UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio and TV Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Specific Vintage Equipment > Vintage Audio (record players, hi-fi etc)

Notices

Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment.

Closed Thread
 
Thread Tools
Old 20th Nov 2018, 7:41 pm   #1
Telegraph-Hill
Triode
 
Join Date: Mar 2017
Location: Totnes, Devon, UK.
Posts: 27
Default 50Hz Hum in Garrard Zero 100

Hello and good evening from Devon,
I am working on a restoration of a Garrard Zero 100 Turntable. When I connect the player to the audio input of an amp with cartridge connected all sounds good (a little bit of hum but mixes with the noise of the MM pre Amplifier). At that moment no power is connected to the record player. If I plug in the record player the hum starts. The record player is not spinning. When I remove the line wire the hum is gone.

It is not the ground wire connected to the mains producing the hum!

I can remove the ground wire and hum is still present. Only by removing the Line wire (phase) the hum is gone.
It does not make any difference if the Turntable is spinning or not. I changed neutral and line at the internal connecting block. No difference. Still a 100Hz hum.

I do not have the schematics for internal wiring of the zero 100. Any capacitors inside the switch box?

Any thoughts about this? Feeling a little bit puzzled.

Cheers,
Oliver

Last edited by Telegraph-Hill; 20th Nov 2018 at 7:52 pm. Reason: Edit: 100Hz hum instead of 50Hz
Telegraph-Hill is offline  
Old 20th Nov 2018, 7:55 pm   #2
Telegraph-Hill
Triode
 
Join Date: Mar 2017
Location: Totnes, Devon, UK.
Posts: 27
Default Re: 50Hz Hum in Garrard Zero 100

Here a picture from inside.
Attached Thumbnails
Click image for larger version

Name:	garrard zero 100.jpg
Views:	492
Size:	80.5 KB
ID:	173170  
Telegraph-Hill is offline  
Old 20th Nov 2018, 8:55 pm   #3
teetoon
Heptode
 
Join Date: Dec 2010
Location: Barnstaple, N.Devon, UK.
Posts: 556
Default Re: 50Hz Hum in Garrard Zero 100

Hi, looking at the cheap audio cable you have there I'm wondering if it's picking up the field from the mains because of the almost non existent screening.
Try moving the audio cable and see if the hum varies.
Maybe you have a better phono (RCA) cable you could try. It would also probably eliminate the hum that you say mixes with the preamp noise.

Also, is there a seperate earth wire going to your amp from the turntable chassis ?

David.
teetoon is offline  
Old 20th Nov 2018, 9:06 pm   #4
Telegraph-Hill
Triode
 
Join Date: Mar 2017
Location: Totnes, Devon, UK.
Posts: 27
Default Re: 50Hz Hum in Garrard Zero 100

Hi David, I think your thoughts about the cheap Audio Cable directs in the right way. I was going to order a decent Audio cable anyhow. There is a ground wire going straight from chassis to the amp. Cheers, Oliver
Telegraph-Hill is offline  
Old 20th Nov 2018, 9:13 pm   #5
teetoon
Heptode
 
Join Date: Dec 2010
Location: Barnstaple, N.Devon, UK.
Posts: 556
Default Re: 50Hz Hum in Garrard Zero 100

Hi Oliver, yes it's quite often the case that these cables are ok at line levels but might just aswell be a piece of twin when it comes to screening at phono levels.

If you have an earth from chassis to amp then sometimes having another earth to the mains plug causes a ground loop which also produces hum, but it sounds like you already tried disconnecting that with no difference ?

David.

Last edited by teetoon; 20th Nov 2018 at 9:31 pm.
teetoon is offline  
Old 20th Nov 2018, 10:22 pm   #6
Telegraph-Hill
Triode
 
Join Date: Mar 2017
Location: Totnes, Devon, UK.
Posts: 27
Default Re: 50Hz Hum in Garrard Zero 100

Hi David, I tried everything to avoid a ground loop. I disconnected the earth ground on the plug and only used straight wire to the earth connection at the amp. No difference.
Cheers, Oliver
Telegraph-Hill is offline  
Old 20th Nov 2018, 10:45 pm   #7
teetoon
Heptode
 
Join Date: Dec 2010
Location: Barnstaple, N.Devon, UK.
Posts: 556
Default Re: 50Hz Hum in Garrard Zero 100

I think it's down to the poor signal leads then. If you try moving the lead away from the mains wires it should vary in volume.

Be careful with the mains terminal covers removed though. I would put them back on before doing anymore testing.
teetoon is offline  
Old 20th Nov 2018, 11:07 pm   #8
Telegraph-Hill
Triode
 
Join Date: Mar 2017
Location: Totnes, Devon, UK.
Posts: 27
Default Re: 50Hz Hum in Garrard Zero 100

No worries, I use a RCD in my workshop But Cover is back on now.
Telegraph-Hill is offline  
Old 20th Nov 2018, 11:30 pm   #9
teetoon
Heptode
 
Join Date: Dec 2010
Location: Barnstaple, N.Devon, UK.
Posts: 556
Default Re: 50Hz Hum in Garrard Zero 100

Well done. Safety is always a concern here when giving advice.
Do let us know when you manage to try a better signal lead. It's always nice to spin some records so I hope you get it sorted and have fun.

