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In Reply to: RE: final update .... posted by vinnie2 on June 10, 2017 at 14:40:04
Vinnie, I don't think TK was being condescending, sometimes it's difficult to interpret the tone of an email or post. This new digital world can be challenging at times.... Engineers deal with facts, statistics and measurement data, sometimes answers may seem harsh but i never take it personal. I work with electrical engineers every day, I always back up my answers with factual data. We all know music is under 12k but I'm sure there's a reason why we choose transformers with extended bandwidth, sometimes 100khz and above.
My Hammond opt performed pretty darn well, especially in the base region but didn't have that live sound of other opts. Could it be the extended freq response of my other opts? Or the amorphous core? I just don't know the answer to that but do hear a difference.
My Khorns reveal everything and makes this process easier to interpret.
On my ribbons, not so much.
Edits: 06/10/17Follow Ups:
" We all know music is under 12k but I'm sure there's a reason why we choose transformers with extended bandwidth, sometimes 100khz and above."
If we look at a simple, single pole 6db per octave low pass filter we see that the amplitude is still down 1db one full octave below the -3db point.
A OPT that is rated for -3db at 15kHz will still be down 1db at 7.5kHz
Then there's the matter of phase shift. A filter causes not only a loss of amplitude but also a shifting of phase. The music's phase is shifted for a decade from the -3db point. So if the amplitude is -3db at 15kHz the phase will be shifted all the way down to 1.5Khz
If we want the response (phase and amplitude) of a system to be flat 20Hz-20kHz we need the filter's (high pass and low pass) -3db points to be 2Hz-200kHz.
If we want response of a system to be flat 50Hz-15kHz we need the filter's (high pass and low pass) -3db points to be 5Hz-150kHz.
These are "tall" orders, especially for an output transformer, but there are real world benefits in meeting them whenever possible.
BTW There are low pass and high pass filter everywhere in a circuit. Every cathode bypass cap forms a filter, every coupling cap forms a filter. The Miller capacitance of each stage forms a filter. Stray inductance, stray capacitance etc. It's not just OPT's.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
I'm sorry deaf, but if it is that easy to misunderstand the tone of a given post, then the poster needs to be more careful. We are talking about being polite here, and being technically inclined does not excuse someone from politeness.
As far as the rest of your post, I am simply trying to show that there may be more involved with this than just opts and old age. I will keep looking to see what turns up.
Edits: 06/10/17
what are your operating points for each stage of the amps?
Do you mean all three of them? What is it you are looking for?
Edits: 06/11/17 06/11/17
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