OTL schematic
OTL Time
Line
OTL schematic
Julius Futterman OTL
Amplifier
OTL-1
Every man needs a Mt. Everest to test the mettle of his soul, and as soon as the NYAL team had perfected the Futterman circuit, we needed to get higher….because once we heard this circuit with a regulated power supply, we knew had to take up the challenge.
Let me not be modest about this challenge. No other company in the history of the audio arts, that I am aware ever dares to design both a high voltage (350 volts) and high current (10 amps) power supply before or since. The OTL had TWO 5,000 watt regulated power supplies…which are testament to Ted Hamond's engineering genius.
At the time this was the most complex, most expensive ($12,000 in 1984) heaviest and most complex tube amplifier and OTL amplifier ever built, and explains why I understand the meaning of complexity, and the value of simplicity.
This amplifier caused quite a stir in Japan and in 1984 Japan's Stereophile Magazine gave it an award.
Now you know why I have such a short fuse when I here tube amplifier manufacturers whine that designing regulated power supplies are too hard.
Both the OTL-1 and OTL-3 were rated at 90 watts into 8 ohms, but the OTL-1 sounded like it had twice the power. I used two pairs of OTL-1 on my West Electrostatic monitors.
An interesting note: I was the first to start using retro-meters in America, and others soon followed…and the meters cost me $55 each.
OTL-2
A special triode version of the OTL-4 that we made just for the Japanese market. I had one specially made for me that I connected a regulated power supply to and it was one of my favorite 10 watt per channel OTLs. How sweet it was.
OTL-3
This was the most popular model and consisted of two mono amplifiers. Quad 63 owners loved them. Each amplifier had their own built in fans to keep them cool, and if used properly would give years of trouble free use. I am aware that many of the original OTL-3 owners are still using their amplifiers with original tubes…and that is fifteen years of ecstasy, because they used these amplifiers properly.
On the other hand musicmaniacs would here these amps on Quad 63s and then used them on their Acoustat Monitors, where were very inefficient, 2 ohm speakers…which I advised against…and then I would get a call from and OTL-3 owner complaining that after only two months his amplifiers sounded distorted. As I suspected the output tubes were exhausted, and for good reason.
The rumors started by the mealy minded that the Futterman amplifiers were unreliable arose because these thermionic feeble never understood that OTL amplifiers can only be used with a very limited range of loudspeakers…and be reliable.
It is understandable that so many would try to use OTL amplifiers…because they sound so good…but the reason OTLs are not more popular is because they have been abused, and been given a bad rap.
My warning about the proper use of OTL amplifiers is wire other OTL manufactures want me taken for a long walk on a short peer. My invitations to debate them on this subject, are unanswered.
OTL-4
Stereo 40 watt per channel amplifier that was perfect for the QUAD 57 because it would never harm/arc the panels.
OTL CIRCUIT BOARD
This why the NYAL OTLs are so easy to service. What you are looking it is the whole Futterman OTL shabang…NO OUTPUT TRANSFORMERS NEEDED. You will also note that this is a hybrid printed circuit/hard wired design with all of the high current running through Teflon coated silver plated copper wire.
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