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In Reply to: RE: stupid OTL question posted by waterfall on June 21, 2017 at 10:55:50
OTL appears to be a very intriguing type of amp! I presume the OTL preamp would be of the same design. What is the lest expensive brand of these amps?
Most preamps ARE "OTL" - but they are not driving low impedance Amps - most amps have an input impedance of 47K Ohms - a tad higher than most speakers...
Wouldn't it be more correct to say that most amplifiers have an input impedance ranging from 10K to 100K ohms, with solid-state amplifiers clustered at the bottom of that range and tube amplifiers up around 50K and above? "47K" is the standard load resistance for an MM phono stage, as I am sure you know.
Most preamps are OTL in that they are Output TransformerLess.
IOW, some preamps do indeed have output transformers.
OTOH, a preamp that does not also have an output coupling cap is a bit different. Since our output circuit for our amps allowed for a direct-coupled circuit, we applied the same circuit to the output of our preamps, so no output transformer and no output coupling cap.
I only know of one company that makes "OTL preamps", Atma-sphere. Because the output stage requires an entirely separate circuit, such a preamplifier cannot be inexpensive. But on the other hand, I have no idea what your limitations are for expense.
If I wasn't rushing off to the dentist, when I wrote the above, I would have fixed it sooner.
When the OP mentioned "OTL preamplifiers", I was thinking of output capacitor-less preamplifiers. Most preamplifiers do not use output coupling transformers. But by far most do use capacitor-coupling. Atma MP1 and MP3 are direct-coupled, which is rare; there is no output coupling capacitor.
Actually, Transcendent is the lowest price, but those generally start out as kits so either DIY or get lucky and find a competent builder. Output power tends to be on the low side.
If you need more power, a good value (IMHO) is a used Atma-Sphere M50/M60 (any version), but you need to find one that is maintained (or at least has power supply caps that are not too old). I am still running a beautiful gold face original pair of M50s (with the original transformers!) with only upgraded coupling caps, and I would not trade those for anything. That pair has been going so long that some of the front panel lights are almost faded out!
Speaker choice will be an issue, but you get a lot more flexibility with a pair of zero autoformers.
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