[TheChairGuy]

The other option is the KAB outboard motor option...which removes the inboard motor from the deck itself and places it outside to eliminate stray fields from the transformer to your cartridge.  Beefs up the power supply for a more stable delivery, too.

However, it still leaves the internal speed regulator operating...which likely give off residual traces of EMI.

The timing of your awesome stainless mat is interesting (for me, and others)....I just bought a 12 x 12" sheet of TI Shield to make a 12" round mat under the Audioquest sorbothane and Herbie's mat.  It was $29.99 from Michael Percy Audio and should provide 100% complete isolation from stray fields under the 1200 platter. So, we're thinking along the same paths at the same time on this one.

I think it probably a very helpful thing for any direct drive deck to have some shield - surely a transformer only 3 or so inches from a delicate cartridge is a bad idea, overall, for playback sonics 



John

[Wayner]

I have found in my experiments that the hum I was mostly dealing with was from the permanent magnets mounted to the platter. I would get the hum with the table turned off and unplugged. Turning on the table added a slight amount and gave the hum a harmonic tone, so I new I was dealing with several sources for the nasty wordless wonder. I'm sure remoting some of the components is a good idea, I was just trying to keep the table as much in its original form as possible. I can pick up a faint hum with the volume control at 3 o'clock with the Van Alstine OmegaStar's mute button out. That is an incredible amount of gain and if I were to drop the stylus onto the record at that volume level, I would have to duck out of the way from speaker parts. The new mat sandwhich has also added some extra weight....at least a pound for the steel. It has had no effect on the torque of the motor and has really silenced any rumble at all. Last night I listened to Roger Waters "The Pros and Cons of Hitch Hiking" and it truly was "dynamic" and awe inspiring. The level of play was increased, so went the dynamics of the music.

Wayner

[lcrim]

John:
A few points need correction- The KAB outboard power supply is just that.  The drive motor stays right where it needs to be, under the platter.  The earlier version of the table which was used for cutting masters also had the motor under the platter and any added distortion from EMI would have been disastrous.  The concept is simply not an engineering error.
If your hypothesis that solder joints are a barrier to low level signals, wouldn't  that hold true also for all the high quality components employing point-to-point wiring? 
I do have the Isoplatmat and the Herbie's mat on mine, as well as the KAB outboard power supply.  I bought the deck with the power supply installed but added the tonearm rewire and the mats later and I have never experienced any hum issues w/ it.  I still maintain that the table  has a deserved reputation for build quality and fine engineering.  Try changing any basic adjustment on it and you wonder why another manufacturers didn't make it as simple and straight forward.
I'm sorry that Wayner had to go to such lengths to eliminate hum but surely his experience is not a common one.

[Wayner]

lcrim,

I'm sure my problem was my cartridge choice. I like the AT and really wasn't in the mood for trying some new types just because of the hum issue. I really wanted to get to the source of the hum and take it out of the equation. I too, believe the SL-1200 to be a fine machine or I would have given up on it the first week I had it. Let's just make a note here that if you plan on putting on a cartridge that may be susceptible to hum, this is what has to be done to use the cart successfully.

On a side note and maybe it's allready been done, maybe a new thread should be started on cartridge make/model success people have had/haven't mounted in the SL-1200/1210.

[lcrim]

Wayner:
I had the 440ML, the previous version on a Rega Planar 3 with an SME Series III tonearm and had some RFI problems with that setup but I can't remember if it was w/ that cart or the Goldring 10xx series that preceeded it.  IIRC the wiring was the culprit. Moved the power cables around until it disappeared. 
If you heard hum with the power off, could it have been coming from a component or wiring below the TT?  That would also have been cured by the shield you installed as well.

[Wayner]

Icrim,

I've moved that table to more places than I can remember. I'm sure it's the AT440MLa. While I am (hopefully) still the pimp, I now realize it is not a universal recommendation. Jazz-vinyl had hum problems with it in his HK. I have a little in my Rega P3 (only slight) and the technics has been the worst offender of all. While IMHO the AT is a stellar performer at its modest price, we are finding out now that care should be taken mating it up with particular tables. My Empire 598 and VPI Hw-19jr have zero hum issues, however, their motors are completely shielded and the grounding scheme is proper.

One thing I am curious about is the fact that the Technics ground strap actually delivers hum into the system, rather than discharging it, telling me that the table has at least 2 ground points. I should take my VOM and see if I get continuity from arm pivot to the RCA shield. If so, there is a multiple grounding scheme with the table...which is bad. All grounds must terminate to a single point and discharged to earth ground, not thru the chassis and interconnects, as I suspect. I will further investigate that issue tonight.

