At numerous requests from radio amateurs, I present an improved and more complete diagram of a hybrid ULF with a detailed description, a list of parts and a power supply diagram. The lamp at the input of the 6N6P hybrid ULF circuit was replaced with a 6N2P. You can also install the 6N23P, which is more common in old lamps, in this unit. Field-effect transistors are replaceable with other similar ones - with an insulated gate and a drain current of 5A and higher. Variable R1 - 50 kOhm is a high-quality variable resistor for the volume control. You can set it up to 300 kOhm, nothing will worsen. Be sure to check the regulator for the absence of rustles and unpleasant friction during rotation. Ideally, you should use ALPS RG - this is a Japanese company producing high-quality regulators. Don't forget about the balance regulator.

Trimmer resistor R5 - 33 kOhm inserts voltage zero on the speaker in ULF silent mode. In other words, by applying power to the transistors and instead of a speaker (!), connecting a powerful 4-8 Ohm 15 watt resistor, we achieve zero voltage on it. We measure with a sensitive voltmeter, since it should be absolute zero. The diagram of one hybrid ULF channel is shown below.

The remaining resistors are 0.125 or 0.25 watts. In short, any small ones. A 10,000 µF capacitor can be safely reduced to 100 µF, but it is drawn according to the old designation. We set all capacitors for anad supply to 350V. If it’s difficult to get 6.8 μF, set it to at least 1 μF (that’s what I did). We will replace the quiescent current control transistor with KT815 or KT817. This will not affect the sound, it simply corrects the current there. Naturally, we need another copy of the hybrid ULF for the second channel.

To power the transistors, you need a bipolar source of +-20 (35) V with a current of 4A. You can use a regular transformer. Since more power was not required, I installed a 60-watt trans from a VCR with a corresponding reduction in output power. Filtration is simple - a diode bridge and a capacitor. With a quiescent current of 0.5A, a capacity of 10,000 microfarads per channel is sufficient. Capacitors C3, C4, C5 160V each, no less. Or more just in case. R8 is a small tuning resistor - turned with a screwdriver. It sets the quiescent current of the output transistors (in the absence of a signal). You need to set the current from 0.3A - mode AB to 2A - mode A. In the second case, the sound quality is much better, but it will not heat up much. It can be used for power supply with an additional ring and 12-turn windings - it receives 12V from the transformer, and two 20V each - this is the secondary. In this case, the bridge diodes must be high-frequency; simple KD202 will burn out instantly.

We feed the filament with 12 volts by connecting the filaments of both lamps in series. I took the anode voltage of 300V using a small transformer (5 watts) from a Chinese multi-voltage adapter. You can't power anything from that parody except an LED, but in this hybrid it comes in handy. We supply 12V to its 15-volt secondary from an electronic (or conventional) transformer, and remove the voltage from the 220-volt network. The current is certainly not that great, but both 6N2P lamps pull only 5mA across the anode, so they don’t need more.

Discuss the article HYBRID ULF

After the successful (and sometimes sad) experience of purchasing a transistor amp/amplifier, the moment comes when our experienced beginner either does not want to tolerate this device in his room anymore, or in his “musical life” at all.

The next stage is a hybrid amplifier or a tube amplifier. Which one should you choose and why? We will tell you about this today.

Is a hybrid amplifier the same as a transistor amplifier?

In a sense, yes, because essentially a hybrid amplifier is the same transistor amplifier but with one or more tubes - the purpose of which is to insulate the cold sound of transistors. Despite this, if you compare the price of hybrid amplifiers with transistor ones, the price of the former sometimes exceeds it by 25 - 35%.

What's the difference between hybrid and tube amplifiers?

Compared to hybrid amplifiers, tube amplifiers contain the second, third and fourth harmonics in the output signal spectrum. Hybrid ones essentially contain only a small part of them, while transistor ones are generally rich only in odd harmonics of sound.

Pros and cons of tube amplifiers/amps.

• From all the above arguments, you, like many, are convinced that tube amps are better! Despite this, we will further consider their disadvantages, because not everything is so clear in Lamp Albion.
• Tube amplifiers and amps are more expensive! If you analyze all the costs, the complexity of the circuits and the cost of good lamps, they turn out to be many times more expensive than any transistor or hybrid amplifier.
• Cheap tube amps have constant shot noise.
• In order to start playing, you first need to wait for the lamps to warm up.
• The output transformer also introduces significant distortion into the output signal, so the purity of the output signal in some sense depends on its quality.
• Powerful lamps have high heat generation and extremely low signal gain.
• If the signal voltage changes (jumps) then you will get an unstable amplifier.
• Its design requires a complex power supply with a large capacitor capacity and more, which is also a costly affair.

