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Old 29th May 2013, 01:29 PM   #121
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The transistors might still be fine, but when using both on 1x heatsink you are pushing +30-50V and -30-50V into each end of the heatsink, and when beginning to apply power from the TDA all you are doing is shorting the 2x transistors (with the resistance that an aluminium plate will provide)
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Old 2nd June 2013, 03:35 PM   #122
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Quote:
Originally Posted by dr frost dk View Post
First the 6.8Ohm is for sync and can't see you can get more efficiency or what ever you are trying to achieve......
I like your design. A WHOLE LOT! A powerful amp without biasing, and easy to build.

I just want to tweak it a bit to see if there is any room for improvement. And if not, then leave it as is.......

Your 6.8 ohms is fine. I want to go to 4.7 ohms sync (or less maybe) so the amp is driving the speaker a bit harder by itself directly before the voltage drop across the sync resistor turns on the output transistors to take over. It's just to reduce crossover distortion, because I'd like to drive 2 or 1 ohm and have full treble quality.

I've also considered adding 0.47 or 1 ohm resistors to the bases of the output transistors to have them turn-on a bit softer during SYNC to reduce any further distortion, at slight expense of voltage drop to improve linearity.

You don't hear the normal crossover distortion you get from driving too low ohm speaker anyway with your chip because the sync resistor adds resistance (less load) at lower signal levels, so you still get to enjoy the class AB biased linearity of the output stage inside the chip.

Also I want to use OTHER chip-amps for this same design. I have SEVERAL STK Video Amplifier Chips that look like good for this....All capable of over +/- 40V
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Old 7th June 2013, 02:12 AM   #123
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Well just at the point where i was about to bridge 2 TDAs, I broke 2 pins of one,
Now what?
I find inmy parts boxes i have 2 pairs of sc5200 and sa1943 !!!
lucky lucky!
Now i have to try this way of yours...
Ill be testing tomorrow with the one that did not get broken.
Ill post pictures and tell you about how it sounds. thanks for your
comments.

Last edited by martin martinez; 7th June 2013 at 02:15 AM. Reason: add
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Old 7th June 2013, 08:45 PM   #124
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Default closer to finish

how does it look? not too bad?
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Old 20th June 2013, 07:27 AM   #125
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Default pcb

Hello
greetings interested in making this project is the pcb ok vcc+ is in centre
and vcc-is on top
warm regards
andrew lebon
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Old 20th June 2013, 04:14 PM   #126
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Hello dr frost
greetings just want to say THANKS for your wonderful design tested it on 2 ohms on 40 0 40 DC supply sound is clear tomorrow i will design pcb for 2 output pairs
and post some pictures THANKS
warm regards
andrew lebon
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Old 20th June 2013, 09:30 PM   #127
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Default hi

this is the final assembly, had to make a time to finish the amp section, later iŽll deal with thepre section, so far last ite itried it but had a bad insulation in teh chips tab, and it was sending 30 something volts at the output. Right now i just put a new insulating mica and washer and itŽs OK as far as the DVM says. IŽll try it and post afterwards. thanks.
It is different Žcause i used Mr. Daniels W schem for the chip part and from there he rest is by yours, so oŽll try and see what i get
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Old 21st June 2013, 02:34 AM   #128
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sound is not ok and have like 1.6 V ofset at the output, loud buzz when i remove the input signal, going back to check grounds
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Old 21st June 2013, 02:38 AM   #129
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i think Mr. Andrewlebon pcb is missing input and output pads
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Old 21st June 2013, 04:25 AM   #130
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i think Mr. Andrewlebon pcb is missing input and output pads
yes just a quick pcb to check if schematic is ok i have tested amp on 2 ohms 4 15 inch speakers in parallel FULLY SATISFIED with performance of amp so i am designing stereo
pcb with 2 output pairs per channel so they can be bridged or used as stereo

warm regards
andrew lebon
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