Please advise about phono-stage hum problem...

[nickbaba]

Hello - I would really appreciate some help with solving the problem of hum in my vinyl system which has recently developed.
I have a Trichord Dino mkII with external power transformer which has always been hum-free for the 2 years I've been using it.
I recently had the phono cables, ground lead and tonearm changed on my TT (Technics 1210) - since then I have noticed the hum. It's quite noticeable at normal listening volume with no music to mask it. Before you ask, yes I have the TT securely grounded to the Dino. I have not changed the location of the Dino or any other components.
OK so, the obvious suspect is the new phono cables, right?
Right, but here's what's confusing me about that. If I bypass the Dino and connect the phono cables & ground directly to my pre-amp, there's no hum! So I don't think it's a fault with the 1210, cart, tonearm or new phono cables.
If I connect the Dino to the pre-amp with the TT disconnected, no hum. (So I don't think it's picking up electrical interference.)
But if I reconnect the TT & ground to the Dino, and the Dino to the pre, I get the hum again...
Could there be a problem with the ground pole on the Dino? Would that make sense with what I have described? Or might I be missing something else?
Any thoughts much appreciated! Cheers, Nick.

[lurcher]

Right, but here's what's confusing me about that. If I bypass the Dino and connect the phono cables & ground directly to my pre-amp, there's no hum! So I don't think it's a fault with the 1210, cart, tonearm or new phono cables.

Unless you have a phono input on the preamp you wont be proving much doing that, the phono stage is adding 40-60dB of gain to the signal so what is inaudible on the preamp input may be clearly audible on the input to a phono stage.

[hifi_dave]

What arm is it now and which phono cable ?

[nickbaba]

Sorry lurcher if I was not clear about that - yes, I was connecting to a phono level input on the pre-amp when testing the TT directly, not a line level input.
The new arm is a Jelco 750, the new phono cable is Yannis Tome Gaia and was fitted by Yannis himself.

OK now I'm really confused - I hooked up my 2nd deck, a stock 1210 with no mods, through the Dino into the pre, and now there's no hum...

So the problem is only when I connect the new phono cables & ground to the Dino... But when they are connected directly to the pre-amp phono input (& the channel gain max'd just to doublecheck) there's no hum... How can that be?
(I can push the channel gain for the phono input cos I am using a high-end dj mixer as a pre-amp in this setup).

The TT & new phonos seem fine when going direct to the mixer... And the Dino seems fine when an alternative TT is connected to it... But something goes wrong when hooked up together... Very confusing.

[phonomac]

Hello Nick,
If the shield side of the RCAs on the Dino are linked to ground in some way within the pre-amp, and one of the shields on the new phono leads has a connection to the ground wire from the t/t, then you may have created a ground loop.

If you have or can borrow a multimeter/continuity tester check out all the connections coming from the t/t and going into the Dino. Core and shield on the phono leads should connect only to the cartridge leads in the headshell, and nothing else.

regards

Angus

[ppat2]

I have had hum issues a few times over the years, and for me every time it has come down to the sensitivity of the phono cables.

Recently, I had a set of Cardas Golden reference for phono cables, and had the same hum you describe. I then swapped them for another set of Golden Reference cables I had for another use, and these ones did not cause any hum. I swapped the faulty and good cables in and out a few times to test, and in every case the faulty cables caused a hum. However, I can use those cables on amp, preamp, and CD player, without any issues.

If I use any cables from Nordost for my phono cables, I get severe hum and have to just take them out. I guess that is because of the thin outer shielding on some of the Nordost cables, they seem to pick up any interference including radio frequencies, such as stray FM signals. I can listen to FM and CD at the same time!

If your phono cable are of the removeable type, I would start by just swapping in some of the cables you have for other purposes. This might isolate the problem, and who knows, you might find a cable you prefer over the current one. Don't buy cables for this though so you don't lose any money due to experimentation.

I have also in the past had success with running a separate ground wire to phonostage, or to other ground on amp, power supply, etc.

[Stratmangler]

Is the armboard earthed properly?
On your stock Techie the entire arm and base assembly is connected to earth.

[nickbaba]

I honestly have no idea, Chris, as Yannis fitted both the new cables and new arm for me at the same time - however I'm certain that he knows exactly what he's doing, so I would assume that the answer is yes. I will double-check with him, though. Thanks for the suggestion.

[OneyedK]

Try hooking up the earth wire to the préamp instead of the Dino...

[nickbaba]

Hi - Just want to say that I found the cause of the problem, and it was an issue with my system.
Just want to say for the record that there was nothing at all at fault with Yannis' cables or the work he did fitting them for me. Just to be clear. Thanks.