Many people believe that lamp amps are not going through the brightest times today. There is some truth in this, because as you can see, manufacturers of such equipment have been trying to squeeze out the maximum for many decades, as well as improve circuits and solve “unsolvable” problems that we cited above.

In some places they succeed, in others they don’t, but we have the same picture as several years ago - lamp solutions are just as expensive, hybrid amps are cheaper. And yet they are bought, still they are produced.

Pros and cons of hybrid amplifiers/amps.

Hybrid amplifiers are half-breeds. Manufacturers are still trying to solve the problem areas of transistor and tube devices through them. To date, somewhere they have succeeded, somewhere they haven’t, and what do we have?

Pros:

• The cost of hybrid amplifiers is lower than tube amplifiers due to a simpler circuit, cheaper components (another principle), 1-2 lamps are used, etc.
• It combines a vacuum triode voltage amplifier and a transistor current amplifier.
• The output sound is cleaner (almost sterile) than tube sound.

Minuses:

• The combination still remains hybrid, even if there is a lamp in the design.
• You need to use a power supply similar (in complexity to a tube one).

Which amplifier should you choose: tube or hybrid?

We have already written about how to choose the right combo amplifier (here), perhaps there you will find more details on this topic, and as for our topic...

Once upon a time, one person gave me good advice when I was choosing my second combo. This is what he told me:

“Tube, hybrid and transistor amps are like 3 categories of cars. Tube amplifiers are Mercedes, BMW and other German expensive cars. There are small cars (10-30 Watt combos) and family cars (35-80 Watts) as well as sports and business class cars (100 – 150 – 300 Watts). Hybrid combos are Volkswagen and Opel, while transistor ones are Skoda, Fiat and Renault. Just like that!”

The topic of hybrid and tube amplifiers can be discussed endlessly; everything we talked about today is our subjective opinion. It is also important for us to know your opinions and, of course, what choice you once made.

For many years, power amplifiers used only vacuum tubes, but today modern amplifiers use transistors almost entirely. Tube amplifiers operate on the same principles as transistor amplifiers, but the internal design may be significantly different. In general, tube devices operate at high supply voltage and low current. Unlike transistors which operate at low voltage but with high currents. Additionally, tube amplifiers tend to dissipate a large amount of energy as heat and are generally not very efficient.

One of the most striking differences between tube and transistor amplifiers is the presence of an output transformer in a tube amplifier. Due to the high output impedance of the anode circuit, a transformer is usually required to properly transfer power to the loudspeaker. High-quality audio output transformers are not only difficult to make, but they tend to be large, heavy, and expensive. On the other hand, a transistor amplifier does not require an output transformer, and therefore tends to be more efficient. Many people find that the sound from tube amps can be excellent and have a unique character. What is certain is that there are sonic differences between tube and transistor amplifiers. I truly appreciate both worlds, and have had the opportunity to hear amazing systems using both technologies.

Figure 1: Simplified hybrid amplifier circuit

When developing this hybrid amplifier (Fig. 1), there was a desire to combine the best of tube and transistor technologies. The tubes offer full and faithful sound reproduction, with rich detail, brilliant clarity, and precision. They also reproduce deep better. The hybrid amplifier retains the signature of a tube amplifier, complementing it with a low-distortion solid-state output stage.

Figure 2: Hybrid Amplifier Circuit

The hybrid amplifier circuit (Figure 2) is very simple, but includes interesting ideas such as Erno Borbely's low-voltage tubes and Reinhard Hoffmann's bipolar-supplied output stage. This hybrid is capable of delivering about 30W into an 8Ω load or 15W into a 4Ω load. You can easily increase the power by adding more output stages in parallel. This will increase the damping coefficient and reduce the dependence on load resistance. An amplifier with two MOSFET output transistors per channel will provide more than 50 +50 W of pure Class A usable power into loads up to 6-8Ω. However, in such conditions the amplifier will dissipate more than 300 W, so you must use suitable heatsinks (at least 0.2 °C/W thermal resistance) in a suitable well-ventilated case.

Figure 3. Power supply circuit

The input stage is based on a double triode 6DJ8/ECC88 (analogous to 6N23P, you can also try 6N6P) and serves as a differential amplifier. I chose the 6DJ8 because of its linearity and good performance at 35-40V anode voltage. For 6DJ8/6922/ECC88/E88CC, MU is constant within 20% of 0.4mA, up to at least 6mA, and this trend continues up to 15mA. I chose an operating current of 3-5 mA for each half of the lamp, and a voltage of 35-40V to keep dissipation well below the nominal value of 1.8 W. The cathode receives current from a constant current source at Q3, while Q1 and Q2 represent a resistive load or current mirror. The active anode/cathode load of both triodes is almost equal, which reduces the second harmonic, promotes linearity and increases the slew rate of the output voltage. With potentiometer P3, you can adjust the bias current from 1 to about 7mA, P1 controls the output bias voltage, which needs to be adjusted close to 0.

