I have a $100 turntable that works perfectly on customers system. The $300 turntable he purchased online has a pronounced hum that varies with the volume. Naturally I am still somehow on the hook for making his turntable work with the system... bc he likes the turntable.

At this time could someone please take this empty bottle of whiskey and smash it over my head?

Both turntables are made without ground wires or any place to attach a ground wire. There's also a built-in preamp and a switch to engage/disengage it.
We are talking about a 70 foot run to the preamp.

I ALSO RAN BALANCED AUDIO and used a high quality active balancer before the run and used balanced inputs on the preamp that didn't help.

Again... my turntable works perfectly, no hum. His turntable hums no matter what I do, even if I hook it directly to the preamp with short cables, even if I use the phono level out of turntable and go into good preamp (tried both balanced and unbalanced outputs out of preamp)

...

Brand of turntables?

Did you try those transformer things.

If all other combos excluding the turntable function correctly and all combos including the turntable do not function correctly, it sure seems like the $300 turntable is defective or maldesigned to me...

Likely, you could patch headphones to the turntable's preamp output. If this arrangement hums, the turntable owns it. Depending on the turntable preamp's output impedance, the headphone level might be low, but our goal is to determine if there is hum or not.

I heard today at a Tech Summit that sometimes I come down hard on people, but jeez -- what the hell brand and model of turntable is this? Can we PUHLEEEZE HELP by knowing what the product is?

Here's what I'd do.
Put the two turntables next to each other on a table, with an AVR or integrated amp and a pair of speakers on the table. Hook each one up in turn. See what happens. I mean, you say it's a 70 foot run but you don't say you've tried the turntable without the 70 foot run.

If you did this, then forgive me -- it wasn't clear to me that you had.

As for where to connect the ground, it should go to the chassis, the metal parts, that the motor is connected to. With more modern motors it might be necessary to play with several ground locations to find the best one. And find out with an ohmmeter if either of the cartridge output grounds is connected to the chassis; in the past, neither cartridge ground should be connected to anything except the RCA cables connected to the outputs of the cartridge.

By the way, what's in between the cartridge and the seventy foot cable?

Sorry Ernie what was I thinking? Mine is a Audio Technica AT-LP60. His is a U-Turn Orbit. I have tried with short cables. I have tried with alligator clip lead from the metal tone arm to RCA output ground. It lessened the hum but still not passable.


Built-in phono->line level preamp I suppose. They say internally grounded but there isn't very much metal in the whole thing

Great idea on the headphones buzz. Ed sorry I'm not sure what you mean by transformers.

I wasn't clear enough. The chassis ground of the amp or preamp is where you connect the turntable ground. A screw on the back panel, if it exists, is usually a good place. DON'T connect to the RCA cable grounds.

If you're not using the internal phono preamp:
If connecting to the tonearm ground helps the hum somewhat, leave that in place and connect from any kind of motor chassis to the preamp ground. Go from tonearm to preamp and use a separate wire from the motor to the same preamp ground.

If you are using the internal phono preamp:
Make those same connections to any ground you can find on the phono preamp, but not the RCA connector grounds.

Basically, connect everything to everything and see what happens; be ready to make multiple grounding connections.

Connecting the tonearm to the RCA ground isn't 'grounding' the turntable, it's making those two equipotential. grounding is connecting the cartridge's negative wires too the electrical ground of the building.

Since you should have a ground wire at the head end, try connecting the RCA ground to the chassis of the preamp/AVR.

I have mentioned using a small amplified speaker from Radio Shack- RS is dead, but Parts Express should have something and a headphone amplifier is a good substitute but it should be battery-powered.

I'm just assuming its the preamp because that's your variable. We have a very similar issue with someone who purchased a "Refab" table from the 80's. We hooked it up to a Rolls preamp with a significant hum. We are bringing out a Parasound preamp to test. I'm hoping I don't have to tell him his $100 turn table needs to be replaced....because that won't go over well.

