Ping Allen Wright - eliminating hum in phono stages - Doug Flynn

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Ping Allen Wright - eliminating hum in phono stages

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Hey Alan
Several years ago I breadboarded your FVP5A preamp (the phono section only). I changed one part - I use 3V batteries to bias the 6DJ8 grid, so it's probably not fair to call it a FVP5A.....
The breadboard has served me well over those years, but now I've tried rebuilding it into something more compact. I have all the signal circuitry on an aluminium board 10cm x 20cm, mounted on Tektronix ceramic standoffs. I mounted it in my linestage chassis, well away from transformers, etc.
The problem is the !@$&*$&# hum in the thing. It's 100Hz rectified hum. I am using a CLCRC (caps are 250uF) filter after the main filter for the linestage. So basically the whole filter is CLCLCLRC. Is this a problem whacking the phono power supply after the linestage power supply?
Anyway, the hum does not exist when I don't have the RCAs from the turntable plugged into the phono stage. I only get the hum once I plug the cables in (including the grounding wire).
Can you think of why this might be occuring? Also, if I turn the volume up past 12 o'clock the power supply goes funky - it collapses and then overshoots (ie. a couple of times a second it drops from 250V to 200 then shoots up to about 280). This sounds like a bird flapping its wings next to one's ears when fed into the power amp/speakers.
Any thoughts on what's causing this? I don't have any of these problems with the breadboard, but it's taking up too much space (and it's butt ugly)...
Cheers. Doug

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Topic - Ping Allen Wright - eliminating hum in phono stages - Doug Flynn 21:13:56 02/11/06 (2)

Try better interconnect. - sser2 15:15:34 02/12/06 (0)

)eliminating hum in phono stages( - Allen Wright 11:10:58 02/12/06 (0)

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