[aprssig] GM-300 speaker output

[Dave Baxter]

Use a low ohm resistor in place of the speaker to keep it's OP stage
happy, and a simple differential input OP-AMP stage to get the audio off
the resistor.

Just musing what I did for something similar a while back, to get clean
audio out of a speech recording/playback IC.  (for a contest calling
machine)  I also used the "common mode" DC bias to signal the end of
playback.  Maybe the radio does something similar in sympathy with it's
squelch?

Or, as you say, a small audio transformer.

Does one side of the speaker have more audio than the other?  Again,
just musing.

73.

Dave G0WBX.

> -----Original Message-----
> From: DALE BLANCHARD [mailto:wa7ixk at embarqmail.com] 
> Sent: 29 September 2009 05:54
> To: TAPR APRS Mailing List
> Subject: Re: [aprssig] GM-300 speaker output
> 
> 
> ----- Original Message -----
> From: "Scott Miller" <scott at opentrac.org>
> To: "TAPR APRS Mailing List" <aprssig at tapr.org>
> Sent: Monday, September 28, 2009 9:20:24 PM GMT -08:00 
> US/Canada Pacific
> Subject: [aprssig] GM-300 speaker output
> 
> What's the best way to hook up a GM-300 with floating speaker 
> outputs? 
> With an isolation transformer, or is there a simpler way that 
> won't blow up the audio amplifier?
> 
> Scott
> N1VG
> 
> _Most late Motorola's use a 2 ohm speaker coupled directly to 
> the out put.
> Saves using a transformer and makes the radio smaller.
> None of the speaker wires may be grounded with out blowing the output.
> Using a transformer is OK. Would also allow for hooking it up 
> to a one side grounded speaker. A 3.2 ohm input transformer 
> will work if you can find the correct impedance output for 
> whatever speaker you have..
> Dale
> 
> 
>