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Just mounted the Monolithmagnetics 8k transformer which replaced a Hammond 6.5K. I chose the S-5 gapped at 90ma, fsat=21 Hz @ 25 Wrms L=57H. Also changed from plate choke to IT driver using modified monolith transformer.
The Hammond surprisingly doesn't perform too bad, I didn't measure it other than checking a Sq wave but compared to the monolith it sounds like it may have a couple peaks in higher freq range. It could compensate for the lower cutoff at high freq. Base is very good as well.
Now comes the good part, the monolith magnetics OPT is more natural, instruments sound more realistic, bass is tighter. On freq sweep at 8ohms, I measured 8-100khz before any drop in response.
This is the before with Hammmond, sq wave 1kHz
Monolith transformer
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Nice square wave response on the Monolith OPT. I'll agree that the Hammond isn't that bad, but I'd also think that the performance gap between these two would be even wider if measured at 10KHz.
10khz performance isn't that bad on the Hammond as well and this is were the monolith shines.
I performed the same sweep on Hammond and it was 8-100khz though the power saturation spec might be different(didn't test for this)
Edits: 05/02/17
Looks like a nice improvement. To be fair, those xfmrs are a bit more expensive than Hammond, yes?
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Buy Chinese. Bury freedom.
Yes they are a bit more. For the money, the Hammond is a good purchase.
With horns, there's a little more synergy with the new transformers
The entire signal path is different. Now that you have the IT running, it would be nice to see what the Hammond does with it being the only thing changed. I suspect the difference will shrink dramatically, both in what you see and what you hear.
cheers,
Douglas
Friend, I would not hurt thee for the world...but thou art standing where I am about to shoot.
My review was based with both scenarios hooked up using IT
I made the IT change and then the new opt months laterHere's a snapshot of the Hammond after the IT change. Still not too bad and mad a difference. Just not as smooth as the monolith
Edits: 05/02/17
When you changed just the output transformer,that changed the 1khz sq wave that much? If you using some global feedback with a resistor/cap combo,you need to add come capacitance across the feedback resistor. Start with about a 70pf and go up a little until the spike ringing in the corner disappears.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Yes, it was pretty dramatic.
No global feedback, SE GM70, 1150v is a little dangerous to starting clipping in caps.
Not so sure this little bit of ringing is important on a sq wave. My Slagle transformers behave similarly to sq waves and they are some of the best opts I've heard to date. I have the leads clipped in right now so it may contribute somewhat at this voltage. Could also be the GM70 tube contributing as well. I might try my copper plates and see what happens.
From what I've heard, ringing sounds harsh and annoying, I don't hear any of this.This is one anomaly we never see in spice.....
The IT gave me some more drive with headroom to spare.
Edits: 05/01/17 05/01/17
The Hammond output transfomers should easily be good for a pure 1khz sq wave but being you have 1150vdc,it is probably breaking down that transformer a bit between the windings.
"For every complex problem there is an answer that is clear, simple, and wrong" H. L. Mencken
Hipot test is 2kv
Add gain on top of that and yikes! The hammonds were a good starting point, i didn't want to invest more until I was sure with my design. This was my first 1kv+ amplifier
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