Re: sotabeams filter installation

howard winwood G4GPF

The onboard LM386 is still used but I have taken the output to the input of the sotabeams filter, the sotabeams filter has two outputs so used the circuit provided by sotabeams (it is on their website) this new LM386 pzrovides the speaker output. The only problem is that you now have two volume pots, one sets the input of the filter so that the red led just starts flickering, the other sets the main volume.
Problem 2 was, no room in my case for a second 10k pot.
Problem 2 solved by AliExpress in the form of a dual 10k pot with separate coaxial shafts. made up a couple of knobs to fit, back one sets filter input, front one sets main volume. You can buy the pair of knobs but I had the facilities so made my own.
the track that needs to be broken is the audio out pin of the analogue connector on the front panel stereo socket board, this is the brown wire, the track goes to the phone socket.
take the audio output from the brown wire (now isolated) to the input of the sotabeams filter. the new speaker out from the second LM386 goes to the other side of the break i.e the phone socket.
mMy second lm386 was built on a piece of perf board 4.5cm by 2.5cm or 10 holes by 16 holes. The sotabeams filter sits in the bottom of a small plastic box 6cm * 5cm * 2.5cm, the amp board sits on top of the filter
with a piece of credit card plastic between the two. Just make sure the pushbutton on the filter board is not pressed.( i made a small cut out in the plastic!)
i used a spare 8 way wired connector that came with the enclosure box to plug onto the filter board, the other two pins 9 and 10 , 9 is not used 10 is another earth so not really needed, i used this pin to connect the two led's to ground. Sounds a lot worse than it is, I mounted the box as near the front panel, left side looking from front, as possible to keep the wiring short .
Howard G4GPF

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