ANALOG SOUND

Analogous recorded sound has a far higher resolution than sound recorded in any given digital format. Both the analog tape and the long playing record contain millions of variations in loudness and frequency. Both the analog tape and the long playing record have - contrary to what music lovers and some technicians tend to believe - many, many times more bits so to speak than the 16, 20, 24, 32 or 64. And of course there is no steep filter in the top and no noiseshaping, multiplication of frequencies and other renderings of the sound to suggest high resolution. If compared to tape recorder and LP, the resolution of each and every digital recording format, really looks poor.

 

ANALOG TAPE RECORDER

The drawback of the audio tape recorder however is its essence: the recording and playback heads. They have coils and gaps. These need to be manufactured in accordance with very strict parameters. Even then one can easily hear the difference between a record cut from a tape and a recording which is cut direct-to-disc during the actual session, the performance.

And then there is the infringing effect which noise reduction techniques like Dolby have. These should be applied with the utmost precision. It is better not to use them at all. But the record companies wanted to eliminate tape hiss and used Dolby. Any incision in the audio band which will be restored with the utmost care is detrimental to the natural harmonics and the transient response.
There are other techniques like compression and the use of limiters that do deteriorate the analog signal even further. Better not use them.
There is one incission in the frequency curve that cannot be avoided and that is because of the RIAA correction that "cuts" the frequency band in two. The low frequencies are engraved with de-emphasis and the high frequencies have a pre-emphasis. That results in the necessary turn over frequency in the RIAA curve. See at the end of this page Phono Cartridge Optimizing

VINYL RECORD

The drawback of the vinyl record is that engraving the lacquer and retrieving the signal from the vinyl is a mechanical process. The signal is read by a diamond tip which is connected to a rod or tube (cantilever). This tube or rod has on the other end a small magnet which moves in between coils (MM cartridge) or it has tiny coils attached to it that move in a magnetic field (MC cartridge). The cartridge is in essence a dynamo generating variations in electricity.

A disadvantage of the long playing record is that (because of the chosen speed of 33.3 revolutions and the chosen size of 12") the quality of the signal is highest at the beginning (periphery) and lowest near the label. Yet the importance of the reproduction of music by means of an analog medium (be it LP or tape) is that it has a wide frequency band, has a high resolution and contains the complete harmonics of acoustic instruments. See also Compact Disc History: 25 Years CD

 

CONTROLLED SPEED

The diamond tip is limited in its movement. The tip follows the meandering of the groove. When a loud passage occurs the groove has a more complicated pattern. This complexity will increase the movement of the diamond tip The contact between needle tip and groove wall will put some strain on the cartridge and it will tend to slow down the turning of the record - even if it is just a tiny bit, it will be noticed.
Therefor the steady and unrelentless turning of the record at the chosen speed is a must despite the fact that the changes in the groove are mere micrometers!

If the record slows down at the occurrence of, and during loud passages of music, each and every instance will be spread out. Hence a drummer's attack and the heavy chords of a pianist will sound muddy and the trumpet player will miss strength and the sharp tonality.

CONSTANT TURNING

A perfect and steady turning of the record is of the utmost importance. This is why an EMT, a Thorens TD 124 and a Garrard 301 and 401 (and also the early Goldring/Lenco L 75 and the later L 78) each have a heavy platter, a strong motor and an idler wheel which make the platter turn in a steady fashion, without a trace of slowing down when loud and complex passages suddenly occur. A slip free contact of record and platter is a must. The immobility of the record can be improved by the use of a record clamp, spindle weight, a vacuum mat, and/or a stabilizing ring.

RUMBLE

The acoustical isolation (separation) of motor and platter should be maximal. When the transmission takes place via an idler wheel, the circumference of the idler wheel needs to be impeccable. If not, the values of rumble, wow and flutter will be increased.
The rubber of the idler wheel should be durable and should not transmit motor vibrations to the platter at the same time. In the Thorens TD 124 the engineers de-coupled the idler wheel from the motor by means of a belt.

FLOATING CHASSIS

In the nineteen sixties Edgar Villchur and Roy Allison (and it is said that Mitchel A. Cotter was involved as well) of Acoustic Research devised a mechanical construction for a record turntable. The way it was designed eliminated or reduced mechanical vibrations and it was what is called now the independent sub-chassis (floating chassis) on which platter and arm are mounted. This chassis rests or hangs on springs (floating suspension) and the motor is completely separated from it. The only connection with the motor is a belt or a thread which has the function of a spring as well without imparing speed accuracy.

