2. tech-talk
  3. 153942-4290

Yet another need help with a ground hum thread

Hi all I am hoping that someone can help me out here. My sources are split between the living room and a small bedroom. I have a pair of Mackie monitors and a pair of SVS sb1000’s in the living room with a Schiit passive preamp and a Schiit mani DAC. I have my Technics SL 1200 in another room with a Icon Audio ps1 mkii. The turntable is in the other room to solve a feedback issue I was having. Upon first setting the turntable and preamp up I got an  immediate  ground hum. I tried the ground lift on the preamp and it didn’t help. The only thing that seemed to help was running an extension cord to the same outlet everything else was plugged into. I lived like this for a while until I could install an outlet on the same circuit thinking that would help. The circuit is run from the panel to a junction box where it splits to go to the living room and the room where the turntable and preamp are. Upon hookup the hum was back. The hum is present even when the preamp is not turned on. No idea what is going on with that. I have a super cheep Pyle phono preamp with a wallwart power supply I keep as a spare. With the Pyle hooked up no hum just a very slight buzz which I assume is the power supply.  My question after all of that is does anyone have any thoughts on how to eliminate the hum with the Icon Audio preamp? Do you think it is a issue with it being a tube pre. Would a solid state pre have the same problem?
128x128wilson667
tablejockey
3,892 posts
 
Timely thread.

I just got an RMA to send my tubed phonostage back for a pesky hum.

Did all the obvious ground connection-lift etc.
Isolated hum to the phonostage output(disconnected input)

Opened up the unit. Followed  connections from the jack, noticed some wire touching each other. 


Saved myself the hassle and expense and most important-downtime .

Nice and quite now! My unit is full tube-rectifier and active gain. Almost as quiet as a church mouse.

I'll leave diagnostic suggestions to more qualified posters. Likely something simple. Tubed phonostages(even the finest) have some degree of noise. You're just not expected to listen with an ear pressed against the speaker grill. Otherwise, it should be acceptable to most ears.
millercarbon's avatar
millercarbon
12,531 posts
 
Do you think it is a issue with it being a tube pre. Would a solid state pre have the same problem?

No, and yes.

Hum is a simple subject that only seems complex because of all the many different situations it crops up in. But hum is as simple as this: Any time you have different paths to ground you risk getting hum.

Your hum happens because in one room you have the turntable plugged into one path to ground, which presumably the ground goes to the phono stage, which is connected to ground via the outlet they both are plugged into. But then its connected via RCA to another path to ground, the amp in the other room, which has its own path to ground. Your extension cord eliminated the hum because then everything had just the one path to ground.

This one simple rule comes in real handy. Like you would never run multiple dedicated lines you would run one. What you have done is, in a sense, build a system with multiple dedicated lines. Only they aren't dedicated. Just different.
wilson667's avatar
wilson667 OP
93 posts
 
Erik. The turntable and pre are in the same room. The longer run of rca’s is on the out side of the pre and is about 20’ from Blue Jean cables. I believe it is fairly well shielded I have other BJ cable in close proximity to power with no hum.
 Table jockey the hum is not an ear pressed to the speaker situation it is audible from the other room at normal volume. 
Millercarbon is it not the same path to ground if everything is plugged into the same circuit using the same ground wire. I don’t understand how a extension cord is different than running romax off of a junction box.
erik_squires
16,056 posts
 
I'm not worried about how well it's shielded. I'm worried that the guage of the shield is too thin. What happens if you shorten the RCA cables to 1 meter, and lengthen the power cable?

That's the kind of diagnostic I was hoping for. :)


But have fun, I've helped all I can.
Post removed 
More to discover