EMG VLPF 18V problem

[Matei]

Hi everybody!

I am experiencing some problems with my PJX pickups.
They are powered over 18 V (measured 17.3 V) and they exhibit a weird behavior:
sometimes when I plug in the sound cable in the bass, the output is extremely reduced. The VLPF knob acts more like a strange volume knob (loud in the middle, quiet on the sides of the rotation).
Then, after a while (1 2 minutes) a quiet hiss follows (kind of ramping up in volume) and the sound gets cut off.

Some other times everything works out.
I checked the current drawn and it turns out that when everything operates OK it draws about 1.5 mA. When problem occur I get about 24 27 mA.

I tested the pickups directly to the output jack and everything was OK
Also tested pickups to the volume knobs and everything was OK
The only time troubles happened was when the VLPF control was connected.

My feeling is that something wrong happens when I plug in the sound cable and the circuit switches on. Any advice?

 

[RyanOh]

Maybe double check the connections? see notes in diagrams that call for 'reversed connector'.

Invalid Link Removed

 

[Matei]

Hi, thx for the quick reply! I've spent the good part of yesterday checking diagrams. Everything is wired properly.
That's why I went one step forward and measured the currents and so on, but still didn't manage to figure it out.

For me it feels like 18V for the VLPF is a bit too much. It seems less problematic when powered on 9V, but as my bass is wired for 18V testing the 9V version extensively is a bit cumbersome...

 

[Matei]

Hi,

I am coming back with a bit of details:
With pickups on 18 V and VLPF pot on 9 V everything works fine. The system only bugs out when the tone pot receives 18 V.

Any ideas?