I got a Massdrop email with a link to an article "5 Amps That Cost More Than Your House." One of those amps is something called an Ultrasound Otello. That's where I found some of the strangest ad copy I've ever seen for an amplifier.
"OTELLO, a dream machine in which the charm of the thermionic tubes is married with the most modern technologies; an OTL with 6 transformers"
OK, an output-transformerless design with transformers. OK.
"...an amplifier with zero damping factor that has the fastest and articulated bass that anyone could hear."
No damping factor? None?? Really? And that results in fast and articulate bass through a loudspeaker?
"Output Impedance 200 Kohm"
???!!!
Yeah, that would make "zero damping factor" alright. More like negative damping factor, rings like a big, low-frequency bell. 8:200,000, or a damping factor of approximately 0.00004.
And best of all, the price is only $600,000 USD.
I'm trying to figure out if this is all a joke, or what. Anybody know?
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"OTELLO, a dream machine in which the charm of the thermionic tubes is married with the most modern technologies; an OTL with 6 transformers"
OK, an output-transformerless design with transformers. OK.
"...an amplifier with zero damping factor that has the fastest and articulated bass that anyone could hear."
No damping factor? None?? Really? And that results in fast and articulate bass through a loudspeaker?
"Output Impedance 200 Kohm"
???!!!
Yeah, that would make "zero damping factor" alright. More like negative damping factor, rings like a big, low-frequency bell. 8:200,000, or a damping factor of approximately 0.00004.
And best of all, the price is only $600,000 USD.
I'm trying to figure out if this is all a joke, or what. Anybody know?
--
The technical description is certainly... enthusiastic.
Current sources are NOT for everyone, especially with passive crossovers since those can have a large impedance peak near the crossover point, leading to an equally large frequency response peak. Output impedance is a large part of the reason tube amplifiers sound different from transistor types.
Given that, current sources do rather well with active crossovers, and especially with an open baffle since the system resonant frequency tends to be shifted down a fair bit from where it would be in a sealed or vented box (two frequencies for that bad boy), plus you get a welcome bit of LF lift not far from the open baffle rolloff frequency so you don't have to punish the voice coil quite so hard.
Current drive also helps flatten HF rolloff from series inductance since the current through the driver will stay the same (within voltage limits) no matter what Le does. A similar argument holds for compression due to VC heating.
Don't take my word for it; try simulating an infinite baffle in WinISD then set the signal source resistance to something around 100 ohms. You may be amused.
tl;dr: Current drive is a bit finicky, but in the right place it's the cat's meow.
Current sources are NOT for everyone, especially with passive crossovers since those can have a large impedance peak near the crossover point, leading to an equally large frequency response peak. Output impedance is a large part of the reason tube amplifiers sound different from transistor types.
Given that, current sources do rather well with active crossovers, and especially with an open baffle since the system resonant frequency tends to be shifted down a fair bit from where it would be in a sealed or vented box (two frequencies for that bad boy), plus you get a welcome bit of LF lift not far from the open baffle rolloff frequency so you don't have to punish the voice coil quite so hard.
Current drive also helps flatten HF rolloff from series inductance since the current through the driver will stay the same (within voltage limits) no matter what Le does. A similar argument holds for compression due to VC heating.
Don't take my word for it; try simulating an infinite baffle in WinISD then set the signal source resistance to something around 100 ohms. You may be amused.
tl;dr: Current drive is a bit finicky, but in the right place it's the cat's meow.
Input, output, what's the difference? The whole description is BS.
Marketing people are so full of it. If they had any skills they wouldn't have to lie for a living.
200k output impedance is a fairly good approximation to zero damping factor, so they got that bit right. Fast and articulated bass would have to depend on the speaker, which would have to be designed for current-mode drive, so can hardly be claimed as a feature of the amplifier.
Maybe the 6 transformers are interstage coupling? If so, the design avoids transformers where they might be useful (output) and includes them where they add little or detract from signal integrity (interstage). A good marketeer can make any design flaw sound like an advantage.
Maybe the 6 transformers are interstage coupling? If so, the design avoids transformers where they might be useful (output) and includes them where they add little or detract from signal integrity (interstage). A good marketeer can make any design flaw sound like an advantage.
Transformers were a big reason to move away from tubes. When I started to learn electronics, tubes were considered quaint, and a waste of time. And transistor circuits were terrible; many were poor copies of tube circuits.
I still built a tube amp in high school and I will hopefully build one more before I die. I'm not a hater of transformers.
McIntosh still uses audio output transformers, and they still wind them in house.
I still built a tube amp in high school and I will hopefully build one more before I die. I'm not a hater of transformers.
McIntosh still uses audio output transformers, and they still wind them in house.
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