Past Life Recall #5 Audio Amplifier

July 3, 2007 – 11:25 am Print This Post

The Kingston Triad DC Audio Amplifier
This document refers to my recall of a device and an experience in what I consider to be a past life. The posting may be incomplete but the concept is well expressed. The recall is regarding a basic amplifier design used by musicians and home users alike. It’s based on a an idea derived from a family business, a group that designed, builds and sells this specific series of audio amplifier.More…
The Kingston Family is a well known british family who design, manufacture, sell and support a line of audio amplifiers based on a special mosfet switch design which enables the use of a single sided DC power supply. The design is called a TRIAD and comes in various models. A few of which I recall: Viga, Vigo, Vigo Timbre and Aida. The biggest difference between this design and designs we use is the implementation of a mosfet SWITCH (rather than a transistor) to change the polarity of the power supply. Using a single sided power supply and switching it’s polarity in response to the input signal is the hallmark of the Triad Design. The Timbre option added what’s called Virginal Outputs to the design, implemented by a power supply circuit designed to shorten and dampen the tank circuit formed between the loudspeaker and the amplifier output stage. Additionally a later model employed a voice coil damping circuit in the power supply winding and was sold as a kit in conjunction with an 18? 3 way loudspeader system designed specifically for this amplifier. All this, combined with the removal of all reactive component (inductors and capacitors) in the signal path, is done to significantly reduce distortion. Especially phase angle distortion, i.e. the instantaneous angular change between any two data points in an impulse response graph. It might be of interest to Audio Enthusiasts and Engineers.
In it’s output it has three separate trans-stators or transistors driven by a single power supply. Each output stage is driven by a filter that uses a digital dividing network operating at about 400 mHz rather than the usual passive crossovers or reactive bandpass filters used in current systems. The result is an almost unbelievably solid bass response combined with the clean midrange one hears in a small (3?) single speaker. It’s design is even used in communications equipment to increase intelligibility for voice communications.

Basic Amplifier Circuitry:

A transitive state device is basically an electronically controlled resistor. It has three connections. The INPUT, the OUTPUT and the GATE. The input is connected to a power supply. The output to a speaker and the gate is connected to the input signal. Seems easy in theory. However, a transistor is also a diode, meaning it passes current in only one direction. Either from the input to the output or from the output to the input.

Audio signals are an alternating current meaning they occur both above and below a reference ground. In the drawing below, the red represents an AC voltage and the black represents a ground reference.

This being the case, two transistors are usually required to amplify the input signal. One transistor amplifies currents that are positive in relation to the input ground (above the black line in the drawing above) and the other amplifies currents that are below ground (below the black line). The basic audio amplifier therefore has a power supply that supplies current both above and below a ground reference called a split supply. The positive side is connected to one transistor, the negative is connected to the other. The gates are connected together so that when the input signal is applied, the output is theoretically a larger version of the input. As with all theories, there is a catch. A transitive state device is generally non linear in its output compared to its input. For example, an input of one and a gain of 10 should result in an output of 10. But the transistor is usually either above that output or below it, depending on the input voltage. This lack of exact input to output tracking results in distortion, sometimes severe distortion of the input signal. It also means that many different controls must be applied to the circuit to correct for the non linear response. Another factor is that in order to get the transistor to begin conducting current, an input voltage must be applied to the gate to preload the gate so all of the input signal will be amplified. Without adding some kind of bias (a small voltage) to the transistor, it will only amplify 80% or so of the input signal. This results in even more distortion. In relation to the input signal. Many different designs have been tried to effect this correction but they all suffer from some form of distortion. Some have fairly low distortion, others are quite high.

Amplifiers are rated by class. Classes are A, B and C respectively.

Class C amplifies less than 100% of the input signal and uses a dual transistor output. Typically little is done to bias the output so part of the input signal is lost. A class C amplifier is mostly used for really inexpensive devices and are seldom used anymore for consumer audio.

Class B amplifies 100% of the signal using a matched transistor pair. Class B amplifiers are the most common as they can have low distortion and they are relatively efficient.

