SL-65B - Irritating hum

the jewel in the crown
amagasakii
member
member
Canada
Posts: 76
Joined: 18 Jun 2017 04:14
Location: BC

SL-65B - Irritating hum

Post by amagasakii » 18 Oct 2019 02:24

Hi everyone,

I've been trying to troubleshoot a hum issue with my SL-65B/AT91 and I'm not sure I'm going about it the right way. Here's the symptoms:
  • 60 Hz; sounds exactly like the hum of unplugged RCA cables
  • Occurs even if the turntable is unplugged
  • Quieted by connecting the factory green ground wire from the the turntable to the ground lug on the amplifier
  • Gets very slightly quieter when touching the tonearm or frame of the RCA output under the chassis
I was following a troubleshooting guide that said to short the input at various stages to check if the wiring is sound. I'm not sure if this is an accurate way to troubleshoot, but I tried it out. Shorting RCA plugs on the phono input of the amp verify no hum in the phono stage. With the cartridge removed and the cartridge leads in the C2 carrier shorted together, the hum disappears. If I reinstall the cartridge and short the outputs, the hum also disappears. I was curious about the cartridge mounting screws, so I left the cartridge plugged but dangling from the carrier; hum still present.

With the carrier removed and the headshell contacts left open, the hum is very loud, which is what I'd expect from open contacts. With the carrier installed and R/L leads shorted to their respective grounds, the hum is gone. As I understand it, this indicates there's no loose connections from the carrier leads right through to the RCA inputs on the amplifier...right? Is the problem with the cartridge, or am I not testing enough variables (the impedance of the wiring, for example)?

Appreciate any help. Thanks!

aardvarkash10
long player
long player
Posts: 1415
Joined: 24 Mar 2009 01:57
Location: Auckland, New Zealand

Re: SL-65B - Irritating hum

Post by aardvarkash10 » 18 Oct 2019 03:55

where is the turntable in relation ot other pieces of electrical equipment, the power outlet socket, and the wall?

amagasakii
member
member
Canada
Posts: 76
Joined: 18 Jun 2017 04:14
Location: BC

Re: SL-65B - Irritating hum

Post by amagasakii » 18 Oct 2019 04:22

Excellent timing, I just got back from relocating it as a test. :-)

The turntable is on a sideboard beside the amplifier (JVC A-E5). It and the amplifier are plugged into an extension cord which is plugged into the wall socket. This is an old apartment, so they are on the same circuit as everything else on the outside walls of the kitchen, dining room and living room. That includes electric motors, dimmers, halogen lighting, LED lamps, computers and associated networking equipment. There really isn't much that I can do about that; there's only three circuits in the entire apartment, one of which is solely for the plug behind the fridge.

That said, I just moved it to the living room and hooked it up to my Sansui 350A in place of my Dual 521. This is on a different circuit which is only shared with incandescent lights, a TV that was off during the test and simple stuff -- alarm clocks, cell phone chargers. Same result, a hum that's loud enough to overwhelm quiet passages in music.

Tomorrow I'm going to unplug everything from that circuit other than the receiver and turntable and see if that makes a difference, but I'm not holding my breath.

Thanks!

aardvarkash10
long player
long player
Posts: 1415
Joined: 24 Mar 2009 01:57
Location: Auckland, New Zealand

Re: SL-65B - Irritating hum

Post by aardvarkash10 » 18 Oct 2019 07:35

hmmmn.

OK it's not likely to be a power circuit problem. It's most likely a RF (induced) hum in the cartridge to amp circuit.

This OFTEN happens in Duals and Garrards when the contacts on the sled are not in good condition. Take the cartridge sled out, and give the contacts to hte headshell and on the sled a clean with a pencil eraser (I used to call them a rubber, but it got me in a lot of trouble...).

Also clean the contacts from the sled to the cartridge.

Failing that, I'd test with a replacement cartridge.

https://www.sound-smith.com/hum-and-or-noise-problems

amagasakii
member
member
Canada
Posts: 76
Joined: 18 Jun 2017 04:14
Location: BC

Re: SL-65B - Irritating hum

Post by amagasakii » 18 Oct 2019 10:27

Thanks aardvarkash10, I'll give that a shot. I was really hoping I wasn't going to have to fiddle around with the contacts simply because they're so flimsy and brittle 50 years on. I hoped shorting the leads had eliminated the contacts from the equation, but i suppose the cartridge introduces more variables. I've gotten pretty adept at manufacturing new contacts for the sled, but I'd be far less confident trying to solder the tonearm wires back on if the old solder joint fails. Gotta take risks, I suppose!

