Linn Lingo 4 ground problem and fix
Posted: 2019-12-12 22:18
PREFACE:
Some of you will know this already, because you asked for more info that I hinted at in the "Lingo 1 recap result" thread in the "On the Inside" section of this forum. I am now making it public, because I have learned that Linn have recognized the problem and will likely present a fix.
I am also posting it because the magnitude of the problem varies with which phono stage you are using. The first time I listened to a Lingo 4, I was using a Slipsik 7. The ground problem in Lingo 4 then results in a faint hum in the speakers which you may not notice unless you really listen for it. It also gives a loss of musicality, which caused me to be underwhelmed with the performance. Now that I've tested Lingo 4 with an Entity MC stage, the hum is more pronounced, so it becomes more likely you will notice that something is wrong. The loss of musicality is still evident, plus an annoying hum in the speakers. When your Lingo 4 is fixed, you will not only get a more musical LP12, but it will also be hum free.
THE ISSUE IN DETAIL:
Normally, your LP12 top plate, crossbrace, inner platter, Trampolin 2 (if you have one) and arm are connected to the ground screw of the phono stage (or the amplifier equipped with a phono stage) through the ground wire in the tone arm cable. That's the thin wire in between the thicker left and right coaxial cables of the tone arm cable. On some arm cables, the wire is separated from left and right cables.
This is the optimal way to do it, as it keeps the metal parts of your LP12 at the same potential as the ground in your phono stage (or amp with internal phono stage). So the music traveling from your cartridge to the phono stage is surrounded by a ground potential, which protects the signals from interference.
In the installation manual of Lingo 4, there is a mention of an optional link called LK1 on the circuit board inside the LP12. What LK1 does is to connect the chassis of the LP12 to the mains ground of the external Lingo 4 power supply (the screen of the cable from the power supply to the Lingo 4 board inside the LP12 carries the ground). This link is normally not used - you only connect it if for some reason, your LP12 isn't grounded through the ground wire of the tone arm cable. There are for instance some arm cables that don't have a ground wire - in that unusual scenario you might notice a hum in your speakers and the solution then is to add a jumper to link LK1 on the Lingo 4 board. Then your ungrounded LP12 becomes grounded to the Lingo 4 external power supply.
The problem is that the XLR connector that Linn are using on the Lingo 4 board (which receives power from the external power supply) has its metal front plate connected to the ground pin of the XLR through an extra metal link on the side of the connector. This metal link is designed to hook into the screw that holds the XLR to the panel. The result is that the optional ground connection that link LK1 provides is by mistake always present. So with a Lingo 4 inside your LP12, your top plate, inner platter, arm, etc are now grounded both to the Lingo 4 external power supply (and there to its mains ground) and the phono stage through the arm ground wire (also to mains ground). This creates a big ground loop, which causes loss of sound quality. In addition it causes either a hum through the loudspeaker (can be faint or strong, depending on the phono stage), some high frequency noise from the Lingo 4 circuit, or both.
The solution is to cut the link of the XLR connector, as shown in the photos below. I recommend that you let your retailer do this and let him know that Linn have accepted it as a fix to the problem. Linn might also choose to solve it by exchanging the metal standoffs that hold the Lingo 4 case inside your LP12 for plastic standoffs, which would isolate the case from the LP12 metal parts. Either solution works.
You need to remove the four screws holding the Lingo 4 unit to the crossbrace and preferably the Lingo 4 board from its metal case (I think it's 4 screws plus the two holding the XLR). Use a sharp pair of cutting pliers, gently cut it off (you might need to clip several times to chew through it) and pull it out. No harm is done to your Lingo 4 or LP12. All you are doing is disconnecting the circuit ground from the metal front plate of the XLR connector (which should not be grounded as it shorts against the metal parts of the LP12).
After I discovered this fault and cut the link on the XLR, my initial disappointment with Lingo 4 vanished. It really is a great motor controller for the LP12!
The XLR connector with its metal front plate. Red arrow points to the ground link that you are about to cut. You can see the tip of the link in the left screw hole of the XLR, bent to the right against the metal front plate.
This is the removed piece. It ends in the screw hole and can be pulled out without any force required. Notice the dents on the left, pointy side - those are from the metal screw digging into it. And that is how the entire metal housing becomes connected, by mistake, to the ground of the Lingo 4 circuit board. Which is the option that link LK1 provides!
This is what it looks like after the cut. The result? Lingo 4 performing as it should. Link LK1 at the bottom right is available if you should ever need this type of grounding.
