OTL amplifiers

Gs & Cluless

The disadvantage (inconvience) I speak of is not of any but consideration of ownership of such an amp that would be a space heater in their room. So far as OTL topology goes Gs, even Class AB OTL's (Transcendent) do run hot because they have so many output tubes although the heat output is less than a Class A topology (Joule, Atma-sphere, Tenor) Many would not consider an OTL simply because of this factor, too bad. Living in Florida or a warm climate is a consideration but it becomes less so after listening.

OTL amps are a subject I really can get excited about in this hobby.

Advantages include, top to bottom clarity, resolution and tonal naturalness more akin to real music. The reason being there is no transformer that CAN add or detract from the signal. These amps when matched properly to the speaker they will be used with can take you to sonic nirvana like no other amplifying device I have heard including transformer coupled tubes, SET with transformers which typically don't offer the frequency extension of the best OTL designs and ss which with few exceptions doesn't offer the immediacy and presence that seems exclusive to tubes. So the best way to describe OTL's are the best world of both tubes and ss with few if any of the weaknesses with the possible exception of bass "slam" which seems more exclusive to ss designs. Bass resolution and natural impact is of much greater interest to me and is harder to get right than slam (dynamic impact, often exaggerated).


Disadvantages of OTL's are as long listed as their advantages:

Since the output tubes provide all the current to drive the speakers without use of an output transformer, it is important that the impedance characteristics not drop below 4 ohms in any case and ideally should be between 8 and 16 ohms at all frequencies without compromising the performance they are capable of. Unfortunately there are few speakers with these characteristics so use of an OTL is not ideal in most instances. Heat is another problem. They run very hot because many tubes are used in parallel to produce the current necessary. They can be designed for high watts but the price is many tubes and a lot of heat, up to 1,500-2,000 watts for a big pair of mono's.

Dependability has always been an issue with these designs but it seems this has become less so with current designs than in the past. The players include Transcendent, Atmas-phere, Joule, Tenor, Graff and the Berning Quasi OTL. They are all great performers with the right speakers.

Dfrigovt

I would like to mention for your information a few other details. I like you have eclectic tastes in music. Without doubt the most difficult music to reproduce accurately as you might hear it live is orchestral and choral music. The natural layering and individual voices you hear in a great live performance is something that I treasure when I experience it. To build a system that can capture that magic in a home environment is a worthwhile goal. It requires committment, but you can really get close. I wouldn't say that OTL's are for everyone as there are many downside considerations as noted above. All I will add at this point is that you try to listen.

So far as expense goes, Clueless is right about the Transcendent, it costs 2.1K for the T8-LN. It produces 25 watts and is great for a very efficient speaker with a stable impedance of say 6-8 ohms in a small room. I've owned this amp and would recommend it in a heartbeat to anyone that meets those specific requirements. I also believe this amp is an excellent value because it does all the things that seems intrinsic to OTL's if to a lesser degree at a very reasonable price. It is a very serious amplifier.

So far as the Joule goes, I had the opportunity to listen extensively to the VZN 80 stereo amp in my system . At the list price of 8K it appears on the surface to be expensive but when one understands that it is handmade (hardwired, no circuit boards) by the owner Jud Barber, has features including a variac to slowly bring up the voltage of the tubes to the correct operating level, individual biasing of tubes for optimal performance, no guesswork, variable feedback setting along with impeccable fit and finish I think its a bargain. I wouldn't have said this before I experienced this amp . Excuse my excitement but I'm not finished yet!

The amp I currently own is the Berning Zh270 ZOTL. I'm not going to even attempt to get technical because I don't completely understand how it works (Clueless's comment about Berning being bright may be a little understated :) It runs cool 100 watts at idle, can be used without a pre-amp, has 3 feedback settings which effectively can match it with lower impedance speakers, those requiring more current, without changing character or showing if you will a "personality" especially one that may be offensive. It is very tweakable and in my 1.5 years of ownership my excitement hasn't subsided, it just gets better. This amp costs 4.5K retail and I would just love to hear the amp at this price point that competes in the area that this amp excells, top to bottom clarity, no grain, glare, grit, grain or any other gosh darn G word you can think of. It is just amazing. And it also does bass very, very well.

The above 3 I have listened to extensively in my system. The rest I have heard on several occasions in different systems so I can't comment beyond the fact that every system except one (I think it was the speaker's I didn't like) had some serious magic going on. They are definitely worth looking into if you are willing to live with the speakers that would qualify their use in your system. Music is all about connecting to the emotion, these amps are better at it because they just get closer to it. In my experience I would say that their price to performance is excellent contrary to Mark. Cavaet, YMMV and IMO a comparably good transformer coupled tube amp will cost more.