OUTPUT CASCADE

Output stage consisting of one or more single-ended, Class A P-channel MOSFETs, similar in configuration to Nelson Pass's Zen amplifier (for more details, see http://www.passlabs.com/

zenamp.htm). It is loaded onto current source Q4, which is set to 3A quiescent current using the specified values ​​of R14. You can experiment with different values ​​of the quiescent current by changing the resistance R14 using the formula Id = (Vz-Vgs)/R14 =0.9/R14.

It should be taken into account that the quiescent current should be 50% greater than the operating current. The overall gain of the amplifier is around 20 and this depends on the value of R8 and R9. Thus, 1V of the input signal will drive the amplifier to full power, so that the output level of a typical CD player is sufficient to drive the amplifier. You can calculate the required gain using the following formula: Av = 1 + (R9/R8). This amplifier's tested PCB is available in Ivex Win-Board format. To receive a free copy of the file, please send an email [email protected]. In this PCB, lamps and transistors are installed on the solder side.

Each channel of the hybrid amplifier requires ±35V DC/6A power supply for the main amplifier, and an adjustable 6.3V DC/0.5A for powering the filament lamps. The rectifiers of the amplifier's main power supply must withstand 20A.

RESULTS

This hybrid amplifier has a flat frequency response across the entire audio frequency range. Even with low-sensitivity speakers, you can appreciate its clarity and detail, especially when the CD player is directly connected to it. With a single output, the amplifier delivers up to 20W with less than 1% THD, but it will perform better with two in parallel. I've had the opportunity to evaluate some of the best Class A amplifiers on the market, and I believe this hybrid delivers the same flavor and fresh feeling when listening to high-end music.

1. “Low-Voltage Tube/MOSFET Line Amp,” GA 1/98.

2. “The Zen Cousins,” AE 4/98.

audioXpress 5/01

www.audioXpress.com

Corrected amplifier circuit.

HYBRID AMPLIFIER

Many have heard and probably made tube ULFs, some say their sound is the best, while others will say that transistors are in no way inferior to them and have much better parameters.

I did both and am ready to make the final conclusion: a cool sound amplifier has both tubes and transistors, to each his own:

The lamps work great at the entrance, and they look so stylish!and field-effect transistors at the output - and there is no need for huge output transformers.

Here are the circuits that I tested during the experiments and they all worked great!

And here is an example of the practical implementation of one of the hybrid ULFs according to the scheme given below:

For this amplifier, I used a circuit based on N-channel field-effect transistors from a radio hobby magazine. The lower part of the housing, measuring 15x20 cm, made of a centimeter aluminum sheet, is used as a common radiator for the transistors. The latter are powered through a conventional diode bridge and two 10,000 uF capacitors. No AC background can be heard. 200 V for the anode is taken using a 12-volt small 10-watt trans, connected in reverse to the secondary of the main transformer. To indicate the position of the volume level, we place a blue LED through a piece of plexiglass. For beauty, the lamps from below are illuminated with red LEDs. The difference in hearing between 6N6P and 6N2P is practically unnoticeable. The setup consists of setting the required quiescent current (within 0.3 - 1 A). And lastly: don’t skimp on the radiator! Class "A" will require very decent cooling. For example, a radiator for a 100-watt ULF class “A” Mac weighs 8 kg! An electronic transformer can be used as a power source for such an amplifier, as in

Hybrid amplifiers, or tube amplifiers without an output transformer

Many beginning amateur audiophiles are deterred from building a good tube amplifier by the complexity of making an output transformer. You need to find somewhere a good powerful magnetic circuit (core) from OSM or TS-180...250, kilometers of wire. And seasoned audiophiles say that the already multi-turn primary winding, which you are tormented to wind, must also be sectioned, separating it with pieces of the secondary. Which way should I put it all in, how can I avoid getting confused when connecting?..

Meanwhile, there is an approach, perhaps very controversial, which consists of replacing the output transformer (and the output lamp, for that matter) with... a transistor. Yes, yes, that same hated “stone” silicon, from which people are so eager to move away to a transparent vacuum.

Using a transistor as a current amplifier allows you to significantly simplify the output part of the amplifier, but is it worth it? After all, here we lose a significant amount of tube power - an entire output tube and transformer. How much will this take away from the sound and how much will silicon add?

Until you collect it, you won’t know. Perhaps someone will like this compromise between lamp-likeness and simplicity. Therefore, here we present two schemes that have been repeated by a large number of people. Some people immediately liked the sound of such amplifiers, while others were puzzled and forced to listen for a long time.

