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Lenco L65 hums, only when playing

R

RudyVerkorst

New Member
I have a Lenco L65 with Stanton 500 cartridge of the old days, and whilst playing, it produces a significant hum. This means it hums while the needle is on the record (or on my finger) AND the motor is switched on.

I've opened it, and everything seemed normal (as far as I could see - the connections inside the arm bearing are impossible to see). When I try to wire the arm with the chassis, nothing changes.

As I could read on Graham Slee's site, there is a metal tag that connects the left channel ground to the chassis of the cartridge. According to Slee, it could give a hum loop when the arm is properly earthed. I didn't remove the tag as it has always been there, probably since my grandpa bought it back in the seventies or sixties.

Please, help!

Thanks
 
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if it is only humming when the motor is turning, it may be the shielding of the arm wiring is faulty or perhaps the connections to the cartridge have at some stage become mixed up. Check your arm wiring and remember, left and right connection colours have changed over the years. white=left+ blue=left-, red=right+ green=right-
old wiring used the red=left, green=right (red to port, green to starboard)
 
Make sure as well that everything associated with the motor that is supposed to be grounded to chassis IS grounded to chassis.

Fred Longworth
 
I don't feel like buying another cartridge yet at this point, so I will keep trying it first with the Stanton 500. The wires are connected correctly on the cartridge. Unfortunately, I can't check the wires inside the arm, nor can I check if they're connected well, because when they coming out of the arm, they all have the same colour. It seems impossible to open the bearing system or the arm to see the inside. Check the photo's on that.

I've also included a picture of the motor. As you can see, there is a third gap in between the power supply + and -, which is unused. Could it be this? Could this be the grounding socket that I have to connect to the chassis?
 

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I do wonder if the grounding of the cartridge shield is intact. One problem with Stanton/Pickering cartridge bodies is that sometimes the shield slides forward and off the rest of the cartridge body, and this can degrade or destroy the grounding of the case, even when pushed back into position.

If this were at my store, I'd take an Xacto knife and make a minute scrape in the paint on the 500 cartridge surface, so as to expose the metal. (Choose a spot that's not visibly obvious.) Then I'd use an ohmmeter to measure between the metal of the shield and the tip of the turntable ground wire.

If the shield portion of the cartridge body is not properly grounded, then you can wind up with a variant of the "Grado hum."

Fred Longworth
 
Hi Rudy,

Lencos of all eras are notorious for their "less than intuitive" wiring strips. Since they were dual/AC exports, a vacant tag doesn't necessarily mean that it's for grounding. If you can take another clearer picure of that wiring strip and also note if any of them are jumpered, I'll take it over to one my Lenco motor historians and get his take. Are you N.A or Europe?

Also:
Most of the time when you are dealing with EMF induction hum (motor induced hum via a poorly shielded cart), it gets louder as you draw the cart/arm closer to the motor. Is this happening?
 
I included some more photos.

Fred, I don't have an ohmmeter, and I don't know nothing about 'Grado hum' (hum that gets emitted by a Grado cartridge?). Maybe you can see something on the pictures.

Mopic, I managed to make a better photo of the wiring strip. I think you can see everything on it I can see with my bare eye.

I live in Europe (Belgium), and the hum doesn't seem to change when I move the cartridge closer to the motor.
 

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Hi Rudy,

I'll post your Pics/problem over at Lenco Lovers. One question after a more careful read of your first post ...

Is the hum absent with the motor on and no pressure to the stylus either with record or finger?
 
The "Grado hum" is due to the fact that turntable motors emit powerful electromagnetic fields. As you might guess, the strength of these fields varies from motor to motor. Also, some motors are well-shielded, and some are not. So, on many turntables the platters are bathed in electromagnetic field energy fluctuating at 60Hz.

Now a magnetic cartridge is an extremely sensitive device to electromagnetic fields. It is, after all, an inductive pickup coil. The problem from an engineering point of view is how to shield the coils from stray field energy. Shure, Pickering and others use a metal case on their cartridges as a shield, and ground the shield through one of the ground wires for the signal.

The Grado cartridge line, on the other hand, is manufactured unshielded. On some turntables (those with strong fields coming from the motors), this leads to a pernicious hum. This hum gets stronger as you move the arm across the record toward the motor.

* * * * *

In your case, you've told us that the hum requires the motor to be running, but does not get louder as you move the arm (and hence the cartridge) toward the center of the record.

This is a real puzzler.

If I were there, I'd have my ohmmeter, and would be checking to see if something is not grounded, if the tonearm wiring has a problem, etc. I urge you to purchase a simple DMM (digital multimeter) with ohmmeter function. It will save you tons of time and stress -- and you can buy a fairly good one for under $30.

Fred Longworth
 
certainly is a wierd one. Looking at your photograph of the wiring strip, the left (white) output lead doesn't look like the arm wire is soldered to it (the terminla strip) (could be the light).
 
