I really like my Technics SL-Q350 turntable other than the higher 60 Hz noise in the right channel. The left channel is great. I want to use it for ripping to digital with the pspacialaudio Stereo Lab software and I'm trying to get an 80 dB SNR in both channels. It uses T4P cartridges that I like, so I am wondering if it is possible to rewire the tone arm at all. The right channel has about 15 dB more hum than the left. I did my best to manage the wires that are easily accessible in the underside of the chassis, twisting the wires for each channel together tightly and keeping them away from other wires had no effect. So the only wire left is in the tone arm and the few inches that go through the gimble. Apparently the wires are far enough apart to create a loop area on just the right channel. The resistance of both channels to the cartridge is the same, around 0.5 ohms. Disassembly looks like hours of work and lots of parts, so I thought I would ask if it's possible to swap wires into that tone arm and T4P head shell?
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Oh, hey, thanks for doing the work as moderator! Yes. When I swap connections at the turntable, the hum is always in the channel connected to the left turntable output. I've actually gone so far as to build my own cables, very short, and now have a very low noise balance input preamp setup. Either channel of the preamp connected to the left turntable output works perfectly. What ever channel is connected to the R turntable output has 15 dB higher 60 Hz noise. So in my mind that leaves the turntable wiring as the culprit. As my setup is now balanced input, twisting is important as it makes the coupled noise common mode, which the preamp rejects. With my current setup, single conductor coax cable would be the worst thing to use.
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I've tried three cartridges. With a cartridge installed I measure around 460 ohms for one side and something like 465 ohms for the other side at the back panel RCA jacks on the turntable. I failed to write down those measurements. So the connections seem to be good. I don't have anything small enough around the house to clean the inside of the T4P pin sockets. I get about the same level of 60 Hz "reception" as I get from the R channel of the turntable when I attached a 5" diameter loop of wire to the preamp input.
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Another test is to take the cartridge out and connect it with four small wires and alligator clips to the preamp.
If the hum is gone, it's the arm wires. Its' a process of eliminating."
Good idea. I will try to attach a cartridge directly to the preamp. It will be a few hours before I can get that done.
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Another test is to take the cartridge out and connect it with four small wires and alligator clips to the preamp.
If the hum is gone, it's the arm wires. Its' a process of eliminating."
Good idea. I will try to attach a cartridge directly to the preamp. It will be a few hours before I can get that done.
Tony, it's a T4P.
Hugo
Oh... one of those.
Time for a new tonearm and cartridge then. ;-)
Going to the all the trouble, and use one of them.
Oh well, never mind then.
Ok, so I just grabbed two clip leads. It actually worked great. I wired the cartridge directly to the preamp as in the picture. The cartridge is sitting on the MOTU M4 USB interface. The photo with a single trace is from that configuration. No 60 Hz above the preamp noise floor. More than 12" of open twisted pair wire between the cartridge and preamp. The last photo shows the noise when the preamp is connected to the turntable. Left channel looks amazing. Right channel has 60 Hz noise and harmonics. This was a peak hold for about 20 seconds on the spectrum.
Time to head out to the Pacific NW Audio Society meeting
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Well, I just bought three cartridges. Ha. Eliptical, Shibata and MicroLine. I'm doing a study of the performance change with different stylus radii. The P4T is idea for this as it is aligned when you plug it in. No screwing around with imprecise mounting holes, screws, nuts, and loose wires.
You can get adapters to install P4T into standard mounts... then you could get a tonearm with a removable headshell.
Heck, I thought the standard Technics tonearms all have removable headshells.
Bingo.
BTW, so you bought three different cartridges... with different stylii... but is the cartridge different too? I fail to see how accurate your performance comparison can be. If you could get one cartridge that could support three removable stylii, yes, the comparison would be limited to the stylus.
Then, you got to deal with the record wear. It will likely affect one type of cartridge more than the others due to riding at different parts of the groove.
Hmm... has anyone thought about changing the preamp equalization given a type of stylus?
Anyhow, so your tonearm has issues.
Heck, I thought the standard Technics tonearms all have removable headshells.
Bingo.
BTW, so you bought three different cartridges... with different stylii... but is the cartridge different too? I fail to see how accurate your performance comparison can be. If you could get one cartridge that could support three removable stylii, yes, the comparison would be limited to the stylus.
Then, you got to deal with the record wear. It will likely affect one type of cartridge more than the others due to riding at different parts of the groove.
Hmm... has anyone thought about changing the preamp equalization given a type of stylus?
Anyhow, so your tonearm has issues.
If I can't work out how to fix this tone arm wiring without breaking something there may be an adaptor in my future.
The cartridges ,LP Gear branded, all seem to be rebranded Audio Technica. The plastic stylus shell? appears to be the
same on all of them, so it looks like I could interchange them on one cartridge body. Here's an example.
https://www.lpgear.com/product/LPGATSER05S.html
The cartridges ,LP Gear branded, all seem to be rebranded Audio Technica. The plastic stylus shell? appears to be the
same on all of them, so it looks like I could interchange them on one cartridge body. Here's an example.
https://www.lpgear.com/product/LPGATSER05S.html
Yeah, I did that to start with yesterday. The setup is the same gain of 100 (40dB) balanced input preamp connected to the channel 3 balanced line level input of the MOTU M4 USB interface. So 0 dB is about 80 mV on these graphs. I didn't use the cartridge, so it really shows how sensitive even a shorted open loop of wire can be. Pretty much an electronics lab test of antenna theory applied to EMI susceptibility. With the cartridge in the loop, it would require a smaller open area between the untwisted wires to get the same sensitivity to the noise. I didn't even do a very good job of twisting the wires here, so the 60 Hz is low, but not as low as the turntable L channel. The first two pictures show the twisted wire and the measured spectrum with a small peak at 60 Hz. I then I opened up a loop area until I reached the same level of 60 Hz noise as I was getting with the R channel of the tone arm. The second two pictures show the open loop wire configuration and the measured spectrum. Both measurements are the accumulated peak values over about 20 seconds. Not perfectly representative of the turn table wiring as they don't have the 400 ohm up to 47k Ohm range of impedance of the cartridge and likely different capacitive coupling of each wire to the chassis contributing to the noise. So I expect if I can get the tone arm wires out, twist them, and reinstall, the line noise susceptibility problem in the Right channel will be solved. It may be a few week before I can get to trying that. It would be great if I can do it with a minimum of disassembly. I need to find a very short screw driver to reach those screws on the underside of the tone arm without removing it from the table. Maybe I can just pull the wires out with out totally disassembling the guts of the turntable.
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