[dlherman]

OK, so this isn't exactly an AVA topic (I do own an Ultra SL with phono and love it)
but maybe some here can help.

First off, I installed the Longhorn mod on my Grado Gold which in turn went on
a Dual 505-2. It sang. I wouldn't have believed such performance was possible
with such a modest turntable.

A short while ago a mint AR EB-101 turned up on Craigslist for a great price so I grabbed it
and mounted the Longhorned Grado. It sang even more than when using the Dual - much more. But at higher
levels there's this awful hum! I'd heard about the Grado hum problem, and just read that it's especially pronounced
on certain tables including the ARs.

I did some searching for a solution but found nothing concrete. Some say to use mu-metal
for shielding, others say to make a platter cover out of copper, stainless steel etc.

Those solutions seem involved or expensive. Does anyone have a cheaper and more practical approach?


Thanks,

Doug

[Tom Alverson]

Does the hum get louder as the tonearm is moved nearer to the motor?  If so, then mu-metal shielding around the motor may be your only fix. 

[TheChairGuy]

http://www.avahifi.com/root/equipment/other_equipment/cartridge.htm

We then internally damp the coils to eliminate microphonics, damp the suspension to eliminate mechanical resonances

It is not recommended for turntables with unshielded AC motors that generate excess hum

It's EM and mechanical affecting the Grado...mu metal (or, possibly better, TI Shield) will only take care part of the issue with AR's.

John

[Wayner]

I speak from experience when I say that trying to tame a magnetic field is a b*tch. You can't "absorb" it, only deflect it. It's that old energy cannot be created or destroyed thing. If it's a magnetic field from the motor, copper won't work as it has no iron in it; that is where mu-metal comes in. You would have to encase the motor completely.

If the motor is broadcasting RF, then copper would work (needs to be grounded). It may actually be doing both! I think you are going to beat your head against the wall on this one.

Wayner 

[Brett Buck]

I speak from experience when I say that trying to tame a magnetic field is a b*tch. You can't "absorb" it, only deflect it. It's that old energy cannot be created or destroyed thing. If it's a magnetic field from the motor, copper won't work as it has no iron in it; that is where mu-metal comes in. You would have to encase the motor completely.

If the motor is broadcasting RF, then copper would work (needs to be grounded). It may actually be doing both! I think you are going to beat your head against the wall on this one.

    I'm not so sure it's the motor - it may be the power supply transformer. That was Frank/Aado's fix for the HK T-25 - remove the power supply from the turntable and put it in an external box. If I recall correctly (and it's been 25 years or so) that particular AR has nothing much but wood between the guts and the platter and was pretty well known for this problem, Grado or otherwise. Try an MC cartridge on that turntable, it will make the Grado seem quiet. It might be worth looking into to see if it was practical to remove the power supply and make it remote.

      Brett

[turkey]

    I'm not so sure it's the motor - it may be the power supply transformer. That was Frank/Aado's fix for the HK T-25 - remove the power supply from the turntable and put it in an external box. If I recall correctly (and it's been 25 years or so) that particular AR has nothing much but wood between the guts and the platter and was pretty well known for this problem, Grado or otherwise. Try an MC cartridge on that turntable, it will make the Grado seem quiet. It might be worth looking into to see if it was practical to remove the power supply and make it remote.

A DC motor in a turntable is actually a "deluxe" item. It requires a power supply, which an AC motor does not.

Most turntables have used a simple AC motor. The utilities are quite good about maintaining a constant 60 Hz (in the US), so the speed regulation of the 'table overall is as good as a much more expensive DC motor and power supply.

Some of the large Japanese companies may have gone to a DC motor because it's cheaper when you have to support both 50 and 60 Hz markets. (Or else it was due to the Japanese practice of needing some new feature every year for the marketing dept. "New! Class AB/XYZ amplifier with Feedforwardsideways DC servo!")

However, I'd bet that the old AR 'tables used an AC motor. They were all about lowest cost that will do the job. They probably also didn't really worry about anything but the US or NA market at that time.

[Wayner]

If the motor in this AR is the same in the AR-XA, it's a 300RPM Hurst synchronous motor. It's 120 volts AC with a starter capacitor.

