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In Reply to: RE: I measured 80Hy in the secondary..... posted by Tre' on February 24, 2017 at 19:24:39
I wonder if that would be enough for a phono stage with 1K output impeadance?
twystd
Follow Ups:
80Hy has a reactance at 20Hz of 10k ohms.
I'm driving mine with about 400 ohms.
It takes a good size coupling cap.
I'm running a 4.7uf in parallel with a 2.2uf for a total of 6.9uf.
6.9uf into 10k ohms has a -3db point of 2.3Hz, not that there's a whole lot of 23Hz on most of my records but I like to cover all the bases/basses :-)
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
6.9uf into 10k ohms has a -3db point of 2.3Hz, not that there's a whole lot of 23Hz on most of my records but I like to cover all the bases/basses :-)
you really cannot extrapolate the impedance of a reactive load @ 20hz down to 2.3hz.
spice says your phase shift @ 20hz is -3.6º and -140º @ 5hz.... and if left undamped I'd watch out for tonearm resonance :-)
(in defense of the autoformers... I generally find that spice shows a much worse case than actually measures in circuit)
dave
"and if left undamped I'd watch out for tonearm resonance"
Would a larger cap help or hurt?
"if left undamped"
There is a 100k ohm resistor from selected tap to ground. Any help?
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Changing the cap value moves and damps / undamps the resonance. Here are a few values (green is always the first value swept (3.5u))
Your 100K load helps damp it a bit but you really need a lower value to show a difference.
Now even though 5K looks nice and is still 10X the source Z to keep the tech heads happy, you now have the same phase shift increase that the guy in the original video complained about. (just at the other end of the spectrum)
dave
.
Have Fun and Enjoy the Music
"Still Working the Problem"
Dave wrote:
"(in defense of the autoformers... I generally find that spice shows a much worse case than actually measures in circuit)"
Spice (psud, etc) are limited tools... that don't take into account, for example, the various core losses of an inductor.
Data retreived especially concerning resonances should be consumed with a grain of salt. They will almost always be overstated nor is the Q of the resultant complex impedances is not captured in these programs.
MSL
Builder of MagneQuest & Peerless transformers since 1989
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