Phantom power overvoltage protection

[juan_felt]

HI!

I finally decided on building this 9V battery powered DI Box

http://www.muzique.com/misc/guitar_di.gif

What worries me is that, by mistake, someone could send phantom power to it via the mixer and blow the thing up.

Is it possible to add some sort of overvoltage protection? Like a Zener diode?

Thanks!

[tubegeek]

http://www.thatcorp.com/datashts/dn140.pdf

[PRR]

That THAT Corp paper does not address the problem he fears.

Change C6 C7 to 220uFd _63Volt_ *Bi-Polar* (non-polar).

[Seljer]

That THAT Corp paper does not address the problem he fears.

Change C6 C7 to 220uFd _63Volt_ *Bi-Polar* (non-polar).

This

It's also pretty easy to power the DI box itself with phantom power. Look at how this one rigged up the switch to select between battery and phantom power (if the battery is to ever go flat for some reason) http://sound.westhost.com/project35.htm <- Figure 3 at the bottom

[juan_felt]

That THAT Corp paper does not address the problem he fears.

Change C6 C7 to 220uFd _63Volt_ *Bi-Polar* (non-polar).

This

It's also pretty easy to power the DI box itself with phantom power. Look at how this one rigged up the switch to select between battery and phantom power (if the battery is to ever go flat for some reason) http://sound.westhost.com/project35.htm <- Figure 3 at the bottom

That schematic is the one I wanted to build, but I needed the DI to be powered by a single 9V Batt. Is this possible?

[slacker]

Yes you can power that off a 9 Volt battery. Where the schematic shows 2 batteries in series, to get 18 volts, just use one instead, no other changes should be needed.

[Seljer]

Yes, it works fine on 9V. I run mine like so (when not running it off phantom power)  because I'm cheap on batteries and don't need that much headroom.


But do note that the AMZ one has a much better input impedance for use with bare guitar and the gain control is also a nice addition. The way the ESP one is good for low impedance line level signals, not so much for pickups.

[TheWinterSnow]

That circuit in the OP already looks protected, there is no way fro phantom power on either input or output to make its way to the amps, the caps act as coupling caps.  You need to make sure though that they are at least 48v so you don't blow them up, PRR said it, switch them to bipolar caps.  Other than that look at the resistors after the cap on the output, you need to make sure that they can handle the power dissipated if 48v is applied to them.  The 47R will need to be at least 1/4W, preferably 1/2W but the schematic calls for 1/2W so you are good there, the 10K will dissipate next to nothing.

[Seljer]

Phantom power's 48V are always supplied through 6.8kiloohm resistors so you can never draw more than 7mA per line.

[juan_felt]

Thanks for all the replies. Very useful information.