Class A amplifier, full Dual Mono

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#1 20 Jul 2023 12:18

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:

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.

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.

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

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:

Aluminum front panel of the case:

Panel with illuminated inscriptions under the glass (with a cutout for the IR receiver and the axis:

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:

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.

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.

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.

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

The amplifier, as in class A, heats up mercilessly:

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!

Cool? Ranking DIY
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Maciek_C Maciek_C

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Maciek_C wrote 214 posts with rating 218, helped 11 times. Live in city Elbląg. Been with us since 2016 year.
#2 20 Jul 2023 17:22

Jogesh Jogesh

Level 28

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#2 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 the old method offers such services.
2. Spray paint thin plexiglass black and burn the paint with a laser.
#3 20 Jul 2023 17:59

katakrowa katakrowa

Level 22

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#3 20 Jul 2023 17:59

Very nice! I admire that you wanted to make "mirror" tiles.

You can easily sell for PLN 14,999
#4 20 Jul 2023 18:01

CMS CMS

Administrator of HydePark

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#4 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 takes up little space, in the event of a failure, to replace one transistor, you have to unscrew the entire plate from the heat sink.

I like the amber backlight. I remember how over 20 years ago I bought a fancy video recorder (which I used as a TV tuner with stereo sound, and it didn't play even 10 cassettes) and had a blue display. And since my Yamaha equipment has amber displays, the day after I bought it, I disassembled the VCR to see how to change its color. It turned out that the display actually glows green, and the blue was achieved with a purple filter. And imagine that I went to a store with supplies for advertisers, bought several different transparent foils and a piece of smoked plexiglass in the size of the display and messed around until I got the same color of the VCR display that the Yamahas had.

As for the inscriptions, print with a laser on foil (only buy a foil dedicated to lasers, because the one for an inkjet printer can melt and you will break the printer) in negative and that's it.
#5 20 Jul 2023 18:27

Maciek_C Maciek_C

Level 14

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#5 20 Jul 2023 18:27

Thank you friends for the kind words :)

CMS wrote:
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 takes up little space, in the event of a failure, to replace one transistor, you have to unscrew the entire plate from the heat sink.

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 problem would be to replace the temperature compensation transistor, two capacitors and two mounting potentiometers. Everything else can be replaced from above.

As for, let's call it, the backlight matrix, the main problem is that when the backlight is off, the inscriptions are invisible behind the glass. I tried with foil and plexiglass, but the print on the laser foil was piercing and the inscriptions on the plexiglass were visible from under the glass. Therefore, these combinations with black soldermask.

Regards!

Matt
#6 20 Jul 2023 19:38

CMS CMS

Administrator of HydePark

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#6 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.
#7 21 Jul 2023 07:35

bodzioluban bodzioluban

Level 13

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#7 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.
#8 21 Jul 2023 09:22

Maciek_C Maciek_C

Level 14

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#8 21 Jul 2023 09:22

Jogesh wrote:
Beautiful construction.
1. Taking on a photographic film. There are digital platesetters for film. Maybe someone who prepares stencils for offset printing using the old method offers such services.

Thanks, I'm looking into it :)

CMS wrote:
Maybe white paper with the same negative print between the foil and the glass?
And possibly delicate white LED backlight during the day.

Could you expand on the idea? I can't visualize it in my head.

bodzioluban wrote:
Maybe white paper with the same negative print between the foil and the glass?
And possibly delicate white LED backlight during the day.

Are you asking if I didn't use ready-made layouts or couldn't I use ready-made ones available on the net instead?
If it's the former, then no - I designed all the boards myself and had them made at JLCPCB. The only ready-made is the Bluetooth module, screwed to the DAC board.
As for the housing, it is a finished product from modushop. At modushop, holes were cut in it according to my design (based on technical drawings sent to them).

Maciek_C wrote:
As for, let's call it, the backlight matrix, the main problem is that when the backlight is off, the inscriptions are invisible behind the glass. I tried with foil and plexiglass, but the print on the laser foil was piercing and the inscriptions on the plexiglass were visible from under the glass. Therefore, these combinations with black soldermask.

