Incurable phono-hum making me reconsider my life

I recently built my own tonearm from scratch. The sound is great but I'm having problems with hum.
The tonearm is completely separated from the motor unit & it's plinth (Garrard SP25). The armtube is made from a carbon composite.

Here are some of the grounding configurations I have tried:

1. No grounding whatsoever -> The most hum.
2. Connecting a wire from the armtube to the ground post on the back of the amplifier -> hum is reduced, but still excessive.
3. Connecting a wire from the turntable chassis to the grounding post -> hum is reduced, but still excessive.
4. Grounding both the chassis and the armtube to the amplifier -> this is the lowest I've been able to get the noise, but it's still audible with classical music during quiet passages. This is how I've been using it so far and it is quasi-acceptable a large amount of the time, but still...
5. As an experiment, running the cartridge disconnected from the tonearm ie. cartridge lying on it's back on the table with wiring going straight to the amplifier without being routed trough the arm. -> same amount of hum as being in the arm but not grounded.
6. Reversing the +- leads on the cartridge. On my ADC cartridge this results in hum and no music output. On the Ortofon OM10 there is output but hum is unchanged.

I need to add at this point that these are the only cartridges I have on hand, and there is no difference in hum no matter which one I use. This includes using the Ortofon with the internal ground tab removed/intact.

The ADC cartridge was previously in use on the exact same table & amplifier with no hum whatsoever, the only difference now is being mounted in the new arm. Everything is plugged into the same outlets and so on as before. The turntable being plugged in the mains or being powered on/off makes no difference. The hum also does not increase towards the end of a record.

The stock arm that was mounted on the Garrard has been dismantled in the process of, as some of the parts were needed for the new arm.

The cartridge is an ADC220 stereo unit. I've strapped the channels together and run a single set of +- leds to an RCA plug connecting to the amplifier. Using the mono/stereo switch on the amplifier, the mono setting (which is what I always use regardless) has noticeably lower hum than the stereo setting.

The hum does not occur with any other device connected into the amplifier. I've also tried using an external phono preamp to no help. Switching any electrical devices in the room/house on or off has no effect. Neither does reversing or moving the plugs in any of the equipment.

My house is ancient, and the electrical outlets are un-grounded, this has however never been a problem with any turntable, cartridge, tonearm or amplifier I've used here.

All connections are secure, and wiggling anything around doesn't affect hum.

I feel like I've tried everything and my patience is beginning to run out.

Help?

 

Just buy a tonearm like everybody else.

 

Which Best-Buy carries a 16" carbon fiber tonearm for €20?

 

I would try connecting ground wire to the ground connection in the wall outlet, rather than the amp's grounding post. You could use a piece of wire with clips on both sides. It worked for me when I had a TT in my teens.

 

Turntables and hum. Never a ho-hum moment.

 

Thank you for the suggestion, but as I wrote in the OP my outlets are ungrounded.

 

I had "incurable" hum problem with my EMT until founded real good phono cable... The cable had separate quality screen for each channel and two signal wires inside every screen. The signal wires were not connected to screens. Ground wire was connected to channel screens and had connections both to turntable and amplifier ground posts(you could try one of them,both or nothing).

 

You could try experimenting with a length of wire . The tone arm is earthed, it is common to connect a wire from chassis to tonearm and from there to the ground on phono stsge.
As has been sussested a wire to ground on mains plug.,
Sorry you don,t have a ground on them?
As you are no doubt aware too many grounds s problem
Some Thorens decks ran a wire from cartridge ground to headshell on route to base of arm and turntable chassis
Just ONE GROUND POINT
Good luck

 

Yep try a crazy long ground wire and touch to pipes etc and see if it affects the hum if so you have new info. I had a similar issue with an old turntable that would have no hum when I touched the head shell. I figured it out using a long wire.

 

Maybe obvious, but have you tried measuring the wires? I would remove the pins from the cartridge, and with the amp powered off, measure each channel from (+) to (-) with ohmmeter. You should read around 47 Kohm if they are connected to a standard MM phono input. Then measure between the (+) pins and measure between the (-) pins. The (+) side reading should be high and the (-) should be low. Also check one of the (-) side pins to the amp chassis phono ground post. Maybe you could quickly sketch a little drawing showing how the wiring is done, or some pictures, that might help. How do you terminate the tonearm wires, are they connected to phono jacks or do you solder to shielded cables for the run to the amp? How do you ground the carbon fiber tube, with a screw? I'm not sure how effective it is as a shield for the wires. Have you tried relocating the turntable to another location in house as a test just to rule out stray magnetic fields in the current location?

I don't quite understand the above, are you saying that you always listen with the amp set to mono? And you still get hum when only one cable is connected to phono input? What is on the other connector at that time, nothing?

 

Thanks for all the suggestions everyone. I'll get back with some pictures and a wiring diagram as soon as I'm done listening to a hot new bootleg I just found

 

I would resolve this first and foremost.

 

Does it hum when: The TT is not plugged in to the wall power; When the cart. is uninstalled and just the TT is attached and What happens if you move the TT away from whatever it is near? Since the tonearm is semi conductive you may not be able to properly ground with it. Have you tried grounding from wherever the cart./arm wiring terminates and becomes the interconnect wiring? It is an important clue to know if the hum is present without the TT being plugged into the wall power.

