rafafredd

Barry Porter phantom powering schem
« Reply #20 on: January 26, 2005, 09:08:36 PM »


Still can´t simulate because of lack of a proper mosfet spice model in circuit maker...

The DPDT should get rid of squib´s worries. At least it looks like it would, as all the ramping circuit would be disconnected. Still when swtching ON, the 48v would be aplied at the same time on both 6k81 resistors.

Should R3 (discharge) be lower?

BTW, I´m thinking about using just one 48v regulator for all channels in a given unit. Only those eight parts will be on each channel, so I don´t think it will end that expensive...


Gus

Barry Porter phantom powering schem
« Reply #21 on: January 26, 2005, 09:36:38 PM »
R3 should be larger.  Maybe 100meg.  As drawn the gate will only go to 30V.  Thats why I was posting about scaling.

Try R1 1meg, R3 10 meg and C2 10uf.  R1 and R3 form a voltage divider.  With a 48V supply you will want the gate at 10V + 48V >=  58V for the mosfet to be at the RDSon resistance

Was the orignal B.P. circuit tested?  The reason I posted in this thread is because in the B.P. circuit  the gate could only go to 48V:however thinking and looking at the circuit again the current draw of the microphone would pull the source down a little.  I don't know if there was a clever design part to the circuit maybe using the the Drain to  Source  resistance as part of a RC filter with C1 and a way to get a voltage difference for the gate to source voltage

I have not built the circuit I posted about.  It should be built and tested first.

What should happen when switched on the gate voltage will rise.  The mosfet will start to turn on maybe between 3 or 4 volt different between the gate and source and will be fully on at about 10V difference between gate and source

I will look around in my parts and see if I have the parts to build a test circuit

I would not trust a spice sim someone needs to build both circuits and see what  happens

rafafredd

Barry Porter phantom powering schem
« Reply #22 on: January 26, 2005, 09:41:31 PM »
Quote
I would not trust a spice sim someone needs to build both circuits and see what happens


If I can find a proper Mosfet locally, I´ll do it!

Samuel Groner

    Zürich, Switzerland
  • Posts: 2935
Barry Porter phantom powering schem
« Reply #23 on: January 27, 2005, 05:45:25 AM »
Quote
Can you provide us with more info on BPs design? Would be great!


No?  :cry:

Samuel

rafafredd

Barry Porter phantom powering schem
« Reply #24 on: January 27, 2005, 08:22:27 AM »
B Porter asked me not to make it available. As I said he designed this thing strictly for me. And he didn´t knew me. I just emailed him asking some questions about DIY mixer and he said, "I´m going to help you"... So, this guy is great.

I´m thinmking about using the front end in a future transformerless mic preamp project. I really think he won´t mind, now that he is gone. So, I will redraw the thing for this. But I can´t share the originla at the moment. Thanks for understanding.

Still, I´m quite sure I have already sent some people here the original dlocuments...


 

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