This page is intended to explain why our components are so different to the run of the mill polypropylene capacitors and to give you a little insight as to what goes into the manufacture of a capacitor.If there are any questions that you have as regards to the technical or production aspects of our components then please feel free to e-mail your questions to us and we will be pleased to answer your questions personally.
Why Polypropylene ?
Polypropylene is used to form the dielectric of the capacitor. Polypropylene has inherent properties which make it the ideal choice for use in Audio applications. The capacitor by its very nature is a ‘break’ in the circuit, it is important to get the audio signal across this ‘break’ with the least amount of degradation. This degradation is know as the loss angle or dissipation factor. Polypropylene has a dissipation factor of 0.0010d which compares extremely favorably to other plastic film dielectrics. Whilst this is the normal dissipation factor, by careful attention to manufacturing quality and a good choice of materials this can be reduced even further and Ansar has achieved dissipation factors to 0.0001d. Other properties of polypropylene which are desirable for capacitors is that it is very stable with temperature over the normal operating conditions (-25C to +55C) and also it has very low water adsorption so even under the poorest operating conditions such as extreme humidity the component will remain consistent ( the finished products are sealed anyway.)
Why Double Metallising ?
The audio signal as it passes through the capacitor is conducted by plates, these are vacuum deposited layers of Aluminium, which are extremely thin, down to fractions of a micron. Because the deposited plate is so thin it causes resistance to the signal passing through it. This is measured in ohms / square, and typical figures for commercial capacitor film is 2-4 ohms / square. Ansar uses material which has undergone the vacuum deposition twice, hence doubling the thickness of the aluminium layer. This has the desired effect of halving the resistance of the conductive layers to 1-2 ohms per square. Unfortunately it is not currently possible to have subsequent depositions of the aluminium as this degrades the quality of the dielectric. However this is still an option for the future as technologies improve.
The choice of material for the termination of the capacitor is essential, since all signals must pass hrough them and every care should be made to ensure that that transition is as clean as possible. On our standard products we use a grade ‘A’ copper lead with a tinned coating. This is ideal for production quantity components as it provides a good conductivity but at sensible cost. For the enthusiast and top end manufacturers however there are alternatives. We are able to manufacture the components with any leadout required, this can range from different thicknesses of copper, multistrand cables, kimber cable, 99.99% purity silver and gold.
The main part of the capacitor, the bit that does the work is a tight coil of dielectric and metallised plates. This process is automated but the machines are attended at all times during this process to ensure that there is consistency in the winding process. It is important to ensure that every batch of product is manufactured to exactly the same standards each and every time. This ensures that once a component has been approved for use in a design then you are sure that future batches will have exactly the same characteristics. We also ensure that if samples are dispatched that the are wound on the production machines and not on a different lab machine for instance. Components are wound under high tensions and during the winding process a pressure roller is used to press up against the element as it is being formed. This is done to remove air inclusions from the winding. If air pockets get into a wound element the dielectric layers are free to ‘vibrate’ in operation and will degrade the quality of the signal.
High Temperature Treatment
Just after the capacitor elements are wound, they are subjected to several hours of high temperature. This is at just below the melting point of the dielectric layer. This has the effect of making the dielectric become slightly plasticised and pliable, it allows the component to contract and for the layers to actually bond to each other. This has several beneficial results, firstly the layers are compressed to further exclude any air pockets from the winding element. Secondly the finished product becomes much more stable with respects to its value. If the capacitor has not been heat treated it is liable to a wider variance of value with temperature. The third is that once the layers are ‘bonded’ they are unable to ‘vibrate’ inoperation and adversely affect the signal.
End Spray Connection
This is probably the most important of the design features after the choice of raw material for the winding element. Once the element is wound, we need to make a connection to it. This is done by spraying metal onto the ends of the component. Ana alloy of tin and zinc is vapourised by high currents and then it is blown onto the winding element with compressed air. When the tin/zinc alloy hits the element it immediately cools and forms a solid metal surface that a connection can be made to. The partical size of the alloy as it hits the element and the composition of the alloy is very important. We use a very small particle size to get the best possible connection and reduce losses in the connection. Many manufacturers of commercial components will opt for a larger partical size as this reduces the ammount of material needed to build up the metal layer to the required thickness. The other important criteria as mentioned is the composition of the alloy. We use a very high tin content to the alloy as this gives us a better ‘sound’ to the finished product. Again many manufacturer’s will use a low tin content as it is much cheaper (some use a pure zinc spray, which oxidises very quickly). High tin content means that the surface of the metal layer does not oxidise or tarnish, and we are able to achieve a very consistant and reliable weld for the terminations.
