One thing vexing me this whole time is referring to the Manley Steelhead phono stage as a preamp. You would not be having these problems if this was a preamp. Your problems stem from the tremendous phono stage gain, something no preamp ever has or does.
These distinctions are important because it helps a lot to understand this stuff. A phono stage includes RIAA equalization. Since the lowest bass on a record is -20dB the phono stage has to equalize this 20dB. That is a lot of amplification, and it comes on top of the 40 to 65dB gain needed simply because cartridge output is so low.
This is the real reason hum is so prevalent in situations like this. Once you understand it you would never in your life even think about putting something like a motor or amp on top of a phono stage. Preamp maybe. Phono stage, never.
If you look inside one of these things you will see the circuit is laid out or organized so that incoming power and transformers are kept as far away as possible from the amplification circuits. Usually both physical distance and physical shielding are used. This is the case with all components. But with phono stages it is taken to extremes, because the phono stage takes everything to the extreme. So it is worth it to call it what it is, and it is not a preamp. It is a phono stage.
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Moving the turntable away from the preamp solved the hum issue. There is no hum regardless of the rpm - it is dead quiet now. While shuffling the gear components around, I've placed a monoblock power amp onto the preamp. That made a preamp generate a different kind of hum. The bottom line, the preamp doesn't like any gear around, otherwise it picks an interference from a nearby component. It's best when it is positioned away from anything else, as far from turntable, a power supply or an amplifier as possible. |
"...Russ, op says he can’t get TT and phono stage any further from each other..."
Can't or won't? I accept only certain compromises but in this case, it needs to be solved correctly. Turntables can be placed in many positions, they don't need to be on top of your gear.
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Russ, op says he can’t get TT and phono stage any further from each other. Maybe sell some of that expensive gear and get a bigger room. (Joke)
ps. I doubt the Steelhead is the source of the EMI. Steelhead has an outboard PS with a long umbilical. I assume the steelhead PS is out of the way on the floor or on a lower shelf. |
Shielding is really just a band-aid. Best to get some distance between components. Electromagnetic fields drop away quickly with distance. |
copper sheet covering tube preamp??
good luck |
You know now that I think of it, at the level of these components what I would do is first test with aluminum foil. Wrap the motor, and fold a sheet for between the table and preamp. Then if that works upgrade the whole thing with some Krissy mats. I have never thought of using them for shielding but that is basically what they are doing. Why settle for eliminating hum when you can get an upgrade out of it?
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Your motor is not well shielded. As others have suggested trying any grounded metal under the turntable might help as would a high output cartridge. It could also be the reverse. Fields from the Manley could be causing the cartridge to hum. Grado's are notorious for this. In either event it should not happen. The phono stage is never that far from the turntable. Mine is also directly under the turntable and the system is dead silent. You might try different grounding schemes. I had run a separate ground from the turntable chassis to the phono stage along with the ground wire from the tonearm. If I disconnect either I get a hum. |
What MC said. Your situation is no surprise, given the extreme proximity of tt and preamp. Cheap and dirty is to use heavy duty alu foil between them or around the motor or whatever works, but it should be grounded. For that you could use a clip lead from foil to ground. Could ground it to the ground lug on the Steelhead. I own a Steelhead too; I think it has two grounds, one for audio and one for chassis. Try each option. I'd be interested to know how it works out for you.
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Never a good idea to stack like that, but we gotta do what we gotta do. Electric motors make electric fields. Preamps are especially vulnerable, phono stages even more so. Distance is your best protection. If you can rearrange to move the preamp lower and farther away that will help even if stuff winds up being stacked simply because it will move the phono stage further away.
Next thing you can do is shield. Vinylzone has one way with the copper sheet. Another is to shield the motor itself. Another is to shield the phono section, or even the whole preamp. Shielding can be anything conductive doesn't have to be copper sheet doesn't even have to be solid. Sheet metal is used inside a lot of preamps to shield the phono section. You can also try battery grounding strap, which is braided tinned copper. Battery strap is fairly cheap and can be cut up like fabric. You could also search for Faraday fabric, more expensive but a lot better looking.
Keith Herron suggested aluminum foil as a cheap and easy test. Never tried it myself but, Keith Herron, worth a shot.
Any of these whatever you try will work better grounded to earth ground- your AC ground will do fine. Just not grounded to the preamp.
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Not certain if the hum is originating from the cartridge and/or the motor.
Anyway, there is a product called Mu-Metal (sold in sheets) that you might try placing over the transformer(s) in the Manley.
You could place the sheet on top of the preamp case.
DeKay |
You can try placing a grounded copper sheet between the TT and preamp, on the shelf where the turntable sits.
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You need to give your turntable it's proper space and support. Stacking a turntable is not going to work. |
The turntable is Oracle AC and the pre-amp is Manley Steelhead. |
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