开云体育

Hello
I 've just test my new scratch build uBITX exciter,
I found that the RX sensitivity is good compare to CB rig Superstar 2000 at 27.305 MHz.
But it has the issue, the audio volume is not adequate.
I think the problem probably is in the preamp, not the LM386 amplifier.

Could someone please give suggestion or schematic for the better AF preamp ?

I don't have capability to find or design the proper preamp schematic,
I make stupid and simple existing preamp and put in front of existing preamp plus inserting a 10k trimpot,
this make the volume sound so much louder and adequate,
but the sound is quite distorted and the maximal potensiometer volume could not exceed 80%,
otherwise it was motor boating.

Note, the 45MHz filter is LC BPF, BW = 1.5 MHz ( yes MHz)
The Si5351 DDS is PY2OHH 3 clock, with independent frequency setting.
Only use 2 DDS clock, the 11.509 Mhz osc is a VXO.
thanks.
Regards
INDRA

Hi Indra,

i also build a ubitx by scratch. My solution you can see in the circut diagramm. The audio preamp has a gain of 40 dB as lowpass with cutoff near 3kHz. I also had problems with motorboating of the audio PA. The solution is decoupling the 12V DC with 4,7 ohm and 10000 uF. See below in the circut diagramm. It works very well without distortion and overload. See MAX9314!!! I hope it helps.

73 de DF1EA, Chris!

Hello Chris