The Magtech Regulated Power Supply White Paper
Many audiophiles have asked if the regulator in the Magtech is truly 100% efficient as claimed. The purpose of this paper is to describe how it works so that you can see that it is, in fact, super efficient. It actually does run cold and truly solves the heat problems of conventional regulators that prevent their use in power amplifiers.
So how does the Magtech regulator work? I'll explain, but readers will need to understand the basics in order to appreciate the problems and solutions involved. Since the technical expertise of readers varies, I will cover the basics. I apologize in advance if some of what I am about to say is review for some readers.
First, what exactly is "efficiency" as applies to a voltage regulator? Efficiency is the amount of energy put into a system compared to the amount of energy that you get out of it. Since energy cannot be destroyed and must be accounted for, any losses in efficiency will be reflected as waste heat somewhere in the system.
Or to put it another way, any heat that is produced by the voltage regulator is a loss in efficiency and results in less power being fed to the electronics than would be the case if the regulator was not present. The exact efficiency percentage can be calculated based on watts in compared to watts out or watts of waste heat produced.
In the Magtech's voltage regulator, you will not find any waste heat. It will pass virtually all of the watts put into it on to the amplifiers.
To see why, it is necessary to understand exactly how a power supply operates. Only then will it be possible to see how the Magtech's voltage regulator works and how it can be so efficient.
The purpose of a power supply is to produce smooth DC (Direct Current) at specific voltages to drive the downstream electronics. A basic, linear power supply consists of three sections, each having different types of output characteristics.
The first section is the power transformer. This converts the mains voltage to the voltage(s) required by the downstream electronics. The output is AC (Alternating Current) in the form of a sine wave.
A sine wave is a smooth wave form without any harmonic structure with alternating positive and negative polarity. There is one positive and one negative wave per mains cycle (60 Hz in North America, 50 Hz in the rest of the world).
The second section is a bridge rectifier. This consists of four diodes. Diodes are electric check valves that flow current in only one direction. These diodes flip the phase (polarity) of alternating waves by 180 degrees so that all the waves are in phase. Therefore the output from the bridge rectifier will be pulsating DC sines at twice the mains frequency.
The third section is capacitance. This usually takes the form of a bank of large, storage capacitors. A capacitor bank acts like a rechargeable battery in that it can store a lot of electrons and release them when needed.
The practical difference between a rechargeable battery and a bank of capacitors is speed. A capacitor bank can be charged and discharged virtually instantly, which is necessary to meet the sudden large current demands of an amplifier.
The main purpose of the storage capacitors is to smooth out the current flow from pulsating DC to continuous DC. The storage capacitors are often called filter capacitors since they "filter out" the DC pulses from reaching the downstream electronics. If there were no filter capacitors, an amplifier would make a very loud hum come from the speakers.
The storage capacitors are also needed to help the power transformer deliver enough peak current to reproduce dynamic peaks that require more current than the transformer can deliver. Think of the current that is required to drive the woofer at that moment when a bass drum is struck . . .
The current required by a Class B amplifier is directly proportional to the energy in the music. So at idle (no music), no current is needed or used. Very loud music will require an equally large amount of current to drive the speakers loudly.
It is this huge difference in current that causes the large voltage changes in the rails (the power supply output voltage) you find in most amplifiers. The difference in the rail voltage between idle and full power in most amplifiers is around 30%. This massive voltage drop causes the distortion, the bias, and the output capability of an amplifier to be modulated by the music.
An electronic circuit's distortion can only be optimized at a specific voltage. Any variation of voltage will result in increased distortion.
Class AB amplifiers are a bit more complicated than Class B amplifiers as they require a constant bias current that requires some power. The bias will be optimized at a specific rail voltage. Therefore, the bias will change directly with changes in the rail voltage.
But the biggest issue is that an amplifier's power will fall as its rail voltages fall. So unregulated amplifiers suffer significant performance degradation as the music modulates their power supply voltage.