Interestingly enough Detlof, Harvey's "wretchedly excessive" Futterman's are still being used by someone I know to good effect (last time I spoke with him) with nary a problem on a pair of Magenapan Tympani 4"s. I suppose he is one of the lucky ones or maybe this particular *Child* of Harvey has an intrinsically sweeter personality or received more attention during the formative years?

Wellfed your points are well taken. I however agree with Trelja in my experience with the autoformers. I found the 1.37 setting the best. 2X was ok but anything above that the sound became whiter or more solid statish losing much of the natural sweetness intrinsic to the Transcendent amp I used it with. Indeed the bass was improved. It seems this device designed with the Atma-sphere in mind decidedly didn't do what I needed in my system. I liked it at first but found myself over time going back to direct most of the time. What I needed was more OTL power.

I feel the zero autoformer is a very well priced well designed product that will benefit some systems more than others but bear in mind that the character of the sound changes the higher the multiplier.

Henry to answer your question, this might be a possibility if there is not a built in circuit or shut off in the event of catastrophic overload, a voltage surge from the outputs. Most OTL amps have some sort of protection circuit in the event this manisfests itself for any reason.

I see you have asked this question on another thread and no one has answered. Maybe you should talk to a dealer. I believe Jtinn is a dealer for Tenor and he should be able to answer your question. This was one of the problems with the Futterman's, it didn't have protection between amp and speaker not to mention its inherent instability when matched to the wrong load. Most of today's OTL's have addressed this problem and do have some type of protection.

Dfrigovt, consider this fact, Atma-sphere has been manufacturing OTL amps since 1980, Joule since the early 90's, Transcendent since the mid 90's. The others I really don't know, but the Tenor is certainly more recent and the Berning which uses a completely different approach, was brought out I believe in 1996.

There were major considerations of owning such an amp in the past. The Counterpoint SA-4 and NYAL amps are really the only ones that contributed to the bad reputation of this design often because folks used them with the improper load. Harvey Rosenberg was very defensive of his design and was adamant that most of the problems were caused by audiophiles not paying close enough attention to this.

I am not trying to sell you on anything. If you like tubes I would say that a OTL is no more maintenance than a regular tube amp. The tubes should last a long time on the above mentioned amps. The outputs on the Joule the 6C33C are projected to last over 5 years. I believe the Tenor uses the same output triode. Audio Research 6550's are recommended for replacement every 2,000 hours, cost per tube is similar, about 30-40.00 each to replace. The Atma-sphere tubes are even less. The Transcendent's are about 20-30.00 each. Atma-sphere even less. I have not heard of ONE incident of catastrophic failure of either speaker or amp with the above designs. The advocates of these designs are speaking from experience. My guess is that Marakanetz is not but purely from an engineer's perspective based on what COULD happen with such a design from a purely theoretical viewpoint and how a transformer would act as a buffer in the event of failure. His concern seems to be about DC at the input of the speaker without a capacitor to act as a buffer. I can't speak for all the designs but I know the Transcendent uses fuse protection but is direct coupled. I'm sure the others have addressed this. Maybe someone else can offer input to Marakanetz's concern regarding this with the other amps. If not call the manufacturer and ask. Knowledge is king, misinformation is of no benefit to you or anyone else reading this thread. Get the facts.

Jud Barber has been working with tubes since the 50's, and also is an engineer. Bruce of Transcendent is an electrical engineer. Ralph I don't know. I think their experience and success with the reliability of their products would qualify them to a greater extent than someone providing theories as to what COULD go wrong and making absolutely erroneous remarks about replacing tubes regularly. The same for Atma-sphere. This design is mature and refined. See if you can find any horror stories about Atma-sphere amps blowing up.

The point is this as it is with anything audio, it is up to YOU to find out to your satisfaction the reliability of these amps. The users of current OTL amps disagree adamently with the naysayers who probably don't own or have NEVER owned an OTL amp. First thing you need to do is listen. The newer designs DO work to 4 ohm loads but as stated above, the OPTIMAL load is 8 ohms or higher. There are many speakers that qualify. Talk to the manufacturers'. Jud of Joule, Ralph of Atma-sphere and Bruce of Transcendent will give you the low down of the do's and don't for their respective designs. Each of these designs are considerate of the past failures that has led to the current reputation (by some) that OTL's are somehow still unreliable.