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Extremely simple amplifier (4 transistors) with low THD.
Extremely simple amplifier (4 transistors) with low THD.
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Old 19th September 2019, 01:40 PM   #1
Renbrant is offline Renbrant  Brazil
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Default Extremely simple amplifier (4 transistors) with low THD.

Hello friends,
Today I tested an extremely simple project (4 transistors) developed and produced by a friend of mine from Brazil.

His website is this: AlfaKits Eletrônica

The cool thing is that on his site is shared free of charge the electrical scheme and layout of the PCB for those who want to produce for their own use. Production for sale is prohibited.

I was impressed by the level of THD he achieved with a simple 12 to 15V power supply and only 4 transistors.

Check out the results:

I couldn't post the photos. Following is the link to the results:
RB Eletronica - UNO


I'll publish on my YT channel the details about that test, soon.
YouTube

Last edited by Renbrant; 20th September 2019 at 04:02 PM. Reason: I couldn't post the photos so I added a link with the results.
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Old 19th September 2019, 02:22 PM   #2
cumbb is offline cumbb
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Gratulation.

One of the best complementary-transistors-pp-design you can do. And listen.
Nearly no grainy too;-)

Have fun!

...and do not switch to a fat complementary-transes-pp-power amp;-!!!!
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Old 19th September 2019, 02:38 PM   #3
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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I can't open the images. Have good luck selling those kits. Interesting for students.
Saludos de Argentina.
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Old 19th September 2019, 04:20 PM   #4
Elvee is offline Elvee  Belgium
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An output of 7W/4Ω with a 12V supply sounds slightly optimistic...
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Old 19th September 2019, 07:45 PM   #5
xrk971 is offline xrk971  United States
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Extremely simple amplifier (4 transistors) with low THD.
Neat design, reminiscent of a singleton input cap-coupled output amps that I have seen around here on DIYA.

Extremely simple amplifier (4 transistors) with low THD.-uno-amp-schematic-jpg
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File Type: jpg Uno-Amp-Schematic.jpg (85.1 KB, 1032 views)
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Old 19th September 2019, 08:47 PM   #6
Elvee is offline Elvee  Belgium
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No emitter resistors, and a single diode as a base spreader as a consequence, to limit the risk of thermal runaway is a good recipe for Xover distortion.
It may give more "edge" to loud music, but for softer programs it could be somewhat unpleasant.
In addition, the speaker will see a permanent 30~40mA DC current.
Not catastrophic for a big 100W or so unit, but not ideal for a 5 or 10W one
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Old 19th September 2019, 09:08 PM   #7
cumbb is offline cumbb
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The already given answer;-?

Quote:
Today I tested ...
I was impressed by the level of THD he achieved with a simple 12 to 15V power supply and only 4 transistors.
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Old 19th September 2019, 09:17 PM   #8
Ramcres is offline Ramcres
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My ZX spectrum used an amplifier like this .


I still remember those good sounds.

BR
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Old 19th September 2019, 09:57 PM   #9
Elvee is offline Elvee  Belgium
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I also had a ZX spectrum, and IIRC the OP stage was even cruder, something like a single, binary-controlled transistor.

The THD figure of the 4-transistor amp might be relatively low (hard data please?), but Xover distortion does generally not have a large impact on the global THD figure, it is simply extremely unpleasant, even at very low numerical levels.
An oscilloscope or an ear is a better detection tool than a THD meter in this case
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Old 19th September 2019, 11:21 PM   #10
cumbb is offline cumbb
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Quote:
An oscilloscope or an ear is a better detection tool than a THD meter in this case
The ear does say: Yeah;-)
... clean sounding sources and speakers are necessary;-!
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