The rail voltage fluctuations caused by amplifier load are only part of the problem. The mains voltage is not stable either.
The mains voltage will vary depending on the load on the power grid and the load on the house wiring. High load conditions can cause the mains voltage to vary by 10% or more.
For example, compare the electrical load and usage in the middle of the night to early evening on a hot summer day. At night people are sleeping so they are not using electrical equipment and the temperature is cool so air conditioners are not running much.
In the early evening, everybody is home from work, dinner is being cooked, electric washers and clothes dryers are operating, air conditioners are maxed out, people are using power-hungry electronics like big TVs, the lights are on, the water heater is running, etc. So the load on both the grid and home wiring is great.
And when do you listen to your music system? Of course, when power demand is the highest and voltage is the lowest. Murphy is hard at work here.
And there is even more bad news. The amplifier itself can severely tax the capacity of your house wiring to which it is attached. A powerful amplifier can draw all the power that is available from your wall receptacle, which is limited to about 2,400 watts on a 20 amp circuit. This will drop the voltage on that line by several percent -- this is in addition to the losses on the grid and in your home from other power uses.
Furthermore, the mains frequency has a big effect on the output of a power supply. This is because a transformer's power is determined by the current it can deliver in its power pulses multiplied by the frequency of those pulses.
This means that a transformer can deliver about 20% more power when operated on a 60 Hz mains than it can when operated on a 50 Hz mains. Therefore, an amplifier with an unregulated power supply will lose up to 20% of its power supply power when operated on a 50 Hz mains.
All this is further complicated by the fact that the relationship between voltage and power in an amplifier is not linear. Power varies by the square of the voltage.
Power is the product of volts times amps. Ohm's Law says that one volt will drive one amp through one Ohm of resistance. If you do the math, you will come to realize that the power of an amplifier is determined by the voltage that it can drive into the loudspeaker (assuming it can also deliver the current required).
The formula for calculating amplifier power is the amplifier's RMS output voltage squared and then divided by the speaker's impedance. As an aside, impedance and resistance are the same thing. Resistance applies to DC circuits while impedance is used for AC circuits. This is because the impedance often varies with frequency in AC circuits but there is no frequency in DC circuits. For calculations, you may use impedance and resistance the same way.
To determine the voltage, the formula is the square root of the product of watts times Ohms.
Using these formula, you can see that for an amplifier to drive 100 watts into an 8 Ohm speaker, it will have to produce 28.28 volts and deliver about 3.5 amps. Now what happens if we drop the power supply voltage by half? The voltage will then be 14.14 volts and the current will drop to 1.76 amps.
How much power will the amplifier now drive into the speakers? It will be just 25 watts. This is a huge loss.
So you can see that the typical 30% loss of rail voltage in an amplifier results in a very large loss of power -- about 50%. If you add an additional loss of mains voltage due to heavy house wire loading, you will lose another big chunk of power.
When you add all the above factors together, you can see that an amplifier's performance is severely degraded by power supply voltage fluctuations and that eliminating them will produce substantially better amplifier performance in terms of power, distortion, and optimum bias levels. So why don't amplifiers have voltage regulated power supplies?
The problem is that the poor efficiency of conventional voltage regulators results in vast amounts of waste heat. Most amplifiers run very hot and adding large amounts of waste heat to an already hot amplifier is intolerable. It is also expensive in terms of both hardware and electricity usage. So it is very rare indeed to find any amplifier that is fully voltage regulated.
So exactly how does a voltage regulator work and what makes it so wasteful and hot that using it is impractical? The most common type of voltage regulator is called a "down" regulator. This means that it pulls down the power supply's voltage so that it remains stable under the worst case conditions.
For example, all quality preamps are voltage regulated so that their power supply voltages will remain stable all the way down to a mains voltage of around 90 volts (using a 120 volt mains). Only if the mains falls below 90 volts ("brown-out" conditions) will the regulation be insufficient and the power supply voltage will start to fall.
