Cutting vibrations from a (Garrard) synchronous motor.

[Triumph]

Cutting vibrations from a (Garrard) synchronous motor.

I am using a idler drive TT witch I improved in many ways like the central spindle bearing to make it more silent and create a black background. With an idler drive you always have the problem that the idlerwheel and therefore the motor makes a direct contact with the platter. If the motor vibrates, and the synchronous motor from my old Garrard does, so the vibrations is detectable, hearable.

I was therefore in the process of replacing my synchronous motor with a more silent DC motor. But I remembered me an article about reducing the voltage on a AC-motor to reduce vibrations. After research I discovered that might help. Loricraft-Garrard does it with the 301-401-501 types and I understand Linn does it with some types of powersupply (high voltage to start the platter and on speed cutting the voltage). So I thought to give it a try.

I took a simple small light dimmer, cheap version €12,- suitable for halogen as well. And placed it between the mains of the turntable. By turning the wheel from the dimmer at more than 15 degr. the motor stopped with some noise so maximum cutting of voltage is only about 10 degr. I measured the voltage is was 202 Volt. Then I used my stethoscope (ideal for detecting vibrations, even a toy version works!) and noticed indeed a reduction of about a third of the vibration noise. I tried it several times, about third was cut.

But now the strange thing; with my stethoscope I heard a reducing of about a third of the vibration noise but after listening records the rumble was reduced far more, at least 2/3 and almost not hearable any more. Strange.

I was very exited of this improvement and therefore like to share this with you. Probable the trick is well known but I could not find it so easy on this forum.

Note: the Garrard I am using is old, from the time that the voltage in the Netherlands was 220V now the voltage in almost whole Europe is 230V so this is maybe the reason in my case it works fine.

[Nanook]

basically an adjustable AC voltage transformer. They are quiet and will allow a finer adjustment of the Voltage.

"Dimmers" (at least here in N.A.) are terrible anywhere near an audio system. The potentiometers are usually not very good and "rattle" at lower voltage.

The fact that reducing the motor noise by approx 1/3 results in an overall reduction in noise of approximately 2/3 suggests that the turntable has other issues (probably mechanical) and that the motor noise has a profound on these other mechanical bits.

stew

[sreten]

Hi,

Thyristor / Triac (simple light dimmer) control of a synchronous motor
is not a good idea. (unless its an electric drill .... not synchronous)

A simple voltage dropping resistor is a far better idea. A variac
even better with its noise filtering but far, far, more expensive.

Perhaps the motor needs a service and possibly new mounting rubber.

/sreten.

[pjpoes]

First, I'm a little confused, but I am not familiar with Gerrard turntables either. It was my understanding that the Thorens TD124 Idler drive still has a belt between the idler drive wheel and motor. This would imply to me that there is no more of a direct connection of the motor to the platter than a belt drive. I didn't think the motor was directly connected to the idler wheel in any way, just through a belt.

As for motor reduction, most people find that a reduction of motor noise has a pretty profound effect on rumble noise and thus background noise. I wont try and quantify it, but I to have felt its as big if not bigger than many other changes we make such as cartridge or tonearm.

The best way, as I understand it, to reduce motor noise is to ensure that a perfect sinwave is sent to the motor, and that the phase shifted wave is equally as perfect, including a perfect shift. Most turntables, yours included, use a capacitor to cause this shift. Capacitors aren't perfect for this, not only is the shift not perfect, but variations in the caps value can create variations in the degree of the shift. You may want to check that and make sure it checks to factory spec. Additionally, some have suggested that, with an oscilloscope, you could try different cap values until you get the right amount of phase shift.

An even better way is to actively synthesize the 60 hz or 50hz sine wave and the shifted sine wave, so that it can be adjusted more precisely. Such devices aren't so cheap to impliment, nor that easy, but is is basically what Thorens, Rega, Linn etc all do to minimize noise. The reduction in voltage helps, but is not as profound as ensuring the right phase shift.

[Nanook]

idlers by definition use a wheel that is in contact with a motor shaft, and with the platter.

AFAIK (and I own a few), the Garrards use this, Thorens and Lenco (as well as Bogen, Rek-o-cut, etc). pjpoes : I think you may be confusing idler wheel turntables with flywheel style, such as some of the VPI models that use a belt between the motor and a flywheel, and the flywheel and platter.

As I previously stated (and sreten reinforced this), a variac is the best way to go, but usually quite expensive.

