I believe that the majority of audio and computer enthusiasts have this experience: are they often scolded by their families when they are reveling in powerful music, charming computer games, and shocking sound effects? ! It's really disappointing. I plug a pair of headphones into the sound card, and the sound is so small that I can't experience the shocking sound effects. How to do? There is a way: we can make a fever-level single-ended Class A surround headphone amplifier! ! Let it play the ultimate effect of headphones! ! Why use headphones to listen to music? This is definitely not simply fear that the loudspeaker listening volume will affect other people. In fact, an ordinary headphone, when the headphone amplifier can match well, in fact, the sound quality can show far more than a pair of thousands, even Tens of thousands of speakers. The reason is simple, because when listening through headphones, you can completely avoid the influence of the surrounding environment, such as reflection, sound absorption in the room, and all are the key elements that affect the quality of listening. Through the headphones, we can easily remove these obstacles that hinder the sound quality performance and get the most realistic sound quality performance!
The main points of the production: use the 12V power supply in the computer, the volume, tone, surround switch, headphone socket are all in one direction, and the width of the entire board cannot exceed 14.5 cm, because the two spaces reserved under the computer CD-ROM, Each cell is about 14.5╳ 4 cm, and these two cells can be detached. We will use one of them to drill holes as the front panel of this headset, so that it is convenient for our use.
Production principle: Use ROHM's stereo DC volume tone surround circuit BH3854 as the front stage, and use a Hitachi fever audio mid power tube 2SD669 as the single-end class A output stage for the left and right channels, and then mix with fever supplement components The composition, color photos and principles are shown in the following figure (in the picture, the headphone amplifier board is decorated with a stereo color advertisement on the computer panel).
BH3854 is ROHM's stereo DC volume, tone (high and low), matrix surround circuit, can also be used for serial control with a single-chip microcomputer to achieve remote control functions. Widely used in CD players, radios, televisions, recorders and other fields. BH3854 features: low noise, low distortion (only 0.03%), the input signal amplification can be adjusted, few peripheral components, operating voltage 5.4-9.5V (recommended 8V), tone control range -15dB to + 15dB ; Pin functions of BH3854: Pins 2 and 31 are the left and right channel signal input terminals, the input impedance is 47K, and pins 3 and 30 are the negative input terminals of the internal amplifier of the left and right channels, pins 4, 5, 6 and 27 Pins 28, 29 and 29 are left and right channel bass filter pins, pins 7 and 8, 25 and 26 are left and right channel treble filter pins, pins 9 and 24 are left and right channels Signal output terminal, pin 10 is the power input terminal, pin 1 is the analog ground, pin 16 is the digital ground, pin 11 is the surround control terminal, pin 21 is the bass control terminal, pin 22 is the treble control terminal, pin 23 is the volume control terminal , 17 feet are 3.8V output pins, 20 feet are CK pins, 19 are DATA pins, 18 feet are LATCH pins, and 12-15 feet are data pins. Detailed application materials about BH3854 can be downloaded.
Principle analysis: The left and right channel audio signals enter the internal volume amplifier circuit through the 2 and 31 pins of the BH3854, and then enter the tone volume surround circuit. After processing, the 9 and 24 pins output the signal to the 2SD669 of the left and right channels for amplification, and the coupling capacitor Send to the headset for work. Note: The magnification of the amplifier inside the BH3854 is determined by the size of the external resistor. The smaller the external resistance is, the larger the magnification (larger magnification will cause overload distortion). The larger the external resistance, the smaller the magnification (without connecting the resistor BH3854 The amplifier only acts as a buffer). The 9H and 24H pins of the BH3854 have a 4V DC voltage, which is just a Class A bias voltage for the 2SD669 of the left and right channels, so that the 2SD669 static current is about 50mA, which can drive a variety of headphones from 32Ω to 300Ω! 2SD669 is working in a single-ended Class A state. The positive and negative half waves of the signal are completed by 2SD669 alone, so there is no crossover distortion, and even harmonics are rich, which has a certain moisturizing effect on the tone, so this headphone amplifier board is very Listening, while 2SD669 is working in a high current state of 50mA (general op amps, headphone amplifier integration is only a few milliamperes), it is easy to deal with large dynamic music signals to obtain the most realistic sound quality performance! Play the ultimate effect of headphones!
