Added a DAC, added a hum. Suggestions?

[etcarroll]

I recently purchased another users Eastern Electric Minimax DAC. It sounded fine at his house. He ran it strictly solid-state, no tube even installed. Also, he had aftermarket op amps. We reinstalled the default op amps and off I went.

At home I installed a Sylvania tube, plug it in, and now have a hum. I also bought one of Triode Pete's 12gauge power cords in the hope that might help, it arrived today, but no change with the hum. So, what to do?

I assume the first step is to remove the tube, and run it solid-state. If that's not it, then plug into a completely different outlet. Right now it runs into a PS Audio quintet with everything else except amp. The amp goes direct to wall outlet, a Leviton hospital grade, and Quintet goes to same outlet.

My fear is that after all the triage, if it still hums, could the problem be the reinstallation of the default op amps? Has anyone ever heard of this as a problem?

I'm feeding the DAC via the Duet receiver, using an AR optical cable.

And the hum is universal, it doesn't matter which source I select at the preamp, it just hums. The only way to terminate the hum, is to unplug the power cord from the DAC.

[etcarroll]

The one positive so far, well, after the overall improvement in sound the dac does make-has been the addition of Pete's power cord!

So far all I've done is run Internet station through the dac, Radio Paradise, at 192 bits, but it's obvious the sound is up another notch. I'm in complete agreement with the following statement made about Pete's power cords in a different thread as follows;

"After installing Pete's cord, everything got a lovely warm glow to it, round and beautiful.. yet forceful.  Some transient attack edginess was missing and replaced with more subtle transitions.  It did make for a more musical sound overall. The mids seemed thick and rich which I liked.  It wasn't mushy, just rounded."

I won't be able to speak to the loss of transient attack until I start running flacs through it which won't be for a few days, but I can already tell this is a keeper.

Thanks Pete!

[Emil]

We reinstalled the default op amps and off I went.

Hmmmm. Did you listen before or after?

[Bill O'Connell]

Did you test the tube? Sounds like a bad tube. Does it hum when the SS output is used and tube still in the DAC.

Pull the tube out and run it thru the SS output.
 Roy called me today and claimed no op-amps were rolled or that he never tried pulling the tube and only ran it in tube mode. Hmmmm.

[machinehead]

Ground issue?

[richidoo]

Congrats on your new DAC Gene, nice choice. Since the DAC plays music OK, then the opamps were installed correctly.

The tube should not cause any trouble, but pull it just to remove the variable. Once you find the quiet then you can start adding things back.

If this is EE DAC version 1 with volume control, connect the DAC directly to the amp. If it is version 2 use Duet to turn down the volume digitally, then connect to amp. By removing the preamp, if the hum is gone you exonerate the DAC and amp.

Hum is usually caused by resistance in the ground circuit. Ground is not absolute zero volts. Silent ground need only be the same ground voltage everywhere, but not necessarily zero volts. Resistance on ground connections causes voltage to vary in the ground circuit, causing current to flow and make the hum.  Your mission, if you choose to accept it, is to find the source of resistance.

Most components do connect the signal and chassis grounds together inside the component, so that's how loops form between signal and power sides, they are both part of the ground circuit. The total ground circuit includes the whole system and the house wiring, not just the grounding inside one component. Their grounds all connect together so it is one big circuit. There is always voltage on a ground circuit, but if it's the same everywhere then it's silent. A few mV is common. But if there is any abnormally high resistance anywhere in the ground circuit then current will flow across that resistance and this current is the hum. It hums like AC because AC power supply is always grounded for safety. But even battery powered components can be a source of hum when connected by IC to an AC powered component.

Clean tight wires is first thing to check. Usually the resistance comes from temporary connections. These can be obvious, like dirty RCA plugs and jacks, or hidden, like two outlets with separate grounds. One outlet ground runs back to service box with dedicated ground wire. The other outlet is a shared circuit with wire stabbed outlets and a ceiling lamp with twisted connections.  All those mechanical connections increase resistance, causing a ground loop in the house wiring when those two outlets are used simultaneously in a audio system that is interconnected with signal wires. Moving your ground testing system to one outlet cures this.

Any kind of antenna, cable or satellite cables will usually cause hum. Also think of whatever other changes may have happened in addition to the new DAC. Moving things around, changing plugs, etc. Often several changes are made at the same time that we don't realize. Simplifying the system to basic components removes those variables.

[Bill O'Connell]

Rich,

 That is by far the best definition of how ground loops are caused. You da man
 I really do think it is the tube though as Roy said he never had any problems with the DAC..
 
ET,
By chance do you have another 12au7 you can try in the DAC?

[etcarroll]

Did you listen before or after?

After, when I got it home.

Does it hum when the SS output is used and tube still in the DAC?

Yes. (Sorry, don't know who Roy is, you may be thinking of someone else)

Rich - great response - as for other wires, this is dedicated 2-channel, no other cables/wires.

To rest, thanks for insight, I will recheck/reseat all wiring, and I have 2 boxes of 12au7s, I just started with the Sylvania  as it was the tube I started with in my Purity One pre.

Going to a 'how to pay for college conference tonight', on my return I'll try this 1st;

'Pull the tube out and run it thru the SS output.'

[Bill O'Connell]

oops,sorry,I was confusing you with somebody else.

[etcarroll]

'Pull the tube out and run it thru the SS output.'

Nope, no change like this.

Guess it's tims to get behind the rack and start re-wiring.

[rollo]

   does the DAC have a three prong plug ?? If so try lifting the ground. Are you using one circuit for all components ? If using two different circuits a possible ground loop.
   The EE DAC in my system would not lock until we flipped the CD ground switch. Hummed as well. It was not the tube in my case. Good luck.


charles

[etcarroll]

While playing with powercords this weekend I also pulled the dac far enough away from my rack o that I could plug it into an outlet on a different wall, 90% of the hum gone.

I tried a ground lift, but TWL makes it's ground prong so big I couldn't get it into the ground lift plug, and didn't want to force it.

[richidoo]

Glad you found a good clue Gene. Sounds to me like bad connection(s) in the house wiring in that circuit.

To fix it, first determine what outlets, switches and ceiling lights or anything else is on the breaker of the audio outlet you want to use. With the breaker open, open up each of those junctions and improve all of the connections. If any wires are back stabbers, moved those to the side screws. If they are already screwed, then tighten them very tightly. If there are wire nuts, open them up and make sure all wire ends are even and all are twisted together and tight when capped. You will probably find some connections that need improvement, hopefully some of those will improve your ground and reduce the hum.

A dedicated line eliminates these wiring problems and their associated resistance (increased even when the connections are perfect.)

One loose connection on neutral or earth anywhere in the shared circuit can cause the problem you had. Because it went away with a different outlet it's probably not the audio gear cause. Maybe the other outlet is on a different circuit, or it is closer to the breaker and ahead of the bad connection. Use a voltmeter to check every outlet before you open it, and be careful. Consider upgrading the audio outlet with a Jena Labs duplex while you have it open.

[eleazar]

I talked to Gene about a dedicated line. It will be a little work as his panel is in the garage but I think when can get it done. I looked and he has plenty of open spaces............Bill

[richidoo]

That's awesome! Have fun guys.

Use 10ga romex instead of 12ga to reduce resistance, especially on a long run. 10ga is used for 20A circuit, but upgrading the breaker to 20A is optional, you probably won't need it and you could do that later. Better to spend on a nice outlet. 

If by chance you end up doing two dedicated runs, they should be on the same leg, so all audio is using the same phase AC.