OTL amplifiers

Dfrigovt, I think you have received a lot of misinformation about OTL's that has confused the issues.

Like Trelja, I can only speak about my experience in relation to Atma-Sphere M-60 amps. I have used my M-60's for over 3 years without one problem arising. Yes, the M-60's do require the right speaker, but that can be said about just about every amp out there (too small, too large, etc.) You can pair the Atma-Sphere M-60 and the smaller S-30 successfully with just about any speaker with a nominal impedance of 8 ohms or higher, this is not a small number of speakers by any means. With the ZERO autoformers you can pair them with any speaker that is efficient enough to be driven by 30 watt and 60 watt amplifiers.

With the Atma-Sphere's you will not have to retube frequently, you will not have to worry about blowing your speakers or amps, you will not have any difficulty finding speakers that sound good with these OTL's. I have no knowledge by which to assess other OTL designs, but it is obvious that Tenor, Joule, Transcendant and Graaf are other OTL designs that people are using successfully as well.

OTL amps are obviously not the only amplifier type that will bring nirvana, but the special qualities they possess just might be nirvana for you personally. As you mentioned in your initial request, you are a tube fan, there is no practical consideration that should prohibit you from auditioning these aside from, perhaps, geography.

There is nothing about using Atma-Sphere amps that will rule anything in your life other than a simple 5 minute biasing procedure that should be done every 6 months. It would be a shame if you missed your nirvana by dismissing OTL's out of hand because of wrong information provided by others. There is nothing pertaining to modern era OTL's that will throw you any curves. I don't know why people keep bringing up issues that don't apply any longer, and haven't for years. This is like saying that it is problematic to fly more than a couple hundred feet because the Wright brothers could do no better.

If you haven't already done so, I encourage you to read the ZERO's Story at ZeroImpedance.com, it elaborates on the effect impedance has on the matching of an amplifier to a speaker. If you don't have the motivation to read all of the document, just read the Technical Sidebar near the bottom. This information is useful whether you end up with OTL's, ZERO's, or none of the above.

Yes, I agree with Wellfed. I think that basically the only challenge in running AtmaSphere amplifiers is finding a loudspeaker with highish impedance.

And, if you don't, there are still two options available. First, you could go with the Zero Autoformers. Although I am not the biggest fan of them, they multiply the impedance of your loudspeaker. So, if you had a 4 Ohm speaker, and ran off the 2X taps, you would have a OTL friendly 8 Ohm load. The 4X multiplier would provide the "ideal" 16 Ohm. Second, you could just buy a bigger AtmaSphere amplifier, with more output tubes. Simple as that.

Again, like Wellfed stated, the AtmaSphere amps are about as low maintenance as things get. Biasing them is a walk in the park compared to my Jadis. The most difficult part I find is waiting the 1 hour for the amp to warm up before I begin the biasing procedures. After that, you can literally do it in less than a minute. Even with an amp with its settings waaaayyyy off, it shouldn't take more than a couple minutes.

And, like Ralph Karsten says, they are all but bulletproof.

I could list the two things I consider as negatives, the awesome amount of heat they throw out and the high amount of power drawn, but nothing like tubes, speakers, reliability, or fuss is anything like a negative.

I would suggest you give them an audition. That would be the determining factor for me, sound.

I have Transcendent 80 watt monoblock OTL's and Berning OTL's (according to some). I know someone who has Atma-sphere M-60's and someone else who has the MA-1's, as well as other Berning owners and people who have extensive experience with Joule OTL's. They are being used with a variety of electronics and speakers, ranging from Merlin VSM to Vandersteen5's. None of us has had any of the problems mentioned above. No blown tubes, no blown speakers, no constant fussing. Maybe we are all lucky, but I don't think so. The Bernings run so that tubes last a LONG time, and are auto-biasing; Transcendents need to be hand-biased, but not every time you turn them on. I forget if someone mentioned this above, but supposedly Ralph at Atma-sphere does a demo where he shorts out the amps with a coin, and....nothing happens. NO boom, nothing.

Dfrigovt, it would be a shame if you concluded that these OTL amps are troublesome or finicky or are only good for "optimal" setups with "perfectly matched" speakers. Proper amplifier/speaker synergy is something you need to concern yourself with regardless of what type of amplifier you choose. When I read comments from people warning of the need to "change tubes as often as they change the oil in their car" or other critical remarks, I have to wonder if this is coming from someone with personal experience with OTLs. As a Joule VZN80 owner I can tell you that my personal EXPERIENCE with this amp over the last few years shares nothing with the comments from Marakanetz. It has been nothing but a pleasure and, next to my speakers, is the smartest purchase I have made in audio. With respect to my amp, the idea that you need to frequently change tubes is absolute baloney. Quite frankly, it's a bit annoying to read comments that broadly label OTLs as having that problem. After three years I am still using the original tubes in my amp with absolutely no problems.

As for speaker matching, one thing to keep in mind (with respect to the Joule at least) is there is no problem using the Joule OTL with 4ohm speakers. In fact, Joule provides power ratings for both 4 and 8 ohm speakers. In fact, Jud Barber of Joule designed the amp to be capable of running his own speakers - Duntech Princess. Those speakers go below 4ohms. One nice thing about the Joule is that the feedback is variable - each channel, progressively. So, that means you can dial in the amount of feedback to suit your tastes - and the damping that your speakers seem to match well with.

As far as being "finicky" I will tell you this. I have had absolutely no problems with my Joule. Zero. From a practical use standpoint this is the way it works. You tell me if this is too finicky for what could be the best, and last amplifier you will ever need to buy... I take 30 seconds to turn a dial up (Variac) to operating voltage which you can read on a built in multimeter. It starts making music right away. 10 minutes later I get off my butt to tweak the voltage (once the tubes heat up). That takes about 10 seconds. That's it. Every half hour or so I may peak at the voltage while I change records. Sometimes I do. Sometimes I don't. No big deal.

In my opinion, saying an OTL amp is finicky is like complaining about engine noise from a V12 Ferrari.

I won't even get into the fact that the amp is built like a brick house, etc. I fully expect it to outlive me (I'm 31). Eventually I will have to replace tubes I guess. I don't view replacing tubes every 4 or 5 years as being a problem.

BTW, I have Merlin VSMs. You owe it to yourself to hear an OTL. I suspect many have no idea what they are missing.

Best wishes.

Jim

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.