Although the first turntable using this principle was made by Acoustic Research, belt drive turntables existed already before the AR-1 was introduced. But this construction was new and effective and therefore it was later copied by Thorens and Ariston. The Linn people produced their LP12 on the basis of the Ariston turntable for which they initially manufactured parts.

HEAVY PLATTER

At the end of the nineteen seventies several manufacturers began using a heavy platter (6 to 20 kg) with the bulk of the mass concentrated at the periphery in order to achieve extraordinary values for wow, flutter and constancy of speed: Thorens Reference (Referenz), Platine Verdier, Melco and Micro Seiki.

If the shaft (spindle) and the bearing are engineered from the best materials and to close tolerances, the playback of an Lp can give stunning results if arm and cartridge are also of a high quality and well set up.
See Notes on The Belt Drive Turntable.

DIRECT DRIVE

There exists another method of achieving accurate reading of the record's signal. That method is letting the platter rest directly on the motor shaft. In fact the shaft of the motor is the spindle of the platter. The platter is in place of the pulley. In this case a heavy motor is necessary as the platter is directly connected to it. The strength of the motor (its accuracy and its torque) can be used completely while eliminating any transmission by intermediate parts. Since motors do not turn smoothly but rotate in steps (the more poles the smoother the rotation), the turning has to be regulated electronically, has to be smoothed out, in order to achieve a continuous and even turning.
This principle is called 'direct drive'.

FIRST DIRECT DRIVE PATENT

Thorens developed a direct drive motor way back in the nineteen twenties. Thorens applied for a patent for this direct drive turntable motor, tourne disque in French. On the document is written: "TD à commande directe". It was issued by the "Bureau fédéral de la propriété intellectuelle" (Federal Office of Intellectual Ownership) in Switzerland, on June 21, 1929 and was described in the "Exposé d'Invention". Thorens however refused to use a direct drive motor in the music lover's turntables. At the time the technique was probably too expensive to make it work to perfection. Thorens applied the direct drive technique in the nineteen seventies in their studio turntable. And so did EMT. It was their answer to the success of the Technics direct drive turntables, especially the SP-10 mk2 turntable.

ON A WOODEN BASE - SH-10B2

The SP-10 had a 20 pole 60 slot DC motor driven at 15 Volt. The platter reached nominal speed within half a rotation of the platter at 33-1/3 RPM. The player had two speeds: 33 1/3 and 45 rpm. These were adjustable. The pitch control had a margin of +/- 2%. Wow and flutter measured 0.03 %. Rumble values were -50 (DIN A) and -70 dB (DIN B). The weight of the platter was 6 lb. - appr. 2.720 kg. A wooden base plus acrylic cover were available as extras. Equipped with an oil damped Technics tonearm the turntable was named SL-1000. Without base and arm it was the SP-10.

SP-10 (Mk1) MOTOR

The motor in the early SP-10 is the same as in the SL-1100. It does not have the strength and torque of the later SP-10 Mk2.

SL-1100

Turntables that worked along the same principle were introduced: SL-1100 (motor deck plus EPA 110 arm), SL-110 (without tonearm), and SL-150 (without tonearm).
At left you see the SL-110 with the original Technics tonearm for the SL-1100.

SL-110

At left you see the SL-110 with a Decca International arm. The machine looks quite impressive with its high platter, the strobe-light in front on the left and a beautiful wooden armboard with white markings.
Like the SP-10 it has a facility to adjust the two speeds to a certain degree, similar to the original SP-10 which is +/- 2 %. Because of the less effective de-coupling by the four feet, the sonics could not entirely match those of a Thorens TD-125 floating sub chassis turntable for instance.

TECHNICS CATALOG LP

A tool in the clever marketing by Matsushita/Technics/ Panasonic of their direct drive turntables was the release of a special Technics Demonstration Lp in a gatefold cover picturing the range of DD turntables: SP-10Mk2 (SL1000), SL-1100, SL-1200, 1300, 1400, 1500, 1800, etc. At left the Dutch edition. I am not sure if this was a typical Dutch affair.

