Re: Dynamic mic on ubitx

Dave Bottom <ars.kd6az@...>

That’s essentially the Mic amp of an SBE SB-33 (1961). They work great with dynamic Mics - I used a Turner high impedance Dynamic Mic on mine as well as the SBE Desk Mic.

Virtually all SDRs and most QRP radios expect an Electret Condenser Mic. They have high output typically and brighter audio than Dynamic Mics (mechanical design differences) so they tend to be preferred over Dynamic Mics . Every manufacture’s VHF/UHF Mobile and all handheld radios use Electret Mics. 

Most PC sound card headsets will work but the stock uBITX needs more gain hence the resistor change.

Dave WI6R

On Feb 24, 2018, at 10:11 AM, Walter <W9KJO@...> wrote:

Dave wrote,

"Modifications to use a Dynamic Mic.
Referring to the uBITX Schematic.  The Gain of the Mic PreAmp is controlled by R63 in the Emitter of Q6 to C62/R64.  It basically decouples the audio bypass of R64 by C62 to limit gain for the high output Electret Mics.  Replacing R63 with a Zero Ohm resistor and putting a 10K at the Mic input should allow a Dynamic Mic to work now with a Mic Gain Control.  Also R60 that supplies Mic BIAS to the Electret-Condenser Mic needs to be removed.  If there is not enough Gain still, you might have to reduce the value of R64 to maybe 470 Ohms or so.  If you cannot look at your transmitted signal on a scope at least listen to your audio on another receiver to verify you are not causing distortion.
More Gain for the Electret Mic
To simply get more gain with an Electret Mic you might try dropping another 47 Ohm chip resistor on top of the existing R63 by soldering another chip resistor one end at a time.
Dave WI6R"

Has anyone actually performed this mod?  Does it work?

73, W9KJO

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