Some of you will know this already, because you asked for more info that I hinted at in the "Lingo 1 recap result" thread in the "On the Inside" section of this forum. I am now making it public, because I have learned that Linn have recognized the problem and will likely present a fix.
I am also posting it because the magnitude of the problem varies with which phono stage you are using. The first time I listened to a Lingo 4, I was using a Slipsik 7. The ground problem in Lingo 4 then results in a faint hum in the speakers which you may not notice unless you really listen for it. It also gives a loss of musicality, which caused me to be underwhelmed with the performance. Now that I've tested Lingo 4 with an Entity MC stage, the hum is more pronounced, so it becomes more likely you will notice that something is wrong. The loss of musicality is still evident, plus an annoying hum in the speakers. When your Lingo 4 is fixed, you will not only get a more musical LP12, but it will also be hum free.
THE ISSUE IN DETAIL:
Normally, your LP12 top plate, crossbrace, inner platter, Trampolin 2 (if you have one) and arm are connected to the ground screw of the phono stage (or the amplifier equipped with a phono stage) through the ground wire in the tone arm cable. That's the thin wire in between the thicker left and right coaxial cables of the tone arm cable. On some arm cables, the wire is separated from left and right cables.
This is the optimal way to do it, as it keeps the metal parts of your LP12 at the same potential as the ground in your phono stage (or amp with internal phono stage). So the music traveling from your cartridge to the phono stage is surrounded by a ground potential, which protects the signals from interference.
In the installation manual of Lingo 4, there is a mention of an optional link called LK1 on the circuit board inside the LP12. What LK1 does is to connect the chassis of the LP12 to the mains ground of the external Lingo 4 power supply (the screen of the cable from the power supply to the Lingo 4 board inside the LP12 carries the ground). This link is normally not used - you only connect it if for some reason, your LP12 isn't grounded through the ground wire of the tone arm cable. There are for instance some arm cables that don't have a ground wire - in that unusual scenario you might notice a hum in your speakers and the solution then is to add a jumper to link LK1 on the Lingo 4 board. Then your ungrounded LP12 becomes grounded to the Lingo 4 external power supply.
The problem is that the XLR connector that Linn are using on the Lingo 4 board (which receives power from the external power supply) has its metal front plate connected to the ground pin of the XLR through an extra metal link on the side of the connector. This metal link is designed to hook into the screw that holds the XLR to the panel. The result is that the optional ground connection that link LK1 provides is by mistake always present. So with a Lingo 4 inside your LP12, your top plate, inner platter, arm, etc are now grounded both to the Lingo 4 external power supply (and there to its mains ground) and the phono stage through the arm ground wire (also to mains ground). This creates a big ground loop, which causes loss of sound quality. In addition it causes either a hum through the loudspeaker (can be faint or strong, depending on the phono stage), some high frequency noise from the Lingo 4 circuit, or both.
The solution is to cut the link of the XLR connector, as shown in the photos below. I recommend that you let your retailer do this and let him know that Linn have accepted it as a fix to the problem. Linn might also choose to solve it by exchanging the metal standoffs that hold the Lingo 4 case inside your LP12 for plastic standoffs, which would isolate the case from the LP12 metal parts. Either solution works.
You need to remove the four screws holding the Lingo 4 unit to the crossbrace and preferably the Lingo 4 board from its metal case (I think it's 4 screws plus the two holding the XLR). Use a sharp pair of cutting pliers, gently cut it off (you might need to clip several times to chew through it) and pull it out. No harm is done to your Lingo 4 or LP12. All you are doing is disconnecting the circuit ground from the metal front plate of the XLR connector (which should not be grounded as it shorts against the metal parts of the LP12).
After I discovered this fault and cut the link on the XLR, my initial disappointment with Lingo 4 vanished. It really is a great motor controller for the LP12!
The XLR connector with its metal front plate. Red arrow points to the ground link that you are about to cut. You can see the tip of the link in the left screw hole of the XLR, bent to the right against the metal front plate.
This is the removed piece. It ends in the screw hole and can be pulled out without any force required. Notice the dents on the left, pointy side - those are from the metal screw digging into it. And that is how the entire metal housing becomes connected, by mistake, to the ground of the Lingo 4 circuit board. Which is the option that link LK1 provides!
This is what it looks like after the cut. The result? Lingo 4 performing as it should. Link LK1 at the bottom right is available if you should ever need this type of grounding.