ashpool
Head-Fier
- Joined
- Oct 16, 2005
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I had a partially-populated Dynahi PSU board that I decided to adapt to +-15V in order to power a phono amp that I'm building. I finished the PSU this week, but it's outputting a lot of noise:
I've changed the PSU design for +-15V output by replacing the 120 Ohm resistors with 274 Ohms, the 3.5ks with 3.65ks, and the 50k resistor with a 20k resistor. I'm using a 160VAC 2x18V transformer and LT1084s. (overkill, but it's what I had lying around).
The AC from the secondaries going into the PSU measures just over 20.3V AC and if I replaced the the regulator resistors correctly, the regulators are supposed to be feeding the OPA541s +18V and -18V. The 20k resistor should be the right value for +-15V output and that's exactly what I measure coming out of the PSU, but when I look at the unloaded output of the PSU in my scope, I get that noisy mess above.
Any idea on what's causing the noise? The AC in my apartment is pretty dirty, but this level of noise seems inordinate for this PSU design...
I've changed the PSU design for +-15V output by replacing the 120 Ohm resistors with 274 Ohms, the 3.5ks with 3.65ks, and the 50k resistor with a 20k resistor. I'm using a 160VAC 2x18V transformer and LT1084s. (overkill, but it's what I had lying around).
The AC from the secondaries going into the PSU measures just over 20.3V AC and if I replaced the the regulator resistors correctly, the regulators are supposed to be feeding the OPA541s +18V and -18V. The 20k resistor should be the right value for +-15V output and that's exactly what I measure coming out of the PSU, but when I look at the unloaded output of the PSU in my scope, I get that noisy mess above.
Any idea on what's causing the noise? The AC in my apartment is pretty dirty, but this level of noise seems inordinate for this PSU design...