The power supply will be driven by a 120 volt mains most of the time, although it might be up to perhaps 125 on occassion. The difference between 120 and 90 volts is about a 30%.
Let's assume that the preamplifier's electronics operate on 12 volts. The electronic engineer will design the power supply to deliver at least 30% more voltage than that (typically about 18 volts). He will then add a "down" regulator to pull the power supply voltage down to 12 volts, which is about the voltage that the power supply would produce using a 90 volt mains. So for any mains voltage between about 90 and 125, the preamp's power supply voltage will be stable at 12 volts.
The regulator actually works by placing a variable load across the power supply in the form of a power transistor that is shunted across the output. A power transistor can be thought of as a very fast-acting, variable resistor whose resistance can be changed electronically. By monitoring the rail voltage, the electronics can adjust the resistance of the transistor to alter the voltage.
As the mains voltage rises, the electronics will reduce the resistance of the loading transistor, which will draw more power and drop the power supply voltage. As the mains voltage falls, the electronics will increase the resistance of the load transistor, which will reduce the power used by the transistor and allow the voltage to rise.
Of course, the action of the electronics are nearly instantaneous, so there is no significant rise and fall of the rail voltages with changes in the mains. The voltage will remain rock stable to within a tiny fraction of a percent.
A down regulator is very inefficient. This is because it operates by feeding a voltage through a resistance. This causes a voltage drop by converting some of the power supply's current into waste heat.
Remember the above concept because it is extremely important. To repeat -- anytime you apply voltage across a resistance, there will be a voltage drop. The loss of current causing the voltage drop will result in waste heat.
The circuitry in a preamp uses only a tiny fraction of an amp (typically just a few milliamps). So the power involved will only be a fraction of a watt or so.
If you waste 30% of a watt in a voltage regulator, the heat produced and the electricity wasted is insignificant. So nobody cares about the efficiency of down regulators when used in small-signal devices.
But now let's look at power amplifiers. Just how much power do we need to regulate?
The typical Class AB amplifier is about 50% efficient. Why? Because it applies its power supply voltage to its output transistors and these act as variable resistors that control the voltage being applied to the speaker. So once again, we have the issue of producing waste heat because we applied voltage across a resistance.
This means that for every watt that the amplifier feeds to the speaker, a watt will be injected as heat into its heat sinks, and two watts will be drawn from the mains. A powerful amplifier like the Magtech will produce 500 watts per channel into 8 Ohms. With both channels operating at full power, 1,000 watts will be fed to the speakers. It also means that about 1,000 watts of waste heat will be fed into the heat sinks, and 2,000 watts will be drawn from the mains.
The Magtech's power supply will produce 2,000 watts continuously, so a regulator must be able to control a minimum of 2,000 watts of power (and more to be conservative). The regulator must be able to regulate at least 30% of the rail voltage in order to eliminate fluctuations in voltage due to the variable music demands. In addition, it must be able to handle more than that to account for voltage variations in the mains and 50 Hz operation.
All together, we are looking at regulating about half of the power supply's voltage. This is a daunting task for a down regulator because it means that under worst-case conditions (maximum mains voltage, 60 Hz mains, and with the amp at idle), the regulator will have to dissipate half the power supply's voltage (and hence half its power) as waste heat.
That means that the regulator would produce 1,000 watts of waste heat. This would turn the amp into a room heater and require truly massive heat sinks. It would waste enormous amounts of electricity, be very large, and the heat would cause failures of parts over time. You should now be developing an appreciation of why amplifier power supplies are not regulated!
Although down regulators are very simple and easy to add to circuits, they are just not practical for use in high power circuits due to their inefficiency. But there are other types of regulators, which are more efficient. These are the "up" regulators.
An up regulator requires two power supplies. These have different voltages where one is set for the worst case voltage and the other is set for the best case voltage (say 120 volts and 90 volts for example).
