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Re: My 26 SE Headphone Amp Using AC Filaments – A Development?

Posted by fatbottle on December 4, 2006 at 03:38:22

In Reply to: My 26 SE Headphone Amp Using AC Filaments – A Development? posted by Perseo on December 3, 2006 at 19:15:08:

Hi ,
Interesting , I have never had any luck with AC filament heating , found the hum to be too much and the sound a bit on the 'opaque' side . To date I've mainly employed Ronan reg type DC filaments with low dropout regs , batteries and a combination of batteries feeding filaments with a CCS . Next on the list is passive LCL with no 3 legged fuses anywhere . Have you tried some shielding around the 26 ? I have an all battery DHT linestage which originally used the P2 and I just could not nail a hum problem , ditto with an earlier project which used the 1LE3 . The 1LE3 used conventional valve rectified supply with shunt regs and a D cell with dropper resistor for the filaments . With 6J5 and AC heaters , no hum , with 1LE3 and battery filaments , tons of hum . When I placed an Ikea steel cutlery holder over the valves , the hum was gone . On the battery linestage , when I replaced the P2 with a 3A/109 , which has a much greedier 250mA filament , the problem disapeared and I did not need any shielding . I'm still at a loss as to why DHT's seem far more susceptible to these problems

cheers

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