Triumph, the end result is what we are all after. But do check the condition of the idler wheel (including bearings), the motor mounts (often rubber and most likely aged hardened), and the motor operation itself.

I've toyed with the idea of making a new, from scratch, idler wheel turntable. The need of course is for a robust and quiet motor, good bearings for the idler wheel itself, and some sort of soft material for the friction surface of the idler wheels. And a platter, main bearing, voltage controller, etc....

stew

[sreten]

Hi,

Some synchronous motors are shaded pole, direct mains power, no capacitors or resistors.

/sreten.

[Triumph]

Hi,

Sreten wrote:

Thyristor / Triac (simple light dimmer) control of a synchronous motor is not a good idea. (unless its an electric drill .... not synchronous)

Maybe not so good idea but…..it works just fine with my Garrard.

Sreten wrote:

A simple voltage dropping resistor is a far better idea. A variac even better with its noise filtering but far, far, more expensive.

Because of this great success I am searching for a variac. Don’t mind of spending a few €, I know it works.

Sreten wrote:

Perhaps the motor needs a service and possibly new mounting rubber.

The motor is just fine. I checked the bearings and mounting rubber. I service this machine myself.
It is the voltage!

Sreten wrote:

I didn't think the motor was directly connected to the idler wheel in any way, just through a belt.

There is no belt.

pjpoes wrote:

As for motor reduction, most people find that a reduction of motor noise has a pretty profound effect on rumble noise and thus background noise. I wont try and quantify it, but I to have felt its as big if not bigger than many other changes we make such as cartridge or tonearm.

The change I made on the arm and spindle bearing had a greater effect but that was because both were of very worse quality. But indeed a silent background has a great effect on the sound tough. I am very pleased with this improvement.

pjpoes wrote:

Some synchronous motors are shaded pole, direct mains power, no capacitors or resistors.

Indeed my Garrard has no capacitor or resistor.

IT WORKS!!! Both detectable with my stethoscope as well with a record. And I am not surprised when it works with more synchronous motors. Tune the voltage with a stethoscope, there is a certain minimum vibration when you change the voltage. In my case it was 202Volt. Lower and it start to vibrate again, until it stops with a lot of vibration.

On this site you can read this:

Once I was satisfied with the arm and cartridge, I plugged the Garrard into a $40 variac that I had purchased off e-bay. Like many turntable motors, the Garrard motor runs with less vibration at less than maximum voltage. My mains voltage is 117v. With the variac, I found that I could drop the voltage to 104v without losing speed. Below 104v, the speed drop could be compensated for by adjusting the eddy brake. Below 92v, the sound quality disappeared. With a little experimentation, I found that 100-102v seemed to give the best sonics.

But again the voltage in Europe is now 230V it use to be 220V.

[pjpoes]

Ah well, like I said, I don't know Gerrard tables, just Thorens. The Thorens uses a belt by the way. I don't know if they ever made an idler wheel with no belt.

Thorens TD124 Description

The TD124 that I am familiar with has only used a belt attached to the idler wheel though. This was true in both the version I and II. You can see the description in the link I sent. It would be incorrect to say that all idler drives imply a direct connection to the motor, but apparently, as is the case with this Garrard, its true of some.

Is the motor in the garrard similar to that used in the old empire grease tables? Well ok, the cap issue wouldn't matter anymore if they don't use a cap for phase shift, and I don't know how these motors work, but I would assume that a synthesized 60hz sinewave would still be better than direct out of the wall in reducing noise. I would even think a decent T filter would improve things.

[Nanook]

really should not be classified as an idler drive then. It would be safest to qualify it a a hybrid.

In this case it seems that it hardly matters (TD124). As I haven't looked at the guts of one , I assumed that if described as an idler,it was. The Garrards I am familiar with use different drives, one with idler (the Lab 80), and one with belt (the Z100 SB).

Regardless, the motors can be silenced as described. And as long as the bearings for all the wheels are good (on the Thorens) then everything else that holds true for the Garrards should hold true for the Thorens, regarding the basic table.

stew

[pjpoes]

yes yes, I am not actually trying to reduce the vibrations on mine. I agree that a variac is a good idea, I was just suggesting that improving the signal is important too, if not more important. A resynthesized 60hz AC signal made a bigger difference on my turntables than anything else I tried. Not that a lower voltage didn't also help immensely, but the quality of the AC is very very important.