Phono Hum
Apr 30, 2002 at 6:39 PM Thread Starter Post #1 of 34

Matt

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Oh sheesh...

OK, I have a Dual CS 5000 (specs: http://www.compassnet.com/concept/tables/5000.htm ) that I am hooking up to my JMT Altoid via a "Li'l Rat" RadioShack phono preamp.

There is a big ol' hum whenever I turn the JMT on. The hum is there whether the turntable is on or off, but when it's on, the pitch changes somewhat.

I am a relative newbie with turntables.

The cartridge on it is an older Grado F3Z or something like that (a universal mount one). I have the table grounded via it's ground wire to a metal filing cabinet. I figured this would be better than the back of an integrated amp (one of which I haven't).

Can anyone help?

Best,
Matt
 
Apr 30, 2002 at 6:46 PM Post #2 of 34

RickG

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Matt, I'm glad you received the Lil Rat, but maybe someone else has the answer to the hum problem. I had no hum with the preamp in my system.
confused.gif


Hope you can remedy the problem. If not, PM me.
(I'm assuming you installed a 9 volt battery)

smily_headphones1.gif
 
Apr 30, 2002 at 6:50 PM Post #3 of 34

Hirsch

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I didn't even have to read your post to know that you had a Grado cartridge. The title said it all.

Grados hum in certain turntables, and I'm not sure there's a cure. Try making sure that the table is as far from other components as you can, and making sure that the cartridge has no electrical contact (metal to metal) with the tonearm except the wiring. Nylon screws to hold the cartridge instead of metal might help.

Best bet would be to try an inexpensive alternative cartridge, such as a Shure or Audio Technica. Hum has been an issue with Grado's for years.
 
Apr 30, 2002 at 6:52 PM Post #4 of 34

Hirsch

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Hang on...I just remembered something. Try grounding the table to the metal lid of the Little Rat, rather than an external ground. Not optimal, but I had that work for me once (I've got a Grado Red).
 
Apr 30, 2002 at 7:19 PM Post #5 of 34

Matt

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...mother****ing problems with this table is this:

the cartridge holder screws off (nylon screw on the tonearm), so you can work on installing the cartridge, I guess. The cartridge does not fit "snugly" in the holder.

It looks like this

This is the plastic holder that screws off and that the cart. mounts into
----------------------
------------------- |
| | | |
| |< a screw ----
-----------------------
|
| This is the front of the cartridge
|
|
-----------------------
--
-- This is the stylus
--

As you can see, the cartridge is too long in the front to fit underneath that little lip. the space between the cart and the plastic holder is not so bad as shown above, but the fact remains that the front edge of the cart is not snapped back behind that lip.

I don't know if this means anything at all.

ALSO: I seem to recall having this problem before and it being solved by fiddling with the connections from the wires that exit the cartridge that go to the part where the four posts on the tip of the tonearm mount the cartridge holder. I seem to recall it completely clearing up after I did *something,* I just can't seem to recall what that something was.

Any ideas?

Best,
Matt
 
Apr 30, 2002 at 7:20 PM Post #6 of 34

Matt

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...mother****ing problems with this table is this:

the cartridge holder screws off (nylon screw on the tonearm), so you can work on installing the cartridge, I guess. The cartridge does not fit "snugly" in the holder.

It looks like this

This is the plastic holder that screws off and that the cart. mounts into
[pre]
----------------------
------------------- |
| | | |
| |< a screw ----
-----------------------
|
| This is the front of the cartridge
|
|
-----------------------
--
-- This is the stylus
--
[/pre]

(EDIT: cripes! Can't a fella use preformatted text?)

As you can see, the cartridge is too long in the front to fit underneath that little lip. the space between the cart and the plastic holder is not so bad as shown above, but the fact remains that the front edge of the cart is not snapped back behind that lip.

I don't know if this means anything at all.

ALSO: I seem to recall having this problem before and it being solved by fiddling with the connections from the wires that exit the cartridge that go to the part where the four posts on the tip of the tonearm mount the cartridge holder. I seem to recall it completely clearing up after I did *something,* I just can't seem to recall what that something was.

Any ideas?

Best,
Matt
 
Apr 30, 2002 at 7:46 PM Post #7 of 34

zowie

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I now recall having had some trouble mounting a mid-90s Grado on a Dual 1229.

I don't remember exactly what I did, but it had to using different mounting screws or shims or something like that (I've a little box of this stuff from my various carts and headshells over the years )so it'd be out of the way of the mounting.

Hum-wise: (a) play around with the ground wire; (b) as mentioned above, it might be a Grado problem (although I've never had any) - try putting a metal shield on the plinth to see if that helps; (c) could be a short in your tonearm wiring or interconnect; the former tends to be very thin and brittle, subject to movement, and unduly cheap, so could be shot.

There are other possibilities, but I'd start with these.
 
Apr 30, 2002 at 7:59 PM Post #8 of 34

JML

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I can't visualize the cartridge mounting problems, but some cartridges just won't mount properly in older tables.

There are two grounds paths you have to deal with to address RFI. One is the cartridge ground -- that ought to be a separate wire with the two signal cables. You may have to ground the chassis separately -- I can't remember what that old Dual did. Either way, the ground must to go to a true ground, not just any old metal chunk lying around your apartment or house. You need to connect it to an real AC ground path --- try the center screw of an outlet.