 

There is no change in hum whether or not the table is plugged in, also no difference with power ON/OFF.
I checked the hum by recording it on my computer and it's composed purely of 50hz and it's associated harmonics, if that is of any help.

 

What else is in the same room and / or on the same circuit?

Have you tried isolating the circuit from any / all other electronics?

 

The most important thing to do is to ground your circuits. This is important for your and your family's safety, as well as for minor issues such as audio hum.

Ungrounded electrical systems, sadly common in old houses, are dangerous. They can lead to fires, and also electrocution in circumstances where you or a family member becomes the ground. Ungrounded systems also risk damage to your electronics.

I recommend you have the house inspected and tested by a qualified electrician. As a first step, you could do some testing with a multimeter. It's possible that your system may be grounded, but that outlets lack a third grounding pin. That was the case in my old house: ground was provided to each duplex box, but no three-prong outlets. I was able to replace the two-pin outlets with proper three-prong grounded outlets, and connect the new outlets' ground to the already-grounded duplex boxes, after which everything was inspected.

It's also a good idea to install GFI (Ground Fault Interrupter, a.k.a GFCI or Ground Fault Circuit Interrupter) outlets anywhere near water. e.g. bathrooms, kitchen, laundry room, and outdoor outlets. These provide much greater protection against electrocution when water meets electricity. In our jurisdiction, these are now legally required by the building code in new construction.

If your house doesn't even have the duplex boxes grounded, then of course it's a bigger job. But, do it. The safety of your family is at risk.

 

Stick this inline with various RCAs to knock out ground loop hum, $6 (or you could pay much more for "audiophile" versions of the same thing):

 

Sea of images ahead.

Hopefully my professional diagram is clear enough.


This is how the cartridge is wired. The grounds from both channels are strapped together, as are the signal tabs.
----------

The +- leads from the cartridge are routed through the armtube, and connect to a separate pair of leads, which are taped down to the "armbase" (brick) to act as a strain-relief.
----------------------------

Ground wire running from plinth.
----------------------------

....and the wire from the armtube, as well as the separate wire from the RCA jack on the Garrard meet here. The outgoing black wire is connected to the grounding post on the amplifier.
------------------------------------------------

As I was taking the pictures, I moved the power plug of the amplifier to a separate outlet. It now shares a power strip with the Garrard unit. I then disconnected the CD-player, which resulted in a noticeable decrease in hum! I would still like to lower it further but now things are the best they've been.

As far as ungrounded outlets go,I appreacite the concern and am aware they pose a risk; getting them sorted is on the horizon. One thing to note though, is that the very same Garrard, with the very same cartridge and amplifier did not hum with the stock arm, only with my new DIY arm has there ever been a hum.

Thank you for all the suggestions everyone! If now I could only eliminate that last bit of hum...

 

Thank you very much for this!
I was looking at a similar option earlier, but that one was much more than I was willing to spend given there was no guarantee of success. If all else fails, I'll give this route a go.

 

I'm in the process of having my house built in 1939 re-wired. The cost was a hard pill to swallow, but at least all my hum issues completely disappeared overnight . (I guess it was worth it for safety's sake too )

 

LOL. I guess this is a sign that I'm in the SH forums. You're happy that your hum disappeared, and safety is a secondary benefit. OTOH, I consider electrical safety the primary concern, and audio hum is a cosmetic issue. Oh well, I'm glad you got both sorted.

 

Op, is the wire from your tonearm to the preamp shielded?

 

I tired to put a winking smiley in there, but it didn't take because I'm on my phone. The electrical work is being done in preparation for other renovations, but I definitely smiled when I turned my amp on and didn't hear any hum for the first time since moving into this house.

(Yay for no more knob and tube!)

 

I did some experimentation with mine at one point before I had dedicated lines. The cold water copper pipe coming into the house is generally below where the stereo outlet is, so I tapped a ground wire from the pipe, up through the floor and clipped onto the raw wire.

It was ultimately less quiet than grounding off a dedicated filtered power distributor connected to a grounded plug, but it might be an easy try in your situation.

 

Hello,

safety first, always.

Apart from this.. also non-earthed units must not hum. (If they use wall warts, then (sometimes or usually), the unit is double insulated and does not need safety earth.)
First issue is to try to have all units connected to the same power outlet, to prevent ground loops over safety earth and shields of RCAs.
Phono cables are sensitive to hum, because of the low signal volume.
Hum has two reasons:
Stray magnetic fields, and stray electric fields.
Against stray magnetic fields, try to twist the + and - leads of right channel, and the + and - leads of the left channel, inside the tonearm tube.
Against stray electric fields, you need a Faraday cage or shield. If your tonearm tube is not very conductive, it will not work as a shield. Then, in this case, use a conductive shield such as copper or aluminium foil, or a wire mesh, or the like.
Connect that shield to the earth tab on your record player. Try, whether or not connecting the RCA cable shield to the earth tab on the record player.

Best regards