RF interference with AT-150MLX vinyl cartridge

[fntms]

My Audio Techina 150MLX (MM) catridge, which I like a lot because of its amazing detail, is giving me trouble: it seems to be sensitive to RF signals or similar interfences.
Indeed, it emits a very high frequency 'binary' sound (it switches on and off abruptly) at random intervals, never lastling more than a few seconds. I suspect that my neighbours TV or something else in their place might be at the origin of my troubles. I've disconnected all mobile/wifi/pc stuff in my flat and still get the noise.
I've tried 'isolating' the cables of my TD 160 with aluminium foil (I know...) and placing aluminium plates above and under the tt to no avail. I also placed ferrites on the cables, which seem to help a little but I still get the noise.
I'm now considering a power filter, and any other suggestions you might have!
Many thanks (I remember the experts on this forum solved the noise problem I had with my little dot 2...)!

 

[fewtch]

The problem is more likely with your phono stage (acting as a receiver) rather than the cartridge. Try messing with that... i.e. shielding it, grounding it, etc.

 

[fntms]

Quote:

Originally Posted by fewtch The problem is more likely with your phono stage (acting as a receiver) rather than the cartridge. Try messing with that... i.e. shielding it, grounding it, etc.

I did add ferrites to the preamp's interconnects and it does make a difference (but the noise still appears). How else could I add shielding? wrap it in aluminium foil? Thanks!

 

[Garbz]

I have a similar problem in various places, but as the noise is so quiet that I can't hear it till the dead of night I've ignored it.

The noise you are describing is a grounding issue. It would not be RF since RF is so far outside the audible band that unless it's causing your phono stage or other components to become unstable, it would be inaudible.

Another thing that I have experienced similar to this was with regards to placement of transformers and the such. Being a magnetic field aluminium shields will not prevent this. mu Metals or bust in this case. Try physically moving the turntable away. Use a long interconnect and move it to the other side of the room just as a test to see if the noise is still there. If it's gone, chances are that the interference was comming from equipment under or above the turntable (thankyou torroidal transformers

)

 

[fntms]

But if it's grounding, I should get the noise all the time (?) Also I thought grounding was more likely to result in low frequency hum than high pitched intermittent ringing beeps.
I admit grounding could be a problem with the TD 160 as its ground connection is inside an RCA cable instead of a separate cable. But when it's badly grounded (when I move the cable), I get a huge loud noise!

My neighbours are still away and I get zero beeping noise (with all my equipment switched on). Also I have plugged all my stuff into a Belkin PC surge with filters (couldn't find anything else), maybe it helps.

 

[fewtch]

Quote:

Originally Posted by fntms But if it's grounding, I should get the noise all the time (?) Also I thought grounding was more likely to result in low frequency hum than high pitched intermittent ringing beeps. I admit grounding could be a problem with the TD 160 as its ground connection is inside an RCA cable instead of a separate cable.

You might try the ground mod, where you disconnect the cable ground and string out a separate wire grounded to the chassis/tonearm (and the other end to the preamp or phono stage). Very easy to do mod, and might possibly fix your problem. It's one of the first things I did with mine, as IMO Thorens really screwed up using the scheme they did.

 

[Garbz]

Quote:

Originally Posted by fntms But if it's grounding, I should get the noise all the time (?)

Yeah I thought so too until I found the exact source of this problem in my subwoofer preamp was a pot that was not grounded.

Grounding can be a tricky person with all sorts of weird problems resulting.

 

[fntms]

I admit it would be nice to ground my TD 160 better than it currently is. However I have no electronics/electrical skills or equipment and haven't even opened it...I bought it in perfect working order and am scared to mess up even a very simple mod. Can't I just connect (ie attach...) a wire from a metallic piece on the tone arm and the metallic coating on the top of the tt to the ground on the preamp?

 

[fewtch]

Quote:

Originally Posted by fntms I admit it would be nice to ground my TD 160 better than it currently is. However I have no electronics/electrical skills or equipment and haven't even opened it...I bought it in perfect working order and am scared to mess up even a very simple mod. Can't I just connect (ie attach...) a wire from a metallic piece on the tone arm and the metallic coating on the top of the tt to the ground on the preamp?

You could certainly try that and see if it helps. I was pretty paranoid about modding mine, but finally just did it and it turned out to not be that hard at all. I know what you mean about not liking to mess with it though, I'm the same way even though I have a bit of electronics experience. I still haven't tried rebalancing the chassis on mine, although it 'somewhat' needs it... just not confident in my ability to get the thing floating properly and level again.

 

[memepool]

Quote:

Originally Posted by Garbz RF is so far outside the audible band that unless it's causing your phono stage or other components to become unstable, it would be inaudible.

How's that? My Cyrus One amp used to sometimes pick up police and emergency services chatter?
Didn't actually matter whether the turntable or CD input was engaged and there was no tuner attached at the time either?

 

[memepool]

Quote:

Originally Posted by fewtch I still haven't tried rebalancing the chassis on mine, although it 'somewhat' needs it... just not confident in my ability to get the thing floating properly and level again.

Neglecting to do this can have a big impact on how it sounds. It's really pretty straightforward.

You need to put it on a surface which gives you access to the underside like a rack with the shelf removed and take off the bottom if you havn't already (it's usually pretty cheap resonant hardboard which you are better off without anyway).

There are three white cups underneath that the springs sit in. You get a really small spirit level and put it right in the centre of the platter then rotate the cups in turn until you get the spirit level even.