But Grados have always been very, very prone to generating hum, esp. in those old tables with the motor in close proximity. That's EMI -- and grounding the cartridge or chassis isn't going to do a damn thing. The magnetic field of the cartridge generator is not getting along with the field of the motor in the turntable. If you move the tonearm, I betcha the tone changes in level. To solve that problem, get a new cartridge...
 
Apr 30, 2002 at 9:17 PM Post #10 of 34

Matt

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OK, I grounded the phono ground to the center screw of an outlet. Suddenly, magic happened: I am now listening to AM radio.
smily_headphones1.gif


Awright, this is awful interesting, but not exactly the intended effect. I guess we must have ****ty wiring around here...

OK, now I've attached it to li'l rat. No more AM (boo-hoo), but hum still there.

Now for the weird part: I just touched the phono ground to the "negative" part of an RCA female plug on the back of my DVD-A player and if the original hum volume a second ago was 10, it has drastically reduced down to 1.

I have no idea what these results mean and the touching it to that negative side of the RCA plug didn't completely kill the hum, but it got it a hell of a lot lower.

Hmmmm...any more thoughts, fellas?

- Matt
 
Apr 30, 2002 at 9:43 PM Post #11 of 34

Hirsch

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My memory is coming back in bits and pieces...I owned a Dual about 20 years ago. Sometimes there is a bad connection between the detachable headshell and tone arm. I'd treat those connections with Caig Pro Gold, if available. look closely to see if you can tell where the contact is bad. If all else fails, jiggle the headshell in place, and see if the hum stops.

The front of the cartridge may stick out from under the headshell. If the stylus is in the proper location, this isn't a problem. If there's a plastic lip on the headshell, so that your cartridge is angled in the headshell, plastic washers between the headshell and cartridge at the screw can level things off.
 
Apr 30, 2002 at 9:51 PM Post #12 of 34

Matt

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...sound comes through the stylus when I play the record, so does that still mean a connection or contact is bad?

I removed the headshell from the tonearm by unscrewing it and the hum increased dramatically. Putting it back on sent it back down much lower. Hmmmm...

Are there any useful details I've left out?

- Matt
 
Apr 30, 2002 at 10:14 PM Post #13 of 34

Hirsch

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If sound comes through the stylus, try reversing your directional interconnects, because it's supposed to come through the speakers...
very_evil_smiley.gif
(j/k)

On a more serious note, that may be a bad contact between the headshell and the arm. This is a problem that occurs with Duals. Are both channels coming through, or just one? If the problem is there, you may lose a channel completely. IIRC, the pins on the headshell make contact with springs on the tone arm. It might be possible to GENTLY try and bend the springs to make a better contact. It might also be possible to damage your table doing this. It's even more possible that I'm remembering the configuration of the Dual arm incorrectly, and I know that you have a different setup than the one I had.

Another weak spot of the Duals...the attached phono cord has very poor strain relief at the RCA plug. I've seen at least two different Duals where an RCA plug had to be replaced, in order to make a good connection. Ignore this if your table doesn't have the interconnect built in.

I'm not sure how much more I can do without actually seeing the table. Is there a good audio repair place near you? That might be the best bet.
 
Apr 30, 2002 at 10:47 PM Post #14 of 34

JML

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I just did a brief Google search on "grado hum dual" and found enough hits and more than enough information to confirm my memory that Grado cartridges are absolutely notorious for hum problems. They've had that reputation for decades -- and I'm pretty sure that Dual tables were often not recommended as good items to match with Grado cartridges (I had the top-line Dual in 1976 as my first table, and replaced it with my Linn four years later). It's not the fault of the Dual -- it's the design of the Grado.

From what you're describing, I think you have no alternative other than replacing the cartridge and using another brand that's designed differently. My suggestion is to contact NeedleDoctor.com and ask them for a recommendation. I'm sure they'll also confirm the Grado as the likely cause of the problem.

When you connected the lead to the house wiring, you probably confirmed that your house wiring is probably not grounded properly. That's a whole 'nother problem.

Disconnecting the headshell will cause a huge increase in hum -- that's normal. I don't think you have a ground problem or a connection problem, but I'm not sitting in front of your setup.

EDIT:

Time for some research! I took a stab with a quick search on "Dual cs 5000" and found a good deal of information about your unit. Many were shipped with Ortofon cartridges, some with special headshells -- and you may have one! -- and the site with the link in your message (!) shows the table with the Ortofon X3-MC, which is a high-output moving coil that I happen to own. That's been a great-sounding unit for about 15 years, and it is still made -- I recently did a retip exchange on mine!
 
May 1, 2002 at 12:25 AM Post #15 of 34

dvw

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" Now for the weird part: I just touched the phono ground to the "negative" part of an RCA female plug on the back of my DVD-A player and if the original hum volume a second ago was 10, it has drastically reduced down to 1."

That's interesting. Is the DVD-A player also connected to the amplifier? I think you could have a ground loop problem.

Try experimenting with different grounding. Try ground it to the amp or the DVD-A player.
 

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