There is a jumper inside the Alinco DX-77T to provide +8v bias on the microphone audio + line If you enable
this Jumper you can use Electret microphones with out having to build a separate voltage insertion circuit.
JP1 is just to the rear of VR14 the Microphone Gain control on the PC board You can find JP1 on the
schematic which came with the radio Just above VR14, and just left of TP1 The bias circuit consists of R338,
R339 and C281 all of which are already present on the board Actual bias voltage will be less than 8v
depending on the load presented by your microphone.
I used a magnifying glass, and a sharp grounded soldering iron to bridge the solder pads JP1 Be sure to open
up the original hand MIC and install a capacitor in the audio line to avoid having DC running through the
coil of the dynamic microphone.
KA9CAR
John Dewey
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I have also seen a mod to change the radio's band plan One jumper sets US Bands, One sets Japanese bands.
Both set EPROM bands and NONE sets the radio unrestricted I saw this information in a copyrighted book, and
once on a news group I have no need to go out of band, so I did not note the details I suspect this would
upset the radio's "band scan" feature, which causes it to scan with in a specified amateur band.
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Source QRZ: The Windows Ham Radio CDROM |