The two power supplies are connected together by a power transistor whose resistance can be varied to allow more or less of the high voltage power supply to be added to the low voltage one. This allows the high voltage supply to bring the voltage "up" and prevent it from falling based on load or mains voltage. The rail voltage can therefore be kept constant between the two extremes by electronically controlling the coupling transistor.
The big advantage of an up regulator is that it only has to handle a percentage of the total power supply voltage (in this example, 30%) instead of all of it. Therefore the losses and waste heat are only a fraction of those produced by a down regulator. But it requires two power supplies, is more complex, and more expensive than a down regulator.
An up regulator still wastes far too much power and produces too much waste heat. So it is still impractical for use in all but very low-power amplifiers.
The next general type of regulator is not a linear regulator like the types I have been describing. It is the switching regulator.
A switching regulator is rather complex, but I'll simplify its operation for clarity. A switcher fundamentally places a transistor in series with the output from the power supply. This transistor is then switched on and off at a high frequency to feed power to the electronics.
The transistor oscillates at a fixed frequency and its "on" time is varied so that it feeds a percentage of the power supply's current to the electronics based on their need. By feeding a capacitor bank, a switcher can adjust the current flow to produce a stable voltage.
Switching power supplies are very efficient (although not 100%) because their transistors are used in only the on or off state. They are not partially turned on like the transistors in linear supplies where a significant resistance is presented to the voltage that produces waste heat.
However, a transistor does not change state instantly. There is still a small percentage of switching time during which the transistors are changing state and resistance is present. So they still produce some waste heat, although this is relatively small, can be tolerated, and therefore switching power supplies can successfully be used in power amplifiers.
But there are big problems when using switching power supplies in high power applications. The main one is noise -- both electrical and mechanical. When switching high power and voltages at high frequencies, radio frequencies are produced. These emissions can adversely affect associated audio electronics and cause instability, oscillation, noise, and general misbehavior.
Powerful switchers also make mechanical noise because there is physical vibration of the switching transistors due to the high currents involved. Switching power supplies are vastly more complex than a simple, 3-part, linear supply and therefore the reliability of switching supplies can be a problem.
There are also many technical problems when designing switching power supplies that make them quite difficult to make work satisfactorily. I won't get into any more detail about this, but rather simply point out that because of all the problems, it is extremely rare to find a linear amplifier with a switching power supply. They do exist, but are not 100% efficient and are not a practical solution for the voltage regulator problem in power amplifiers.
Of course, I have just outlined the basics at this point. There are many variations on the theme that are beyond the scope of this paper. But you should now have enough information to appreciate the solutions that follow.
So how can the efficiency problem of high power, regulated power supplies be solved? Well, the answer came from thinking outside the box. Specifically, since the heat is produced by applying a voltage to a resistance, the solution had to come from figuring out some way to eliminate doing so.
There is a way. But it could not be done by regulating the continuous DC from the output of a power supply's capacitors because voltage is always present there. The solution had to be done by figuring out a way of regulating without having voltage present. That sounds crazy and impossible, but it can be done.
What about the output from the rectifiers? This is pulsating DC. While the peak of each pulse is at high voltage and power, the voltage at the end and beginning of each pulse is at -- ZERO!
If the regulating power transistor operated only when the voltage was at zero, then there would be no current present, none would be wasted, and no waste heat would be generated. But how can that regulate the voltage? Here's how:
The Magtech uses two power supplies as you would in an up regulator. I call the low voltage one the "ride" supply. It is exactly like the power supply in a conventional, unregulated amplifier.
The second power supply is the "boost" power supply. It has a higher voltage and current rating than the ride supply and can add massively more power to the ride supply when needed.
The ride supply voltage is set for "easy" operation under optimum conditions, i.e., when the mains voltage is at maximum and the amp is at idle. Under these conditions, only the ride supply drives the amplifier circuitry and the boost supply is just on standby.
Note that for the Magtech amp, this is the "easy" condition when the regulator does nothing. By comparison, this is the toughest condition for a down regulator because it has to drag down the power to the worst case level and dissapate massive amounts of power and heat when doing so.
