The Concept

Introduction to the Music First Audio Passive Pre amplifier

A high end Hi Fi system can be divided into four discrete stages; Source, Pre amp, Power amp and loudspeaker.

Source. This is usually a CD player, turntable, radio, television, tape machine and occasionally an MP3 player. These pieces of equipment take the media (record, CD etc) and generate an electrical signal.

Pre amplifier. This is the control center for the system. A pre amplifier simply allows the listener to switch between sources and control the level of volume of the sources and therefore the volume of the system

Power Amplifier. This is the ‘muscle’ of the system. A power amplifier takes the small signal from the output of the pre amplifier and makes it bigger (amplifies it). Usually high end power amplifiers do not have any controls other than an on/off switch. The output from a power amplifier is capable of driving a loudspeaker.

Loudspeaker. Uses the signal from a power amplifier to generate sound.

Sometimes, principally for economic reasons, the pre amplifier and power amplifier are physically tied together in one box, called an integrated amplifier.

Pre amplifiers fall into two categories; active (much more common) and passive. Ours is a passive pre amplifier. Briefly, prior to the advent of the CD player in the early nineties all pre amplifiers were active. Sources generally offered wildly differing output levels some of which (specifically turntables) required ‘boosting’ with active electronics. When the CD player appeared it offered an output level (commonly referred to as line level) capable of driving a power amplifier directly. Most tape recorders and radios also offer line level outputs.

As the CD replaced the vinyl record as the standard domestic music media it quickly became apparent that the active element of a pre amplifier was no longer necessary. The theory is that active pre amplification introduces three distinct problems; noise, coloration and reliance on the quality of the power supply. Furthermore, it can be said that active electronics are unreliable in comparison to passive designs because with a passive design there is very little to go wrong.

Active pre amplification introduces additional gain (level) to the signal. This was essential before the CD because the output from a turntable requires significant boosting before it reaches a power amplifier. Once the CD appeared enthusiasts realized that this extra gain was redundant. In fact, by introducing active electronic to the signal path the sound can be compromised. All active electronics generate noise. This can be heard as ‘hiss’ which is most obvious when no music is playing but is also still present while the music is playing, which is far from ideal.

Furthermore, poorly designed (or economically compromised) active electronics can introduce ‘coloration’ to the sound. This coloration changes the sound of the music, making it more treble heavy or adding bass, not ideal especially when you have chosen a source that accurately reproduces your music, usually at considerable expense.

Finally, active electronics are entirely dependent on the quality of their power supply. Power supplies are expensive and are therefore often an area where accounts departments insist on cost-cutting, despite the designers’ specification.

So, if the sources are capable of driving the amplifier directly all that is required is attenuation of their levels (otherwise everything is always at full volume) and the ability to switch between sources. Early in the nineties several products appeared which did just this. The attenuation was accomplished by a potentiometer (a standard volume control) and a switch was used to change sources. As this approach developed the potentiometer was replaced with a multi position rotary switch that selects resistors with various different values. This allows the use of very high quality resistors for improved sound.

However, there are many drawbacks to this approach (called resistive passive pre amplification). It is not electrically ideal practice and requires that careful attention be paid to the choice of source components and amplifiers and to the lengths of the leads between them to minimize the ill effects of the design. Furthermore, as the attenuation increases (the volume goes down) these problems become more severe and the sound quality is compromised. Traditional passive pre amplifiers quickly faded into obscurity and enthusiasts returned to their active solutions, the lesser of two evils.

In early 1997 Jonathan Billington (BSc. Hons) owner at Stevens & Billington Ltd  decided to design the very best line input audio transformer possible, irrespective of cost or complexity. Twenty plus years of transformer design and manufacture for some of the worlds best audio companies had left him with a considerable understanding of complex relationships involved in transformer design. After many months of painstaking research he finished the ultimate line input transformer, the TX101.

