Thorens Turntable Strange Noise

Hi, I am currently resurrecting my old analogue audio system to give to my son and his girlfriend who have just moved in together and wanted a turntable system. So this consists of a Thorens TD316 which I bought new in 1985 and an Arcam Alpha 7 amp which I bought in 1998. These have both been sat unused for 15 years or so gathering dust.

So I have cleaned everything up and fitted a new belt to the turntable and oiled the bearing etc and the turntable is working great except for one small issue. As soon as the turntable audio cable is connected to the phono inputs on the amp there is a low volume fluttering sound from the speakers. This happens without the turntable even being switched on and even with the power supply cable disconnected so it is not interference from the motor speed control circuitry.

If I disconnect the turntable earth cable from the amp then I get 50hz hum as you would expect but I think the fluttering stops but it may just be that the hum is drowning it out.

If I play a record then the sound is good and drowns out the fluttering. Also if I disconnect the turntable cables from the amp then there is no noise at all except the hiss from the phono pre-amp stage in the amp at high volume levels.

I just can't figure out where the fluttering sound is coming from. Does anyone have any suggestions.


Many thanks

Russell
 

Galu

Member
2018-04-17 6:50 pm
Some possible causes worth eliminating:

Do not place the turntable on the same surface as the loudspeakers as acoustic feedback can take place between speakers and cartridge

Check the electrical connections on the cartridge are tight.

Change the stylus assembly as age can cause the cantilever suspension to weaken and more likely to be forced into oscillation.
 
Thanks for the replies guys, really appreciate it.

Shorting the phono RCA plugs on the amp if I'm understanding you correctly does not create the noise, just a little hum.

There are no cell phones or any other electronic devices in the room.

The turntable is on a different surface to the loudspeakers and I have checked the cartridge connections and even changed the cartridge. Also the noise I am referring to even happens with the stylus removed from the cartridge. Also I currently have a different cartridge connected but not fixed in the headshell so it is just hanging from the wires meaning that the cartridge is completely decoupled mechanically from the turntable and the noise is still present.

Just one other thing, I may have been a little misleading when I described the noise as fluttering. It's not the sort of fluttering you get when a loudspeaker oscillates, it's more of a fluttering combined with crackling like you get from a noisy volume pot. It's not easy to describe.

I do know it's driving me mad though.
 

Galu

Member
2018-04-17 6:50 pm
It's not the sort of fluttering you get when a loudspeaker oscillates, it's more of a fluttering combined with crackling like you get from a noisy volume pot. It's not easy to describe.
Sounds kind of like a bad connection. I see the turntable has a removeable headshell. Check the electrical contact points are clean. The contacts inside the arm will be spring loaded - use a cocktail stick to check if they are springing in and out freely.

I don't know the solution I'm afraid, we can only eliminate possible causes.

Thorens TD316 - Manual - 2-Speed Manual Belt-Drive Turntable - Vinyl Engine
 
The TP21 tonearm that is fitted as standard on the TD316 doesn't have a removable headshell in the normal sense. The headshell is clamped onto the arm but the audio connection pins are fixed on the end of the arm itself. If you unclamp the headshell you can't then remove it without disconnecting the cartridge wires first.

I will attack the problem with new vigour tomorrow. There must be some connections in the base of the turntable to connect the thin wires from the cartridge to the main RCA wires coming out so maybe there is something amiss there. I'll see about removing the tonearm and checking that out.

I'll let you know how I get on.

Thanks again for your time.
 
Hi again, just a quick update.

Firstly, in answer to as_audio's question, I'm not 100% sure what popcorn noise is but from the descriptions I've read online I don't think it is that.

Anyway, I remembered that I have another amp in the loft, albeit a 5.1 channel AV amp but it does have a phono input. So I tried that amp in place of the Arcam Alpha 7 and low & behold there was no noise. I could turn the volume right up and apart from very slight hum at max volume the fluttering sound was not present. So it now looks as though it is something to do with the Arcam amp and not the turntable.

As the unwanted noise is coming from both channels I thought it might be power supply related but I've checked that out thoroughly and it all appears ok. The +/-37v voltage rails are both ok with no undue ripple (checked with oscilliscope) and the +/-15v rails are also ok.

I have made a recording of the noise which, if I've done it correctly, is attached to this message. This was recorded with the amp volume up high. At normal listening volumes it is barely audible.

See what you think.
 

Attachments

  • Unwanted Noise.zip
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I used to have an Arcam integrated amp, and the input selector switch got bad and noisy, especially more in some positions than others. Contact cleaner on all the pots and switches might help, especially input selector and volume control. See if the noise improves or changes when you wiggle the input selector knob a bit.

Thanks for the suggestion but I've already eliminated that as a potential cause. Neither the volume control or the input selector are at all noisy and no amount of flexing in any direction effects the noise in any way. I have however cleaned them with contact cleaner just in case. I do need to replace the volume pot though because when it is at minimum volume there is still sound coming out of the left channel whereas the right channel is silent. Looking at the circuit diagram one side of the pot is connected to ground and so should the wiper when at minimum volume (or as near as makes any difference). However, upon checking with a meter the left channel has a resistance of 30 ohms between the wiper and ground whereas the right channel it is less than 1 ohm. Cleaning the pot has brought the resistance down to about 14 ohms but I cannot get it any lower. Strangely though there is absolutely no noise coming from the pot at any point in it's rotation.

Unfortunately I can't find a pot with the same length 'D' shaft, I can only find one slightly shorter so I hope it will be ok. If not I may have to disassemble the original pot and clean it up and make sure the wiper touches the earthed pin properly.
 
Another update. I've made significant progress today with regard to the strange noise. I had a feeling that it may be earthing related so as well as the turntable ground wire I connected a second wire from the metal base of the turntable to the amp grounding post and the noise disappeared. If I remove the second wire then the sound comes back again so I now know that it is a grounding issue.

I removed the bottom cover from the turntable and found that the ground wire from the amp post connects to the tonearm circuit board and then there are three other internal ground wires linking this to other metal parts of the system in a daisy chain fashion and terminating on the bottom cover. Two of these earth wires had been trapped and squashed where the metal base screws onto the MDF board. All the internal earth wires had push fit spade connectors that pushed onto tabs on the various metal parts. I have removed and cleaned all the connectors and refitted and there is now no noise coming from the system although the turntable is still upside down on the bench with the bottom cover removed.

So, I am now going to replace all the internal earth wires and I'm contemplating soldering them onto the metal tabs instead of the spade connectors. While I am at it I am going to replace the audio cables as well because there is a moulded strain relief boot where the cables exit the bottom cover and this is cracked and broken and the cables look a little suspect there. So, while I've got it in pieces I thought it would be prudent to replace them as well.

So I'm hopeful that once I've replaced all the earth wires and the audio cables then all will be well.

Fingers crossed. I will obviously update this post when I know one way or the other.


Thanks to everyone for your help with this problem.