[Mass. Wine Guy]

I just got a used ClassD Audio SDS254 power amp to replace my old Adcom GFA 535, and now I'm getting a low level hum where there was dead, total silence before. I would be extremely grateful for suggestions or ideas about getting rid of this noise.

My setup is simple. Just the amp, a Morrison E.L.A.D. preamp, an Arcam CD-72 player and a pair of Silverline Minuet speakers. I don't have any special interconnects or speaker cables, though the 12 gauge wires I run for speakers are much longer than they really need to be. I connect them using just bare wires. The only additions I made are a BPT C-9 power cable for the amp and Beresford TC-7520 DAC that I'm evaluating on loan.

I'm thinking perhaps I connected the output on the DAC to the wrong set of connectors. There are line fixed and line variable outputs and I have the cables attached to the line variable outputs. The thing is that the hum is there even if I turn the DAC off.

Everything I've heard and read about the amplifier mentions how quiet it is. Still, could it be amp?

I'd be extremely grateful for any tips on trouble shooting this problem.

Thank you very much.

[raindance]

It is grounding. How is the ClassD amp wired? Try a cheater plug on the ClassD amp.

[Mass. Wine Guy]

By cheater plug do you mean the little thingie that you plug a three prong plug into so you can plug it into a two prong outlet? Will this be risky in any way to the amp? Actualy, it sounds a little dangerous. The third prong must be there for a reason.

I didn't build the amp so I don't know how it's wired.

This seems to get some good comments from people who buy it:

http://www.audiomidi.com/Hum-X-Ground-Hum-Exterminator-P4803.aspx

Does such a device filter out some desired frequencies along with the hum?

[srb]

By cheater plug do you mean the little thingie that you plug a three prong plug into so you can plug it into a two prong outlet? Will this be risky in any way to the amp? Actualy, it sounds a little dangerous. The third prong must be there for a reason.

The theory of a safety ground is to protect against a hot internal power connection accidentally coming in contact with the metal case and causing an electrical shock when you touch the case and your body provides the return ground path for electrical current.
 
Not all amplifiers have safety grounds, and a few that do have a ground lift switch to possibly eliminate hum in a ground loop situation.  If I'm not mistaken, your Adcom amplifier has a captive two-conductor non-grounded power cord and therein lies a difference between your previous and present system.
 
While I'm not necessarily recommending that you permanently operate the new amplifier without a ground, a simple 3-prong to 2-prong "cheater" plug can sometimes be an easy temporary troubleshooting tool.
 
Steve
 
 

[Wayner]

Odds are, and you should check this out, is that one of your other components also has a 3 prong grounded plug. If that is the case, only one component should be grounded (and that's not even true), as the ground will be carried thru to the other components via the interconnects shields. That is why you have a ground loop, because you have several sources to ground and not thru a common point. Putting a cheater plug on the amp, as Raindance has suggested, will cure your problem and the install will be safe. Your new amp will simply be connected to the power grid, as your old amp with the 2 wire system, still probably grounded thru another component.

Wayner

[Mass. Wine Guy]

Well, ok. But are you sure I'm not in danger of ruining my equipment (or me) by using that cheater plug? Worth a try. Thank you.

[Speedskater]

My standard "hum" troubleshooting procedure:

a] Un-plug everything.
b] Use all plane-jane cables.
c] Connect amp power to the wall outlet and connect loudspeakers.
d] Using a portable battery powered music source, does it hum?
e] Connect one control or input unit, does it hum? (use a plane-jane outlet strip)

Continue on adding units and fancy accessories.

Another question to ask is:
Does it hum 24 hours a day, seven days a week?

[timind]

Well, ok. But are you sure I'm not in danger of ruining my equipment (or me) by using that cheater plug? Worth a try. Thank you.

Wayner's suggestions are perfectly safe for your application.

[Ericus Rex]

Cheater plugs are perfectly safe as long as you have one component grounded.  All others would ground through this one component via the interconnects.

Also try putting your new amp as far away from the other components as possible.  I have experienced amps picking up noise from other nearby transformers.

[srb]

Although another grounded component will provide a ground connection to a non-grounded component through an interconnect, it doesn't follow conventions for a safety ground.
 