A chance meeting with a well respected DIY Hi Fi enthusiast led Stevens & Billington Ltd. to design a version of the TX 101 with multiple outputs which could be wired to a switch to produce a volume control of the highest quality. Considerable further research coupled with listening test after listening test, revision after revision resulted in the TX102.

By using a transformer rather than resistors all the problems associated with passive pre amplification are overcome. The transformer volume control (or TVC) is the ultimate solution to pre amplification and to signal attenuation. Quite simply it offers the performance of the most expensive active pre amplifiers at a fraction of the cost. The awards we have won are testament to our products’ ability to significantly outperform the competition.Active vs. Passive Pre amplification

While it might be theoretically possible to design a sonically transparent active pre amplifier, in practice sonic coloration and alteration (and distortion) of the signal is an unavoidable aspect of their design. This coloration comes from three main areas:

The power supply: Any active circuit is dependent on the quality of its power supply. Unfortunately, high quality power supplies are an expensive component so while designers may specify the best, economics often dictates otherwise.
The components: Even the simplest of circuits the audio signal must pass through several components even the very best of which degrade the signal resulting in lower quality.
The introduction of noise (specifically Johnson noise): Physics dictates that active electronics generate heat and this heat introduces noise. The noise is most apparent when no music is playing (or in very quiet passages of music) and is usually heard as ‘hiss’. Worse, this noise is still present when the music is playing which reduces dynamic range and affects frequency response All that is needed from the pre amplification element of a Hi Fi System is to switch between sources, control level and integrate different signals in terms of impedance matching with as little effect on the overall sound a is possible.TVC vs. Resistive Pre amplifier

The traditional role of the Pre amplifier within a high end audio system is the matching of signals from different source components (Turntable/ Phonostage, CD Player, Tape Deck, Tuner etc), selection between these source components and control of volume.

The introduction of the CD player in the early 1980’s changed the role of the pre amplifier. Modern Sources, such as CD-Players, DVD Players and SACD Players offer output levels sufficient to drive power amplifiers to full power and sufficient drive for external devices and cables. Many CD-Players and similar devices have output impedance’s lower than 1k Ohm, some are materially lower. So the role of the pre amplifier was changed because sources were now fit for direct connection to power amplifiers.

The first and most simple approach to passive pre amplification is a simple switch for selection between sources and a level control. Early Passive Pre amplifiers used basic potentiometers to accomplish level control. Next came high quality resistor ladders where level is selected via a switch which in turn selects different resistor values. These designs came to be called Passive Pre amplifiers and initially created notable interest as an extremely pure method of controlling volume and selecting inputs.

However they soon faded back into obscurity because most suffer from substantial impedance mismatches with either sources or loads. For example, if a 5k Ohm variable resistor (potentiometer) is used as a volume control, the source (CD player etc) is required to drive 5k Ohm, quite a severe load. If this is then combined with a with a 1k Ohm source impedance, the worst case output impedance of the combination is 1500 Ohm at -6dB attenuation, while at -20db attenuation the output impedance would still be around 540 Ohm. To make matters worse it this is then combined with around a 1nF load capacitance (easily found in longer, high capacitance interconnects), this leads to a 0.3dB attenuation at 20 kHz for a 20dB attenuation setting, almost showing the absolute permissible limit for load capacitance. The worst-case attenuation at 20kHz almost reaches 1dB!

If we choose a 50 kOhm resistive volume control (to provide the source with an easier load) we must either accept considerably higher levels of roll off at 20kHz or we must limit the load capacitance to less than 100pF. Such a level of capacitance (100pF) can easily be found with only 1m of high quality interconnect cable and is often exceeded by the input capacitance of many amplifiers! So the resistive volume control employed in passive control units must navigate a course between the Scylla of excessively loading the source, leading to increased distortion and the Charybdis of excessively high output impedance.

