Synchronous motors for turntables?

[tcpip]

How many of us have turntables which are powered by synchronous motors, and how many of you drive it straight from the mains without any power re-generator?

Basically, I've always wondered how turntable owners accept synchronous motors for their turntables. A synchronous motor aligns its rotational speed to the frequency of the AC mains, and the AC mains frequency is not steady in our country (and in most other countries whose power supply infrastructure is in the same state ours). A turntable is a precise instrument, and our ears are very sensitive to pitch changes, thereby making all AC mains frequency changes audible when you play your turntable.

So I was curious: do most of you have a power re-generator (which electronically generates clean and very steady 50Hz 220V AC output) for driving the motor? If you don't, isn't the frequency unsteadiness a problem?

I have a clearer understanding of mains frequency changes than many of you. My dad was an electrical engr in one of the country's largest power generation and distribution corporations and I've accompanied him many times as a schoolboy to his power stations, control rooms, central load dispatch stations, etc, and have seen the mains frequency fluctuating on large meters on the control panels there. Pretty exciting stuff for a 12-year-old. One can say I've grown up with a pretty strong exposure to AC mains at the megawatt levels.

Therefore, decades later when I see very fastidious audiophiles using turntables with synchronous motors, I am forced to wonder how they do it. My query doesn't impact those turntables which run by DC power or those which run by AC mains but don't use synchronous motors.

For example, VPI turntables all come with synchronous motors, AFAIK. This means that they are geared to work with 60Hz AC mains of North America. You can't drive them from the Indian mains, and it's not a matter of having a step-down transformer to convert our 220V to 110V. A transformer doesn't change the frequency of the AC.

 

[sachu888]

Most of the TTs have speed adjustments. 110V, 60hz TTs including VPI can be used in India. One will need a step down and 50hz pulley for belt drive and 50hz motor shaft for idler drive TTs. Both things are mostly available.

Regards
Sachin

 

[arj]

A Lenco has a AC motor and hence is governed by the frequency. When I had measured it in bangalore there is a variation which means that the speed varies. I could see it was mostly between 48-49.5 hz odd during day and 50 during night.

I use a re-generator to keep it at 50 Hz and that had the obvious impact on sound.

This is going to be City/location specific eg Mumbai apparently has one of the best quality ie minimum frequency variation.

 

[greenhorn]

I have a TT with a synchronous motor, and I have not noticed any noticeable wow or flutter
I have used it in the UK, and i do not notice anything worse in india or compared to my DC/quartz TT's

 

[arj]

Its not a wow or flutter but a change in the speed of TT..but a motor for 50 Hz and set at 33.33 will run at 32.33 at 48.5 hz..so the sound will be slower and musical instrument will drag.

 

[tcpip]

Most of the TTs have speed adjustments. 110V, 60hz TTs including VPI can be used in India. One will need a step down and 50hz pulley for belt drive and 50hz motor shaft for idler drive TTs. Both things are mostly available.

Great. This solves the internationalisation problem. What remains is the problem of unsteady mains frequency. What do you do for that?

 

[tcpip]

I have a TT with a synchronous motor, and I have not noticed any noticeable wow or flutter
I have used it in the UK, and i do not notice anything worse in india or compared to my DC/quartz TT's

The official spec of mains frequency range, adhered to by all distribution companies, is +/-3%. This means for a 50Hz nominal frequency, the discom will do nothing if it is anywhere between 48.5Hz and 51.5Hz. And in India, I've seen those variations on dozens of occasions from a privileged position as I had described earlier. I am sure no vinyl lover will want to see such variations. What sounds bright and "dynamic" at night is going to sound "subdued" and "warm" in the morning. (Heavier loads on the electrical grid during the day sometimes results in frequency drop.) Are you ok with it?

 

[tcpip]

A Lenco has a AC motor and hence is governed by the frequency. When I had measured it in bangalore there is a variation which means that the speed varies. I could see it was mostly between 48-49.5 hz odd during day and 50 during night.

I use a re-generator to keep it at 50 Hz and that had the obvious impact on sound.

Yes, this is the only guaranteed "cure" for the synchronous motor challenge, I feel.

The reason I was thinking about this re-generator idea is because one can use a cheap 100W power amp kit, a frequency generator, and an output transformer to build a re-generator for synthesising accurate, clean 50Hz AC. I was wondering how many of the turntable lovers here dream of having such a gadget. This will have a much more tangible and measurable impact on the TT sound quality than all those power cable rolling and other tweaks we TT lovers indulge in all the time.

 

[arj]

The regeneration I use by Monarchy audio does exactly that but with a 150W power amp and the impact is pretty significant even with digital equipment since the transformers in the re generator keep the digital isolated from the rest of the system.

 

[tcpip]

Ya, I can believe that.

 

[greenhorn]

The official spec of mains frequency range, adhered to by all distribution companies, is +/-3%. This means for a 50Hz nominal frequency, the discom will do nothing if it is anywhere between 48.5Hz and 51.5Hz.

Depends on the frequency of the variance. If it's a long term drift, I don't care. If it's a low frequency wow, still not really that concerned. But if it gets into flutter, it becomes concerning, but beyond a certain point, if the flutter frequency is high enough, the belt and the inertia of the platter should be able to damp it


This regenerator sounds like an online sine wave ups minus the power backup. Am I missing something here?

 

[jls001]

It's the frequency variation of the mains power constantly fluctuating? Or does it drop/increase and stay at some freq other than 50 Hz?

If it's fluctuating, it should show up as speed variation but if it's fairly stable though of wrong frequency, it will be much harder to notice.

