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Old 9th April 2004, 06:18 PM   #1
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Unhappy TDA 7293 parallel problem !

When I turn the amp on (with mute/st-by pins floating in the air) nothing happens. When I try to connect mute/st-by pins to GND both chips explode

Does anyone know what could be the problem ?
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File Type: zip modular tda7293 pcb.zip (13.5 KB, 304 views)
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Old 11th April 2004, 10:37 AM   #2
BN is offline BN  Germany
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Hi,

I think, as long as StDBY and MUTE pins were floated, the amplifier outputs were disabled and Mute was enabled. This is a secure state. When the pins were grounded, then the amplifier outputs became active. When then the chips explode there are two possibilities:

a) There is an error in your circuit, this means your circuit is different from the circuit given in the 7393 datasheet for parallel connection.

b) Unfortunately 7293s explode or are dying the "silent death" (without smoke, fire and flying cabinet parts) due to reasons, nobody can explain (perhaps STM can). This happens only with parallel 7293s. A single 7293 normally works fine and stable. This was reported in German audio forums and this is my experience too.

A fact is, that the parallel mode description in the 7293 datasheet is incomplete. What is the maximum n? What is the maximum load for output pin of the master, how much is the impedance of the input pins of the slave and so on.

But also it is a fact, that some amplifiers with parallel 7293 are working well. For example Linn has an High-End amp with parallel 7293. Some companies in Germany sell amp kits with parallel 7293 and the customers are obviously very pleased.

Bernhard
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Old 13th April 2004, 07:34 PM   #3
ir is offline ir  New Zealand
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if their mute circuit is anything like the LM series one you can't simply ground the mute pin, you need to run it to ground via a resistor whos value is equal in KOhms to the value of the voltage rails (eg, +/-32V rails means use a 32K resistor, 22V rails = 22K etc). i've never tried just straight shorting to ground myself but i'd assume it's really not a good idea.

the standby pin should be active low however so leaving it floating should infact mean standby is effectively off
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Old 14th April 2004, 07:23 PM   #4
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Quote:
one you can't simply ground the mute pin, you need to run it to ground via a resistor whos value is equal in KOhms to the value of the voltage rails
I haven't connected them directly to the GND. I used recommended circuit from ST datasheet (3 resistors, 2 caps and 1 diode).

I haven't told you the whole story. At first, i already had pover supply 300VA, 2x40V. Also, i have 4 ohm speakers. So, i decided to build new amp. Driving that speakers with supply voltage of +/-40V with only 1 chip isn't recommended, so i decided to use parallel mode.
Now, after burning several chips, i finally decided to rewind transformer to have less voltage (2x22V~), so I can use only one chip per channel. I'll try to assemble this amp this weekend with only one chip per channel, and see what will happen.
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Old 4th May 2010, 09:13 AM   #5
Cuda is offline Cuda  France
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This amp work now ?

Any problem with PCB ?
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Old 4th May 2010, 01:57 PM   #6
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The problem was so trivial, I reversed the polarity of bootstrap cap, that's why it kept exploding. If you look at .pcb file in my first post you will see that it has bootstrap cap upside down. I was 6 years younger and greener back then
Recently I made another amp with parallel TDA7293 and this is working without problem. You can see it here:
My parallel TDA7293
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