[scottm_dj]

As mentioned in my intro, I have dabbled with TWO of the vintage and exceptional Technics linear tracking turntables--SL7 with a Ortofon cart and the coveted SL10 with the original 310MC cart--complete with a Hagerman Flugelhorn phono amp.  Those combos should sound great but unfortunately with vinyl I have had some nearly "throw in the towel" frustrations...I have an unbearable level of hum and noise with either i just can't get rid of.   

The main one I'm trying to use is the SL10 and I do not have the original grounding/RCA adapter and Technics in all their wisdom, placed the grounding hole too close to the audio outs.   I picked up one of those ebay "replacements" and think it's grounded well enough...but i have tons of noise through my Flugelhorn.   I know the table itself introduces some of that and I've tried different outlets and power configurations but nothing seems to fix.  Of course the .2mv MC cart probably doesn't help...and the built-in preamp is not clean enough...so i picked up a custom Beyer SUT.   That improves things somewhat with it's added gain but I can tell through the noise that it still sounds best directly through the Hagerman and highest gain--but that hum is a killer.   I've tried several preamps and all give the hum to some degree---about to try one last time with a fully-returnable Pro-ject Phono Box DS+, before i call it quits--or try that "leviating" or "love turntable" high-tech options.  Anyone have any ideas of what i could try to fix this?
Could this really be considered a "turntable" in the truest sense of the word since it's effectively digital?
http://www.loveturntable.com/

[stonedeaf]

Owned a couple of SL-7's and several of the models below that in the linear tracking Technics line - none hummed.
1.) Are you sure that you are getting a good ground connection from your aftermarket ground connector ? IIRR - these had a goofy miniature banana plug connection on the turntable end of things - does  your replacement fit reasonably tightly ?
2.) What are you using for a interconnect ? Are the plugs on the interconnects oversized in terms of diameter to fit into the RCA females on the SL7/SL10 ? IOW -do they touch each other or the ground connector when plugged in ? Are they reasonably tight ? Have you tried RCA plugs that may have damaged the RCA females on the turntables ?

[timind]

Suggest you try a turntable that you know has a known functioning ground. If that tt works fine then you know the problem is with the Technics. Or, you could swap your tt into a functioning system. The goal is to determine whether the problem is your turntable or system. Sounds like tt to me though.

[Letitroll98]

Likely a loose connection somewhere.  Check RCAs and tonearm leads.

[stonedeaf]

Let's back up a couple of steps - exactly what happens if you feed the output of the built in MC headamp into a MM phono stage ( never into a MC input) ? Don't care about quality other than humm ?Can you get or make up shorting plugs -RCA males that are either soldered together between pin and shield ? or if you want to get fancy - have some one solder anything from a 5 to 30 ohm resistor across between the pin and shield (very roughly simulates a  MC cartridge) . Plug this into the INPUT (NEVER EVER THE OUTPUT OF ANYTHING) - turn off or turn down before plugging or unplugging -into the input of your phono pre-amp . Is it dead quiet -no noise or ? Are you using conventional co-ax cable interconnects between phono pre-amp and turntable or something of more exotic construction ?

[RPM123]

That's so frustrating. Here is a link below for steps you can take to isolate and reduce the source of the hum.

http://theobjectiveturntable.com/documents/turntablehumreduction.pdf

You may also want to consider on of these: https://www.sweetwater.com/store/detail/HumX, and/or this: https://www.sweetwater.com/store/detail/Hum

Good luck!

[scottm_dj]

Hey guys...thanks for the input.  I plan to do more troubleshooting this weekend.  In answer to stonedeaf...yep...although i got great sounding slimline cables (from cable solutions BTW), i'm having to shed the molding from the RCA plugs to fit them (see pic)...and yes, timind, i am planning to take the entire vinyl rig as configured to a friend's house and set it in his system.  I have tried moving the 310MC to the SL7 (built-in RCAs and i still get a degree of hum)--and yes i do have some shorting plugs somewhere as well.  Remember this is linear tracking so it's the infamous P-Mount cart, with very little tinkering available.  I'm pretty sure amplifying that .2mv cart plays a part, but the sound is worth investigating.  I'm in FL and it's been hurricane watch more than anything of late, but I will re-address this very soon as I've heard what the table can do under the hum.

[scottm_dj]

More pics (similar grounding wire, awesome Hagerman preamp that i know doesn't hum on it's own, original combo wire i can't find anywhere, another shot of the tight cable fit)

BTW:  These are the RCA cables--I have .9 meter runs for all my analog connections (analog CJ MET1 preamp) & they sound fantastic. 
https://www.cs1.net/products/canare/LV-61S_precision_SACD.htm

[stonedeaf]

ya know - ya learn somthin new everyday. I lost out on bids for SL-10's several times - don't think I ever paid any attention to the unique ground plus R+L Signal connection on these turntables. BTW - damaged female RCA jacks on vintage equipment are a fairly common failure - in at least a few cases -I know that what caused this was someone forcing either a large diameter grip male RCA or one of the impressively stiff uber expensive cables into a female connector never designed for this kind of strain.Point of this is -if you find a fault with a vintage piece -see if you can borrow a DVOM ( or buy even a really cheap one) and see if you can find a mechanical fault with the input jacks. Double check that after pulling the insulators off the RCA's they are still making a connection on all four points? Are you listening for noise at a volume setting that is as loud as you would ever listen to a record on your system or at "full crank" ? Equal noise on both channels ?

[scottm_dj]

Thanks for all the input.  I'm going to do some testing this week as this legendary SL10 is in beautiful shape, complete with gleaming original 310MC (also in pic is the custom Beyer-based SUT I tried to minimize external electrical gain--and one of the shorting plugs i found).  The second record is the incredible-sounding Sheffield Labs Pressure Cooker 1975 release (RIP Doug Sax).  i think you all would agree this table is worth fighting the hum issue!