Golgoth
Well-known member
I just installed a vintage LA3A in the racks, .5U above a Lexicon PCM 42.
While working well when the PCM is off, the LA3A is picking up a bad 100Hz (and its harmonics) hum, from what I assume is the PCM power transformer when that unit is powered on. No other gear around it in the racks seems affected by that PCM 42 (a PCM 70 sits directly under the 42, and a DBX 160 sits left to the LA3A). The PCM's output itself is very quiet when used, but the power transformer is loud.
Are LA3As prone to picking up noise? Or are PCM 42s known to have noisy transformers?
I've read they use custom wound transformers that might be hard to replace?
Below measurements are both of the LA3A's output, gain knob at 0.
PCM off:
PCM on:
While working well when the PCM is off, the LA3A is picking up a bad 100Hz (and its harmonics) hum, from what I assume is the PCM power transformer when that unit is powered on. No other gear around it in the racks seems affected by that PCM 42 (a PCM 70 sits directly under the 42, and a DBX 160 sits left to the LA3A). The PCM's output itself is very quiet when used, but the power transformer is loud.
Are LA3As prone to picking up noise? Or are PCM 42s known to have noisy transformers?
I've read they use custom wound transformers that might be hard to replace?
Below measurements are both of the LA3A's output, gain knob at 0.
PCM off:
PCM on:
