MA-70 - 70-Watt Magnetic Amplifiers


If there is one thing that can be said about the MA-70 for certain, it's that it's unique amongst amplifiers. It has a wonderful inner clarity and realism like no other amplifier we know of, at any price.

Operation type:
70 watts Class A/B Current injection construction - a purely current driven amplifier
Single stage equivalent amplifier

Specifications:
Speed/Slewing rate: 400 V/µs
Input impedance: 5k
Frequency resonance 1Hz-2MHz
Signal to noise ratio: 120db
THD: 70 watts below less than 0.0001%
IMD: Measured with 19 & 20Khz intermixed equally 0.0005%
Total square wave distortion: Less than 0.001% Musical signal
Damping Factor: 1000
Musical Fast Fourier transform distortion: Less than 0.01%

First, MA-70 amps utilize a magnetically coupled transistor. This transistor uses a powerful magnetic field to help align electrons as they go through the transistor. This makes the transistor more linear, lowers quantum noise in the transistor, and gives electrons a pathway of powerful magnetic lines of flux to follow through the transistor. We refer to this as a "magnetically driven transistor" however it does not actually amplify in the magnetic domain. The amplification of the transistor is simply improved by lower noise.

The MA-70 uses 4 magnetic waveguides. One pair on the A/C side of the secondary of the transformer, and one pair on the rectified path in DC. These waveguides are the same as the ones used in the Professional series power cables.

A 1.5 KVA transformer powers 400,000µF of capacitance per amplifier, and is coupled with a infinite capacitor circuit. Each 100,000µF power supply caps are further dampened with 2.2µF coupling capacitors. The transformer floats suspended in a viscous silicone gel that dampens vibrations caused by the transformer function. Transformers inherently vibrate and this vibration is a major cause of hardness and noise associated with solid state amps. By holding the transformer in a flexible viscous gel, it halts the transfer of vibrations to the chassis and circuit board, as they are instead absorbed by the gel.

Special high-speed rectifiers supported by the wave guides drive the 400,000µF of capacitance. It takes a few minutes to power down, as the capacitors act as a battery to feed the circuit. At no point is the amp ever starved for power! It has enough energy storage to last minutes playing the most demanding music. The power supply works very similar to very large batteries, yet has more current capability.

Power supplies are a major key to a great amplifier and this power supply is the most advanced available.

TThe entire amp is mechanically grounded for vibration control. The chassis is made of stressed brass and aluminum to deal with any vibrations within the component. The brass back plate and bottom plate are coupled with brass standoffs that apply a small amount of stress to the circuit boards. This stress helps move vibrations more freely to the brass stands and off the bottom plate. The bottom plate is coupled to specially designed brass points, stands and footers. The footers can also be filled with dampening liquid if so desired.

The idea is to move vibrations out of the chassis to reduce ringing that otherwise leads to distortions. Brass is a very special material capable of high speed transfers of vibrational energies. Studies once done by Stanford University help guide our design theories on vibration transfer.

Of course, the heart of any amp is the actual circuit - and here we stand alone. We had to invent new ways of testing the amplifier to help explain just how radically advanced this circuit is. Circuit design is by Steve Keiser, formerly of B&K, who has worked as a freelance analog circuit designer for some of the largest companies in the world. This is the most advanced circuit ever created. Its distinct advantages come from two unique innovations.

First, the amps deliver sound as if acting as a single amplification stage. Most amplifiers have at least 3 individual stages of amplification, which adds dramatically to distortions and hinders the amplifier's ability to operate in a real world listening environment. By operating as a single stage, the MA-70 has a huge advantage over the competition and has subtleties similar to—but even better than—low power SET amps. This means it can be used on very efficient speakers when simplicity of circuit key and typically only low powered tube amps are used. It can out-produce delicacy of even the very best SET amps.

Secondly, the MA-70 amplifies in the current domain with a technology called current injection. In all speakers, it is current that is key to the driver movement. Voltage itself will not move traditional drivers. This means SET amps are transformers coupled to covert a tube amp's voltage domain back to current. In the MA-70, the amplifier operates by amplifying current. This is an inherent trait of all transistors. The MA-70 is different as it injects current into the signal path. Using a bypass around the transistor of a portion of signal the transistor becomes linear in signal process and is inherently incapable of producing distortion even under a load.

Current injection makes this amplifier truly unique as it combines the best worlds of amplification, working almost like a tube yet having the current-carrying of a transistor.

Why solid state? Solid state is inherently better at driving a speaker voice coil. It delivers the current that is required to build the electromagnetic field the voice coil needs to move. Tubes need to convert the voltage domain they operate in back to current to drive a load - this is a technical disadvantage of tubes. Tubes can sound great, of course, but for those who are looking for the best of both worlds the MA-70 should be your clear choice.

With the creation of this new circuit also came the need for new testing parameters. In the world of audio, amplifiers are most often tested without music signal or load, and therefore the testing is not in a real world environment. Two brand new tests that have been added to the specifications of the amplifier are: "Total Square Wave Distortion" and "Musical Fast Fourier Transform Distortion". These new specifications tell us what the amplifier does, in the real world, with music and under load. Operating under load in a real signal-flow environment is the most difficult part for any amplifier. The challenge for any amp is to actually reproduce music accurately. So these new tests are critical to understanding the potential of this circuit to deliver reproduced music like never before. These tests are performed to allow the user to know what will happen to the music signal when the amplifier is actually in use playing music. This is a surprisingly new concept, something we hope will eventually become commonplace.

These are measurements that make an amplifier truly unique and truly in a class by itself.

Here's a brief description of both of these new tests:

Musical Fast Fourier Transform Distortion: "Real world test" using a music sample of 1/10 of a second intervals. By breaking down the music samples into 1/10 of a second bit and/or keeping the bits small, they are reasonable enough in size to fully analyze the data. This measures the "input to output" data of the amplifiers performance allowing you to know the total sum of all distortion that will actually be added to your music.

Total Square Wave Distortion: Although it's not uncommon to see square wave distortion testing on an amp, it is quite uncommon to see it as important. It is also uncommon to see square waves accurately reproduced by an audio amplifier. A square wave is the most demanding of signals. We feel it is critical for amplifier to be able to reproduce square waves without distortion. The amp, if required, could reproduce "any" signal without distortion.

More about the amps:

This new amplifier design only amplifies current. It is a current amplifier "only" as transistors can only amplify current and are only linear when operated in a current mode.

Current injection is unique. All transistors inject current into one common line that then drives the speaker. Each transistor is connected to the input instead of to the stage before it, effectively creating a one-stage amplifier.

Overall, this new amp design is a revolution in thinking. It is truly a new concept from one of the great designers Steve Keiser. Steve has been an analog circuit designer dating all the way back to early B&K. His circuits have been exceptional in the past, and are certainly proving to be once again in our more modern era.

Only top quality, premium, hand-picked parts go into each and every amplifier, but the innovation doesn't stop there. Magnetic Innovations uses new technology brought forth to filter the power supply. Our unique dampening technology filters unwanted noise from the transformer and Magnetic Conduction Technology assists to deliver signal accurately and cleanly.

Contact us for more details and pricing.




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