This block (all components are already soldered on 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 block will allow a radio amateur to assemble a simple and reliable pre-stereo adjustable amplifier with balanced inputs, which has a low level of self-noise, maximum functionality and a wide range of supply voltages. A pre-amplifier is installed between the linear or powerful output of the signal source and the input of the power amplifier to adjust the level of the useful signal at its output.

The preliminary stereo adjustable amplifier is made on 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.
The DA1.1…DA1.4 op-amp has two balanced input blocks. The adders are made on the OS DA2.1 and DA2.2. Such a construction allows you to use almost any source (linear output(s), PA output(s)) to remove a useful signal. Op-amps DA2.3 and DA2.4 are equipped with variable gain amplifiers in the range of 20 dB. The contacts X9 (+ supply voltage), X10 (- supply voltage) are supplied with supply voltage.

When using VM2118 after preamplifier, the signal from the line output should be applied to contacts X1 (left), X5 (right), while X3 and X7 are connected to the ground of the power source.

When using VM2118 after power amplifier, the signal from the output of the power amplifier should be applied to contacts X2 (left), X6 (right), while X3 and X7 are connected to the ground of the power source.

When using VM2118 after preamplifier with differential outputs the signal from the line 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 contacts X2, X4 (left), X6, X8 (right).

From contacts X11, X13 (left) and X12, X13 (right), a useful amplified / suppressed signal is removed for further processing or feeding to the PA. Potentiometer R17 adjusts the output signal level.
Attention! With a possible imbalance in 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 the resistors R18 and R21.

Pins 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

Pins used when connecting BM2118 after preamplifier with differential outputs
X1, X3 - left channel signal input
X5, X7 - right channel signal input
No common wire

Pins used when connecting BM2118 after power amplifier with differential outputs
X2, X4 - left channel signal input
X6, X8 - right channel signal input
There is no common wire.

I have a bass guitar that I once made myself:
http://www.youtube.com/watch?v=Lj5knLzVSns
http://razar.livejournal.com/113252.html

The peculiarity of this instrument is that it does not have pickups as such, the signal is taken directly from the strings vibrating in a magnetic field, and each pair of strings is connected to a differential (microphone) preamplifier. In professional equipment, this is a common standard - you can plug this bass directly into the console, connect it to microphone inputs sound card or, or use a mic preamp. At home, I usually record it in Echo Audiofire4, at performances I either stick into the console through a multicore, and they put a separate monitor for me, or I connect to the bass amp through the peratronika MAB2023 Mk.1 microphone preamplifier.

In terms of sound, this instrument differs from traditional bass guitars, with a flatter frequency response and different dynamics, as if more compression. In acoustic ensembles, this is cool, but on recordings you can process the bass with an equalizer and get the desired frequency response with the desired resonances. But recently I began to rehearse with a group with live drums, two electric guitars, and it turned out that the readability of the bass part in such a loud version is not very good. Of course, you can turn something on the combo, especially if there is a parametric equalizer, but in general I thought about a special preamp that would make the sound closer to traditional bass guitars, in which the pickups (due to their inductance and capacitance) themselves have resonance somewhere around 2 kHz.

I would like a special preamp, unlike a microphone one, to take into account the existing features of the bass:
- low signal level
- very low output impedance (together with the cable, less than 3 ohms is obtained)
- balanced input, unbalanced output
- the output level can be lower than the linear one, maybe a little higher than the bass pickups, the main thing is to keep the signal-to-noise ratio

So far I've come up with this:

This is a circuit for one channel, the second is the same. The output transformer is Edcor TPC15K / 600, I once bought them with a margin for a tube microphone preamp, now I think to use the rest, and in this case turn them on as boosters. Even if you connect the 15k output windings of two channels in series, you will get much lower output impedance than what bass amps are designed to handle. I think to choose the capacitor in the source circuit so that, together with the inductance of the transformer, the desired resonance is obtained, and adjust its depth with a potentiometer. Powered by 9-12 volt adapter.

The question is, in fact, about transistors. As for field workers, I’m thinking about KP103M, I once assembled a guitar booster on such and I liked it :) And for the input you need something low-noise and with a high gain, I’m still sorting out what Chip-and-Dip offers, parallel to Google different diagrams with them. 2N3904? BC549? BC338?

