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Pink Triangle PT Too

Modifications and Enhancements

by Phil King, August 2007

1. OVERVIEW

1.1 Basic Principles

Much was learned during production of the original Pink Triangle turntable and the later PT Too, culminating in the production of the Anniversary, Pink Triangle’s “statement” turntable. Whilst the Anniversary looks superficially similar to the earlier turntables, much of the thinking applied to it deals with damping the lightweight sub-chassis and reinforcing the plinth, and as a consequence these major components are not interchangeable. However, this does not suggest that the earlier turntables cannot be improved by applying some of the principles used in the Anniversary.

The other notable difference between the Anniversary and Pink Triangle’s earlier turntables is the sub-chassis mounting of the motor. This marked a return to the use of a DC motor (the PT Too, Export and LPT all using AC synchronous motors), but in an implementation very different from that of the original.

Sub-chassis mounting of the motor presents some serious hurdles, in terms of both the engineering involved and the cost of sourcing components of adequate quality, and falls outside the scope of these modifications, which are intended to be reversible and relatively inexpensive.

Therefore, the treatment of the top plate becomes an important factor in these modifications. Whereas in the design of the Anniversary the top plate is almost purely cosmetic, in the earlier turntables it plays a structural role in supporting the motor, making it necessary to carefully consider the potential for transmission of motor vibrations into the top plate (and subsequently the plinth and suspension).

The modifications detailed in this document thus deal with the control of resonances (through damping, the addition of plinth mass and the proper coupling of components), whilst retaining the lightness of the sub-chassis assembly, which is a fundamental part of the Pink Triangle design and determines the turntable’s overall sonic performance.

1.2 Commercial Modifications

Currently only one company, The Funk Firm, offers substantial and commercially available modifications to Pink Triangle turntables. In fact, The Funk Firm proposes that it is possible to create a turntable which surpasses the performance of the Anniversary, using any of Pink Triangle’s suspended sub-chassis turntables as a basis.

However, the scope of their ‘Vector’ upgrade far exceeds the modifications in this document, both in content and price, completely replacing items like the sub-chassis, motor and top plate. The ‘Vector’ upgrade delivers an end product that is not only fundamentally different from the PT and PT Too, but also from the Anniversary.

Instead of this approach, the modifications in this document seek to establish how much it is possible to improve the performance of the earlier turntables without either replacing major components or spending the sums of money required to carry out a full ‘Vector’ conversion.

The Funk Firm is, though, at the time of writing a useful source of replacement parts and technical information for Pink Triangle turntables.

1.3 Limitations

As previously stated, the intention of these modifications is not to create a clone of the Anniversary turntable, but merely to attempt to upgrade the sonic performance of the standard PT and PT Too. The character of these early turntables is derived from a combination of the rigid plinth, lightweight sub-chassis and soft suspension, and all of these elements remain. The modifications seek to enhance these properties whilst adding some resonance controls not found in the original.

The modifications are generally reversible, although some changes might require more effort than others to return them to their original form. This ensures that any undesirable alterations can be undone, and that the resale value of the turntable is not diminished.

Where items are fabricated to fit a part of the turntable, it is not possible to provide guidance on measurements due to variations in the dimensions of Pink Triangle’s turntables. This was not immediately apparent until an early plinth (PT2085) was compared to the one being used as the subject of these modifications (PT4068). It was found that the plinths differed subtly in every dimension, with the earlier one being smaller all around than the later one. This may be an unusual sample variation, but it nonetheless prevents any definitive dimensions being quoted in this document.

The subject of the modifications is a PT Too, so there should be every certainty that the same modifications will suit another PT Too. However, it is worth noting that PT4068 started life as a PT and was later converted to PT Too specification. It is probable, therefore, that these same modifications could be applied to a PT (allowing for differences in the top plate material, motor position, etc.) and can possibly also be applied to the later Export model.

These modifications require the total disassembly of the turntable, thus providing the opportunity to lubricate, tighten and adjust parts that may not otherwise be accessible. Given the likely age of most subject Pink Triangle turntables, this alone may be beneficial to the performance. However, there is no readily available reference for component tolerances, fastener torque settings, recommended lubricants, etc. and the final results will, in part, rely on the competence and experience of the person carrying out the modifications. Care should be exercised throughout, as some parts are difficult and/or expensive to replace.