First scheme of an 8W hybrid amplifier authored by Vladislav Kreimer was published in one of the issues of the Radio Amateur magazine. According to the author, the overall sound character is formed by the 6N23P triode, and the emitter follower on the KT825 composite transistor only amplifies the current, “matching” the high resistance of the lamp with the low resistance of the acoustics. The output stage operates in hard "A" mode with a quiescent current of 1.25 amperes, which is dissipated by resistor R3 - 27 watts of heat, however. The voltage drop across resistor R2 provides a small amount of feedback. The author notes the excellent sound qualities of such a hybrid. SOI - less than 1%.

Amplifier sensitivity - 0.6V. The linear frequency response in the lower part is determined by the capacitance of capacitor C1; with the nominal value indicated on the diagram, it is about 5 Hz.

Resistor R3 is a wire-wound resistor with a power of 20W. As already noted, it gets very hot. R2 - two-watt, can be made up of two parallel-connected one-watt ones. By changing its resistance within 0.2-1.2 Ohms, you can change the amount of feedback. With less resistance, sensitivity will be greater, and the sound will be “warmer” and “fat,” as the author described it. As you increase the sensitivity, the sensitivity will decrease and the sound will become more transparent. The lamp must be selected so that the transistor emitter has a voltage of 10-12.5 V. About the transistor itself: here you can use KT825 with any letter index. The author notes that old transistors produced during the USSR “sound” better. Perhaps imported analogues will be even better. You can also use two ordinary transistors instead of a composite one; it is especially tempting to do this with germanium. Requires the use of a 1000 sq. cm radiator. The transistor and R3 will total about 30W.

The amplifier's power supply must be of high quality, without ripple. The diagram shows one of the options. The choke must have at least 300 turns with a diameter of 0.3-0.5 mm on the magnetic core from a 10-20 W transformer. Winding resistance - 1...2 Ohm. The power supply should provide a voltage of about 22 volts at the top terminal of R3. Don't forget about the lamp's filament power supply, it's not shown in the diagram.

If the amplifier will self-excite at HF, anti-ringing chokes of 15 turns on small ferrite rings can be added to the lamp grids.

Those who like to experiment with the “fatness” of the sound can bypass R2 with a capacitor with a capacity of 4700 μF, which will eliminate feedback. This will significantly increase the amplifier's sensitivity and slightly reduce power.

The resistance of resistor R3 must be equal to the load resistance.

Second scheme by V. Grishin with SOI 0.3% at rated power (16-20W). Unlike the previous circuit, here the lamp operates in linear mode. The bipolar transistor is replaced by a field-effect transistor, the bias of which is formed by the chain R5, R5, R6, D1, C2 to set the required quiescent current (3A) in class “A”. The high capacitance of C2 ensures a soft transition of the transistor to operating mode when turned on.

The transistor mode and ratings in the diagram are calculated for a load with a resistance of 4 Ohms. For 8 Ohms, the supply voltage of the output stage should be increased to 20 V, the quiescent current should be set to 2.1A, and the inductance of the inductor should be doubled.

This unusual designation of the throttle is no coincidence. In the author's version, its magnetic core is combined from ferrite and iron. The winding resistance is very small, so the transistor current is “constantly” shorted to ground. The variable component is supplied to the acoustics. A description of how to make a throttle can be found in Radio No. 3, 2013.

As in the first scheme, it is very important to ensure good nutrition. The capacitances in the filters of the output stage power supply can reach up to 47000 μF (to power two channels). In the anode supply, the author used a kenotron rectifier, which gives a smooth increase in voltage. When using a diode rectifier, the transistor gate should be protected with a zener diode.

The lamp can be replaced with 6S2P, 6N1P, recalculating the values ​​of resistors R2 and R3 for the desired linear section of the characteristic. The zener diode can be replaced with KS175Zh, KS210Zh. The field-effect transistor can be replaced with a similar one in parameters (for example, IRF830, IRFZ24N), but the author considers it irreplaceable in terms of sound quality. Transformer for powering the output stage - with a threefold power reserve, 150...250 W. With 4-ohm acoustics, the voltage of the secondary winding of this transformer should be 12 V, for 8-ohm - 18 V. Anode transformer - no more than 15 W. You can try to select a step-down transformer by connecting it “in reverse” to the secondary winding of the output stage power transformer.

The choke can be made on an armored magnetic circuit ShLM 20x40. For 4 Ohm speakers you should use a wire with a diameter of 2 mm, for 8 Ohms - 1.78 mm. Those who want to get rid of winding products can recommend ideas from the so-called. followers: scheme. There is also a diagram with a current generator in Radio No. 12, 2012.

This hybrid amplifier is configured by setting the required quiescent current, monitoring it during a 3-4 hour warm-up period.

The input voltage should be no more than 2 volts. The power of the acoustics used should be doubled. It is important that two-way acoustics are preferable for this amplifier, because If there is a mid-frequency filter in the acoustics, the advantage of directly connecting the load to the output stage is lost.