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Original Message
SET Headphone amp
Posted by OldNuke on August 1, 2016 at 22:14:32:
In the spirit of not bothering Mike on every little problem, I'm posting here for help. I've built a 45 SET parafeed amp for headphones/speakers (Oppo PM3's at 28 ohms mostly). I can null the 60 Hz hum but have a constant 120 Hz hum (or background since its on AC heaters) that I'd like to damp or eliminate completely. Also I have only a 12th turn of volume pot now (with a 75K/33K Lpad on the 100K pot). Mike has been advising because the amp is with MQ plate chokes and output transformers.
My question is to damping the amp without losing the great qualities it now has. My next move is to pad the input more to hopefully lower the background hum to the hairy edge with series resistors on the input and keep the magic the 45's give.
I'm looking for ideas and options before resorting to DC heaters, I'm open to rebuilds (already in the plan to improve the wiring layout) and adding parts.
Thanks in advance. This amp is sweet on my HD650's but I need closed back phones for my office cube.