Turntables - what moves the groove.

Idler Wheel and Belt drive turntable experiments.

Turntables:

Kuzma Stabi S

(stock photo)

AC synchronous motor, conventional bearing, aluminium platter with rubber/textile mat and rubber ring insert, rubber belt, brass plinth and arm support, no suspension. 

Scheu Premier

(stock photo)

DC regulated motor, inverted ceramic bearing in oil bath and damped by shot filled enclosure, treated acrylic platter, acrylic arm support, non-elastic, plastic thread, no suspension.

Kuzma Stabi XL

Two AC synchronous driven motors with controller, two rubber belts, inverted ruby bearing in oil bath, acrylic and aluminium sandwiched platter, massive brass plinth and arm support, no suspension.
(Kuzma has since upgraded to a three phase, frequency controlled DC motor and precision, non-elastic belt.)

Leno L75 Heavy Platter

Shaded pole motor driven with Martin Bastin motor controller, conventional, overbuilt bearing house with ruby bearing in oil, zinc alloy platter, idler drive, slate and stainless plinth (OMA & PTP4), no suspension.

Garrard 301 - grease bearing

Shaded pole motor driven with Martin Bastin motor controller, conventional bearing with grease. Bearing house mounted into massive bronze and stainless steel support, spun aluminium platter, idler drive with flywheel and brake, slate and stainless steel plinth, no suspension.

Galibier Stelvio

Very low Torque, battery powered, regulated DC motor, high precision - over sized - conventional bearing, oil and shot loaded plinth, arm support and platter. Platter also has brass and graphite inlays, non-elastic, plastic tape belt, no suspension.

Platine Verdier

High torque, low inertia, core-less DC regulated motor, battery power supply, inverted hydraulic bearing with magnetic support, heavy aluminium platter, non-elastic, linen thread, terrazzo plinth, pneumatic and spring suspension.

The Galibier platform was chosen to experiment with a variety of different motors and belts: Pabst motor driving Galibier platter with plastic belt.

Motors:

AC synchronous, AC synchronous with voltage and frequency control, Garrard shaded pole, Lenco shaded pole, non regulated DC, regulated DC, Speed controlled DC.

Belts:

Rubber, non elastic plastic tape, nylon string and linen string.

Higher compliance cartridges were used with low/medium mass arms. 

Lower compliance cartridges were used with high mass arms.

Both type arms were installed on each turntable for easy comparison.

Decca H4E, FR66S, Garrard 301

Idler Drive Turntables:

1) Lower compliance cartridges performed best with stronger motors and drive systems. The sound gathered impact, frequency extension and presence.

2) Higher compliance cartridges were more affected by the noise of these decks. Presentation lost integrity, depth and sometimes became edgy and fatiguing.

(Idlers need to be tuned and adjusted to reduce noise. A stethoscope is very helpful)

Belt Drive Turntables:

1) Higher compliance cartridges performed best on low noise, high mass systems. They were also more sensitive to platter mats and clamps. Some slippage seems to work better than tighter coupling to motor.

2) Lower compliance cartridges stressed the motors and drives systems significantly more and lost extension and impact. Here they sounded soft and loose.

(Elastic belts did not perform as well as non elastic belts on belt drive turntables. Non elastic belts need to be tension adjusted. Some of the DC motors were too weak and this created slow speed variation, the greater the platter mass the slower the variation. This added an artificial lushness as well as uneasiness. The Galiber was a good example of this)


Thoughts:

1) Varying drag is caused by groove/stylus interface. Average drag is changed by the compliance of the cartridge - low compliance cartridges have greater overall drag than high compliance cartridges with peaks which are logarithmically greater.

2) Sensitivity to noise is relational to cartridge compliance - low compliance cartridges are less sensitive to noise than high compliance cartridges.

3) Motor torque and cartridge compliance matching is indicated as in tonearm mass and cartridge compliance matching - wild cards aside. Cartridge compliance and the motor type (combined with drive type) matching seems to be overlooked especially in regard to low compliance cartridges. Reduction in noise has been given more attention than has the need for strong motors for low compliance cartridges.

4) Different motors have different characters in sound, just like cartridges and tonearms.

Conclusions:

The motor is the foundational component of the turntable.

Nothing is more important than something that is not doing its job well or not matched well. e.g: Better to have a well setup and matched Denon 103 on a heavy arm and idler than a Koetsu on a light arm and/or weak motor.

Select the elements to match. e.g.: Run a Koetsu on an idler with a heavy arm to hear what it was designed to do. 

Summary:

There is extensive data on cartridge / arm combinations but very little on motor and cartridge relationships. The above experiments indicate that a motor is as much a consideration as a tonearm or cartridge and that the three elements should be considered together. When the variables of greater drag for low compliance cartridges are considered this is a logical and natural conclusion. 

Conjecture:

A shaded pole motor (found on Garrard,  Lenco and others) is an inductive device, like a choke, and resists changes to speed inductively. Stylus/groove interface is measured in microns and is sensitive to small changes - as the groove moves under the stylus the motor is compensating to maintain speed. I propose that the nature of the way it compensates greatly influences the character of the sound. "Natural Motion" was a term used in an old tube manual concerning chokes and is perhaps a hint why the shaded pole motor has been favoured in many turntable applications of note.

Thank you for reading.

Flux cycle of an ac shaded pole motor (animated).


Other information:

Cartridges used:

Koetsu: Coralston, Onyx, Urushi MKI, Longbody, Fidelity Research: FR-7, FR-7f, MC702, Decca FFSS: H4E, MKII (mono), Dynavector: DV XX-2 MKII, Denon: 103 Ebony, Accuphase AC-2, Signet TK-7su, Audio Technica: AT -ML180, AT-25, Kondo IO MKII, Allnic Puritas, Benz Micro Scheu/Glider.

Tonearms Used:

Fidelity Research: FR64s, FR66s & FR64fx, Ikeda 407, Triplanar MK VII, Reed: 2A & 3Q Audiomods Series Five, Kuzma Airline, Analog Instruments: Apparition & Siggwan, Scheu Classic,  Acus Lustre, GST-801

Cartridge dampening also has a quantifiable effect on drag. Look at the difference of the Decca from the others...

(Determination of Sliding Friction Between Stylus and Record Groove, - Robert Pardee)

M. Hulot