Re: Express Receiver Audio stage for uBitx

Tom, wb6b
 

Hi,

If you don't need all those audio buffer stages and are OK with the audio output to the speaker, maybe something like this chip to directly replace the volume control pot of the uBitx.

https://www.digikey.com/product-detail/en/maxim-integrated/DS3501U/DS3501U-ND/1642373

This part cost a dollar rather than six dollars. It has the zero crossing detector that the specification sheet says eliminates the "zipper effect" when changing the volume level.

If you don't want to do the logarithmic calculation in software there are logarithmic versions for about two dollars. 

This one, with no "extra" features for only 53 cents.

https://www.digikey.com/product-detail/en/microchip-technology/MCP4018T-103E-LT/MCP4018T-103E-LTCT-ND/2060161

These chips seem to only rate the analog voltage to -0.6 volts below ground. So, assuming they work with negative going analog signals, they need to be in a low level signal portion of the circuit. 

The data sheets are a little weak in their specifications and example circuits, but the Express Receiver looks like it is running the audio through its digital potentiometer as A.C. referenced to ground.

Tom, wb6b

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