API-312 with Balancing Board and Sowter 4220 Transformer

[Harpo]

sorry, in the test which i was doing i wasnt using a mic i had it patched into the patch bay and was using it to sum a mix.
on the setting where the audio passes through the highest when the 48v is engaged...

Very effective way to kill a lot of your sending devices when kicking their butt with +48V DC and much more elegant than using a hammer. Good luck continuing with this method.

 

[Spencerleehorton]

hi harpo,

i dont really get what you mean but thanks!! 

regards

Spence

 

[Harpo]

i dont really get what you mean

A lot of devices (D/A-converters, compressors, equalizers, ... without galvanic/transformer insulation) are missing a protection from accidentally applied phantom voltage.
FI the GSSL has 100uF/25V caps connected to its output to block any DC from the GSSL when feeding the next device. No problem for usual and expected operation. Now your next device (your API-312) feeds +48VDC back to the GSSL output thru the 6K8 resistors. There are 47K resistors on output in the GSSL, acting as voltage dividers, but with a +48V feed, the caps still see a 48V/(6K8+47K)*47K=42VDC across its pins. If these caps are only rated for 25V, they probably will blow. If they are fitted as shown on schematic (caps negative side to output, positive side to opamp) they sure will blow from reverse powering.
What you presume is a HPF might be the dying caps of connected gear when being hit by phantom voltage (the caps won't instantly explode because of the 6K8 current limiting resistors).

 

[Spencerleehorton]

HI Harpo,

noted what you have explained thankyou, but this API-312 is only patched in on its own into a line in of my GS3000 mixer, i am using the SPDIF output from my 96 i/o into a tascam DA-88 and using the DA/AD converters to then sum this signal back into the digidesign 96i/o.
When the unit is just used on its own it does this lowcut thing?

regards

Spence.

 

[Harpo]

When the unit is just used on its own it does this lowcut thing?

On its own the unit does nothing (maybe light up some LEDs on the frontpanel) and on its own (nothing connected except AC mains) you will not notice any hpf or lpf or whatever. The device that connects to the input of your API-312 is in danger when by activating phantom voltage you send common mode +48VDC to the outputs of your FI DA-88 (thru your probably passive summing device or a direct connection).