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In the Forum: Melquiades Amplifier
In the Thread: The one-stage Melquiades.
Post Subject: LF limit in single stage and Sowter mumetal coresPosted by cv on: 5/1/2007
Hi Romy,
Agreed about the S2 transformer being the most prominent it is here I think that mumetal will shine. I should have said that I was referring to the upper S2 covering 1k-12k or so.
I wasn't too clear earlier - when I suggested rolling off LF for the S2, I didn't mean at the x/o frequency. I was thinking more around 200Hz or so. This will ease the work of the single stage melq and on the mumetal, which can't handle the flux that comes with LF. It may be difficult to get 2W at 500Hz with the biggest core Sowter can do.
Actually, that applies to the usage of all small core transformers - you must limit LF before the output stage or risk saturating the core; even if the speakeror OPT doesn't see any LF power, it's the voltage swing on the primary that determines the core flux.
The exact Sowter model I used was custom but all of Sowters stuff is in a way. Just need to spec out the Lpr, turns ratio, dc current and power at given frequency and if possible they will build it at no extra cost to the "standard" models.
Alas I have no time these next coulple months to build anything but would like to try it out when my horns are eventually delivered.
My concerns in giving the mumetal an unequivocal recommendation is not that you may simply prefer amorphous, but rather that it could sound rather different to amorphous (esp. with the lower S2 driven by amorph).... hence my offer to purchase them from you if unsuccessful. That mumetal core material is getting more expensive and difficult to get hold of. I can use the OPTs for a 6e5p spud or I can always use a diffeent bobbin with the laminations and restack them for a different application!
The issue I had with my mumetal OPTs is very noticeable magnetostriction - core singing along with the music. But they had a rather larger airgap which wouldn't have helped.
Anyway, the offer stands - if you'd like to try them at cv's risk, just let me know the spec and I can optimise with Brian.
Also bear in mind that the winding geometry and materials affect tone. To my mind, the masters here are Pieter from Tribute and Dave Slagle, both of whom build wonderful transformers. Bud has some fascinating ideas but I have not been lucky enough to hear his ironware yet.
regards
cv
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