The reason why the ground wire in 3-wire power cords and Romex wire is the same or close to the gauge of the current carrying conductors is that when a breaker does trip due to a hot wire connecting to ground, although the breaker trips quickly, it's not instantaneous and the extremely short duration of high current flow is not designed to be returned to ground through an interconnect shield or small 26 gauge conductor of a non-shielded interconnect.
 
If very tiny gauge safety ground wires were acceptable, manufacturers wouldn't incur the added expense of a building their cables with larger third ground wires.  Although I agree that not using the ground wire on your amplifier would be likely be OK, for liability and legal reasons didn't want to go on record and recommend it for purposes other than troubleshooting.
 
A larger gauge single ground wire separately connected between metal component chassis will also provide safety grounding.
 
Steve
 

[Wayner]

The inclusion of a ground lug on hifi equipment offers no additional "safety" to the consumer, unless he/she was going to listen to music naked, wet, standing on a damp surface, like wet concrete or wet grass, and the component had a failure, that the line hot would come into contact with the chassis. In a class II install (2 wire), it is perfectly safe. Equipment manufacturers that produce products with ground wires and not offering a way to defeat the ground, ask for nothing but audio gremlin ground loop problems.

Many components I have only have a 2 wire cord, like my Marantz CD player, Onkyo Tuner, all of my turntables and even my toaster only has only 2 wires. If you still are completely scared, then have an electrican install a GFCI outlet for your cheater plugged amp.

Wayner

[Wayner]

Steve is correct that the interconnect shield is not an official ground, but it is "unofficially" and is capable of delivering badness, or goodness, depending on the situation. It is the conductor component that unifies all of the system components.

Wayner

[srb]

Many components I have only have a 2 wire cord, like my Marantz CD player, Onkyo Tuner, all of my turntables and even my toaster only has only 2 wires.

Just wondered why no inclusion of the obvious ones in that statement - your Audio by Van Alstine components !
 
Steve

[Wayner]

You know in my entire house I have many, many components and there are only 2 components that have the 3 prong power cords, those being my MartinLogan reQuests. Tho they run on very high voltage, like 5000 volts, the shock value is very low.

Even my Sunfire II poweramp is only a 2 pronger. Anyway, that is probably the only way the OP will get rid of his hum problem, and then be done with it. However, there is another way to power everything and it might help. That is with a unified power strip where every component is connected to the same power plane. Remember that even eddy currents leaking to ground will cause the nasty 60 cycle (50 cycle other places) hum. PS Audio offers a big buck power cord for the 3 prong IEC socket with a removable ground pin, if that would help, assuming the ClassD has an IEC power inlet.

Wayner

[srb]

PS Audio offers a big buck power cord for the 3 prong IEC socket with a removable ground pin, if that would help, assuming the ClassD has an IEC power inlet.

On most every ClassD amp I have seen posted on the ClassD build thread, the builder used an IEC inlet.  I have one of the PS Audio cords that an amp seller threw in the box as a surprise bonus (although I really didn't hear any improvement over my Volex 17604), but I was kind of impressed with the rather sturdy screw-in removeable grounding pin which I had never seen before.
 
Steve

[Mass. Wine Guy]

Ok, I'm willing to defy death and use a cheater plug to see what happens. My main concern is that I don't want to wake up in the middle of the night to a fire. This doesn't seem to be a close possibility.

[mjosef]

FWIW, I built my CDA amp without a ground, this was just the initial build to make sure everything worked. ANd it was fine, was dead quiet. ANd I left it on continuously for 2 days.
I am in the process of drilling out an IEC hole on the chassis...so on completion of final build I will have a ground connection via a three prong power cord.
You won't go up in flames even if you massage the chassis while naked. Dunno bout the dripping wet part. 

[bside123]

Mass. Wine Guy:

Not that you haven't gotten enough reassurances, but just to throw another positive hat into the ring...

I have an SS amp in one of my systems that I was having a ground loop, hum problem. I lifted the ground of the amp with a "cheater plug," and although I didn't like having to do it, the hum went away. Oh by the way, that was two years ago AND I never turn the amp off. It's on 24/7. Nothing's been burnt with the exception of my pocket book. It's audio ya' know.

[srb]

Not to mention the people who have homes that aren't equipped with grounded receptacles.
 
Steve

[Mass. Wine Guy]

Alright everybody. I will be brave and report back (if able).