Velodyne SMS-1 and ground loop

G

georgep

Audioholic Intern
I have read this site's article on ground loops, but am having some trouble understanding my situation.

First of all, my house is old and has original wiring from the late 20s, which incidentally does not have ground wires. None of my previous AV equipment is grounded save my subwoofer (unfortunately have to use a cheater plug). My AVR is connected to my television, and I have never had ground loop problems in the past. All my AV equipment utilizes one outlet, except the subwoofer, which utilizes a different outlet, though it may share the same circuit as the rest of the AV equipment.

After adding the SMS-1 to the picture, my system developed a light "hum", and although the transformer that is between the SMS-1 and the outlet has a ground prong, the wire supplying power to the SMS-1 has only two conducters. As well, the SMS is plugged into an ungrounded outlet. Removing any connections to the subwoofer would not alleviate the ground loop. In swapping cables, only removing the sub-in cable that is coming from the AVR will alleviate the hum. The cable itself is a 75 ohm coaxial cable originally sold as a composite video cable.

Does a solution seem apparent without using one of those ground loop cheater thingys, and how is it that I have a ground loop in an ungrounded system? Any help would be greatly appreciated.

Thanks,

George
 
mtrycrafts

mtrycrafts

Seriously, I have no life.
georgep said:
I have read this site's article on ground loops, but am having some trouble understanding my situation.

First of all, my house is old and has original wiring from the late 20s, which incidentally does not have ground wires. None of my previous AV equipment is grounded save my subwoofer (unfortunately have to use a cheater plug). My AVR is connected to my television, and I have never had ground loop problems in the past. All my AV equipment utilizes one outlet, except the subwoofer, which utilizes a different outlet, though it may share the same circuit as the rest of the AV equipment.

After adding the SMS-1 to the picture, my system developed a light "hum", and although the transformer that is between the SMS-1 and the outlet has a ground prong, the wire supplying power to the SMS-1 has only two conducters. As well, the SMS is plugged into an ungrounded outlet. Removing any connections to the subwoofer would not alleviate the ground loop. In swapping cables, only removing the sub-in cable that is coming from the AVR will alleviate the hum. The cable itself is a 75 ohm coaxial cable originally sold as a composite video cable.
Does a solution seem apparent without using one of those ground loop cheater thingys, and how is it that I have a ground loop in an ungrounded system? Any help would be greatly appreciated.
Thanks,
George

Two more experiments if you would.
Unplug the cable TV to the audio receiver or any connection to the tv or both. What happens?

If still humming, try to wrap the sub power cord 'tightly' around the sub input cable and see what happens. Jneutron, a most knowledgeable person posted this solving his completely. Won't hurt trying.
 
N

Nick250

Audioholic Samurai
I am weak on electrical stuff, but how about a second cheater plug?

Nick
 
mtrycrafts

mtrycrafts

Seriously, I have no life.
Nick250 said:
I am weak on electrical stuff, but how about a second cheater plug?

Nick

Not sure I see where he would use it. He uses one on the sub amp. Where on the 2nd?
 
N

Nick250

Audioholic Samurai
mtrycrafts said:
Not sure I see where he would use it. He uses one on the sub amp. Where on the 2nd?
On the SMS-1.

"After adding the SMS-1 to the picture, my system developed a light "hum"
 
G

georgep

Audioholic Intern
Thanks for the replies, but the SMS-1 is also plugged into a cheater of sorts - although I couldn't ground it if I wanted to because the wiring in my house in ungrounded, which is the source of my confusion as to why I have any hum at all.

mtrycrafts, I haven't had a chance to try your suggestion about wrapping the power cord, but the SMS causes the hum even when it is not plugged in at all - i.e. with every other cable and cord disconnected, only the 75 ohm coax cable coming from the LFE output on the receiver is causing the hum when plugged into the SMS - makes me wonder if it is the cable itself?

George
 
G

ggunnell

Audioholic
Any way you can get everything plugged into one outlet? This should eliminate ground loops through the house circuits...
 
G

georgep

Audioholic Intern
It is all connected to one receptacle when i disconnect the sub - but the hum is still there. There is an intermediate gound-defeated power bar to provide additional outlets to the system, but I do not know if this makes a difference.
 
G

ggunnell

Audioholic
You mentioned the coax between the recvr and SMS-1 -- have you tried swapping it with another cable in your system?

The hum comes out of the sub, right? Not audible in main speakers? And with the SMS out of the system (coax run directly from rcvr to sub) there is no hum?
 
mtrycrafts

mtrycrafts

Seriously, I have no life.
Nick250 said:
On the SMS-1.

"After adding the SMS-1 to the picture, my system developed a light "hum"

Yes, he had to use one cheater for it. The rest of his components apparently have 2 prong connectors, no cheater needed.

Oh, maybe you meant piggy back them; the second eliminates the firsts issues:D
 
G

georgep

Audioholic Intern
ggunnell said:
You mentioned the coax between the recvr and SMS-1 -- have you tried swapping it with another cable in your system?

