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Garrard 86SB

vicdiaz

vicdiaz

Just another analog freak...
Hi,

Just repaired a Garrard 86SB for an acquaintance and there is a barely discernible hum at medium to high volume. I've checked every single mm of tonearm cable, head shell connectors and contacts, and reseated the RCA connectors within the internal tonearm assembly but the hum is still there. In fact, RCA connectors were soldered to the RCA sockets and I desoldered and readjusted them for proper tension. Seems the previous owner disassembled and painted the entire metal chassis and I'm suspecting paint is interfering with proper tonearm grounding.

Checking the exploded parts diagram there is mention of a grounding strap for the phone socket connector below the tonearm, but I did not see it in this one. The only ground cable I can identify is the one that comes out of the motor which is also used as the metal chassis star ground point.

Any ideas?

Been looking for pictures but no luck so far.
 
There should be 5 wires coming out of the tonearm - the four cartridge contacts and an additional one that earths the tonearm tube and internals. Is this one still there?
 
As 86SB and Zero 100SB are siblings, the dedicated Zero 100 service manual is the one to get, as this includes a fault chart (with "No. 12 Noise (b) Electrical hum, heard through speakers" mentioning where the tonearm should be grounded to the metal chassis. This mentions the same chassis connection point as is the motor ground point, however, this does not always appear to be the case (i.e. the manual may include legacy details from prior to 'SB').

In the Zero 100SB photo below the tonearm is grounded to the same chassis point as would be the ground wire of a 3-wire mains connected version*. It matters not where really, as long as there is a connection to chassis metal. If you zoom in on the photo you'll see where this connects to at tonearm end.

Gerrard Zero 100SB [image credit: user Allenkeys of vinylengine]:
garrard_zero_100sb_3.jpg


* See 'International Models' at the end of the service manual (no page no. so likely an addendum). This suggests ignoring the earlier instructions and using a 3-wire connection with mains earth connected to that same point next to the mains terminal block. Should your acquaintance's deck employ a double insulated 2-wire mains connection then perhaps changing over to 3-wire (plus tonearm ground to chassis) might well do the trick (i.e. in addition to having a dedicated tonearm ground connection).
 
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@vicdiaz,

Found some decent photos of 86SB over on audiovintage.fr. This example appears to lack a dedicated ground wire from RCA terminal plate (or from the bracket this attaches to) to metal chassis. The second and third photos confirm that the internal tonearm ground wire is yellow and connected to the metal tab at the top (i.e bottom) corner of the RCA terminals plate (same as for Zero 100SB above).

I'd definitely be wanting a dedicated ground wire from here to chassis, myself, perhaps soldered onto that hook at the top (bottom) of the tall bracket that the RCA terminal plate is attached to, and running over to the main ground terminal beside the mains input block as per the Zero 100SB above. It appears that they didn't bother grounding the motor to the chassis either. You'll rarely even see one of these motors for sale that doesn't still have a green ground wire hanging off one of the tabs. Perhaps the inclusion or omission of same had to do with intended market electrical safety regs wrt double insulated 2-wire vs. 3-wire grounded mains in.

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Beobloke said:
There should be 5 wires coming out of the tonearm - the four cartridge contacts and an additional one that earths the tonearm tube and internals. Is this one still there?
Click to expand...

Yes, there are 5 wires coming out of the tonearm, and there were two ground cables coming out of the turntable joined into a single one. When I connected it there was a very loud hum coming out of the speakers so I decided to disconnect the hacked tonearm ground cable and only connect the one coming out of the motor. A lot less hum but still some.
 
This image helps a lot since I can see a green cable running out of the tonearm base to a chassis ground which is missing in my acquaintance's 86SB (top part of the picture). Thanks a lot!!!

garrard_zero_100sb_3.jpg
 
vicdiaz said:
Yes, there are 5 wires coming out of the tonearm, and there were two ground cables coming out of the turntable joined into a single one. When I connected it there was a very loud hum coming out of the speakers so I decided to disconnect the hacked tonearm ground cable and only connect the one coming out of the motor. A lot less hum but still some.
Click to expand...
Tonearm ground to amp is via Rch -ve. Having a separate chassis connected ground wire to amp is likely causing a ground loop. Basically, the tonearm ground scheme involves having yellow (tonearm ground) connected to the metal RCA terminals plate with the plate then strapped to Rch-ve/green.

Here is a better photo, this time from a first generation Zero 100 in which the same RCA terminals bracket is mounted direct to the metal chassis. Note the thick solid wire link to Rch -ve (green) from the same metal plate that tonearm ground (yellow) is soldered onto.

garrard-ground-link.jpg


The service manual doesn't explicitly mention this link, however, it does make clear that green must be used for mono cartridge connections.

"For a mono cartridge use the right-hand channel connections only".​

This is a big hint as to how a given tonearm is grounded from back in the mono to stereo days.
 
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Craig B said:
Tonearm ground to amp is via Rch -ve. Having a separate chassis connected ground wire to amp is likely causing a ground loop. Basically, the tonearm ground scheme involves having yellow (tonearm ground) connected to the metal RCA terminals plate with the plate then strapped to Rch-ve/green....
Click to expand...

Thanks!!!
 
Hi Vicdiaz,

How did you resolve this in the end? Did you just sever the link between the tonearm ground and Rch -ve and then add a new wire to connect that to ground on the amp? I have an 86 SB MkII with a similar issue and this thread feels like it holds the solution.
 
johnnysouth said:
Hi Vicdiaz,

How did you resolve this in the end? Did you just sever the link between the tonearm ground and Rch -ve and then add a new wire to connect that to ground on the amp? I have an 86 SB MkII with a similar issue and this thread feels like it holds the solution.
Click to expand...

Yikes! Can't recall what I did!!!
 
johnnysouth said:
Hi Vicdiaz,

How did you resolve this in the end? Did you just sever the link between the tonearm ground and Rch -ve and then add a new wire to connect that to ground on the amp? I have an 86 SB MkII with a similar issue and this thread feels like it holds the solution.
Click to expand...
The link that connects Rch -ve (green) to the terminal plate is what provides tonearm ground connection to the amp, this via RCA outer ring. If severing this link then, yes, you'd need a dedicated ground wire from terminal plate to amp. Just make sure that yellow* from the tonearm also connects to the terminal plate and all should be good (that is, provided yellow shows continuity with tonearm metal).

* Assuming tonearm ground was still yellow on MkII. If not, then likely to be black.
 
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