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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 20th September 2019, 05:45 AM   #11
xrk971 is online now xrk971  United States
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Extremely simple amplifier (4 transistors) with low THD.
I ran a quick simulation using commonly available actives for the typical roles here.
Extremely simple amplifier (4 transistors) with low THD.-uno-amp-ltspice-v1-jpg

Increased the operating voltage to 24v and got this:

For 8Vpp (2.83vrms) into 8ohms for 1w:
Code:
Harmonic	Frequency	 Fourier 	Normalized	 Phase  	Normalized
 Number 	  [Hz]   	Component	 Component	[degree]	Phase [deg]
    1   	1.000e+03	4.087e+00	1.000e+00	    2.16°	    0.00°
    2   	2.000e+03	1.525e-03	3.732e-04	  113.93°	  111.77°
    3   	3.000e+03	2.855e-04	6.987e-05	  178.73°	  176.57°
    4   	4.000e+03	2.991e-04	7.319e-05	  178.34°	  176.19°
    5   	5.000e+03	2.397e-04	5.866e-05	 -179.55°	 -181.70°
    6   	6.000e+03	1.984e-04	4.855e-05	 -179.62°	 -181.77°
    7   	7.000e+03	1.701e-04	4.162e-05	 -179.72°	 -181.88°
    8   	8.000e+03	1.488e-04	3.642e-05	 -179.75°	 -181.91°
    9   	9.000e+03	1.323e-04	3.237e-05	 -179.78°	 -181.94°
   10   	1.000e+04	1.191e-04	2.914e-05	 -179.80°	 -181.96°
   11   	1.100e+04	1.083e-04	2.649e-05	 -179.82°	 -181.98°
   12   	1.200e+04	9.923e-05	2.428e-05	 -179.84°	 -181.99°
   13   	1.300e+04	9.160e-05	2.241e-05	 -179.85°	 -182.00°
   14   	1.400e+04	8.505e-05	2.081e-05	 -179.86°	 -182.01°
   15   	1.500e+04	7.938e-05	1.942e-05	 -179.87°	 -182.02°
Total Harmonic Distortion: 0.040360%(0.292814%)
It has 2nd order dominant distortion with a monotonically decreasing profile. So should sound good. I do not see it as particularly low THD though, but that is to be expected of a 4-active singleton amp:
Extremely simple amplifier (4 transistors) with low THD.-uno-amp-ltspice-v1-fft-jpg
Attached Images
File Type: jpg Uno-Amp-LTspice-v1.jpg (201.5 KB, 419 views)
File Type: jpg Uno-Amp-LTspice-v1-FFT.jpg (185.3 KB, 414 views)
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Last edited by xrk971; 20th September 2019 at 05:47 AM.
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Old 20th September 2019, 06:20 AM   #12
xrk971 is online now xrk971  United States
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Extremely simple amplifier (4 transistors) with low THD.
It is able to make 7w into 8ohms with fairly low distortion:
Code:
Harmonic	Frequency	 Fourier 	Normalized	 Phase  	Normalized
 Number 	  [Hz]   	Component	 Component	[degree]	Phase [deg]
    1   	1.000e+03	1.075e+01	1.000e+00	    2.16°	    0.00°
    2   	2.000e+03	9.502e-03	8.841e-04	  100.52°	   98.37°
    3   	3.000e+03	2.996e-03	2.788e-04	    7.43°	    5.27°
    4   	4.000e+03	1.224e-03	1.139e-04	 -122.71°	 -124.87°
    5   	5.000e+03	2.125e-03	1.977e-04	 -173.41°	 -175.57°
    6   	6.000e+03	1.677e-03	1.560e-04	  118.78°	  116.62°
    7   	7.000e+03	9.150e-04	8.514e-05	   18.63°	   16.48°
    8   	8.000e+03	1.325e-03	1.233e-04	  -92.76°	  -94.91°
    9   	9.000e+03	1.647e-03	1.532e-04	 -167.37°	 -169.53°
   10   	1.000e+04	1.374e-03	1.278e-04	  120.45°	  118.30°
   11   	1.100e+04	9.276e-04	8.632e-05	   25.36°	   23.20°
   12   	1.200e+04	1.068e-03	9.935e-05	  -82.19°	  -84.34°
   13   	1.300e+04	1.302e-03	1.212e-04	 -161.21°	 -163.36°
   14   	1.400e+04	1.126e-03	1.048e-04	  125.30°	  123.14°
   15   	1.500e+04	7.646e-04	7.114e-05	   33.56°	   31.40°
Total Harmonic Distortion: 0.102280%(0.309343%)
I should add that this is a fairly high bias current of 640mA (sort of Class A) and dissipating about 8w per output active.
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Old 20th September 2019, 11:34 AM   #13
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Amps like that were abundant in 70's, 80's. I've built shitloads of small amps with above topology back then. The ones with germ. outputs (a popular pair was AD161/162) were particularly "good" sounding (had a really good presentation of new-vawe and punk guitars - which used to be popular then). Another popular Si pair for car-radios was BD433/434.

If made with a darlington input (or a bit more heavily bootstrapped than above amp); it can be fed directly from a ceramic cartridge record player (audiophiles beware!)
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Old 20th September 2019, 12:28 PM   #14
gannaji is offline gannaji  India
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JLLH class A also uses four transistors !
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Old 20th September 2019, 01:44 PM   #15
xrk971 is online now xrk971  United States
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Extremely simple amplifier (4 transistors) with low THD.
Yes, but JLH did not have push pull output.

One thing I noticed with this amp that is unique: despite having output coupling cap, there is a slight 500mV DC offset due to the connection from the base of the PNP to the output after the cap.

This offset is not a good thing as voice coil will heat up a bit.
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Old 20th September 2019, 02:12 PM   #16
Renbrant is offline Renbrant  Brazil
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Excuse me. The photo link has broken.
Here you find all the results:
RB Eletronica - UNO
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Old 20th September 2019, 02:53 PM   #17
Elvee is offline Elvee  Belgium
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Quote:
Originally Posted by anti View Post
Amps like that were abundant in 70's, 80's.
The originals were generally much better than this example: here is a large collection from various sources:
A collection of vintage, single supply, low to medium power amplifiers for Daniel

This one from a Motorola appnote probably served as a model:

Click the image to open in full size.

I have also described a number of evolutions based on the same theme, and they really bring novel features and good performance.

Otherwise, stick with the good old original circuits: they are still current and usable, unlike some pale copies
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Old 20th September 2019, 03:11 PM   #18
Renbrant is offline Renbrant  Brazil
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Quote:
Originally Posted by Elvee View Post
The originals were generally much better than this example: here is a large collection from various sources:
A collection of vintage, single supply, low to medium power amplifiers for Daniel
It's almost the same topology.
This is a very cool material!
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Old 20th September 2019, 03:54 PM   #19
xrk971 is online now xrk971  United States
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Extremely simple amplifier (4 transistors) with low THD.
Amps like this are fun to make. You can even do it on veroboard or P2P. They certainly sound nice.
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Old 20th September 2019, 04:19 PM   #20
EDDELARUE is offline EDDELARUE  Brazil
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Quote:
Originally Posted by xrk971 View Post
I ran a quick simulation using commonly available actives for the typical roles here.
Click the image to open in full size.

Increased the operating voltage to 24v and got this:

For 8Vpp (2.83vrms) into 8ohms for 1w:
Code:
Harmonic	Frequency	 Fourier 	Normalized	 Phase  	Normalized
 Number 	  [Hz]   	Component	 Component	[degree]	Phase [deg]
    1   	1.000e+03	4.087e+00	1.000e+00	    2.16°	    0.00°
    2   	2.000e+03	1.525e-03	3.732e-04	  113.93°	  111.77°
    3   	3.000e+03	2.855e-04	6.987e-05	  178.73°	  176.57°
    4   	4.000e+03	2.991e-04	7.319e-05	  178.34°	  176.19°
    5   	5.000e+03	2.397e-04	5.866e-05	 -179.55°	 -181.70°
    6   	6.000e+03	1.984e-04	4.855e-05	 -179.62°	 -181.77°
    7   	7.000e+03	1.701e-04	4.162e-05	 -179.72°	 -181.88°
    8   	8.000e+03	1.488e-04	3.642e-05	 -179.75°	 -181.91°
    9   	9.000e+03	1.323e-04	3.237e-05	 -179.78°	 -181.94°
   10   	1.000e+04	1.191e-04	2.914e-05	 -179.80°	 -181.96°
   11   	1.100e+04	1.083e-04	2.649e-05	 -179.82°	 -181.98°
   12   	1.200e+04	9.923e-05	2.428e-05	 -179.84°	 -181.99°
   13   	1.300e+04	9.160e-05	2.241e-05	 -179.85°	 -182.00°
   14   	1.400e+04	8.505e-05	2.081e-05	 -179.86°	 -182.01°
   15   	1.500e+04	7.938e-05	1.942e-05	 -179.87°	 -182.02°
Total Harmonic Distortion: 0.040360%(0.292814%)
It has 2nd order dominant distortion with a monotonically decreasing profile. So should sound good. I do not see it as particularly low THD though, but that is to be expected of a 4-active singleton amp:
Click the image to open in full size.
What about AC analysis ??
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