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Class A amplifier, full Dual Mono

Maciek_C 
Elegant audio amplifier with aluminum front panel and central knob.

Hello,
By way of introduction:
The amplifier is visually very similar to the Gamut design. It's a coincidence. Wanting to build an amplifier, I was looking for a damaged enclosure donor. The housing of the Koda AV-600X receiver caught my eye, but the knob was asymmetrically placed. I didn't find anything interesting, I started to draw something similar to this pattern myself, but with a symmetrically placed knob. There were many iterations until an almost final form emerged, very similar to the present one. Then I accidentally came across the Gamut DI 150 amplifier and noticed that it looks almost identical to the amplifier in my concept. I began to hesitate whether to change my idea to something else, because it is someone's technical idea, someone's industrial design. I started to study the regulations in this direction and it turned out that the law allows the use of an industrial design for personal use, so a stone from my heart and I started to act.

The inspiration for the new amplifier was the occasional purchase of the Vincent SV-121 amplifier and comparing its sound with my existing amplifier, described in this topic:

https://www.elektroda.pl/rtvforum/topic3780837.html

It turned out that acoustically Vincent is several classes above. Unfortunately, Vincent does not have a signal output, BT and, most importantly, a phono preamplifier.

This is where the search for an interesting scheme, design and construction began.
The amplifier was built for seven months.

Its design consists of separate plates of individual modules, so that you can easily upgrade, upgrade, etc.
Everything was packed into the 1NPD02300B housing purchased from modushop.

The input selector board is integrated with the phono preamplifier. In the phono preamplifier I used a circuit known from more expensive Pioneer and Denon designs with FET transistors at the input. The sound from this circuit is clearly better than the circuits I've made before (including the Emerald circuit, praised on the web).
The board also has a signal output buffer for driving the previously presented Equalizer on IN-9 tubes.
Scheme and selector board (for one channel) below:
Schematic of an amplifier circuit board with a phono preamp.
Amplifier PCB design.

The preamplifier is a slightly modified circuit taken from the following source:
https://www.electroschematics.com/class-a-preamplifier/

Diagram of one channel and board below.
Electronic schematic of a single amplifier channel.
PCB layout of an amplifier showing traces and components.

The power amplifiers are based on the Pioneer A-09 scheme, but they have been redesigned to use currently available and cheap transistors. The board has been designed to be screwed together with the transistors on the heat sink.
Below is the schematic and PCB for one channel.
Schematic and PCB layout of an audio amplifier for one channel.
Audio amplifier PCB design with integrated circuit.

The amplifier additionally has a Bluetooth receiver and a DAC also working in Dual Mono. The DAC board has been designed in such a way that it can be screwed onto the PA214 Bluetooth receiver (bought on a well-known Asian website).
The signal in the SPDIF format is fed from Bluetooth to the DAC board. There, through the 4052 multiplexer, one of the three SPDIF (Coaxial / Optical / Bt) sources is selected, whichthen, through optocouplers, it is fed to SPDIF decoders independent for each channel, and from there to converters.
The "primary" side of the DAC (Bluetooth receiver, selector, Toslink receiver) is powered from the power supply of the digital part, the "secondary" side (SPDIF decoders, converters) - from the output of the audio power supply switched on with a relay.
The DAC is based on the Cirrus Logic CS4334 converters, because they are one of the few that can still be purchased on the market, and they are also easy to use.
Below is the schematic and PCB
Amplifier schematic with digital processor and power supply circuits.
PCB design for an amplifier with a Toslink module.

The amplifier's control section is not too complicated and was designed parallel to the front panel to handle the backlight, buttons, have a hole for the potentiometer axis, etc. It is based on the Atmega16 microcontroller.

A 10x5mm model bearing with a flange was fitted into the hole for the potentiometer axis, through which the potentiometer axis with a diameter of 5 mm passes. The bearing is the fulcrum of the axle.