Class A uses a single transistor to amplify an input signal.. To overcome the single direction flow of the transistor, a direct current voltage is applied to the circuit generating a greater than usual voltage in relation to the output. This causes the output to swing between power supply ground and full output in relation to the input signal. The supply ground becomes the lowest voltage the amplifier can deliver, the bottom of the red curve in the graph above. The output ground reference is a floating ground, meaning it’s not the same in reference to the power supply or the input. The result being that there is no switching on and off of a pair of transistors, The output swings between full on and full off with the center of the swing being a extrapolated ground reference roughly centered in the middle of the voltage range. This causes the output to change polarity in relation to the ground so it can drive a loudspeaker. This setup works well in reducing linear distortion but can add distortion if not well designed. Additionally, the transistor can be biased (the voltage range increased) such that it operates in a much more linear voltage range for the transistor.

Power supply Primers:

A typical audio amplifier power supply uses a single transformer with either two separate output windings or a center tapped single winding. It’s basically a large coil of copper wire plugged into the wall socket. The first coil, called the Primary Winding generates a magnetic field that takes a bit of time to build up. When the input voltage changes from above ground to below ground the field reverses it’s polarity. The more turns of wire on the primary winding the more time it takes for the field to build and collapse. Power from the wall socket alternates at 60 times a second. So, when a primary winding has just the right number of turns on it for the wire size, the magnetic field is collapsing at the same time as the voltage is rising causing a delay in the collapse. The delay time is typically measured as a phase angle (rotation around an arc). The delayed collapse of the magnetic field results in what’s called reactance. Its like resistance but it only works with Alternating currents. Think of a ball on the end of a rubber band attached to a paddle. If you hit it at just the right speed, it will bounce nicely, too fast and you miss the ball. A Direct Current applied to the transformer will overheat the primary winding and burn it up in a few seconds. But the 110 volts from the plug, due to the reactance of the primary winding, will just sit and cycle endlessly with very little current flowing at all.

To get usable power from the transformer a second winding is added to the primary call a Secondary Winding. Usually wound around the outside of it. The second coil is immersed in the rapidly changing magnetic field of the primary winding and as such, can be used to capture some of it’s energy. A secondary with fewer turns of wire than the primary winding will reduce the voltage. A secondary with more turns of wire will increase the voltage available at the output. A transformer that increases voltage also reduces the current available and a transformer that decreases the voltage will increase the available current.

If a wire is attached to the secondary at the center of it’s winding, (a tap), it can serve as a ground reference for the transformer. This is the basic type of transformer used in most audio amplifiers. The center tap is the ground and the two ends of the winding are the plus and minus voltage in relation to the ground.

In the drawing above, the red line represents a voltage between the left output and the center tap, the green represents output between the right output and the center tap, assuming the tap is at the center of the secondary winding.

Simple enough. Now we have power but if we hook it up like this we’ll hear the 60 cycle per second hum in our amplifier and probably little else. So, we need a way to convert this output from AC to; DC (Direct Current). For this we can use a transistor. But rather than use a transistor with three wires, we’ll use one with only two. An input and an output. A transistor like this is called a diode. DI-meaning unidirectional. Ode, meaning to pass. So hooking a diode up to the output (making three wires; left, ground and right) produces an output that represents current passing in one direction. When we combine a few diodes into a bridge, we can get a full wave DC output. The colored lines above become like those in the graph below. It’s a rippled output because the diodes, being transistors, don’t turn on until they have some voltage applied, they switch on and off a little bit. But, notice that they are above the black line which means they have a DC (forward, directional) component. They have forward or reverse flow. The red would be a forward or positive bias and the green an backwards or negative bias, in relation to the center tap of the transformer. Keeping in mind that we are using two bridges, one for each half of the transformer output. The result is three wires. Plus, ground and Minus.

Now, to remove the ripple, several techniques are used. I prefer whats called a PI MU filter. It’s made using a separate bridge identical to the first one hooked up in parallel. The second bridge has it’s output leads reversed (plus is hooked up to minus and minus to plus) and is connected through a large value resistor to reduce its voltage. Both bridges are connected to the same output. This way the ripple that’s generated by one bridge is reversed by the second. Its called PI MU because it uses a transform function PI (the second bridge) to MU or Moot the DC ripple in the output. Using the same bridge as that being in the current drawing part of the power supply ensures a similar switching characteristic. The result is a very smooth DC output with less than a few millivolts or ripple . Some people like to add a capacitor to the supply as well. However, as I’ll note later, this can have a disastrous effect on the stereo imaging quality of the amplifier. There are additional circuits that can be employed to further reduce noise but this arrangement is a very good, clean, unregulated power supply. Note that a PI~MU filter will also deaden voltage spikes from noisy motors and other unfiltered devices like electric drills, blenders, etc. which is a definite plus.