SP-10 Mk 2

In 1975 the SP-10 Mk2 (together with its Power Supply SH-10E) was introduced. It was a great step forward if compared to the technique of the Mk1 and other DD-turntables. The functioning of the Mk2 was quite different. Now -to put it simply- the motor was turning at a given speed which was steered by a set frequency which was generated by a quartz crystal. Hence the turntable's performance is not affected by any altering in the frequency of the mains nor any voltage fluctuation. A fluctuation in speed is instantly corrected by the motor itself without the use of a tachometer or a playback head which reads the magnetic imprints on the inside of the platter (a method Denon used in their DD turntables). This meant a mere perfect performance as far as speed accuracy, wow and flutter are concerned.

In order to avoid fluctuations from temperature and those caused by mechanical parts no speed adjustment facility (variable pitch) was incorporated. This was a drawback for people with perfect pitch and for those music lovers who wanted to play a variety of old shellac records which are not always cut at 78 RPM.

A new and unique feature of the SP 10 MkII was the incorporation of a mechanical and electronic brake not encountered on other DD turntables, not even the SP10MKI. It reminded of the direct start of the EMT turntables and the clutch of the Thorens TD-124 and it made the SP-10 Mk2 a true Studio Turntable. Many radio stations installed the Mk2 for playing 33.33 and 45 rpm discs for the broadcast of music programs.

By increasing the capabilities of the motor and designing refined and complex electronics to regulate the motor's rotation (for smoothing out the shocks when moving from one pole to the next) the SP10mk2 attained its practically incomparable specifications.
(Technics applied this principle -except for the breaking feature- lateron in the newer, less costly MK 2 versions of SL1300, SL1500 and SL1800. And these SL 1310, SL 1510, SL 1810, etc. got a new styling in the Mk2 versions. Although these turntables in the lower echelon were a step ahead of the earlier SL110, SL120 and SL-150, they could not match the sound quality of some high quality, heavy, belt drive turntables with a floating chassis or the Thorens TD-125 Mk2 for example.

Instead of the soft mat which was used on the earliest SP10 (SL1000) and SL110, now a hard mat adorned the heavy platter. The hardness is not without significance for the sound performance which is an essential feature of the SP10Mk2.

It goes without saying that an Mk2 or Mk3 is practically worthless without the appropriate power supply (SH-10E). A power supply is hard to find separately. And if only the motor is offered in an auction you will never be sure to find a separate power supply unit (PSU) and you will not be able to play records with your SP 10. For an expert it would be possible to build a power supply as in the Service Manual all circuits and values of components are given.

The platter of the SP-10 mkii weighs 2.9 kg / 6.4 lb. To prevent a turntable platter from sounding like a bell, the inside has to be covered with a sound absorbing material. This can be a layer of a resin like substance as with the early Melco turntables or - as in the case of the Technics SP 10 mkii - with a relatively thick bituminous sheet. Of course not in the middle part which is connected to the motor section.
The turntable has a starting torque of 6 kg/cm-2 (5.2 lb.inch-2). The moment of inertia is 380 kg/cm-2 (130 lbs.inch-2) a starting time of 0.25 sec. to reach the nominal speed. The motor of the later SP-15 model has half the torque (3 kg-cm) and a starting time of 0.4 seconds.

SHIPPING BRACKET

Note: If the motor unit of an SP10, SP10mk2 or SP10Mk3 is being transported, instructions in the owner's manual have to be followed carefully.

In case of the Mk2, the platter has to be removed and packed separately, and the motor has to be secured with the original metal clamp which should be fixed with three screws to the disc of the motor and with four screws to the chassis.

This in order to avoid damage caused by shock. If the clamp is not available, a clamp should be borrowed or made by you. The omission of a clamp will damage the motor and the spindle and impair its accuracy.

Many prospective buyers and also owners of the SP10Mk2 have asked for details of the special clamp which is necessary if the turntable has to be transported. If your SP-10Mkii does not have this clamp, you can make this shipping bracket yourself or have it made in a machine shop. It is a simple piece cut out of a thin sheet of metal. Aluminum of 2 mm thickness will be OK also. Thinner sheets may bend though.

The seven screws you need to fix the clamp with have the same thread as the three original Technics bolts for fixing the platter. Take one screw to a specialist's shop to buy 7 pieces.

