Bakoon Products AMP-5521 MK4 Power Amplifier

In addition to the SATRI-IC, the AMP-5521 MK4 uses a bipolar transistor instead of a J-FET that is no longer available, a temperature-compensated constant current bias circuit, a bias separation circuit for the output stage, a bias turbo circuit that reduces the bias setting time from 4 minutes to 30 seconds or less, and most of the components are surface mount components.
The number of parts has exceeded 350.
The output is 35W + 35W in stereo and 100W in mono BTL specification.
The most significant feature is that the components that make up the amplifier are completely surface-mount components that do not have lead wires, and we have been able to achieve an amplifier that is about 50 times more accurate than an amplifier that uses conventional lead wire components. If there is a lead wire, the sound will be colored due to its material and nature. By eliminating the lead wires, we eliminated their coloring, and reviewed the design method of the printed circuit board on which the components are placed when using surface-mount components. We have also developed a number of new circuits that can improve the accuracy of printed patterns that are colored in the same way as lead wires by reducing the length of the wiring to less than 1/4 and using surface-mount components. Until now, it took about 4 minutes for the bias current to stabilize, but with the AMP-5521, we have succeeded in reducing it to less than 10 seconds. In combination with the SATRI speaker, it is possible to play realistically as if there is a player in front of you.


The maximum output is 35W to reduce the heat generated by the SATRI-IC.
The feature of this amplifier is that the accuracy of the circuit is very high. The drift is stable in the 10 micro V range.
Changing the constant current source used for the bias circuit from a CRD to a temperature-compensated constant current circuit is working well.
In addition, since the components on the PCB are surface-mount components, the inductance and stray capacitance are reduced, and the elements that affect the music signal are extremely small. Thanks to this, there is no incidental sound in the music. Frighteningly realistic sounds.

BTL mode is great

The maximum power output in normal mode is 35W, but in BTL mode it is 97W. In addition, the distortion rate is one order of magnitude lower than in normal mode. For non-feedback SATRI amplifiers whose distortion cannot be reduced by negative feedback, BTL is an option to improve accuracy. The powerful sound of BTL mode is fascinating.

*Switching between stereo and BTL is set at the time of manufacturing of the amplifier board, so the specifications cannot be changed by the customer.

The feature of the SATRI amplifier is that it does not apply negative feedback, so it has excellent transient characteristics and low distortion of the time axis.
This photo shows the characteristics of the 10kHz square wave of AMP-5521.
The top is the input and the bottom is the output, and the load resistance is 8 Ω.
In this way, there is no waveform disturbance at all.

There is no amplifier that reproduces the information of the recording as much as Moro

When you listen to a recording that pays attention to spatial expression, you can clearly see the sense of depth. One of the features of the SATRI amplifier is that noise is reduced when the VR is lowered, so the S/N when the VR is lowered is improved by 27db. Another feature is that there is little change in bandwidth depending on the output. Pinpoint localization feels good. Instead of the two J-FETs that are no longer available, it may be a feature of a buffer circuit consisting of 12 bipolar transistors and a temperature-compensated constant-current circuit. The accuracy of this circuit is far superior.

