LH0021 1.0 Amp Power Operational Amplifier

I'm looking for some ideas to design a power amplifier with tone controls for a Heathkit GR-17 AM/FM Portable Radio. All the chip amps I found have about 50 mA bias current, which would be in addition to the 10 mA for the radio battery current.

I have several LH0021 1.0 Amp Power Operational Amplifier, with 1.5 mA bias current. I realize the LH0021 was not designed as a low distortion amplifier, however, the amplifier portion of the radio may have similar distortion.

The radio battery pack has a connection at the center of the 6 batteries, which can be used for the LH0021 ground connection.

Another option is to modify the radio amplifier tone control circuit to incorporate bass and treble in the feedback loop.

See 10W Audio Amplifier application circuit:


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  • LH0021 sch.png
    LH0021 sch.png
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A couple of points of note - firstly the DS of the LH0021 only shows operation down to 10V total supply, but you want to run at 9V. It may still work OK but there's something of a risk there.

Second - if you use the centre point of your 6 cell stack as the ground then you'll need to add another power switch to fully isolate your batteries when switched off.

It does look to be a very power supply frugal choice of chip. Even classD amps draw a fair amount more current than this sitting idle.