I want to achieve the same effect as the current one (photos below), only that much more light would pass through it (this soldermask "cuts out a lot of light").
#9 21 Jul 2023 11:29

LemuRR 11 LemuRR 11

Level 26

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#9 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 pour the top layer (the one with inscriptions) with black resin. After complete hardening, polish the top layer so that the inscriptions emerge, and then pour the top layer with a slightly smoky resin (mix with pigment, such resins are available).
What are the dimensions of this item? Maybe I can help
#10 21 Jul 2023 12:12

kris8888 kris8888

Level 38

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#10 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 are completely covered with a screen, which probably additionally increases their temperature.
And the two smaller toroidal transformers mounted vertically look like they were placed loosely, but it's probably due to lack of space.
With what supply voltage and what terminal current does it work? How much power can it deliver to the load and with what impedance?
#11 21 Jul 2023 15:16

efi222 efi222

Level 13

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#11 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. Most of them are covered with dark glass with a tint of about 50% and the effect is very good. Have a look at my projects.
#12 21 Jul 2023 17:38

CMS CMS

Administrator of HydePark

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#12 21 Jul 2023 17:38

Maciek_C wrote:
Could you expand on the idea? I can't visualize it in my head.

I got the idea that you want the subtitles to be visible when they are not highlighted. And you want the opposite. My mistake.
#13 21 Jul 2023 18:55

Maciek_C Maciek_C

Level 14

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#13 21 Jul 2023 18:55

LemuRR 11 wrote:
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 pour the top layer (the one with inscriptions) with black resin. After complete hardening, polish the top layer so that the inscriptions emerge, and then pour the top layer with a slightly smoky resin (mix with pigment, such resins are available).
What are the dimensions of this item? Maybe I can help

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 :)

kris8888 wrote:
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 are completely covered with a screen, which probably additionally increases their temperature.

That is why the openings through which the wires are led out are enlarged, and a recess is cut out in the mounting plate, near the front panel. This creates convection that exchanges air under the screen. Transformers heat up to about 48 degrees (checked with a thermal imaging camera). The transformer of the digital and standby section reaches a higher temperature when listening to Bluetooth :)

kris8888 wrote:
And the two smaller toroidal transformers mounted vertically look like they were placed loosely, but it's probably due to lack of space.
With what supply voltage and what terminal current does it work? How much power can it deliver to the load and with what impedance?

Exactly, no space and the need to mount "edgewise" as I wrote in the description, I regret not taking a larger case.
The voltage of the terminals is 2x28V DC. The quiescent current of one branch is 375 mA, i.e. a total of 1.5 A per channel.
This gives 2x35W into 8Ω and 2x70W into 4Ω :)

efi222 wrote:
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. Most of them are covered with dark glass with a tint of about 50% and the effect is very good. Have a look at my projects.

I saw this method once on an electrode (it's very possible that in one of your devices ) and I wanted to do the same. Unfortunately, in Elbląg, 3 glaziers had windows with a maximum tint of 30% and this turned out to be too weak, hence the idea to use a soldermask (note that the hole for the IR receiver is very visible at a certain angle). This solder mask restricts the light too much.
Maybe the key will be, as you say, getting a much darker glass and peeling off the soldermask
#14 21 Jul 2023 22:21

E8600 E8600

Level 40

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#14 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?
#15 22 Jul 2023 00:09

LemuRR 11 LemuRR 11

Level 26

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#15 22 Jul 2023 00:09

Maciek_C wrote:
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

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 for dimming, self-adhesive films for tinting windows are available on Allegro. Similarly, 3 mm plexiglass can be purchased with quite low permeability.
#16 22 Jul 2023 00:12

mmaker mmaker

Level 19

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#16 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 or 10% tones.
In addition, a very nice amplifier, I was aiming for some class A myself, but I think I'm too old for such toys
#17 22 Jul 2023 09:55

nyquist nyquist

Level 26

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#17 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?
#18 22 Jul 2023 10:33

Maciek_C Maciek_C

Level 14

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#18 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, i.e. I will remove the black soldermask from the current PCB and darken the glass with foil. If I fail at this, I will turn to You for help. Many thanks again!

