Graz - APOGEE ACOUSTICS
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I have no experience of the active crossover, though I believe Rich has compared this and the better version.
Visit to Henk van der Hoeven -- Apogee Acoustics Re-builder/Restorer
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Graz and Rich agree on this. For me personally (as a tube person) this answers my questions on how to drive Graz-ribboned Divas and Full Ranges.
I've told Henk what I think that is and it isn't related to amp power IMHO. Surfice to say it isn't anything to worry about in that particular case.
Graz - APOGEE ACOUSTICS
Active Member
It is almost entirely related to a standard tube interface, connected to a bass and MRTW at the same time. A similar problem can also be observed in a state of clipping (valve or ss) on the mrtw...
If you look at the distortion of SET compared to frequency, you will see that a lot of SET distortion occurs below 100HZ (obligatory air gapped transformer?). SET tend to be quite a bit less distorted at the lower midrange and higher frequencies than below 100HZ. When using my Wavac SET amps and active crossover, I would cross my Bass panels over to subwoofer at 100HZ, and use a SS amp for subwoofers with a tubed preamp to drive SS solid state sub signal.
This, of course, also spared the Bass panel SET the extra energy required to drive the panel into the lower frequencies.
This, of course, also spared the Bass panel SET the extra energy required to drive the panel into the lower frequencies.
I found an interesting comment feel Atmasphere in audiogon, posted back in 2002, referring to the original Scintillas.
"There is also a guy on the ASOG (otlamp.com) named Paul Speltz who makes a torroidal autoformer (a variation of one we used to make) for this sort of application. It has taps for 4,3,2 and 1 ohm loads and sets the amplifier load at 16 ohms. Works quite nicely on those otherwise hard to drive loads that tubes don't normally like.
Allows one to use tubes with, say, Appogee Scintillas, if you could find a set these days. For the most part though 3-4 ohms seems to be the most challenging most speaker manufacturers are doing these days."
"There is also a guy on the ASOG (otlamp.com) named Paul Speltz who makes a torroidal autoformer (a variation of one we used to make) for this sort of application. It has taps for 4,3,2 and 1 ohm loads and sets the amplifier load at 16 ohms. Works quite nicely on those otherwise hard to drive loads that tubes don't normally like.
Allows one to use tubes with, say, Appogee Scintillas, if you could find a set these days. For the most part though 3-4 ohms seems to be the most challenging most speaker manufacturers are doing these days."
I have got a pair of those Paul Speltz Zero autoformers, to be used with the FR ribbion mid-range when I active tri-amp it 
I don't have the specifications infront of me, but if I remeber correctly, the autoformer has taps to raise the impedance by 2, 4, 8, 16, and 32 times!
I don't have the specifications infront of me, but if I remeber correctly, the autoformer has taps to raise the impedance by 2, 4, 8, 16, and 32 times!
Not sure how transparent the autoformers are as I have not tried them yet! As far as I understand, autoformer is a lot easier to made than the typical output transformer, as it required much less turns. So hopefully it is transparent enough, or at least more transparent than the inductors and capacitors in the passive Xover.
No choice with FR mid-range anyway, what amp can handle 0.25ohm
No choice with FR mid-range anyway, what amp can handle 0.25ohm
On Duettas, I am pretty much with theKong. I've tried a few dual amp combos. The overriding advantage with single amps is that there is no obvious change in the personality of the sound between bass panel and MRT.
A Denon POA with my 211 amps on the mids was an obvious instant DISASTER.
Conversely, though, the 211 amps on the MRT with W4S 500 Watt amps on the bass panels was made to work well at a bake off with dual TVC preamps. The mid range became astonishgly good and we were all gobsmacked by it. The walls literally disappeared... but I wouldn't like to say that it would work longer term - that setup only existed for an hour or so, so on wider exposure it may well have sounded odd.
A Denon POA with my 211 amps on the mids was an obvious instant DISASTER.
Conversely, though, the 211 amps on the MRT with W4S 500 Watt amps on the bass panels was made to work well at a bake off with dual TVC preamps. The mid range became astonishgly good and we were all gobsmacked by it. The walls literally disappeared... but I wouldn't like to say that it would work longer term - that setup only existed for an hour or so, so on wider exposure it may well have sounded odd.
Agreed, it is a hit or miss situation with mixing amps! At the time, I tried mixing a Sonic Frontiers Power 2 with a Mesa Baron for the Duetta. Even though both were tube amp, it was a disaster too !
So, while using a powerful SS amp for the bass, and SET / tube amp for the mid-range and treble, may be a good idea technically, it is not as easy as it sounds!
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Graz - APOGEE ACOUSTICS
Active Member
I have no allegiance to any amp brand and am completely dispassionate when it comes to commenting about amps with Apogee's. But that has gotten me into a lot of trouble in the past Up for an email or a call, I believe you have both details at hand...
Take care - Graz
. . .
No choice with FR mid-range anyway, what amp can handle 0.25ohm
My understanding from Henk is that the original Apogee transformer for the midrange driver on the Full Range is not well thought of. What are the options for people who want to drive that midrange driver and who do not have a special autoformer?
Graz - APOGEE ACOUSTICS
Active Member
A properly considered/designed transformer is a good option here
Graz, stop teasing us here!
If there is enough demand, I hope you can make a special run of your top-secret Definitive transformes that fit for the FR midrange
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