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In Reply to: Re: Your bypass C's posted by Tre' on April 12, 2007 at 09:51:58:
Hi Tre:just a few comments\observations
:::A good output transformer that will do 2-200k is hard (expensive) to find?:::
I don't know... 10hz to 100khz =/- 1db tranneys are out there. And I've seen PP output transformers with even wider bandwidth.
It takes a special design... a good design... to acheive this extension of bandwidth on top and bottom but it can be done.
Heck, there is a drawing in the Peerless archives... where on the bench a small cap was put in para across one half of the pri winding to take out a small blip in the FR (out at 250 khz)....
there is a Freed PP output trans.... that sails way out over 200khz and goes down below 10 hertz--- it was a very evloved coil design with all of the capacitive and leakage gradients carefully controlled and thought out. Had to be a "stellar" OT cause it was used in an amp with 80db of feedback!!!!
that said--- i've said many times--- to me freq response is about the thirteenth most important thing in a transformer design--- and getting good bw top and bottom is not gained by aiming at that parameter directly but usually is the result of doing the first twelve most important things well.
and with all of this said--- it is perhaps moreso important to get the bottom end "tuned up" properly--- i.e., to focus on good bottom end response--- simply because that is where the core has to work the hardest--- i.e., where the flux density will be the greatest. So a wimpy bottom end not only has poor FR--- but will also tend to exhibit a much greater degree of core generated harmonic distortion as well. so if you want good distortion free response at 40, 30, or 20 hertz you better design the iron to behave well an octave or two below that....
:::Even if we are using a transformer that is rolling the top (or bottom), do we want the circuit to roll the top (or bottom) more?::::see my notes above re: distortion and bottom end response.
where and how the top end rolls off is largely determined by coil geometry characteristics... above 1, 2, 3, 5 or 10khz the core can conceptually be removed from trans in explaining the behaviour of the device.
And at high frequencies the flux density of the core is very, very low and tends not to be a large contributor to the generation of core-induced harmonic distortion.
:::Maybe, to keep the transformer out of "trouble", we do want to roll the extremes?::::
nah... more important to tailor your circuit to the capabilities of the transformer. If your transformer has good phase response (and good FR and low THD) from X to Y... then it won't be the limiting factor. And you should be able to deploy a wider BW circuit without running into gremlins.
again... all of this said about bandwidth and freq response--- I'm responding to the technical issues--- not endorsing or claiming that FR in-and-of-itself is the barometer (nor sole determinant) of sound quality in an amplifier.
msl
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Follow Ups
- Re: Your bypass C's - mqracing 10:28:34 04/12/07 (3)
- Re: Your bypass C's - Tre' 18:01:48 04/12/07 (2)
- Re: Your bypass C's - mqracing 18:37:42 04/12/07 (1)
- My bad - Tre' 19:11:32 04/12/07 (0)
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