Thanks for the informative thread. I have been hearing great things about his designs.
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This is going to sound silly to some, but most of the time I use my micro-zotl in my study to drive a pair of Spendor LS3/5a's, which have only 83dB efficiency. I admit freely that this combination does NOT get loud, or even close, but the sound is quite nice and I never have to worry about my kids blowing my speakers by cranking the volume. I also do not have to worry about damaging my hearing, which is especially sensitive to harm because I played in a rock band as a youngster. I use an Optimus CD3400 as my source, and since it runs off 6 volts DC, I can run the whole setup with a rechargeable, portable battery designed for jump starting cars (from Sears, $35). [I have also used the battery to jump start a friend's car.] It's a pretty cool hifi when I take it outside. I also use my micro-zotl for driving my Sennheiser HD600's. With that combination I can hear details that are inaudible on excellent speakers even after I know what to listen for. The Berning Micro-ZOTL is a wonderful little amp. For those of you trying to decide on color, I'm convinced the ones in the original blue sound the best. ;)
Thanks, guys. I wanted to do a good job for you. I appreciate your support.
Patrick, there are higher power ZOTL Berning models. The Seigfried(8watts, 300B or 12 watts, 811) costs around $5k-$6k. The ZH270(70 watts) costs around $4500. I have a custom model SET ZOTL based on Type 45 tubes(2watts) being hand made for me by David Berning. It is not a production model, but a one-of-a-kind custom prototype designed for my particular need to get that last few db out of my system. It will also be battery powered.
Yes, ohlala, that's true. I think that the sonics of this amp are superb, and not at all inline with the price point. The low power is the only thing that might be considered a drawback for those with less efficient speakers. Otherwise, this is a fantastic amp with features like ZOTL that cannot be gotten from any other amp, except the expensive Bernings.
Well, something isn't adding up here. It's laughable to think that the Micro is a colorless amp, but maybe you do not consider its coloration a weakness. This is a 'review', though, and I believe it is necessary to include any deviation from nothingness as well as price-point comparisons. As we all (should) know, the best thing you can say about a component is nothing. I am thinking that maybe you have not heard it in enough situations to make that judgment. Is that possible?
Ohlala, perhaps I was overcome a bit with the positive qualities of the MicroZOTL, and didn't mention any negatives. It is push-pull, so it doesn't have the ultimate midrange purity of some of the great single-ended designs. But it is really good midrange, nonetheless. And it does have the strong bottom end that would normally be associated with a good PP amp. I suppose that there could be a tiny amount of detail that could be improved upon with some Caddocks and Black Gates, and possibly the removal of the Noble pot. Potentially, eliminating the circuit board, and hand wiring the unit could yield a touch better sound. Now with only 1 watt, there is not the chest thumping bottom end that would require alot of power to move the air, but I don't really consider that a sonic deficiency, only a side effect of the low power output. With speakers that drop low in impedance, the sound would harden up some and lose some "life", so it is not the greatest match for 4 ohm speakers. With the stock JAN Philips 12AT7 tubes, there was definitely a glare that needed eliminating. The NOS Mullards I bought took care of that. The stock Sovtek 6SN7 output tubes were a bit "flat" and lifeless, so I put in some 1940s Sylvanias. This perked things up real nicely. So, it wasn't perfect, and still isn't. But, it is a very good sounding amp, considering its power limitations. With a few easy upgrades from the stock tubes, it reached an excellent level. You see, the ZOTL has a much shorter signal path than any other OTL made, so it can pass a better signal to the speaker, and drive the impedance of that speaker, better than any OTL. It can be equalled by good SETs for short signal path and impedance matching, but then they have the transformer difficulties to deal with(phase-shift,ring,saturation and bloat). If we combine OTL phase-coherence and frequency extension(due to no output tranny), with SET short signal path and impedance matching(due to having an output tranny), then we get the ZOTL. This combination makes the ZOTL circuit nearly unmatchable in the amp world today. Cost remains low because there are no very expensive output transformers to push the price up(as in SETs), and there are not rows-upon-rows of tubes required to match up the output impedance(as in OTLs). So the price/performance ratio is excellent. Even the entry level model like the MicroZOTL has sonics that would be expected in amps at $5k or more. Albeit with much less power. But efficient speaker designs, like the Lowther, reduce this apparent power deficiency to minimum. The result, in my system, is the sonics of a high priced amp, with the cost of a mid-fi or budget component. And I can still get 100db peaks of SPL. So now perhaps you can see why I am so thrilled with the purchase. Not because it is perfect, but because it is so close to perfect for a very low price. And if you configure the system properly, you can get good SPL results too. You'll never run Maggies with this amp, but if you can live with a high efficiency speaker system, it can give sound far beyond its price point with them.
Thanks to all the previous folks who wrote such thoughtful reviews. I use my Micro ZOTL strictly as a headphone amp; source is an unmodified Sony 333ES SACD player; 'phones are Sennheiser 650s (the 600s before them), connected with Stefan Audio's Equinox cable. The sound is simply glorious; the best in my house. Detailed and involving, but also totally liquid; one of those rare products that's just crazy good.