Tda 7293

[Slib]

Hey
I have a marshall 150 valvestate and need to replace the tda 7293s. now on the site mouser there are two different output power. does anyone know which one i need to purchase? there is 50 or 100 watt output
thanks
nic

[Enzo]

Go back to Mouser and enter "tda7293" into the search window. I only get two responses, the TDA7293V and the TDA7293HS. Both are 100 watt ICs, I am not aware of a 50 watt TDA7293. I would expect a 50 watt IC to have a different part number.

Note two things.

One is that the only difference between the two parts is the wire leads. The two differ in how the legs are shaped, the V version is intended to be mounted vertically - sticking up from the circuit board, like on your Marshall. The HS version is meant to be mounted flat against the circuit board. Electrically they are the same part.

The other thing is that Mouser doesn;t stock the TDA7293HS version.

That leaves only the TDA7293V, which is in fact the one you want.

I note that you did say plural. One should always replace both of them when one fails, even if the other one seems OK.

[R.G.]

Yeah, what Enzo said.

The TDA7293 is an interesting chip. On the surface of it, it gets around the power limitations of its obvious competitor, the LM3886, by having a much higher power supply capability.

However, the killer in all power applications is how to minimize waste heat, and how to get rid of what you can't minimize away. The package of the TDA7293 is the same size (more or less) than the package of the LM3886. It uses MOSFETs for output devices, so it generates more waste heat in the output devices for the same power output, and has the same overall operating setup, that of a class AB complementary amplifier. So how do they get more output than the LM3886?

They don't. You're stuck with how much heat can get out the metal heat sink tab. The TDA7293 has a built in provision for using a second device for a current-sharing slave. So the real way they get to 100W is to use another chip as a slave.

I have read that the 7293 is touchy about how you sequence the power supplies and exactly where what is hooked up. So replace both chips, get it running and get it back into the owner's hands before it blows up again.

Enzo's advice can be extended to output transistors. If you have one of a pair dead, replace both. The extra $5 in parts is cheaper than treating the ulcers you'll get.

[Enzo]

In the real world, what I find them sensitive to is connecting the power connections - the cables down to the rest of the circuit - while there is any charge left in the supply. You can run the rest of the amp with the power modules unplugged while you make tests. But if you have fired it up recently, always check the power connections to make sure the main filter caps have fully discharged before re-connecting things. Discharge them with a clip wire if necessary.

What happens when you connect the cable with some voltage still stored is that the pins of the connector do not make contact all at the exact same time, so voltage may be applied to one pin before the other makes contact. From the IC's point of view this can seem like the same thing as a reverse voltage coming at it. If you see a tiny spark at the connector when plugging it in, hold your breath, it may have just fried the new IC. This is more or less what RG said but in different terms.


And to add to RGs other point, getting heat out of them is critical. That is why they have the little CPU fans blowing on them. Those fans absolutely must be running, and if the fan bushings are getting noisy - the fan make noises other than just air blowing - then the fan is probably running below speed. Get that fixed.

[Slib]

Thank you both for your very fast replies. Appreciate all the help you have provided! I will replace both of them and see how it goes
Best
Nic