4 x BTL 300W/8R - a TDA8950j based 4 channel power amplifier - diyAudio
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Old 1st January 2014, 06:38 PM   #1
astx is offline astx  Austria
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Default 4 x BTL 300W/8R - a TDA8950j based 4 channel power amplifier

Just 4 fun I have designed (now some years ago) a 4 channel class D power amplifier to get some feeling and knowledge about building class D amplifiers.
Attached some schematics and pictures of the result.
After searching for a simple chip I found the TDA8950j which has from low to mid range an acceptable good THD performance.
The TDA8950j can be clocked externally which I have used in this design to avoid interferences of the different pwm clocks in the audible range.
Maximum output power per channel is 300W/8R.
The amp pcb is single sided and uses some smt devices to save space and to fulfill some datasheet requirements.

For DIY use only feel free to build your party power machine.

BR, Toni
Attached Images
File Type: jpg 1200x900-2012-03-04 18.25.50.jpg (58.6 KB, 708 views)
File Type: jpg 1200x900-2012-03-04 18.51.55.jpg (155.2 KB, 690 views)
File Type: jpg 1200x900-2012-03-12 19.26.59.jpg (128.4 KB, 663 views)
File Type: jpg 1200x900-2012-04-01 17.28.09.jpg (122.9 KB, 650 views)
File Type: jpg 1200x900-2012-04-01 17.32.34.jpg (215.4 KB, 640 views)
File Type: jpg 1200x900-2012-04-01 17.33.11.jpg (198.4 KB, 245 views)
File Type: png tda8950_btl_schematic.png (148.8 KB, 371 views)
File Type: png class_d_preamp_powersupply_schematic.png (125.5 KB, 343 views)
Attached Files
File Type: pdf tda8950_btl_schematic.pdf (19.5 KB, 107 views)
File Type: pdf class_d_preamp_powersupply_schematic.pdf (19.6 KB, 87 views)
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Old 1st January 2014, 06:59 PM   #2
astx is offline astx  Austria
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Some more pictures and schematics.
Gerber file for amplifier pcb.

BR, Toni
Attached Images
File Type: png class_d_powersupply_schematic.png (146.0 KB, 289 views)
File Type: jpg 1200x900-2011-12-28 13.52.25.jpg (35.8 KB, 211 views)
File Type: jpg 1200x900-2012-01-06 19.04.33.jpg (47.3 KB, 186 views)
File Type: jpg 1200x900-2012-02-14 16.09.10.jpg (83.4 KB, 185 views)
File Type: jpg 1200x900-2012-04-01 17.30.26.jpg (95.7 KB, 229 views)
File Type: jpg 1200x900-2012-04-01 17.31.35.jpg (60.9 KB, 206 views)
File Type: png tda8950_btl.png (45.7 KB, 205 views)
Attached Files
File Type: pdf class_d_powersupply_schematic.pdf (10.7 KB, 73 views)
File Type: zip tda8950_btl.zip (63.5 KB, 111 views)
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Old 1st January 2014, 07:20 PM   #3
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Good job, congratulations, but the maximum power output can not be 300W/8Ohm/channel when loading circuit to + / 35VDC. Power can reach max.150W/4Ohmi/ch but with high THD (~~10%). Remember, the human ear begins to perceive distortions if THD reaches about 2% (or more so). For this reason "audiophile power" of that TDA is at most 100W/4Ohm/channel (but stamp sound is far below the desired).
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Old 1st January 2014, 07:40 PM   #4
astx is offline astx  Austria
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Thx! The TDA8950j is running in mono BTL mode and is capable to deliver maximum 300W/8R on dual 37V rails - see datasheet: TDA8950 :: NXP Semiconductors
I wouldn't use this amplifier for audiophile listening - party mode!
If you drive the above prototype amplifier to a maximum of 1% distortion you will get > 200W@8R

BR, Toni
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Old 1st January 2014, 07:43 PM   #5
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BTL mode is something else (in the bridge circuit is capable of more power), but do not believe all datasheet specifications, for the reality is quite different.
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Old 4th January 2014, 04:17 PM   #6
astx is offline astx  Austria
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Quote:
Originally Posted by donpetru View Post
BTL mode is something else (in the bridge circuit is capable of more power), but do not believe all datasheet specifications, for the reality is quite different.
This value is not from datasheet - it is measured:
If you drive the above prototype amplifier to a maximum of 1% distortion you will get > 200W@8R
BR, Toni
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Old 21st April 2014, 07:00 PM   #7
astx is offline astx  Austria
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FYI: Toroid inrush current control and other housekeeping (DC protection ...) is done using this microcontroller controlled circuit:

amp2012 inrush control from project: LM3886 running inverting only bridged for 8R


BR, Toni
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Old 22nd April 2014, 02:08 PM   #8
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Default Seriously? WOW :D

Quote:
Originally Posted by astx View Post
Just 4 fun I have designed (now some years ago) a 4 channel class D power amplifier to get some feeling and knowledge about building class D amplifiers.
Attached some schematics and pictures of the result.
After searching for a simple chip I found the TDA8950j which has from low to mid range an acceptable good THD performance.
The TDA8950j can be clocked externally which I have used in this design to avoid interferences of the different pwm clocks in the audible range.
Maximum output power per channel is 300W/8R.
The amp pcb is single sided and uses some smt devices to save space and to fulfill some datasheet requirements.

For DIY use only feel free to build your party power machine.

BR, Toni

Really, this is just awesome, I mean real classy, great cabling and layout and great finish.. The finish is of commercial worth and it would fetch you a high amount if you decided to go commercial.

Excited to see your build and will be hoping someday i could do the same.
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Old 22nd April 2014, 07:51 PM   #9
astx is offline astx  Austria
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Quote:
Originally Posted by saheb11123 View Post
Really, this is just awesome, I mean real classy, great cabling and layout and great finish.. The finish is of commercial worth and it would fetch you a high amount if you decided to go commercial.

Excited to see your build and will be hoping someday i could do the same.
THX for your nice words!

BTW: Building different amplifier topologies is just a hobby for me. Everybody can reuse my designs as long as this is done for non commercial DIY usage only.

BR, Toni
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Old 22nd October 2014, 06:14 PM   #10
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Quote:
Originally Posted by astx View Post
I wouldn't use this amplifier for audiophile listening - party mode!
Hi Toni

I'm curious... what you mean by you wouldn't use the amp for audiophile listening?

I explain, I am new to Class D and I don't know if what I hear is a defect inherent to the TDA8950j or there is a design problem. At mid to high power it sounds very well, but from silence to 10w or so (I didn't measure anything yet) I hear a pretty audible distortion, likewise the old famous crossover distortion known on poor calibrated Class AB amps... is it a weak point of Class D, of TDA8950j or a serious problem with my amp?

I didn't build the amp, it was made by another guy who told me it is normal, that the amp is intended to be used at high power. Is that so?

My doubt is because reading the datasheet of the chip the real life result is not consisten with the 0.05% THD @1watt 8 ohm load. My amp is also BTL mono configuration.

Thanks in advance!

Rei.
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