Grounding problem with Lenco L70

[jasperv]

I'm new on this forum and this will be my first post. I think it wont be the last since I recently got myself three lencos, a B51, a L78SE and an L70. So far I've more a DUAL-man and I've collected many dual 1009's, 1019s and 1229's. However, I thought it was time to broaden my horizon and explore the world of Lenco.

Well, I'm posting here since I'm hoping to find some help with a grounding issue of my L70. Its a really nice turntable, but I hear a hum thats annoying me a lot. It seems like the hum wasnt there when I bought it and listened to records when it was still connected to the amp of the guy I bought it from. I tried to solder a different cable to the plate on which you connect the cable to the rca wires coming from the tonearm, but to no avail unfortunately.
I also tried to connect a din cable instead of an rca cable. When I connect this cable directly to my amp (with din in's)  there is a lot less hum than when I connect it to my pre-amp with rca ins.

I wonder what else I could try. I dont think its a problem with the headshell, even though I dont have a second headshell to try out. When I take the headshell off the hum remains the same. Touching the headshell or the wires coming from the cartridge doesnt give a loud noise (which it could do if the problem was with the headshell).

Do I need to make a ground loop? (I'm not even shure what this does exactly).

Hopefully I could get some advice. Thanx in advance!

[Kalimero]

First you should cut the link between right and left signal ground and see if something changes. Signal grounds should not touch shielding and neither be linked to any other ground.
Which cartridge are you using?
Did you try with another one (even if you don't hear any difference between with or without cartridge)?
Did you ground the power supply as the L70 comes without?
You should also have a look underneath and discover where that yellow cable is linked to. Originally I think it is the shielding of the tonearm ...
So take a picture also underneath.

[jasperv]

First you should cut the link between right and left signal ground and see if something changes. Signal grounds should not touch shielding and neither be linked to any other ground.
Which cartridge are you using?
Did you try with another one (even if you don't hear any difference between with or without cartridge)?
Did you ground the power supply as the L70 comes without?
You should also have a look underneath and discover where that yellow cable is linked to. Originally I think it is the shielding of the tonearm ...
So take a picture also underneath.

Hi Kalimero,

Thanx for you reply and help. Yesterday I already cut the metal bridge between the grounds and I even connected the signal ground (the yellow wire) to a ground cable going to my (pre) amp. It didnt chnage anything. Not more and not less of a hum. I did try out several cartridges, so the problem for sure is not there. Unfortunately I dont have a second headshell to try (since they are so expensive).
The yellow wire is indeed going into the tonearm. Tomorrow I'll take a picture of what I see underneath. How do you ground the power supply?
I do think its within the tonearm. When I play music the hum is not audible, but when i lift the tonearm and turn up the volume a bit its more audible than with my other turntables and it can be quite annoying. How can you shield a tonearm? Does that mean I need to put something around the wires in the tonearm? Like a nylon cover?

[Adelmo]

Hi,

I would try the following:

Motor and top plate grounded to the main only, main must have a good ground.

Tonearm isolated from the top plate and motor ( no common metal to metal contact )

Avoid to have close to the motor and motor cable any TA wires.

Ground the TA wire to the pre amp ground only ( not to any main ) , if still hum, try without this ground to the pre amp.


Hum should disappear, hopefully. If not may be the additional solution is to try a stacked platter that increase the distance between cart and motor.

Best regards

Adelmo

[Kalimero]

In any case:
- you should be aware about grounding and shielding. They are two different things and reading your reply I think you are mixing them up;
- before trying and/or testing you should know how and where your cables are linked to. You can find out a lot with a simple tester/multimeter.
Signal grounds are connected through signal cables and not with anything else. The same goes for shielding. In your place I would perhaps even try to connect your turntable to the preamp or integrated amp without shielding cable.
In terms of safety about electrical power connections you should have a ground wire (normally yellow/green) connected to the top plate. If there isn't any still, wait for it. You can add it afterwards.
Hums are sometimes audible just because of a faulty or loose connection/soldering.

[aamodtasan]

Hi,

I would try the following:

Motor and top plate grounded to the main only, main must have a good ground.

Tonearm isolated from the top plate and motor ( no common metal to metal contact )

Avoid to have close to the motor and motor cable any TA wires.