Effects below.
Control board:
Schematic diagram of an amplifier with various modules and connections.
Printed circuit board design for an amplifier with electronic components.

Aluminum front panel of the case:
Sketch of the front and rear panel of a DIY amplifier.

Panel with illuminated inscriptions under the glass (with a cutout for the IR receiver and the axis:
Amplifier panel design with symmetrically placed knob.

The control section is powered from a stand-by power supply connected to the power transformer switching system and soft-start.
It is presented below:
Power supply schematic for the digital section and transformers in the amplifier.
Printed circuit board schematic with electronic components, traces, and connectors.

The audio part is powered by the power supply system with independent circuits of power transistors, power stage voltage amplifier and preamplifier. In addition, through the relay, the DAC and BT are powered. The relay turns on only when selecting digital sources, so when playing audio from other sources on the DAC and BT, no voltage is applied.
The audio power supply is shown below and is one of the two channels. The tile of the second channel is a symmetrical reflection.
Circuit diagram of power supply for preamplifier and Bluetooth module.
View of a printed circuit board design with red and blue traces.

And finally, the speaker protection board. This protection is supervised by the microcontroller that controls the amplifier and is screwed directly to the loudspeaker terminals.
Electrical schematic of an amplifier circuit.
Audio amplifier PCB design.

In general, the launch did not cause any major problems. The analog part started right away. only adjustment of the offset, transistor currents was required and it was possible to twist. The mechanical part turned out to be a big problem due to the use of a slightly too small housing. On paper, everything was nice to fold, but in reality it was not so colorful. The housing also required a few modifications, especially the way the radiators were screwed to the frame.

In terms of electronics, I had the biggest difficulties with starting the DAC. The reason was my negligence, because I downplayed the requirement to delay the Reset pin relative to the power supply in the DIR9001 chip. It took me several hours to figure out what the source of the problem is. Using an inertial system on the Reset pin solved the problem.

Below are some photos of the construction.
Amplifier printed circuit board on a black base. Printed circuit board with electronic components on an amplifier heatsink. Interior of an audio amplifier with visible electronic components. Interior of DIY amplifier showing circuit boards and electronic components Interior of a custom audio amplifier with visible transformers and electronic components. Interior of an open audio amplifier with visible electronic components and heatsinks. Interior of an amplifier with visible components and connectors. View of the interior of an amplifier with an open casing, showing electronic components and cooling. Audio amplifier in a silver and black case on a wooden desk. Audio system on a shelf with an amplifier, CD player, and turntable. Silver audio amplifier with centrally placed knob on the front panel.

I also add a video showing the operation of the amplifier icon illumination:




The amplifier, as in class A, heats up mercilessly:
Thermal image showing an electronic component with measured temperature. Thermal imaging of an electronic amplifier interior. Thermographic image of two toroidal transformers inside an audio amplifier Thermal image of an amplifier interior showing heat distribution. Thermal imaging of a DIY amplifier on the floor. Thermal image of a DIY amplifier showing temperature distribution. Thermal image of an amplifier showing temperature distribution.

problems
- low brightness of the subtitles backlight - they were etched on the PCB and covered with a black soldermask. Unfortunately, this is not the best solution and I am in the process of looking for something else. If you have any ideas - please give me a hint :)
- very little space inside - I chose a casing with a depth of 30 cm. On paper everything fit, in reality it would be much better to use a larger housing,
- too small radiators - the amplifier heats up to about 75 degrees. I wish I had taken a 3U case
- drifting with the temperature offset - the offset must be set on a well-heated amplifier.

Sound - no comparison to anything I've had before :) Previous GainClone or Vincent are far behind.

Regards!

About Author
Maciek_C
Maciek_C wrote 224 posts with rating 245 , helped 11 times. Live in city Elbląg. Been with us since 2016 year.

