If you were going to build a OTL?

[leadbelly]

Whatever. If the mods and gurus leave you alone to post your pseudo-science because of your celebrity, what can I do about it? Bye-bye...

 

[atmasphere]

Whatever. If the mods and gurus leave you alone to post your pseudo-science because of your celebrity, what can I do about it? Bye-bye...

Right- a sort of 'drive by' sniping then? Who is the bully here? If you have facts to back yourself up, present them.

There is no 'pseudo-science' (whatever that is) involved. The issues of global negative feedback have been known for over 50 years. Norman Crowhurst has mentioned this issue in his writings; General Electric proved the issue with human hearing and odd ordered harmonics in the mid 1960s.

What is 'pseudo science' is to deny the knowledge that has been around for decades, simply because it is inconvenient, or disagrees with a made-up world view.

You might consider the fact that the oldest OTL manufacturer in the world exists today solely out of the reliability of its product (I leave the comments about how it sounds to others). In that time of over 3 decades, I've seen a lot of amp manufacturers, tube and transistor, come and go. Is 3 decades by chance then? Out of something made up? Business in general being what it is, competition and all, the former and the latter both seem highly unlikely...

I don't contest the OTLs have a reputation of unreliability. In a nutshell, that myth has been our biggest marketing problem in the history of our 33-some years.

 

[tympani1d]

Right- a sort of 'drive by' sniping then? Who is the bully here? If you have facts to back yourself up, present them.

There is no 'pseudo-science' (whatever that is) involved. The issues of global negative feedback have been known for over 50 years. Norman Crowhurst has mentioned this issue in his writings; General Electric proved the issue with human hearing and odd ordered harmonics in the mid 1960s.

What is 'pseudo science' is to deny the knowledge that has been around for decades, simply because it is inconvenient, or disagrees with a made-up world view.

You might consider the fact that the oldest OTL manufacturer in the world exists today solely out of the reliability of its product (I leave the comments about how it sounds to others). In that time of over 3 decades, I've seen a lot of amp manufacturers, tube and transistor, come and go. Is 3 decades by chance then? Out of something made up? Business in general being what it is, competition and all, the former and the latter both seem highly unlikely...

I don't contest the OTLs have a reputation of unreliability. In a nutshell, that myth has been our biggest marketing problem in the history of our 33-some years.

Bravo!! Well stated.

 

[sepolansky]

Whatever. If the mods and gurus leave you alone to post your pseudo-science because of your celebrity, what can I do about it? Bye-bye...

I read these forums to learn. I've been at this quite awhile, but freely admit that the more I learn, the less I seem to know. The informed opinions of others, whether engineer or golden ear types are a valued addition to my knowledge. What is most distasteful are the ad hominem attacks, baseless accusations, ridicule of other's work and other actions of the self-perceived righteous.

I would think the manufacturer of a truly unreliable product would not survive long in the marketplace, failing as would a company that produced sonically inferior products which were touted as superior. I'm sure there are examples of the opposite being true, but I think in general, the market reaction would be negative to a failure prone, lousy sounding product.

Many of us have participated in this thread trying to learn how to build a better OTL, possibly a product we'd love to buy in the commercial market, but can't afford; possibly a unique variation. The fact of "celebrity" participation in our discussion adds invaluable insight into the necessary design considerations and 33 years of real world market/field experience to help guide us pass potential pitfalls so that our own DIY projects might benefit from this freely given knowledge.

Thank you, Atmasphere. Please continue in spite of the sniping.

Stuart

 

[kevinkr]

I recommended copying an Atmasphere design originally in post #4 of this thread, and for good reason. I've long been acquainted with various Atmasphere amps although I have never owned one and run small DHT SE amps at home. They have never failed to impress, and IMLE have a proven track record of reliability - just ask anyone who owns or has owned one.

I have a lot of respect for what Ralph Karsten has accomplished over a 30yr run. Keeping a small audio business alive over this length of time is no small accomplishment, and I think tends to vet that he knows what he is talking about.

Incidentally I didn't take his comments in post # 20 to be a direct challenge to anyone other than the poster of the original negative comments in post #12. FWIW his comments echo my experience quite well.

 

[wobbly]

I built an M60 kit over 12 years ago, its used nearly all day,every day, sounds stunning and has never been touched except to check the bias.
They now finally drive the perfect speakers for OTLs,16 ohm 100Db Bastanis Atlas.
I ditched the nfb after hours of testing with a remote switch and multi listeners.
The differences were obvious, and 0Db was a "clear" winner.

Forget theoretical biases,what works - works.

 

[Alastair E]

Wow. When someone states something that is outright false, the product of opinion rather than fact, would you prefer that it go unchallenged?

Global negative feedback, while reducing overall THD, actually **adds** distortion to the odd harmonics. Not by much (100ths of a percent), but since our ears use these harmonics to gauge the volume of a sound we are very sensitive to this 'enhancement'. Go read a book indeed: the use of GNFB is thus violating a fundamental rule of human perception- how we perceive volume.

If built right, OTLs are as reliable as any other tube technology. 'If built right'- and IME experience, many are not. One of the primary issues that plagues many OTL designs is the means of biasing the power tubes. Quite often there is a tension between the value of coupling caps used and that of the divider network values in the bias network. Most power tubes used in OTLs need the divider network to be a lower set of values (you aren't going to control the tubes with 1M bias resistors...) and that means larger coupling cap values. The problem is that these amps are very transparent so the artifact introduced by large coupling caps (needed to play bass) is easily audible. So to fudge that, the bias network gets pushed to higher values.

The result is an amp in which bias drifts easily, has poor overload recovery and a variety of other ills, all of which are avoidable. Add to this an excessive amount of feedback to compensate for the distortion of an asymmetrical drive or output, and you have an unstable and unreliable amp.

Design problems are not unique to OTLs; as long as humans are making things, flaws will be found. But at the same time there will be designs that overcome flaws of the prior art; anyone who ignores this fact is at risk of engaging in mythology.

Absolutely!

Rightly or wrongly, on my designs I use followers, MOSFET or Tube to directly drive the output bottles for this very reason...

I wont say there's Zero drift, But its darnd low and you can use more normal range of coupling caps and bias resistors....

Works for me....

 

[markusA]

Gotta love these forums and threads.
There's always small bits of informaton that make you think and pushes your line of reasoning a step further.

 

[banat]

Right- a sort of 'drive by' sniping then? Who is the bully here? If you have facts to back yourself up, present them.

There is no 'pseudo-science' (whatever that is) involved. The issues of global negative feedback have been known for over 50 years. Norman Crowhurst has mentioned this issue in his writings; General Electric proved the issue with human hearing and odd ordered harmonics in the mid 1960s.

What is 'pseudo science' is to deny the knowledge that has been around for decades, simply because it is inconvenient, or disagrees with a made-up world view.

You might consider the fact that the oldest OTL manufacturer in the world exists today solely out of the reliability of its product (I leave the comments about how it sounds to others). In that time of over 3 decades, I've seen a lot of amp manufacturers, tube and transistor, come and go. Is 3 decades by chance then? Out of something made up? Business in general being what it is, competition and all, the former and the latter both seem highly unlikely...

I don't contest the OTLs have a reputation of unreliability. In a nutshell, that myth has been our biggest marketing problem in the history of our 33-some years.