Is it possible he just got a defective unit? Cant he just replace it? I doubt that was the last turntable ever produced on Earth.

If the TT is far from the preamp (like the OP's case), it's not a $100 turntable, it's whatever the whole setup + labor costs.

"Refab"- refurbished? Never assume this was done correctly when there's so much BS flying around the internet. It's possible that the person ("expert") who did the work tied the negative for the cartridge to the ground wire, separated it or used some super special cable and boogered up the solder joints. What turntable are you referring to?

Remove the head shell and clean the contacts- the dirt on the contacts is what caused the hum and RFI on mine.

You're doing what I sometimes do: you're letting words get in the way of finding a solution. You're defining grounding in an accurate but too narrow way. Ground and grounding mean different things in different situations.

This is from wikipedia. Notice the word OR:

Okay, so ground may be exactly what you say it it, but it might be something else instead or something else also.

As preamble to a question, a statement at electronics.stackexchange.com says
| Automotive electronics generally use the metal chassis as the negative ground connector for the DC circuits.
This is a perfectly reasonable way to describe a situation in car wiring. (Note that circuits using PNP transistors might use "ground" to refer to the positive terminal of the battery or power supply, which would probably be connected to the chassis enclosing the circuit.)

People correctly use the term "ground" in automotive electronics without meaning driving down the road while wired to a copper stake driven into the earth.

In talking about turntables, "ground" is the reference point from which voltages are measured. This is usually the chassis of the preamp that the cartridge is connected to. Grounding is connecting together the chassis of the different components in a system.

In analog consumer audio, most such grounding is done by the shields of the RCA cables. We don't even think to mention ground or grounding until we have hum; at that point we say we have a ground loop. It's a fact that connecting a pair of RCA cables between two components creates a ground loop, but we're generally not even aware of that until there's hum. To be totally accurate in a manner similar to your grounding definition, we should say "What is commonly referred to as a ground loop is a ground loop that causes hum; many ground loops do not cause problems, so we are not even conscious that they exist." But that's not really a helpful definition.

If one were to connect up a turntable that had a ground wire by plugging the RCA cables into a preamp and connecting the ground wire to an earth ground, the amount of hum would be AMAZING! That's because what's meant is chassis ground, not earth ground. Chassis ground might be connected to earth ground for other reasons. For instance, if you have an AM antenna on an AVR, connecting the chassis to earth ground makes the antenna signal appear stronger.


RS is not necessarily dead.

That's an excellent tool and will do EXACTLY what buzz's suggestion of a headphone will do: if hum is present at the output of the turntable all by itself, it will prove that the turntable itself is causing the hum. If there's no hum when using headphones or an amp like this, that means the problem is due to something about the interconnection of the turntable with other products. That's no proof, however, that messing with the connections of chassis or other internal parts, dare I say circuit grounds, of the turntable will solve the problem.

Turntables had a ground wire and new ones may or may not have this. I have seen situations where disconnecting this wire caused the hum to stop. I already called this 'equipotential' vs actual grounding- not much else should be needed, other than the knowledge that the turntable ground may need to be connected to the preamp/AVR ground, although I forgot to mention that Pin 1 might need to be disconnected in the event that it's the cause of the hum.




I know this and it's the reason connecting the ground wire is optional. However, it might be possible to reverse the power plug if the turntable is old enough. FOr a 1980s model, that can't happen unless someone installed a grounded power cord or clipped the + tang on the plug.



But the best way (and the reason the battery-powered amplifier/speaker works best) is because it's completely isolated until the signal cable is inserted. Using a headphone amp that uses a wall wart or any other connection to the AC supply raises the risk of some kind of interaction.

Well, if RS isn't dead, I'll paraphrase Frank Zappa- "RS isn't dead, it just smells funny".

FWIW, I went to the only local RS store last week and if RS had hired the guy (and others like him) behind the counter years ago, they might not be in this position. They hung their hats on the wrong products.