Мастеркласс Н.Сухова по питалову топовых фонокоров
Do you know what, until recently, irritated me most about the design of my phono corrector? - the fact that with the ideal design of the corrector board itself, measuring 20 by 45 and 3 mm thick, which can easily and naturally be placed in the basement of the tonearm of any turntable, so for organizing power plus minus 18 V 50 mA, most often for some reason everyone uses external circuits that have set their teeth on edge from these sources. For example, Douglas Self has a page, in my opinion, 570, let’s see what he offers there, which means Well, According to these circuits, most often everything is made by stabilizers on LM317\337 or on 78L18\79L18 Well, or other more modern microcircuits. But the main thing is not so much in these microcircuits, but the fact that they are powered by huge network transformers. I don’t mean such huge ones the fact that there is half a kilowatt, even fifteen watts, this is such a transformer, it’s basically awesome in size relative to everything else that is inserted inside the vinyl of the correctors. So, not only do these
transformers stupidly not fit inside the majority of turntables; everything that needs to be stuffed is already packed there. But they also dissipate strong interference around them with a mains frequency of 50 Hz and its harmonics. here are examples for you. This is Yura Panchenko's power supply, well, a normal one from Soviet times, a military network transformer is still alive, then that means a rectifier with smoothing capacitors and bipolar stabilizers on LM317 and 337, that there is no way to place all this jam inside the turntable in a separate box. With all the desire even if there is a very large turntable, look further Oh, this is a more modern version of Alexander Shestakovsky toroidal transformer network rectifier smoothing electrolytes and stabilizers are the same 317 337 And the phono stage itself is in this small box, look further Oh, this is the high-end version of Andrey from Odessa, here the dimensions of the power supply are even double - not only does it have a network transformer and very large-sized electrolytes 4700 uF rectifier so it also has a double stabilization In addition to the fact that here are LM317 337, here are a couple yes And here in the second channel, too, you see these tiny TPS7A39s, that is, here it is first stabilized by these stabilizers and then by modern TPS7A39. Well,
these two tiny scarves are just a phono preamplifier, but this is a high-end option, let’s look further at the options. Oh, this is an option that, even before it was hidden in a normal box, Yura soldered a depo196 network toroid rectifier stabilizer and here are actually two phono preamplifier scarves, and that’s it scarf Oh miniature That's what annoyed me. But recently, when analyzing new products from competitors, my attention fell on this phono stage from the China , which, in terms of dimensions 98x58x14 mm, is an order of magnitude smaller than other box designs, both contemporaries and earlier ones. But of course it’s much larger than my Cy-XXI with dimensions of 20x45x3 mm. As usual, there is no circuit, but as the autopsy showed, this device is designed as a phono preamplifier on a couple of good NE5532 operational amplifiers, I must say, but it didn’t particularly touch my attention because, well, the circuit, you probably all understand that it’s something like this, that is, so cheap the average for the Chinese is worthy of use Yes, but this is not about that, but my attention fell, you know where, but look at the power supply diagram here, you can see the power of this entire device goes through 5V USB. How
it is organized is what interested me. It turned out that the 5 V USB charger goes to this microcircuit - this is a Chinese microcircuit, here it is XL6007 from the Chinese company XLSEMI, this is such a small microcircuit in SOIC-8 that produces an output voltage from an input voltage of 3.6 to 24 volts up to 20 with something volt. Moreover, it is important for us that in the recommended application circuit there is also a bipolar output, both plus and minus, so according to this circuit, it looks like there is a 5 Volt converter to plus or minus, something like 16, I intended yes or 17 and then installed a couple integrated stabilizers 79L12 and 78L12 and from the output of these now integrated stabilizers the operational amplifiers were powered with a voltage of plus or minus 12 IN. As you can guess, I couldn’t resist the temptation to buy and test the XL6007 as power supply for the Cy-XXI century phono stage version 7. Here it is, but before we move on to the next
datasheets, I want to draw your attention to one point from the XL6007 datasheet. this is that it, like a pulse boost converter, the converter operates at a frequency set by an internal generator and which cannot be changed externally; the frequency is 400 kHz remembered Yes, the frequency is 400 kHz. Well, let’s go to AliExpress and select a device like this on the same microcircuit with an output voltage of plus or minus 18 V. This pleasure costs $2.71; the board itself is assembled and shipping to Ukraine is one and a half dollars. Well, let’s assume that such a scarf costs $4 for a single copy . Let's just check one more thing: 18 V, we should have a current of 25 mA twice on both channels, this means we have a current of 50 mA. Let's check whether this device will give out our current, let's
go, let's go, yeah, here it is, well, first of all, we note that the input voltage range can be from 3.7 to 24 volts for an output of 18, what does this mean - this means that almost any voltage source from 4 up to 24 V, which we have in our turntable. And in any turntable we have a power supply, even if there is no phono stage inside the turntable, then there is someone there - an electric motor that is powered by either 5 V or 12 V, right? So this range covers and we can, without using any additional network transformers, connect the input of our this microcircuit Well, our whole device here Yes, let's say the motor is powered and it will give us plus or minus 18 V at the output. Well, let's now check So will we have an output current of 50 mA, which we need now? Let’s get there Oh, 18 Volts, that’s what it looks like Yes, but what does it have in the specifications for the input voltage 5 V and output plus or minus 18 V, our device produces 0.1 And this is twice as much as we need, that is, everything is fine for 2.7 bucks in China or for 4 bucks including shipping, which means we get what we need and according voltage and current are like this. Now there is one more point that
I want to draw your attention to before we move on. The Chinese have a flaw in their phono stage, a glitch. They smooth out the XL6007 Well, you understand that any step-up pulse converter operating at a frequency of 400 kHz will not produce a pure DC voltage at the output - there will be some kind of ripple.
