1073mic pre 48v & led indicator problem???

hello,
after many tests with my 1073mic pre,when I want to indicate 48v with a led it makes a (big) problem (transistors=bc184 starts to oscillate :evil: )

I'm using a simple ON ON switch.

I explain me : I use the same position on the switch to supply 48v at the xlr input and to have the correct supply to the led via a resistor.
As soon as I put 48v on, the led illuminate correctly and...I have some oscillations.... :?:
is this the good reason or is problem coming from anything else?

Any idea :?:
I've made before a search on the forum and here is a result :
http://www.groupdiy.com/index.php?topic=17809

Thank you

(edited title)

A very simple way to add phantom a power LED to a Neve circuit is to use a DPDT switch with one half feeding the +48v phantom power, via 6k81 resistors to pins 2 and 3 of the mic input XLR. Use the other half of the switch to feed the 24vdc power (used to power the Neve circuit) to the LED via a 1k5 1-watt resistor to audio ground.

As for which ground is which (Earth/chassis vs. audio/psu ground) do a search and you will find much discussion on properly grounding Neve circuits.

Hope this helps.

JC

Hope this helps.

Click to expand...

yes :thumb:
I'd like to know why I have this problem (transistor oscillations), but the most important, you give it to me
Thank you :wink: