speed inaccuracy Garrard 401 - diyAudio
Go Back   Home > Forums > Source & Line > Analogue Source

Analogue Source Turntables, Tonearms, Cartridges, Phono Stages, Tuners, Tape Recorders, etc.

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 12th January 2004, 11:09 AM   #1
PeterW is offline PeterW  Netherlands
diyAudio Member
 
Join Date: Jan 2004
Location: The Hague, The Netherlands
Default speed inaccuracy Garrard 401

Dear all,

Several years ago I bought a second-hand Garrard 401 in immaculate condition. Altough the unit operates smooth and very silent, there is no audible rumble, something is wrong its speed accuracy.

After a warm-up period of approximately 30 minutes, the motor starts to drift from the nominal speed. The stroboscope pattern slightly revolves in counter-clockwise direction. Sometimes, after several hours of operating, the motor stabilizes to its nominal speed.

I already contacted Loricraft (Terry O'Sullivan) about this. Terry replied that this form of fluctuation is normal for a Garrard 401.

Exactly the same fluctuations I observed on my Thorens TD 124 MkII. Both turntables are equiped with an AC 4-pole asynchronous induction motor (of shaded-pole type).

Does anyone know if an external Power Supply (i.e. a Wienbridge Oscillator) will solve the problem, or is this phenomenon typical for this kind of motor type?

regards,
PeterW
  Reply With Quote
Old 12th January 2004, 06:14 PM   #2
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
You appear to be observing the minor variations of the AC power
supply frequency, which does vary slowly, usually to allow a
overall frequency correction.

Why ? A mains powered wall clock has a sychronous motor. For
it to remain accurate the overall average frequency of the mains
must be its nominal value, 50 or 60 Hz. The electricity companies
strive to acheive this, hence the minor variations.

IMO a standard wein bridge will be worse then the mains - IMO
you'll need a quartz crystal referenced phase locked loop to
achieve a consistently higher frequency stability than the mains.

But what is confusing me is the methods of fine speed adjustment.
I know the 401 has a magnetic eddy current brake speed
adjuster but this wouldn't change the speed of synchronous
motor, only increase its slip angle, perhaps it works by
increasing relative slip of the drive wheels.
I can't remember the exact 401 variable speed arrangement.
The TD124 I'm not familiar with.

Also just realised the above is completely wrong as presumably
you are using mains powered lighting to observe the strobe,
so any variations in mains frequency would be undetectable.

I have just painted myself into a corner ...............................


sreten.
  Reply With Quote
Old 12th January 2004, 06:52 PM   #3
PeterW is offline PeterW  Netherlands
diyAudio Member
 
Join Date: Jan 2004
Location: The Hague, The Netherlands
sreten,

Thanks for your reply.

Indeed, the Garrard 401 and the Thorens TD124 MkII are equiped with an eddy-current speed adjuster to change the slip angle. This works only in conjunction with an asynchronous induction motor.

Maybe this speed control-system is the cause of the fluctuations.

regards,
PeterW
  Reply With Quote
Old 12th January 2004, 08:46 PM   #4
Raka is offline Raka  Europe
diyAudio Member
 
Raka's Avatar
 
Join Date: Aug 2002
Location: Close to Oistrakh
Quote:
Originally posted by sreten


IMO a standard wein bridge will be worse then the mains - IMO
you'll need a quartz crystal referenced phase locked loop to
achieve a consistently higher frequency stability than the mains.


sreten.

Why do you say that? What are the flaws of the wien system? I ask this by ignorance.
__________________
What is beyond the speaker?
  Reply With Quote
Old 12th January 2004, 09:01 PM   #5
docjoe is offline docjoe  Europe
diyAudio Member
 
docjoe's Avatar
 
Join Date: Jun 2003
Location: Paris, France
Default 401 speed

http://www.nakedresource.com/phpBB2/...asc&highlight=
you've got perhaps a form or answer
too bad you didnt go a little further in reading the thread in vinyl engine
  Reply With Quote
Old 12th January 2004, 09:25 PM   #6
sreten is offline sreten  United Kingdom
diyAudio Member
 
Join Date: Nov 2003
Location: Brighton UK
Quote:
Originally posted by Raka

Why do you say that? What are the flaws of the wien system? I ask this by ignorance.
I did say IMO, that is I'm not definetely sure, but temperature
dependence and long term drift come to mind, though of course
the speed could always be reset for long term drift.

sreten.
  Reply With Quote
Old 12th January 2004, 11:05 PM   #7
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Quote:
or is this phenomenon typical for this kind of motor type?
Absolutely not.
I've worked with AC motors for TTs for many years and it certainly isn't a normal condition.

Maybe the TT has some worn out parts elsewhere.

Using external controllers for AC motors usually degrades the sound IME.

Cheers,
__________________
Frank
  Reply With Quote
Old 13th January 2004, 02:45 PM   #8
PeterW is offline PeterW  Netherlands
diyAudio Member
 
Join Date: Jan 2004
Location: The Hague, The Netherlands
Quote:
Absolutely not.
I've worked with AC motors for TTs for many years and it certainly isn't a normal condition.
The motor fitted in the Garrard 401 and Thorens TD124 MkII is an asynchronous induction motor. The working principle is quite different from its synchronous counterpart.

regards,
PeterW
  Reply With Quote
Old 13th January 2004, 03:20 PM   #9
DRC is offline DRC  United Kingdom
diyAudio Member
 
DRC's Avatar
 
Join Date: Jan 2003
Location: UK (south west)
Lightbulb Drift

I don't think this drift is due mains frequency as the fitted strobe (401) is also syncronised to mains (or are you using an independant strobe ?).
Dave
  Reply With Quote
Old 13th January 2004, 04:04 PM   #10
diyAudio Member
 
analog_sa's Avatar
 
Join Date: Aug 2002
Location: Sofia
Quote:
Using external controllers for AC motors usually degrades the sound IME.
Frank,

Care to elaborate on this? My experience differs. Are you saying you'd prefer a Linn with a Basic rather than Valhalla or Lingo? Don't tell me to stuff that Linn

The 301 IME sounds a LOT better with a synthesised supply.
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Garrard 401 mrfeedback Analogue Source 16 27th July 2008 06:46 PM
Garrard 401 60 Hz pulley wpod Analogue Source 5 27th February 2008 11:32 PM
Garrard 401 PSU lt_texan Analogue Source 30 4th May 2007 06:39 PM
Garrard 301 Colour 405man Analogue Source 3 24th November 2005 02:51 PM
Modifying a Garrard Arne Analogue Source 3 9th May 2005 02:28 PM


New To Site? Need Help?

All times are GMT. The time now is 06:56 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2