The Chinese in their phono preamplifier attached 78L12 and 79L12 to the output of the XL6007, these are integrated stabilizers that provide +- 12 V to power operational amplifiers, but I want to scold the Chinese, look at what they didn’t pay attention to, but you need to pay attention. This is the datasheet for 78L12. Pay attention to Fig4, the dependence of the coefficient suppression of ripple from frequency while our frequency is low, that is, 78L12 and 79L12 we use to stabilize the voltage of a conventional network rectifier which has 50-100-150-200 Hz, then the suppression of 60 dB is 1000 times good, and then we remember what pulsation frequency is 400 kHz and not 50 Hz and what is here and here is higher than 20 kHz there is a fairly sharp decline and the maximum that the manufacturers give in the datasheet is, well, consider 40 dB at a frequency of 100 kHz, and here we have 400 kHz, let’s extend it and what we’ll get there is almost 20 dB Well, worse than 40 and even worse than 30, there’s 20 with a small decibel, that is, at a frequency of 400 kHz LM78 and LM79 as Ripple suppressors are not suitable. we understand, that is, for a regular network rectifier they are super inexpensive and suitable, but for our case neither the seventy-ninth nor the seventy-eighth (well, like the Chinese here) they are not suitable here. They will not be able to effectively suppress pulsation XL6007 understood and agreed. here is the datasheet on the LM 78L12, the same thing, look at figure 10 on the 79L12, here you also see at a frequency of 400 kHz it will be somewhere here. Somewhere here it will be well, 20 dB or 10 times only 10 times and not
1000 times as at 50 Hz and 150, that is, we cross out LM79 and 78. Just in case, let’s check again the same characteristic LM317 LM337 We look at the network frequency, also more than sixty dB, even it is a little bit better than LM78, and what we have at a frequency of 400 kHz is 200 300 400 Well, you see Yes, at best 25 dB, that is, how much - in Suppress 20 times but not 1000 times as we are used to, but suppress 20 times at a frequency of 400 kHz it’s practically weak. Yes it is no good. Are you sure? - Fine. Now let me show you how to correctly and cheaply fix this Chinese glitch of incorrectly using integrated stabilizers 317\337 78\79 to suppress XL6007 ripple at a frequency of 400 kHz. Well, the most astute of you have probably already guessed that I am now using Microcap 12 correctly to develop our solution, look. Let me first show you the diagram of our experiment; we have assembled such a stand in our laboratory.
