Measuring A Capacitor

I can't imagine a scenario where shorting an input would cause noise on the output but I suppose it won't hurt to turn it off first.

Here's one possible scenario: As he is inserting the foil or whatever he uses to create the short, it comes into contact with the center pin an instant before coming into contact with the ground. Meanwhile, his body is in contact with the foil. The static electricity on his body (perhaps he's even just been walking on a carpet) discharges into the center pin, then is amplified by the 80db or thereabouts that the system gain is likely to be, from phono input to speaker output. That's a voltage gain of 10,000 times.

Not something I would want to risk doing on my system!

Regards,
-- Al

The buzzing noise is at 60Hz (my guess), and is pretty loud (volume dependent). I know it's there, so I get bothered by it's presence.

OK, I did the shorted IC exercise, and there was no hum. What does that tell me?

It says that the problem is not the preamp! It is outputting hum because hum is going into it. There are many threads at Audiogon on phono hum problems that you can search through. A few possible causes that come to mind:

-- Your power amplifier is too close to either the preamp or the turntable or the turntable cable.

-- Lack of good grounding between the turntable and the preamp (as you mentioned in your first post).

-- The phono cable being in close proximity to ac power cords, or to the power amp.

-- Ground loop issues between the preamp and other components, which become more apparent in phono mode than when other sources are selected because the signal levels are much lower for phono. Try disconnecting everything from the system except for the turntable, preamp, power amp, and speakers.

-- Try reversing the polarity of the ac plugs of each of those components, and/or floating them (using a cheater plug).

-- When the turntable is connected, is the hum present both when it is turning and when it is not? What kind of cartridge are you using? Grado's in particular often have a problem picking up hum from the turntable motor (when it is on), because they are unshielded. (It could be that the hum you hear when the turntable is connected is not the same hum that you heard when nothing was connected to the preamp inputs).

HTH,
-- Al

Here's what I did: I used shorted RCA cables on the phono input - no discernible hum. Then I used tin foil (as a shield) between the phono cable and the power amp power cable - hum still present. Then I went wild with the tin foil, and put a few 2" squares between the phono input, and the adjacent input (tuner - unused) on the preamp - buzz still present. Then I put a sheet of it between the amp, and the preamp - buzz still present. So, either tin foil is a bad shield material, or the problem is in the preamp. Here's why I say that: the hum can be reduced, or eliminated by my touching the faceplate of the preamp. It's possible that when I did the shorted RCA plug test, the hum was gone anyway.

FYI, the TT I am now using is an MMF 2.2 LE, with an MMF Tracker cartridge (Goldring Elektra) moving magnet type. It has a 2 pronged plug. The same can e said of the NAD preamp. The amp, which is a very recent addition, is a B&K Sonata ST-140, with a detachable IEC, 3-pronged plug/cable. My old Carver M-500T was put back in place as a test - still buzzed. I used to have an old Denon DP37F in the place of the MMF. It had a Sumiko Blue Point MC on it's tonearm (and it never buzzed).

What do you think my next move should be, given all that?

Yours, in vinyl,

Lee