The introduction of the magnetic volume control TX-102 neatly cuts through this tangled Gordian knot of contradicting requirements, making passive control units that actually work more effectively and in a much wider range of systems a reality. By using transformers The Music First Audio Passive Magnetic Pre amplifier offers all the advantages of passive pre amplification (no dependency on quality of the power supply, no added noise, no coloration) without any of the compromises associated with traditional passive pre amplification (poor impedance matching, incompatibility across a wide range of systems and uneven frequency response)

The concept

The Music First Audio passive pre amplifier was conceived to position itself at the very heart of a true high-end hi-fi system. A pre amplifier’s role is relatively simple, it provides for source selection (recordings and transmissions of all types ) and enables the listener to adjust volume level. Simple. The design of Music First Audio pre amplifiers is remarkably simple, and the audible benefits are demonstrable. One of our most respected innovators of audio design once said that, ideally, an amplifier should be little more than “a straight wire with gain” and we like to think our products aspire more closely to this objective than any other pre amplifier.

Basically, there are two types of pre amplifier; active and passive. Historically active pre amplifiers tackled the problem of wildly different output levels from source components, particularly vinyl systems which demanded additional ‘boosting’ with active electronics. However, times change, and these issues have now largely been addressed in different ways.

Active and passive pre amplifiers work in different ways. All active electronics generate noise or coloration, sometimes it’s not readily detected but it’s there. In the most sophisticated active circuits additional components can be introduced to ameliorate these problems, but that just adds to the cost. More than this, the performance of active electronics are very much dependent on the quality of their power supply so that also has a significant influence on cost.

To be fair, despite commendable efforts, we’ll be first to accept that a few early passive pre amplifiers were equally, but differently compromised in their performance capabilities which is why it’s vitally important for us to state that Music First Audio products bear no relationship nor have any history with those early designs. Music First Audio passive pre amplifiers are the products of twenty-first century thinking. Having said that, our pre amplifiers do owe their heritage to the sister company, Stevens & Billington Ltd, who, for more than twenty years have successfully designed and manufactured superior quality transformers for some of world’s leading audio brands.

Just like you, we’re serious music lovers and hi-fi enthusiasts so it was almost inevitable that we should set ourselves the task of designing a truly outstanding pre amplifier, at the heart of which would be our ultimate transformer. After months of research and experiment we launched the TX101, our supreme achievement. But we didn’t stop there, soon after that followed a version, the TX102, with multiple outputs that could be wired to a volume control of the highest quality. To reach this stage had involved further research, many revisions and, most importantly, hundreds of hours of listening tests. The passive magnetic pre amplifier was born.

By using a transformer instead of resistors consigns to history any resistance to passive pre amplification, all prejudices overturned, all orthodoxy defeated. Fresh thinking has created our Transformer Volume Control (TVC), the quintessential solution to pre amplification and signal attenuation. The Music First Audio passive pre amplifier accepts both balanced and unbalanced inputs and any combination as required. Our pre amplifier’s utter transparency ensures its compatibility with almost any hi-fi system within which it will improve the quality of sound reproduction as well as your enjoyment.

We can state with absolute confidence, as well as much shared experience, that Music First Audio pre amplifiers offer at the very least, a level of performance comparable with the world’s most expensive pre amplifiers, but at a fraction of the cost.

Our pre amplifier has been reviewed in almost every high-end hi-fi publication and generated an unprecedented level of critical acclaim. As testimony to the success of the design, many hi-fi equipment reviewers who have heard a Music First Audio pre amplifier have purchased the review sample. Our preamplifiers have won numerous awards and luminaries of the audiophile world who’ve installed them in their reference systems include Sam Tellig of Stereophile, Andrew Harrison of Hi-Fi News, David Price of Hi-Fi World, Paul Eros of TNT and Srajan Ebaen of 6 Moons. Such knowledgeable and generous support has frequently seen the Music First Audio Passive Pre amplifier described as the best pre amplifier ever made.