New York Audio Laboratories Futterman OTL-1 power amplifier Specifications

Sidebar 1: Specifications

Description: Four-chassis stereo output transformerless tubed amplifier. Nominal output: 150W into 16 ohms. Large-signal frequency response (–3dB down): 2Hz–40kHz. Small signal response: 1.4Hz–200kHz. Phase shift: 15° at 10kHz and 45° at 40kHz. Output impedance: 2 ohms at 10Hz, 0.15 ohms at 1kHz, and 0.3 ohms at 10kHz. Signal/noise ratio: 85dB unweighted, 92dB A-weighted. THD: less than 1% at full power from 100Hz–100kHz, dropping to less than 0.1% at lower levels. IM distortion: 1.2% at full power, dropping steadily at lower levels.
Price: $12,000 (1986); no longer available (2018).
Manufacturer: New York Audio Laboratories, Elmsford, NY 10523 (1986); company no longer in existence (2018). Web:

New York Audio Laboratories
Company no longer in existence (2018)

Anton's picture

Thanks for the trip down memory lane.

I would be willing to chip in to get Art or Herb a fresh example of this amp and see how it holds up vs. the current crop.

What a classic piece of kit!

Herb Reichert's picture

All the way through reading this report I kept saying to myself, damnit I should have leaned a little harder on Harvey and bought one of these beautiful monsters. Harvey was my friend, but he would not cut me a deal I could afford. I did however buy an old Futterman H3aaa but it was kind of a mess. I always wanted an OTL-1 and a Levinson ML-2. I was thinking this afternoon how cool it would be to do a followup on the ML2 comparing it to the latest Pass Labs stuff. Ahhhh I feel a Dream coming on.

Ortofan's picture

... Harman-Kardon Citation II?

If you ever do that follow-up comparison of the ML-2 and a Pass Labs amp, try to include the Accuphase A-250.

Herb Reichert's picture

is one of the finest amplifiers I have used
I have owned a few IIs (including one I was told was modified by Mike Moffit)
it had best output transformers which were only surpassed by Acrosound's UL-II trannys


Anton's picture

....would be reading about you hearing one!


rwwear's picture

The Fourier amps were a continuation of the Futterman design although they had their problems.

Bogolu Haranath's picture

I would not hold my breath :-) ...........

Bogolu Haranath's picture

Promises, promises, promises :-) ..............

tonykaz's picture

Headphone people like our Tyll & Steve G will boast about the OTL Bottlehead Crack. I claim that the Schiit OTL Valhalla is superb.

Loudspeakers don't get built with high enough impedence for OTL Amps so we don't have anyone offering the darn things,

do we ?

Tony in Michigan

Bogolu Haranath's picture

If someone builds it, they will come :-) ............

Bogolu Haranath's picture

May be the loudspeakers get built with low impedance, because they can draw more watts from solid-state amps? ..........

"Watts are cheap" ........... Jim Theil :-) ..............

eskisi's picture

OTL amps can work wonderfully. I have a 2 X 30W Atma-sphere and the sound it produces in combination with a pair of 16 ohm Sterling LA3/5As is remarkable and addictive.

But with an electrostat? OTLs are a compromise of sorts...the design is forcing a low voltage and — relatively — low impedance output from high impedance / high voltage devices by consuming a ton of power: it really wants to see a transformer. An ESL is a reciprocal compromise — it has very high impedance and requires high voltage and it uses a transformer, its and all non-OTL tube amps’ Achilles heel. So the far preferable way to drive an electrostat is with a “normal” tube amp driving it without a tranformer. Like Acoustat did in the 70s and which I do with a Berning tube amp driving Martin-Logans.

Roger A Modjeski's picture

I met with Julius Futterman while he was still building OTL amps himself. I saw his power transformer winder and potting setup. He liked to make his own because the transformer had to be very low impedance to provide the current needed for 6-8 output tubes.

The key design feature of the Futterman and its clones is very low output impedance which is achieved with gobs of feedback which is properly applied and sounds great. I recommend Futtermans early papers which can be found on the internet.

He gave me a copy of an impedance chart he had run on the KLH-9 ESL. He noted it was high and never below 12 ohms or so. Not at all like modern ESLs that dip to an ohm. Even the ESL 57 gets down there at 18Khz.

As one who has designed Futterman type OTLs (the Counterpoint SA-4 and my own) these are not the mate for modern ESLs where the impedance falls to an ohm or so. The famous marraige of the OTL and ESL is particular to the KLH-9 and Futterman OTL.. ONLY.

Beveridge and Acoustat had the right idea in making a Direct Drive amplifier at high voltage and reasonable current. The Beveridge Model 2 and 2SW amps put out 1,500 VA (like watts in this application). The Acoustat amp was not quite as good on current, construction or reliability. It used the wrong output tube.

Since few amplifiers can put out 1,500 VA nor can many step up transformers easily pass it, the DD amp is the way to go. I have made several that put out 2,000 VA for use with the Acoustats, ESL 57 and ESL 63.

One other comment on OTL. Sadly the Atmasphere amps do not drive ESLs or any speaker with varying impedance well as they have very high output impedance (low damping). So lets be careful when considering how OTLs behave with ESLs and in general.

Bogolu Haranath's picture

Nice to hear from you Mr. Modjeski ....... Any comments about OTLs driving electrostatic and/or planar magnetic headphones? :-) .............

John Atkinson's picture
We published a characteristic letter from Harvey Rosenberg in 1999:

John Atkinson
Editor, Stereophile