Hum Help! Clearaudio Concept/GS Era Gold/GS Solo

Firstly we need to tackle the fundamentals.

Taking this slowly and methodically...

There are five pieces of wire in the loop from the tone-arm pictured above: four of them are the two pairs carrying the audio signal from the cartridge; the black wire is the arm-tube earth or ground.

This black wire is essential in holding the arm tube at the same ground potential as the phono preamp (Era Gold V) ground (0 volts).

It should, via the manufacturer's interconnect wiring (usually a separate black wire), make connection with the phono preamp grounding post marked "TT Ground".

In an earlier case regarding a VP turntable, its black arm-tube wire was terminated to a grounding post contained in a connection box at the back of the turntable. The user had not been supplied with the piece of single core hook-up wire required to go from the VP grounding post to the phono preamp grounding post. Once connected by a piece of hook-up wire, the hum was controlled.

If I knew the turntable I could say exactly how to hook it up, but I don't.

If, for some reason, in this case such a wire is connected, and it is not controlling the hum, then it is because the arm-tube is still "floating" compared with the phono peamp grounding post.

Fiddly wires such as are required in the "loop" from the arm tube to the deck, do sometimes break. We need to establish if the black wire is conducting from the arm-tube metalwork through to where it exits the turntable. That, unfortunately cannot be done without a suitable continuity detector such as is found on most DIY shop multi-meters. A word of warning: anodized aluminium such as the arm-tube is made of, does not conduct, and therefore some has to be scraped off (in a place which will not be seen...).

If then, the black wire is conducting the arm-tube potential (the hum voltage it picks up) all the way back to the phono preamp ground, and hum persists, then we need to take another look...

Is the turntable metal? If so, does it "earth" to the mains plug? If it does, then is there continuity between the arm-tube and the turntable metal? If so, this is a hum loop. In days past we would simply lift the earth connection from out the plug. Today, I am not allowed to suggest such an action.

Same question again, but let's say it does not "earth" to the mains plug. If it neither earths to the arm-tube, then the turntable is floating at its hum potential, and will induce hum into the cartridge coils. Remedy: the turntable metalwork must also be connected by a hook-up wire to the phono preamp ground post.

Now, this arm is what is called a uni-pivot arm. Its two parts: the fixed and the moving, connect electrically by a single gimbal bearing (a pointed stick!). A single gimbal bearing has a high contact resistance - it will not be an ideal ground path (it may as well be made of plastic), and hence, rather than relying on conduction through it, the manufacturer here has sensibly used a separate wire (the black wire in the "loop"). What about the fixed part of the arm? Is it mounted to an insulator? or mounted directly to a non-metallic "motor board" or deck plate? In this case the fixed part of the arm-tube would be floating at hum potential, but not carrying any signal wiring, and being of small mass, may not have any influence on hum pick-up, but is worth mentioning...

...because if it had been a Hadcock arm, the opposite situation would be the case: the Hadcock arm fixed portion was grounded, but the arm-tube did not carry the "fifth wire" so that all the user had to rely on was the gimbal conduction which varied in effectiveness as the record played... need I say more?

OK, that deals with the fundamentals, and if that doesn't fix the problem we now have to look at RF (radio frequencies) where better shielding comes in.

In the case of the VP, the interconnect from the turntable to the phono preamp was totally unshielded - I could not get my breath!

I guess the manufacturer thought that only low output moving coils would be used, because they have such a low source impedance/inductance as to "hold down" the wires to RF "take-up", but here we had a high output moving coil fitted which did not have that really low source impedance/inductance and therefore properly shielded cables were required and we sold the customer a Cusat50 of suitable length - end of problem.

RF can cause hum because of the low frequency TV "raster" information (screen refresh signal) transmitted in old fashioned analog (even for digital I am told) to keep it from "buzzing" the rest of the picture/sound signal is transmitted on an AM carrier. Instead of being FM, it is AM, which is so very easily detected by any diode junction (and in an audio system there are a few hundred... usually). Now, that can get in anywhere, and that is why I get so stinking angry about the way normally sane people go stupid and buy snake-oil unshielded audio interconnect cables. Yes, I know we are not all blessed in the rocket science department, so there should be a law against such peddlers, but we live in a desolate world (don't get me started...)

As for the loop of wire on the turntable, that is also a good aerial: although it has twisted pairs they are completely ineffective into a phono preamp input which all are single sided (unbalanced). Such wiring is an afterthought full stop. There is no solution apart from turning your listening room into a lead-chamber if this were to be the cause. No, I think we stick with the fundamentals above.

For reference, the hum had been caused by none of the components having an earthed connection, the resolution of which was to run an earthing cable from either the TT Ground post on the Era Gold or earthing post of the Solo to mains ground.

Thanks to those of whom contributed, esp. Graham for his informative piece.