Difference from competitors
The main idea of the creators of the preamplifier is “Minimum bells and whistles - maximum sound” or “Your money will be in Hi-End parts and the right circuit, and not in a bunch of functions that are not used in 90% of cases + a beautifully milled case.” If you like fashionable Hi-End with thick front panels, large dial or LED indicators, exclusive-shaped radiators, exotic materials (IMHO - absolutely not affecting the sound) and other external attributes of expensive audio equipment, then this device is not for you. Fidelity makes 95% of its products for people who want to get the maximum quality of design, components and sound for the lowest possible amount.
This is exactly how the company positions its line of Hi-End components, which includes the Musical Fidelity m8 PRE balanced preamplifier and two power amplifiers, the m8 500s and m8 700s. In the top products of competitors, most of the production costs go to the body elements: a chassis milled from a single piece of aluminum, exotic-looking radiators, luxurious designer finishes, etc. “Metal work” can take up to 90% of the cost of an amplifier, which usually has nothing to do with sound. An amplifier is not a speaker, in which the most expensive and important thing for sound is a complex multi-layer housing. By the way, the best-sounding tube amplifiers are made by enthusiasts in cases made of non-magnetic materials, not metal at all, but for example, wood. Here!
The main investments were made in the most important components for m8 PRE sound: high-quality transformers, audiophile transistors, precision resistors, low-impedance electrolytes, high-end connectors, etc., that is, in the DETAILS... The printed circuit board is also very, very high quality. Inside, everything is fair. The body is made according to the residual principle: a steel chassis, radiators made of a standard profile, a front panel of an ascetic shape and without decorations. With obvious external minimalism, the m8 preamplifier looks very convincing and solid.
Construction and instrumental achievements
Welded steel chassis with stiffeners, two toroidal 350-watt transformers, one per channel, high-capacity electrolytes, stabilizer radiators, overall film tanks, other heavy audiophile elements... The weight of the Musical Fidelity M8PRE pre-amplifier reaches 17 kg, the detailed mass is usually power amplifiers, but not preamps. Plus, a separate power supply with a tenfold reserve is of course a strong move... No one does this in preamplifiers. Full dual mono circuitry does not mean a mirrored design; rather, they tried to make the tracks on the boards of minimal length, so the preamplifier does not look like “mirrored” terminals inside.
The extra energy reserves of the power supplies, together with a multi-stage filter and voltage stabilizers (available wherever possible), made it possible to obtain a transient attenuation between channels of more than 96 dB. Bipolar power supply of the stages with a fully balanced amplification circuit provides a record high signal-to-noise ratio (> 117 dB), the most effective suppression of network interference, internal interference and noise. The operation of all stages in class A made it possible to obtain vanishingly small harmonics and intermodulation distortion, high overload capacity and linearity from the Musical Fidelity M8PRE preamplifier.
The Musical Fidelity M8PRE has five unbalanced RCA inputs and two balanced XLR inputs. One of each XLR and RCA - switches are switched to the “direct drive” mode, bypassing the volume control (for using a preamplifier as part of a home theater). M8PRE includes a high-quality turntable head equalizer. The sensitivity of the vinyl “Phone” MM/MS input is set by a switch. There is an option to convert a symmetrical signal to an unsymmetrical one and vice versa. Control the preamp and other Musical Fidelity components from an ergonomic remote control or via trigger inputs. The set of connectors and their switching capabilities is quite enough to build almost any Hi-End audio path of any complexity. The volume control is electronic with encoder control and a digital attenuation level indicator. The adjustment step is 0.5 dB. A small retro-style LED display above the volume control shows the current output level also in 0.5 dB steps. A row of small aluminum-turned buttons on the front panel duplicate the remote control buttons.
A high-quality element base, combined with manual adjustment of each device, made it possible to achieve “shelf” linearity in the frequency range: 5 Hz - 100 kHz, with uneven frequency response at the edges - only 0.1 dB. The input impedance in the full frequency band does not change either.
