Re: 40M QCX problem uponpower up


Glen Leinweber
 

Bill,
Have reviewed this thread and realized we could learn more about the unwanted audio tone
just by you listening to its quality. Can you answer these questions:

  • What frequency (lower than sidetone, higher)?
  • Is its frequency stable when you make changes to volume, or when you add the sidetone?
  • Is it a "pure" tone, rather than raspy?
  • If you change to different earphones, does the tone change in any way?

Hans has said that he's seen an oscillation caused by pots riding at one end.
At 200 kHz ! You certainly can't hear this, but it apparently caused an audible tone in
the audio chain. This kind might be hard to track down without a 'scope.

Now that you can kill the tone by running at low volume, the DC voltage checks should be
done, especially in the audio chain of op-amps - any deviations from those voltages listed
in the manual could help a great deal to narrow the problem area. Can you beg or borrow
a multimeter and let us know if these DC voltages check out?
Glen VE3DNL

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