GAINCLONE-2007. ULF on the LME49810 chip. Scheme, description

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GAINCLONE-2007. ULF on the LME49810 chip. Encyclopedia of radio electronics and electrical engineering

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The National Semiconductor Revolution Continues

Having received a press release and samples of new chips from National Semiconductor Co (NSC) in the spring, I could not help but pay attention to SML49810, and immediately started the project, which he dubbed the working title "GainClone-2007". This name came to my mind immediately, because it was simply impossible not to notice the attractiveness of this microcircuit. One study of the press release was enough to see that the LME49810 is not just a microcircuit, the LME49810 is a fighter for Levinsons, Brystones, Krells, Akuphases, Links, and everything on a discrete. I foresee the brightest future for her and no less popularity than the LM3886, which became the basis of the first Gainclone'a - the most popular repeating amplifier in the world, received in its time.

LME49810

GAINCLONE-2007. ULF on the LME49810 chip

So what is this SML49810. In April-May 2007, NSC introduced its latest development and its "secret weapon" to the electronics market - the powerful LME49810 audio amplifier driver, designed to set new standards in Hi-End Audio and PRO Studio electronics. Inspired by the number of pre-orders, NSC decided to make an unprecedented marketing move and lifted the confidentiality ban on this chip. On July 23, 2007, an information material was published on the NSC website: national.com/news/item/0,1735,1269,00.html and a datasheet in the public domain: cache.national.com/ds/LM/LME49810.pdf. There is also a two-channel version of the LME49820 and several other more powerful versions, in particular the LME49830, which allows you to do without compound transistors at the output, but, unfortunately, they remain secret for now.

As already mentioned, the LME49810 is a single-channel driver for the output stage of high-power audio amplifiers. The LME49810 supply voltage range from + -20 to + -100 Volts and an output current of at least 50 mA, allows you to create audio amplifiers based on it with an output power of up to 500 W at a load of 8 ohms, with the highest sound quality. NSC positions this product as an electronic component for creating amplifiers in the Hi-End and PRO categories, which is fully confirmed by the declared parameters of this microcircuit - distortion (THD + N) does not exceed 0.0007%, and the slew rate of the output voltage is not less than 50 V/µS. The LME49810 has a built-in sophisticated thermal protection that ensures the chip's performance at temperatures up to 150C, a built-in soft-clipping system that protects speakers from damage, a built-in LED clip indicator, and a mute circuit that mutes the signal when the corresponding circuit is opened.

The soft clipping system built into the LME49810, or the "Baker Clamp" system, is nothing more than a circuit proposed by RHBaker that brings the driver transistors out of saturation and prevents a sharp increase in high harmonics at the output when the input reaches limit signal. It was the use of such a circuit that was previously one of the pride of the designers of expensive top amplifiers based on discrete elements, for high-end and professional use. Now they have nothing more to be proud of. After the advent of the LME49810, there is no point in wasting time on "inventing the wheel" in the form of complex voltage amplifiers. All of the above suggests that the LME49810 is just going to be wildly attractive and popular among both professional developers and amateurs. The LME49810 has a factory selling price of $8.15 for purchases of 100 or more.

Amplifier

So, amplifier. For the first experience with this microcircuit, I decided not to be particularly tricky and build a circuit based on the datasheet. The LME49810 chip is single-channel, and this pleases, because in my opinion, it was the dual-channel nature of the predecessor - the LM4207 driver that made it, in some cases, not very convenient for use. In addition, unlike the LM4207, the LME49810 has a good supply voltage range up to +-100 V and an output current >50 mA, unlike the 3-10 mA LM4207. In general, there is progress, the manufacturer's work on previous mistakes, and as a result, an excellent product at the output.

Despite the fact that the LME49810 has very good noise suppression in the power circuits and, in principle, can do without an unstabilized source, in order to obtain higher quality indicators, I decided to power it from a + -100 Volt stabilizer. I don't know how the LME49810 is affected by the power supply through the "Mute" circuits, but just in case, the "Mute" and "Clip" circuits will also be powered by a separate parallel regulator on the TL431. Considering that this is my first experience with the LME49810 - whether I was right, following the path of stabilizing everything that is possible, or not, measurements and listening will show. When designing input circuits, I was just tempted to apply an inverting connection, remove the capacitor at the input and add an integrating servo amplifier to the circuit, but I decided not to risk it yet. In this version of the amplifier, the input circuits of the amplifier are built in a non-inverting connection.

The second experiment that I wanted to conduct was to put the LME49810 on a common heatsink with output transistors and abandon the VT1 transistor that provides thermal stabilization, i.e. make the LME49810 work with all its claimed complex thermal stabilization circuit, in combination with output transistors, but I will also save this option for future versions of the amplifier. The output stage is built according to the classical complementary scheme on Darlington deuces. As output transistors VT3-VT5, VT7-VT9, three parallel pairs of transistors MJL21195/96, known for their high sound qualities, are used, along with driver MJE15032/33. Quite a worthy company for the LME49810.

Power supply unit

The output stage is powered by an unstabilized + -75 V source, LME49810 from a + -100 V stabilizer. Each amplifier channel uses a separate 600 W transformer with 4 secondary windings - two of 57 Volt 5A each, and two of 95 Volt, 0,3A . Of course, you can take into account the crest factor of a real music signal and use transformers of half the power, but I am building a top-class amplifier, and I want to squeeze out everything that developers and manufacturers put into it from the LME49810. To facilitate starting processes when charging large capacitors, the PSU uses a soft start circuit based on thermistors Rt1, Rt2.

When the amplifier is turned on, the NTC thermistors have a high resistance, which limits the inrush current, then they warm up and reduce the resistance, gradually increasing the voltage across the transformers. After 1-2 seconds, the thermistors are blocked by the contacts of relay K1 and the amplifier goes into operating mode. The soft start and load delay circuitry is powered by a separate TR2 transformer common to the two amplifier channels. The delay for a soft start of 1-2 seconds is formed by the DA1 NE555 timer by the control relay K1, the load connection delay of 7-8 seconds is formed by a similar DA2 timer that controls the relays K2 and K3. It will not be superfluous to supplement the service part of the amplifier with a protection circuit as well, but in order not to burden the article and the circuit, I am not considering this node yet. I'll leave it for additional posts.

I can't wait to hear how the LME49810 sounds, and here's the amp assembled on a breadboard. Output power measurements showed an estimated 250W into an 8 ohm load and a THD of around 0.001%, which is very close to what the manufacturer claims. I'll save the admiration and epithets for later, to listen to the finished design, but the layout also makes it clear that the efforts and expectations are directed in the right direction. The sound of the layout "GainClone-2007" makes it possible to talk about the beginning of a new era in the design of high-class semiconductor UMZCH. Well, let's wait and hear how the amplifier will sound in hardware after the final assembly.

DATASHIT LME49810
Download wiring diagram, PSU, etc.

To be continued. In the second part, read the description of the design, settings and measurement results.

Author: Yuri Novikov (aka Mr. Golfinger), mr.goldfinger [dog] mail.ru; Publication: cxem.net

See other articles Section Transistor power amplifiers.

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