Musical Fidelity M8PRE testonsound
Musical Fidelity M8PRE is a Hi-End preamplifier, which is today the flagship of the 8 line in the Fidelity production program. Laconically strict, somewhat old-fashioned classic design of the preamplifier is organically combined with ultra-modern technologies. There was no point in listening to the Musical Fidelity M8PRE pre-amplifier separately from the powerful one, and we arranged a sound session in two versions: with m8 500s and m8 700s terminals. You can see the report from the sound competition in the reports:
Testing 1
Testing 2
Options:
- Number of channels: 2;
- Sensitivity: 352 mV;
- Harmonic distortion: 0.003%;
- Harmonic distortion with RCA inputs: 0.005%;
- Harmonic distortion from XLR inputs: 0.004%;
- Signal-to-noise ratio: 118 dB;
- Reproducible frequency range: 5Hz - 100 kHz;
- Frequency response unevenness in the frequency range: +0, -0.1 dB;
- 2 balanced XLR inputs;
- 4 RCA inputs adjustable;
- 1 RCA home theater input not adjustable;
- 1 RCA input for RIAA pickups;
- 1 input for external control: Trigger;
- 1 adjustable RCA output;
- 1 balanced XLR output;
- 1 fixed RCA output;
- 1 Trigger external control output;
- Weight (unpacked / packaged): 17/23 kg;
- Dimensions WxHxD (mm): 440 x 162 x 400.
P.S. In our online store you can buy a pre-amplifier Musical Fidelity M8 PRE, the review of which is given above. For any questions you can contact us by phone on the website.
Circuit design
Transistor (class A)
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Pre-amplifier
Reviews of Musical Fidelity M8 PRE review balanced preamplifier Hi-End
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listened before and after
Solomin 2016-12-01
5 / 5Recently I listened to the MF M8 PRE with their own 2x500 amplifier, with PSB Synchrony One acoustics. It was true that it was quite cold. After half an hour of warming up, a certain veil remained, there was not enough transparency, but otherwise everything was quite good: resolution, bass, dynamics. I really liked the vocals, so sensual. I liked how it held the stage - the instruments had real dimensions, their arrangement was very natural, like in real life... In general, its spatial characteristics are very good. I listened for about an hour, compared to the very beginning it became noticeably better, but some muffledness remained. The tall ones constantly wanted to add some spice. I think that with careful warming it will go away. Or with normal network cables, or even included standard cords to a Chinese extension cord, God forgive me.
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IA 2016-11-27
5 / 5I have had a Fidelity 8 balanced preamplifier for about a year, I came across a beautiful description here and wanted to answer. Most of what is written in the article is true. The device is decent, for example, I won’t change it for something in the foreseeable future at all, because... I’m quite pleased with the sound, and have calmed down about the equipment. Before that I had a full powerful Marantz, I sold it, it was very sweet. Fidelity is not like that, here accuracy is paramount. In terms of music, I listen mainly to New Age and unforgettable psychodenlica. Jazz and violins are not my thing, I end up with a ten-year-old Denon top 2x300 at 8 ohms. Acoustics PMC floor standing speakers 2 strips 200 watts. I don’t listen particularly loudly, only sometimes when I’m in the mood. The fact that there is inconsistency is nothing to worry about, the main thing is that everything plays as it should. I recommend Fidelity as a brand. He is very neutral, not like the Marans and Japanese pioneers. guano...
NM2118 - Pre-stereo adjustable amplifier with balanced inputs buy in Master Kit. Driver, programs, diagram, reviews, instructions, do it yourself, DIY
From us you can buy Master Kit NM2118 - Pre-stereo adjustable amplifier with balanced inputs: price, photo, DIY, do-it-yourself, technical specifications and equipment, reviews, review, instructions, driver, programs, diagram
Master Kit, NM2118, Pre-stereo adjustable amplifier with balanced inputs, price, description, photo, buy, DIY, do it yourself, reviews, review, instructions, delivery, driver, programs, circuit
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NM2118
Stereo pre-amplifier with balanced inputs
BM2118
Not available
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about arrival at the warehouse
To favoritesThe set has been discontinued. Use functional analogue BM2118
This device is specially designed for use both at home, as part of a home audio-video complex, and in a car (when generating a signal for a car power amplifier). The proposed assembly kit will allow the radio amateur to assemble a simple and reliable pre-stereo adjustable amplifier with balanced inputs, which has a low self-noise level, maximum functionality and a wide range of supply voltages.
Specifications
| Max. input voltage up to, V | 2 |
| Max output voltage up to, V | 2 |
| Weight | 1 |
Peculiarities
- A preamplifier is installed between the linear or power output of the signal source and the input of the power amplifier to adjust the level of the useful signal at its output!
