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Thorens 320 hum/ground loop

M

marblesmike

AK Subscriber
Subscriber
I just bought a Thorens 320 from a reputable guy on Facebook Marketplace to replace my Thorens TD 147. The table is beautiful and has been restored, with the RCA/ground wires being replaced by input jacks to use external cabling. I believe it has the TP 16 mkIV tonearm.

After setting everything up with my Lyra Delos cartridge and plugging it into my Rogue Ares preamp, I'm getting a persistent humming sound, even if the Thorens isn't plugged into power. I've tried swapping cables and messing with the tonearm wires to no effect. I tried moving the Thorens further away from the Ares, no effect. Everything is plugged into the same surge protector. I swapped cartridges (AT33PTGii), no effect, hum is still there.

One thing I tried was to plug the Thorens into a cheap Chinese preamp I have, and strangely, the hum went away. That led me to try hooking my old Thorens TD 147 back up to the Rogue Ares (in case something was jostled loose inside), but there was no hum.

So I'm thinking that something was wired incorrectly in the Thorens TD 320 when the RCA/ground wires were removed in favor of the inputs. The only thing I can do to manipulate it is to remove the two earth tonearm wires from the back of the cartridge (blue and green).

The seller is willing to take it back, but if I can get this resolved relatively easily/cheaply, I'd prefer to keep it.

Any suggestions? I do have some basic electrical/technical knowledge.
 
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Standard Amazon RCAs between the Thorens and Rogue. There is a ground, but a loud buzz is introduced when it's connected to the Rogue.
 
Try turning power cord on tt over. ( assuming it is non polarized ) Also might want to check between TT and a known good ground with a DV Meter for voltage.
 
marblesmike said:
Standard Amazon RCAs between the Thorens and Rogue. There is a ground, but a loud buzz is introduced when it's connected to the Rogue.
Click to expand...
Without the ground wire, you have the hum? with = buzz?
With the 147 (no hum or buzz), did you use the attached 147 cables? with ground wire? was it plugged into the same outlet as your buzz trial with the 320?

I would continue with your troubleshooting.
For me, sometimes it's just trial & error. At a minimum, (1) ensure your TT is plugged into same ground as the rest of your system, and (2) try cables recommended for phono use w/known shielding & capacitance.
 
mrwood200 said:
Without the ground wire, you have the hum? with = buzz?
With the 147 (no hum or buzz), did you use the attached 147 cables? with ground wire? was it plugged into the same outlet as your buzz trial with the 320?

I would continue with your troubleshooting.
For me, sometimes it's just trial & error. At a minimum, (1) ensure your TT is plugged into same ground as the rest of your system, and (2) try cables recommended for phono use w/known shielding & capacitance.
Click to expand...
Thorens TD 320 (with or without AC adapter plugged in):
-Ground connected to Rogue has hum and buzz
-Ground disconnected has hum and no buzz
-Ground disconnected and only one channel's RCA connected has no noise

Thorens TD 147:
-soldered/attached (aftermarket) RCAs and ground connected: no hum or buzz, works as intended
 
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