When my phono stage is running at high-gain (59dB), I pick up a nearby radio station through it. I've tried all sorts of things with cables and positioning. I realized that if I lean my arm on the cables, or grab them, or even just hold a lead clipped to the body of one of the connectors, it completely attenuates the radio signal. I haven't been able to replicate this with any other technique.
What's happening? What is my body doing that connection to ground isn't? I should note that my phono stage uses a wall-wart AC transformer and is not grounded, although it does provide a ground lug.
UPDATE: Clipping a 3' test lead to the ground lug on my phono stage and simply draping it under the shelf my equipment is on eliminates 90% of the interference. It's not connected to anything. In fact, connecting it to anything, including another lead, brings the interference back. I'm so confused...
What's happening? What is my body doing that connection to ground isn't? I should note that my phono stage uses a wall-wart AC transformer and is not grounded, although it does provide a ground lug.
UPDATE: Clipping a 3' test lead to the ground lug on my phono stage and simply draping it under the shelf my equipment is on eliminates 90% of the interference. It's not connected to anything. In fact, connecting it to anything, including another lead, brings the interference back. I'm so confused...
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Is this from touching the output cables, or the input cables?
Have you tried actually connecting the ground wire to ground?
You need a book on antennas.
Have you tried actually connecting the ground wire to ground?
You need a book on antennas.
Touching turntable to phono stage cables and connectors, and touching phono stage to preamp connectors. Both had similar effects.
Yes, I’ve connected the ground wire directly to wall ground, as well as to the grounded chassis of my amp. Neither improved things. “Loose cord under desk” continue to be the best solution.
I understand the general principles of antennas. And if I move the ground wire(s) around I can *increase* the signal quality of this radio station. What confuses my is why grounding doesn’t fix anything, and why adding a hanging cable makes the interference *better*. I would have thought it would do nothing, or make it *worse*
Yes, I’ve connected the ground wire directly to wall ground, as well as to the grounded chassis of my amp. Neither improved things. “Loose cord under desk” continue to be the best solution.
I understand the general principles of antennas. And if I move the ground wire(s) around I can *increase* the signal quality of this radio station. What confuses my is why grounding doesn’t fix anything, and why adding a hanging cable makes the interference *better*. I would have thought it would do nothing, or make it *worse*
At RF, a wire isn't a wire, it's a circuit.
So which radio station's antenna is right next to your house?
Maybe you'll grow to like it.
So which radio station's antenna is right next to your house?
Maybe you'll grow to like it.
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Yeah, that's pretty close! AM, or FM, radio station?
So .. probably AM -- and the 3' test lead is probably adding a common-mode signal (that is the same demodulated audio phase) to the phono preamp ground, giving the effect of attenuation.
Just guessin' -- Cheers
edit: Do you have a schematic for the phono preamp that you could post? Is it a commercial product or home-brew?
SoaDMTGguy said:
So .. probably AM -- and the 3' test lead is probably adding a common-mode signal (that is the same demodulated audio phase) to the phono preamp ground, giving the effect of attenuation.
Just guessin' -- Cheers
edit: Do you have a schematic for the phono preamp that you could post? Is it a commercial product or home-brew?
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Have a schematic for the input side of the preamp? It might need a small capacitor across the input or possibly a stopper resistor to avoid the problem.
I haven’t caught their call sign, but I assume AM. Sometimes they play good stuff!
Interesting theory… I can believe it.
The phono stage is a Schiit Mani.
Ok, then focus on the input to the phono stage. Try a clamp-on ferrite filter on the turntable leads.
Both channels ideally should go through the same filter, but use two if necessary.
They look like this, but this specific one is not necessarily a recommendation.
https://www.mouser.com/ProductDetail/Fair-Rite/0446173951?qs=JTtBSkyWskgCxUauHOD6DQ==&mgh=1
Both channels ideally should go through the same filter, but use two if necessary.
They look like this, but this specific one is not necessarily a recommendation.
https://www.mouser.com/ProductDetail/Fair-Rite/0446173951?qs=JTtBSkyWskgCxUauHOD6DQ==&mgh=1
I was getting a static-hum in my system between the outputs from the preamp to the 3 way crossover. What rayma said is a ferrite bead, it worked for me, the ferrite clamp on for the left and right channels.
PCC
PCC
Yes, do the first one, and if it's still there, try more on the other cables.
I'd do all of the cables in your system. You can SEE the antenna.
I'd do all of the cables in your system. You can SEE the antenna.
I had two ferrite rings, so I installed them on the turntable-to-phono-stage leads (can't believe I forgot I had them). That helped, maybe 50% improvement. Dangling a lead from the preamp lug still has the biggest effect (connected to the turntable-side lug, it makes the problem *worse*). I also switched to a solid-core ground wire (just happened to pick it up), and found that bending it into different shapes improved or worsened the situation.
I'd do more cables, but it only comes through on the phono stage. So, I'll count myself lucky there.
Would any kind of shielding work? Like if I built a faraday cage around the connection between the turntable and the phono stage?
I'd do more cables, but it only comes through on the phono stage. So, I'll count myself lucky there.
Would any kind of shielding work? Like if I built a faraday cage around the connection between the turntable and the phono stage?
Is the phono stage in a metal enclosure and if so, are the input connectors connected straight to the metal enclosure? If so, you already have a Faraday's cage.
This gave me much pleasure. I'm glad I wasn't drinking coffee at the time or I'd be cleaning my screen and keyboard right now.
PS. Shielding is interesting.
I'm not a fan of Schiit gear ... but, to be honest, radio pickup can happen with any phono stage that hasn't got an appropriate correction installed.
Take the lid off and have a look at the inside of the RCA input sockets; they should have a small ceramic cap from the ground tag to case earth (which should be connected to mains earth, through the IEC socket earth pin).
The value of this cap should be 0.1uF. If the Mani doesn't have this ... I suggest you install it.
Andy
Mmmm - not to my way of thinking! 🙁
If you have a metal case which is connected to the earth pin of the IEC mains socket (or the earth wire, if it is a captive mains cord) ... then you have a 'Faraday cage'.
The ground tags of the input RCA connectors should be isolated from the case.
Andy