Hum chasing...

[steveinaz]

The recent addition of a Direct TV HD STB and BluRay disk player has me chasing hums again....*sigh*

I think I have this one sorted out, but I'll have to settle for "good enough" with the damn STB. The Panasonic BluRay was introducing some minor hum--I cured that by going Toslink into the Benchmark DAC--all good, quiet all the way to max volume (CDP and DVD share the "CD" input on the PRE; the HDTV goes to the "AUX" input on the PRE).

Now, the STB. Believe it or not, it's not your typical satellite/cable feed hum. Unplugging the coax feed does nothing, the hum is still there. I think the STB just has what they call "dirty power." I actually got better results (less hum) by running the TV audio out from the HDTV via RCA's to the preamp.

So now I've got the CDP and DVD perfectly quiet, the satellite signal fairly quiet (hearing the hum requires almost maxing the pre's volume). Just a little disappointed that they can't build a quiet damn box. I think the problem is, both the STB and the BluRay player use the 2 prong AC plugs, no dedicated ground. Everything else in the system is 3 prong, and quiet. Then again, if it was ground loop hum, it would pass it on to all of the connected equipment at the preamp--which it isn't. Must just be a noisy STB?

You'll note in the diagram that everything except the power amp is plugged into a common grounded Panamax 4300--so I don't have mixed potentials there, and the amp/pre when running by themselves are dead-quiet--so using the amp plugged direct isn't causing any mismatch.

[PolkThug]

Maybe try one of these:

[steveinaz]

The problem is, all the evidence points to it being a noisy power supply in the STB, not a ground loop hum. The strange thing is, the HDTV takes the HDMI signal, then provides the analog audio out to the preamp--with less noise. You'd think the extra "step" would increase noise? Trying to run analog audio out from the STB to the Preamp increases the noise.

The other evidence is that a ground loop hum would be passed on to anything connected to the preamp--but it doesn't effect the "CD" input from the Benchmark DAC--it's totally quiet; it only effects the "AUX" input. I'm baffled.

Has anyone experimented with replacing 2-prong AC's with 3-prong, and grounding the chasis with the extra wire? Don't know if that would help though...

[steveinaz]

Maybe a Toslink splitter? Run both the STB and DVD via Toslink into the DAC?

[billbillw]

Ah, Parasound amps....
I've found that Parasound gear is very picky when it comes to ground loops. I had to lift the ground on my HCA2200 and my PLD2000 to get rid of hum. You might try using a cheater plug just with the Parasound amp and see if it helps. Parasound even suggests this in their manuals when trying to eliminate hum, so there isn't really any harm to be done.

Also, have you tried coax (or optical) output from the Directv box straight to the DAC? I think you'd like the sound better that way. In my bedroom setup, I noticed a big improvement when I started going straight (via dig optical) to the receiver versus using the sound output from the TV. The TV sound output sounds dull in comparison, like it is downsampled or something. Granted, that's a Panny Plasma and a Denon receiver combo, but it might be worth checking out.

[steveinaz]

Toslink works fine from the STB, problem is I need my 1 toslink input for my DVDP. Cheater plugs are a band-aid fix, and a dangerous one at that--I don't like'm. Working backwards, connecting 1 item at a time; ie. AMP--PRE--DAC--CDP-->all is quiet until we get to connecting the STB or the DVD player. I cured the DVD with a toslink connection--dead quiet now. The STB is noisy even with the cable feed disconnected from the wall, so it's not a ground loop from the satellite set-up.

The amplifier isn't contributing to the problem, it's upstream.

[AndyGwis]

Back in my high school / college days, I would spent a lot time looking for a hummer.

[steveinaz]

I like this setup for 3 reasons; (1) Good bye hum (2) Video components are totally isolated (in terms of electrical connection) from my 2-channel components (3) Only 2 sets of IC's and 1 set of speaker cables used; less is more.

[danger boy]

ok. i'll take a STaB at it. what the hell is an STB?

[steveinaz]

STB=Set Top Box (Direct TV HD box)

[shack]

ok. i'll take a STaB at it. what the hell is an STB?

That would be Set Top Box I believe.

[danger boy]

That would be Set Top Box I believe.

Duh! DOH!! :p

[billbillw]

Toslink works fine from the STB, problem is I need my 1 toslink input for my DVDP. Cheater plugs are a band-aid fix, and a dangerous one at that--I don't like'm. Working backwards, connecting 1 item at a time; ie. AMP--PRE--DAC--CDP-->all is quiet until we get to connecting the STB or the DVD player. I cured the DVD with a toslink connection--dead quiet now. The STB is noisy even with the cable feed disconnected from the wall, so it's not a ground loop from the satellite set-up.

The amplifier isn't contributing to the problem, it's upstream.

The ground loop is from combining grounded and ungrounded equipment. It doesn't have anything to do with the satellite feed or the satellite box. I've had no hum problems with any of my Directv boxes (I've had 8 different ones all together), whether hooked with coax, RCA, or toslink.

I can practically guarantee its the Parasound. It doesn't matter where the component is in the chain (upstream/downstream), current will seek the easiest path to ground. You can find dozens of posts at AVS, Audioasylum, and other forums regarding Parasound problems with ground hum.

Did you try listening with headphones? Disconnect the amp, connect the STB using dig coax to the DAC, and listen to headphones and see if the hum is still there. If you hear hum with the amp disconnected, I will concede that its not the Parasound.

Either way, I would think that an optical splitter would definitely work to isolate the non grounded components.

[steveinaz]

I'll give that a shot--I'm open to any suggestions...

[steveinaz]

Found my solution. Connect the STB via toslink to input 1, BluRay via toslink to input 2, connect output to Benchmark DAC toslink input. Total video isolation from my preeeciousssssss 2-channel. Yeah baby: