2stageEF high performance class AB power amp / 200W8R / 400W4R - diyAudio
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Old 1st May 2013, 01:04 PM   #1
astx is offline astx  Austria
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Default 2stageEF high performance class AB power amp / 200W8R / 400W4R

Heavily inspired from books of Douglas Self, Bob Cordell and other great authors I decided to design a discrete power amplifier to learn how LTSpice can be used for my DIY projects.
Attached is the current simulation file and some information about the real world result: a very good working 2stageEF power amplifier with high performance.
The simulated THD performance is about 0.0004% at 20kHz@200W@8R.
Real life THD+N performance of working prototype amplifier is about 0.0015% at 20kHz@200W@8R (80kHz bandwidth).
Using the HP3585A spectrum analyser (100dB resolution) while running 20kHz@200W@8R test only H2 and H3 are visible above the noise floor.
To download the needed BJT/JFET/MOSFET/DIODE ltspice library file "Cordell-Models.txt" please visit CordellAudio.com - Home

During the years some smaller amplifiers based on the same topology have been developed. These projects have been discussed in detail and have been built successfully by different users. See the index below for more information.
In addition a high performance discrete opamp "MyDOA" and housekeeping circuits have been developed and built many times too.

More test results, THD plots and other information will be updated from time to time.

Have fun, Toni

-----------------------------------------

A) SA2014 (200W@8R, 400W@4R) Rev 3.4.2 amplifier (partially old name is SA2013) using 8 matched pairs TTC5200 and TTA1943:
  • Latest valid PCB gerber files for input/VAS and output stage board can be found in post 979 and 980
  • PCB gerber files for power supply (single diode bridge; v3.x; see F) and G) below for dual diode bridge) for one channel in post 1005
  • Latest schematic and corrected BOM in post 1145 and 1146
  • R28 (100R) needs to be reduced to 68R to get some extra PM stability.
  • CCS mod for better thermal stability post 2028
  • "asc" files can be found in post 1149
  • if there is interest for pcb's please email me: sa2014 (at) aws-it.at

B) MyDOA v3.1 (my discrete operational amplifier) have a look at
C1) SA2015 V-MOSFET (70W@8R, 140W@4R) using 3 matched pairs IRFP240 and IRFP9240:
C2) SA2015 V-MOSFET (100W@8R, 200W@4R) using 1 pair IXYS IXTH80N20L and IXTH48P20P:
D) housekeeping circuits 4.3:
  • Schematic and BOM part 1 is here
  • Schematic and BOM part 2 is here
  • some pcb's and PIC microcontroller firmware are available via: sa20xx-hk (at) aws-it.at

E1) SA2016 - L-MOSFET (70W@8R, 140W@4R) - 3 matched pairs Exicon ECX10N20 and ECX10P20:
  • preliminary schematic for ECX10N20, ECX10P20 can be found in post 1761
  • some pcb's are available via: sa2016 (at) aws-it.at

E2) SA2016 - L-MOSFET (100W@8R, 200W@4R) - 3 matched pairs double die Exicon ECW20N20 and ECW20P20:
  • preliminary schematic for double die ECW20N20 and ECW20P20 can be found in post 2105
  • some pcb's are available via: sa2016 (at) aws-it.at

F) SA2014 - power supply v4.0
  • schematic for dual diode bridge ("big" sized: 150x150mm) can be found in post 2000 and 2001
  • updated gerber files in post 2067, 2068
  • some pcb's are available via: sa2014 (at) aws-it.at

G) SA2014/SA2015/SA2016 - new resized universal power supply v4.0
  • schematic for dual diode bridge (smaller size: 150x90mm) can be found in post 1987 and 1988
  • updated gerber files in post 2067, 2068
  • images of working test samples in post 2071
  • some pcb's are available via: sa2016 (at) aws-it.at


INDEX / UPDATES

USERS BUILD:
Attached Images
File Type: png 2ef_simulation.png (207.2 KB, 12313 views)
File Type: jpg SA2013_assembled_1.jpg (250.8 KB, 11588 views)
File Type: jpg SA2013_assembled_2.jpg (326.5 KB, 10923 views)
File Type: png SA2013_discrete_class_ab_input_vas_stage_schematic.png (191.8 KB, 11392 views)
File Type: png SA2013_discrete_class_ab_output_stage_schematic.png (178.2 KB, 11098 views)
File Type: jpg SA2013_high_power_stability_test.jpg (277.9 KB, 5404 views)
File Type: jpg SA2013_THD_20kHz_200W_8R.jpg (151.6 KB, 2462 views)
Attached Files
File Type: asc 2stageEF_class_AB_power_amplifier.asc (37.3 KB, 883 views)
File Type: zip ltspice_libs.zip (1.3 KB, 526 views)

Last edited by astx; 18th March 2017 at 02:09 PM. Reason: Update index / Update to reflect current state of development
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Old 1st May 2013, 02:46 PM   #2
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Using 2N5401 for Q1 and Q2 is a mistake. At low Vce these transistors perform badly.

The BC5x0, BC3x7, and 2SA1015 are known to have excellent okay quasi-sat behavior. There are virtually no transistors with Vcemax>50V that have good quasisat behavior.

Because SPICE does not model quasi-saturation, this problem will not show up in your simulations. However, since the above recommended transistors are pretty close to ideal, if you use Cordell's or NXP (Phillips) models for them they will get you within 6db of real life at low Vce.
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Old 1st May 2013, 03:16 PM   #3
astx is offline astx  Austria
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... think you are referring to ltspice simulation file as the part numbering of the attached schematic pictures is different:
Maybe you are right that 2N5401 is not the best BJT for the current mirror.
Using BC560C instead of reduces THD simulation indeed about 3ppm.
BTW the used transistors for Q1/Q2 are hand selected from a big number of measured devices and have hfe > 220. Perhaps this is the reason, that the real world amplifier THD figure is better as simulated one...
Will try your BJT tipps the next days in real world.

Thx,

Toni
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Old 1st May 2013, 03:25 PM   #4
astx is offline astx  Austria
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Default minor fix ...

Output stage's R48 has to be 33R instead of 150R.
Attached corrected output stage schematic.
Attached Images
File Type: png SA2013_discrete_class_ab_output_stage_schematic_V2.png (178.8 KB, 4005 views)
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Old 1st May 2013, 04:01 PM   #5
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In your setup matching the CM transistors isn't going to do anything if the CM degeneration isn't also matched. I posted about it here:

diyAB Amp - The "Honey Badger"
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Old 1st May 2013, 04:22 PM   #6
astx is offline astx  Austria
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Default Q1/Q2 CM matching data ...

Your explanation is very interesting.

Q1 and Q2 matching data:

Left channel:
BJT#30: hfe=224 vbe=-0.5670
BJT#173: hfe=224 vbe=-0.5660

Right channel:
BJT#35: hfe=230 vbe=-0.5670
BJT#128 : hfe=230 vbe=-0.5660

100R resistors are matched < 0.5% tolerance.

So what would be your choice for Q1/Q2 CM and degeneration (2.2mA per leg)? (Amp is using nominally +/- 66V and max. +/- 72V power supply)

BR,

Toni
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Old 1st May 2013, 04:44 PM   #7
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I go by Slone's advice to degenerate by 50mV. 50mV / 2.2mA =~ 22R. Degeneration is specified as voltage drop because Gm is proportional to Iq and so is the degeneration voltage drop. This way degeneration can be described conveniently independent of Iq.

I would use BC560C in the CM because they are very fast, have high gain, and have good enough Vcesat. For a CM, I think they are as close to ideal as you can get.
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Old 2nd May 2013, 07:13 AM   #8
astx is offline astx  Austria
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Default PCB and input stage assembling details ...

Before soldering the heat sinks place pvc washers between pcb and heatsink solder legs to avoid short circuit with rail voltages. Do this even if your pcb has a very good stop paint!
Attached Images
File Type: jpg SA2013_input_vas_1.jpg (210.1 KB, 3454 views)
File Type: jpg SA2013_input_vas_2.jpg (180.9 KB, 1861 views)
Attached Files
File Type: zip SA2013_pcb_gerber.zip (166.8 KB, 620 views)
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Old 2nd May 2013, 10:48 AM   #9
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slobber slobber Congratulations on this beautiful piece of engineering.
It looks looks really professional to me - you must do this for work too and not just as a DIY hobby!

Thanks for sharing this btw - really very inspiring stuff
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Old 2nd May 2013, 11:00 AM   #10
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by keantoken View Post
I go by Slone's advice to degenerate by 50mV. 50mV / 2.2mA =~ 22R. Degeneration is specified as voltage drop because Gm is proportional to Iq and so is the degeneration voltage drop. This way degeneration can be described conveniently independent of Iq...............
I have been using 200mV to 300mV as the Vdrop of the degeneration resistor, in LTP, & VAS & Current Mirror.
What is wrong with doing it that way? excess added noise? or many other avoidable problems?
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