You can e-mail me to receive the real size drawing to make the clamp/shipping bracket.

ORIGINAL SCREWS OF MK2

For many years I had not been aware that the sleeves on the platter screws are os silicon rubber instead of bronze. Rolf Aisenbrey from Germany pointed this out to me.

In some cases the original screws of an SP-10 MKii are lost and have been replaced. At left the original screws. These screws are sometimes offered on eBay.

SP-10 Mk2 CLOSED MOTOR

The MkII has a completely closed motor, similar to the SL110. The relatively large disc which is the top of the motor supports the platter.

In addition to the electronic brake there is an adjustable belt which helps break the motor/platter combination mechanically. Belt and the adjustment facility are hidden under a plate which surrounds the motor/disc so dust is kept out.

INDEPENDENT MOTOR

The stator of the motor of the SP-10 MkII. The motor is a complete unit which in principle can be used for any platter which is not too heavy. Constructing the motors of direct drive turntables in this way was the custom in the 1970's.

OILING THE SPINDLE

Apply two or three drops of oil to the motor shaft.

If oil has leaked out around the rotor of the motor during transportation wipe it with a lint free cloth.

KENWOOD L-07

Kenwood (Trio in Great Britain) manufactured quality turntables likes the KD 500, 550 and 650. Undoubtedly inspired by the vast success of the Technics DD turntable series, they designed a high quality direct drive turntable along with a series of electronics. This was Kenwsood's answer: L-07D, with a powerful motor and electronics, weighing 35 kg. in total, with a periphery ring and turntable weight added. There are many Kenwood aficionados who find their peers via the Unofficial Kenwood Web Site.

SONY PS-X9

There are other high quality direct drive turntables: Denon DP-65, 75 and 80 are well known. Denon and also Sony came up with specific studio turntables: PS-X9 and DP-100M respectively. These are complete systems, tone arm included. Not only the price but surely the design may have been the reason that the DP-100M and the PS-X9 were less popular among audiophiles and serious music lovers who like to add a tone arm of their choice.

DENON - NIPPON COLUMBIA - DP-100M

While the Technics SP-10 and the Denon DP-65, 75 and 80, can be mounted on any sort of plinth and can be combined with a variety of tone arms, the Kenwood came with its own arm and there was a possibility to mount a second arm. Although the Technics SP-10mk2 and Mk3 are considered as studio turntables, Nevertheless audio magazine 'La Nouvelle Revue de Son' in France awarded the DP-100M their "Decibel of Honor" (Décibel D'Honneur).
(The four pictures of the DP-100M below, courtesy Richard Huxley from France.)

The DP-100 boast of a very strong and heavy motor which is used in quality cutting lathes. Wow and flutter is also excellent: 0.003 %. The heavy chassis and motor rest on appropriate springs in order to isolate the chassis and platter from the environment: mechanical feedback is practically non existent.

The magnetic pattern on the inside of the platter is read by a recording head as used in tape recorders. The recorded signal is compared instantly with the frequency of the quartz crystal in the electronic circuitry for steering the motor. The smallest deviation is recorded and corrected.

SP 10 Mk III

Technics went even a step further in designing the perfect turntable. In 1981 the SP-10 Mk 3 was introduced. It had a platter consisting of a copper alloy inner section and an aluminum outer part, weighing a mere 10 kg = 22 lb. and the complex electronic circuitry to regulate the speeds and constancy of the rotation of this heavy platter. The total unit itself weighs 18 kg (=40 lb.). This machine was not sold in great quantities because digital media were emerging on the horizon and few owners of an SP-10 mk2 saw the need of switching to this newer version of turntable. In hindsight they may regret it.

VARIABLE SPEED

The advantage of the Mk3 is not only the practically unmeasurable wow and flutter, but the fact that now all speeds can be adjusted in 0.1% steps to +/-9 % which makes this unit ideal, also for transfers of all records including all sorts of shellac records. Note: if you look carefully you can see that the SP-10 Mk3 has a softer turntable mat (at least in the picture) compared to the mat on the SP10Mk2 which is harder.