Yeah, that left channel wiring looks suspicious. There should be four signal wires coming down the arm and four wires (two hots and two shields) in the audio cables.

In some designs, the tonearm is grounded through one of the signal grounds in the arm. In other designs, there is a fifth wire grounding the arm to the turntable chassis. In still other designs, the arm grounds through the arm bearings. But, this is always true: the arm should be grounded to the turntable's metal chassis, and the chassis should be grounded to the amplifier, either through one of the shield lines on the audio cables, or via a separate ground wire, usually green or black.

I get the impression that on your turntable the chassis is grounded to the amplifier via the shield for the left channel audio cables.

Fred Longworth
 
I agree Fred and there is also the possibility that the right return from the cartridge (the right arm wiring shield) is broken and the return for that channel is coming back through the earth strap on the cartridge, headshell,down the arm tube and chassis to the output cable, whereas the left may actualy be ok. Two completely different earth returns and one picking up all sorts of 60Hz.
Honestly, it's fun trying to work it out, but 5 seconds with a DMM and it'd be solved...
 
Okay then...

I'll go and buy a multimeter, I also have a ceiling lamp where I have to check the wiring, that thing is lying there a few months already, waiting for my dad's volt meter, but okay, I'll go and find a DMM myself.

Only you guys have to tell me exactly what to do with the meter, as I really know nothing about electricity, volts and ohms... ;)

And while I'm out at the audio store, maybe I also should upgrade my cartridge, or at least the stylus. Some people say it might damage your records when its more than 30 years old, isn't it?;) Any suggestions which one I should buy? Shure? Or unshielded Grado (don't know if I can find it here in Brussels)? And won't I have to be careful that the cartridge fits in the headshell?

By the way, I double checked the wiring, it's all okay and attached.

Cheers and thanks for all your time!
 
The more ohms you have between points A and B, the harder it is for electricity to flow between points A and B.

If I take a piece of wire about 16" long and measure the resistance (ohms) from end to end, I should get very close to zero. This means that the wire does almost nothing to oppose a flow of electrical energy.

In this case the "flow of electrical energy" is the music coming from the phono cartridge.

Now, if you measure the resistance between two different wires in the tonearm, you should get infinity. This simply means that the wires are isolated from one another. No energy flows between them.

Fred Longworth
 
Hey Fred, I don't know whether we are talking a cross purposes here, but one low resistance return and another taking a complicated and higher impedance return through a metal chassis, pins, bearings etc will result in two slightly difference potentials at the RCA outer shield (l compared to right). Combine that with a high impedance front end and more dubious earthing and it is so easy to induce hum into the phono stage it is a wonder it works at all. We also know nothing about the amp, whether it is a double insulated unit and the case is ' floating' at goodness knows what, and also whether the turntable is a two pin or three, with or without earthing. If it was me, I'd change cartridge first, after I'd checked all the wiring with my ESR meter as it goes more than low enough and gives me a nice high reading where inductance could be an issue.
 
Long live the DMM

Okay, I checked out the DMM I bought for 15 euros (a model that's often bought by students and beginners like me,the vendor said). First, I checked the resistance of all cartridge outputs and their corresponding wirestrip inputs. Although the numbers sometimes changed fast, I managed to get all of them close to zero.
Then I checked the cartridge (didn't have to use a knife, there already was scraped off a little bit of the metal) and the wirestrip, an immediate zero.

And then...

I checked the wirestrip grounding and the grounding cable tip... and it stayed on '1'.

We found it!

And maybe you were puzzled because I didn't tell you that the connection to my amplifier is quite abnormal. The phono output is a 5 pin DIN cable. I connected it to an old female DIN-cinch cable. The grounding is on pin 2 of the DIN (I think, it's the one in the middle). But when I just plugged it in my amp, I had hum all the time. Then I discovered that when I made the connection shown on the picture (connected the chassis of the DIN connector to the grounding on the amp), the alround hum was gone. Except for the hum when the motor was turnt on.

So... I guess I'll better buy a proper cinch connection, and solder it again to the wiring strip, together with a proper grounding cable to connect it to the grounding input of my amp?
 

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I do not know about yours but I am very familiar with the Lenco L75. These used to have 2 transport screws under the platter to secure the motor. If these were not removed, the motor suspension was bypassed and vibration went straight to the chassis. It was a mechanical hum only heard when the stylus was on the record. Many dealers did not know this and delivered the units with the motor transit screws in place. The difference once removed was astounding. Check your manual. Atlernately remove the platter and look for 2 screws with red marks.

Fernando
 
When I got home I checked the Lenco manuals at the vinylengine.com. Just about every Lenco has these motor transit screws. I have heard them without the screws loosened or removed and the sound is exactly what you describe. It sounds like an electrical hum, but it is really the mechanical vibration from the motor being transmitted straight into the arm and platter. It only occurs when the stylus is on a vibrating surface. I did not see a manual for the L65 but the others I saw had the instructions on loosening them to release the motor. They are normally marked in red for easy identification.

Fernando
 
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