Protect line from 48v

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Hi everyone.

is there a solution to protecting a line instrument from 48v phantom power.
Basically what im doing is wanting to run a line input on my mic pre. I dont like the idea that every time you have to switch off phantom power. cause of course i will forget. So without complicated rerouting im wondering if there is a solution without degrading audio signal.
would something like the standard hot plug/esd circuit work?

thanks
 
If you want to add a DI feature (Line in) on your Mic preamp I would suggest that you use a seperate Input Buffer for the DI/Line Input.....

You could use a dual opamp (one as a Buffer and one with adjustable gain) that will output to your Mic preamp after the INA217 but before the Line driver stage so you will have unballanced inputs (Like most Line and DI inputs) but have Ballanced outputs.....

You could make it so when you stick something into the 1/4in Input jack it also disconnects the Ina217 from the Line driver stage so no extra noise is introduced or if you want, it could sum the Mic preamp signal with the DI input signal and give you a Ballanced mono mix of both......

I would strongly suggest that you do it this way or in a simular way because the INA217 isn"t really designed to handle Line inputs and it also has a much reduced performance at higher Input impedances .......

My next Rack of Mic preamps based on the INA217 are going to have DI/Line inputs useing pretty much the same topology I just talked about, but I have so many projects on the go right now (One 20w Guitar amp(Opamp Input Discrete Output), One 100w Bass amp(based on 2 LM3866 in Bridged mode) and a 75w Guitar amp(That is fully discrete with a High power Darlington output stage)that I don"t know when I"ll get arround to designing it.......


Good luck
 
Hi Impsick,

Yes I have used eagle But I find it very hard to use, Much harder than I thought....I actually haven"t really been able to do anything with it yet as it takes Practicly forever to find even the most basic component and I don"t have the time or Patience to to do this with every Part, I actually can"t find pretty much any Parts that I use regularilly......

I"m sure it is a great program for those who use it but I haven"t been able to do a single thing with it and I have spent several hours trying to tigure it out.....



Thanx
 
Minion check out this layout.
see how pins 1 & 4 from the jensen, go to the THAT1510 / or INA217 after the diodes. is there any potential problem here? do you think this would work?
 

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Yes, the 47uF caps are for blocking the 48v DC Phantom power so I would connect the Jensen between the Caps and Diodes or between the Diodes and the INA217.....

The INA217 schematic says to use Non-polar Caps if turning off the Phantom power but I have found that You can use Polar electro"s without any problem......

Cheers
 
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