Re: uBitx has a bit too crispy / semi-distorted audio even on low signal levels #ubitx #ubitx-help


Good Mike,

To make it ultra neat: solder back the diode and cut the track inbetween the diodes. Solder a fixed resistor
between the cut track (you need to scrape it but a resistor may fit between the two diodes pads!).
Not forgetting to measure the value you have currently adjusted the preset!

Just for information please check the DC voltages on the finals CBE points.

I guess the diode voltage drop is less than that of the transistor Vbe! I hope Farhan is listening!
This issue would not have been there if there was one more transistor and DC feedback from output
to input like an opamp!


At 17/06/2018, you wrote:
Did the biasing mod. That solved the crossover distortion issue. I took a 500 ohm pot and paralleled that with a 125ohm resistor. The mod doesn't look so good  (LOL) but it works. One of the transistors became warm if the voltage difference due to the pot became too large. I adjusted this while feeling the temp and listening to  a cw carrier: low distortion AND low temperatire, became the setting point.
(Disregard the screened cable in the lower left of the pic. That was the tap to my external amp, before biasing the original amp more properly).

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