Loud Speaker Basics:

Next is a discussion of the basic speaker system and how it interacts with the amplifier. A Speaker, also called a transducer or transitive state inducer, is a coil of wire wrapped around a small tube. The tube is mounted to a speaker cone and has a permanent magnet mounted inside the tube. The amplifier is connected to the coil of wire wrapped around the tube. When the amplified signal flows through the winding on the tube, it generates a magnet field. The EM field generated by the coil, (called a voice coil) interacts with the permanent magnet such that current in one direction (Plus to Minus) moves the coil, the tube and the speaker cone in a fixed direction. When the current reverses it’s polarity (Minus to Plus) the coil, tube and speaker cone move in the opposite direction. This is how a speaker converts the electrical energy from the amplifier to the air so we can hear it.

Again, in a perfect world there would be no other interactions. However, if one hooks a voltmeter to the speaker without an amplifier and pushes the cone, a current can be noted. A voltmeter is sensitive but only to the aggregate of the input voltages. A scope that can draw the voltage on a display is more useful in visualizing the current generated. In some cases the current can be very high. This effect is called Back Emphasis or Back EMF (electromotive force) and it’s a force the amplifier must deal with. When the speaker is connected to the amplifier output a tank circuit is formed. The circuit is a closed loop with the amplification signal added to the tank. The size and shape of the tank will have an effect on how the entire system sounds. Thus, the Back EMF can cause significant distortion in the signal of an amplifier if its not dealt with appropriately.

As an example: if you have a speaker with a woofer larger than 5 or so, and you remove the grille so you can push gently on the cone you can try this: Disconnect the speaker leads from the speaker and gently tap on the largest cone, called the woofer. Note how it moves rather easily when tapped gently. Now connect the speaker leads together with a wire. Not the amplifier outputs but the leads that are on the rear of the speaker. A paper clip usually works for speakers with push connectors. If there are bare wires, you can just twist them together.

Now tap on the cone and note the difference. Now you can begin to appreciate how much influence the back EMF has on cone movement.

This issue comes up later in the discussion.

Amplifiers and Back EMF (Back Emphasis) Damping:

When the amplifier is operating, the Back EMF from the driver is driven back into the transistors being used to drive the voice coil. Since the transistor conductance is a function of the input signal, the transistor itself is where most of the EMF is applied. Since the transistor is a transitive state device, the quantity of EMF damping available is relative both to the transistors themselves (via the input signal) and to their source of power. So, the greater the applied input signal, the better the damping. But, because the EMF is always AFTER the initial signal, it’s difficult to measure just how well an amplifier damps it’s effects. The EMF from a cone with a stiff surround and spyder (the amber looking thing at the base of the cone), can be very large as the surround and spyder push the cone back towards center. Regardless of the input signal, there is some current being generated this way. If a signal such as a drum beat ends suddenly, the transistor is turned OFF and the Back EMF has nowhere to go. Since there is no such thing as a free lunch in reality, it usually bounces back and forth in the wiring of the tank circuit until the voice coil eats it up as movement (ringing or booming) or as heat in the voice coil, or both. In general, the lower the aggregate DC resistance of the output transistor pair, the better the damping because the tank circuit is electrically smaller so less echo occurs. In a Class A design, there is somewhat better tank damping because the transistor is operating at a lower impedance (it’s ON to some degree all the time) than in either Class B or Class C designs. The result in listening tests is a more Solid sound. Not just in the lower frequencies but over the entire range. However, much of the improved damping of a Class A design is offset by it’s enormous power supply which means a rather long secondary winding and complementary high impedance. That High impedance cannot dissipate the EMF, being part of the tank as well as a short winding, as I’ll discuss later.

While it’s correct that the bridge rectifier will block some of the Voice Coil EMF, the EMF itself changes the load that the power supply sees (by changing the load into which the power supply drives) which causes the power supply windings in the transformer to absorb some of the impact. If the winding is long and has relatively high impedance, it will provide little damping and may even add ringing to the overall output. If the supply winding is short (few turns) and has low impedance, or it has an effective path for the EMF, the power supply winding (transformer secondary winding) will be able to absorb the energy by generating an EMF in the form of a magnetic field within the transformer winding itself. This field then transfers the energy to the primary winding and eventually back to power line itself where it can be dissipated in the power grid. The overall result is called Damping. In general, and strangely enough, the larger the power supply the less it will damp or absorb the back EMF from the driver. Reason being a larger power supply has more turns of wire on it’s secondary making it less effective at damping the EMF from the voice coil. In an amplifier that operates with the driver voice coil in mind, the Back EMF is accounted for and an appropriate path for its disposal is provided. The most effective means of disposal is as described above, short secondary winding in the supply output.

