Complete Hi-Fi preamp. How I built my own hi-fi amplifier for just $200
A preamplifier (also known as a preamp or preamp) is an important element of any audio configuration. Its main role is to ensure the most convenient and varied switching (all kinds of connectors for various signal sources), coordination electrical characteristics signal with a final amplifier (few configurations, even expensive ones, can do without a preamplifier and not suffer in stability and sound quality due to disagreements between the source and the amplifier), as well as high-quality volume control and sometimes timbre. Here it is worth paying attention to the importance of volume control: cheap circuits tend to mercilessly distort the balance of channels, and even small deviations in it can significantly change the spatial characteristics of the sound: its volume, the width of the stage, the correct placement of instruments, and so on. Developing high-quality level controls is not as trivial a task as many people think.
Preamplifiers are often endowed with a wealth of additional functionality - from built-in DACs that allow you to connect sources digital signal directly for high-quality analogue conversion, and to full network media players or wireless receivers.
However, when it comes to true Hi-Fi sound, attention to each element of the path and competent assembly of the system as a whole, we are talking about the use of specialized separate components High Quality. This is how a truly stunning level of reproduction is achieved, realizing all the subtlest nuances, all the emotional and dynamic depth, all the volume and air previously hidden from your ears - even in well-known recordings. And if this is your approach to completing home (and maybe professional) audio, then separate Hi-Fi preamplifiers are for you!
Pre-amplification stages are particularly sensitive and vulnerable to all kinds of interference, noise, and distortion. As you know, you cannot remove interference from a signal, and only further attempts at compensation are possible using even greater influences on the signal. So for the purest, most natural and reliable sound, the optimal choice would be to separate the preamplifier into its own shielded housing, with its own power supply (preferably stabilized and filtered using additional devices), using high-quality interconnect cables.
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“After a long search and a series of failures,” that’s exactly what happened to me. I looked through a hundred different magazines and brochures in search of a decent pre-amplifier circuit, and it seems I found it... I won’t lie, during the assembly and testing process I had to modify the circuit - remove and add some things. In particular, an additional signal level control was introduced at the PU input (R1), with its help the input signal is attenuated to the nominal level and a high-frequency volume control (R21), as well as the possibility of stepwise attenuation of the signal by 20 decibels (SA2). The results exceeded all expectations - a correctly assembled PU according to the scheme I proposed in terms of sound quality far exceeds active PUs and many passive ones installed in high-end equipment. Therefore, I recommend that everyone who uses domestic amplifiers (regardless of the class) replace the pre-amplifiers with the one offered to your attention. The sound will change beyond recognition, naturally for the better, transparency and purity will appear with a low level of noise and nonlinear distortion.
The amplifier uses dual variable resistors R11 and R17 of any type of group B, R1 and R21 of any type of group B or A. A 100 kOhm variable resistor (tapped from the middle) can be used as a loud-compensated volume control (R21). Transistors can be replaced with KT3107I, KT313B, KT361V, K (VT1, VT4) and KT312V, KT315V (others). Replacing the K574UD1 op amp with other types of op amp is not recommended. If the DC component is at a significant level (in rare cases) at point A, it is necessary to install a capacitor with a capacity of 2.2 - 5 μF.
The described PU is connected to an AF power amplifier with an input impedance of at least 10 kOhm. With a significant increase in Kg, this control unit can also be loaded onto an UMZCH with Rin up to 2 kOhm (which is extremely undesirable), in such cases (if the Rin of your UMZCH is less than 10 kOhm), you just need to once again power up the output stage (a copy of the circuit section VT1-VT2- VT3-VT4-R4-R5-R6-R7, connect to output DA2), connect resistors R23 and R24 in the same way as resistors R2 and R3, although in this case the noise level may increase. And if Rin of your UMZCH is greater than or equal to 100 kOhm, then it is recommended to use K574UD1A(B) as an operational amplifier DA2, this will reduce the level of distortion and noise.
Possible changes in the scheme (improving):
- To exclude from the passage path sound signal P2K switches (very unreliable in operation), it is recommended to exclude switch SA1 from the circuit (together with resistors R8, R9), and move switch SA2 to the last stage by short-circuiting resistor R23 (resistors R13, R14 are excluded from the circuit).
Please send any questions you have about this amplifier to: [email protected]
The amplifier circuit is shown below.