The termination or lead that you see is connected to the component by a resistance weld. This is acheived by a very high current (low voltage) being passed through the termination which then heats up very quickly and melts nto the end spray as described above. This method of connection is highly repeatable for all components to ensure consistancy of product. It is also quick which does not allow enough time for the plastics of the dielectric to be damage by the heat, and there are no detremental fluxes left behind as with a soldered connection. On our larger products and some specialised product we do have to use a soldered connection, this is only done on the larger products as the can more easily cope with the heat dissipation to prevent damage to the dielectric. Low flux content solder is used.
Our components have a unique look and feel to them. We use a heat shrink outer wrap of polyolefin. This is a plastic which at temperatures in excess of 120C shrinks tightly around the component. This sleeve is then printed. We are able to offer a free printing service so that the components are text printed with your company’s requirements, such as compant name, part number, part code, product etc. this service is available to all our customers, there is a one time only charge of £45.00 for the printing plates. There are no charge thereafter. There is also a choice of colours for the finished product if required. the standard unit is black, but we can also offer red, and blue.
All components undergo a proof test, this is generally a 15 minute test where the component is subjected to voltages 50% higher than their normal working voltage. The test is carried out to ensure that the components are capable of comfortably withstanding voltage spikes during opperation. The test also has the added benefit of ‘clearing’ the capacitors. With plastic film capacitors, you get areas of the dielectric that are slightly weaker than other areas and can sometimes ‘fail’, this may sound a bit drastic, but in fact what happens is a very tiny area of the dielectric fails and a high current flows momentarily. The high current is sufficient to melt away the aluminium plate surrounding the week area, thus effectively sealing that area off from the rest of the component.
This process known as ‘ageing’ isolates all the weeker areas which means that there will be no failures when the capacitor is in operation. A component that has not undergone this process may ‘crackle’ for quite some time when it is first used, obviously not good in a crucial signal path. Capacitors that are built and rated at close to their limits may also experience this crackleing, that is why we have a 50% undervoltage rateing to avoid this effect.
Capacitance and Tolerance
All components are tested before leaving the factory 100% to ensure reliability and that our customers do not have to rework product due to a faulty component. The capacitance is measured and the tolerance calculated. Components are normally rated at 5% tolerance, however we also offer 2% 1% and 0.5% tolerances for special requirements. Our components are wound to value, so a batch of components will have a nominal spread of values about the quoted value. Many mass produced components are deliberately manufactured to below the nominal value to save on material costs.
Also known as loss angle this is probably the most important measurement for audio grade components. It gives an indication of the ammount of losses within the capacitor element. The losses are generally caused by resistance to the signal passing through the capacitor. Energy is lost from the signal and dissipated as heat. Any loss of signal will obviously degrade the final signal that reaches the loudspeaker, so ever effort is made to ensure that the lossses are minimised to give the most transparent capacitor we can. For Polypropylene capacitors the accepted loss factor is 0.001d., our components are tested to twice this limit ( 0.0005d )
Which Capacitor Range to use
Loudspeaker Crossovers – CPA range, the values available in this range will cover almost any loudspeker requirement, and if it doesn’t then please enquire about our special and custom designs.
Power and Pre-amp – Generally these are specially designed components or larger values found in our CPA range.
CPA – Axial design
This range of components was designed mainly for the loudspeaker crossover manufacturers. The components are manufactured with the aim of producing a highly transparent component for use in critical signal paths such as the crossover network. They are an excellent all round product which have been designed to offer the best compromise between quality and cost. Highly regarded throughout the industry they are used by many of the UK’s leading loudspeaker manufacturers.
Values range from 1u to 200uF ( 200V range )
Values range from 1u to 120uF ( 400V range )
Values range from 0u1 to 75uF ( 630V range )
Values range from 0u1 to 22uF ( 930V range )
Tolerances Available 5%, 2% 1%
Leadouts available, copper, silver, multistrand.
CPR – Radial Design
This range of components is designed for use on circuit boards. The components are housed in flame retardant black nylon cases. General areas of usage would be in Amps, pre-amps, CD players, decks, mixing desks.
Values available 0u1 to 4u7 (400V)
There are also a variety of special designs in this axial format, please ask if you require a specific item.
Tolerances Available 5%, 2%, 1%, 0.1%
Leadouts Available – copper.