OTL amplifiers

I think it's very WRONG to use the ZERO,You get out of not using an output transformer and there you are using them again.What is the use of using an OTL with transformer at the OUTPUT??

The advantage is this:

Its not possible to build and use an autoformer with the performance of the ZERO if you don't start with an amplifier that does not already have a fairly low output impedance and does not put DC through the winding of the transformer.

The result is that the ZERO has greater bandwidth than is normally possible- about 2Hz to 2MHz and you did see MHz just now. So in this way it gets around one of the traditional limitations of an output transformer which is limited bandwidth.

It is also designed for and used specifically in cases where the OTL might other wise not work; IOW low impedance loads. You would be amazed at how many people want to use a lower powered OTL to drive Magnaplanars! I completely understand that sentiment- Magnapan is in our back yard (or we are in their's, not sure how that works) so we've been dealing with that issue for the last 30 years. The ZEROs allow our little M-60 monoblocks to drive a set of MG3.7s or the like quite successfully in many moderately sized rooms (being a local manufacturer and with an excellent local dealer, Magnapan has lots of product in the field here in the Twin Cities). So in this case, the combination works quite well- the M-60 makes 80 watts instead of 40, has lower distortion and bandwidth is unaffected, and at the same time all the other aspects of the amplifier remain obvious (Class A, triode, single stage of gain, etc).

If the impedance of the speaker is higher OTOH, you simply don't use the ZEROs. IOW its a **problem solver**. Interestingly though, several solid state manufacturers have reported that using the ZEROs with their amps to drive lower impedance (4 ohms and less) speakers results in better sound with their amps as well. Apparently the increased distortion that all amps have with lower impedances is audible- enough so that the ZERO is a way of getting better sound, **apparently** regardless of the amplifier!

These are your choices from an OTL amp.1)Tubes used as output,DHT or not DHT.2)output in watts.3)Topology.4)compare/audition each one if you could before buying.Forget others opinion,trust your ears. .

A few people here have mentioned the Berning ZOTL amps. They are now produced by a company called Linear Tube Audio. LTA is able to build these amps at a higher volume than David could by himself and the price is lower. My ZOTL40 with EL34's sounds spectacular, highly recommended.

While the ZOTL amps are a brilliant design, they are very much not an OTL, as they employ an output transformer (see Dave Berning's patent).