THAT1510 quesition

[nonoxxx]

Hello,

I started to make a mic preamp with the that1510 chip and when looking at the documentation of the chipset.

I wander what is the purpose of C4/C5 and R3/R4 on the figure 5 , I know that the caps are here to block the 48 v phantom power and also blocking the 15V but the resistors are supposed to make an high pass at 720 (approximatly) wich is pretty high.

It seem to be the correct design because FiveFishaudio and www.diyrecordingequipment.com are using the same filter value on their transformerless preamps, but I would like to know why lol.

http://www.thatcorp.com/datashts/THAT_1510-1512_Datasheet.pdf

Thanks

[ElectricDruid]

C4/C5 are definitely to block the 48V phantom power from coming back into the chip, which is only powered from +/-15V. If you've got the phantom power on, your mic signal is riding in on top of 48VDC. That requires hefty DC blocking.

R3/R4 look like they're probably basic current limiting protection in case of an overload, but I'm not sure.

[anotherjim]

D1 to D4 are overvoltage clamping diodes. R3 and R4 are current limiters in case the clamp diodes ever conduct - we don't want those diodes blowing open circuit as it would lose protection. Note that those components are probably designed in against some catastrophic event such as an adjacent lightning strike inducing seriously big voltage spikes.

The high pass of C4/5 should be seen against the input resistors R1/2. R3/4 are sized to be negligible in there. It's more like 6Hz.

The 6k8 value of resistors R5/6 should be remembered. 6k8 is the standard feed resistor for 48v phantom power into balanced lines.

[PRR]

http://www.diyaudio.com/forums/instruments-and-amps/327176-mic-preamp-that1510.html