PRICES

Stereo Buyers' Guide (USA) from 1989 still lists both SP-10mk2 and Mk3 turntables and their respective bases (plinths). Prices were then:

OPEN MOTOR

The newer generation of Technics turntables introduced at the end of the nineteen seventies/beginning of the nineteen eighties do no longer have a closed motor compartment. Now the stator with the green coils (core) is solid with the plinth/chassis. The bearing housing of the spindle is fixed in the center. The supporting disc on top of the spindle is actually very small. This "simpler" method of construction was applied in the Technics SP-10Mk3 design and later found in the cheaper models like SL 1810 and SL 1310, the 10 referring to the SP-10. (In the cheaper models the spindle may just rest on a thrust plate fixed to the print board with the electronic circuit. This cheap construction does not allow a heavy platter.)

HEAVY PLATTER

At left the underside of the heavy platter. Much of the weight is of the large ring with magnets: the rotor. The mass is not concentrated at the periphery of the platter as would be the case with heavy belt drive designs. Not in the SP-10 Mk3 because that would slow the starting and stopping time of the platter. It is obvious that care has to be taken to prevent dust to settle in the stator and rotor. Check and clean with compressed air from a can (Dust-Off) or use a hair blower set to cold. Then you can put the platter back again.

The turntable has a starting torque of 16 kg/cm-2, nearly three times the value of the SP-10 mk2.

The rotor and stator of the SL 1810 (shown below) are of course less sturdy and quite small if compared to the large and heavy rotor and stator of the magnificent SP-10 Mkiii. The electronics of the simpler turntable match of course this small motor with light platter and do not differ much from the design of the later SP-15 and SP-25.

WARNING

3. Never let dusts or iron fillings come in contact with the rotor magnet.

4. If lubrication becomes necessary after approximately 2,000 hours of playing, remove the turntable platter and apply 2 or 3 drops of the enclosed special oil to the top of the bearing.

This goes for the SP10-Mk3 and the similar cheaper models. The Mk2 has a small hole next to the spindle for applying a few drops.

HANDLE WITH CARE

The platter of the Mk3 consists of an aluminum base topped by a copper platter. The aluminum platter connects directly to the spindle.
The copper top platter is connected to the aluminum platter with four screws. Before lifting the platter, the small centering disc has to be removed by means of a special tool.

You need two handles for carefully lifting the heavy platter.

Pictures of the Mk3, rotor, stator and platter with handles courtesy photographer and audio enthusiast. Albert Porter.

VOLCANIC GLASS

The technicians of Technics designed a special base for the SP10 mk2. It was made of obsidian (volcanic glass) which had a nice shape and was beautifully polished. Hi-Fi Choice from Great Britain however reported that the bass in the reproduction was somewhat slender and that there was some shallowness in the mid and upper mid frequency region. This is certainly caused by the amorphous "structure" of volcanic glass. Glass sometimes used for plinths, racks and platters has this same characteristic. The use of glass is not recommended.

OBSIDIAN BASE FOR MK3

The Technics SP-10Mk3 was a totally different turntable. The opening for the motor in the obsidian base for the Mk3 is a round hole and it can not accomodate Mk2.

EPA 100: OIL DAMPED TITANIUM TONE ARM

They also designed a special arm to match the new SP10MkII by using a very innovative damping mechanism with an oil reservoir inside its counterweight, and by applying the then new space age material titanium: EPA 100 (1976). The titanium arm tube and the damping of the resonance by means of an oil reservoir in the counter weight made the signal very precise and clean. Also the head shell contributed to that much controlled signal. The arm is intended to be used with relative low compliance phono cartridges. The sound with the EPA 100 is somewhat less chiseled and vigorous, but rather dull, if a high compliance cartridge is mounted.

EPA 500: INTERCHANGEABLE WANDS

Technics introduced a tone arm with an even more revolutionary design: EPA 500 (1979) with various arm tubes for use of a variety of cartridges from low to extremely high compliance. The arm consist of the base EPA B 500 and the arm unit EPA-A501H.

SLATE

At left my second SP-10 Mk2 mounted on a 30 mm thick slate (stone) plinth. It needed special care when de-coupling the base to the cabinet/surroundings.

ADAPTATIONS

Instead of the A501H other arm tubes can be inserted: A501M and A501L with more mass, for medium complaince and low compliance cartridges respectively.

Technics EPA-100P Tonearm

Japanese brochures often show images of the black version of the EPA-100 tonearm. There is yet another black version of the EPA-100 and that is the EPA-100P. It is a tonearm specifically made for broadcasting sound studios and radio stations where a more sturdy use of the equipment is inevitable. Thomas Kiefer from Germany wrote to me about this tonearm. The EPA-100-P has no facility to adjust VTA. The arm in his possession does not have a lift either. But the image he sent me of the total broadcast SP-10Mk2 shows that the arm support is obviously lowered and raised by means of the switch at right in the front of the plinth. Furthermore it has a safety bracket so the arm cannot sway and drop when accidentally touched.

More Differences

At left is another image he sent me. He says that the mounting hole is larger than that of the original EPA 100. The counterweight (which is not oil damped) comes in two versions, a heavy one and a lighter one. These should obviously be chosen in relation to the cartridge used. The heavier weight is meant for heavy cartridges like those of Fidelity Research and the old Ortofons. The lighter weight is to be used with common cartridges weighing more or less 10 gr.

The Antiskating range is adjustable by turning a knob. The highest indication on the scale is 4 which means that also mono cartridges playing with a relative substantial down force can be used. On the common EPA-100 there are two horizontal bearings (red rubies). They can be spotted on the sides. On the EPA-100P however these are metal bearings as far as can be seen.

Thomas Kiefer did send these four images. Anyone who has information and/or specifications is invited to take action and help out: Click to send an email.

Technics SP-15 and SP-25

The EPA-500 was initially intended for the SP-15 turntable which has the values for accuracy of speed, rumble, wow and flutter of the SP-10 MkII. However the motor was less powerful, 11 Watt for the SP-15 and SP-25, and 26 Watt for the SP-10 Mk2. But the SP-15 and 25 have the possibility to adjust the three individual speeds by a margin of +/- 9.9% like the SP-10 Mk3. The deck includes the electronics which are hidden by a circular cover. The unit easily fits the SH-15B1 base. And it should be no problem to construct a DIY base with the appropriate circular hole. If prices a SP-15 or SP-25 turntable is being offered for higher prices than appropriate for the SP-10Mk2 or Mk3, one should decline.

SH-50-P1

The SH-50-P1 is a beautiful analog scale for measuring the down force from 0.5 gr. to 3 gr. Modern digital scales are of course more accurate in displaying the values. But when using this electronic scale a while, it is easy to know what the positions between the markings mean. Though the user should be born with a carpenter's eye.

Because of the high torque the platter of both SP10mkII and mkIII starts within a fraction of a second. There is an electronic and mechanical stop. When the platter is not spinning it is mechanically locked, hence the SP10 is not suitable for scratching even if the mechanical brake has been disabled (which can be done). The time of mechanical braking (the speed) can be adjusted to one's own needs. If you want to use this quick start and stop capabilities while the diamond tip is in the groove, a heavy base is imperative.

If you do not own the obsidian base you will have to construct a solid and relatively heavy base and decouple it from its environment by means of insulating rubber feet. Various materials can be used for the base:

• plywood covered with a thin sheet of aluminum (1 mm)
• layers of thin wood glued together
• serpentino (thin plate of stone with a sort of grainy and not too dense structure), and - as some people suggest -
• corian.

Better not use corian as it has a frequency curve with emphasis on high frequencies. The properties of corian are also not always as desired because the percentages of aluminum varies.
And better not use MDF, also because of its odd frequency characteristic which shows uneven sonic qualities with emphasis in the lower mid area. This anomaly may disappear when you use many layers and construct a very heavy base. But then the fact remains that it is in fact "dust" pressed and bonded together.
I myself am not an advocate of too heavy plinths made of materials with a high density. Better choose the material and the volume in accordance with speed of sound and an even characteristic without abrupt filtering of the signal. Look for the data of density, sound propagation, stiffness, etc. in The practicing Scientist's Handbook by Alfred J. Moses (Van Nostrand Reinhold Company, New York, 1978).
The frequency of the isolating rubber feet or springs supporting the base plate (the SP10mk2 unit included) should preferably be between 2 and 4 Hz.

A SOLID BASE

There are many solutions on how to build a plinth for the SP-10Mk2 and Mk3. You can find several proposals with drawings and pictures on the www.
The picture at left was sent to me by professional photographer Albert Porter. It shows the solid base he constructed for his SP-10 mkII with SME 312S (Magnesium), and Air Tight PC1 Moving Coil cartridge.
He used multiple layers of Bass wood and Birch plywood, an aluminum sheet, brass mounts for the arm board, and a relatively heavy piece of iron.

SP-10 MK3

At left the new base Albert Porter made for the Technics SP-10 Mk3 which he acquired. This time other kinds of wood were used. He also made a larger base plate for the SME 312S magnesium arm. But the principle of a solid base and the incorporation of a rod to minimize motor noise remained.

You can see more pictures and read about Albert Porter's base for the Mk2 and Mk3 here.

SPRING SUSPENSION

In his audiophile high-end magazine, The Audio Critic (1979), Peter Aczel and his staff rightfully warned against the use of the Technics obsidian base and any other heavy base on rubber feet if one wants to listen to music at high sound levels via big loudspeaker systems. The rubber feet do not decouple (isolate) the heavy base from its surrounding sufficiently, although the fundamental resonance of the complete system was measured 5 Hz. according to Hi-Fi Choice No. 12 from 1978.

Because of the combination of volcanic glass and the titanium arm with the specific Technics headshell will give some "shyness" in the low bass. On top of that volcanic glass, like any kind of glass, is an amorphous material. It has practically no structure and this somewhat smoothes out fundamentals and harmonics. Glass should be used for esthetic reasons only. Not for the best sound! That is why different wooden bases have been constructed. A famous one was designed by Mr. Kaneta from Japan.
Consequently a glass platter, a glass mat, and glass shelves in your audio rack, do not give the full sound picture.

Peter Aczel tested the Technics SP-10 Mk2 on the special base made by Mitchell A. Cotter, in short Mitch Cotter. The Audio Critic advised the use of this special base (B1) specifically for the Technics SP10 (and also for the Denon DP6000).

In 1980 the German high-end magazine 'HIFI exklusiv' reviewed the Cotter B1-Base, in this case with the Denon player and Fidelity Research tonearm. The staff measured the acoustic breakthrough and the mechanical resonances and compared these to other high-end turntables (Platine Verdier, Win SDC 10, Marantz TT1000). 'HIFI exklusiv' also compared the sonic qualities to the Marantz TT1000. Cotter's modifications of the player and the base he designed was the winner of the lot on all points.

If you are - like I am - a lover of classical music and jazz and like to play at very realistic sound levels through relatively big loudspeaker systems connected to quality amplifiers, then you need to eliminate mechanical and acoustic feedback. In that case you should build a different plinth in which you use springs instead of rubber feet and decouple the SP10mk2 from its surrounding to the max.

I let myself be inspired by Cotter's design (and any other floaring chassis turntable), though the article in "HiFi exklusiv" did not give insight into the details of how to dismantle the motor. So I did not strip the turntable like Mitch Cotter did, but kept it intact and made my own design for a base. I also did not use the special layered base plate but just two layers of black laminated chip board (particle board) and glued and screwed these together, then cut out the appropriate hole and drilled the holes for the screws for fixing the motor deck to this base plate.

The base plate rests on 3 springs. The positions of the springs can be determined empirically by shifting the positions in relation to the total weight of the base plate with motor unit. Use a spirit level to find the best positions of the springs. Do this when the arm is mounted or at least placed in the corner (at the back at right). This is important if you use a heavy arm. You also can determine the positions of the springs without the arm and later adjust the springs when you have put on the arm.

In my construction, the base plate with springs rests on beams which are fixed to a bottom plate, also consisting of two panels (layers) of particle board. These do not have to be laminated, but can be the ordinary kind.

To make it look better and to keep dust away, a rectangular box consisting of only four side panels is constructed. This box can be easily lifted in order to change or adjust the position of the springs in relation to the weight. Also it will be easy to adjust the height of the springs, to determine the damping of the springs and to connect a cable to the tonearm.

The box is not fixed to any part but rests on top of the beams fixed to the bottom plate. For the mounting of the arm I used a sandwiched board of acrylic 4 mm thick covered on both sides with 1 mm thick aluminum.

In my construction the base plate's measurements are: 58 cm (W) x 44 cm (D). Two 18 mm particle board panels with a black veneer coating (plastic) are glued together.

The bottom of the construction consists again of 2 layers of particle board, but now the plain kind.