- 05.10.2014
This preamplifier is simple and has good parameters. This circuit is based on the TCA5550, containing a dual amplifier and outputs for volume control and equalization, treble, bass, volume, balance. The circuit consumes very little current. Regulators must be located as close to the chip as possible to reduce interference, interference and noise. Element base R1-2-3-4=100 Kohms C3-4=100nF …
- 16.11.2014
The figure shows the circuit of a simple 2-watt amplifier (stereo). The circuit is easy to assemble and has a low cost. Supply voltage 12 V. Load resistance 8 Ohms. Amplifier circuit PCB drawing (stereo)
- 20.09.2014
Its meaning is different for different hard drive models. Unlike high-level formatting - creating partitions and file structures, low-level formatting means basic layout of disk surfaces. For early model hard drives that were supplied with clean surfaces, such formatting creates only information sectors and can be performed by the hard drive controller under the control of the appropriate program. ...
- 20.09.2014
Voltmeters with an error of more than 4% are classified as indicators. One of these voltmeters is described in this article. The voltmeter-indicator whose circuit is shown in the figure can be used to measure voltages in digital devices with a supply voltage of no more than 5V. LED voltmeter indication with a limit from 1.2 to 4.2V through 0.6V. Rin of the voltmeter...
Introduction
I avoided building a full hi-fi preamp including tone controls (and ensuring the controls are mounted on the PCB) because the variable resistors available in different parts world are not always compatible. But due to high demand, this project was nevertheless developed (along with full printed circuit board) to fill a gap in the lineup available from ESP.
The proposed preamplifier is very simple to manufacture on a printed circuit board and has an innovative tone reduction function. Instead of completely disabling the tone control, a deep reduction in its sensitivity has been applied. In this state, the adjustment has a maximum range shown in Figure 3 (see below). It can be increased as desired. So you can have two tone control settings - one with a normal 10dB boost and cut, and one with a very fine tone control of +/- 3dB. This will be sufficient for minor adjustments you may need to make during daily listening.
The design of the device is quite conventional, but the main advantage over other designs is that it has virtually no wires. Switching sources can be done in any way, I suggest using a rotary switch at the rear of the case and an extension shaft to bring the handle to the front panel. This will keep wiring to a minimum and reduce crosstalk from other active inputs.
As you can see, the printed circuit board is very compact. The volume control is positioned a little further back than others to allow for the use of a larger knob, as it is the most commonly used control in any preamp. The use of 16mm potentiometers ensures a small and neat layout and allows the preamp to be easily connected to a power amp to create an integrated amplifier.
Note that the Rev-A board is slightly different from the Rev schematic shown here.
Description
The input stage shown in Figure 1 provides a gain of 2 (6 dB) and acts as a buffer for the tone control circuitry. The tone control is a typical Baxandall design, but the addition of resistors R117, 118, and 119 provides flexibility and ease of reconfiguration that traditional units don't offer.
R119 is a unique part of this circuit (I haven't seen this solution before). The specified 100k impedance limits the tone control range to a reasonable ±10dB. To get more range the R119 (and R219) can be omitted altogether. Conversely, decreasing its value will give a smaller range of adjustments: about 6 dB at 20 Hz and 7.5 dB at 20 kHz with a resistance of 22 kOhm.
The frequency response of the tone block is shown in Figure 2 (step - 10% of the resistor value). As you can see, the midrange is practically unaffected. This is in contrast to most designs where the controls are concentrated at 1kHz and there is a very audible effect in the midrange.
For those who don't want to use tone controls at all, I suggest the DoZ (Project 37) or Project 88 preamp. Both were designed without a tone block and are more in line with the criteria of true minimalist designs.
In contrast, Figure 3 shows the tone control range when SW1 is closed. It can be seen that when the controls are in the center position, any deviation (due to resistor tolerances) is minimal and the response is completely flat (within 0.1 dB). As you can see, the adjustment range is much smaller and it is likely that this mode will be used for most of the time.
Figure 3 shows the curves for 100%, 75%, 50% 25% and 0% tone control settings. The HF change is more pronounced than the LF, but is still limited to ±3 dB amplitude at 20 kHz. Overall, the circuit has excellent flexibility and meets all the requirements for listening to music of all genres.
Adjusting balance, volume and output stages
The balance control is deliberately designed to have little effect near the center position. This allows for more accurate positioning. A variable resistor with linear characteristic, connected according to the circuit with an additional resistor (Project 01) to obtain a logarithmic dependence. The output impedance is 100 ohms. Using the proposed 2.2uF polyester capacitor allows the power amplifier to be loaded with an input impedance of 22k, providing a frequency response as shown in Figures 2 and 3. The lower cutoff frequency is about 3Hz with a rated load of 22k. A higher value can be used for the C103/203 if desired, but the value given is expected to be sufficient for all normal power amplifiers. It is possible to use an electrolytic capacitor. Polarity, in this case, does not matter, since constant current here will not exceed several mV. I suggest using a 10uF electrolyte.
