Hum and general SQ issues transferring vinyl to hard drive

nooshinjohn wrote: »

My table has only the tonearm cable going directly to the arm itself. There is no reason for it to do what it’s doing unless there is something wrong with the cable.

You, sir, are acting as an antenna -- inducing a signal into a conductor that's not at RF ground potential.

Not to sound like a broken record but I still think your fundamental problem is (probably) what's called a ground loop. Ground loops happen when multiple components' grounds are connected together but are not connected to the "global" ground. Such a ground loop can be at a slightly different absolute potential than earth ground, and a small current can thus flow. Since our environments are utterly saturated with induced AC at 60 Hz from power lines and our home wiring -- the result of the ground loop is a low hum.

Actually, nowadays, we're awash with far "dirtier" sources of RFI -- specifically all that wireless digital crrrrap that we're surrounded by... but that's a somewhat different subject

Breaking the ground loop can be accomplished a couple of ways -- one way (arguably the best) is just to connect the looped grounds to "true" ground. That's what that bag of clipleads is for!

Sorting out grounding issues can be vexing and is largely empirical, IME/IMO. Not hard, but it requires some patience and luck.

It's a much, much bigger deal in commercial sound reinforcement -- think of those poor goobers that have to set up a rock band's sound system every night from scratch...

Because of the commercial implications (them poor roadies, man!), there's another way to attack ground loops -- the so-called "passive box". These are typically designed for balanced interconnects (XLR or TRS connectors), or unbalanced interconnects using "pro-style" connectors (1/4 inch phone plugs, like a TRS phone plug but only two-conductor) -- but of course they could be adapted for home use (RCA unbalanced connectors).

Here's a typical gizmo of such ilk:
https://www.parts-express.com/art-zdirect-professional-passive-di-box--245-874
see also: http://artproaudio.com/passive_di/product/zdirect/



Now it's certainly possible your hum has another source -- but I'm bettin' on grounds.
It's also possible that I am 100% clueless and talking out of my... well, you know...

Here's a fun experiment you can try (just keep any volume levels low if you do!): Assuming your interconnects are (all) unbalanced -- take one of the two RCA plugs (L or R channel) and pull the plug half way out of its socket... enough to disconnect the outer shield, but leave the center pin "in". Since grounds between the two channels (e.g., in a preamp) are usually "common", this may still allow both signals to pass, but eliminating one ground path. Sometimes (sometimes) the hum may magically go away. Other times, not so much.

-- that sounds like either microphonics or a cold solder joint (or other loose connection). You can swap tubes between channels (if the topology permits such) and see if the 'issue' follows a tube.

also...

Might wanna try -- with everything off and de-energized, of course -- pulling the preamp tubes and cleaning the pins (I use a Q-tip shpritzed with a little DeOxit, then dry with another Q-tip or paper towel) and re-inserting 'em into their sockets. Might even want to re-tension the sockets, but I'd (FWIW) start with the pins.

EDIT: Power output tubes are not terribly likely to be (or to become) microphonic (IME/IMO) -- I can't say it's not possible, but it's usually preamp (small signal) tubes -- particularly if there's some substantial gain involved (although it can happen with other small-signal tubes, such as phase splitters, IME, too).

Some tube types are (were) notorious for microphonics, e.g., the 7199 used in the ol' Dynaco SCA-35

nooshinjohn wrote: »

My preamp is solid state, so no luck on that one.

mmm -- well, soiled state stuff can get microphonic, too... less common but not unknown.

Are the only tubes in your "tube amp" the outputs? If not... any and all small signal tubes are suspects. Usually at least two per channel upstream of the power outputs (assuming a push-pull amp), the voltage amplifier (driver) and a phase splitter. That stuff could be solid state (e.g., the early McIntosh hybrid integrated MA-230, if memory serves, was all transistor upstream of the power amp), but usually not (again IME... I have no idea what your amps are like).

Still, your 'issue' sounds like a dodgy connection someplace. Also worth checking the condition of any and all switches (toggles, pushbuttons, etc.), multipole selectors (e.g., "function" or "source" selectors, if so equipped) and pots. They may be dirty/noisy and need to be cleaned of oxidation.