warpboy

1073mic pre 48v & led indicator problem???
« on: August 31, 2007, 06:08:03 AM »
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


gyraf

1073mic pre 48v & led indicator problem???
« Reply #1 on: August 31, 2007, 06:19:39 AM »
(edited title)
..note to self: don't let Harman run your company..

rascalseven

1073mic pre 48v & led indicator problem???
« Reply #2 on: August 31, 2007, 10:59:09 AM »
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
"If you dig the gig, do it. -But listen to the signal, not the person talking."  -Keef

warpboy

1073mic pre 48v & led indicator problem???
« Reply #3 on: August 31, 2007, 03:06:06 PM »
Quote
Hope this helps.

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:


 

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