On the 4 sides I have glued (and screwed from underneath) 4 pieces of wood of 4 x 7 cm. They are positioned at a distance of 10 mm from the periphery of the bottom plate.

On the inside of the side panels I have glued 4 pieces of wood of 10 mm x 10 mm at such a height that they will rest on the 2 layers of particle board and disguise the bottom.

The measurements of the bottom plate are 60 cm (W) x 54 cm (D). Height of the box (side panels) depends on the height of the springs used when they are pressed down by the weight of the unit on its base plate (including the weight of the platter and arm).

In the drawing below I have omitted the amount of foam to be inserted inside of the springs to dampen the resonance and to prevent the swinging of the subchassis.
If you make the base on which the motor and platter are bolted very heavy, you need stronger springs. If you just stick to the two panels of laminated chiboard, you will benefit from a sturdy base and keep the musicality and warmer sound with a good mid band which you could loose somewhat when constructing a very heavy, solid base.

The measurements of the outside are: 640 mm wide, 500 mm deep, 200 mm high. There is 10 mm space between the baseplate and the outside panels.

Using springs has another advantage. By filling the space inside the springs with plastic foam it is possible to tune the Q of the springs, which means actually adjusting the de-coupling. A lot of foam will make the sound heavier and give more bass (more coupling). Little foam will give the sound more air and speed (less coupling). Not enough foam will impair the speed constancy (stability). So be careful to determine the best sound with no fluctuations.

The total weight of this construction is about 35 kg. That is 15 kg for the unit and the base plate it is mounted on, including the arm and armboard. The remaining some 20 kg is for the rest: the bottom, side panels, springs, hooks, etc. That is all in all a total of about 77 lb.. Cotter's Base B1 weighs 100 lb.. (45.5 kg.) I am told. Cotter's sandwiched plate for the motor has a high percentage of aluminum and is much heavier than wood glued together with one or two layers of 1 mm aluminum sheet. Cotter located the power supply inside the base, that also may add up to reach 100 kg.

Once you have chosen the kind of baseplate you are going to construct and you know its weight, you can determine what springs are to be used best. The frequency of the springs depends on the total weight of the unit mounted on its base plate. You certainly can be advised by an expert from a factory or a specialized shop what springs you should use. I myself took about 12.5 kg of weights to the shop in my neighborhood and the owner permitted me to search in boxes and drawers until I had found 2 sets of 3 springs. This was done by trial and error while evaluating the behavior of the springs while they supported the weights I had brought along. So in the final evaluation I had the choice between a supple and a more sturdy type of spring and could determine the frequency. Read more info about SP-10 Plinths.

The result can be extraordinary. The sound is that of a belt driven turntable with a floating subchassis, but has the high accuracy of one of the best direct drive motors ever made. The accuracy depends a great deal on finding the right springs and make them stiff enough by inserting foam otherwise the turntable does not show the precision it should have. I have not tried using spikes but that could probably also be an alternative to just rubber feet with a large contact surface. If you use a special Record Stabilizer Weight you can improve the retrieving of the signal from the record even further. I am interested to know about experiences of visitors of the page.
Of course it would be better to strip the SP-10 completely if you dare to and just mount the platter and motor with circuit boards on the new top plate. In that way you get rid of the material Technics used which included some damping material which was incorporated to make the production of the design cheaper, as I have been told.

Do not forget to glue three pieces of ultra thin double sided tape on the platter to keep the turntable mat from moving even one micrometer. You will see, the high frequencies will be cleaner, more precise.

My SP10 Mk2 with the long SAEC WE-308L and Denon DL-103 Moving Coil cartridge plus the Stabilizing Weight and The Universal Record Stabilizing Ring. This is the complete SP 10mkii (not a stripped version as Mitch Cotter did use). My SP-10 Mk2 has the original hard rubber turntable mat which gives the best mid band, precise high frequency reproduction, and firm bass. There is a lot of room at the right. It is for practical reasons: Not only 10 and 12 inch tonearms can be mounted, but even longer arms can be accommodated.
(Images edited and all original drawings made by R.A. Bruil).

If you have any questions you can mail me.

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Audio&Music Bulletin - Rudolf A. Bruil, Editor - Copyright 1998-2008 by Rudolf A. Bruil and co-authors