Note on regulators: there is some evidence that a power supply that uses a regulator to maintain its output voltage has an even more difficult time dealing with back EMF than does an unregulated supply For this reason many power amplifiers don’t use a regulated supply. Those that do suffer from poor EMF damping, even if all other measurable aspects of the amplifier are rated very high. Sometimes a Class B amplifier can outperform a Class A in terms of focused acoustic image because of it’s lower output impedance and subsequent high EMF damping.

I’ll be discussing an amplifier design that takes all these things into account, and much more. Very much more.

Simple Tranitive switching Primer:

A transistor, also known as a Transitive State Resistor is just that, a variable resistor with an output that can be varied by a control voltage. Even though it’s used in many applications as a switch, it’s actually a rather slow device in terms of switching currents. The two general types are the Junction and the Field Effect.

In a Field Effect Transistor, the input is linked to the output directly and controlled via a gate voltage. The FET transistor contains a conductive channel with the field gate partially embedded within the channel (either in the side or on top). In the FET or Field effect transistor the current either flows or is reduced by the field current, depending on it’s basic arrangement and the materials used.

In a Junction Transistor the channel is separated by the gate (usually called the base). This means there are actually two junctions. Input to base and output to base. One can increase or decrease the current through the transistor by altering the base voltage. Usually between the output and the base but having two junctions has advantages at times.

A Trans-stator device is a semiconductor device similar to the stator winding in an alternator. I recall them being used in a large power plant as replacements for the stator windings in the alternators that generate power for a large city. (such a device can also be used to generate a stable magnetic field which is why it’s included here. It gives one something to think about) A transtator contains chemicals impregnated within a very long, very large channel. The unique thing about a transtator is that it will generate current when exposed to a changing magnetic field. They usually contain a field channel as well but unlike the FET transistor, the field is mounted atop the stator channel rather than being embedded within it. The TSField connection has a rather large current applied to it to crowbar the alternator output (generate very high stator resistance) while the alternator is being started. Once running the TSField current is reduced which increases the conductivity of the transtator. It’s then used to monitor the grid as a way of regulating the field coils in the alternator. The more power the grid uses, the lower the field current and the greater the output to the grid. Kind of a neat idea as long as safety measures are taken to prevent a TSF short… The Trans-stator itself is made from very clean elements: Hyde copper (copper with hydrogen replacing the oxygen molecules), Lead, and a alkaline buffer, usually some kind of cull from Peroxides. The large transtator channels are mounted inside the alternator housing and when properly aligned (1/16th inch clearance or so), provide much greater power output due to their efficient conversion of magnetic to electric current, than a copper or aluminum stator winding. The stator can also withstand collisions better than a wire stator winding. The power plant that used them was able to generate 5 terawatts using three large alternators on a large DAM. A place I visited and pondered at great length. Imagine using such a device to build a silicon chip based power transformer.

Metal Oxide Switches:

After much experimentation, a rather clever pair of engineers designed a semiconductor Metal Oxide switch that has NO transition between on and off like a transistor. It’s called an INMOS (Indium Niobium Metal Oxide Switch). The device is similar to a junction transistor but it has switching times in the gamma (as in gamma radiation) range. I don’t know how to express it in nanoseconds but it’s powers of 10 faster than a transistor. I also recall them being used for computer memory circuits. When doped properly they have a benefit in addition to switching currents. They can also store a static charge. With appropriate circuitry they can be used to store analogous data as well as digital data. I recall being able to purchase them in what’s called a TerraBlock, The T indicates Terra so they contain a trillion bits that can each store a voltage which can be read as either a digital ON or OFF, or as a discrete voltage level. They are used to store any kind of voltage level within their rated range. One purchases them as either Flat (binary) or multi Dimensional.

The 2DTB6400 is a Terra Block that can store 64 discrete voltage levels. The multi dimensional blocks all come in various voltage levels from 64 to 1024. So a terrablock semiconductor can store just over 100 gigabytes of binary data or 1,000,000,000 discrete voltage levels. They are really cool because the junction maintains the voltage without any refresh, just like a CMOS making them perfect for carrying around large amounts of data. As long as they are protected from accidental discharge, they are just like a CMOS but they can be both read and written at several hundred terahertz.

