Hi Bob, R101 provides bias on the MII. The mic bias is provided by the microphone plug in the MVP. Remove it, and you remove the mic bias.
Shorty, K6JSI --- In [email protected], [EMAIL PROTECTED] wrote: > > At 10/18/2007 14:11, you wrote: > > >But you have a chicken and egg situation, is it the controllers fault > >or the radios? Not all radios have bias and not all controllers charge > >caps backwards. You can solve the problem by removing the mic bias > >resistor from the radio, > > I'd like to do that, but I think I just discovered a difference between the > MVP & Mastr II exciter boards: the Mastr II supplies bias via a resistor > connected to pin 11 of U101 (audio processing IC), whereas in the MVP there > is no resistor - the bias appears to provided internally within the > IC. This is a problem because there doesn't appear to be any way to remove > the bias. > > > installing a non-polar cap anywhere in the > >audio path > > I suppose that's the only choice I have, but since there's already a 1 µF > cap in the controller, the 2nd series cap needs to be a significantly > higher value to avoid the combination of the 2 causing another high pass > rolloff. > > > or replacing the polar cap with a non-polar. > > Can do that, but then I have a 2nd big ugly leaded cap hanging off the > bottom of the SMC board. > > >Take a look at the schematic I posted earlier, it will suit your needs > >but I do not program that well, hence the open source of the hardware. > >If there is any intrest I will finish the PCB, which will measure 1.9" > >X 2.5" and about 0.5" tall and doesn't use any surface mount > >components. > > I appreciate the effort, but for this task I need a ready-to-go solution. > > Bob NO6B >
