Measuring A Capacitor

Most problems of this type are not caused by pickup of electromagnetic fields through the air, which would be potentially helped by shielding (if it is properly grounded).

They are more often caused by differing ground potentials between the chassis of the components that are involved, which causes extraneous currents to flow in the shields of the interconnects between them (which are connected to chassis, and which serve as the return path for the signals the interconnects are carrying, resulting in the extraneous currents being seen as signal by the load device). That will only be helped by foil if it provides a path between the components that is both complete and of lower impedance than the shields of the interconnects.

With both the TT and the preamp having 2-prong plugs, and ac safety ground therefore not being connected to the chassis, they both have chassis that are pretty much floating with respect to ground. If they happen to float to different levels, it would result in the extraneous current flow that I spoke of. When you touch the faceplate, you affect the level to which the preamp chassis floats.

So I would again suggest trying all possible combinations of ac plug polarities (which affects the levels to which the components float). Also, try connecting a wire between the preamp chassis and ac safety ground (the screw at the center of the ac outlet cover). Also, the other things I mentioned in my last post that have not yet been addressed. And seeing if anything can be done to improve or shorten the connection between preamp and turntable ground.

HTH,
-- Al

Yet another reason why I gave up on LPs: phono pre-amps :)

Lee, the tin foil must be grounded to be an effective shield. Simplest way to do that is to use an alligator clip from the a known ground on the (pre/integrated)amp (chassis ground lug, chassis, outside of a RCA jack,etc) on one end and then clip the tin foil on the other. That will create an effective EMI/RFI shield... which still may not be your problem.

You are chasing the wrong problem with the aluminum foil. You have a grounding issue. They can be very frustrating and confusing as evidenced by the fact you touch it and it goes down. I was once trying to track down a hum problem by using a clip lead to connect various points on various pieces (preamp, power amp, phono stage, turntable) and after having no luck I clipped one end on the preamp with the other end hanging in space just as place to put it while I thought about it and the hum went way down. This was very repeatable and I called in others to make sure I wasn't insane.

Almarg gives good advice on things to try but his paranoia about static being amplified 10,000 times is just that, paranoia. In order for static to jump you need quite a few volts so you aren't going to get quite a few times 10,000 volts out of your system. At worst you will get a very, very, very brief pop equivalent to a very, very, very, brief clipping of the amp. However, it could be a problem because that static discharge into the input could damage the transistors it hits, so his advice is once again good even if the reasoning why is flawed.

Almarg gives good advice on things to try but his paranoia about static being amplified 10,000 times is just that, paranoia. In order for static to jump you need quite a few volts so you aren't going to get quite a few times 10,000 volts out of your system. At worst you will get a very, very, very brief pop equivalent to a very, very, very, brief clipping of the amp. However, it could be a problem because that static discharge into the input could damage the transistors it hits, so his advice is once again good even if the reasoning why is flawed.

Please re-read my post. I said nothing about static jumping, in the sense of a spark such as might occur if a static-charged person puts his finger near a grounded light switch. I also said nothing about 10,000 volts.

I referred to the static charge being directly conducted into the phono input, through a conductor (the foil). And obviously any significant discharge (greater than the few millivolts that the cartridge would normally put out) would clip the system before the full 80db gain (10,000x) were realized, but that is beside the point. The point is that there would be a very large transient put into the system, albeit a very brief one (as you stated). And its very brevity could very conceivably exacerbate the problem, because the consequent high frequency spectral components would cause the transient to be routed by the speakers' crossovers to the tweeters, which are much more vulnerable than the lower frequency elements.

I certainly can't prove that damage would occur, or even that it would be likely, but it would certainly seem prudent to turn the system off.

Regards,
-- Al

Please reread your own post. You did say it would be amplified 10,000 times. And it would not be "a very large transient." it would be a slight pop that clipped it for a minuscule amount of time. Look, it happens all of the time in the winter. I walk across the room to change the record and when I touch the tonearm I feel a discharge which creates a pop in the speakers. Over and over and over and over again. The tweeters still work just fine.

please reread my post. You evidently don't understand electrostatic discharge. You don't have to have a spark like the kind that jumps from your hand to the light switch for a discharge to occur, Most are never felt. For it to occur it would have to at some point jump the gap. When it did, however small it was, it would drive the system to clip for a instant. There is no way in the world that a very brief pop from the system would take out a healthy tweeter. It is however not unlikely that a static discharge through the input devices could damage one of them and that is the point that we both missed earlier. As a matter of fact, turning off the system would do nothing to protect those input devices. The static discharge through them would be the same no matter if the system was on or off. The only protection in that case would be to follow safe ESD practices.

You seem to be one of these people who loves to give advice but can't stand it when they are offered it. I stood corrected and admitted that my advice was bad because a static discharge into the input could damage the system by damaging the input devices. Suck it up and admit that this same pop would never take out a tweeter.

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