For many years, only vacuum tubes were used in power amplifiers, but today modern amplifiers Transistors are used almost entirely. Tube amplifiers operate on the same principles as transistor amplifiers, but the internal design can be significantly different. In general, lamp devices operate at high voltage power supply 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– the presence of an output transformer in the 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 believe 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. Hybrid amplifier preserves the signature of a tube amplifier, complementing it low level distortion of the semiconductor 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 job at 35-40V voltage at the anode. 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. Current is supplied to the cathode from the source DC to Q3, while Q1 and Q2 represent the 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. So 1V of the input signal will output the amplifier to full power, so 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 amplifiers are different high quality sound and ease of execution. We offer you enough simple diagram manufacturing that uses simple components. Using such a hybrid amplifier will allow you to get enhanced, clear and detailed sound at the output.

Zarathustra amplifier circuit

More detailed and well-presented information can be found from the author of this amplifier on the forum:

Hybrid amplifier Zarathustra

One of the features of hybrid amplifiers is output current limitations. At the same time, the amplifiers are characterized by stable operation and minimal heating. No need to perform additional systems cooling. The output current is equal to the output current of the cascade, and can reach 15A.

It is possible to operate in supply voltage mode. Improved cascade symmetry at high frequencies allows you to significantly improve sound quality when operating at maximum volume and when playing high frequencies. Minimal distortion has a positive effect on sound quality.

To manufacture a hybrid amplifier, an SRPP output stage was used on bipolar transistors, two 6E5P lamps are installed at the input. The use of a tetrode cascade ensures voltage stability and excellent output voltage performance. The output stage uses a virtual average using capacitors instead of bipolar power supply.

This eliminates the appearance of DC load in the circuit and avoids overcharging the power supply. This eliminates impulse distortion that can occur at peak power levels. The output signal is connected to the midpoint, and the capacitors used are eliminated from the audio circuit. This eliminates the influence of capacitors on sound quality.

Capacitors are connected to the windings, which makes it possible to suppress the electrical background in the incandescent circuits. This improves the sound quality. The use of capacitors makes it possible to make the filament voltage on the output filaments completely symmetrical. At the same time, the implemented amplifier is simple and can be easily implemented by every radio amateur.

We also note the affordable cost of the components used. If in the manufacture of other amplifier circuits it is necessary to use high-quality foreign capacitors, then in this case it is possible to use inexpensive domestically produced capacitors. The influence of their quality on the generated sound is minimal, which allows us to slightly reduce the cost of manufacturing the amplifier without losing sound quality.

DIY hybrid ULF

At numerous requests from radio amateurs, I present an improved and more complete hybrid ULF circuit with detailed description , parts list and power supply diagram. The lamp at the input of the hybrid ULF 6N6P circuit was replaced with 6N2P. You can also install the 6N23P, which is more common in old lamps, in this unit. Field effect transistors interchangeable 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, zero voltage is inserted on the speaker in the 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 10000uF capacitor can be safely reduce 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). The quiescent current control transistor will be replaced 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+-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 - 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 are 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. You can also use an electronic transformer for power supply with an additional ring and 12-turn windings - it receives 12V from the transformer, and two 20V each are 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 travesty except an LED, but in this hybrid power supply 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.

So. As I wrote earlier, I have a desire to make an amplifier for a bass guitar. I went through several options and made a decision. I refused the option of a purely tube amplifier due to the large size and high cost of the output transformer. It was decided to collect hybrid amplifier.

Here is an example block diagram. Everything will be collected in one small building.

" " on Yandex.Photos

It's a mixture tube stage pre-amplifier (in my case) and transistor or microcircuit final amplifier
The tube pre-amp is made according to the classical design, one tube (double triode) for 2 stages. 2 volume knobs (gain and master) with a tone block between them.
To be continued.

" " on Yandex.Photos


" " on Yandex.Photos

Having reviewed the principles a little, let's try to make a pre-amplifier using this circuit as a basis.

Tube pre amplifier

We are developing a board, since it is really easier to etch it than to invent something with a canopy.

Here is a visual diagram of the pre-amplifier; we deviated a little from the original plan. So I decided to try this scheme preamplifiers. Actually, the pre-amplifier ends (if you look at the diagram) where from pin 8 there is a contact for 2 capacitors of 6.8 mKF each. In this article we will only consider the property itself tube pre amplifier.

