Rewiring a Thorens TP..

[The Abbot]

Hi chaps.

Got a TD-160 with its std TP-15 which had a light buzzy noise prob, earth-like it seemed to me. I decided to try a rewire, with std litz stuff and all is fine BUT for a similar (tho not exactly the same- it ceases mostly when needle on lp/ odd) earth issue. More irritating than anything, as only faintly aware of it thru spkrs once lp playing.

Any ideas? Afai remember when I did it last year, the ground litz wire goes from the cartridge 4th pin all way down thru arm to a lug underside of TT. The mains plug, whether related or not, is an old 2-wire L/N affair ie has no ground at all: don't suppose this has anything to do with the prob?

Thanks, capt.

[Pac67]

It sound's like you need to earth the tonearm. If your mains plug has no earth wire, then the chassis isn't earthed to anything. The power supply cable and plug ought really to have an earth which connects to the lug on your chassis in case of a fault where the chassis may go live (if that's possible) and drains it to the mains earth. I'd not mix that earth point with the tonearm in case an earth loop is created. Better to take the tonearm earth to the earthing point on your amp/phonostage. That should cure the problem. When you say "4th pin" this is a little confusing. The top two pins on your cart should be signal (left and right) and the bottom pins should be return (cartridge earth) left and right. Some tonearms don't use a separate earth which means that your cart pins are connected to the RCA sockets (signal/return for each channel, the return also being the earth for the amp/phonostage) but many tonearms have a separate earth. If you PM me, I'll send you my email address. If you can email me a sketch of how you wired it (schematic) I should be able to help further.

[The Abbot]

Thanks Pac67, very helpful info there. Yes by the '4th pin' I meant either btm cartridge pins: so the litz wires from these two btm pins both go to the two same points exactly as the old wires did- IE some sort of earth points presumably underside of deck.

One thing that might help narrow down the issue: when motor starts there's the feint buzz from spkrs but as said just audiable/ liveable wth.. but as I touch the arm the buzz starts (so clearly an earthing issue s'where) & once arm on lp the buzzing goes, just the feint buzz/ hum remaining behind music: even this mild buzz is defo this TT and not spkrs as Ive an lp12 which is absolutely silent as this one should be.

[Pac67]

Sounds like you haven't got an earth connection on the tonearm and if you are connecting the bottom pins to the chassis earth as well as the signal return, you're shunting earth voltage to the ground return of the signal cable which is possibly why you're picking up hum. DONT earth the ground returns to the chassis...these are the ground returns for the signal and you don't want spurious ground voltages in these from other sources which is why the chassis and tonearm need their own earth points. Personally I'd replace the 2 wire mains lead with an earthed mains lead and connect the chassis to the ground wire, and run a separate earth from the tonearm. If you aren't sure or confident with mains electrics, best to leave it alone or have someone who's competent in electrics do this for you. It is an earthing issue by the sounds of it but easily sorted.

[The Abbot]

Hi Pac- yes I have diy'd alot so fine with basics (built my diy'cap naim clone/ gtr valve amp etc).

I have a mains lead ready to replace the 2-core oldie: that bits the easy bit, tho as the oldie was 2-core and obviously once perfect as it was, I dont suppose it will solve my prob.. IE a good idea to replace anyway as matter of course/ as Im faffing with the base off etc.

Now the slightly tricky bit, both in terms of v thin pesky wires, and basic anatomy/ understanding specifics of 'tonearm earthing' is redoing the 2 gnd/ rtn litz wires from the cart. I assume the actual tonearm shaft tube -must- be grounded to the same point the two signal ground rtns do? at the mo my 4 litz wires run from cart to underside of TT (exacly following to where the originals terminated) BUT neither of the tw gnd wires from cart are connected along the way to they're terminal point. I wonder whether one at least (or both) should 'stop off' and touch the armtube at a soldered point, and then continue to the underside TT terminal points? the orig wiring didn't as I could see.. but did have a lug (a connecting plug so headshell can remove etc) I whipped off and replaced simply with my litz 4, so I cant remove headshell now/ its n/a. I wonder if within this lug there must have been a path that connected one or both of the signal gnd's from cartridege to the actaul armtube, and so this is maybe what I've glossed over/ ommitted, hence my prob. This is pure conjecture, as Im not clued up on tonearm grounding as Ive mentioned. What do you think?

cheers capt.

