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Vintage Audio (record players, hi-fi etc) Amplifiers, speakers, gramophones and other audio equipment. |
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14th Apr 2021, 2:12 pm | #21 | ||
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,833
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Re: Garrard 401 idler bearing
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14th Apr 2021, 2:57 pm | #22 |
Nonode
Join Date: Jan 2009
Location: Bristol, UK.
Posts: 2,062
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Re: Garrard 401 idler bearing
The rotation speed (at some speeds?) is not an integral of 20mS/50Hz to there is a bit of a jump each revolution! This is probably what you are seeing /
dc |
14th Apr 2021, 3:59 pm | #23 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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Re: Garrard 401 idler bearing
Hmm, I may not have been as fastidious with my restoration as I had hoped. I am having a slippage of the platter and the general speed is very fast, when I switch on from cold the speed adjustment needs to be right on minimum. Any suggestions welcome.
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14th Apr 2021, 5:26 pm | #24 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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Re: Garrard 401 idler bearing
Okay, I calmed myself down and went through the manual again. I went through the section on adjusting the speed, and found that bolt in the motor casing, the one with the screw that adjusts the magnet assembly. I wound it down as the book instructs, but found that the magnet rubbed on the fly wheel (is that the term)? It was still too fast, so I took a leap and lowered the collar on the fly wheel. I am still getting it fine tuned, but I believe I can get this right. We shall find out if that sorts out the "wobble" in the speed.
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14th Apr 2021, 6:01 pm | #25 |
Dekatron
Join Date: Sep 2011
Location: Rugeley, Staffordshire, UK.
Posts: 8,833
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Re: Garrard 401 idler bearing
That's very interesting Dave, thanks. What's the explanation behind it?
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A digital radio is the latest thing, but a vintage wireless is forever.. |
14th Apr 2021, 6:32 pm | #26 |
Heptode
Join Date: Oct 2007
Location: Southampton, Hampshire, UK.
Posts: 821
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Re: Garrard 401 idler bearing
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15th Apr 2021, 5:19 am | #27 | |
Tetrode
Join Date: Aug 2010
Location: Mumbai, India.
Posts: 98
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Re: Garrard 401 idler bearing
Quote:
Regards, Anwesh
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Anwesh |
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15th Apr 2021, 7:15 am | #28 |
Dekatron
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 4,991
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Re: Garrard 401 idler bearing
The 401 was a real workhorse. The BBC used them for all music broadcasts when records were the only show in town. And before that they used the 301. They turned them on in the morning, left them running all day, and turned them off after the last broadcast.
They are extremely rugged, and the strobe markings are machine cut around the periphery of the turntable, so not a chance that there is any error in the strobe. The motor is a massive unit in a serious cast metal shell to shield hum field. It is so chunky to compensate for any cartridge that needed a high tracking force. To set the speed accurately there is an eddy current brake on the motor shaft. That is an aluminium disc with magnets below and above the disc on a pivoted arm whose position is controlled by the middle knob at the front. You adjust it so that the strobe markings remain stationary. The mechanism is similar in the 301, other than only one magnet being used. Because the magnets are balanced above and below the disc in the 401, the braking effect is certainly to at least first order independent of the position of the magnets relative to the disc, and to disc wobble. Craig Last edited by Craig Sawyers; 15th Apr 2021 at 7:22 am. |
15th Apr 2021, 10:48 am | #29 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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Re: Garrard 401 idler bearing
Namaste Anwesh, thank you for clearing that up for me.
Craig, your in-depth and concise posts have helped a lot with my knowledge of the workings of the 401. Thanks. I looked at everything again last night, and found a little gap between the thrust plate and the bearing housing at one end. That seems to solve the problem once the deck has been going a few minutes. The sound is fabulous and the P8ES now tracks everything I have thrown at it at .75gm. Thanks guys, from Bill. |
15th Apr 2021, 11:11 am | #30 |
Octode
Join Date: Dec 2017
Location: Morden, Surrey, UK.
Posts: 1,560
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Re: Garrard 401 idler bearing
My memory of using a brand new 401 in the seventies was that it always started slightly fast then settled down after 20 minutes or so. You could adjust this with the speed control but it wasn`t noticeable in practice.
This effect (and a sensitivity to mains voltage) was mentioned in the original HiFi News review which suggested it was due to motor changes from the 301 in order to reduce the notorious hum problem that Decca FFSS users found. I still have the 401 but it has not been used for nearly forty years, I intend to bring it back to life soon. |
15th Apr 2021, 12:44 pm | #31 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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Re: Garrard 401 idler bearing
Barry, when you do get round to the restoration, take a look at the Classic Turntable Co.
www.classichifi-shop.co.uk I used the service kit that they offer, and their bearing kit and Thrust Plate bearing upgrade with integral seal. My turntable is much better for all of it. They offer a restoration service (haven't used it myself so can't comment on it). Peak Hifi have also been very helpful to me. www.peakhifi.co.uk Cheers from Bill. |
15th Apr 2021, 3:15 pm | #32 |
Dekatron
Join Date: Jul 2008
Location: Kington, Herefordshire, UK.
Posts: 3,675
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Re: Garrard 401 idler bearing
That's pushing it, really - you would do much better to run at 1 or 1.25g. Record wear is negilgible at these pressures, and far more damage is caused to the disc by mistracking, however marginal it be.
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15th Apr 2021, 3:35 pm | #33 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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Re: Garrard 401 idler bearing
Thanks for the advice Ted. Better safe than sorry, eh?
Cheers from Bill. |
16th Apr 2021, 3:21 pm | #34 |
Nonode
Join Date: Jan 2009
Location: Bristol, UK.
Posts: 2,062
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Re: Garrard 401 idler bearing
50Hz Strobe at 33 1/3,45 & 78 RPM
At 33 1/3 RPM, each revolution takes 1.8 seconds and 90 x 20mS (@50Hz) divisions fit exactly at the exact speed. At 45 RPM, each revolution takes 1 1/3 seconds so you can either have 66 (1% slow) or 67 (0.5% fast) divisions. Even 0.5% is a bit rubbish so the better option is to have a single 2/3 division. This makes a bit of a jump when you view it! For 78 RPM the error is gross! dc |
16th Apr 2021, 4:27 pm | #35 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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Re: Garrard 401 idler bearing
I love it when people write out the maths, it really helps me. Cheers Dave!
Bill. |
16th Apr 2021, 5:27 pm | #36 |
Hexode
Join Date: Jun 2018
Location: Buckinghamshire, UK.
Posts: 387
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Re: Garrard 401 idler bearing
A 401 turntable is marked with 77, 133, and 180 timing divisions. (For 50Hz mains.)
A neon strobes at 100Hz, i.e. 0.01 sec. When the marks are stationary the turntable has rotated 1 division in 0.01 sec, so:-
Last edited by Trigon.; 16th Apr 2021 at 5:33 pm. |
16th Apr 2021, 6:23 pm | #37 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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Re: Garrard 401 idler bearing
I like that! Thanks so much for taking the time to write that out and post. That fills it out a bit more in my mind.
Cheers from Bill. |
24th Apr 2021, 4:31 pm | #38 |
Heptode
Join Date: Jan 2016
Location: Wolverhampton, West Midlands, UK.
Posts: 777
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Re: Garrard 401 idler bearing
Final report time! The thrust plate had been unevenly tightened and a gap of <1mm had appeared as stated above. I tightened the screw and the turntable runs steady now. My new Plinth from Peak Hifi should be done soon, hurrah!
Bill. |