K8118 ultrasonic bat detector

Hi all!
I have just finished my k8118, and it seems to be ok, but in my opinnion gain is soooo high even at lower volume that i think that something must be wrong.
is there any way to know if it is ok this way? Too much noise and i think is because of really high gain.
Maybe sending a recording? maybe changing volume pot with another value?

thank you in advance!

The noise you hear may be ok.
The noise is a “side effect” of the mixer.

Yes, you can do the following tests:

  1. Set the volume control to about middle position.
  2. Turn the frequency control to the lowest position.
  3. Now rub two fingers together near the microphones or slide a fingertip over a sheet of paper held near to the microphones. A scraping sound should then be heard in the headphones. Also jingling bunch of keys near the microphones can be used as a test.

If all the tests are ok, I think the unit is working properly.

Thank you!
As i said, i can hear ultrasonic now, but the noise is SO SO strong even at lowest volume that i cant believe i cant do nothing to modify it! :frowning:

what about the idea to change potentiometer value? would it work?

Can you hear some noise even if the potentiometer is in its minimum position?
Should be muted.

It is not muted at all :frowning: You can hear the effect of the volume pot and the effect of the freq. pot, but, in order to record something with my external recorder, i must set input gain to 0.1 !

If this is the right way, i wouldnt recomend this product :frowning: But maybe with some helo i can fix this ‘issue’.

This is not normal. Should be muted when the volume potentiometer is turned fully counterclockwise.
The trace between the potentiometer RV2 and C22 may be broken.
Please make sure C22 is properly soldered and the points +V/2, marked red in this picture, are connected together:

Hi, and thanks for the detailed potential solution.
I have two questions, ilustrated with the attached files.

Is this the right way to number the pins of the Volumen pot?
I suposse REV2A and B are the stereo audio channels, and numbers 1,2,3,4,5,6 are the pins.

If so, you say that 1 and 4 must be connected to the positive pin of the C22? May i do that with an aereal wire to be sure?

(sorry about my english, i’m doing my best…)

thank you very much for your patience and help!


Yes, if you have no multimeter to check the connection, you can add a separate wire between these points to verify the connection.

Please be very careful when soldering to the pin of C22 to avoid damaging the traces on the board!

Hello again!
I have tried your solution and I think it helps, but not as good as I expected. So I would like to know if it is now your best noise quality or if I am missing something else.

Could it be possible that the fact of having used some cables to put some components in a box (pot’s, switch, mics …) has led to this increase in base noise?

Is there a possibility to optimize this cable design to improve this noise a bit?

I would like to share later a couple of images of the box adaptation that I have been able to do.

thanks once again!

There is always some amount of noise due to the mixer.
Here you can listen a sample: