I guess you know that it is not really the "turntable" causing the channel imbalance you observe. It's gotta be the cartridge, cartridge alignment, or the phono stage. You say you're using an oscilloscope to observe the imbalance, but unless I missed it, you don't say where you are connecting the 'scope. Your observation that only extreme deviations of azimuth affect the imbalance makes good sense; azimuth is for minimizing crosstalk and is a crude tool for correcting imbalance that usually results in mechanically unacceptable angles. (Stylus usually riding too far to one side or the other.) So you ought to look elsewhere. You say you reversed "the leads" and has an effect on imbalance. if you're talking about the leads from the cartridge to the phono stage, I would say you are looking at very tiny voltages direct from the cartridge and unless you have a very good scope or unless you can obviously hear the difference and it's bothersome, I would not believe the data. If you are talking about the leads at the output of the phono or linestages, then that observation is consistent with the options I mentioned. I personally with just live with it. 1db is not much.
Thorens TD-160MKII Channel Imbalance
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.