Then you can tune the suspenison. if you push down gently on the spindle from above with your forefinger and let go quickly all the springs should bounce evenly. While you work at this turn the system on and off intermittently and play a record so that you can gauge what effect you are having on the sound.

Getting the bounce right will give you really amazing pace especially apparent with live drumming which sounds amazing on the TD160.

 

[fewtch]

Quote:

Originally Posted by memepool Neglecting to do this can have a big impact on how it sounds. It's really pretty straightforward. You need to put it on a surface which gives you access to the underside like a rack with the shelf removed and take off the bottom if you havn't already (it's usually pretty cheap resonant hardboard which you are better off without anyway). There are three white cups underneath that the springs sit in. You get a really small spirit level and put it right in the centre of the platter then rotate the cups in turn until you get the spirit level even. Then you can tune the suspenison. if you push down gently on the spindle from above with your forefinger and let go quickly all the springs should bounce evenly.

They pretty much do, it's just not perfect. Frankly I wonder how much impact it's having given that I listen to headphones and there are no speaker vibrations going through the table. I can tell it's still level and isolated from the motor by the fact I don't hear any noises or have any problems that would tell me otherwise.

Yes, the tuning could be better... no, I'm not gonna do it. The main problem is finding a surface that gives me access to the bottom of the table (actually this is surprisingly difficult -- two chairs/stools really don't cut it, and I don't have a rack, AND it requires basically lying on your back looking up at the bottom). Not to mention, I think such a surface would have to be perfectly level itself if any leveling I do would be effective (?). I just don't have the resources to do much of anything but make a big mess of suspension tuning. Believe me, I gave it a preliminary shot and in horror tried to get it back to the way it was (think I succeeded). I think this kind of thing is best done by a relaxed type of person, an obsessive like myself will have a heart attack in the process.

I should add that I'd really prefer to not own a suspended table at all, but I got the Thorens for a $75 packing fee. And that I rarely listen to it these days. Something of a waste, but shipping turntables is such a PITA that I haven't sold it (and the price of Thorens tables has dropped some, making it not really worth selling in my estimation).

 

[memepool]

Quote:

Originally Posted by fewtch It pretty much does, it's just not perfect. Frankly I wonder how much impact it's having given that I listen to headphones and there are no speaker vibrations going through the table. I can tell it's still level and isolated from the motor by the fact I don't hear any noises that would tell me otherwise. Yes, the tuning could be better... no, I'm probably not gonna do it. The main problem is finding a surface that gives me access to the bottom of the table. Not to mention, such a surface would have to be perfectly level itself if any leveling I do would be effective. I just don't have the resources to do much of anything but make a big mess of the suspension tuning.

right. The surface I use is a Sound Organisation stand which is basically a tubular steel frame with removable mdf shelves mounted on upturned spikes. This in turn is mounted on adjustable floor spikes so the whole stand can be levelled quite easily.

Apollo and Target make similar ones which also come in wall mounted versions but you could just as easily use any identically proportioned objects like 4 paint tins for example, resting on your level surface which the table ususally sits on.

By lifting the frame of the deck up at the edges enough to allow your hand into the innards you can then access the suspension.

Setting up a turntable properly has a huge effect on how it sounds. It's not just a question of isolating it from external electronics which is of course important. But the electronics of turntables and phonostages is something which people seem overly to dwell on.

The amount of influence that this can have on the sound is far less than the characteristics of the platform on which the whole thing sits. You are not just isolating it from spurious elecronic signals but trying to help it to separate out the vibrations you want (ie those in the groove) from those that you don't ie everything else in the immediate environment.

Absolutely every mechanical part and support surface has an influence on the sound from what kind of platter matt you use to whether your floors are made of concrete or wood. In this sense it is exactly like a musical instrument.

So while these kind of fancy stands can seem unimportant compared to a stylus upgrade or whatever, they are actually crucial, especially with modern budget turntables in the Rega/Goldring mould.

Your Thorens is a much better isolated design than this, but the suspension is what acheives this so tuning actually has a large part to play in the character of the sound.

Try tightening the suspension nearly all the way while keeping it level and playing a record and then loosening it almost completely and listening to the same record and you'll see what I mean.

 

[lini]

Quote:

Originally Posted by fntms My Audio Techina 150MLX (MM) catridge, which I like a lot because of its amazing detail, is giving me trouble: it seems to be sensitive to RF signals or similar interfences. Indeed, it emits a very high frequency 'binary' sound (it switches on and off abruptly) at random intervals, never lastling more than a few seconds. I suspect that my neighbours TV or something else in their place might be at the origin of my troubles. (...)

Hmmm, maybe a cell/cordless phone related interference... Might be worth a try to call up your neighbours when they aren't at home for a check...

Greetings from Munich!

Manfred / lini

 

[fntms]

Quote:

Originally Posted by memepool You need to put it on a surface which gives you access to the underside like a rack with the shelf removed and take off the bottom if you havn't already (it's usually pretty cheap resonant hardboard which you are better off without anyway).

memepool: Are you saying that the underside should be altogether removed and the tt left w/o anything underneath? I could imagine this adds a little 'airyness' to the sound...
And that's a mod I can see myself doing! I could also see myself replacing the underside with a nicer piece of wood (solid oak?) if it can just be glued in place of the original underside.

lini: Yes, I'll try calling my neighbours in their absence, good idea! Thanks.

If I want to build an 'isolation' box for my preamp (the rega fono is quite small, although very pleasing), what metal should I use? Steel, aluminium,...?