1.4 Materials and Components

The modifications largely fall into two categories – those where a component is modified in some way, and those where a component is either renewed or fabricated. In nearly all cases, however, the use of some material (be it a damping agent, adhesive, lubricant, etc.) is required.

When considering what materials and components should be used, two basic criteria were applied: They needed to be a) commonly available and b) offer an advantage over the original item. Additionally, it was felt that it should be possible to carry out the modifications without resorting to either specialised tools or outsourced fabrication, although this is a matter of personal choice and also dependant upon skill levels.

It was also intended that the standard structural items should be improved wherever possible, rather than replaced. Once again, the primary intention was to preserve the character of the original turntable, but there are also cost benefits in this approach. Without budgetary constraints it would be simpler to buy an Anniversary.

In the years since the PT and PT Too were last produced, new materials have come to market. Panel damping materials (such as Dynamat) are commonly available and in widespread use, and their properties are as equally applicable to a turntable top plate as they are to the car body panels for which they were originally intended. Similarly, the titanium fastenings used in these modifications, where once restricted to aerospace applications, are now widely available at reasonable prices, and offer benefits in terms of reduced weight and increased tensile strength over the steel fastenings originally used.

It is feasible that some of these materials would have been used in the PT and PT Too had they remained in production, and some other parts of the modifications may also have found their way into the turntables (such as increasing the mass of the plinth in the style of the Anniversary) where cost allowed.

Some caution needs to be exercised over the selection and use of materials however. Whilst one of the main tenets of these modifications is the control of resonances, it is possible to adversely affect other areas of performance by the injudicious application of damping materials. For example, Dynamat or similar is well suited to application to the top plate, but its use in damping the sub-chassis would add undesirable weight and hence upset the performance of the sub-chassis and suspension. To this end, the sub-chassis should be damped only with a lightweight material or (in the absence of such lightweight material) not at all.

2. DISCLAIMER

These modifications have been carried out by the author, and to the author’s own turntable. It is not the author’s intention to offer these modifications commercially to other owners or prospective owners of Pink Triangle turntables, or to gain financially from doing so.The author therefore offers the advice in this document freely and without copyright. However, anyone wishing to replicate these modifications (whether wholly or in part), should be satisfied that he/she (or any third party, where applicable) is competent to carry out this work to a suitable standard.The author cannot be held responsible for any loss, damage or injury that may arise during or as a result of these modifications, and nor does the author accept any responsibility should any party modifying their turntable in a similar manner be unhappy with the end result.

3. COMPONENTS AND MODIFICATIONS

This section deals with the components both individually and as assemblies, so as to provide an understanding of the interactions between them and how modifications may affect more than one part or assembly at a time. For example, the top plate and the suspension frame are separate parts, but the performance of one is dependant upon its interface with the other.

It would be tempting to either deal only with individual parts or with the turntable as a whole, but this may be more confusing than the approach taken in this document. However, sections might need to be read more than once (or in combination with other sections) for the relationships to be understood. Wherever possible, photographs are provided.

The modifications are described in details (both in terms of their intended aims and method of application) as each component/assembly is discussed.

3.1 Plinth and Top Plate

As the plinth, top plate and baseboard are rigidly fixed to each other (either by screws or glue) they are treated as a single assembly for the purposes of these modifications. Interestingly, although the top plate is glued to the plinth at its periphery it also rests on the suspension frame, but is not bonded to it in the standard turntable.

There is no obvious benefit in this approach, as neither the top plate nor the suspension frame are removable under normal circumstances (e.g. for servicing or adjusting the suspension), and this loose interface between the top plate and suspension frame was, in fact, seen as a potential source of resonance.

Note: This is slightly different from the construction method used for the PT, where the top plate is held in place by screws secured into the suspension frame, but similar principles apply.

The suspension frame itself is discussed in 3.3, below, as are the limited modifications to it.