The final stage is inversion - correcting the inversion in the tone controls and returning to normal phase. Again, this stage operates at a nominal gain of 6 dB, although this value changes as the volume is adjusted. The lowest noise level is observed in the middle position of VR4 - exactly in the area where the regulator will be used most often.
The gain of the last stage depends on the position of the volume and balance controls. With the balance control in the central position, we have the following odds gains:
- -8 dB (VR4 25%),
- -3.6 dB (VR4 50%),
- 1 dB (VR4 75%),
- 9 dB (VR4 100%).
To determine the overall gain, add the input stage gain (6 dB). The overall system gain is about 2.6 dB when the volume control is centered.
If the gain is found to be excessive (or insufficient), the resistance of resistors R113/213 can be decreased (or increased). With a resistance of 15 kOhm, the gain of this stage will be 1 at maximum volume. A reasonable compromise might be a 22k resistor. It all depends on the input sensitivity of the power amplifier, so to decide, I recommend conducting several tests. The PCB has connectors for quick replacement R113/213.
Figure 5 shows the shunt elements of the op-amp - ceramic capacitors with a capacity of 100 nF and electrolytes with a capacity of 10 μF, which are necessary for protection against radio interference. This is important, and especially where high-speed operational amplifiers are used.
Electrolytes should be rated at least 50V, as should ceramics. Here it is necessary to use multilayer ceramic capacitors. Do not use polyester bypass capacitors as their high frequency performance is inferior to that of ceramics. They can be used with the TL072 op-amp, but ceramics are still better.
Device
Although the circuit is shown using NE5532 op amps, OPA2134 or something else can be used instead. TL072 – not bad a budget option, but I don't recommend using anything cheaper than the TL072 as the result may be excessive noise levels. This in turn severely limits the usefulness and quality of the preamp.
Below is a typical dual op amp pinout. If the op amp is installed backwards, it will almost certainly be damaged, so be careful when installing.
When first powering up, use 100 ohm resistors in series with each power circuit to limit the current if you make a wiring mistake.
All resistors should be metal film and preferably 1% tolerance for best channel matching and noise reduction. Likewise, capacitors for tone controls should be matched as closely as possible using a capacitance meter. Linear potentiometers with a diameter of 16 mm for PCB, which are ubiquitous.
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Strict, elegant appearance. Minimum control elements on the facade. The sound is clear, transparent, very detailed. With the ELAC 407, it is somewhat shifted towards the treble and upper mids, and after prolonged listening it begins to tire; with the pr200, the sound was more comfortable, but less detailed. Cons: periodically loud hiss from the tweeters and a slight wheezing background. It does not depend on the network voltage, it occurs and goes away spontaneously. Perhaps a disadvantage of this instance.
After numerous “wobbles” and searches on the Internet for an audiophile preamplifier from advanced brands of audio equipment at an affordable price, and thanks to the specific participation of the Audiomania company in the person of manager Arthur Voinov, I chose the Atoll PR 300 Signature Black preamplifier. The sound quality exceeded expectations (this is without changing interconnect cables). The sound is very detailed, a lot of “air”, richness, excellent vocal reproduction, good stage. The sound quality of audio tracks is no worse than in the showroom listening room. At the request of manager Arthur, a power amplifier (two monoblocks) was brought for a “date” with Atoll. In my opinion, a successful marriage took place (amplifier-preamplifier), in the hope of a long-term mutual understanding between them on audio issues. But, as you know, sound is a never-ending topic and, if possible, we will conquer the peaks - the obstacle is low-quality content. And the question of the timbre block, for which I was previously worried, disappeared (there were even persuasions to purchase a preamplifier with a timbre block from leading audio equipment manufacturers, and at a high price). Maybe the timbre block is at its limit for the base, but fortunately everything turned out OK for me even without it. Yes, and taking into account the mentality of the manufacturer, prev. The atoll is made in France, not China (haven't checked yet). M. b. Is France a development country??
I am very pleased with the purchase of this product, it was not in vain that I waited 3 months for it. A very musical device. In combination with the Atoll AM 200 SE power amplifier and the Elac FS 247.3 acoustics, you want to listen to music and listen to it. BUT! This preamplifier has one significant drawback - it works as expected only at a reduced voltage of 210-215 Volts. At a voltage of 220 - 230 Volts, there is a strong high-frequency hiss and a slight background from the speakers. Therefore, if you decide to buy this pred, then take care of nutrition first.
They dissuaded me from buying almost everything - they say the modern ones are no longer the same, etc. Neutral, but somehow it sounds cozy. Multifaceted scene, detail, good low end. Pairs perfectly with Atoll AM 100 SE and Artauiolab p25.2., acoustics - Davis Acoustics Stentaure L.E. p.s. Alas, the remote control is still a “masterpiece” of design and ergonomics.
