Grace 707 hum (what am I missing?)

snap, crackle and pop
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Percivilla
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Grace 707 hum (what am I missing?)

Post by Percivilla » 08 Jan 2020 03:32

I feel like I'm missing something obvious here but maybe not...

Newly acquired Kenwood KD500 with a Grace 707. It sounds like a million bucks but It's got a fairly good hum going that I can't seem to wrap my head around. It's not from the table as it hums even when off. I'm using a known to be good Shure M75.

The ground wire is good as the hum gets much louder when I disconnect it from my pre amp. Here's the weird part: the hum gets louder when I touch the arm but if I kind of run my fingers up and down the arm a bit, it crackles and then the hum disappears. Then, as soon as I pick up the arm to move it to the record the hum starts back up. The hum also... Changes?... When I fiddle with the headshell wires but doesn't get any better or worse. All of connections on the little solder board in the headshell are intact.

Could it be the ground wire shorting out inside the arm?

Any insights would be very much appreciated!

Alec124c41
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Re: Grace 707 hum (what am I missing?)

Post by Alec124c41 » 08 Jan 2020 04:49

First, check that all connections are tight.
The clips on the cartridge pins should be clean and tight. Cartridge pins are not all the same size, and sometimes you have to pinch them carefully, to make them tight.
When handling these, do not pull on the wires. Use small needle-nose pliers to grasp the solder tags on the end of the clips.
The RCA plugs can also be loose. They should require a bit of effort to put them on the connectors. If they are not tight, pinch the skirts to make them so.
The 707 has an integrated headshell, so there is no connection there.
The cable plugs into the bottom of the tone-arm. Make sure it is firmly set.
You can check the integrity of the wiring using a digital (or analog) multimeter.

Cheers,
Alec
Last edited by Alec124c41 on 08 Jan 2020 04:52, edited 1 time in total.

sturgus
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Re: Grace 707 hum (what am I missing?)

Post by sturgus » 08 Jan 2020 04:52

Try running a second wire from the base of the arm to ground. I had to do this on my Audiomods arm. The builder provided a second ground wire just for this case.

Percivilla
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Re: Grace 707 hum (what am I missing?)

Post by Percivilla » 08 Jan 2020 21:05

Thanks gents, I did try disconnecting and reconnecting the headshell leads to no change. The RCA ends are clean and twisting/wiggling them made no difference. I'll check the din connection underneath tonight, didn't think of that one.

The audio signal is completely clean, no crackling, it seems to just be a grounding issue. By touching the arm I must be temporarily discharging the static? It'll crackle and then be perfectly quiet, then as soon as I move the arm the hum is back.

nat
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Re: Grace 707 hum (what am I missing?)

Post by nat » 08 Jan 2020 21:27

Is the grounding strap on the Shure missing?

Percivilla
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Re: Grace 707 hum (what am I missing?)

Post by Percivilla » 09 Jan 2020 01:30

nat wrote:
08 Jan 2020 21:27
Is the grounding strap on the Shure missing?
Nope, the cart is a known quantity, sounds great on other tables.

Percivilla
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Re: Grace 707 hum (what am I missing?)

Post by Percivilla » 09 Jan 2020 03:27

Ok, looked at everything again. Din pins are all clean and seated. Re-did all the headshell leads, they're clean and tight. No change.

I figured I'd try the second ground wire, but the trouble is that the whole arm is powder coated black. Thing is though, when I touch the secondary ground to the small bare metal area near the gimbal, the hum almost disappears. Not fully but almost. I'm beginning to suspect that there's something up with the internal din connection.

It's strange that the RCA ground is functioning, just not enough.

I should add that the arm acts almost like a stylus, it's microphonic in that moving it around and tapping it can be heard through the speakers.

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Re: Grace 707 hum (what am I missing?)

Post by PederP » 10 Jan 2020 23:46

I am not sure about the KD500, but on my KD600 (w/Grace 707) there is also a separate grounding wire from the back of the turntable grounding the chassis and the motor. I have never had any problems with hum on this record player.

Peder

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Re: Grace 707 hum (what am I missing?)

Post by Percivilla » 14 Jan 2020 19:44

Tried the secondary chassis ground. It helped for sure, but the hum remains. It's something in the arm I guess.

Interesting side note: Comparing my KD 550 with the Kenwood arm to the KD 500 with the Grace, I'd actually give the edge to the Kenwood arm. Bit more transparency, separation and punch. Both have Shure M75's mounted tracking at 1.5g with the arms level. I'm swapping the stylus back and forth to keep it fair.

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Re: Grace 707 hum (what am I missing?)

Post by Kingshead » 14 Jan 2020 21:44

My Grace G707 exhibits no hum on the KD500, just for shits and giggles have you tried a different cartridge?

As for preferring the OEM arm? That surprises me, the Grace is really special, especially with a Grace cartridge installed. The synergy of having a cartridge on the arm it was designed for can not be denied.
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Percivilla
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Re: Grace 707 hum (what am I missing?)

Post by Percivilla » 15 Jan 2020 00:59

Kingshead wrote:
14 Jan 2020 21:44
My Grace G707 exhibits no hum on the KD500, just for shits and giggles have you tried a different cartridge?

As for preferring the OEM arm? That surprises me, the Grace is really special, especially with a Grace cartridge installed. The synergy of having a cartridge on the arm it was designed for can not be denied.
I was thinking I should probably try that next just to rule it out. I've had that cartridge on a couple different tables without issue, but who knows...

Surprised me too, I fully expected it to be better. Now that's only with the one cartridge mind you. When going back and forth, the Grace gets a bit more... Muddled in the upper mids and bass is a bit softer and less defined. It's a small difference, but it's there. There are so many other variables though, and the wiring clearly has something up so who knows. It still sounds fantastic, the KD 550 is just really, really good. It beat out my Mint, in a box since it was a month old, Thorens TD 147 Jubilee.

Speaking of variability, I have accumulated a bunch of old Shure Carts, mostly variations of the M75. I've compared quite a few of them back to back with the same stylus, also being sure to keep tracking force consistent, and you know what? They all sound different. Similar, but not identical.

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