see if the hum returns.  If it does, try another ground from the TT chassis to the phono box.

Lmaloney
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Joined: Mar 17 2013 - 1:09pm
Thank you.    I tried this.

Thank you. 

 

I tried this.  All 3 devices are hooked to the same ac.  When I disconnected the Tt RCA from the phono box, the hum got louder. So I tried ground between phone box and several locations on the amp chassis and the hum never went away.  When I re connect the Tt RCA the humm gets about reduced in half.  I tried this with multiple sets of RCA cables to try and eliminate that variable, and it that had no effect.  Does this mean my phono box is shot? Maybe struck by lightning?

Kal Rubinson
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Joined: Sep 1 2005 - 9:34am
2 more things to try.   1.

2 more things to try.  

1.  Insert shorting plugs into the phono box and see if there's hum.

2.  Try grounding link from TT chassis to phono box or preamp.

Lmaloney
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Last seen: 1 year 9 months ago
Joined: Mar 17 2013 - 1:09pm
I am not familiar with

I am not familiar with shorting plugs?

Kal Rubinson
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Last seen: 17 hours 12 min ago
Joined: Sep 1 2005 - 9:34am
They are RCA plugs with the

They are RCA plugs with the signal and ground pins shorted together.  You can approximate this by gettting the cheapest RCA interconnect you can find, cutting it in half and twisting together the shield (ground) and signal wires on each side.  Result: two shorting plugs.

The reason to use this is that some phono inputs will hum like crazy with no input load.

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