Wayner

[oneinthepipe]

If the motor in this AR is the same in the AR-XA, it's a 300RPM Hurst synchronous motor. It's 120 volts AC with a starter capacitor.

Wayner

A little off-topic, but if anyone ever needs a replacement motor, the Hurst motor was available, at least when I replaced mine a few months ago, from Allied Electronics for about 60.00.

[avahifi]

As I recall, the original AR motor assembly was mu-metal shielded and had a non-magnetic shaft and  pulley so the assembly stayed quiet even with a Grado cartridge.

Later versions might vary.

Grado claimed. I am told, that shielding will distort the necessary magnetic fields that make the cartridge work well, thus they hum with most AC motor turntables.

I moved the AC to DC circuits on the HK 25-30-45-60 series turntables to a separate box, with a big filter cap on the 12V DC supply - connecting to the turntable with coax cable and have had excellent low noise performance for years with these.

Another alternative is a turntable with a "wall wart" AC to DC converter.  No AC fields running around inside the turntable seem to be a good thing.

Regards,

Frank Van Alstine

[Wayner]

That's about right Frank. I have one older AR with the smaller "clock motor" that is very quite and perhaps it is shielded with Mu-metal. The later (and noisier models) came with a more powerful, but noisier Hurst motor. However, the only available Hurst motor is not the one used in the later AR tables. The only one available now is a PA 3201-001 120v, 60c 300 RPM motor with .68 mfd cap. Beware of shaft size!

If anyone can find a DC version of this motor, spill your beans as it would be nice for some of these folks looking for a replacement motor.

Wayner

[Wayner]

I may have found the other AR motor. It has the specs for it.

Hurst model A 3009-001 120 volt, 60c 300 rpm with .25mfd starting cap. This is the 2 ear mounting flange version (more like the AR version). The motor from the earlier post is used by VPI. Shaft size may not be the same for the pulley.

Wayner

[Wayner]

The origianl motor was by A.W. Haydon motor company from Waterbury Conn. It was a 1.5 watt with a .01 mfd starting capacitor.

Wayner

[oneinthepipe]

I believe that I installed a Hurst 3001-001 as a replacement motor, which Dave Archambault @ Vinyl Nirvana told me to use.  Shaft size was perfect.  The 3001-001 has a little less torque that the 3009-001, according to Hurst's spec sheet, but seems to operate without any problem.    I suppose higher torque is better, but I didn't know about the 3009-001.  (I should have asked Wayner.)   

A while back, there was a discussion, on Vinyl Engine, IIRC, about special ordering a DC motor.

[G E]

I have the HK 720 turntable, predecessor of HK30 and when I installed the Grado Longhorn years ago I had the hum problem big time.  It was worse as the tonearm tracked toward the label and also had a "wah-wah" effect caused by two large platter cut outs.  You can imagine how that was to listen to.  I saw Frank's "Audio Basics" article about moving the transformer and associated electronics and tried it.  Problem fixed and I still enjoy humless sound today, although the Longhorn is long retired.  Still use a Grado cartridge, one of the cheapies.  Amazing how good a $50 cartridge on a 28 year old $150 turntable can sound.

[Tom Alverson]

I used to use the original AR table with  a Grado and only noticed a very slight hum.  If I would move the tonearm way over near the motor it would get louder.  Perhaps the  newer AR tables have motors that put  out more magnetic fields.  Make sure the hum goes away when you  unplug the motor, just to verify that you are not picking  up hum from somewhere  else.

Tom

[Wayner]

If I knew how to get  rid of motor hum, I'd be a millionaire. We have the same problem at work. Big three phase motors make big electrical fields that bother analog signals (making noise). Some signals are very low, feeding an input of an analog PLC and we are always re-routing wires, grounding things and always using shielded wire.

My new table project is featuring a Hurst motor in a stand alone motor assembly to distance the motor from the table in an effort to minimize the motor's magnetic field. Luck has it that I have a machine shop in town friendly to walk-ins and they have altered some things for me to make it possible.

Wayner

[turkey]

If I knew how to get  rid of motor hum, I'd be a millionaire.

Teach them the words?