Additional Information
The pre-stereo adjustable amplifier is made of eight operational amplifiers DA1.1 - DA1.4 and DA2.1 - DA2.4. An artificial midpoint is made on the resistive divider R26, R27 and capacitor C8. Op-amps DA1.1 - DA1.4 have two balanced input blocks. The adders are made on op-amps DA2.1 and DA2.2. This design allows you to use almost any source (linear output(s), PA output(s)) to pick up a useful signal. The op-amps DA2.3 and DA2.4 are used as amplifiers with variable gain in the range of +/-20 dB. Contacts X9 (plus supply voltage), X10 (minus supply voltage) are supplied with supply voltage. When using a low-power source (linear output, etc.) with differential outputs, the input signal to the processing unit is supplied relative to contacts X1, X3 (left) and X5, X7 (right). When using a powerful source (PA output, etc.) with differential outputs, the input signal to the processing unit is supplied relative to contacts X2, X4 (left) and X6, X8 (right). When using a low-power source (linear output, etc.) with conventional potential outputs, the input signal to the processing unit is supplied relative to contacts X1, X3 (left) and X5, X7 (right), and X3 and X7 must be connected to the ground of the power source. When using a powerful source (PA output, etc.) with conventional potential outputs, the input signal to the processing unit is supplied relative to contacts X2, X4 (left) and X6, X8 (right), and X3 and X7 must be connected to the ground of the power source. The useful amplified or suppressed signal is removed from contacts X11, X13 (left) and X12, X13 (right) for subsequent processing or supply to the PA. Potentiometer R17 adjusts the output signal level. !Design. Structurally, the pre-amplifier is made on a printed circuit board made of foil fiberglass with dimensions of 54x40 mm. The design provides for installation of the board into the case; for this purpose, there are mounting holes with a diameter of 3 mm at the edges of the board.
This block (all components are already soldered on a printed circuit board) is specially designed for use both at home, as part of a home audio-video complex, and in a car (when generating a signal for a car power amplifier).
The proposed unit will allow the radio amateur to assemble a simple and reliable pre-stereo adjustable amplifier with balanced inputs, which has a low self-noise level, maximum functionality and a wide range of supply voltages. A preamplifier is installed between the linear or power output of the signal source and the input of the power amplifier to adjust the level of the desired signal at its output.
| Parameter | Meaning |
| Upit. constant, V | +3...30 |
| Upit. nom. constant, V | +12 |
| Iconsumption Max. at Upit. nom., mA | ...50 |
| Recommended power supply not included | , , |
| Uin. (range), V | 0...Up |
| Uout. (range), V | 0...Up |
| Number of inputs (left, right) | 2 |
| Number of outputs (left, right) | 2 |
| Gain (adjustable), dB | -20...+20 |
| Overall dimensions, LxWxH, mm | 54 x 40 |
| Recommended housing, not included | |
| Operating temperature, °C | 0...+55 |
| Relative operating humidity, % | ...55 |
| Production | Contract manufacturing in Russia |
| Warranty period | 12 months from date of purchase |
| Lifetime | 5 years |
| Weight, g | 100 |
The pre-stereo adjustable amplifier is made of eight operational amplifiers DA1.1... DA1.4 and DA2.1... DA2.4. An artificial midpoint is made on the resistive divider R26, R27 and capacitor C8.
Op-amp DA1.1…DA1.4 has two balanced input blocks. The adders are made on op-amps DA2.1 and DA2.2. This design allows you to use almost any source (linear output(s), PA output(s)) to pick up a useful signal. Op-amps DA2.3 and DA2.4 are used to make amplifiers with variable gain in the range of 20 dB. Contacts X9 (+ supply voltage), X10 (- supply voltage) are supplied with supply voltage.
When using BM2118 after preamp, the signal from the line output should be applied to pins X1 (left), X5 (right), while X3 and X7 are connected to the ground of the power supply.
When using BM2118 after power amplifier, the signal from the output of the power amplifier should be applied to pins X2 (left), X6 (right), while X3 and X7 are connected to the ground of the power supply.
When using BM2118 after preamplifier with differential outputs the signal from the linear output should be applied to contacts X1, X3 (left), X5, X7 (right).
When using BM2118, the signal from the output of the power amplifier should be applied to pins X2, X4 (left), X6, X8 (right).
The useful amplified/suppressed signal is removed from contacts X11, X13 (left) and X12, X13 (right) for subsequent processing or supply to the PA. Potentiometer R17 adjusts the output signal level.
Attention! If there is a possible unbalance of the gains of the left and right channels (since the tuning is carried out by a dual resistor), it is necessary to select the values of resistors R18 and R21.