I do have a Shure M72B cartridge I can try first.

Re: Language differences. Imagine my surprise when I moved to Britain and discovered that they don't use the word fanny to mean backside like we do in Canada... :-o

amagasakii
member
member
Canada
Posts: 76
Joined: 18 Jun 2017 04:14
Location: BC

Re: SL-65B - Irritating hum

Post by amagasakii » 18 Oct 2019 23:46

Well, I don't like the look of that ground wire on the right of the picture nor its mismatched contact, but it still works (for now).

Contacts are pretty clean but I gave them a once-over. I also fiddled around with different power outlets and grounding different points, including directly to the outlet ground (that made it worse, which makes me feel better).

I swapped the cartridge from the Dual (also AT91) which also hummed. Going to grab my Shure this afternoon and see if that helps, as well as try some new RCA cables.
sled.jpg
(111.19 KiB) Downloaded 74 times
sled2.jpg
(79.43000000000001 KiB) Downloaded 72 times

amagasakii
member
member
Canada
Posts: 76
Joined: 18 Jun 2017 04:14
Location: BC

Re: SL-65B - Irritating hum

Post by amagasakii » 19 Oct 2019 05:43

*sad trombone* Hum from the Shure as well. Onto the RCA cables!

A70BBen
senior member
senior member
Posts: 810
Joined: 16 Feb 2014 21:56

Re: SL-65B - Irritating hum

Post by A70BBen » 19 Oct 2019 20:29

You say it is quieted by connecting the green ground wire to the amp chassis. If that fixes it, why not run it that way, as it is intended to be run? Or do you mean the him is lessened but still there?

amagasakii
member
member
Canada
Posts: 76
Joined: 18 Jun 2017 04:14
Location: BC

Re: SL-65B - Irritating hum

Post by amagasakii » 19 Oct 2019 21:24

Sorry, wrong word. It's lessened but not eliminated when connecting the ground wire.

AsOriginallyRecorded
senior member
senior member
Canada
Posts: 862
Joined: 26 Jun 2018 06:05

Re: SL-65B - Irritating hum

Post by AsOriginallyRecorded » 20 Oct 2019 01:27

Always hook up a ground wire if it is on the turntable, it cannot do any harm. It is unfortunate that you have so few connection to power options, as many of the items you listed can introduce hum into the system. The topic of RFI was raised,and this too may be a major problem. It need have little to nothing to do with the actual physical setup of your cartridge, although the contacts along the circuit should be generally checked anyway. Alternately, RFI is very easily introduced by simple things like too close cable runs, too close components and sloppy/loose connects. Often, the simplest of adjustments will solve the hum. I always (ALWAYS) use a good quality circuit/surge protector between the wall plug and the amplifier/receiver, as the better ones will offer built in auto grounding. TT ground to amp or receiver only. Don't run connects and power cords in parallel. Keep wire runs as short and direct as possible. Ensure connects make a solid contact.....pull them off and replace if necessary, tighten collar if required, get a solid feeling click when reinstalled. Try flipping the plug terminal 180 degrees (one at a time, re-check for hum). This alone can eliminate hum in many instances...believe it or not! Mostly a bunch very easy checks, just time consuming. Messing with cartridges and tonearm wiring, unless reasonably obvious, is just as likely to lead to problems as eliminate them. My first thought when reading your original post was.....Lose the extension cord...get a surge protector instead. Hopefully one or more of these simple to do checks will exorcise the evil hum. They have for me in the past. Best of luck...... [-o<

+Wurly1
Canada
Posts: 2
Joined: 09 Oct 2019 19:23

Re: SL-65B - Irritating hum

Post by +Wurly1 » 22 Oct 2019 00:55

Hi, I have encounter that sort of humm before with a Garrard SL55B and i got it solved by reversing the AC plug of the turn table. If your amp does not have a plug with a tab larger than the other, try to reverse it too. Sometimes ac noise is picked up simply because the neutral VS live wire is connected in opposites sides thus AC power supplies are not in phase.

Pure_brew
member
member
Posts: 109
Joined: 15 Nov 2011 07:14

Re: SL-65B - Irritating hum

Post by Pure_brew » 22 Oct 2019 12:31

Ok -so the hum is present without an AC connection and it's pretty lively when things are touched, and goes away when contacts are shorted to respective grounds.

