Are there drivers with with Qms of about 1? Around 3 is more typical for hi-eff full range. I thought speaker in closed box becomes more boomy than free or open baffle, because of added spring effect of compressed air. I also thought that box stuffing doesn't reduce Q, it reduces standing waves and reflections. Please correct me if I am wrong...
Yes, bi-amping is what I am considering,. I want to use current drive for the subwoofer too. More on these things later.
Oh, and the biggest, heaviest motor with most iron is #3, the black one. #2 has the biggest FC, indeed.
With a current amplifier the speaker’s impedance is convolved with its frequency (driven by a voltage amp) response. The LF resonance is certainly an issue, low Qms, aperiodic enclosures can (largely) deal with that, but impedance swings from XO or rising at the highest frequencies (no shorting ring or equivalent) will also affect things.
One can avoid the resonance peak issue in a more conventional/available bass solution, by biamping with a voltage amp on the bottom and the current amp driving the midTweeter in its flat impedance range.
dave
One more problem solved! 🙂
But with non-feedback pentode amplifier you are introducing more distortion! Why do you think pentode high-harmonic distortion products are better than speaker low-harmonic distortion? Good speakers have moderate amount of second and third harmonic, higher harmonics are insignificant. Pentodes generate higher harmonics, on which ears are more sensitive.
That looks like crap IMHO... I like this much better:
Seriously, Why use a pentode when a MOSFET exists? For me the whole point of tubes is triodes!
Seriously, Why use a pentode when a MOSFET exists? For me the whole point of tubes is triodes!
I could have missed this but I have not seen low Qms drivers advertised as such. Nor do they appear to predominate in a particular class of loudspeaker - some full-range drivers have low Qms, others have high Qms. Ditto for midrange drivers, mid-woofers and woofers.
I agree, experiments show stuffing has much less effect on Q than it has on the enclosure reflections that can accentuate boominess - stuffing is one factor to consider in the trade-off between running a speaker in an enclosure or open-baffle.
There were two different kinds of FC: parallel and series. The former had DCR of 5-6 K and drew current from B+, typically about 300 V. The latter, with DCR of 0.2 - 1 K, were in series with power supply, and, yes, in the case of class AB, drew variable current, however, it didn't cause much change in VC gap flux. The issue of how much current through FC is optimal is a very interesting one, and I will put it for discussion later.
Btw, the common belief that FC was used as a smoothing choke in power supply is wrong. FC is a very poor choke; when energized, it has very low inductance and acts more like a resistor.
MOSFETs have large nasty non-linear capacitance. By contrast, tube capacitances are relatively small and of highest quality possible - vacuum.
That's why I use them as followers. I can drive an ixth6n50d2 follower with a 6L6 easily... 6L6 loaded 5k6, 300R for cathode - not bypassed, driven by 6SN7.
Just saying... It's not the capacitance... It's the curves!
VFET was awesome, but Sony gave up on it. Unless you're Nelson Pass, you probably can't buy VFET parts. Triode is the alternative for us simple folk, right?
IMHO the best triodes aren't really triodes but "psudotriodes" from the standpoint they are pentode/tetrode/beam (read sweep) tubes that make AMAZING triodes if you strap them with 240R and you like that kind of thing 🙂 I know I do!
People love their 300B amplifiers, and good for them. But to me, directly heated tubes seem like a real pain in the butt. Isn't that why they (Ted Rogers Sr... See http://www.broadcasttechnical.com/articles/22rogerstotherescue.htm and no it's not perfect - he certainly didn't invent the rectifier tube, but he did invent the heater/cathode) invented the indirectly heated cathode in the first place? It makes it so much easier! LOL
Just saying... It's not the capacitance... It's the curves!
VFET was awesome, but Sony gave up on it. Unless you're Nelson Pass, you probably can't buy VFET parts. Triode is the alternative for us simple folk, right?