Contacts used when connecting BM2118 after preamplifier
X1 - left channel signal input
X5 - right channel signal input
X3 - common wire
X7 - common wire
after power amplifier
X2 - left channel signal input
X6 - right channel signal input
X3 - common wire
X7 - common wire
Contacts used when connecting BM2118 after preamplifier with differential outputs
X1, X3 - left channel signal input
X5, X7 - right channel signal input
There is no common wire
Contacts used when connecting BM2118 after a power amplifier with differential outputs
X2, X4 - left channel signal input
X6, X8 - right channel signal input
There is no common wire.
High-end devices are usually equipped with balanced connectors. This connection has many advantages, but is not cheap. Modern microcircuits help find a compromise solution.
It is generally accepted that balanced inputs and outputs are attributes of purely High-End technology. XLR connectors can be seen in amplifiers and CD players from audiophile companies Accuphase, Burmester, Krell, Mark Levinson, Luxman, etc. Symmetrical lines are widely used in professional audio equipment, in circuits for amplifying small signals and, if necessary, transmitting signals over long distances. As a rule, the organization of balanced lines is associated with high costs, since it requires either high-quality transformers, or differential amplifiers and cunning inverters capable of operating a reactive load. How can you make such a connection yourself?
Before we try to answer this question, let's remember where they came from and why we need balance lines at all. Their main advantage is the ability to suppress common-mode interference, i.e. any interference from outside with a very long cable length. This is important, but at home, where the distance between components does not exceed a few tens of centimeters (unless you place monoblocks next to speakers), another advantage of a symmetrical connection is more attractive. The fact is that the standard for it was initially developed for sound studios, where the line resistance is 600 Ohms. Such a small value makes the cable inductance and capacitance uncritical, and this is exactly what we need. Most high-end devices allow both balanced connection via XLR sockets and regular connection via RCA. So, many years of listening experience show that in the first case, the detail of the sound picture and spatial characteristics improve, the sound becomes more accurate and organized. Balanced lines will also be very useful where the signal is initially balanced, for example in single-bit DACs (see Andrey Markitanov’s publications in the previous and current issues) or phono preamplifiers with a differential input. There is simply no point in converting the signal to single-ended, and then, in the amplifier, again to push-pull. By the way, about amplifiers. Anyone who has ever tried to make a tube push-pull knows how difficult it is to assemble a good bass reflex - with low distortion on large signals, with the same frequency response and output impedance across the shoulders, good symmetry at any levels...
In most cases, transformers are used to solve these problems, and it is this circumstance that has long held back the use of balanced lines in home appliances, and here’s why. The transformer, being an absolutely simple and understandable device, is very labor-intensive and difficult to manufacture. You need good iron for the core, preferably with the addition of nickel or manganese, sectioned winding and careful laying of the wire, slightly thicker than a human hair. Otherwise, the trans will cut off frequencies at the edges of the audio range and twist the phase of the signal as it pleases. Add to this the need for double or even triple shielding and completely manual work, and it becomes clear that the price of a decent product will be very high. For example, a pair of Tango NC-22 interstages costs about $400 according to the catalogue! Trying to use miniature transics from microphones or taken out of decommissioned mixing consoles will lead to nothing - at best you will get a band of 80 Hz - 13 kHz plus large distortions at amplitudes greater than 0.775 V. Is it possible to find a way out?
Rice. 1. Balanced line with transmission coefficient K=1. The cable length can reach 150 m without compromising quality.
It is possible, if we remember that, in essence, transformers are impedance converters, i.e. devices that allow optimal matching of the signal source with the consumer. If there are two identical windings, they are capable of converting a single-cycle signal into a push-pull signal. Such a need, as already mentioned, arises quite often, so many semiconductor manufacturers began to produce specialized amplifiers - linear drivers and receivers. In the specifications for such microcircuits Burr-Brown and Analog Devices it is written: “transformer like driver”. Since the chips of these companies have almost identical circuit design and parameters, let’s consider the construction of a balanced line using the example of the SSM2142 driver and the SSM2143 receiver from Analog Devices (Fig. 1). Almost exact analogs from Burr-Brown are INA137 and DRV134. Their main feature is the high accuracy of the “built-in” resistances that set the gain. It is achieved by laser adjustment during the manufacturing of microcircuits and is 0.005%, which is absolutely unattainable when building a circuit using discrete elements. Thanks to this, common mode noise suppression averages 100 dB, and distortion in the frequency range 10 Hz - 100 kHz does not exceed 0.0008%. It is noteworthy that both chips provide all the declared characteristics with input signal amplitudes up to 10 V.
