Audio Circuits
All of our line-stages consist of three stages of amplification, for which two stages have a gain of less than one. The gain stage consist of a grounded grid configuration which is rarely used in audio today. This is due most likely to historically it has been used in radio frequency applications. This is the same reason why we have chosen this configuration. In properly designed circuits this results in a circuit with at least 10 times the speed of its alternate plate loaded configuration.
All three stages are non-inverting and the grounded grid stage has a gain of about one- third that of a plate loaded circuit configuration. This produces the ideal gain for a line-stage without the use of feedback to limit excessive gain that is not required.
So by trading off two thirds of the available gain from one device [ triode] we manage to increase the speed by a factor of 10 or more. The result is that all of our line stages maintain an exceptional bandwidth that extends well beyond 250,000 Hz and in some cases beyond one megahertz.. The primary design philosophy that LESS IS BETTER THAN MORE has been fully implemented in the design of our line stages.
We use two different methods to control the biasing in the critical coupling between the first and second stage. The passing of the signal from the first stage to the second stage is done through only one resistor and through this resistor must pass the current from both stages. This control can be done in one of two ways. Either by varying the DC plate voltage to each of the two stages or by cathode biasing of the first stage. Some of our line stages use the former and some use the latter method. Another significant fact is that all three stages are DC coupled. Only the output cathode follower uses a signal capacitor to isolate the DC component from the output signal. We use a very large signal capacitor for this in order to bring our low frequency response down to below 10 Hz. This results in a flat frequency bandwidth from 20 Hz to at least 100,000 Hz or more in all of our circuits.
Power Supply
The high voltage power supply in all our line stages are analog and linear as opposed to digital or switching. We chose this method because it is a tried and proven method of obtaining pure power while both maximizing reliability and maintaining the longest life expectancy. This is done through multiple π stages [ Greek pi symbol ] of filtering using either RC or LC configurations. [ R= resistor, C = capacitor, L = inductor ]
Since all our circuits operate in class A1, the current drawn from the power supply is steady and unchanging which negates having to use any sort of feedback regulation in our designs. In some we have implemented passive shunt regulation of the DC plate supply. While in the Opal we use large electrolytics to sink [ regulate] the DC voltage from varying with the signal.
The object is to lower the ripple and the impedance of the DC high voltage power supply, as well as cross-talk and [ EMI ] electro-magnectic induced interference. It is our belief that the power supplying the circuit is as critical to the outcome of the sound as is the circuit itself. So we pay very close attention to this area in all our designs. In all but our lowest priced unit, we use varying numbers of polypropylene capacitors in the power supply filter for ripple reduction. This speeds up the power supply > charge / recharge cycles > over that which would occur when using all electrolytic type capacitors. In the Opal, the large electrolytic capacitors are not needed to suppress ripple. The polypropylene caps together with two large inductors are capable of this on their own. The electrolytics are there only to regulate the DC so that any drift has such a large time constant as to be of no consequence. This is passive regulation without the use of servo feedback or regulators which have some negative drawbacks which we wish to avoid.
We use the best quality parts commensurate with each price point. The object is to match all the varying types of parts so that we maximize the benefit of each one. The old adage that it is only as good as the weakest link is something we take considerable care to insure it's being implemented.
Wiring implementation types
Printed circuit board (PCB)
This is the universal method of wiring all electronic devices today with the exception of some audio tube products. The reason is due to the enormous complication and number of parts in most modern devices in advance technology. Audio tube technology can if desired avoid this method only because of the simplicity derived from vacuum tube circuits in general that require fewer stages of amplification than solid state as well as less complicated circuit configurations such as Single Ended Triodes; that being our specialty.
Point to point wiring (PTP)
In this method, each component is connected directly to the next component in a circuit by soldering wires between components. Most implementations of point to point wiring are done poorly due to failure to properly think out the layout and securing of each type of component to the chassis. You will see what looks like a rats nest in most of the products done this way.
Their are some products that do go to a higher level by using dual terminal rows whereby all the components are lined up like soldiers. The wiring is then soldered to each via these terminals.
Fixed terminals on printed circuit boards (FTPCB)
This method provides extended reliability and consistent performance. Our fixed terminals together with using printed circuit boards have allowed us several advantages over our previous method. Because our circuits have minimal parts, we can use 2 layer printed circuit boards with the same densely populated construction as is obtained with hard wiring, while retaining the ability to replace parts without removing the board just as before. Our circuit traces are much wider than normal and result in a life expectancy equal to hard wiring while enhancing the quality control and consistency between production units. Lower cost of assembly allows better value and consistent performance between units to meet an ever demanding competitive market. Our circuit board layout is identical to previous hard wired boards with the added advantage of modular construction using screw down wire connections between boards. This enhances repairability while greatly reducing time and cost to repair.
These boards are held elevated from the surrounding metal chassis to avoid capacitive coupling between components. Capacitive coupling should be avoided as much as possible in order to reduce channel cross-talk which affects stereo imaging and dimensionality of the sound stage. The ease of replacing parts and the tenfold increase in lifetime durability of the product are added benefits resulting from this type of board construction.
Fixed terminal board (FTB)
The best implementation of point to point wiring is to design a fixed terminal board (FTB) - just as printed circuit boards are designed to retain the advantages of PCBs - which is the method we previously used in our products that were hard wired.
There are companies working with new materials for PCB boards that may achieve higher levels than the industry standard insofar as printed circuit boards are concerned.
No one that we are aware of in the audio industry, beside ourselves, are building custom designed PCBs with fixed terminals and screw down connectors.
Parts Quality
We use the best quality parts commensurate with each price point. The object is to match all the varying types of parts so that we maximize the benefit of each one. The old adage that it is only as good as the weakest link is something we take considerable care to insure it's being implemented.
We consider only parts that fall into the following four grades :
Good
We do not use substandard parts in any of our products. These parts are selected for a minimum quality standard and are always overrated. For example we use resistors so that the wattage consumed is less than one third their rated power. We use metal film or wire wound resistors because their stability over the long term is much better than carbon resistors and the noise floor is much lower. Capacitors used here would all be electrolytic in the power supply. Quality polypropylene metalized film would be used in the signal path.
Excellent
These parts are better built than the standard parts even though they are in the same family type. An example being metal film resistors that come in varied quality and price points. Switches here would be quite expensive and not normally found in all but the most expensive equipment.
Power supply capacitors in this class would be a combination of highest grade electrolytics and polypropylene metalized film. We rate our PCB boards in this class because they are manufactured using much larger copper traces than what is normally found in other products which increase the life expectancy & reparability.
Ultimate
These parts are the best value that money can buy when pursuing perfection of design. They may not always be the most expensive parts, but they will always be the best parts for the purpose at hand from our point of view. We consider our FTPCBs to be in this level.
Supreme
A supreme rating would require raising the bar beyond anything that has ever been done to date.
These parts are the most expensive in the world and would rarely be found in any but the most exotically priced equipment. This does not however, guaranty enhanced sound over less expensive alternatives. For example: pure Silver wire cost a lot more than pure copper wire, though which sounds better is not universally accepted. [ a lot depends on where the wire is going to be applied - it makes sense to have pure silver wiring from a phono cartridge to the headshell, since the price can be within reason, seeing that the length and size of wire is very small ] Again 99.999% copper cost 10 times more than 99.99% copper, but again any difference in sound is pure conjecture and most likely unprovable.
We don't however, outright reject such parts and we are always open minded when researching new ways in our never ending quest for perfection. We also understand that constant improvement in quality and methods must be always an ongoing practice to remain competitive.
Since perfection is our goal, we don't think parts should impart a signature sound but rather allow the sound to flow through unaltered. The type of parts used therefore must have a synergistic relationship not only to the other parts but also to the circuit configuration that they are placed in. It is this relationship of which type of part to use where, that drives our research efforts.