Comments

Jogesh 20 Jul 2023 17:22

Beautiful construction. As for subtitles, there are two methods: 1. Taking on photographic film. There are digital platesetters for film. Maybe someone who prepares stencils for offset printing using... [Read more]

katakrowa 20 Jul 2023 17:59

Very nice! I admire that you wanted to make "mirror" tiles. You can easily sell for PLN 14,999 :-) [Read more]

CMS 20 Jul 2023 18:01

The construction of beauty. However, I don't like one thing, actually two, because these are two amplifiers in one housing. It's about the way of mounting plates with power amplifiers. While it... [Read more]

Maciek_C 20 Jul 2023 18:27

Thank you friends for the kind words :) You do not need to unscrew - removing the transistors is not a problem, and to insert a new one, just slightly hook the ends of the legs. Checked ;) The only... [Read more]

CMS 20 Jul 2023 19:38

Maybe white paper with the same negative print between the foil and the glass? And possibly delicate white LED backlight during the day. [Read more]

bodzioluban 21 Jul 2023 07:35

The construction is ok, but aren't they sometimes ready-made modules or for self-assembly? But it looks nice. [Read more]

Maciek_C 21 Jul 2023 09:22

Thanks, I'm looking into it :) Could you expand on the idea? I can't visualize it in my head. Are you asking if I didn't use ready-made layouts or couldn't I use ready-made ones... [Read more]

LemuRR 11 21 Jul 2023 11:29

Prepare a 3D model of this glass so that the inscriptions are protruding (approx. 1 mm). Then find someone with a resin printer who will print it for you in transparent resin. The next step will be to... [Read more]

kris8888 21 Jul 2023 12:12

Great and thoughtful design, I'm impressed. Almost like it came from the factory. The only thing that puzzles me is that, due to the fact that the whole thing gets quite hot, is it right that the transformers... [Read more]

efi222 21 Jul 2023 15:16

Beautiful design. I always admire my own audio equipment. When it comes to pictograms, I have been etching them on laminate for years. It's just that the laminate should be thin. Within 0.4, 0.6mm.... [Read more]

CMS 21 Jul 2023 17:38

I got the idea that you want the subtitles to be visible when they are not highlighted. :) And you want the opposite. My mistake. [Read more]

Maciek_C 21 Jul 2023 18:55

The dimensions of this tile are 74x154. As for 3D, I only have AutoCad and 3D modeling is a pain in the ass, but I'll try to prepare something tonight or tomorrow, thank you :) That is why the... [Read more]

E8600 21 Jul 2023 22:21

It's been a long time since there was such a refined structure on the forum. I wonder how long it took from the idea to the implementation of such a miracle? [Read more]

LemuRR 11 22 Jul 2023 00:09

Insert a drawing in SVG format, I'll convert it to a 3D model in a few moments. I will also try to print, but I do not promise success, because the working field of the printer is "on contact". As... [Read more]

mmaker 22 Jul 2023 00:12

I used to etch such inscriptions on a 0.3 mm laminate and put 3 mm smoked plexiglass on the front. It worked. If it's supposed to be glass, aim for tinted car window film. You probably have every 5... [Read more]

nyquist 22 Jul 2023 09:55

A fine piece of work! I admire and envy ;) Out of curiosity, a question - what did you shield the power transformers with? Is it permalloy or plain copper? [Read more]

Maciek_C 22 Jul 2023 10:33

Thank you guys for your kind words and good advice :) Buddy LemuRR 11, I am very grateful for your willingness to help, but I don't want to bother you for now - I will try what you suggested first,... [Read more]

efi222 22 Jul 2023 11:22

Let me have a "three cents" on tinted glass. Just like my colleagues, I covered plexiglass with foils, but something was always wrong. And this is a bubble, and this is some kind of scratch on the plexiglass... [Read more]

gdkj 23 Jul 2023 18:54

Out of curiosity, C102 = 100µF/25V. Why so much value? [Read more]

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