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Stu, is this noise you refer to a speaker noise (60hz hum) or physical noise (xfmr hum) from the amps?
Thanks Frank ! - Sorry for not explaining the noise more - YES , its 50 hz hum . Im using Electro-H 6sn7's . My output stage filament windings ( two sets ) naturally needed to be phased correctly ..I did this on the bench with the DDM , so as to get both banks wired correctly with pins 7 & 8 working together .
However , what wasnt known by me till now , is the relavence of the phasing of the Driver stage toroid winding for pins 7 & 8 for the 6SN7's . Im also aware that the original amps had EI style transformers , and mine are made with all toroids . Thankyou for discussion
My pleasure Stu, just don't jump ahead too quick for me!
My amps are MA 1 (12 tube) with 12SX7 input/driver/cascode and 12SL7 CCS.
From the get-go, one amp has had noticable 60hz hum when my ear is near the speaker, even with the stock 6SN7s, and the other is quiet. (I'm in the US 120V/60HZ, I know you're down under 220/50). All my 12V filaments are driven from an e-core tranny separate from the toroidial now, (it used to have V1 & V2 off the toroidial and V3 & V4 from an ecore) and both amps are wired the same. When I get a chance, I'll invert the filament supply of the offending amp and see if that makes any difference.
YES - YES & YES !
I feel exactly the same way , and yes , The sound you hear is only when I get right beside the speaker too . Enough though , that after even quiet listening , youre senses get so tuned to detail , that this is when the humm is picked up . Right at the point when tracks are muted , or ended , or starting . Eureka - Frank ...I cannot promise anything , but both of my amps had this issue at first . I corrected one in the workshop , and asked a Fitter what he thought ..Now , I can tell you , his deaf ears heard the diff in the workshop ...( ear to speaker , muted input ) . The second amp , I built with the toroid wired the same ( ie , colour coding ) . However , I note that at a quiet session with Newform ribbons & Ceramic Bass , we hear humm on the 2nd amp in between tracks . At work , I decide to swap the winding over , visa versa for a double check ..and YES , its now reversed from the same colour coding that was supplied from manufacturer . Seriously Frank , a BIG thankyou for responding to this , im a newbie to building amps in this league - I mean , ive built some P/P but not OTL , untill now that is . Im stoked that you have noticed something . I have two amps , and both should be the same ..but were not ...NOW they are ! Cheers Frank - good man
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