The CD player is a necessary audio source device for HIFI fans. There are many options for models, but most people still use the "Yangchun Baixue" type of popular products. The sound quality effect is general, so many audiophiles "move" through various methods. It is also one of them. Replacing fever capacitors, op amps, motorcycle power supplies, etc., has certain effects. To be honest, the effect is not very obvious. Most are in the stage of "self-deception" (there is no qualitative leap due to the limitations of the chip). Seeing foreign (Russian, Japanese) motorcycle information, using the electronic tube to modify the audio output of the CD player, it is said that the effect is obviously different, there is an impulse in my heart, I would like to experiment, but because of the limitations of my knowledge level, I always feel that the electronic tube Working in a high-voltage state is more harmful to the CD than the benefits. Moreover, due to the heating of the tube, the installation height, the induced noise of the high input impedance, the filament-induced hum, etc., no actual test has been conducted.
Seeing the actual application of Shanling's tube CD, low voltage 60V 6N3 cathode follower, changed the limitation of my tube must be used in high voltage. My father once told me that the previous preamplifier, 6N1 tube There is a working condition of 50 volts filament DC 5 volts (which has exceeded the reasonable voltage range of the filament), which is mainly used for MIC amplification, which can greatly reduce the noise of the electron tube. At first, I do n’t believe it. It has been proved that it can be used for a long time. Occasionally got a ONE BCD-497 cheap CD player, the chassis height is appropriate, there is a certain space inside, suitable for the installation of the electronic tube, the bottom plate has a cooling hole to facilitate the heat dissipation of the electronic tube, and immediately conduct a hands-on experiment, let alone the price is very low, Failure is not a big loss, so there is no psychological burden.
The specific circuit adopts the application state of 6N3 in low voltage. Firstly, it is first-level amplified, and then has the form of cathode output. Originally, there is no filter network. I want to filter out the interference signals above 20kHz by the tube structure itself. Older fans recommend adding For better, because the general voltage amplifying electron tube can work above MHz, after calculation, use the existing resistance-capacitance components at hand to design the circuit as shown in Figure 1 (circuit principle part):
Figure 2: (Power part)
The main consideration for the above low-voltage applications is that the CD player does not require a high output voltage, and the tube can reduce some noise in low-voltage applications, and the coupling capacitor can use a variety of lower voltages to tune the tone and other reasons. The low-voltage transformer adapts to the internal space and height of the CD player, but has to be used for voltage multiplication. The electronic tube adopts DC power supply to avoid the generation of filament hum.
For the choice of the tube, theoretically, the low voltage application of the 6922, 6DJ8, 6N11 and other tubes is better, but, through the actual listening experience, it is indeed not as good as 396A, 5670, 6N3, mainly because the 6922 has some meaning close to the op amp, although the resolution Better than 5670, but I personally prefer 5670 more, and finally chose 5670.
The actual production uses a hole board, and the pin of the tube socket is cut with a diagonal pliers to facilitate welding from the welding hole of the circuit board. One trick is to insert the tube into the socket before welding. The electronic tube is difficult to insert to avoid damage to the circuit board and excessive force to remove the solder joint.
During the installation, the original op amp part was not canceled, so that the CD player has dual outputs, that is, one output in the form of an op amp (the capacitor is WIMA, the op amp is AD827), and the one in the form of a tube (USA gold foot 5670), also Easy to compare sound. During the test, the plug is manually selected, and the input of the circuit is directly welded to the output pin of the DAC chip. The DAC of this machine is KDA0316LN, and the output is 1 and 20 feet respectively. The output of the original transistor radio follower earphone is changed to the output of TDA2822, and the volume of the earphone is appropriately fixed by resistance voltage division through the test.
See Figure 3 for details: (Physical photos)
In order to increase heat dissipation, the computer CPU fan half-pressure application is used to increase the heat dissipation effect and reduce the fan noise, which will not affect the music appreciation at low volume.
The circuit is basically welded once, and the actual data can be adjusted free.
After switching to electronic tubes, the sound quality is obviously different from that of op amps. Personally, I think it is better than op amps, especially for listening to guitar, lute, guzheng, erhu, violin, saxophone and other musical instruments. Without losing the details, it has a thicker sense than the op amp, which can make people integrate into the music. Of course, the battle for gallstones is tasteless, and I feel that each has its own advantages. The key is where it is most reasonable to use it.
To sum up experience is to consider the design of an application circuit.I personally think that it is mainly on the basis of my own existing components, and if objective conditions allow, try to develop to the best. Don't go to the highest level at all times, but the final result is not satisfactory. .
Please correct me if it is inappropriate.
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