Servo or Quartz

snap, crackle and pop
Post Reply
reis99
Portugal
Posts: 4
Joined: 29 Jun 2019 10:50

Servo or Quartz

Post by reis99 » 11 Oct 2019 00:36

Hi,

Could someone explain me in a very simple manner what is the difference between Servo and Quartz motors and which one is the better option?


Thanks.

lenjack
long player
long player
Posts: 1860
Joined: 23 Jun 2017 02:11
Location: Liverpool,PA

Re: Servo or Quartz

Post by lenjack » 11 Oct 2019 01:22

Servo references and reads the platter speed and keeps it steady, while quartz references the vibration of a crystal, which cannot change. Quartz is far more accurate. Servo tables have speed adjustments, because their speed can vary. Mny quartz locked units do not have, and do not need a speed adjustment, since their speed cannot change, unless there is a defect. This a very simple explanation. Others can give it to you in far more detail.

paddypaws
junior member
junior member
England
Posts: 24
Joined: 21 Nov 2018 23:04

Re: Servo or Quartz

Post by paddypaws » 11 Oct 2019 08:53

Not quite. Both servo and quartz tables have speed control. A prime example of a quartz table is the Technics sl-1210 which of course has speed control, and quartz being a key feature. The difference is the servo turntable uses feedback from the motor or platter to compare to the electrical mains frequency, which although pretty good isn’t 100% accurate. And can waver over time. A quartz turntable uses a quartz crystal to generate a frequency that is accurate and doesn’t vary like a digital watch. The frequency generated by the crystal can be processed by electronics to provide quartz lock at any speed the turntable can do. Again just like an SL -1210. Not all quartz locked decks have a speed control but many do, and they vary the speed of the comparators frequency to lock the motors speed.

reis99
Portugal
Posts: 4
Joined: 29 Jun 2019 10:50

Re: Servo or Quartz

Post by reis99 » 11 Oct 2019 11:12

Thank you lenjack and paddypaws for the both explanations, i understand how it basically works now, have a good one!

Coffee Phil
vinyl addict
vinyl addict
United States of America
Posts: 5744
Joined: 20 Sep 2008 08:22
Location: California

Re: Servo or Quartz

Post by Coffee Phil » 11 Oct 2019 17:49

Hi reis99,

A servo controlled turntable implies that the platter or motor speed is measured and compared to some reference to generate an error signal which is used to control the variable speed motor. The reference can be an RC time constant or a quartz clock. Most quartz turntables are "servo" however a quartz clock can be divided down to drive an AC synchronous motor. If a turntable is to have variable speed the RC time constant is the easiest approach as part of the R can be the speed control pot. It is also possible to achieve adjustable speed with a quartz clock, but it typically involves a programmable divider to divide the clock frequency to use for the reference.

Phil
reis99 wrote:
11 Oct 2019 00:36
Hi,

Could someone explain me in a very simple manner what is the difference between Servo and Quartz motors and which one is the better option?


Thanks.

georgesgiralt
member
member
France
Posts: 230
Joined: 05 Mar 2019 08:44

Re: Servo or Quartz

Post by georgesgiralt » 11 Oct 2019 18:31

Hello
Both are very accurate. More than needed in fact.(*) See the difference as the difference between a digital watch and a mechanical one. If High end, both are very accurate instruments. The quartz is said to be more precise and without risk of variation... This is why they still put adjustable controls on the Quartz lock tables ;-)

Look at a classical motor and belt turntable. The motor can't lock on the mains frequency and slips a bit. This is sufficiently precise to drive our turntables.... So do not bother and buy whatever one you find in good shape !

ravelax
member
member
Sweden
Posts: 199
Joined: 25 Oct 2016 16:15

Re: Servo or Quartz

Post by ravelax » 11 Oct 2019 18:41

georgesgiralt wrote:
11 Oct 2019 18:31
The quartz is said to be more precise and without risk of variation... This is why they still put adjustable controls on the Quartz lock tables ;-)
There are other reasons for having pitch controls besides speed accuracy of the turntable. For instance, it's widely known that there are many records around that were mastered at a slightly wrong speed. If one is very sensitive to pitch accuracy, it's nice to be able to correct even a very slight deviation in the recorded material! :)

And in the case of the previously mentioned Technics SL-1200 (and the copies of it), the pitch control enables DJs to match the beat between different tracks, so as to make a smooth, continuous mix for people to dance to, without sudden rhythm changes between every track.

lenjack
long player
long player
Posts: 1860
Joined: 23 Jun 2017 02:11
Location: Liverpool,PA

Re: Servo or Quartz

Post by lenjack » 11 Oct 2019 18:59

Keep in mind that some quartz controlled units do not have any speed adjustments at all.

georgesgiralt
member
member
France
Posts: 230
Joined: 05 Mar 2019 08:44

Re: Servo or Quartz

Post by georgesgiralt » 11 Oct 2019 21:14

Frankly, we are splitting hairs, here. Both system are precise enough if well executed. The servo on Technics turntables use a 50 kHz signal internally generated and is good enough to set 33 1/3 RPM or 45 RPM precisely.
The Quartz lock version use a 3 .x MHz quartz which is another factor overkill.
When Technics devised these, there was a tremendous war on marketing about speed accuracy. And still, Thoren and others rely on an old asynchronous motor to set their speed and are very successful at that... And still sell for high prices !

Post Reply