Sounds like a bad contact somewhere to me.

Another thought - I've seen lots of ground loop issues in audio equipment with cable boxes causing ground loops, where the distribution blocks aren't grounded properly or at all. You don't have one connected up to the same system do you lol?

DSJR
long player
long player
Wales
Posts: 2935
Joined: 01 Feb 2009 20:29
Location: Suffolk

Re: SL-65B - Irritating hum

Post by DSJR » 22 Oct 2019 17:07

The contact wipers' in the headshell must be straight and correctly aligned if they're to contact and 'wipe' the strips on the headshell properly as slight misalignment here will cause bad or no contacts. I went through hum agonies with my similar-shell AP76 until I discovered what it was.. Wipers are frail and easily broken, see comments below.

The pic of the wires and contacts on the headshell shows the left negative wire (should be blue I think - can you check on the terminal block under the deck as black is the tonearm ground to chassis and blue is usually the signal return for the LHC?*). Someone's been 'at this' headshell by the looks of it and may have got blue and black wired wrongly.

I believe by this time, Garrard used a five-wire setup in their tonearms -

White - L+
Blue - L-
Red - R+
Green - R-

Fifth wire in the arm was black I recall* and this one linked the tonearm metalwork to the central chassis connector on the underside terminal block - confirmation needed please as my Garrards are currently in storage and can't be readily accessed to check.

*Earlier decks may have had the tonearm-to-chassis wire as yellow just to confuse things with L- which may have been bkack at first, but this may well have been on mid 60's models - A70BBen may confirm. I'm sure the wiring changed to the conventional colour codes listed above by the late 60's though.

amagasakii
member
member
Canada
Posts: 76
Joined: 18 Jun 2017 04:14
Location: BC

Re: SL-65B - Irritating hum

Post by amagasakii » 27 Oct 2019 04:21

Hey everyone,

Sorry for the delay in replying -- last week was a little frantic so I didn't have a chance to do much until this afternoon.

AsOriginallyRecorded and +Wurly1, appreciate the replies! I redid all the cabling and disconnected anything other than the turntable and speakers. Flipping the AC cord around also makes no difference; the hum is there whether it's plugged into AC or not.

Pure_brew, no cable box hooked up; no cable, other than internet. (I bought a 75/300 ohm transformer last year only to discover our cable company discontinued FM radio signals years ago. :roll:)

DSJR, you're definitely onto something here, in that there's no fifth wire at all.
terminal-block.jpg
(81.5 KiB) Downloaded 31 times
I looked at my 40B, which is wired almost as you described -- red, green, white, black (LG) and yellow from tonearm to terminal block. The terminal block has a short wire soldered to LG which, I gather, grounds the whole chassis to LG and eliminates the need for an external grounding wire.

Looking at the picture above I see a big blob of solder on the terminal block with nothing attached. I assume at one point this had the yellow wire attached to it. Where it went, who knows, but I suppose I should solder on a suitable replacement!

DSJR
long player
long player
Wales
Posts: 2935
Joined: 01 Feb 2009 20:29
Location: Suffolk

Re: SL-65B - Irritating hum

Post by DSJR » 27 Oct 2019 11:08

Thanks for pic of terminal block underneath. garrard may well have decided the fifth wore wasn't necessary and these tonearm wires do look original.

In that case, four wires it's always been for this particular deck, so my initial suggestion would be to consider cutting the link from chassis to LG and try wiring a separate ground wire from deck to amp (always best for limiting hum levels but not always used for cost or simplicity reasons in decks like this where a little bit of hum may not have mattered so much).

I'd also look very carefully at the tabs in the headshell now, as one has obviously been fabricated and replaced - the black LG one. The arm may need to be removed from the main cradle by removing the left hand (from the front) vertical pivot screw (watch while removing/unhooking the tracking force spring as you lift the arm away) so it can be gently turned upside down for proper examination. There's usually enough slack available in the tonearm cabling to allow this. The main tonearm 'cradle' can stay where it is.

Try to get the solder joint as clean and neat as possible and ensure the replacement 'wiper' is straight, parallel as viewed from the front to the other three and not bent to the side as this causes all manner of hum issues as I found on my similar shaped (but plastic) headshell connections on my AP76.

I'm sure you'll get it sorted. Good luck and pics are always helpful so 'we' can see what's going on. It'll help others too.

Post Reply