Rice. 2. Simplified diagram of the SSM2142 driver. This tiny chip is capable of driving the pre-terminal stage of an amplifier.
The SSM2142 driver (Fig. 2) costs about 200 rubles. retail. It has a gain of 2 (6 dB) and creates two absolutely identical clones of the output signal with an amplitude of up to 10 V at a load resistance of 600 Ohms. This microcircuit is insensitive to its reactive component and is capable of “pumping” a line up to 150 m long while maintaining the ideal meander shape. With its help, many design ideas can be easily realized. For example, by replacing a conventional op-amp at the output of a CD player with it, you can easily obtain a high-quality balanced output. The author successfully used the SSM2142 in the phase inverter of a tube amplifier, feeding the signal from its outputs directly to the grids of the 6N7S triode driver. Where else will you find a bass reflex with a linear frequency response up to 1 MHz, absolutely symmetrical and with an output impedance of 50 Ohms? The chip easily swings the lamp even when grid currents arise and does not care about the Miller capacitance. True, there are limitations. It must be remembered that there should not be any correction circuits or resistive dividers in the output circuits of the SSM2142, otherwise the symmetry may be broken. When using a driver in a power amplifier, it should be avoided to be covered by a common feedback loop, since excitation at microwave frequencies is possible. The SSM2142 performs best in triode circuits where the OS is not needed at all. Another personally tested application of the chip is organizing a balanced output for the GZ-102 generator to capture the characteristics of a tube preamp with XLR inputs. Here, any attempt to cheat by shorting one of the lines to ground or bypassing the input transformer led to unreliable measurement results.
Rice. 3. In the SSM2143 receiver, the resistances are adjusted with an accuracy of 0.005%.
Sometimes there is a need for reverse conversion, for example, for all kinds of adjustments and corrections. In a symmetrical stereo path, this will require precision quad potentiometers and twice as many parts, which are very expensive. Therefore, a balanced input signal is often converted to single-ended, corrected, and returned to its original form at the output. It happens that you need to correctly connect a single-ended tube circuit to the balanced line. In both cases, the SSM2143 receiver can help out (Fig. 3), which, having received a symmetrical signal, converts it into a normal one with minimal distortion and noise, and the coefficient can be 0.5 or 2, depending on how the connections are connected microcircuit legs. It also has another useful option - the ability to obtain a constant voltage from -10 to +10 V at the output. Thus, it is easy to set the bias on the lamp grid by connecting the cathode directly to ground. To do this, you will additionally need a low-noise op-amp, for example OP27 (Fig. 4). The SSM2143 easily handles load capacitance up to 300 pF and delivers current up to 20 mA. One chip costs about 130 rubles.
Rice. 4. This way you can get a constant voltage at the output of SSM2143 in the range of ±10 V.
Now a general note for all types of such microcircuits. As experience has shown, their sound is very dependent on proper nutrition, and saving here is at your loss. All characteristics of drivers and receivers are stated at a supply voltage of ±18 V, but it makes sense to assemble two complementary 15-volt stabilizers, either on LM317/337 or on discrete elements. The best results were obtained when powered by parallel push-pull stabilizers (if you are interested, we will publish the circuit). Try germanium diodes in the rectifier and Black Gate capacitors in the filter, you won’t regret it. Each leg of the chip, to which “+” or “-” is applied, must be shunted with 0.1 - 0.47 μF ceramics and a tantalum droplet capacitor.
It probably makes sense to dwell on ethical issues. Many “tube” audiophiles do not even allow the thought of using microcircuits in High End circuits. I agree, transformers are much more musical, since they do not produce an endless “tail” of higher-order harmonics. But in this case, you have to pay too much for the purity of the idea. Of course, if you have 300 - 400 extra bucks in your pocket, I wholeheartedly recommend spending it on Tango, Tamura or MagneQuest products. If you have some experience, you can wind the trance yourself. And if you don't have either, then a couple of tiny chips in a DIP8 package can be very useful. At least in most cases they sound very decent, and their inclusion even in the most “polished” path does not cause any noticeable degradation. In addition, you save on cables, which is confirmed by experiment - replacing the expensive symmetrical XLO cable with a regular studio twisted pair cable 6 m long was absolutely not noticeable.