[TheChairGuy]

John:
A few points need correction- The KAB outboard power supply is just that.  The drive motor stays right where it needs to be, under the platter.  The earlier version of the table which was used for cutting masters also had the motor under the platter and any added distortion from EMI would have been disastrous.  The concept is simply not an engineering error.
If your hypothesis that solder joints are a barrier to low level signals, wouldn't  that hold true also for all the high quality components employing point-to-point wiring? 
I do have the Isoplatmat and the Herbie's mat on mine, as well as the KAB outboard power supply.  I bought the deck with the power supply installed but added the tonearm rewire and the mats later and I have never experienced any hum issues w/ it.  I still maintain that the table  has a deserved reputation for build quality and fine engineering.  Try changing any basic adjustment on it and you wonder why another manufacturers didn't make it as simple and straight forward.
I'm sorry that Wayner had to go to such lengths to eliminate hum but surely his experience is not a common one.

Lar -

I'm not getting all you're saying here I think 

The KAB outboard leaves the drive motor and regulator (it has to as it's direct drive) and the transformer is indeed outboarded.  A transformer generally would have large amounts of emitted EMI (unless shielded in the deck and I don't think it is) and the drive motor and regulator would emit smaller amounts.  Anything that is fed AC or DC will...unless shielded.

A shield, be it Wayner's stainless or a TI Shield, could only be potentially helpful for DD playback.  I'll know in a few days when I cut mine and apply to platter.

I didn't write anything about point-to-point wiring nor have I professed any particular preference for it versus PCB's.  In fact, I think a PCB more direct (less pathway) and has less joints and can secured better....so it may be superior method. My vintage, point-to-point wired amps sound great...but I have no idea if they could sound better if they had thick copper PCB traces. It's not a belief that I will ever test head-on/firsthand as I'll never have the same amp/preamp both wired point-to-point and with PCB's to see 

Nonetheless, there is a lot of difference between a low level signal of 5mv or less......and after they've been amplified 40db+.  Joints likely matter less with higher level signals and there is more significant voltage to pass thru barriers.

John

[Wayner]

FYI, I calculated the steel weight in the mat sandwhich and it is 1.995 pounds, which means the new platter weight is at least 4.735 pounds, 28% heavier.

W

[Wayner]

I am home now and have done a VOM check for continuity from chassis ground to RCA outer sleeve and...........................we get tone! That means the Technics is grounded via the interconnects as well as the chassis ground wire.............the now obvious source of a ground loop. Somewhere internally the two points have been connected. This does not happen to the Empire or the VPI which are dead quite. Very interesting! You can't blame the cartridge for everything.

Wayner

[lcrim]

Wayner:
I'll reach out to someone I know, who knows Technics intimately.  I don't know off the top of my head if that is abnormal.  I left my multimeter at work along w/ my circuit tester and I've been home a few days ill.

John:
In an earlier post, you stated that

The other option is the KAB outboard motor option...which removes the inboard motor from the deck itself and places it outside to eliminate stray fields from the transformer to your cartridge.

I think you meant to say power supply not motor.
Point to point wiring in components necessarily has many solder joints, some of those circuits must be low level so I'm not sure that your suggestion the multiple solder joints in the wiring from the cartridge to the phono section is a valid concern.

As you know I got a new cartridge, Benz Micro Ruby 3H,  has .67 mV output, w/ 5751 tubes in Minimax to give more headroom, is proving to be very detailed and uncolored.  No trace of ringing. 
Changed speaker cables from the DIY cables to DNM Reson Precision w/ bananas.  Reasonably priced @ $196 for 8' and also very honest and full range.  Its still early but I thik they are keepers. 

[Wayner]

Please keep me from going insane.

I was listening to Thomas Dolby "Wireless" (great album), and all of a sudden this incredible "hum" started. I fiddled around for awhile, then connected the ground wire (which caused hum before, when connected) and now the Techinics is acting like a normal table.

What the hell is going on? Have I had some wired static charge going on.........................lost for any scientific explanation at all.

 

[Wayner]

Actually, what happened was that I touched the balance control of the preamp and got a rather large static charge off of my hand. I started the record (first song is kind of loud) and when that song fadded out, I heard this god aweful hum. I touched the knob again (another static zap) and the hum went away. But then in the middle of the next song, I heard the hum again. The only way I could cure it was to connect the ground wire up. lcrim thought I had a possible short, even suggesting that I get a new headshell......perhaps he is right after all. I really don't want to tear this thing apart. Maybe it's time for a KAB phone call.

Wayner 

[TheChairGuy]

wow - that's a weird one.  I guess try a headshell first.

If you don't have extra, they're cheap.....www.turntablebasics.com is in your neck o' the woods.

Ciao, John

[Wayner]

I believe I have the answer to last nights static problem. I think my new sandwhich mat is actually a disc capacitor now. I have been using my ZeroStat more often, perhaps making the mistake of zapping the records on the platter. This energized the steel center of the mat with gobbs of static and when it reach some higher level, it started to discharge probably thru the spindle and what I was hearing was a steady but slow static discharge.

I will now ZeroStat the records off of the platter.

Wayner