LM380 in positive ground circuit???

[wb0ldj]

I have a Racal receiver that was designed with a 1 mW line output and a 10 mW headphone output. I'd like to add an LM380 stage to provide a speaker-level output. My big issue is that the receiver uses positive ground circuitry throughout. The entire receiver uses Vcc of -16V, and all capacitors have their + lead connected to common ground.

My question is -- can I use an LM-380 as an audio amp in this receiver by connecting -16V to the ground point on the PCB and grounding the + terminal? I'm not familiar enough with the LM380 internals to know whether this would work. I guess the big issue would be in interfacing the LM380 amp module to the existing signal lines coming from the 10 mW amp stage.

Help!
Thanks,
Mike, WB0LDJ

 

[crutschow]

Below is a typical circuit LM380 circuit diagram.
For your application just connect the Vs connection to ground, and the ground connections to -16V except the bypass capacitors and speaker ground.
Reverse the polarity of the 500µF output capacitor (+ towards speaker)
Also add a 0.1µF ceramic capacitor in series with the input 75k resistor.
The signal input ground will be your system ground.

 

[wb0ldj]

Thanks Crutschow! That will sure make my job a LOT easier!

I was kinda thinking that approach would work, but it sure was nice to hear someone else's ideas on the subject! This receiver is a very strange animal indeed. They were almost all made tor those assorted TLA (three-letter-acronym) government agencies. I think mine came from either the FCC or the CIA. Coverage is AM/FM/CW/MCW/LSB/USB from 980 kHz to 30 MHz continuous tuning!

Thanks again!
Mike Harmon, WB0LDJ