[Pac67]

I think it should be more simple than that. The tonearm should have its own earth which is routed along with the interconnects to the grounding post on the phonostage and the cart wires are routed to the RCA sockets. Some tonearm earth wires do merge with the cart ground returns (which go onto the RCA sockets) and a separate combined earth lead is taken to the phonostage grounding post. I would avoid grounding the cart signal grounds to the TT chassis ground and leave that to be connected only to the mains ground connection. That should simplify things and may reduce or eliminate any buzz.

[The Abbot]

Hi Pac. Yes that simplifies things, and what I sort of assumed. But when stripping old wires out/ redoing I didnt see any specific tonearm earth wire. I understand the difference/ importance of separation between mains earth to chassis point, and a separate tonearm earth(s) point.

Its the tonearm earth itself I cant get my noggin around.

Below link (V) is effectively exactly what I did in 5 photos (not my handiwork, a v useful site I followed). I cant see any tonearm earth specifically you see, even in orig thorens wiring format, but for the two signal earth running -through- the tonearm (what I had assumed previously was the tonearm earth as they ran thru it- seemingly not).

http://www.vinylengine.com/thorens-t...rewiring.shtml

thanks, yr abbot.

[stewartwen]

http://www.theanalogdept.com/
There is a stage by stage rewire on the site I put the link up for.
S

[The Abbot]

Thanks that's damn useful- brilliant site, in fact such info/ sites are the best of tinternet IMO.

I can see the seperate tonearm earth screwed in at the back on tonearm- and mine is the same (IE I didnt forget this/ its there tightened well too, I clearly remember doing it now). Afair it goes to one of the signal rtn ground points, either, on the TT wiring section. This is away from the chassis at the sideof plinth underside, so cant be any cross-contamination there.

So Im back a step: what the dickens is causing this buzz, its clearly the tonearm tube/ headshell that when I touch its distinct, when I let go onto lp it recedes.

[The Abbot]

Pac.. are you suggesting removing the existing arm ground-to-chassis entirely (twds lwr middle of pic).. and add a 3-core mains lead instead of the oldie 2-core (btm lhs of pic)? If so where would I attatch the 3rd mains ground wire to?

By nature the arm signal grounds travel along the TT leads-to-preamp, to where they obviously will go to the 'star' ground in there in my case, being a naim nac 32.5.. Im wondering if this i what you mean by taking the tonearm ground to the preamp.

I wonder how the LP12 is config'd, anyone remember?

[Pac67]

I'd attach the mains ground wire to a beefy copper spade connector and fit it to the chassis grounding screw which you already have. Disconnect the tonearm ground wire from the chassis screw and take a new tonearm ground wire from your arm's block connector (bottom centre right of pic) to be terminated in a spade connector which can then be attached to your amp/phonostage grounding post. You can join the signal grounds to the tonearm ground on the block connector as well if you wish as well as running them to the RCA interconnects but I'd try it without to start with.

[The Abbot]

Cheers Pac- that's what I was hoping you'd suggest (IE disconnect that arm gnd and use it for the mains earth).

I sorted one of the buzzes- now when I touch arm its silent/ by redoing the screw gnd point at rear of arm scraping etc etc. The continous mild buzz from spkrs seems to have got a tad louder tho! Its there when TT is connected to amp but unplugged from mains, gets a bit louder when mains plugged in, and same when motor turned on fwiw.

Very helpful- thanks.

[stewartwen]

Sounds to me like you need to replace the mains wiring with three core, ie pos, neg and ground return. Earth the t/t as Pac has suggested then all should be well.

[The Abbot]

Hi Stewart-

but doesnt it mean as its the same buzz through speakers w'out the TT's mains plugged in, and now the armtube doesn't buzz when I touch it/ sorted that out.. that the buzz thru spkrs is therefore narrowed down to the armlead ground pair to the preamp?