HELP with making two mono amps in to one stereo amp (with more output power)

[mhj1r]

I know this is an old thread, so I hope you're all still around.
I need a bridged mono amplifier circuit that can drive a 2-Ohm load. I was considering this bridged TDA2003 circuit. I'd rather not have to have a trim-pot on the board to zero out the offset difference, so I wanted to know if I'd be able to AC couple the outputs, as was mentioned before.

Also, will this circuit be able to drive a 2-Ohm load? I've tried to build a circuit using the TDA7350, with an inverting op-amp with a gain of -5 as a pre-amp, but it doesn't seem to be able to drive the load. If I blow into the condenser mic, i can hear it, but if I speak into it, it doesn't seem to work.

Any help would be appreciated.
Thanks!

 

[audioguru]

Bridged and offset-adjusted TDA2003 ICs and a bridged TDA7350 IC cannot drive a load as low as 2 ohms. They are spec'd to drive a 4 ohm load when bridged. The output current is doubled when bridged which would blow them up if they are bridged and have a max output swing into the "dead short" of only 2 ohms.

 

[mhj1r]

Even the bridged TDA2003 cannot drive a 2-Ohm load?

Is there another IC you'd recommend? I'm unable to change the speaker configuration so I'm stuck with the 2-Ohm load.

 

[audioguru]

Even the bridged TDA2003 cannot drive a 2-Ohm load?

Of course not. Look at its datasheet. It is not designed to be bridged and its max repetitive output current is only 3.5A.

Is there another IC you'd recommend? I'm unable to change the speaker configuration so I'm stuck with the 2-Ohm load.

My car has 2 ohm speakers on its back shelf but I have never seen its amplifier to see which one it uses.

Use a bridged amplifier designed for a 4 ohms load and make a video recording of it blowing up with a 2 ohms load.

 

[mhj1r]

I have used the TDA7350 bridge tied on a 2-Ohm load. It doesn't blow up or even get very warm. I can get sound out of it when i blow on the mic, but when I speak into it, my voice is very low out of the speakers.

If I increase the signal into it (potentiometer with signal in at one end, output to TDA7350 at the wiper and other end at ground), it starts oscillating. It's possible that the oscillation is the overcurrent shutdown kicking in.

My guess is that you'd have a hard time blowing up the TDA2003 or TDA7350 since they have short circuit protection.

Would a 2:1 transformer at the bridge output change things? It'd require twice the voltage swing but 1/2 the current.

 

[bountyhunter]

I know this is an old thread, so I hope you're all still around.
I need a bridged mono amplifier circuit that can drive a 2-Ohm load. I was considering this bridged TDA2003 circuit. I'd rather not have to have a trim-pot on the board to zero out the offset difference, so I wanted to know if I'd be able to AC couple the outputs, as was mentioned before.

Also, will this circuit be able to drive a 2-Ohm load? !

YES, depending on how you define "drive a load". I ran that bridge amp in my car driving a 2 Ohm load for many years. The TDA2003 can output peak currents of around 5A (typical) so it can drive about a 10V signal across a 2 Ohm load. Running off a car system of about 14V maximum, that's all the voltage headroom you will have anyway since you will have several Volts used up in the saturation/bias voltages of the power output stages so it will limit the voltage swing. So, yes it will drive a 2 Ohm speaker load and did to ear splitting levels for many years. It might not drive a subwoofer to ground rattling levels, but it will play music.

I don't know if SGS still specs peak output current, but they did back in 1980 when they brought this part out. Their part (as well as the one we did at Fairchild) would put out about 5A peak current typically (I characterized theirs and ours). Continous power is lower, but that allows music peaks into low impedance loads.

 

[mhj1r]

Thanks, that's great to know!
So about the currents due to different offsets, would AC coupling the load help? My application will probably run off of a bunch of AA NiMH batteries totaling 12V.

 

[bountyhunter]

You can AC couple to the speaker if you want. You will need a pretty big cap with good high frequency characteristics.