Before I found decware, I was reading about Susan Parkers Zeus mosfet amplifier.  simple design, no feedback, described sound is similar to the described sound of a zen.  I've always been interested in building one.  But to get the transformers, shipped from UK, costs 2 arms, several legs, and more.  I recently read her quote "the transformers are the heart of this amp" or something like that.

I know that the turns ratio of a transformer dictates how much AC voltage is stepped up or down, but I had no clue about bandwidth issues, and internal losses based on construction of the transformer.

So I searched. And found this page (I guess Lenard sells their own stuff, but there's a great deal of educational type pages at this site).

http://lenardaudio.com/education/14_valve_amps_5.html

It's a very interesting page if you want to understand your output transformer.  

I never really thought about the fact that all our musical information goes through the output transformer.  I mean, there's no electrical connection between the amplifier and the speakers.  It all goes through a magnetic field.  So the quality of that device really matters.

I didn't realize power transformers are made to operate at a single frequency (60hz). and so.. they act like higher frequency filters. So a triplite isolation transformer filters some line noise by virtue of the transformer wanting to pass only 60hz (well, whatever it's bandwidth is).

I didn't realize that output transformers are layered in complicated ways in order to get the widest bandwidth through them, on the high end.

And size and weight is the thing that limits the low frequency range because lower and lower frequencies will saturate an inadequately sized core.  There's a 60 lb experimental output transformer in the link.

I'm awe struck how much there is to know about OPT's.  I think this helps me understand the statement about the zen opts seasoning over time.  all the music is transferred by that magnetic field.  If anything about the iron core changes (metallurgical things) the field will change.  the sound will change.  season.  

thought I'd share. (some of you guys already know this stuff.)

Great article!

BTW, I always wondered why no one has ever offered super Cryoed versions of transformers?

Or maybe putting the entire little Zen amp (except the wooden base) through a CRYO processs?
I bet it would sound even sweeter.

Even if you're not interested in the MA....the read is important. He truly is selling the Amp at an introductory price. I am glad I can afford one now.   

Re: The MYSTERY AMP !
Reply #96 - 07/12/13 at 02:32:52    

Transformers have the biggest effect on a tube amplifier's sound in my world, so it came as no surprise that this latest intrusion into the amplifiers voicing would be big. (No that's not true... it came as a big surprise!)  And now having just witnesses how different transformers effect the sound again, I still can't help but be amazed at just how much things can change!

After several evenings discussing the output winding topologies we recently tested some classic secondary arrangements with the typical taps against some dual secondary arrangements where windings of different lengths are combined on the same bobbin.  The differences ranged from something that sounded typically real good, to something that sounded magical.  Some interesting stuff since the only main difference is in the pattern of core saturation.  I expected to have to strain to hear the difference, but instead I had to check and see if we were still listening to the same amplifier.

With this rather pleasant discovery I now know this amp is going to be hugely successful.  Optimized for (but not limited to) KT66 output tubes, I'm currently witnessing it sound better than both the Zen Mono's and the TORII MK III.  That doesn't mean it is, because it's still to new and there is some infatuation that will need to wear off before I can actually hear it objectively.

I'll keep you posted as I put the fine polish on it and continue to wrap my head around it.  Right now my comment about the sound would be this:  Generally liquidity and honesty are rarely found in the same amplifier, but this seems to be a reference for both.  Almost too good to be true.  


Steve

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How is the sound affected by going OTL?  Would it be more neutral and have more accurate tone and detail to the original recording? 

Transformers inherently cause distortion and some smearing - hearing an OTL amp nearly melted my brain with the amount of detail I was hearing.

At Steve's place, listening to the OTL amp was like someone turned on a 7.1 surround sound; except nothing had changed but the amp!

I'm glad he only gave me a sample of it, because I'd otherwise be hounding him to somehow make me one, and he said it was extremely expensive to make, used a ton of power, and was expensive to maintain tube wise. All of those "features" go against my better nature.

It's all about impedance.

The whole reason we use transformers in the first place is because the circuit, the tubes, have a specific impedance, usually in the thousands I think - and our speakers have a completely different, much lower impedance. So the transformers are setup at a ratio - if the speakers are 4ohm, and the tubes are 4000 ohm, you need a transformer 1000:1 to get that tube to actually drive the speaker.

I believe there is also a danger of how much voltage an OTL puts out to the speakers...like dangerous to people.

So the first trick would be finding good sounding tubes that happen to have the right impedance to drive typical speakers. Some companies have found ways around that which is beyond me, and from the articles I've read it almost sounds like they aren't OTL anymore...but what do I know. After matching the impedance, it's all about building an amp around that tube, and doing it safely.

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LOL, yes I agree I would not think that either unless Steve puts one out

I was curious though as to OTL by removing the tranny would lead to a more pure sound.  But when I look at the market there a very few manufacturers that I could call out that even make them, so it would lead me to believe that they are either (a) too complicated, (b) too expensive, (c) impractical/unreliable, (d) or they are not as great sounding as one would think and/or (e) all of the above.