EX-DEM MUSIC FIRST AUDIO REFERENCE MM PHONO AMPLIFIER
Why use a step up transformer, click here to view ###
The Music First Audio reference MM phono pre-amplifier has been 10 years in the making, it is designed to give the best possible sound quality from vinyl. Used with a MF Audio step up transformer or any high end SUT the music will be so life like it will reach out and touch you. We are writing from experience having heard this phono stage in action, it really is set to become a landmark product.
Music First Audio’s new Reference MM Phono Stage is a high end, premium priced valve phono pre-amplifier. The result of years of development, it combines vacuum tube and solid state circuit topology to bring the beauty of valve sound with the long term stability that transistors afford.
The front end of the Reference MM Stage employs a very low noise pentode originally designed for the demanding European communication industry, combined with a dual triode to provide the ideal characteristics of high gain, low noise and low impedance drive.
This first stage, then drives an inductive equalisation network showcasing Music First Audio’s many years of coil winding expertise. The accurately equalised signal is then amplified and passed through Longdog Audio’s signature line driving stage. Power for the dual mono circuitry is provided by an isolated and regulated power supply which feeds, via high quality locking connectors, four discrete high voltage, low noise regulators that power the active circuitry.
The Reference Phono Stage is housed in superlative quality non-ferrous aluminium casework and is designed and built exclusively in the United Kingdom. The result is a phono pre-amplifier of exceptionally high ability, offering unparalleled transparency, harmonic accuracy and reliability.
Some notes from the designer of the phono amplifier……………………………
The Music First Reference Phono Amplifier is an all valve moving magnet phone stage, employing innovative (possibly unique) circuit design, careful component selection and LCR RIAA equalisation.
Whilst on paper, the requirements for a phono amplifier are simple, in practice, they are far from it.
We start with a signal from the cartridge or step up transformer of only 1mv, then apply enough gain to convert that to a line level signal while at the same time applying a accurate RIAA equalisation curve. while at the same time providing a low impedance drive to the following system. Firstly, the 1mv signal. If we want to aim for the best signal to noise ratio, we need to look at at least 80dB S/N here. For a 1mv signal, then that means the noise needs to be below 100nv (0.0000001v). But it goes further that that, the RIAA curve means that the low frequencies will be 20dB (10 times) lower. That means we are looking for an input stage that can give us a 100dB S/N ratio, we are down to 10nV. But to prevent surface noise, clicks and pops from affecting the sound, we need a stage that will not be disturbed by these impulse signals. The reason why many phono stages seem to make records sound noisier than other is down to how well (or not) they handle these signals. This is one of the reasons why valve phono stages can often be better sounding than solid state ones, the power rails of a typical valve phono stage are in the 250v area, this gives far more headroom than the typical 18v supply in a solid state unit. So, we need to handle impulses which can be up to 40dB (100 times) above the normal level. So we need a front end that can handle signals from 100mv to below 10nv, a 140dB S/N ratio. Not a simple task.
To provide the huge dynamic range required of a signal from a cartridge we use an innovative circuit that makes use of the best of the valve and solid state world in conjunction. An ultra low noise pentode (D3a) from when the last days of valve technology, was at its peak, is used. This combined with an active load and output buffer with self adjusting stabilisation circuity means that super low noise, low distortion (good as most solid state designs), wide bandwidth (DC to over 1Mhz), high slew rate (can swing 60v at 300kHz), stability from component ageing and large overload margins makes it the ideal front end for any phono stage.
Once we have amplified the delicate signal from the cartridge, we now have to apply the RIAA equalisation. While many designs split this EQ over two or more stages, or use it as part of a feedback loop. We believe that the best sounding RIAA is done in a single stage, using no overall feedback loops. Further to that we believe the best sounding RIAA can only be achieved by the use of a LCR T-Network. Unlike most RIAA stages that employ just resistors and capacitors an LCR design adds carefully chosen inductors to the mix. By the addition of these inductors, it becomes possible to create a network that provides the accurate equalisation needed, while also (and most importantly) provide a fixed impedance load to the driving stage. It is this constant impedance characteristic that allows LCR based phono stages to produce the uniquely realistic and transparent midrange and detailed bass response that only they can achieve.
While the LCR network provides an idea solution, driving it from the preceding stage has often been the problem area in previous designs. In the case, the innovative first stage we have already described, provides the ideal solution to driving the LCR network.
Once our precious signal has been through the LCR network, its up to 100 times smaller than before. So we again need to amplify it and make it ready to drive the following system. Now we use one of the best sounding 9 pin valves, the 6072a dual triode, we use this valve for the same reason many other top designers use it, it provides good gain, low noise, and good sounds. In this case its used in a active load (SRPP) configuration. This stage then feeds an output buffer. We use a 5687 triode for this job. This is just one of the best output buffers around, and we make no apologies in using it once more in this design.
So, that’s the amplification part of the design, but anyone who knows our previous award winning products will know that at least 50% of the sound of any design is down to the quality of the power supply (well, maybe 75%). So we have not skimped in this area. Each channel board in the phono stage contains two independent low noise high voltage shunt regulators to provide the cleanest, quietest power to the circuit. We don’t forget the heater supply either. Two stages of heater supply regulation is provided on each phono board, each with a dedicated supply for the input valve.
Given that we are dealing with such minute signals, it would be foolish to put all this circuity next to the mains transformer (and the box would have to be huge, as it is, its full). So we have made this a two box design. Not wishing to allow any noise into the phono casework, the power supply contains first stage high voltage and heater regulation, reducing the power rail noise and ripple to the sort of levels that would normally be accepted for many traditional designs, but here is just the input to the primary regulators.
To connect the two boxes, we use industrial connectors designed for the purpose, with voltage and current ratings that exceed what is needed here, so will provide long lasting service. The casework of the two boxes are non magnetic to avoid interaction with the circuit, while providing shielding for the precious signal. All the components are chosen with their sonic characteristic as well as their electrical suitability. Charcroft Z Foil resistors provides the cartridge loading, and Takman carbon and metal film resistors are used through the signal circuity. Elna electrolytic and Mundorf film capacitors are used throughout the circuitry.
Two Box LCR Valve Reference Phono Amplifier:
Valve line up:
D3a * 2
6072a * 2
5687 * 2
Input sensitivity 1mv at 1kHz
EQ: Within +- 0.1dB 30-20kHz
Input impedance 47k + 75pF (designed for MM, high and medium output MC and low output MC with a step up transformer).
Overload margin 300mv at 1Khz
Power consumption 100W
The Music First Ref. MM Phono Stage is supplied in 120V or 230V versions with an IsoTek power cable to suit your country, standard warranty is 2 years.