(Fig. 1) Plinth with suspension frame, viewed from underside (top plate removed)

The top plate is steel and of relatively heavy construction. Despite the thickness of the steel plate (approximately 1.5mm) it has a tendency to ‘ring’ noticeably when struck. Given that the motor is rigidly attached to the top plate, it is desirable to prevent motor vibrations being transmitted through the top plate. Moreover, as the top plate normally rests loosely on the suspension frame there is every probability that vibrations (whether from the motor or airborne) are passed from the top plate to the suspension frame.

The top plate was, therefore, damped with Dynamat. The Dynamat sections are cut to allow for mounting the motor rigidly to the top plate (as in the original design) and whilst this can be carried out with the top plate in situ, it does not deal with the interface between the top plate and suspension frame. The top plate was, therefore, removed by carefully breaking the adhesive bond at its periphery.


(Fig. 2) Top plate with Dynamat and copper foil applied.

Before applying the Dynamat, a layer of thin self-adhesive copper foil was applied to the area around the motor and switch to provide electromagnetic shielding of these components from the top plate. This copper foil can be seen around the motor and switch mounting areas in Fig. 2, above.

The Dynamat has been applied so as to allow for clearance around the suspension frame, and around the periphery so that the top plate can be bonded to the plinth.

The plinth is well constructed and has internal corner bracing (just visible in Fig. 1). This particular example is fabricated from Rosewood, and as other woods were available, the weight of the plinth is likely to vary from model-to-model. In this case, the weight of the bare plinth (top plate and suspension frame removed) is 1445 grams.

3.2 Baseboard and Plinth Cavity

No modifications have been made to the plinth itself, and its outward appearance remains entirely standard. However, the internal cavity of the plinth has been filled, to increase its mass and reduce any tendency to resonate, or at least the lower the frequency at which the resonance occurs.

There are a number of ways this ‘mass loading’ could have been undertaken, including filling the plinth with dense material, or fixing materials to the inside of the plinth. However, as previously stated, it is intended that the modification should be reversible. In this case it is also desirable to allow for normal servicing, and to ensure that the normal movement of the sub-chassis is not impeded.
This has been achieved by fabricating a replacement for the original baseboard. The standard baseboard is fashioned from 3mm thick hardboard and is secured to the bottom of the plinth by four small, self-tapping screws. This item is barely adequate for its purpose, tending to flex under the weight of the turntable and deform over time.


(Fig. 3) Fabricated baseboard.

The new baseboard is constructed from bonded layers of medium density fibreboard, sculpted to allow clearance around the turntable’s internal components whilst filling the bulk of the remaining void areas inside the plinth. In essence, this is similar to the plinth construction of the Anniversary, although in this case it is not bonded into the plinth and, instead, forms an interference fit with the inside of the plinth. It is also held in place by the normal baseboard fixing screws.

The new baseboard does not abut the top plate, therefore not directly coupling the two components and preventing the direct transmission of shocks from the baseboard to the top plate.

Holes in the baseboard allow clearance for the platter bearing at the limit of suspension travel, and for the circulation of cooling air around the motor. The baseboard utilises the turntable’s four original rubber feet. Further detail can be seen in Fig. 15.

3.3 Suspension and Suspension Frame

The suspension uses a relatively traditional system of three coil springs, from which the sub-chassis hangs. In the case of all Pink Triangle turntables, levelling of the suspension is achieved by altering the height of the top mounting point of each spring, using adjusters accessed through holes in the outer faces of the plinth sides. These adjusters act on sliding wedges which, in turn, act on pivots to which the springs are connected. A further similar adjuster is mounted at the rear (variously accessed dependant upon turntable model), but this is intended to be pre-set at the factory.

The suspension components, together with the adjustment mechanisms, are all housed within a suspension frame (shown in Fig. 1, above). This frame is constructed in a T-shape from lengths of aluminium channel, and is attached to the sides and rear of the plinth using machined aluminium bosses. Under normal circumstances, the frame and bosses are bonded together and, as the bosses press into holes in the plinth, the assembly is not removable without breaking the bonds.