Transitive State Switch:

As noted above, a transistor is a transitive state resistor. Using the same type of experimentation that was originally used to design the first INMOS device. Later experimentation led the two young professors to try various elements in an attempt to slow down the gamma speed switching of the INMOS. Their idea led them to using lead as the channel and platinum as the gate. The result is a transitive state switch. A switch that varies it’s output voltage as fast as a INMOS but the output can be controlled by the gate voltage. The most useful thing about the Plexus Switch is that it’s output nearly perfectly matches it’s input. It requires NO forward bias to begin conducting current and as an amplifier, it’s output is so linear it can amplify a near gamma signal.

Because: It’s not a transistor, it’s a SWITCH!

While at present I can’t open a catalog and purchase such a thing, they will be available soon. I suspect within the next 20 years or so.

Note that present computer RAM relies heavily on the transitive state resistor as a switch. And a transistor is a very slow device compared to a switch. Transistors have to swing the output current by generating a conductance field whereas a switch does not. It’s usually either ON or OFF. For the most part.

The Kingston Triad DC Audio Amplifier:

Vigo: a term indicating saturation

Viga: a term indicating just below Vigo

VigaDeVigo: a term used to describe crossing a saturation boundary. In this context it refers to saturation of the output transistors. When operating properly the output transistor is in Viga – De – Vigo. Meaning it’s on the saturation boundary.

Most Kingston Vigo amplifiers for stage or outdoor use are VDG or VDV type amplifiers. Because they use a switch in the power supply they like to run wide open. It’s difficult to get them to settle down for home use. The Kingston Vigo timbre 440S has a single 60 turn 440 volt primary winding and a 62 turn secondary and the Vigo timbre 440D has two 440 volt ilolation transformers in it’s power supply. It has to have a special secondary winding and a special slow start circuit to get it up to idle. Trying to turn on such a transformer can be difficult because it appears as a dead short to the power grid and pops the breaker. Once running though it idles fine and can deliver many thousands of watts through the bridging switches to the 22? Carson Engineering or Coherent Technologies coaxial stage drivers. VDV is generally not desirable in a home system where the amplifier runs at 30% or less most of the time. So, a newer design was made using the Plexus switch to reduce the voltage available to the output stage and thereby reduce the gain. It actually changes the voltage availale to the output stage thereby reducing gain. There is still a fixed gain output stage but the Vigo timbre (no VDV) is a variable (power supply regulated) gain amplifier whereas the VDV version is a fixed gain, variable input amplifier.

See my post on Yorkshire Pass Concert for examples of how they are used (may not be written yet but I’ll get to it)

As indicated above, current audio amplifiers usually employ a split power supply to drive their outputs. Such a supply is generally considered necessary to properly amplify an AC signal because the input is also an AC current.

The Kingston Triad DC Audio Amplifier is a design that uses a single, short secondary winding in a single sided supply. It provides a single Direct Current supply voltage and a few silicon devices called switches to effect a power amplifier that operates in single transistor Class A output mode without any need for high current consumption bias.

The basic idea is simple; In current audio amplifiers the input signal relies on a supply voltage that provides potential both above and below the output ground reference (called a return path). In the initial Kingston design, a single DC supply voltage is used to drive both sides of the output. When the input signal is above ground, the supply is connected in a positive configuration. When the input voltage is below ground, the power supply is connected in reverse. This allows a single output transistor to be used without the usual DC bias that chews up lots of current to maintain it’s output ground reference. It also has the added benefit of providing a single, short transformer winding to absorb the Back EMF from the driver. While conventional thinking may lead one to conclude that because there is a bridge rectifier between the supply winding and the voice coil that the transformer winding has little or no effect, such thinking is not based on experimentation. In reality terms, the shorter the secondary winding in the power supply, the better damping the driver sees. In fact, in some cases the drivers can be over damped which sounds OK but the lower frequencies tend to vibrate the house rather than project into space. Some people like the boom from un under damped driver. Kind of like the BONG bells that people put in the back of their cars. Not very musical but they sure can BONG really loud!

Note: Voice Coil damping is also contingent on an effective return path to the power supply as well as the output impedance of the supply itself. A concept that will be revisited in the Asymmetric Virginal output design. And refined in the Timbre option that is available on the Kingston VIGO Timbre. An option that helps maintain the timbre, the minute angular changes in the waveform, of a high quality recording. To take advantage of such a device one either needs to use a live input or store a recording at a minimum of 40 MHz sampling rate. Tests show that with well designed systems, the average person can detect changes up to a sampling rate of about 4 GHz, although such a recording would be prohibitively large. However, in studio work, such high sampling rates could be converted to a more efficient storage and used to make extremely high quality master recordings.

