Created on 23.01.2008 16:50.
Updated on 04/05/2020 20:43.
A big request to readers – not to consider the first paragraph a journalistic device …
Recently, my “Home-made” amplifier started to jam one channel a little, and I had to come to grips with checking the details. It turned out – it’s all about a poor-quality capacitor at the inlet.
After the completion of the repairs, I was persuaded to borrow this amplifier with speakers for a while for “events” (it was just the time of the holidays). And what is left to do at home when there is nothing to connect to the output of the sound card, but you want to listen to music or just drive into the next shooter (now it’s “Call of Duty”)?
So I got out of the pantry pretty dusty columns – “Cheburashka”, which I once used. Their price was about 300 rubles, and they played music with the appropriate quality. So after a “high-quality” sound (a good amplifier + more or less normal speakers), it became simply unbearable to hear the cardboard sounds made by stunted little ones.
But there was still a headphone-out on the Cheburashkas. Okay, so it’s time to use the headphones. In stores, among all sorts of different “works” I came across a headset from SONY CD-268M.V.
Of course, connoisseurs of quality will frown with displeasure – yes, really yours, because the price of these “mugs” is about $ 10, not $ 100 … But compared to the cries of “buttons” for 30 rubles, it was “Sound”.
Although, of course, it is still far from “SOUND” (the Cheburashkas had a perceptible sound …).
Headphones could be connected directly to the output of the sound card, but then one question arose – what kind of load, in fact, are these outputs designed for?
The fact is that distortion measurements are almost always made when the output of the sound card is loaded at the input of the measuring device, and its input impedance is hardly 32 Ohm. But after all, with a decrease in the load resistance, the current increases, and now, with an increase in volume, distortions increase – look at the characteristics of any microcircuit – a bass amplifier (there are graphs in almost every description).
It turns out that when headphones are connected, a sound card is unlikely to be able to provide a high standard of sound quality and fully reveal its potential. (Or can it still be?)
So the idea came to assemble an amplifier specifically for connecting headphones – after all, there is no special jack on a home-made amplifier (the circuit design is such that ordinary headphones simply cannot be connected there). There were quite a few schemes in magazines and on the Internet, but only four were chosen.
The quality of “sound products” for them increases gradually, and the complexity of the assembly practically does not increase. I hope many music lovers and gambling addicts will find useful information here. Yes, and wives will be able to take a break from music and rumblings … (Only now it will be much more difficult for them to shout to you.)
Attention! Continuous use of headphones at maximum volume leads to permanent hearing impairment! The Ministry of Health warns!
The first scheme, simple
The headphone amplifier circuit is pretty simple. (Author – Valentiy Svyaty, Practyczny Elektronik No. 2/2000, pp. 4-6.) Actually, which at a supply voltage of 9 Volts can develop a power of up to 1 W at a load of 8 Ohms. The microcircuit normally operates on a load of up to 4 ohms and at an output power of 150 mW it provides a harmonic distortion of no more than 0.2%. This means that when working on headphones, the amplifier will not overwork, it will not get too hot and will not distort the sound.
The main feature of this circuit is automatic power on / off. When an audio signal is applied to the input of the amplifier, the voltage at the output of the detector on the diodes VD1, VD2 becomes sufficient to open the transistor VT2, which then opens the transistor VT1, through which the supply voltage passes to the microcircuit.
The amplifier is powered by a 9-volt battery (“Crown”, for example). In the absence of a sound signal, the voltage at the output of the detector decreases to zero, the transistors close and the microcircuit is de-energized. The headphone amplifier works with a supply voltage of 1.8 to 15 volts.
Naturally, if you do not suffer from forgetfulness, you can discard the “unnecessary” parts (detector and transistor switch) from the circuit and install a simple switch in the power circuit.
Scheme two, advanced
I came across a headphone amplifier circuit called “Volume and tone control unit for stereo headphones.” (Author – Andrzej Kosminski, Hobby Elektronik, No. 2/2000, pp. 48–49). The volume and tone controls themselves are made on the A1 – TDA1524A microcircuit in a typical switching circuit. (So it was written in the magazine, in the original description of the microcircuit the circuit is slightly different. But here the circuit is given in the “published” form).
A “powerful” amplifier is assembled on a dual operational amplifier A2, capable of driving low-impedance headphones.
The depth of volume control (R2) is from –80 to +21 dB, the bass tone (R4) is +/- 12 dB at a frequency of 100 Hz, and the treble tone (R5) is +/- 10 dB at a frequency of 10 kHz.
The maximum input voltage is no more than 2.5 Volts, the supply voltage is 12 Volts, and the current consumption is 40 mA. The adjusting resistors should be 47 kOhm with a linear dependence of the change in resistance on the angle of rotation of the slider (the so-called group “A”).
There should be no difficulties in manufacturing. If you want to power the amplifier from a +12 Volt source from the computer’s power supply, you will have to take measures to protect against interference in the power circuits (in the same way as the manufacturers of car radio tape recorders do – they put special filters).
Fans of shooters can limit themselves to these designs, and music lovers are encouraged to read the text further.
The third version of the headphone amplifier, cool
This circuit is a slightly revised version of an amplifier from the “almost” Hi-End “category (let the fans of lamps not frown – there are also transistor circuits of this class). The scheme was published in the magazine “Radiohobby”, No. 6 for 2003, the author is Vyacheslav Shchutsky.
In its original form, it was a class “A” amplifier with an output power of 25 watts at a load of 4 ohms, a dissipated power of 60 watts and a quiescent current of the output transistors of 2 amperes (!).
This is a complete unit that is an input voltage follower with a voltage gain of slightly less than unity. It had to work with a high quality voltage amplifier. (The sound card will fully provide this amplifier with the required signal level; it only needs to be amplified in power.)
The load (in the original) should be highly sensitive speaker systems, for example, monitor type. In this case, this “heater” will be used as a headphone amplifier.
Naturally, in this case, the quiescent current can be made smaller (for this you will have to change the resistance value of some resistors), and replace the output transistors with KT854A (I had to leave the KT819 transistors in the circuit – there were no others). Capacitors marked with an asterisk were installed during rework. The values in brackets refer to the “original” amplifier circuit (if you want to get 25 watts out).
In this diagram, it can be seen that the amplifier has no feedback, which, according to …