Thorens TD160 E no low frequencies - Help needed

[ChronoSee]

I've done the job according to the pictures and instructions (at least I think I did). If someone can take a look ...View attachment 3094407

Hello again! I didn't have the time to take another shoot at fixing the issue.
But I had some time to think about the issue, I would like to summarise the issue and make sure I understand it correctly.
As far as we know, we should ground:
- right channel negative lead
- sub chassis
- main chassis
- tonearm

The way it is grounded now:
Right jumper screw connects to sub-chasiss, sub-chassis to main chassis by the wire.
Right jumper screw than connects to right channel negative wire and two tonearm wires, green wire connects to headshell. Two tonearm wires (god knows where)
We don't know why there are two ground leads coming into tonearm.
I'll make sure today to check the ground leads with multimeter and edit this post with findings.
Something is creating a ground loop which results in hum.

But I started to wonder, on previous configuration there was no hum with external ground. Moreover the green wire wasn't connected to the right screw post, only to the headshell. Maybe I should skip connecting green wire to the right screw, it's already connected to the headshell which is supposed to be grounded?

I don't know anything about grounding, but am I onto something here?

 

[tnsilver]

Grounding is an illusive bitch when it comes to turntables. To my observation, your turntable is now wired correctly as per the classic Thorens scheme, which excludes an external grounding lead. I agree we don't exactly know what the two ground leads from the tonearm are doing, and it's very likely I've missed something having to do with the TP-63 wand grounding (having to do with the green lead).

The good news - it's very easy to experiment and test on the fly. All you have to do is de-solder suspect leads, or jumper suspected missing connections - or both. Unless you accidentally hook a power supply lead to ground, your chances of screwing up anything are extremely slim. You can't cause any harm by messing with audio leads, so have no fear. I suggest you experiment (you have a good idea of what's going on there) and share the results with us.

 

[tnsilver]

As far as we know, we should ground:
- right channel negative lead
- sub chassis
- main chassis
- tonearm

In essence, the classic Thorens grounding scheme looks like this simplified sketch:

It is exactly identical to this configuration:

It doesn't matter where ground is connected - it's important that the sum of the metal masses of the different parts of the turntable is seen at the ground output (right channel ground) as if it was one bulk metal mass. Not different masses - and only once.

It is quite easy to achieve correctly. The pitfalls are obscured when the tonearm is composed of different metal masses, which are grounded separately, taking into account (or not) the cartridge grounding with the headshell. That's where most of the problems are.

 

[Fishead]

You can't cause any harm by messing with audio leads, so have no fear.

Yes . That's what I was thinking also and when I suggested unhooking that wire that connects the sub and main chassis.....free and no danger of doing damage, and if one of those wires going up in to the arm pillar connects to something that connects to the main chassis, then I'd think there would be a chance of that loop we've been talking about. However, at this point I'd just be trying various configurations of wiring (always keeping the picture of where I started) to see if I can find one that is without the hum.....

@ChronoSee, thanks for reporting back and do let us know what you find with the multimeter test. I think that was a good suggestion Tom made a while back so let's see what that might reveal......the answer is there, just making itself a bit difficult to see at the moment.

 

[ChronoSee]

Hello there! I finally found the time to redo the solder job. First I checked the 2 transparent wires and tonearm with multimeter. Those two wires have continuity in exactly same spots. You can see on the picture where, I marked them with X. They don't have continuity anywhere else (with any other wire or chassis).

Right now, I'm about to redo the RCA cables which I left two long without shielding. Should I try, to solder only one of the transparent wires if both of them are connected the same way?

Additionally I noticed the the hum is only audible in left channel.

 

[tnsilver]

Those two wires have continuity in exactly same spots.

Continuity on a meter simply means low resistance (20 ohm - 40 ohm YMMV). That would be too odd for both to be grounded to the same place.

Did you de-solder the leads coming out of the tonearm from the ground terminal for this test?

If not, de-attache those leads and measure the tip of each in ohms (resistance mode of the meter, not continuity) to the chassis.

If it's the same ohms value, leave one of them soldered, and cancel the other.

NOTE: If you measure resistance between the two tips of the detached leads, and they are genuinely connected to the same place, you should read about 0.2 ohms on your meter, which is the resistance of your probes.

 

[ChronoSee]

That would be too odd. Did you de-solder them for this test? If not, de-attache those leads and measure the tip of each in ohms (resistance mode of the meter, not continuity) to the chassis. If it's the same, leave one of the soldered, cancel the other.

Yes, I did exactly that. de-soldered them, check with ohms. They show the exact same thing. I re-soldered one of them and re-did the RCAs.
I'm waiting on Phonostage to warmup before checking how it sounds now. But static without playing is much less noticeable now, I'll have to turn the volume of amp past my normal volume levels or near to hear it. It's much more prominent in the left channel.

 

[tnsilver]

OK good. Swap the connection from the pre-amp to your speakers - put the right jack in the left speaker, the left in the right. Does the left speaker still hum?

 

[ChronoSee]

OK good. Swap the connection from the pre-amp to your speakers - put the right jack in the left speaker, the left in the right. Does the left speaker still hum?

Nope, the right one started humming. They both hum a little bit, left speaker just louder and with additional "tick tick tick" kind of static.
I did the same with phono stage to amp, when switching RCA the hum is following the change. So we know it's an TT issue.

 

[tnsilver]

Try to pinch the green lead connector in the headshell, the one that goes to the pin on the top, gently with nose pliers. While at it. carefully tighten all connectors on the cart pins. Any change?

...and, one more little thing... The ground terminal (screwed to the chassis) seems to only be laid on top of the green lead terminal. Can you apply some solder to that bond, to make it a good electrical connection?

 

[ChronoSee]

Try to pinch the green lead connector in the headshell, the one that goes to the pin on the top, gently with nose pliers. While at it. carefully tighten all connectors on the cart pins. Any change?

...and, one more little thing... The ground terminal (screwed to the chassis) seems to only be laid on top of the green lead terminal. Can you apply some solder to that bond, to make it a good electrical connection?

I'll try with pinching lead connectors later.

There is a fair ammount of solder there. I checked every ground connection with multimeter while I checked the transparent wires. It seems it's all well connected.