The suspension itself is left unaltered, retaining the original springs, pivots and adjustment wedges. However, whilst the turntable was dismantled the opportunity was taken to secure all of the pivot screws with a thread locking compound, and to pack the pivots and adjusters with petroleum jelly. This is not intended to act as a lubricant – under normal circumstances the pivots do not need to move once properly adjusted – but serves to damp any potential ‘chattering’ of the pivots as vibrations pass through them.

With the top plate removed, the suspension frame was found to be standing proud of the plinth’s top plate recess (Fig. 4, below). It is not clear whether this is an intentional design ‘feature’ but this does not, anyway, lend itself to bonding the top plate to the plinth.


(Fig. 4) Suspension frame/plinth joint

Consequently, the suspension frame has been removed and the top edge height of the supporting bosses reduced to allow the suspension frame to sit flush with the top plate recess.

It was found on removing the suspension frame that the adhesive used to attach the bosses to the aluminium channel sections had become brittle, thus not bonding the elements together securely: The same had also happened to the adhesive joint between the top plate and plinth. The exact nature of the adhesive is not known and, given that many PT’s were converted to PT Too specification by dealers rather than Pink Triangle themselves, might never be satisfactorily identified. It is doubtful, however, that the brittleness of the adhesive bond was intentional, and this is most probably the result of deterioration through age.

During reconstruction, a 2-part clear epoxy adhesive was used to secure the suspension frame to its bosses, and the top plate to the plinth. Additionally, the top plate was bonded to the suspension frame using the same adhesive, which not only serves to strengthen the assembly but also prevents any vibration arising in the otherwise loose interface between the top plate and suspension frame.

3.4 Sub-Chassis

The standard sub-chassis is constructed from Aerolam, a honeycomb of aluminium cells sandwiched between thin aluminium sheets. This material is both light and strong, and is notable for its use as an aerospace flooring material. In this application it provides ample rigidity, with only its damping properties at the frequency extremes called into question. This was addressed on the Anniversary by supplementing the Aerolam material with a further layer of end-grain balsa.

The platter bearing and armboard are bolted rigidly to the sub-chassis using high tensile steel fasteners.


(Fig. 5) Coated sub-chassis, with later bearing and ‘sandwich’ armboard.

As only the high frequency damping needs to be addressed, it is not clear whether adding substantial amounts of material to the sub-chassis is either necessary or desirable and, instead, a sprayed-on damping agent was used.

In this case, ‘Quiet Kote’ (manufactured by Cascade Audio) was used, and this dries to a soft rubber consistency. Areas where the armboard, bearing and suspension affix to the sub-chassis were masked before application, and a relatively thin (approximately 1mm) coating applied in order not to add noticeable weight.

Almost as an aside, the method used for fixing the lower ends of the suspension springs was changed. In the standard turntable, a split plastic disc is slipped over the looped end of the suspension spring, but two of these (rather flimsy) washers tore during re-assembly.


(Fig. 6) Sub-chassis, plinth and top plate underside view.

Rather than trying to replace these discs, they were substituted by X-shaped nylon mouldings (Fig. 6), commonly used as spacers for ceramic tiles, placed through the looped ends of the springs. This would normally result in the sub-chassis sitting slightly lower than standard, but there is a large enough range of suspension adjustment to compensate for this. However, rubber grommets are used between the sub-chassis and the plastic discs, and substituting slightly thicker grommets compensates for the change of effective spring length. These grommets are held in place with a contact adhesive, and a small amount of contact adhesive applied to the nylon mouldings also prevents them moving relative to the grommets.

Prior to assembling the sub-chassis and suspension, a small modification was made to the transit screw. The transit screw passes through the suspension frame and is normally loose. It can be removed if vibration is a concern, but is easily lost. In this case, the transit screw was fitted with two tight fitting rubber ‘O’-rings, one directly under the head of the screw to prevent vibration and the other further down the thread, effectively ‘capturing’ the screw in the suspension frame.

3.5 Platter Bearing

All Pink Triangle turntables use a version of their proprietary inverted bearing, the opposing thrust faces being a tungsten ball and ruby cup. There are, however, some detail changes between models and production years.


