1

MP512 Microphone preamplifier / Re: Phantom Power At About 4.5v

« on: March 30, 2023, 06:18:06 PM »

There is about 1mm between the transformer and the pcb. The relays as well as c4 are in the correct direction. The value of r3 is correct and the preamp is receiving 48v with the switch off. The pre otherwise works as expected.

2

MP512 Microphone preamplifier / Re: Phantom Power At About 4.5v

« on: March 29, 2023, 06:20:16 PM »

I've only been testing disconnected. It drops to about 3.8 with a phantom powered mic connected.

3

MP512 Microphone preamplifier / Phantom Power At About 4.5v

« on: March 29, 2023, 05:43:35 AM »

I'm a bit at a loss. Everything else about the pre works correctly. I can trace the 48v coming from the switch at roughly the correct voltage all the way to r1 and r2. On one side it reads 45v and the other it reads 4.5v. I can't find any obvious problems.