TDA7293v Parrallel / Bridge Application Theory and Concepts
Ok, so here's the deal. I love audio, and I recently came across this TDA7293v chip amp. I have lots of experience with lm3886 and I am also building a discrete amplifier from Anthony Holten's webpage, the AV800, nice amp! www.aussieamplifiers.com.
Anyway my real question is this, does anyone have any experience with paralleling more then 2 slaves with the TDA7293v?
I am thinking about using 1 master and 3 slaves in a single sided amplifier using current sharing resistors and a zobel network on the output. I would like to run the rails at the +/- 50VDC maximum rating.
After I have constructed the single sided amp mentioned above I plan to take (2) of these, run one with a non-inverted input and the second with an inverted input and use the two amplifiers in a BTL configuration.
Anyone think it's doable? Or am I asking for trouble, any advice?
I KNOW, IT'S TOO MUCH POWER, BUT SOUNDS LIKE FUN TO ME!
Paralleling 4 chips is very hard for routing. Believe me. I tried.
I know that Quekky (also member of this forum) has made amp with 3 chips in parallel and it works well (but he uses double sided PCB).
Linn also uses 3 chips in parallel in his Klimax Twin amplifier (9000$)
Some people say that it isn't possible to parallel more than 3 chips. Maybe no one has ever tried that because of complexity of routing :)
Unless you want to drive very low impedance speakers there is no need for paralleling so many chips. Try to bridge pair of 2 paralleled chips. They will give you 400W into 4ohms (350W undistorted power).
Or if you want more power maybe you could bridge 2 pairs of 3 paralleled chips to get 600W:) I think You would be the first who have done that. But be prepaired for possible failure.
And one more thing. You don't need to put current sharing resistors because these chips don't share any current when paralleled.
Thanx for the good information...
Cro maniac, thanx for the good information. I would have to agree about routing the PCB and it being difficult. I think what I might do is make a modular board, do 3 chips in parallel with an option for the fourth and go from there.
As long as the smoke stays in everything is good!
I'm also working on an LM3886 amplifier with the simlar layout as the TDA7293 if anyone is interested. I will reply back in a while when I find out my results.
One more question, I'm assuming that the difficulty from PCB layout comes from noise and oscillation? I've always done 2 side PCB layout in principle, i saw one board that has a nice star connection with a large pad in the center, I wonder how that worked out.
The real problem with using three slaves in not in the routing.
The real problem is in the drive capability of the input stage which in your application would need to drive 4 output stages. Because these output stages are MOSFET based, they have a high input capacitance, which means slew rate and distortion (and sound) get worse when you parallel the ICs. 3 seems to be the maximum "acceptable" IC count.
So if you want to parallel ICs, don't use the slave mode, which is obviously intended for low cost application. You can easily parallel amplifier blocks based on TDA 7293 (the same way as it is explained in the LM3886 application note, just add up the mute standby circuitry). Obviously, these is what Linn does, with servos dedicated to each of the TDA to ensure proper current share between ICs
Or if you want to use the slave mode, you can always try to buffer the signal between the input stage and the output stage (needs one dedicated IC for the input stage)... or use only ICs in slave mode mated with a custom designed input stage
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