E8600 wrote:
I wonder how long it took from the idea to the implementation of such a miracle?

I started working on it at the end of November, finished it a week ago, spending about 6 hours a week on it.

nyquist wrote:
Out of curiosity, a question - what did you shield the power transformers with? Is it permalloy or plain copper?

There is 0.3mm brass sheet on top for appearance, there is 0.7mm steel sheet underneath as magnetic screen
#19 22 Jul 2023 11:22

efi222 efi222

Level 13

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#19 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 and other artifacts (maybe I can't do it right).
I'm done with it. I now order glass by mail order from a glazier from Gdańsk. The guy cuts to size, polishes the edges and his prices are also friendly. Such lenses really look "pro". Flawless surface. In the photos there is Antisol black 6 mm (there is also 4 mm with less darkening).
The disadvantage of Antisol 6 mm is the limitation of IR to about 3 m.

Fast lying directly on the ground.

A few centimeters moved away.
#20 23 Jul 2023 18:54

gdkj gdkj

Level 26

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#20 23 Jul 2023 18:54

Out of curiosity, C102 = 100µF/25V. Why so much value?
#21 24 Jul 2023 00:28

pikarel pikarel

Level 36

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#21 24 Jul 2023 00:28

Beautiful construction, perfect workmanship, but for me it's too much steam in the whistle (I grew out of the A class several decades ago, along with the ClassA of a certain Japanese company).

gdkj wrote:
Out of curiosity, C102 = 100µF/25V. Why so much value?

It results from the time constant for the lowest frequencies (look at how low the resistance value of the resistors connected to ground is).
#22 24 Jul 2023 17:45

gulson gulson

System Administrator

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#22 24 Jul 2023 17:45

Beautiful design, if you write to me in a parcel locker, I will send a small gift.
#23 25 Jul 2023 15:54

Olkus Olkus

Level 31

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#23 25 Jul 2023 15:54

A great amplifier, everything is refined, the elements are mainly of good quality. Just congratulations ;)

Regards,
AND.
#24 28 Jul 2023 10:38

robert123 robert123

Level 16

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#24 28 Jul 2023 10:38

I have a question about the potentiometer - I can't read its markings from the photos - what model is it (producer I suspect Alps)? Can a colleague share the pcb source file of the preamplifier itself? Alternatively, I would buy such a pcb if it was left.
I will also ask about the value of C104, C105 in the phono preamp, is there really 4µ7? Congratulations on a great build and best regards.
#25 28 Jul 2023 23:26

Maciek_C Maciek_C

Level 14

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#25 28 Jul 2023 23:26

Hi,
The potentiometer is RK271 Alps 2x50k
I ordered the boards at JLCPCB, and there the minimum is 5 pieces, so I have them left for at least another such amplifier (there are 3 pieces of power amplifiers and selectors left, and 4 pieces of all others) - if anyone is interested, please contact me via PM (I don't want to make money from this, so I'll be fair to take 1/5 of what I paid for each tile).

Of course, I can also easily share gerberas, eagle files or microcontroller code - here, too, I am asking for information on PW.

This capacitance is obviously a mistake, it should be 4.7 nF.

