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My audio system.....
My audio.

For outside listening I use the kit:
Xduoo X3II with Rockbox installed (Haas Surround is sensational for long headphones listening)
Koss Porta-Pro headphones (they have no different in their price class, open design, the best review was: on these headphones I heard the bass player for the first time ...).
In this player I use compressed files with the amazing OPUS codec with an average variable bitrate of 224kbit / s (this codec has a low latency and minimized pre-echo effect, it replaced the tuned OGG Vorbis for me)

At home:
Currently Moodeuadio 6.5.2. on Raspberry Pi with DAC ES9038Q2M

Two amplifiers:
The first is an experimental own tube construction based on the Super Triode Connected topology built on the EF80 and ECL86 electron tubes in each channel plus the EM83 double magic eye (only produced in DDR). The STC topology is used to obtain triode characteristics from a pentode, a meter or even an integrated audio amplifier, which are characterized by high linearity at independence with load impedance. Higher powers are obtained than in the case of pentodes or tetrodes in a triode connection. Because the triodes have a low impedance as a signal source, it is also easy to get a wide bandwidth using cheap speaker transformers. 

The second amplifier is a simple Chinese board with the TPA3116D2 chip - a digital class-D amplifier. Waiting for a slightly better board (at the input of the amplifier, e.g. polyester instead of ceramic with too low capacitances or cheap electrolityc capacitors, better coils in the output filters....).
Despite the very low price and the fact that it is a D-class, it sounds sensational, even on cheap plates from China offering a sound not worse than many expensive HiFi sprats as far as modern and vintage. The variant with a lower maximum power of 2 * 30W, i.e. TPA3118D2, can handle without a heat sink when running at full power. It is solidly secured - instead of a loudspeaker, a screwdriver will survive Wink

TPA3116D2 datasheet:

There is a second series with better parameters, higher powers, and unfortunately a higher price. TPA3241, TPA3245, TPA3250, TPA3251 and TPA3255. Double the clock speed offers a lower level of distortions in the upper part of the acoustic band.
TPA3251 datasheet:

In these systems it is worth using additional external negative feedback, which improves the load and more importantly, especially with the TPA32xx series allows to eliminate accidental shutdowns during loud playing triggered by short momentary moments at the maximum peak level
It is described here:

TPA3116D2 and TPA3118D2 play in great detail. Some say that in comparison to the TPA32xx series they have a minimally withdrawn midrange but this is a subjective rating. At audio freaks and vintage audio events, the chineese kit on the TPA3255 was able to remove the heigh-end tube amplifier for several thousand USD from the pedestal.

I plan to make a hybrid amplifier, quite unusual because instead of the traditional transistor unity-gain buffer in class-A or class-AB after the tube stage where all voltage gain is to be TPAz 32xx series chip with external negative feedback. TPA with external feedback has a gain of about 4, so it does not differ from typical hybrid amplifiers. Maybe I will add a sensational tone control used in the Revox B251 - a bit similar to a two-channel parametric equalizer (35Hz and Q = 1 +/- 12dB, 13kHz and Q = 0.6 +/- 6dB). Electron tuber ars EF80 polish production or EF184 made by RFT from DDR due to a nice mesh screen, ECC81 maybe ECC82 (both ECC are made by RFT) and magic mesh EM83 (also RFT).

The visible speakers are for a monitor used as a television connected to the Dreambox DM900UHD

My little brick in this device - a tube buffer similar to the diamond topology (double cross coupled balanced path).
Tubey goodness :-)
Magic eye? I haven’t seen one of those since my dad’s 1951 Magnavox radio console died Smile  I have fond memories of all things based on vacuum tubes, some I designed and built and some I bought, but I won’t go back.

These new-fangled Class D amps still seem like magic to me. The components which make them possible at a reasonable price didn’t become available until long after I was designing my own amps. Like every other class of amplification it has its minuses as well as pluses but when done well the amps are a marvel.

Kudos for your builds.

Class D amplifiers from these series are worth interest. Chinese modules made of the cheapest elements sound really good, but the carefully applied these chips will repay with very good sound. Of course, the optimization of the layout, the correct layout of the PCB is no longer a trivial matter, here you need to feel fast clocked pulse systems. Engineers from Texas Instruments carefully approached the topic. These are no longer clumsy buzzers as at the very beginning of the production of these systems. There was a really significant qualitative and engineering leap as well. The second series (TPA32xx) is clocked at around 2MHz, the first around 1MHz. Quite complex timing schemes were used to smooth out the output waveform to even limit the output filter even to the ferrite "pearl" on the wire plus the Zobel circuits.
These circuits surprise with a very detailed sound, they do not forgive any signal at the input mercilessly exposing the low quality of the signal source. The price is .... the module with TPA3116D2 is 10USD. Only switched mode power supply, e.g. industrial mounted on a DIN35 rail, and you can surprise Hi-Fi fans.
Magic eye EM83 in action:
My little brick in this device - a tube buffer similar to the diamond topology (double cross coupled balanced path).
EM83 and EF0 in close-up
My little brick in this device - a tube buffer similar to the diamond topology (double cross coupled balanced path).

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