Pin 21 of the BH3854 is the bass control terminal, pin 22 is the treble control terminal, and pin 23 is the volume control terminal. They are all controlled by DC voltage. The advantage of using DC voltage control is that there is no noise in the control process. In this regard, BH3854 is better than the LM4610. One point: BH3854 is adjusted from the minimum voltage, LM4610 is adjusted from the voltage near the middle (the potentiometer must be turned on about halfway to work, some enthusiasts who do n’t understand think it is wrong!).
Component selection: ①The circuit board is silver-plated, and pay attention to the wiring of the input and output grounds, so that there will be no noise, the volume, tone, surround switch, headphone jack are all in one direction, so it is convenient to use; ② To obtain the most Excellent sound quality, electrolytic capacitors adopt Japanese ELNA high-speed supplements, electrodeless capacitors use Thomson MKP capacitors; resistors use metal film; ③ potentiometers are used in parallel with double connection, which is durable, and the double connection is strong enough; The Hitachi audiophile power amplifier 2SD669 in the road should be paired (within 5%), and a radiator must be added; ⑤ The headphone jack uses 3.5mm, which is commonly used for this specification, and the power input socket uses a computer-wide D-shaped, so it is convenient to add Outfit.
Installation and use: After making a good check, use a CD player to test. After connecting the cable, do not play the CD. Insert the earphones and turn the volume potentiometer to the maximum. There is no current sound at all. It ’s great. Note: There will be a slight background noise when installed into the computer, this is a problem of the computer). It is easy to install into the computer: disassemble the main body of the computer without powering on, remove one of the two reserved spaces under the CD-ROM, and then press the electrical appliance, switch and earphone on the headphone amplifier board Drill holes for the location of the socket, fix the headphone amplifier board and put it back into the computer, and then connect the power supply to the headphone amplifier board D-shaped socket (there are several groups of 12V + 5V in the computer, do not connect the 24V group , It is best to use a multimeter to measure), and finally connect the audio signal, there is audio output on the sound card of the computer (if the motherboard with its own sound card can refer to the manual, if you do n’t understand "chicken intestine", connect it from the back of the host, if If the signal is too strong, please double-click the speaker icon in the task bar with the mouse before using the headphone amplifier board, and turn down the volume in the pop-up menu). Don't rush to plug in the headset after installing the headphone amplifier board. Observe the power for ten minutes to see if there is smoke. Please turn off the power switch if there is any. Check the problem and use it only after eliminating it! In order to obtain the best sound quality, please turn on the power for about ten minutes in advance every time you use it, because the Class A amplifier needs a little temperature and the best sound! Of course, it can be used immediately after power-on, and it will be better to listen to for ten minutes. When using it, flexibly and flexibly adjust the high and low frequencies and the switch surround (if you turn on the surround, there will be a surround effect of widening the sound field). The tone is too high, because the bass of the BH3854 is very harmful (a little bit more harmful than the LM4610). If the tone is too high, it will be distorted and not pleasant.
Listening experience: plug in the headset for about ten minutes after power-on, and use a CD test disc to put it into the computer's CD-ROM. The first sound of broken glass scared me, and my hands quickly removed the headset. Because I turned up the volume a lot! After turning down the volume, I continued to listen to music. After that, I also listened to CDs such as "Cai Qin" and Hugo's "Love Bamboo". After listening to them for about four or five hours, why? ? I still need to ask! Of course it is good to listen for so long! !
This single-ended Class A surround headphone amplifier has excellent resolution, low frequency control is very good (freely retractable), on the whole rich sense of layering, high frequency slim, beautiful and beautiful, fully reflects the advantages of single-ended Class A circuit! The details are vivid, the treble is silky smooth, and the sound quality is very pure! !
If you are an Internet cafe, you can make a batch for each computer, so that netizens will prefer to surf the Internet at your place, but this is a magic weapon to increase the number of customers! Do n’t forget to thank me at that time!
Finally, remind fake enthusiasts to pay attention: pay attention to the design of the input ground and the output ground on the circuit board must be separated to the power supply before connecting. In addition, the components mentioned in the article must be selected to make (the overall cost is only tens of yuan). Only in this way can you get good results! This single-ended Class A surround headphone amplifier can be used at the current level, and can replace and upgrade existing audio. If you want to assemble the power amplifier, it can be equipped with a class A post-stage amplifier (for example, Meishun ME-308 pure DC current negative feedback type A amplifier, the circuit schematic is available on the website of Meishun Electronics Factory http: //).
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