The hum comes out of the sub, right? Not audible in main speakers? And with the SMS out of the system (coax run directly from rcvr to sub) there is no hum?
I intend on trying a different cable when I get a chance (away from home for the next few days) to see if the cable is somehow responsible, but the hum actually comes from all my speakers. There is also no hum when the sub is directly connected to the AVR. Only since the SMS was installed has the hum developed - and the hum is there even if the sms is not plugged in. It is strange.
 
G

ggunnell

Audioholic
Yeah, sure sounds like a ground loop. I lived in a 2 wire house for a long time so I know what you are going through.

One thing you could try when you get home is touching the tips of an interconnect (or any piece of wire) between the AVR chassis and the SMS chassis -- does this affect the hum?

Do you by chance have another wall transformer of the same voltage/
polarity/tip size you could try to power the SMS-1? The Velodyne transformer may NEED a separate ground, most are just two-prong...

I don't want to get into this too far, but you can check into the building ground in this house -- greatly oversimplifying, all the white wires should be bonded to an earth ground but these old structures vary a lot, call an electrician if you are inexperienced in residential electric...
 
G

ggunnell

Audioholic
Yet another thing you could try (although this shouldn't make a difference you never know) is plugging the SMS-1 transformer into the accessory outlet on the back of your receiver, using a cheater plug to adapt 3-prong plug to 2-prong outlet...
 
jeffsg4mac

jeffsg4mac

Republican Poster Boy
Also, some other appliance may be the cause. I have a hum generated by a remote dimmer switch that I put in. When it is on I get hum, turn the lights off and the hum goes away. Try turning everything off and see if it goes away. If so, then turn back on each thing until you find the culprit.
 
G

georgep

Audioholic Intern
These are all interesting suggestions. I will have to try them when I get back home on the weekend.

By the way, the SMS transformer appears to require a ground as it has a ground prong. But from my recollection, the cable going to the SMS from the trasformer appeared to be two-conducter - but I would have to double check this.
 
W

westcott

Audioholic General
If you try another subwoofer cable, get a Belkin design or a cable with double braided shielding.

Try to keep power cables away from AV cables.

The suggestion to get an electrician to help with this older wiring in your home is always a good idea. Without proper grounding, it is hard to protect your valuable equipment as well as one could.
 
G

georgep

Audioholic Intern
So I have tried a number of things including many of those suggested:

- hum is there whether SMS is plugged in or not
- hum is there whether television coax cable is attached in to TV or not
- hum is there whether AVR is connected to TV or not
- hum is there whether subwoofer is connected or not
- hum goes away when the coax from the AVR's sub out is disconnected from the SMS
- the hum goes away when the sub is connected directly to the AVR
- hum was still there when I tried a different (supposedly higher end) coax between the AVR and the SMS.

Any thoughts?

And if I were to use one of those ground loop disruptors where should it be placed?
 
W

westcott

Audioholic General
georgep said:
So I have tried a number of things including many of those suggested:

- hum is there whether SMS is plugged in or not
- hum is there whether television coax cable is attached in to TV or not
- hum is there whether AVR is connected to TV or not
- hum is there whether subwoofer is connected or not
- hum goes away when the coax from the AVR's sub out is disconnected from the SMS
- the hum goes away when the sub is connected directly to the AVR
- hum was still there when I tried a different (supposedly higher end) coax between the AVR and the SMS.

Any thoughts?

And if I were to use one of those ground loop disruptors where should it be placed?
I agree with the others. They make a test plug to test ground problems at the outlet and even light fixtures.

The transformer needs to go at the destination end. Well, you say, where is the destination end??? There in lies the crux of the matter. You may have to experiment but I would really try to find the ground problem, circuit by circuit, if necessary. It is long and tedious and requires a TRUSTED friend or electrician to try to isolate the problem.

If you are lucky, a transformer between the sub and the outlet would work. I would need clarification to help you narrow it down. There are audio connections and power connections. Both can contribute but I suggest focusing on what is powered or not and what changes when you attempt a process of elimination as you have above.

Good Luck and let us know how it works out.
 
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G

georgep

Audioholic Intern
westcott said:
They make a test plug to test ground problems at the outlet and even light fixtures.
Thanks for the suggestions, it has been quite frustrating. But do they make a test plug for an ungrounded wiring system? And who makes such a plug?

Thanks,

George
 
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W

westcott

Audioholic General
georgep said:
Thanks for the suggestions, it has been quite frustrating. But do they make a test plug for an ungrounded wiring system? And who makes such a plug?

Thanks,

George
Your only option is to run new grounded wiring for all branch circuits from the box. If you follow the procedure of pinpointing which circuit may be causing your line noise issues, you may only have to ground that circuit.

Wish I had better news for you but it is not as difficult to do with a little patience or money.
 
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