But in the Magtech, this is the voltage that is desired and that the regulator will maintain. Under these easy conditions, the boost supply is not needed.
When significant power is required, the rail voltages will start to fall. This is detected by the power supply's monitoring circuitry, which then switches on the coupling transistors to connect the boost supply to the ride supply. The additional power provided by the boost supply prevents the rail voltage from falling, thereby regulating it.
The key to efficient operation lies in the way that the coupling transistors are operated. First, they are either fully switched on or fully turned off. This means that they have either infinite resistance or essentially none. This prevents them from putting any resistance in the circuit that would cause them to dissipate heat.
Secondly, digital control circuitry is used to monitor the rectifiers' wave form and cause the transistors to switch states (either on or off) at the exact point where the DC pulses cross the zero voltage point. This is important because even though transistors change states very quickly, they do not do so instantaneously. So there is some resistance during the change of state. This is the same problem that causes switching power supplies to be less than perfectly efficient.
If the transistors changed state while the power supply voltage was applied to them, there would be waste heat generated. By only allowing state changes at the zero voltage points, there is no waste heat.
Now if you are observant and thoughtful, you might comment that this does not sound like a very good regulation scheme because the two power supplies are either at maximum voltage or minimum voltage because the regulator operates as an all-or-nothing affair. Your thinking is good, but you are overlooking an important feature in the Magtech's power supply.
The digital control circuitry constantly monitors the pulsating waves from the regulator and the rail voltages. It will then make a decision to turn the coupling transistors on or off at each zero point to add as many or few pulses as required to hold the voltage constant.
Under heavy load, the coupling transistors would remain on (possibly even continually), letting most or all of the pulses through. Under light load, they would only be switched on occasionally to let a few pulses through.
While it is true that the regulator has a maximum resolution of 120 pulses per second, each pulse has to charge up a very large bank of capacitors (80,000 uF). Doing so takes time and much current. Therefore, even though each pulse has a lot of current and energy, it can only make a very small change in the capacitor bank's voltage.
The electricity and voltage in the capacitors are analogous to the water in a swimming pool. You can dump a large, 55 gallon drum of water into the pool (a pulse from the boost power supply), but it won't change the level of the water in the pool (the voltage in the capacitors) very much.
By adding more or less pulses as needed, the regulator can maintain a stable voltage to within 0.2 volts. By comparison, without the regulator, the power supply's voltage would vary by more than 50 volts. Which would you prefer?
You can now see why the Magtech regulator produces no heat and is virtually 100% efficient. Technically, I can't claim that the regulator is absolutely 100% efficient because nothing is perfect and there is a very tiny amount of resistance in everything, including the coupling transistors when they are "on."
But the resistance of the transistors is less than one Ohm, so they still do not get even warm when operating. Furthermore, they only operate when the amplifier is working fairly hard, so the regulator isn't even active when the amplifier is at idle or at very low power.
In some ways, the Magtech's power supply is like a switcher in that its transistors are either on or off. But there is no specific oscillation involved as in a switcher. Also, it is relatively simple and operates very little and at low frequencies, so its reliability is outstanding (no failures have ever occurred). And because it never switches under power, there is no noise or radio frequency problems with it.
In short, the Magtech's power supply is unique and solves all the problems of other regulators that have prevented power amplifiers from being regulated -- something they badly need even more than other types of electronics. The Magtech regulator's circuit, and particularly the digital control technology involved is the subject of a patent, which currently is pending.
The Magtech amplifier modules are the same sophisticated ones used in the ESL amp that are capable of very high power, the ability to drive 1/3 Ohm loads, can handle the most difficult loads (as presented by electrostatic speakers), and need no protective circuitry that ruins the sound of many solid state amps.
When the ESL amplifier modules are combined with a practical voltage regulator, the result is an amplifier with seemingly unlimited power, virtually unmeasurable distortion, and the ability to drive even the most difficult loudspeakers with ease. The Magtech offers a truly new level of performance in amplifiers.