 

[arj]

Depends on the frequency of the variance. If it's a long term drift, I don't care. If it's a low frequency wow, still not really that concerned. But if it gets into flutter, it becomes concerning, but beyond a certain point, if the flutter frequency is high enough, the belt and the inertia of the platter should be able to damp it

you will get wow due to power only of the frequency changes a lot ..which may happen only due to some rare loads.What is happening here is that your speed is consistently lower and hence you will hear distorted sounds. Unless you have some kind of auto speed corrector every AC motor will have that problem

But if the frequency is continuously say 49 and you have set your turntable to 33.33 based on that, you will not have a problem. The problem I have is different times of the day the speed keeps changing. hence the regenerator

This regenerator sounds like an online sine wave ups minus the power backup. Am I missing something here?

I am not sure of the online UPS design , but I understood it as a Rectifier to convert to DC and then an inverter to convert to AC in order to give higher efficiency ( 90% and above) . Amplifiers ,I would guess , must have a much lower efficiency ( 80-85%depending on load) and are more expensive

 

[jls001]

Depends on the frequency of the variance. If it's a long term drift, I don't care. If it's a low frequency wow, still not really that concerned. But if it gets into flutter, it becomes concerning, but beyond a certain point, if the flutter frequency is high enough, the belt and the inertia of the platter should be able to damp it

Both my turntables are AC synchronous types and both have (stupidly) heavy platters. Neither uses electronic speed control. I have never felt a speed variation. I do check platter speeds occasionally using a regular strobe wheel and calibrate as needed. I think the high momentum of the heavy platters is doing a good job of masking speed variations, if there is any.

 

[tcpip]

Both wow and flutter are fluctuations which are much quicker than the AC mains frequency changes. The frequency changes will change the tonality of the music. As I was saying earlier, something which sounds sharp and dynamic now may sound a bit dull when the speed is 2-3% lower. I think this is the kind of difference based on which an audiophile chooses his cartridge or speakers. It's definitely audible.

 

[greenhorn]

Both wow and flutter are fluctuations which are much quicker than the AC mains frequency changes. The frequency changes will change the tonality of the music. As I was saying earlier, something which sounds sharp and dynamic now may sound a bit dull when the speed is 2-3% lower. I think this is the kind of difference based on which an audiophile chooses his cartridge or speakers. It's definitely audible.

When i first heard jim reeves on CD, i was rather taken aback - I was used to hearing him though our cassette player which ran slower, and made his baritone sound even deeper than it was - Somehow removing that made it feel like i was missing something.
Modern pop music did sound better though.
Speed being low is something that should be fairly easy to diagnose.


my TT was noticeably slow earlier because its pulley had sagged, and was rubbing - After fixing it, the speed difference was no longer noticeable. I tried a comparison with my SL1200 running identical LP's. starting at an identical point on the record. Yes, it did finish slower, but the difference was very small, and not particularly noticeable

 

[Hari Iyer]

tcpip, I have different views about your observations. I always have a habit of measuring my line frequency whenever I remove my multimeter for some other work. It's not for doing any work on it, but just for fun. I have always observed that atleast in my area the line frequency is always 50 Hz or max 51 Hz. This is 99.99% time. As I write this I measured line frequency even yesterday and it showed 50 Hz. I can show this when you plan to visit me.
Imo avariation of line frequency from 50 Hz to say 55 Hz or 45 Hz will cause " Grid" failure.
Thanks,

 

[tcpip]

I have always observed that atleast in my area the line frequency is always 50 Hz or max 51 Hz. This is 99.99% time.

This is Bombay. I doubt even Bangalore has such steady frequency and good quality of mains supply. Most other smaller towns are much worse off.

Imo avariation of line frequency from 50 Hz to say 55 Hz or 45 Hz will cause " Grid" failure.

I totally agree. The internationally accepted range for mains frequency error is +/-3%, which for us translates to 48.5Hz to 51.5Hz. Going to 45Hz or 55Hz will definitely cause severe failures and the load despatch chaps will disconnect sections from the national grid if they see such signs anyway.

 

[tcpip]

When i first heard jim reeves on CD, i was rather taken aback - I was used to hearing him though our cassette player which ran slower, and made his baritone sound even deeper than it was - Somehow removing that made it feel like i was missing something.
Modern pop music did sound better though.

Yes, this degree of tonal change is going to be quite noticeable. Look at the numbers.

An "acceptable" variation range is +/-3%, not in India alone but globally. This means a range of 6% over which the frequency may drift over time. This, in the case of vinyl, translates directly to a range of 6% over which the frequency of notes may change. This is huge. No other analog or digital medium of music playback gives you even a 1% error in tonal accuracy, be it cassette decks or any other source.

Now look at how audiophiles go to great lengths to "tune" their system to get the sound they think is accurate. They will even change RCA interconnects, re-wire their house mains wiring, replace speaker cables, and what not, to get this thing right. All these tweaks have a tiny impact on the sound, if at all, compared to a six percent fluctuation in the measurable frequency of the notes from a vinyl LP. A slower RPM will make the sound "warmer" or "duller", and a faster RPM will make it "brighter" or "more brilliant" or "sharper" or "harsher", much more than any cable swaps will do. And these changes can happen from morning to evening and back again next morning. How do audiophiles tolerate this?

 

[newlash09]

Iam completely dumb at TT's, and haven't ever owned one so far. But if motor speed is a problem due to variation in frequency, will it not be corrected by a optical speed sensor that many of the direct drive TT's seem to be having. Just my 2 ignorant cents