(Fig. 8) Bearings, showing the threaded base and transposed bearing surfaces of the later type (left).

As seen in Fig. 8, the earliest bearings were constructed with the ball at the top of the shaft, the ruby cup being located in the aluminium upper housing, whereas the later bearing design has the thrust surfaces transposed, moderately improving lubricant retention.
This later bearing also has a slightly slimmer, threaded base. By threading the base (removing the need for retaining nuts), and making the base thinner, a small weight benefit is gained over the earlier bearing. Further weight advantage has been gained by using titanium fasteners in place of the original high tensile steel items. The combined weight saving is not large, but probably suitably offsets the weight added by damping the sub-chassis.

It would, of course, be possible to tap threads into the base of an earlier bearing, although over-size fasteners would need to be used and the sub-chassis drilled to accommodate them.

As with all other threaded fasteners used in the turntable, the bearing bolts have been coated with a thread locking compound during assembly.

There is a slight overall height difference between the two bearings when installed (taking into account the difference in base thickness) in the order of 1.5mm.


(Fig. 9) Base thickness and height difference in late (left) and early bearings.

This slight height difference allows the sub-chassis to hang slightly higher in the plinth, with a corresponding additional clearance to the baseboard. However, there is no particular performance benefit to be gained from this, and the sub-chassis does not ‘bottom’ anyway during normal use.

3.6 Platter and Funk Firm ‘Achromat’

At the time of its introduction, Pink Triangle’s use of an acrylic platter was deemed quite radical. The practice has since become more commonly accepted, with a number of major manufacturers and aftermarket suppliers embracing the use of acrylic materials for platter construction. As such, there is no need to modify or replace the Pink Triangle platter.

However, in the intervening period this record-platter interface has been studied in great detail and a new generation of platter mats developed. In particular, the Funk Firm have developed the ‘Achromat’ which is, at least in part, based on the principles which led to Pink Triangle’s original use of acrylic platters. The ‘Achromat’ is considered to provide a better impedance match between the record and platter and, if nothing else, certainly seems a softer and more ‘forgiving’ interface.

The Funk Firm manufacturer the ‘Achromat’ in a range of thicknesses, but the thinnest variant (3mm) was considered adequate for use with the PT Too, and has less impact on tonearm adjustment. Whilst not strictly a specific PT Too modification, and applicable to a wide range of turntables, the opportunity was taken to install the ‘Achromat’ on the subject PT Too.

3.7 Armboard

Pink Triangle used a number of different armboard materials and styles throughout production, ranging from pressed steel, through aluminium section, to ‘sandwich’ construction and ultra-lightweight aramid composites.


(Fig. 10) Armboards: aluminium section, medium density fibreboard, aluminium/balsa ‘sandwich’.

The armboard originally fitted to this turntable was of the aluminium section type, cut to a pseudo-Linn pattern (e.g. with six tonearm mounting holes rather than Linn’s normal three). This has been replaced with an alloy/balsa ‘sandwich’ armboard, cut to the same tonearm pattern.

Care should be exercised when selecting an appropriate armboard. Many of the lighter armboards were fitted with a supplementary weight to permit proper levelling of the sub-chassis when fitted with light tonearms, and using one of these weighted armboards with a heavy tonearm will over-stress the suspension (and will probably not allow it to be levelled properly). In general, the weight can be removed.

3.8 Electronics

No significant changes have been made to either the motor, switchgear or power supply. Any alterations that have been made generally deal with the practicalities of a 20 year old turntable. Therefore, the wiring from the power supply to the turntable has been renewed in order to deal with some brittleness of the original wiring (the change from a grey sheath to a black one is purely cosmetic) and, in the process, the original equipment DIN plug has been substituted with a modern metal-bodied, gold-pinned equivalent.

In turn, the power supply unit is unaltered, other than having a new mains plug fitted. The case was opened to check for obvious signs of overheating and none were found. Other than removing some dust from the PCB and cleaning all electrical connectors, no other action was taken.


