Amplifier/speaker question

[Nigel Goodwin]

I'm worried that the SBC might have a bridged PWM output like your Maxim amplifier. I wouldn't know off hand how to attach another amplifier to it.

As I've repeatedly said, you just use one of the outputs - a simple study of how a bridged amplifier works makes it obvious.

 

[DSGarcia]

mneary,
Thanks for the link. I am not much of an analog circuit person, but I now have a general idea of what is going on.

Nigel,
As best as I understand from your comments, I simply use the Left+ and Right+ signals out of the amplifier. Instead of using Left- and Right-, I just use the power supply ground as common for the speakers. Also, I would presume that because I would be using half the amplifier on each channel (because we are ignoring the Left- and Right- signals), then I would have about 3 watts of output instead of 6 watts. That would solve my speaker problem of the 3 watt maximum power.

Should I just let the Left- and Right- outputs float or should I terminate them with a resistor?

I could also use the same trick for the output of the SBC to condition the inputs to the amplifier.

If I figured this right, I think I now have my solution. Thanks everyone.
Dale

 

[audioguru]

The output pins of a bridged amplifier have a DC voltage on them. A coupling capacitor is required for one output pin plus ground to feed a speaker.

The output power is about 1/4 of the bridged output power into the same load impedance. It is because the voltage is half which also makes the current become half.

 

[Nigel Goodwin]

mneary,
Thanks for the link. I am not much of an analog circuit person, but I now have a general idea of what is going on.

Nigel,
As best as I understand from your comments, I simply use the Left+ and Right+ signals out of the amplifier. Instead of using Left- and Right-, I just use the power supply ground as common for the speakers. Also, I would presume that because I would be using half the amplifier on each channel (because we are ignoring the Left- and Right- signals), then I would have about 3 watts of output instead of 6 watts. That would solve my speaker problem of the 3 watt maximum power.

I'm now a little confused?, we were talking about the output of the SBC, which (as AudioGuru mentioned) needs coupling via a capacitor to the input of the extra amplifier stage you're adding. It will also need attenuating, depending on the gain of the extra stage. It won't affect the power output of the following stage, apart from the amount of attenuation/gain you use.

Should I just let the Left- and Right- outputs float or should I terminate them with a resistor?

Just leave them.

I could also use the same trick for the output of the SBC to condition the inputs to the amplifier.

I was talking about the input, is the output IC you're using a bridged one?, if so, using half of it will give 1/4 of the power.

 

[DSGarcia]

The 1/4 power output when using only the + output signals helps me a lot. Maxim does have a 10W stereo amplifier. This would mean, as I now understand, the output would be in the range of 2.5 watts which is well within the range of the rating of the speakers (2 watts/3 watts max) when using only the + outputs. The chip has differential inputs and so I can drive the inputs directly (through a voltage divider and input capacitors) from the SBC outputs.

Now do I have this right?

Nigel, I'm sorry for the confusion. With the realization that I could use only the + signal, I recognized that I could use a higher-power output amplifier to get the correct power output to match the speakers. When I mistakenly thought 1/2 of the output meant 1/2 the output power, the particular amplifier I had in mind had single-ended inputs which meant that I needed to use 1/2 the output from the SBC to create the single-ended signals I needed. The amplifier with the 4x power does have differential inputs so I can now use the SBC differential outputs.

Thanks everyone for all your patience and help,
Dale