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I have been thinking about using a SET amp, but I would only need it to cover about 70 Hz on up. There is an actively crossed over bass system below that.
I'm wondering should I go with an OPT that has full frequency response or go for one that rolls off in the bass? Either way the OPT is going to be custom wound. Going with the latter it would also open me up to some more exotic iron options.
The reason I ask is I'm wondering if there will be any phase issues if I go for an OPT that has -3 db at say 50 Hz.
Follow Ups:
I am using a setup where I am rolling of a SET amp at 250cps; by adjusting the RC time constant between stages to set the roll-off. The output xfmr is small (permalloy) and gapped to roll-off at ~ 80cps. It is easier to set the roll-off with a cap/resistor time constant.
The easy choice here is to go parallel feed, then you can actually control your roll off by sizing the parallel feed cap. If you don't do that, you'll have to rely on your winder to get it right the first time, which may be a bit of an issue.
In addition to this, if you ever decide to sell the amps, just plop in a bigger pair of caps and you can market said amplifiers as full range units.
He has Quad ESL63s according to his profile..Wouldn't he need at least a 10 watt SET? Bankpuku is running a 27 watt PP design full range on his ESL63s but how much power can you get from a parallel feed design?
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
My profile is a bit out of date, only the speakers and TT source remain. But these amps will not be for the Quads, they are for another living room setup with high efficiency full ranger listened to in somewhat near field.
The amp will be series feed. I was not a fan of any parafeed amp I've heard, though they all used solid state CCS loads not plate chokes.
A solid state CCS as the plate load for an output tube is a bit difficult to implement because of the heat. Could you describe how it was accomplished in these amps?
ray
These were all headphone amps using high transconductance triode or pentode wired as triode. Not that difficult to do a SS CCS with these sort of preamp tubes, ~ 2" tall heatsink is plenty for the IXYS CCS part.
Parallel feed actually makes higher power SET possible by splitting the OT duties, designs beyond 20 Watts are certainly possible.
I know there are a lot of SET amps now that can run on ESLS and Maggies when biamped especially but that's good to know about parallel feed.
Nobody ever went broke underestimating the intelligence of the American public
H. L. Mencken
As mentioned by JJ Triode, there are benefits to a smaller transformer core at mid / high frequencies.
Give Jack Elliano (electra-print ) a call as he can custom wind a transformer to your particular needs.
Going with an OPT that is optimized (no pun intended) for the targeted frequency range has advantages. The standard air-gapped SE transformer has a tradeoff between LF (inductance) and HF (capacitance) bandwidth, so you can get better HF performance going this route.
The persona non grata (at AA) who has probably gone the furthest in this direction has a whole website about it (www.goodsoundclub.com). Look under the Super Melquiades amplifier thread and Macondo speaker system threads. Certainly there are phase issues to deal with but those arise anyway in designing the crossover filters and are best dealt with there.
Good luck,
JJ
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