Transcendent OTL T8 Vs. Atma-Sphere M60

[Tyimo]

Hi!

Has somebody any experience with this two OTL beauties??

Which one is worth to build......???

Greets:

Tyimo

[Tyimo]

O.K.
Nobody listened the amps in the question?!?

After heavy info hunting about these amps the Athma-sphere M60 is out of the question, but there is a new competitor:
The Graaf GM-20!
I would use with normal 8 Ohm, 90-92dB dynamic speakers....

Has somebody listening experiences??

Tyimo

[kevinkr]

Hi Tyimo,
I have heard the Atmosphere M60, a very good amplifier to be sure.
Why is this design eliminated? Atmosphere has a longer track record than just about anyone with continuous commercial OTL production, and in my experience they are reliable - something not always associated with OTL designs.

I haven't heard anything else you mention as they are uncommon here, and in any case I only build things I design. Comparisons have been against other DIY amplifiers and a couple of AN products (like the Ongaku and Keegon) I have been lucky to get my hands on in the past.

My one foray into OTL land was quite humorously tragic, and you can read the entire sordid tale on my website.. You probably should too before embarking on your own project.

Perhaps others have the answer you seek.

[Tyimo]

Hi Kevin!

Thanks for the answer!
I red your website. Interesting story....

I don't want to build an own design. Just a KIT or better to say a clone.
I have the book from Bruce Rosenblit with the T8 amp. He wrote very nice thinks about his design, but it is too nice to be true....
So I am looking for builders of his amps to get to know theirs opinions.
Unfortunately I never listened these amps, but I found some "negative" info about the Atmasphere amps from peoples whom I believe. i.e. :too much neutral = steril, not enough bass, too high output imp, etc.
About the Graaf I found more positive infos, however the two amps are very similar as I know....

Well, I am still looking for opinions!

Greets:

Tyimo

[kevinkr]

Hi Tyimo,
Of course those you talk to will be expressing their opinions, you'll not have the opportunity to determine whether what they hear and what you hear would be similar under the same circumstances.

I have never heard anyone complain about the Atmosphere being sterile, I've heard several different models over the years. They are very transparent and neutral. Bass response with the M60 was very good imo. The only way to get low source Z with an otl is with lots of feedback, something I try to avoid.

Start with something very simple, several designs exist using 6C33.
You're probably going to have to build something to figure out what you like. Listening opinions are just that, your experience with the exact same amp may be quite different.

I have never heard any of the Rosenblit stuff so I can't say for sure how it sounds, but plenty of people do build his amplifiers and reputedly they at least work, something not guaranteed in the world of OTLs.

[BHD]

I've heard the Atma-Spheres at great length and they are great amplifiers.

I've read Bruce's books and he places great importance on reliability. I haven't heard his amps, though.

[HollowState]

Many years ago (17?) a friend of mine, George Tice, purchased a pair of Atma-Sphere MA-1 50 watt monoblocks. Yes, the same George Tice of Power Block fame. I knew him as a mutual member of the New Jersey Audio Society.

These amplifiers were early versions of the model and were entirely hand wired without PCBs like current production. Wanting a schematic of his amps, he asked the manufacture for one but Karsten refused claiming he didn't even have one for himself!

Being resourceful, George came up with a copy of the patent. (#4,719,431) Still not satisfied, he brought his amps to my shop where I reversed engineered them and drew up a schematic.

For those interested, a 6DJ8 LTP cascodes into a 12AU7 that's capacitor coupled to a differential 6CG7 cathode follower. This follower directly drives the 12 6AS7G output grids. (6 per side) The output stage is powered from two floating 150V/750mA supplies and is configured as a Circlotron® There is no overall NFB. Only un-bypassed cathode degeneration in the first stage.

Curiously, Atma-Sphere was not manufacturing what was patented. The above numbered patent clearly depicts and describes an anode follower output stage. This amp, and I assume others, is a cathode follower output.

After making sure the DC balance and bias settings were correct, I made some harmonic distortion measurments. At rated output the THD was a little over 12%. This improved as the power level went down but never went below about 1%. George loved them and couldn't hear any distortion. Some time later I did visit him on Long Island and listened to them on his system. They were very dynamic and powerful, but I did feel I heard some distortion. This may have been because I knew it was there.

Victor

[Tyimo]

Hi!

Of course those you talk to will be expressing their opinions, you'll not have the opportunity to determine whether what they hear and what you hear would be similar under the same circumstances.

Yes, it is very true.

I know the best would be to listen these amps myself....

Greets:

Tyimo

[Zero Cool]

Originally posted by HollowState
Many years ago (17?) a friend of mine, George Tice, purchased a pair of Atma-Sphere MA-1 50 watt monoblocks.

These amplifiers were early versions of the model and were entirely hand wired without PCBs like current production. Wanting a schematic of his amps, he asked the manufacture for one but Karsten refused claiming he didn't even have one for himself!

Being resourceful, George came up with a copy of the patent. (#4,719,431) Still not satisfied, he brought his amps to my shop where I reversed engineered them and drew up a schematic.

For those interested, a 6DJ8 LTP cascodes into a 12AU7 that's capacitor coupled to a differential 6CG7 cathode follower. This follower directly drives the 12 6AS7G output grids. (6 per side) The output stage is powered from two floating 150V/750mA supplies and is configured as a Circlotron® There is no overall NFB. Only un-bypassed cathode degeneration in the first stage.

Victor

This sounds like the exact amp i am rebuilding now. I have one of Ralphs very early prototypes. I have it running at the moment and it sounds great. I am using a old set of RCA Black Plate 6as7G tubes and they are not expected to survive. Already lost one section of one tube. I have some 6N13S tubes on there way from overseas now. But the amp i have has 8 tubes per side.

Ralph lives not far from me. He is a friend of a friend and i have been to his shop recently and i can tell you he does not have schematics himself of anything! I am reversing this old prototype amp so he has a set for himself!

Lots of upgrades since these old amps. LOTS! and these old amps sound great! His kits are well worth the $$$ But take his word, use the Russian or chinese tubes only. americano tubes doest last long.

And yes, let those tubes cook filiments only for a good 24 hours if you can stand the heat before hitting that HV switch.

I am considering building a cooking stand to cook tubes a few at a time. i have 40 on there way and really dont want to run the amp with 16 tubes in it for 24 hrs. maybe this winter would be better for that.


Zc

[HollowState]

"use the Russian or chinese tubes only. americano tubes doest last long."

How things have changed! I've always been of the opinion that American made tubes were the best. The only exceptions were the older Europeans like Amperex, Mullard, Telefunken, Siemens, Valvo etc. I guess I remember the old days too well when Chinese tubes began to hit the market, They were garbage with specifications all over the place and plagued with high infant mortality rates.

The early MA-1 I saw used 6AS7Gs that were labeled "made in England" but had no brand name.

The need to burn in receiving tubes yourself is a modern phenomenon. American tubes were always burned in by the manufacturer and needed no more. When the RCA plant in Harrision NJ closed it's tube division I could have had all the burn-in racks I wanted, but didn't. I did get a pile of nice expensive Westinghouse panel meters which I still have.

One day, in the not too far future when I retire, I'll probably build a big triode OTL. But I'll use the NOS American stuff I've stockpiled over the years. Whether 6080WA's, carbon plate Bendix 6082's, 6336A's or B's, 6528's or even those 6394's (26V 6336A's). Too many projects and so little time.

Victor