Ground the TA wire to the pre amp ground only ( not to any main ) , if still hum, try without this ground to the pre amp.


Hum should disappear, hopefully. If not may be the additional solution is to try a stacked platter that increase the distance between cart and motor.

Best regards

Adelmo

+1 - and the screw on the coupling needs to be removed or you will connect the TA ground to the topplate, I remove the yellow cable/ground from the coupling entirely

hth
henrik

[bazzast]

You could try to connect tonearm cables directly to rca jacks.
Put them on a isolated base ( wood, plastic ecc..ecc..) then connect signal wire to each one and the yellow wire that comes from tonearm to the shield of one channel.
On my L70 I've done like this and have no hum.
You could even bridge the two shield and connect both and the yellow wire in one point. Nothing change.

[jasperv]

You could try to connect tonearm cables directly to rca jacks.
Put them on a isolated base ( wood, plastic ecc..ecc..) then connect signal wire to each one and the yellow wire that comes from tonearm to the shield of one channel.
On my L70 I've done like this and have no hum.
You could even bridge the two shield and connect both and the yellow wire in one point. Nothing change.

Thanx for your reply Bazzast. I could try that indeed. So, do I solder the yellow wire to the shield of one channel just like I do with the mass of both channels?

[Kalimero]

Actually I disagree with this method, but it is worth a try if bazzast is telling that it is working fine ... As far as I could understand it is exactly your starting situation. On top of that I am still thinking that we are mixing up two different types of connections: grounding and shielding!
I read a very interesting article about this topic. It was a link I followed here on Lenco Heaven, but I am not able to find it any more ...  

Edit: I found it   !
Here you have the thread: https://www.lencoheaven.net/forum/index.php?topic=44982.0 Even if it is about an L75S it is worth reading it as the difference between the two models is the tonearm. In the "S" model the tonearm is connected electrically to the top plate. And while trying different connections of grounding and/or shielding, don't forget that the middle contact of the junction box is linked/connected to the top plate!!

and this is the interesting article (it explains a lot!): https://korfaudio.com/blog98

[bazzast]

Actually I disagree with this method, but it is worth a try if bazzast is telling that it is working fine ... As far as I could understand it is exactly your starting situation.

I done this becouse if you look in any phono stage, cable shield goes to ground.
Plus, on my L75, when I've changed the damaged 5 pole din cable I've had a bridge between the shield of each chanel and the yellow wire that comes from tonearm. This allows me to eliminate ground wire. No hum even in this case.

[stratokaster83]

I done this becouse if you look in any phono stage, cable shield goes to ground.
Plus, on my L75, when I've changed the damaged 5 pole din cable I've had a bridge between the shield of each chanel and the yellow wire that comes from tonearm. This allows me to eliminate ground wire. No hum even in this case.

There are balanced phono preamplifiers that do not connect tonearm mass to signal return internally.

[bazzast]

There are balanced phono preamplifiers that do not connect tonearm mass to signal return internally.

Sorry, I've not considered the balanced connection.

[frothy]

Hi Jasperv, first off one thing no one has mentioned is "ground loops" are bad and
quite often the cause of HUM. We should be trying to eliminate any ground loops in our system.
One way is to have "star ground" check out "star ground configuration"in your search engine, it will give you a clear, concise, simple explanation.
I have all my gear grounded this way including a non-modified L 70.
frothy

[jasperv]

Well, I spent quite some time trying things. I tried to connect the tonearm directly to the rca cable that leads to my pre-amp without using the top-plate. The result was the same. I measured all with a multimeter.. All connections seemed good.

So what I did next was taking off the tonearm and taking it apart. In the end I didnt manage to slide the stylus pressure guide assembly off the end of the arm, so I could replace the tonearm cbles. Thats where I got stuck. In the end I tried to put together the tonearm again, but by doing so i ruined two small bearings (i do think they were already in a bad state). Now the tonearm doesnt work as good as before. I think I kind of ruined it...and in the end the hum is still there. I need to put this project aside now. It has given me too much frustration.
Maybe one day Ill find another tonearm for this L70 and maybe it will solve all problems. But for now Im done with it. Thanx all for you help on my previous messages.

[Kalimero]

Oh, what a pity. I'm so sad for your frustration    Sometimes it happens ...