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David Berning headphone amp


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Recently I sent an e-mail to David Berning asking whether he has any intention to build a headphone amp and he offered to build me a 6V6-based amp for around $2K based on one of his low power (7 watts per channel) stereo amps. He would customize the amp to add a volume control, RCA ins, and a headphone jack. He says the final amp would sound better with low impedance headphones than high impedance headphones because it was originally designed to drive speakers.

I know Berning is highly regarded for his power amps but don't know if that reputation extends to headphone amps. I know he used to make the his "micro ZOTL" headphone amp but it was discontinued a few years ago.

Does anyone have any thoughts on whether a custom-build headphone amp from Berning is a good or bad idea? Was the Berning micro ZOTL a good headphone amp? Is the 6V6 tube a good one for audio/headphone applications? And is his claim accurate that an amp built to drive speakers is better suited for low rather high impedance headphones? Should I instead plan to buy a Zana Deux or Decware CSP-2 and avoid a custom built amp?

Any thoughts would be appreciated.

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Berning uses an OTL designs

From the Berning homepage

Established in 1974, The David Berning Company manufactures vacuum tube audio amplifiers based on an unique Impedance Converter that replaces the traditional audio power output transformer and greatly extends and improves amplifier performance. We call our technology "ZOTL" for Zero-Hysteresis Output Transformerless.

Operating at a fixed high-frequency without traditional audio output transformers, the ZOTL Impedance Converter eliminates the frequency-dependent performance limitations inherent in all transformer coupled tube amps.

Berning amplifiers using the ZOTL technology exceed the performance of traditional OTL tube amplifiers by properly matching the tube impedance to that of the speaker. Berning amplifiers depart from traditional OTL amplifiers in that they do not require a large number of hot power tubes to supply adequate current for driving speakers.

That said for around $2k you could get close to a Zana or a used Cary 300 SEI

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The headphone jack on the MicroZOTL was an afterthought. It reportedly came about when Berning was discussing the ZOTL with reviewer Dick Olsher, who suggested the idea. The ZOTL was originally conceived to be a 2WPC speaker amp for office use. It was also designed to show that Berning's zero-hysteresis OTL technology could be implemented in a relatively low cost design. There were no transformers in the amp (not even the power supply, which was a switching type). That accidental headphone jack probably sold more ZOTL's than the original concept. The MicroZOTL was my reference amp for a long time back in the day.

As a headphone amp, the bass on the ZOTL was never completely convincing, but the mids and highs were superb. Berning is a talented designer, and if he went about designing a headphone amp for that purpose without cutting corners, I for one would really be interested in hearing the result.

A speaker amp modified for headphone use is likelier to be better with low impedance headphones. Remember that speaker amps are designed for loads around 4 to 16 ohms. A "low" impedance headphone is normally around 32 ohms, so would already be at the high end of the impedance range for which the amp was designed. A high impedance headphone (300 to 600 ohms) would not be the type of load for which a speaker amp is built. The designer would be the best judge of how the circuit would be affected by load. Since it doesn't exist yet, nobody can actually have heard it.

Edited by hirsch
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I am with JP in that for that amount of money, you can get a really nice amp from other manufacturers.

For 2K you could have a really nice custom amp made for you as well (which is the route I ended up taking).

EDIT: After reading Hirsch's post, wanted to add that the custom route, as long as you can find the right person, can really tailor the amp specifically to headphone usage. Headphone loads are not necessarily the ideal loads for output transformers that are built to feed nicely into speaker loads, though I have heard great sound from them, such as the Moth/Eddie Current stuff. My custom amp, for example, uses custom made autoformers with a more appropriate stepdown ratio (I think 8K:32) that it will play nicely into headphone loads.

Edited by recstar24
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After a few more e-mails exchanges with Berning, I am left with the impression that this custom-built amp would be a bad idea. In his last e-mail, Berning wrote that the cheapest amp he sells is a 7-watt power amp for $1800. He would add a few features (volume control, RCA inputs, headphone jack) so it would drive headphones for an extra $150. Doesn't exactly sound like he plans to voice the amp for headphone usage, but rather would add necessary features so it would work with headphones but eventually be used as a low-power integrated in a speaker rig.

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I am not sure what you mean by voiced for headphones. Generally, headphones and speakers like similar things, just in different quantities. Lots of power, flat response, low output impedance, low noise, enough, but not too much gain.

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With one big difference in that speaker amps are rarely quiet enough.

Yep, that's been my experience as well. I've never come CLOSE to audibly clipping a headphone amp (barring severe impedance mismatches, of which I have observed with OTL tubes and low-impedance headphones). With a typical headphone setup you can hurt your ears badly a good deal before you hear clipping. However, I THOUGHT a stout 55 Watts into an easy 93dB/Watt and > 8 ohm speaker load, would be more than enough for any sane situation. Not so, and it's relatively easy to reach audible clipping with dynamic peaks of orchestral works, even well before the ears get uncomfortable. I have a direct-to-disc Sheffield Labs recording of "Firebird Suite" that is just sick in its dynamic range - more power would certainly yield a more convincing rendering of this piece.

Headphones are efficient in terms of "milliwatts" and "millivolts". Yet many headphone amps can still push out a full watt or more!

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That ad is rough, but the seller is gold. He is a good guy who buys and sells top gear and maintains it in pristine condition. I bought something from him years ago and talked to him recently when he had a Doshi/ATC setup similar to what I now have.

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FYI, in Berning's last e-mail he said the 7-watt power amp he offered to modify is still in the design phase and is meant for speakers, not headphones, so he was uncertain how good it would sound if modded into a headphone amp. He recommended I just try to find a used Micro ZOTL.

So the bad news is that Berning is not entering the headphone amp market for now.

The good news is that he is planning to release an $1800 power amp that might sound really good with efficient speakers. That is a lot cheaper than most Berning gear, new or used.

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  • 10 years later...

Here's some measurements of my Linear Tube Audio - MicroZOTL mk2, with Linear Power Supply.

I'm powering a pair of Lowther TP1 speakers. 100mW output is the loudest I listen at, usually much lower. 200mW would be @pabbi1 levels.

Tube Complement 1:
 - Brown base Sylvania 5692 
 - Valvo (Philips) 6201 gold pin

Tube Complement 2:
 - Red base RCA 5692
 - Sylvania 12AT7

It looks like my tubes may be better matched than the rest of the circuit :)

1567625514_ScreenShot2020-06-19at10_23_11AM.thumb.png.2a520a846f10c80ef64cbffce4ed50b2.png

1mW output at 8 ohms

2121663701_MicroZOTL-1mWat8ohms.thumb.png.0da49c5dee8f92621a88d826555b1e03.png

10mW output at 8 ohms

1108217325_MicroZOTL-10mWat8ohms.thumb.png.3f6f9bd95054ade54af205d4b1cc0ca4.png

100mW output at 8 ohms

275474021_MicroZOTL-100mWat8ohms.thumb.png.3b07c5e4a5a62e94dc9beccf56580903.png

Edited by luvdunhill
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