David.
teetoon is offline  
Old 21st Nov 2018, 8:04 am   #10
crackle
Rest in Peace
 
Join Date: Mar 2011
Location: Basildon, Essex, UK.
Posts: 4,100
Default Re: 50Hz Hum in Garrard Zero 100

Quote:
Originally Posted by Telegraph-Hill View Post
Hi David, I tried everything to avoid a ground loop. I disconnected the earth ground on the plug and only used straight wire to the earth connection at the amp. No difference.
Cheers, Oliver
You dont say which plug you disconnected the earth from.
Lets be clearer, one would normally disconnect any mains earth in the power cable to the record player. Then use the separate ground wire from the record player to connect from the record player to the amp chassis.
Your amp should normally be earthed, but sometimes they are not.
Ensure that the audio cables do not run close to the record player motor or mains cabling.
This should help to minimise hum pick up.

I believe the service manual is available on Vinyl Engine

Mike

Last edited by crackle; 21st Nov 2018 at 8:24 am.
crackle is offline  
Old 21st Nov 2018, 10:35 am   #11
gramofiend
Pentode
 
Join Date: Aug 2010
Location: Cowbridge, Vale of Glamorgan, UK.
Posts: 137
Default Re: 50Hz Hum in Garrard Zero 100

The way in which the Zero 100 decks left the factory was that the mains connections were nominally 3 core and the motor deck plate had a recognisable green earth wire to a self tapping screw in the metal deck plate, thus all metalwork of the deck was earthed to mains earth. The thin pick up wires were led separately to a tag strip. On early models generally before the Belt driven ones, that tag strip had solder conections to send to the pre amplifier. A lot of third parties used to strap the earths of the pick up wiring to the centre mounting strap which secured the entire mess to the chassis! This, as you will observe immediately undid all the good work and ensured a hum loop! Simple solution is to separate the L and R earths from the central tag support and lead these to the phono plugs to the pre-amp. Later revisions of the production, especially those for export were fitted with tag strips containing phono sockets!

I have one such Zero 100 connected the above way, using a very low O/P Goldring Eroica moving coil cartridge and feeding a Quad 66 preamp with low level input card. It is as silent as the grave!! The only other place where you might have a little trouble is where the slide in cartridge carrier mounts with the front of the pick up arm. The contacts, over time, tend to absorb moisture and dirt and as the old saying goes, cleanliness is next to godliness!

best of luck.

Mike
gramofiend is offline  
Old 21st Nov 2018, 12:08 pm   #12
G8HQP Dave
Rest in Peace
 
Join Date: Sep 2008
Location: Solihull, West Midlands, UK.
Posts: 4,872
Default Re: 50Hz Hum in Garrard Zero 100

You appear to have mains wiring which is either loosely twisted or not twisted at all. That will radiate a hum magnetic field.

You appear to have tonearm wiring which is loosely twisted. That will pick up a magnetic field. The problem is that the tonearm wire need to be flexible - which means a loose twist. You may have to seek a compromise. It may be worth checking whether someone has 'upgraded' the tonearm wiring - audiophile 'upgrades' 'often destroy performance.
G8HQP Dave is offline  
Old 28th Nov 2018, 1:25 am   #13
Telegraph-Hill
Triode
 
Join Date: Mar 2017
Location: Totnes, Devon, UK.
Posts: 27
Default Re: 50Hz Hum in Garrard Zero 100

Just the outcome. Installed a new Audio cable and used different Amp. No noise, dead silence. All right.

The reason I had a 100Hz hum in my workshop was the long (2m) Power cable and a mission cyrus2 which seems to have problems with hum at MM input stage as I had similar problems with other decks like Dual. But never was so loud.
Telegraph-Hill is offline  
Old 28th Nov 2018, 2:14 am   #14
teetoon
Heptode
 
Join Date: Dec 2010
Location: Barnstaple, N.Devon, UK.
Posts: 556
Default Re: 50Hz Hum in Garrard Zero 100

Hi TH,if you search in the box at the top of the page for Cyrus amp hum there are a few threads on this. It is down to leaky electrolytic capacitors and is a common problem on these amps.
Otherwise, great to hear you can now use your deck. Thanks for the update.

David.
teetoon is offline  
Old 12th Mar 2019, 3:14 pm   #15
sam9999
Retired Dormant Member
 
Join Date: Mar 2019
Location: London, UK.
Posts: 1
Default Re: 50Hz Hum in Garrard Zero 100

Quote:
Originally Posted by Telegraph-Hill View Post
I am working on a restoration of a Garrard Zero 100 Turntable. When I connect the player to the audio input of an amp with cartridge connected all sounds good (a little bit of hum but mixes with the noise of the MM pre Amplifier). At that moment no power is connected to the record player. If I plug in the record player the hum starts. The record player is not spinning. When I remove the line wire the hum is gone.
Funnily this was happening to my Zero 100s I'm restoring, switched off the mains the hum disappeared, switched the mains back on low & behold no hum, weird!

But the hum does appear when the motor is running, now to de-grease it and sort out the hum.
sam9999 is offline  
Old 15th Mar 2019, 11:20 pm   #16
qualityten
Octode
 
Join Date: Feb 2009
Location: Wallasey, UK.
Posts: 1,308
Default Re: 50Hz Hum in Garrard Zero 100

With the Zero 100 I'm restoring at the moment, there is a ground hum which only goes away when a put a ground wire between the chassis and the amplifier. At present, the chassis ground point and the amplifier is not effective. I need to check continuity. However, once grounded, it is very quiet.
qualityten is offline  
Closed Thread

Thread Tools



All times are GMT +1. The time now is 8:35 am.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
Copyright ©2002 - 2023, Paul Stenning.