Need help with TDA7294 bridge circuit with 18V power supply, in to 4ohm speaker load - No sound

[meidinad]

Hey all,

I copied this TDA7294 bridge circuit from the manuall:

To this schematic:

I have checked and double checked the schematic and it seems accurate to the manual's circuit. All parts are correct values to the manual's circuit. The PCB board is correct to the schematic that I made. All solder joints are done well without bridging.

I am powering it with an 18V, 300mA power supply.

I am using this power filtering circuit in to the power bridge amp's power circuit (substitute 18V for 9V).

I am running it in to a 16ohm speaker load.

The application is to test guitar pedal overdrive circuits.

I am getting no sound and I can not figure out why.

Based on this information, does anyone have any theories as to why? Based on the chip's specs, it should be able to be powered with 18V.

Any help would be appreciated.

Thank you!

[Peter BENSCH]

Welcome, @meidinad​, to the community!

I don't quite understand your problem yet, so I'll try to summarise it again:

1. you want to connect two 100 Watt amps in BTL, which is typically used to (theoretically) quadruple the output power by doubling the output voltage
2. you start by talking about 18V and 4 ohms load, but you do not really supply the TDA7294 symmetrically with ±18V, but only with a single supply of +18V
3. then you are talking about a power supply of 18V and 300mA,
4. plus a power filtering circuit
5. and finally a 16 ohms load.

Now, to the aforementioned points:

1. what parameters do you actually want to achieve with the amplifier? Did you even switch on the amplifier with the signal St-By/Mute by putting the signal on +VS?
2. Do you realise that the voltage supply of min 10V to max 40V given in the data sheet is for balanced operation, i.e. +-10V...+-40V, and not for single supply?
3. do you seriously want to use a supply with 18V and 300mA, which could deliver a maximum power of 5.4W, but not really >>100W?
4. Such voltage dividers can be used for small operational amplifiers or applications with small currents, but not for a BTL amplifier in this circuit. So you should provide two separate voltages.
5. Approximate calculation: if you would separate the supply voltage to +-9V (which is not sufficient, see [2]) and connect two amplifiers in BTL, you theoretically get (2*9V)^2 / 2 / 16 ohms = 10.125W with a 16 ohms load. Somehow the use of two TDA7294 is clearly inappropriate.

Can you please enlighten me a little?

Regards

/Peter