Hi all,
I made a very nice preamp using THAT 1512/1646 chips. The schematic is the standard one with minor changes. I gave it to a friend and he's using in his studio recording great musicians.
BUT... another friend is experiencing some noises with 48V. The noise appear only with some microphones (e.g. neumann u87) or without any mic plugged.
The power supply use an external transformer (2x18/2x650mA), 7815/7915 for the chips and the schematic taken from the G9 for the 48V. I modified the schematic by making it doubler and not tripler and replaced the trimmer with two 24v zener in series.
Simulating in LT Spice the 48V should be perfect, but in real life it produces some noises. The noise is like pops and cracks, not hiss or hum (I attached a sample whitout mic plugged, I don't have a u87, and 70dB gain).
I tried also the original G9 schematic, but the noise is the same.
I don't know what to do or what to check.
Unfortunately I don't have an oscilloscope.
Any idea?
Thanks in advance!
PS. sorry if my english is not ok, I'm italian and so I'm better at eating then learing foreign languages.
