OTL tube amps

If you have experience with OTL (output transformerless) tube amplifiers, please describe your observations, singularly and preferably in comparison to what you’d like to compare to.

Berning has me totally convinced with his thorough explanation of how his OTL amps operate. He also has me convinced that the vast majority of OTL amps are simply not viable - I’m not sure if he’s the sole patent holder for a practical OTL design, I’d wager not. Just don’t know any others yet.

Anyway, here’s a brief explanation of how Berning figured it out:

Here’s the in-depth patent document:

Essentially driving speakers directly with the output tubes, with an advanced interleaved impedance conversion trick is just WILD.
Oh… and these products ARE expensive.

Check Linear Tube Audio for a less expensive version OTL Ultralinear+ Amplifier (20 watts). I think is a licensed Berning design.

Atmas-Shere.com is another OTL amp manufacturer (30+ watts). Thanks

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Sexy stuff and apparently well-reviewed/well-loved.

The build quality looks great, but I have not had the pleasure of listening to any of their kit.

Ohh, LTA has headphone amp/preamp/fleawatt speaker amp combos too.
It only lists power output for speaker loads… " with 4-ohm load: 1W, 1% THD, with 14-ohm load: 0.5W, 1% THD"
I wonder what kind of power output I could expect with 70ohm Audeze LCD-2 headphones? Impossible to know?
I read of someone driving everything but the HE-6 well with it, so no problem, but I do think the Audezes enjoy some moderate power to thrive…

Reach out to them directly by e-mail they have always been very responsive. With the currency conversion, shipping and VAT I would think there would be similar products available made in the EU though maybe not OTL based. You can also search the forum at Head-Fi and see if anyone has tried the combination.

I will.
Oh and there is an EU website for LTA.

That’s good didn’t realize that had branched out that far. You will find dozens of LTA users on Audio Circle as they are a popular combo with Spatial Audio speakers.

I’ve owned a number of amps over the years across push-pull, Class A, SET, and OTL. The OTLs I’ve owned are the Atma-Sphere MA-1 and the S-30, the latter of which I still own today and use in my second system.

In my experience, with the right tubes and the right speaker matching, an OTL amp can be endgame. The lack of output transformers provide, simply, just more music compared to any other amp type out there except for ultra high end solid state (like in the ~$20k+ range). But there are always limitations.

In order to be dynamic, most OTLs require a speaker that doesn’t dip lower than 6-8 ohms anywhere in its impedance curves. If the OTL is more that 100wpc, a speaker can dip lower, but at that point you’re also then using an OTL with a heck of a lot of tubes, and that means a bit more noise.

The best I’ve heard an OTL perform is to handle the mids and treble of a bi-amped Oris horn setup. Most high efficiency drivers are a match made in heaven when paired with OTLs, and being able to drive the bass sections with higher wattage and higher current amps enable the speed and punch that an OTL would generally sag.

With electrostats, it’s the other way around. The impedance curves dip in the treble, and the bass is easier to drive. If you don’t have enough power and current, using an OTL on electrostats will sound closed in and boomy. But with the right pairing, say the MA-1 with a pair of Quad, is another incredible match.

With this in mind, it’s been near impossible for me to settle with one amp, so I absolutely love my T+A HV stack in my primary system while still believing I will always own my Atma-Sphere S-30 even if I ever decide to consolidate my second system.

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Not with Berning’s design. The Quadrature Z is 220W, here’s an image of its innards:

It’s a heck a lot of money though.

Fair point, yes Berning is an exception. But his circuits do introduce a number of transformers to help generate the power even if they are not output transformers.

I don’t doubt the amp is incredible - I have heard great things about it. But sometimes I wonder about the benefit it claims of being an OTL when a series of transformers are used elsewhere in the circuit along the way. Sometimes classifying an amp can be misleading, when really perhaps the Berning circuit deserves a class all of its own.