It was I who disassembled some completely rootless, low-power USB charger that produces 5 V 0.4 according to the passport. And from there I output 5 volts to the input of the XL6007 GND VIN, and connected the outputs to the power pins of the phono preamplifier. now we will see what happens when we look at the ripples at the output of the XL6007 with oscilloscopes, this is what we have, a positive output, this is a negative output, that is, +18 and -18. Realistically, how many are +18.07 and -18.06, and so at these outputs the XL6007 creates
ripples like these on the oscilloscope screen are large because I stretched it well yes But in fact, with 18 V power supply full from here to here from Peak before the Peak there is 50 mV and here there is 50 mV. 50 mV ripple is not particularly large as for an eighteen-volt full voltage. Well, a little more than the ripple of a good mains-powered fifty-hertz rectifier with good capacitors, there is 470 uF or 1000, so of course there will be less ripple, but there is 50 Hz And here it is 400 kHz, so look what I came up with in order not to use integral stabilizers 78 79 317 337 incorrectly, I placed them in series power circuit what? - that’s right, high-frequency chokes L1A and L1B, the inductance value of these chokes is from here we take 2.2 millihenries. Well, 31 ohms is the actual resistance of the windings of these chokes. Let's see how much our simple
filter suppresses 400 kHz. Another nuance, this is C1 200 nanofarads or 0.2 microfarads, this is in my phono stage. This is on the phono stage board I have C1 at 0.1 microfarads C2 at 0.1 μF C9 at 0.1 μF and C10 also at 0.1 μF . Here they are 1 2 3 4 these are blocking capacitors which are at the beginning and end of the power buses this is -18 this is +18 directly to ground 0.1 uF each and then after all the elements at the end of the board from the other end of the board also C1 and C2 also 0.1 each There are microphones
on the phono preamplifier board. Well, let's look at the frequency response that this choke sets for us Analysis - AC Run F8 let's press and see, then our frequency is 400 kHz, just like that, just a little bit 400 kHz, look guys, this choke provides ripple suppression with a frequency of 400 kHz by -69 dB. Well, to round it off and make it easy for us to count, let's remember that 60 dB is 1000 times, 66 dB is 2000 times, that is, such a simple circuit with only one choke allows you to suppress pulsations with a frequency of 400 kHz by 69 dB. 69 guys This is more than any of those microcircuits that were here, well, how much 100 times better because they suppress there by 25 dB And we have 69. That is, 100 times our cheap choke works better than 10 or even 20 times more expensive, these integrated stabilizers. Chinese, learn, you probably know how to count money better than me. here are two chokes like this for you. Well, you need to understand that separate chokes will need to be
installed, which means both plus and minus, and separately in the left channel and separately in the right channel, that is, for a stereo set we need four chokes like this. And then we get, look what we get. If you calculate those 66 decibels with some margin, then 10 and 20 mV rms ripple before the choke, then after the choke it turns not into millivolts but into MICROvolts 10 μV and into 5 microvolts, remember 10 microvolts . We have
ripples on our phono preamplifier that do not exceed 10 microvolts. Well, a small constant voltage, of course, at these 30 ohms, the internal resistance of the windings of these chokes, of course, drops and instead of 18 V we get 17.2 V, but this is within the tolerance for the supply voltage of this same corrector, I will remind those who do not know + 0.2 ... - 1 V, that is, plus or minus 18 V at a maximum of 18.2 or at a minimum of 17.0. And we have 17.22 - everything is within the tolerance and in terms of current, we also need 25 mA for each channel or 50 mA for both, and the XL6007, as we looked at on the datasheet, produces 100 mA. Here you go. Well, look at the final touches to the portrait of integrated stabilizers.
So we have 10 μV and 5 μV chokes at the output. Well, let's take 10 μV. And let's see what kind of noise is specified in integrated stabilizers. Well, let's say 78L. Let's look at where we have it... And by the way, you hear that means look, we don’t have 18 volt ones either in 78L or 79L - they have a maximum of 15 V and therefore are not suitable for us, because they have eighteen volt ones then no = another reason why they cannot be used. In 317 337 you can have an eighteen volt output, but these 78\79L do not. Well, let’s see what I wanted to show for complete happiness, as they say, look at the highest voltage fifteenth and such a parameter as Output noise voltage, this is the noise that this microcircuit itself generates, that is, not suppression of input voltage ripple, but simply output noise, even if we have an ideal input voltage will be stable, then the output will be, look, 90 microvolts, you see, yes, 90 microvolts at the output 78L15 = 90 microvolts then there is almost 10 times more than our 10 microvolts, here we have a 10 microvolt oscilloscope, if we see here before the chokes that we can still somehow observe pulsations on the oscilloscope, then here it’s no matter how I increase the sensitivity of the oscilloscope 10 I can’t see microvolts and 5 microvolts. That is, a completely clean signal.
All I can do is provide a link to the datasheet of these chokes. As always, I buy everything at the Imrad store, these chokes, their price is much cheaper than these integral stabilizers. datasheet here we have EPCOS, firstly and secondly, we have 2200 microhenry or 2.2 millihenry, what we have is that the current is up to 80 mA, the maximum resistance is 35 ohms (it turned out to be 31 in real measurements) and the resonant frequency at which it 1.1 MHz inductance ceases
to be a good one; we have 0.4 MHz. that is, it is 100% suitable. EPCOS here is his first and last name ordering code, you order Well, or come here and buy it in the store here in Kiev, here it is. Guys, look and now compare this board with this board compared to those large transformers and integrated stabilizers with radiators there were some of them. This is much smaller, it will fit just like the phono stage board itself into almost any turntable. Moreover, if we have a constant voltage source from 5 to 20 volts in the turntable
, and it is there because we are powered by an electric motor from something, to the power supply of the motor, we connect these two wires and get a ready-made power supply together with a phono preamplifier . so the power supply turns out to be of good quality and is several times better in terms of its own noise at the inductor output than any of those microcircuits that we looked at. Well, that’s all for today That's it, until next time, good luck! always yours, Nikolay Sukhov
2025-01-07 11:22