IMHO the best triodes aren't really triodes but "psudotriodes" from the standpoint they are pentode/tetrode/beam (read sweep) tubes that make AMAZING triodes if you strap them with 240R and you like that kind of thing 🙂 I know I do!
People love their 300B amplifiers, and good for them. But to me, directly heated tubes seem like a real pain in the butt. Isn't that why they (Ted Rogers Sr... See http://www.broadcasttechnical.com/articles/22rogerstotherescue.htm and no it's not perfect - he certainly didn't invent the rectifier tube, but he did invent the heater/cathode) invented the indirectly heated cathode in the first place? It makes it so much easier! LOL
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For fun! This is not serious for me, I experiment for my own amusement and satisfaction and I like using valves - diodes, triodes and pentodes. 🙂 There are good solid-state current amp designs out there but I am not interested in building them, a choice that I don't ask or advocate anyone else to adopt.
Nothing per se, but a pentode is so much like a good depletion MOSFET that it seems like a waste of heater power.
Indeed I'm trying to create a MOSFET amp based on a Williamson 🙂
Somehow though, I just like the sound of a triode amp. To be fair, I also like the sound of a tube driven MOSFET SE amp I designed based on a Pass Lite 🙂
I made it a source follower driven by the triode strapped 6L6 driven by a CCDA 6SN7.
Indeed I'm trying to create a MOSFET amp based on a Williamson 🙂
Somehow though, I just like the sound of a triode amp. To be fair, I also like the sound of a tube driven MOSFET SE amp I designed based on a Pass Lite 🙂
I made it a source follower driven by the triode strapped 6L6 driven by a CCDA 6SN7.
Hmmmmm .... something jolted my memory and I need to correct my own statement!! On pages 212-214 of his book Current-Driving of Loudspeakers, Esa Meriläinen documents experimental measurements showing lowered Q by stuffing the enclosure. The advantages are lower Q as well as damped enclosure reflections.
Mosfet gm varies even worse with current.
Crazy Drive gives you a near mythical device. Constant gm.
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Aha! Where this myth of high order pentode distortion is coming from? Lynn Olson's blog? Lynn tells a story of using HP spectrum analyzer to compare triodes and pentodes - and - o horror of horrors! pentodes had all high order stuff, but triodes were squeaky clean. Somehow, there weren't a variety of spectra shown, so one had to believe him.
Luckily, we have a detailed data sheet for the 807 pentode that shows distortion components at various operation points. In comparison to 2A3 distortion data, the 807 actually has less distortion than 2A3 at the same power level. The big difference is that one has predominantly 2H and the other 3H, both benign low order distortion. Higher harmonics only begin to show up close to maximum power output.
Fair, but you don't need the trafo... If the trafo was crap in the first place it might be better without much work or thought into it...
I've never used MOSFETs as an amplifier ( that's a lie, I tried it in the Pass lite amp I first built, but it was awful ) but as I said I used them as a follower. They are good enough that if I have that amp on I could mistake it for tubes. Of course it's driven by tubes so it should do what the tubes tell it to do (in human speak anyway).
Only takes a few resisters to fix transformer distortion. (Patent US4614914 ) The problem with transformers (good ones) is cost and weight. But I'll take them over OTL. Mosfet followers are fine too. The world needs a low cost source of progressive wound toroid OTs.
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Thanks, Icsaszar, I read that thread with interest and appreciation. In this thread, I am particularly interested in the synergy between a suitable speaker and an amp with high output impedance. As Planet10 highlights, there are trade-offs to be made, everywhere.
??? Why are you comparing distortion of pentodes and triodes???
My question was about comparing distortion of pentodes and loudspeakers:
Please show us distortion spectra of the best pentode you can find (in amp without negative feedback!) compared to the distortion spectra of a good (not the best!) quality loudspeaker!
Why are you trying to "decrease" benign low distortion of loudspeakers by introducing much bigger (and with higher harmonics) distortion of pentodes?!