Well, maybe someone has some ideas or advice about the scheme. The only thing I would like not to complicate too much, but to do something simple, but quite effective, and not just take a couple of operational amplifiers. I am inspired by things like Fuzz Face and boosters on one fielder, and it seems that similar solutions can work here too.

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 details and the correct circuit, and not in a bunch of functions that are 90% unused + a beautifully milled case.” If you like trendy Hi-End with thick front panels, large arrows 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 construction, components and sound for the lowest possible amount.

This is how the company positions its line of Hi-End components, which includes a Musical Fidelity m8 PRE balanced preamp and two m8 500s and m8 700s power amplifiers. In the top competitors, most of the production costs are spent on body parts: a chassis machined from a single piece of aluminum, exotic-looking radiators, luxurious designer finishes, etc. "Metal work" can take up to 90% of the cost of the 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-layered case. By the way, the best-sounding tube amplifiers are made by enthusiasts in cases made of non-magnetic materials, not in metal at all, but, for example, in wood. Here!

Major investments have been made in the most important components for m8 PRE sound: 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 case is made according to the residual principle: a steel chassis, radiators from a standard profile, an ascetic front panel without embellishments. With obvious external minimalism, the m8 preamplifier looks very convincing and solid.

Construction and instrumental advances

Welded steel chassis with stiffeners, two toroidal 350 watt transformers, one per channel, large capacity electrolytes, stabilizer heatsinks, overall film tanks, other heavy audiophile elements... The weight of the Musical Fidelity M8PRE preamplifier reaches 17 Kg, detailed mass is usually power amplifiers, but not preamps. Plus, a separate power supply with a tenfold margin is, of course, a strong move ... Nobody does this in preamplifiers. Full double mono circuitry does not mean a specular design, here they rather tried to make tracks on boards of a minimum length, so the preamplifier does not look like “mirrored” endings inside.

Over the reserve of power supply units together with a multi-link filter and voltage stabilizers (they stand wherever possible) made it possible to obtain a crosstalk attenuation between channels of more than 96 dB. Bipolar power stages with a fully balanced gain circuit provide a record high signal-to-noise ratio (> 117 dB), the most effective suppression of mains 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 each of XLR and RCA - are transferred by switches to the "direct drive" mode with bypassing the volume control (for using a preamplifier as part of a home theater). The M8PRE contains a high quality equalizer for turntable heads. The sensitivity of the vinyl "Phone" input MM / MC is set by a switch. There is an option to convert a balanced signal to an unbalanced one and vice versa. Control the preamp and other Musical Fidelity components from an ergonomic remote or via the trigger inputs. A set of connectors and their switching capabilities is quite enough to build almost any Hi-End audio path in terms of complexity. Volume control - electronic with encoder control and digital indicator attenuation level. The adjustment is in 0.5dB increments. A small, retro-style LED display above the volume control shows the current output level, also in 0.5dB increments. A row of small buttons turned from aluminum on the front panel duplicates the buttons on the remote control.

High-quality element base in combination with manual adjustment of each device made it possible to achieve linearity "in the shelf" 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 also does not change.

Musical Fidelity M8PRE teston thesound

The Musical Fidelity M8PRE is a Hi-End preamplifier that is today the flagship of the line 8 in the Fidelity production program. Laconically austere, somewhat old-fashioned classic preamplifier design blends seamlessly with ultra modern technologies. It didn't make sense to listen to the Musical Fidelity M8PRE preamp separately from the powerful one, and we arranged a sound session in two versions: with m8 500s and m8 700s amps. You can see the report from the sound competition in the reports:

Testing 1

Testing 2

Options:

• Number of channels: 2;
• Sensitivity: 352mV;
• Harmonic factor: 0.003%;
• THD from RCA inputs: 0.005%;
• THD from XLR inputs: 0.004%;
• Signal-to-noise ratio: 118 dB;
• Frequency response: 5Hz - 100 kHz;
• Frequency response unevenness in the frequency range: +0, -0.1 dB;
• 2 balanced XLR inputs;
• 4 RCA inputs adjustable;
• 1 home theater RCA input not adjustable;
• 1 RCA input for RIAA cartridges;
• 1 entry for external management: Trigger;
• 1 adjustable RCA output;
• 1 balanced XLR output;
• 1 fixed RCA output;
• 1 Trigger external control output;
• Weight (unpacked / packed): 17/23 Kg;
• Dimensions WxHxD (mm): 440 x 162 x 400.

