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In Reply to: RE: Transformer Phase Inverter - Several Questions posted by Tre' on July 14, 2014 at 16:41:56
Gibson used that design in the late 60's. The interstage transformer was a step-up which provided some voltage gain, but I suspect a 12V filament xfmr might be too much. Maybe a 24v or 36V xfmr?
Follow Ups:
I think FC is thinking of a center tapped grid choke phase inverter.
Check out the Seth 240 amp on Mikes pages.
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Yes, or at least an arrangement that would mimic (at a much lower cost) something that was designed for this purpose. Again, it just has to be good enough for a guitar amp.
Having read a long thread in the archives that degenerated into an argument about what constituted an autoformer, I was a bit hesitant to try to put any particular label on it. =8^)
If it functions well enough, I don't care what it's called.
. . . Charlie
I have used the primary of a small push pull output transformer for that purpose with good effect.The ElectraPrint PSA-2n Phase splitter auto former (that's what Jack calls them) was better for Hi-Fi though.
Mike has one also. EXO-173 PPS Ni
Tre'
Have Fun and Enjoy the Music
"Still Working the Problem"
Edits: 07/15/14 07/15/14
I tried a design for a phase-inverting center-tapped secondary transformer driven by a single-ended cathode follower, and found it hard to get good balance at high frequencies (above a few kHz) between the two ends of the secondary. This is probably something you should measure with the transformers you are using.
No way to measure, all I have is my ears and a DMM.
According to a chart I found, a guitar's fundamental range is roughly 82 hz to 1.2 khz with harmonics going up to about 5 khz.
. . . Charlie
Yeah, I remember seeing some guitar amp schematics that used ITs. I hadn't actually thought about using a filament transformer like that - I was thinking of just using the secondary. Any thoughts on that?
Also, as I mentioned in my original post, I had seen a suggestion that a 1:1 transformer - like an isolation transformer - could be used by connecting the two sides in series and creating a CT between the two sides.
Could an isolation transformer also be modified to mimic an IT by connecting the two secondary wires with a pair of resistors in series and then forming a CT off of the junction of the two resistors? If so, this would eliminate the need for a large value parafeed style cap.
. . . Charlie
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