The board was developed in the layout 5 program, so you can download the file for it.

The file contains a circuit template and the program itself, in the layout 5 program in macros in the user folder there are 2 templates for lamps, the macros were made by my friend but they are suitable for ordinary finger lamps and the second for an octal socket.

Let's go back to our pre-amp. I suggest using 6n2p (6n2p-ev) lamps, with a dividing grid installed on the 9th leg. Which, logically, can hit the ground and probably! I emphasize that there will probably be fewer interferences. But in reality I haven’t checked it yet.

Combine the beloved timbre color, natural sound and overload resistance of tube amplifiers with the reliability, durability and fidelity of RF transistor designs. The idea is far from new. Today we will talk about modern hybrid Hi-Fi amplifiers.

At the dawn of the formation of the AuDDiolab section, I talked about this interesting class of devices. It's time to give it the attention it deserves. What exactly is the struggle for when creating a hybrid amplifier? After all, a “purebred” class A tube unit is fully capable of playing music more than well. Yes, that's true.

Richter Sorcerer - this is what the dream of many audiophiles looks like

But even class A has an Achilles heel. The same fatal flaw that limits its widespread distribution. And this is an exponential increase in the complexity of the design and cost of such an amplifier when trying to increase its power to any serious indicators. The point here is that without simply sky-high requirements for the quality of the element base and installation, and even for the power supply of the device, it is simply impossible to achieve a nonlinear distortion coefficient (THD) that fits within the Hi-Fi framework. Therefore, the destiny of class A tube single-ended circuits remains low-power, but produces amazing high quality sound solutions.

Incredibly, a THD of 1.2% is considered good for high-power tube amplifiers.

This is where the need arises for an alternative solution that can provide comparable sound levels and high power levels at the same time. And at the same time be economically feasible. Thus began the need for powerful hybrid amplifiers.

Hybrid monster Magnat RV 3. 2 x 200 Watt and THD 1%. Indicators unattainable for a simple “lamp”

But the market does not live by power alone! There is also another extreme - headphone amplifiers. Where, in addition to the power sufficient to drive high-impedance headphones, the requirements for the SOI level reach a completely different level. Hi-Fi headphones by default are a much more precise instrument than acoustics. And they will definitely “voice out” all the sins behind the amplifier. Directly into the listener's ear canals. Therefore, it would be great to curb the “tough temper” of the lamps, reducing distortion to a minimum, and make the design as cheap as possible. This is how hybrid headphone amplifiers appeared. Often simple, relatively cheap transformerless solutions. But many models are really capable of producing sound at such a level that their “purebred” tube counterparts have to blush profusely.

Apex Peak/Volcano will make your headphones sing

Of course, the list of varieties of “hybrids” does not end there. Any modern “tube” microsystem for players and smartphones is in practice equipped with a hybrid amplifier. Samsung, Roth, Fatman. The list goes on and on. Just remember that Kickstarter.

One thing is absolutely clear - in the foreseeable future, “classic” lamp solutions will only have a place in the ultimate Hi-End segment. And the near-budget and mid-price pieces of the lamp pie will entirely go to hybrid designs.

Stereo Hybrid Tube Amp. $149. No comments

So what is their secret? The answer is simple - in transistor control of lamp operating modes. In fact, a small number of transistor elements with minimal wiring can replace long, expensive and at the same time increasing the SOI level “garlands” of capacitors, resistors and other elements designed to keep the tube standards within the limits of decency using old-fashioned methods. On the one hand, we get an increase in sound reliability, and on the other hand, simplification (and therefore reduction in cost) of the design.

Simplicity is the key to great sound

Yes, many venerable audiophile “gurus” still do not take such decisions seriously because they supposedly contain feedback, which has a detrimental effect on sound. In practice, transistor elements in such circuits do not act as signal-amplifying elements. Therefore, such concerns should not be taken seriously.

That's all for today. I strongly recommend that all readers of the AuDDiolab column become familiar with the sound of “hybrids” if possible. This may well be exactly what many of you were looking for. And also write in the comments if you would be interested in a series of materials about building a hybrid amplifier on your own. If I understand that a “critical mass” of responses has been reached, such a project will not take long to come. See you soon! :)

If you find an error, please highlight a piece of text and click Ctrl+Enter.