P.S. In our online store you can buy the Musical Fidelity M8 PRE pre-amplifier, the review of which is given above. For all questions, you can contact the phones on the site.

Circuitry

Transistor (class A)

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preamplifier

Musical Fidelity M8 PRE Review Hi-End Balanced Preamp Review

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listened to the pre and end

Solomin 2016-12-01

Recently I listened to MF M8 PRE with their own 2x500 ending, with PSB Synchrony One acoustics. The truth before 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 the way it holds the stage - there were real dimensions of the instruments, their arrangement is very natural, as in nature ... 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. Tall constantly wanted to add spice. I think that with a thorough warm-up it will completely pass. Or with normal network wires, otherwise it included standard laces to the Chinese extension cord, God forgive me.

Prev

IA 2016-11-27

I have a balanced fidelity 8 preamplifier for about a year, I came across a beautiful description here and I wanted to answer. Most of what is written in the article is true. the device is worthy, for example, I will not change it for something in the foreseeable future at all, tk. I am quite satisfied with the sound, and calmed down about the equipment. Prior to that, Marantz had a full powerful one, he sold it, he was very sugary. Fidelity is not like that, here accuracy is above all. From music I listen mainly to New Age and non-killing psychedelics. Jazz and violins are not mine, I have a ten-year-old Denon top 2x300 on 8 ohms. Acoustics PMC floorstanders 2 bands 200 watts. I don't listen very loudly, only sometimes when I'm in the mood. The fact that 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 - Stereo adjustable pre-amplifier with balanced inputs buy at Master Kit. Driver, programs, circuit, reviews, instructions, do-it-yourself, DIY

You can buy Master Kit NM2118 from us - Pre-stereo adjustable amplifier with balanced inputs: price, photo, DIY, do-it-yourself, specifications and equipment, reviews, review, instructions, driver, programs, circuit

Master Kit, NM2118, Pre-stereo adjustable amplifier with balanced inputs, price, description, photo, buy, DIY, DIY, reviews, review, instruction, delivery, driver, software, schematic

https://website/shop/1320097

On order

NM2118
Pre-stereo adjustable amplifier with balanced inputs

BM2118

Not available

To report

on arrival at the warehouse

The set has been discontinued. Use a Functional Analog 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 a radio amateur to assemble a simple and reliable pre-stereo adjustable amplifier with balanced inputs, which has a low level of self-noise, maximum functionality and a wide range of supply voltages.

Specifications

Peculiarities

• The pre-amplifier is installed between the linear or powerful 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 preliminary stereo adjustable amplifier is made on 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. On the OS DA1.1 - DA1.4 two balanced input blocks are made. The adders are made on the OS DA2.1 and DA2.2. Such a construction allows you to use almost any source (linear output(s), PA output(s)) to remove a useful signal. Op-amps DA2.3 and DA2.4 are equipped with variable gain amplifiers 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 (line output, etc.) with differential outputs, the input signal to the processing unit is applied 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 applied relative to contacts X2, X4 (left) and X6, X8 (right). When using a low-power source (line output, etc.) with conventional potential outputs, the input signal to the processing unit is applied relative to contacts X1, X3 (left) and X5, X7 (right), and X3 and X7 must be connected to the power supply ground. When using a powerful source (PA output, etc.) with conventional potential outputs, the input signal to the processing unit is applied relative to contacts X2, X4 (left) and X6, X8 (right), and X3 and X7 must be connected to the power supply ground. From the contacts X11, X13 (left) and X12, X13 (right), a useful amplified or suppressed signal is taken for further processing or feeding to the PA. Potentiometer R17 adjusts the output signal level. !Design. Structurally, the preamplifier is made on a printed circuit board made of foil fiberglass with dimensions of 54x40 mm. The design provides for the installation of the board in the case; for this, there are mounting holes with a diameter of 3 mm along the edges of the board.