Regards
Matt
#26 29 Jul 2023 15:36

OTLamp OTLamp

Tube devices specialist

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#26 29 Jul 2023 15:36

Maciek_C wrote:
and 2x70W into 4Ω

But rather far from class A. Have you measured other key parameters such as non-linear distortion, intermodulation distortion, frequency response?
#27 29 Jul 2023 16:06

kris8888 kris8888

Level 38

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#27 29 Jul 2023 16:06

Maciek_C wrote:
Problems [...]
- 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

Isn't it better to reduce this quiescent current a bit? From what you have given, it follows that almost 170 W is unproductively converted into heat, and only in the power amplifiers themselves. But that's a lot. If this quiescent current were halved, it would still have a high value, the amplifier would work in the deep AB class (more A than B for small drive), the level of distortion would still be very low, and problems with this unstable offset and temperature would be eliminated.
Well, unless you really care about an additional electric heater in the room.
#28 30 Jul 2023 10:57

Maciek_C Maciek_C

Level 14

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#28 30 Jul 2023 10:57

OTLamp wrote:

Maciek_C wrote:
and 2x70W into 4Ω

But rather far from class A. Have you measured other key parameters such as non-linear distortion, intermodulation distortion, frequency response?

Exactly - in full class A the amplifier works up to about 32W at 8Ω and 18W at 4Ω (determined on the basis of the current shape of the emitter resistors). Later it goes to AB.

I did not measure the distortion - I have nothing to measure it with (an 8-bit oscilloscope will not be reliable). At full drive, the -0.5dB drop came out at 21kHz. I did not check for -3dB.

kris8888 wrote:

Isn't it better to reduce this quiescent current a bit? From what you have given, it follows that almost 170 W is unproductively converted into heat, and only in the power amplifiers themselves. But that's a lot. If this quiescent current were halved, it would still have a high value, the amplifier would work in the deep AB class (more A than B for small drive), the level of distortion would still be very low, and problems with this unstable offset and temperature would be eliminated.
Well, unless you really care about an additional electric heater in the room.

The assumption was to make a class A amplifier and it was achieved now it's time for combinations with quiescent current and other improvements
#29 30 Jul 2023 11:59

kris8888 kris8888

Level 38

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#29 30 Jul 2023 11:59

Maciek_C wrote:
The assumption was to make a class A amplifier

But even these 375mA of quiescent current for a single power transistor now does not cause the amplifier to operate in class A for its full drive range. There is a power threshold at which one of the branches is cut off at the expense of an increase in the current in the other. It's a matter of determining what output power you are interested in working in a pure class A amplifier. Because listening at home with a power of even, for example, 30W with low-efficiency columns still gives a big impression of volume. Therefore, it is enough to set the pure class A threshold at a relatively low level, sufficient for normal listening, and to amplify the events with an AB class amplifier.
There are some system solutions, e.g. Pioneer used them in their amplifiers, where the quiescent current is dynamically increased as the drive increases, and it is increased only in the branch that is trying to cut off at the moment. This actually causes the amplifier to work in pure class A in the full power range and at the same time it is not an additional radiator in the room.
#30 09 Aug 2023 15:19

aaanteka aaanteka

Level 42

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#30 09 Aug 2023 15:19

I have a few questions regarding the design in terms of electronics:

Maciek_C wrote:
was only required offset adjustment transistor currents

Maciek_C wrote:
offset drifting with temperature - the offset must be set on a well-heated amplifier

1) What and how do you regulate the offset?
2) What is its initial value and what is its drift?

Maciek_C wrote:
too small radiators - the amplifier heats up to about 75 degrees.

3) For what operating parameters (conditions)?

Maciek_C wrote:
The voltage of the terminals is 2x28V DC. The quiescent current of one branch is 375 mA, i.e. a total of 1.5 A per channel.
Give this 2x35W by 8 ohms and 2x70W by 4 ohms

4) Where did these power values come from?
5) Calculated, physically measured?

Maciek_C wrote:
There is 0.3mm brass sheet on top for appearance, there is 0.7mm steel sheet underneath as magnetic screen

6) For what purpose did you do it?
7) Why this way?
8) What is the total gain of the sound path from the input to the output of the amplifier?

Maciek_C wrote:
in full class A, the amplifier works up to about 32W at 8Ω and 18W at 4Ω (determined on the basis of the current shape of the emitter resistors)

9) Can you explain the idea behind the mentioned measurement/determination based on the shape of the current?
10) What shape are you writing about?
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