Converting a rail-to-rail waveform for a single rail analog amplifier 5

[redtreetoad]

Greetings,
I’m putting together a circuit that uses a digital waveform generator that is supplied by +5V, GND, and -5V. I've fed this output into an OP-Amp that then attenuates the +/- 2.5 Vpp output to approximately 1 Vpp.

This works fine using a PIC to set the frequency, and I can see the output on the scope, etc.

My problem is that I would like to feed this 1 Vpp output to the input of an audio amplifier that only uses a single supply voltage (+12V and GND).

In other words I have a waveform that goes positive and negative WRT to GND and I want to amplify this waveform with an audio amplifier (TDA1516BQ) that only uses a single supply voltage.

Q1: Is this a feasible idea (am I worried about something that should just work)? The reason I'm even asking is that I smoked the first incarnation of the audio amp (which I had to rebuild), but I think may have been poor soldering or connection errors.
Q2: If Q1 is yes, are there any key considerations I should be aware of?

Unfortunately, I'm bound in the design by the waveform generator chip (ML2036) and the +/-5V, +12V power supply.

I thought of using a DC-DC converter to increase the -5V from the power supply to -12V and use a different amplifier design, but the power supply only provides 500 mA @-5V and I need >16 W into a 12 ohm load. I built the audio amp around the Phillips TDA1516BQ chip used in BLT mode.

Thanks in advance.
Mike

 

[Noway2]

Check out instrumentation and difference amplifiers. Analog Devices may be a good place to start. If you are looking for a part to begin with, check out the AD628. I used this in my application, which sounds similar to yours in this respect.

These devices have a reference pin, which will designate the output signal for a zero input. You can aslo typically use one or two external resistors to set a gain and or attenuation factor as needed. What you can do, is supply a reference voltage that is 1/2 of the ADC input and choose a gain factor so that the full scale signal corresponds to your ADC input range and Voila, you have a bipolar signal suitable for use with a single supply amplifier and ADC.

 

[VEBill]

Since the 'digital waveform' is headed to an audio amplifier anyway, can you simply capacitively couple the (presumably audio bandwidth) signal into the amplifier?

 

[itsmoked]

Or use a tiny audio transformer to shift your ground reference to your follow-on amp.

 

[Comcokid]

There is no problem feeding the signal into your TDA1516BQ audio-type amplifer. If you look at the datasheet, Figure 3 stereo-input example you will see that a 220 nF blocking capacitor is suggested. In-other-words, even though it is a 12V powered amplifer, they already suggest feeding it with a signal centered around ground. Capacitor coupled inputs is the norm on many audio amplifers, because speakers don't want to be mistakenly driven at 0Hz or DC. This is what VE1BLL is pointing out.

Now, if you were driving a single supply op-amp, THEN you would typically need to offset the signal 1/2 way between your 0 to 5V rails. But not with the part you are using.

 

[logbook]

redtreetoad,

what you don't say is if your waveform has DC content. If the signal has values that vary at a rate below say 10Hz you may have trouble using the transformer coupling or AC coupling suggested above. If the repetition period is more like 50Hz then transformer or capacitive coupling will be fine.

If you need a DC coupled system for response down to arbitrarily low frequencies let us know.