Go Back   Home > Forums > >
Home Forums Rules Articles diyAudio Store Blogs Gallery Wiki Register Donations FAQ Calendar Search Today's Posts Mark Forums Read

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

Turntable speed stabilty
Turntable speed stabilty
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 26th June 2017, 09:04 AM   #11
luckythedog is offline luckythedog  United Kingdom
diyAudio Member
 
Join Date: Nov 2009
Location: London, UK
Hi Volken, I have an archived 3rd party 3150Hz test recording from an EMT 930, it's polar plot is attached below.

I think one can see that for this example of a EMT930, there was something big going on at a few Hz, but the 25Hz drive component was there but not prominent. It does show up in the amplitude spectrum, but not so much in the FM.

Also inset in this is the conventional spectrum, which also only hints at a 25Hz component.

I don't know what cartridge was fitted, unfortunately, but the cart-arm resonance isn't prominent either in this case.

LD
Attached Images
File Type: jpg EMT 930 polar plot.JPG (233.2 KB, 611 views)
  Reply With Quote
Old 26th June 2017, 06:19 PM   #12
sq225917 is offline sq225917  United Kingdom
diyAudio Member
 
Join Date: Jun 2004
Location: sheffield
Send a message via MSN to sq225917 Turntable speed stabilty
That's not even vaguely round, is the 930 idler driven?

I have the hifi news test record, badly centered and poor pitch on the 3150 cut. Acquiring a good din record of an optical disc as per regas dev unit is on the cards.
__________________
Paradise Pre-reg PSU PCBs
  Reply With Quote
Old 26th June 2017, 10:42 PM   #13
Hearinspace is offline Hearinspace  Canada
diyAudio Member
 
Join Date: Jun 2008
Turntable speed stabilty
Quote:
Originally Posted by kaputt View Post
Please crank up some peer pressure so I finally try that feature

Your moniker gives you instant street cred with me!

+873.2 grams.
  Reply With Quote
Old 26th June 2017, 10:58 PM   #14
billshurv is online now billshurv  United Kingdom
diyAudio Member
 
billshurv's Avatar
 
Join Date: Mar 2014
Turntable speed stabilty
Quote:
Originally Posted by sq225917 View Post
Acquiring a good din record of an optical disc as per regas dev unit is on the cards.
wossat? (either the optical disk or regas dev unit).
  Reply With Quote
Old 27th June 2017, 04:54 AM   #15
Hiten is offline Hiten  India
diyAudio Member
 
Join Date: Jun 2010
Location: India
Any other method other than test records ? Since offcenter and warps can not be avoided any modern method to measure speed stability ?
A Postscript printer can print precise dots (or markings) we can make perfectly center thick white sheet with such markings and optically measure the speed variations. Right ?
How do classic tables like Thorens, Garrard, Lencos and Technics compare with regards to speed stability. Any one has measured them and have data on them ?
Regards.
  Reply With Quote
Old 27th June 2017, 04:57 AM   #16
Hiten is offline Hiten  India
diyAudio Member
 
Join Date: Jun 2010
Location: India
....if table is direct drive can we measure current required in motor in speed control circuits and ***** its speed stability ? Heavy platters with tight tolerance highly polished/lapped bearings will have comparatively stable speed isn't it ?
Regards.
  Reply With Quote
Old 27th June 2017, 08:19 AM   #17
billshurv is online now billshurv  United Kingdom
diyAudio Member
 
billshurv's Avatar
 
Join Date: Mar 2014
Turntable speed stabilty
Hiten: You certainly can use a non-record method to measure things. The question then becomes what you gain and what you lose from this. My Kenwood has a 300 slot optical code wheel on the spindle that is used to provide the correction signal to the electronics. So that would give a 540Hz square wave if you probed the opto connectors.

