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Thorens TD-160MKII Channel Imbalance

Hello.

I have a Thorens TD-160MKII turntable that has a problem with channel balance. The left channel is around 1dB louder than the right. Below is my current set up and a list of things I’ve checked.

Currently I have an Ortofon Super OM cartridge and an OM20 stylus. They’re mounted to a TP63 arm-wand (the upgrade to the fiddly TP62) on the stock TP16 tonearm. I’ve kept modifications to a minimum only changing the bottom plate to one with leveling legs, certain parts of the suspension (new foam, leveling washers), replaced a broken arm-lift cable and upgraded the RCA cables to ones from Blue Jean. I wired the cables the exact same way as the originals, grounding through the left channel as opposed to an independent ground. Also, a new platter mat. The table has been professionally serviced and meticulously taken care of. I rebalanced the suspension in the last year.

I use an Oscilloscope application on my computer with the Analogue Productions test record.

-I have aligned the cartridge using both the Thorens gauge as well as the Feickert Protractor using Baerwald geometry. Same result.

-Azimuth is spot on.

-VTF is set to the recommended 1.5g. Increase and decreasing has no effect. All measurements are done on a digital scale, not by eye.

-VTA is currently set at the factory height with the needle aligning with the Thorens gauge. I had a 1.5 mm shim under the cartridge before and the result was the same.

-Anti-skate seems to make no difference either. Setting it to 1.5g, dialing it all the way up or down has no effect. I know the AS is working to some extent because when the arm is floating, increasing the AS increases the speed it pulls outward toward the arm rest fairly significantly.

-Turntable leads both measure around .990 ohms. I think one is like .992 and the other .987.

-Tried going through my SX-1050’s preamp and a standalone Cambridge Audio one and get the same result.

-Reversed the leads, reversed the cartridge wire. The problem reverses in both scenarios.

-I thought maybe the OM20 had a crooked needle. Tried the OM10 stylus. No change.

-Turntable is leveled from the platter. As it has a suspended subchassis leveling from the plinth isn’t as accurate.

The only thing that helps is if I skew the Azimuth way off I can get the levels on the Oscilloscope to match.

I had a modified arm with an Ortofon Blue before and got the same issue. Frustrated, I changed everything back as close to factory as possible, which is where I am now. I switched from the Blue to the Super OM because the latter is higher compliance and better matched to the arm, or so I thought. Also, it was the closest in spec to the original VMS (or something) cartridge it shipped with.

What am I missing? Is the AS way too strong even when dialed all the way down. Does the arm need to be rewired? Please help.

Thanks in advance.

-Doug

 

 

 

 

 

dtgarf
dtgarf OP
4 posts
 

lewm,

Thanks for the reply. I guess I should clarify a couple things.

It can’t be the phono stage as I got the same result when I plugged the scope into the tape out of the Pioneer SX-1050 and when I plugged it directly into the Cambridge phono amp. So, first the scope was connected to the tape out from the SX-1050 amplifier with built in phono stage. Then I plugged the turntable into a standalone phono pre-amp with the scope attached to the pre-amp out. Does that make more sense?

As far as the turntable leads are concerned, I unplugged the leads from the amplifier and touched one tester probe to the pin of the right RCA and the other to the inside collar of the same RCA. Repeated the same thing for the left connector. Each resistance value was nearly identical. I figured that because each signal path was giving me the same reading, that that ruled out a bad electrical connection somewhere in the cartridge and turntable leads. Is this flawed?

Then came the flip-flopping. I switched the L and R turntable leads on the SX-1050 - weak channel would flip. Did the same thing when connected to the Cambridge phono pre-amp - weak channel would flip. Then I put everything back to normal and switched the L and R wires on the back of the cartridge that come out of the tonearm - weak channel flipped sides.

I had the issue with two different cartridges, attached to two different arm-wands. That’s why I was wondering if the Anti-Skate was way too strong or if it was some else I could be missing.

Thanks.

-Doug

 

 

 

 

mr_m
1,900 posts
 

Unless I missed something here  it sounds like a cartridge imbalance. Did you try another cartridge?

fiesta75
1,378 posts
 

To me it sounds like you've narrowed it down to the cartridge itself. Am I missing something?

noromance's avatar
noromance
9,763 posts
 

Is the table level?

lewm
12,982 posts
 

Most cartridges only claim R and L channel balance +/-0.5db, so your cartridge may be within manufacturer's spec, but it does seem the imbalance problem resides in the cartridge.  Like I also said, when the voltages are as tiny as those produced by a phono cartridge, measurements are always suspect. I guess this problem is plainly audible to you(?)  If it's not, then....

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