(Fig. 11) Motor with sorbothane damping ring, and new cable connected to switch PCB

Although there was no indication of significant motor vibration, the opportunity was taken to install a sorbothane damping ring around the periphery of the motor. The damping ring as supplied (by SRM/TECH) requires some minor trimming to work with the PT Too, due to the close proximity of the motor to the suspension frame. This is easily achieved with a craft knife. The thrust bearing carrier was also removed, the components cleaned and the whole re-assembled with a small amount of graphite grease applied to the thrust ball.

3.9 Re-Assembly

As previously mentioned, the opportunity has been taken to ensure that all fasteners have been checked for tightness, and coated with thread locking compound where appropriate. Similarly, all electrical connections and wiring have been checked and made good as necessary.

The internal cabling has been carefully routed to avoid interference with the internal moving parts of the turntable, and secured to the inside of the plinth using nylon ‘P’-clips, replacing the inadequate self-adhesive aluminium clips originally used.

The bearing is lubricated using a small amount of Castrol CL high melting point grease. Lubrication is often a matter of personal preference, and the only guidance given here is that the lubricant should be sufficiently ‘heavy’ to allow it to be retained by the small bearing surfaces, whilst also having a high enough viscosity that no slowing of the platter occurs. To this end, Castrol CL (which is commonly used in car wheel bearings) was found to perform well. It should, however, be applied in relatively small amounts, especially to the shaft of the bearing where otherwise it acts to force the bearing up with an hydraulic action.

The belt is dusted lightly with talcum powder, and all of the running surfaces (e.g. platter and motor pulley) scrupulously cleaned to remove any traces of grease.

4. FURTHER ILLUSTRATIONS

The photographs below provide additional views of components and assemblies mentioned in this document. These views may help to clarify the relationships between the components, and how the turntable is constructed.


(Fig. 12) The basic component parts of a standard PT Too turntable (excluding power supply).

Additionally, the photograph on the front cover of this document shows the finished turntable with its partnering power supply.
For purely cosmetic reasons, the power supply has been encased in a timber frame that matches the plinth material. This was not standard on the early PT Too, only appearing with the later (wider) power supply casework. In the main, the later PT Too models were only available in a black ash finish, as were the wood trimmed power supplies. This being an older turntable, the plinth is constructed in rosewood.

At the time of carrying out these modifications, the turntable is fitted with a van den Hul wired Zeta tonearm and a Koetsu Urushi cartridge.


(Fig. 13) Completed plinth, sub-chassis, suspension and baseboard assembly (top plate removed).


(Fig 14) Plinth, suspension frame and sub-chassis (top plate and baseboard removed)..

The photographs above show the sub-chassis in its proper position, with and without the baseboard. In both of these photographs the sub-chassis is clamped to the suspension frame by the transit screw.


(Fig 15) Underside, showing bearing and motor.


(Fig 16) Motor, switch and wiring.

In these two photographs it is possible to see the motor bolted into place on the top plate, together with its associated wiring. Normally, the wiring from the power supply to the switch is held in place with self-adhesive aluminium tabs, but these have been replaced with nylon P-clips for greater security.

The wood blocks fitted to the corner of the plinth support the power supply board in an original Pink Triangle. Although redundant, these were not removed and the baseboard was shaped to pass around them.

5. SOURCES AND RESOURCES

Sources for replacement Pink Triangle parts are scarce, although the situation has recently improved now that the Funk Firm has committed to maintain and upgrade Pink Triangle turntables. However, many of the items used in these foregoing modifications are not specific to Pink Triangle products and, in all likelihood, could be applied elsewhere.

Through the use of their products and/or guidance the following are worthy of specific mention:

The Funk Firm
Suppliers of Pink Triangle parts and modifications, and the ‘Achromat’ platter mat:
www.thefunkfirm.co.uk

Dynamat
Manufacturer of ‘Dynamat’ vibration damping products:
www.dynamat.com

Cascade Audio
Manufacturer of ‘Quiet Kote’vibration damping spray:
www.cascadeaudio.com

SRM/TECH
Suppliers of sorbothane motor damping rings and other anti-vibration products:
http://stores.ebay.co.uk/SRM-TECH-Audio-Products





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