AEDB-9140-A13 | Broadcom Incremental Encoder -0.5 ? 7 V dc | Broadcom is an example of a 500 slot code wheel with detector that is fairly cheap. You'd need to work out how to fix it in place. If you want more resolution then HEDS-6140#B09 | Broadcom 1000 Pulse Code Wheel with a 0.5 in, Through Hole | Broadcom but the cost nearly doubles as you have to buy wheel and sensor seperately. You could also on tables with a strobe marking on the platter pickup off that.

I think all of these are work investigating and comparing to the test record method.

Ref your direct drive question, the answer is yes and no. Yes you can measure current and back EMF to do magical things in DSP, but the motor is turning too slowly to really make use of it. But this is an area I would love to have time to explore further (and would require another thread).
  Reply With Quote
Old 27th June 2017, 09:59 AM   #18
luckythedog is offline luckythedog  United Kingdom
diyAudio Member
 
Join Date: Nov 2009
Location: London, UK
Quote:
Originally Posted by sq225917 View Post
That's not even vaguely round, is the 930 idler driven?

I have the hifi news test record, badly centered and poor pitch on the 3150 cut. Acquiring a good din record of an optical disc as per regas dev unit is on the cards.
Yes the EMT 930 is idler drive. It's very well respected and was part of the EMT studio family that has serious heritage. I also have a test tone recording from an EMT938 in the archive that I can dig out..............

How round the polar plot appears depends upon the radial scale, and I set it to deliberately see the variations. I always use 3Hz as the spacing, because that is said to be the threshold of most people's ability to hear the difference. I try to keep the plots consistent, so there are 18 radial lines and the peak excursion clips the outside.

What we generally find, IME, is that TTs with excellent sonic reputation don't necessarily have good pitch stability when looked at this way - often far worse than those considered good or mediocre..... which is interesting and surprising at the same time perhaps?

Also, focus on accurate motor speed control is typically misplaced, IMO, because that's seldom a dominant factor in overall pitch stability, it seems.

LD
  Reply With Quote
Old 27th June 2017, 11:03 AM   #19
luckythedog is offline luckythedog  United Kingdom
diyAudio Member
 
Join Date: Nov 2009
Location: London, UK
Quote:
Originally Posted by Hiten View Post
Any other method other than test records ?
I like the idea of displaying a servo signal where there is one, if nothing else, for a health check......!

But pitch stability is only partly about platter speed stability. Typically factors like spindle centering, platter vertical run-out, warp, and cart-arm stability contribute far more in an otherwise healthy TT. So this is where bang-for-the-money is, and is well within most DIYers capabilities methinks.

LD
  Reply With Quote
Old 27th June 2017, 11:21 AM   #20
Kay Pirinha is offline Kay Pirinha  Germany
diyAudio Member
 
Kay Pirinha's Avatar
 
Join Date: Oct 2011
Location: Somewhere in Germany
Luckythedog,

your polar diagrams, translated into conventional xy graphs, represent the rotation angle by the x and frequency by the y axis, respectively. How did you record the angle/x axis, in order to get the x/y relationship in your diagrams?

@Hiten: Maybe you've frogotten Dual in your list of classic TT manufacturers?

Best regards!
  Reply With Quote

Reply


Turntable speed stabiltyHide 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

Forum Jump

Similar Threads
Thread Thread Starter Forum Replies Last Post
Modifying turntable speed AlexanderN Analogue Source 11 25th October 2016 01:26 AM
Turntable speed question........ JoeDJ Analogue Source 21 28th December 2013 06:29 PM
Turntable speed billone Analogue Source 7 13th February 2012 06:20 AM
Turntable speed under load YNWOAN Analogue Source 6 5th April 2008 11:01 AM
Turntable speed diyman Analogue Source 3 23rd May 2005 06:44 PM


New To Site? Need Help?

All times are GMT. The time now is 08:55 PM.


Search Engine Optimisation provided by DragonByte SEO (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Resources saved on this page: MySQL 15.00%
vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2018 DragonByte Technologies Ltd.
Copyright ©1999-2018 diyAudio
Wiki