The AMP-5521 is also expandable, allowing users to use more speakers. An uninterrupted continuously variable resistor volume is standard, and an upgraded version such as a 23-stage non-inductive winding resistance attenuator version can be selected as an option. It is also possible to connect directly from DACs and other source devices, but of course there is a difference in sound quality compared to pair-matching with the company's preamps. The AMP-5521, which is a linear system using an R-core transformer, uses two outputs per channel to obtain an output of 35 W. When the gain is set at 9 o'clock, the volume of a typical solid-state amplifier is about 100-150 watts. The monoamp version has a 97W output. The output ratio also expands rapidly, which is not felt by ordinary linear amplification, and the output does not consume a lot of volume. Another indispensable feature of the Bakun amplifier is that it exhibits its unique charm when the entire system is configured. Compared to the previous version of the product, the sound is more agile, and the drive is incomparable. The phase characteristics are also very good, and the overall freshness and stimulation make the strokes easy and natural, making them "realistic". Even with fast beats and large orchestras, you can hear a stable and pure sound quality.
* Monthly Audio (http://www.audioht.co.kr)
A world of reproduced sound as transparent as a fountain. The moment I heard the 5521, I thought, "After all, it looks like a satori circuit, and it looks like a bakun amp." The sound was as clear and transparent as a spring. There is no one-piece distortion or coloring, linear amplification is performed, and there is no time delay. The key to these pure regeneration is the fact that SATRI-IC and the SATRI-IC limited the output so that the SATRI circuit can maintain optimal conditions, and the unwritten rule of Bakun amplification is "non-negative feedback".
The feature of the 5521 is "pinpoint localization". The sound from both speakers overflows instantaneously, and when they gather in the center, the delicate sound image is pinpointedly connected, and the appearance is spectacular. From the beginning, the sound seems to be dancing on the 5521 top panel placed in the center of both speakers. After all, it is said that the sense of localization is good, but what really happened in 5521? The supply of a fixed bias current is an important factor that allows Bakun amplifiers to achieve ultra-precise reproduction. In a general bias circuit, the bias current is controlled so that the temperature of the output transistor is kept constant, so that when the power supply voltage rises, the bias current decreases and the bias current increases when the temperature of the output transistor decreases. In this way, the bias current is always variable, so the overall operation can only become unstable. In comparison, the Bakun amplifier supplies a fixed bias current at a level of 1/100,000 of the fluctuation rate. This ultimately made it possible to accurately amplify and replay, and it seems to have played a decisive role in pinpoint imaging.
35W is an unbelievable amount of driving power. While monitoring the 5521, I was reminded that the Bakun amp is strangely similar to a tube amp. 7511A If this output of 15W is like driving two KT150 bullets with push-pull, the 5521 is like driving 300B and two direct heat triodes in a parallel single. The one that pushes through the speaker is rather 7511, and the one that strokes the speaker with room is 5521. In the 7511, you can feel the unbridled speaker driving ability unique to push-pull vacuum tubes, and the relaxed output and delicate expressiveness unique to the direct-heating triode composed of parallel singles in the 5521. The most surprising thing about the 5521 is its bandwidth balance and signal-to-noise ratio (SNR), which is still so good that the 35W output is so good that it seems to mean nothing, and when the volume is lowered, it shines brighter.
Bill Evans' album - "My Foolish Heart" - Knowing that the coughing audience is a woman. Obviously, the sound particles became larger and harder. The cymbal touch of the drums was powerful, and the image expanded. The sense of rhythm also persisted. The sense of space in a jazz club can be felt more easily. Seeing that there is no significant change in SNR when the volume is turned up, it seems that the quietness of the current system is very high. It captures all the whispers of the audience. In "Waltz For Debby (Take 2)," the sound coming out of the side speakers seems to gather holographically in the center. The difference in height between the bass and the piano is not a prank. The friction sound and playing technique touching the bass strings can be heard vividly. The forward and backward feel of each instrument sound is amazing. The expression "depth" would be appropriate. Bill Evans' piano is clear and sharp.
Brian Blomberg's "Come Together" (Wood Album) - The texture and perception of the 300-year-old wood base is astounding. That's when the powerful bass overflows. It's a life-size base. To play a Beatles melody on four bass strings, you need to count your fingers. This momentum and energy is still felt. Tapping, clipping, fingering... It's like the clapping of gospel hands in church. The expression and texture of the sound are captured one by one, and it is also in the center of the stage, completely pinpointed, life-size...
Vladimir Ashkenazy and Ada Mainnik Shoshakov Beach Viola Sonata (DG) - Overwhelmed by energy and space. I began to take a shower of sound in earnest. The front wall finally began to disappear, and so did the speakers. The instruments and tones became more three-dimensional. As a whole, the viola is on top and the piano is on the bottom. However, they seem to play separately and are intricately woven together. The texture of the weave is exquisite. The 7 minutes and 30 seconds viola's treble part is quite a sense of energy. The sense of color shines. Transfer, might, high profile, majesty, white, savage, raw.... Words burst out of many images. From this point on, the viola player catches his breath. This means that the player needs so much energy. At 12:28 p.m., Ashkenazi even takes his foot off the pedal.
The complete reduction of the bias current from the signal current, as well as the use of surface-mount components to eliminate the various resistance values caused by the leads, led to the pure and precise reproduction of the music signal. Right. The Bakun amp is a world of infinitely transparent reproduction without any distortion or coloring, and without a single time delay. It's also a world of painfully fast, cool, ultra-fast, ultra-precise amplification.
* Monthly Audio (http://www.audioht.co.kr)