You are here

Log in or register to post comments
Tandrew
Tandrew's picture
Offline
Last seen: 3 days 11 hours ago
Joined: Jul 10 2014 - 11:12pm
I need help tracking down the hum in my set up

So I've been going crazy trying to hunt down the hum in my turntable set up. The hum only appears between songs and on piano ballads. Any thing with acoustic guitars and the him seems to fade away. I've got the ground wire connected between the preamp and turntable using Pro-Ject's stock wires. Here are the suspects:

Bellari VP130: Hum has been reported in several reviews of this Preamp but supposedly it disappears with an Enercell 15v 1A power supply. The first Enercell power supply I used worked sporadically and when it first refused to power the unit I stupidly switched to the incorrect polarity. I fear this may be the cause of the hum now. I switched to a working power supply and it powers the unit but the hum isn't different from the stock wall wart.

Pro-Ject Audio Debut Carbon: The hum becomes more severe when my fingers are near the cartridge and the slip mat has a significant static charge since it always comes off with my vinyl. The hum also goes away when I unplug the inputs in the preamp.

Etymotic ER6i: When I swapped to Apple's garbage EarPods I couldn't hear any hum even with the volume maxed out but that could be due to the poor quality.

Power Strip: It's a cheap Best Buy strip and my building was built in the 1800s.

Thank you for any help you can offer!

commsysman
commsysman's picture
Offline
Last seen: 15 hours 18 min ago
Joined: Apr 4 2006 - 11:33am
Hum

The fact that it changes when the signal changes indicates to me that the problem is in the circuits of the phono preamp. I don't think anything else could do that.

It sounds as if the phono preamp circuit has some sort of internal grounding problem. There could be a loose connection or cold solder joint in the wiring.

I would open up the preamp and look for any loose mounting or grounding nuts or screws.

I would also make sure there is a ground wire from your amplifier chassis to the phono preamp and turntable grounding point. They should all be tied together to a good ground. Since your wiring may not include a good ground, it would be good to get a grounding clamp and clamp it to a metal water pipe and run a wire from it to your amplifier chassis.

Catch22
Catch22's picture
Offline
Last seen: 3 hours 59 min ago
Joined: Nov 21 2010 - 1:58pm
Your 12AX7 could be noisey

Just another possible consideration. Hums are often grounding issues, but don't discount the tube creating the problem. It could be a simple reseating of the tube in its socket or replacing it. 12AX7 tubes are prone to being noisey to begin with and I would think it would be particularly problematic in a phono stage. I had to replace one just a couple of weeks ago that had become microphonic and was humming its own tune.

Touch the tube with your finger when you notice the hum and see if it changes pitch.

Tandrew
Tandrew's picture
Offline
Last seen: 3 days 11 hours ago
Joined: Jul 10 2014 - 11:12pm
Catch22 wrote:
Catch22 wrote:

Just another possible consideration. Hums are often grounding issues, but don't discount the tube creating the problem. It could be a simple reseating of the tube in its socket or replacing it. 12AX7 tubes are prone to being noisey to begin with and I would think it would be particularly problematic in a phono stage. I had to replace one just a couple of weeks ago that had become microphonic and was humming its own tune.

Touch the tube with your finger when you notice the hum and see if it changes pitch.

Actually it does when I touch the tube! It functions on what feels like a much lower wave.

Tandrew
Tandrew's picture
Offline
Last seen: 3 days 11 hours ago
Joined: Jul 10 2014 - 11:12pm
commsysman wrote:
commsysman wrote:

The fact that it changes when the signal changes indicates to me that the problem is in the circuits of the phono preamp. I don't think anything else could do that.

It sounds as if the phono preamp circuit has some sort of internal grounding problem. There could be a loose connection or cold solder joint in the wiring.

I would open up the preamp and look for any loose mounting or grounding nuts or screws.

I would also make sure there is a ground wire from your amplifier chassis to the phono preamp and turntable grounding point. They should all be tied together to a good ground. Since your wiring may not include a good ground, it would be good to get a grounding clamp and clamp it to a metal water pipe and run a wire from it to your amplifier chassis.

I cracked it open and things look ok: http://imgur.com/n8Nm6Es But I will look into figuring out a way to ground it to a metal water pipe since one is in another part of my apartment. Also, currently there's no amplifier in the set up since I only use the Bellari as a headphone amp.

Catch22
Catch22's picture
Offline
Last seen: 3 hours 59 min ago
Joined: Nov 21 2010 - 1:58pm
Try reseating it

Sometimes just reseating a tube cleans the connections well enough to get rid of a hum, but it's always a good idea to have a few (hundreds in my case) spares. lol

Tandrew
Tandrew's picture
Offline
Last seen: 3 days 11 hours ago
Joined: Jul 10 2014 - 11:12pm
Catch22 wrote:
Catch22 wrote:

Sometimes just reseating a tube cleans the connections well enough to get rid of a hum, but it's always a good idea to have a few (hundreds in my case) spares. lol

Thanks! I tried reseating it and putting in the stock tube (Ruby 12AX7AC5 HG) it came with. Both displayed some hum, albeit a little differently. Is it just bad luck or do you think something's wrong inside the preamp?

Also the hum disappears when I unplug the RCA inputs in the preamp.

Tandrew
Tandrew's picture
Offline
Last seen: 3 days 11 hours ago
Joined: Jul 10 2014 - 11:12pm
I just fiddled around with

I just fiddled around with the headphone jack and noticed if I rotate the 1/4 to 3.5mm adapter to a certain position the hum stops. However, when it does stop the music sounds like it's playing in a tin can.

Catch22
Catch22's picture
Offline
Last seen: 3 hours 59 min ago
Joined: Nov 21 2010 - 1:58pm
Sounds like you might have found your problem

Hopefully it's just a bad reducer or simple grounding of the plug-in for the phones.

  • X
    Enter your Stereophile.com username.
    Enter the password that accompanies your username.
    Loading