The initial Kingston design used an INMOS switch rather than a transistor to reverse the power supply voltage because it’s not a transitive state device, it’s a switch. At least in the initial design. Later designs used a hybrid Plexus Switch (made using platinum and lead) to switch the voltage from +/- to -/+ mode and as the main voltage amplifier for the output. Reason being that the hybrid trans-state switch has an extremely linear output voltage in relation to the drive or gate voltage. The final output in both designs is driven through a large, high quality plexus switch or transistor to ensure correct output polarity and to limit overall gain. The early device had a variable Gate knob to alter the output volume, the later version uses a Gain knob to alter the output gain. The gate control is just that, it alters the signal applied to the gate of the output transistor. The later design alters the signal applied to the power supply amplifier such that it alters the overall gain of the amplifier. The output is then gain limited by a fixed resistor on the output stage gate.

The result is an amplifier with NO transistor crossover distortion at all and even with a transistor output it can easily outperform any currently available audio amplifier. While this may seem like a good idea at first, the amplifiers in use today are quite effective at smoothing out the rough high frequency distortion of most digital recordings. Consider that at the standard CD recording at 48 KHz sampling rate, there are less than four data points in the output to represent a 20 KHz signal. At half that (10 KHz) there are only a few more. The result is a very gritty, low quality high frequency reproduction and the Kingston Vigo would no doubt let you hear every square edge on those high frequency waves.

Presently such switching devices aren’t available but they will be very soon. I’ve already seen actinides being uses as transitive state devices and it’s only a matter of time until a usable mixture is found that will replace the lowly transistor for this kind of duty. However, since there are few if any actinide switches or Plexus transtators available in the current market, (they were designed originally for use in a Power Distribution grid for a Power Utility), a transistor will have to do if I’m to build one.

The Kingston Triad output:

Uses a single transistor output and switches the polarity of a single power supply rather than using a matched pair of output transistors coupled to a split supply.

Benefits of such a design:

A Single sided supply means a single secondary winding providing better voltage uniformity, better linearity, NO DC offset and consequently less overall distortion.

A high, unregulated supply voltage means faster rise times and more accurate angular reproduction of the input signal. (Much more accurate phase characteristics, even at low volume levels)

Building the supply with high voltage available means a shorter output winding and consequently and shorter tank circuit which provides more uniform damping of driver EMF.

The Kingston design also used a separate output stage for each driver, gated by a high sample rate (400 mHz) digital dividing network (two way, three way etc.) which eliminates the loudspeaker crossover altogether and therefore most of the tank circuit issues related to damping.

Switching the supply voltage rather than using two separate supply windings provides a much simpler power supply. In fact, for the most part the transformer is a 1:.75 or 1:1 transformer. In a more advanced design the primary is wound short (60 turns or so) and additional EMF is supplied in the secondary winding to prevent primary burnout. This enables a very short secondary winding which is far more effective at delivering high currents at low frequencies and damping loudspeaker EMF.

No capacitors or inductors are used in any part of this amplifier to prevent reactive distortion (phase distortion). The complex and absolutely necessary phase relationships of the input are maintained from head to tail resulting in the ability to focus an acoustic image as one might focus a camera. It makes sense and test prove over and over and over again that the use of any reactive components in the signal path introduce significant phase relationship distortions that destroy the acoustic focus of the stereo image.

Please post a short comment below so I know you were here.

  1. 6 Responses to “Past Life Recall #5 Audio Amplifier”

  2. i still do not which one to choose? Vacuum Tube audio amplifiers or the Transistorized ones~;-

    By Sebastian Sanders on Aug 11, 2010

  3. the best amplifiers are made boy Bose and Sennheiser;”.

    By Brian Hughes on Sep 30, 2010

  4. my audio amplifiers are built on LM series integrated IC’s and they sound great too::-

    By Granite Tiles  on Oct 17, 2010

  5. Okay – here are some suggestions:

    Crate V5. This is a 5 watt amp without any effects. Before you laugh – hear me out. It’s a “class A” circuit. I’d take 5 watts of “class A” power over 50 watts of a regular circuit. If it doesn’t sound like much, you have to keep in mind that, for example, when you blast your 400 watt stereo, you’re operating under 10 watts most of the time.

    By Zoey on Apr 19, 2011

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