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Old 23rd October 2002, 06:05 AM   #1
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Default OTL Help

Try to build an OTL, looking for schematics of Atmasphere, Croft, Diefenbacher and Klimo. The last two are germans,

Can anybody help?

Reinhard
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Old 23rd October 2002, 06:33 AM   #2
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what output tubes did you have in mind?
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Old 23rd October 2002, 06:46 AM   #3
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reinhard,

Give a look at:

http://www.transcendentsound.com/

kits and knowlege

The owner of Transcendent Sound wrote an excellent book for the glow-fet hobbiest.

Beginner's Guide To Tube Audio Design
by Bruce Rozenblit

As well as being an excellent book about tubes in general, it contains a schematic and article on an otl design.

Regards,

Aud_Mot
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Old 23rd October 2002, 07:30 AM   #4
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Hello guys,

Iīm not sure which tube to use, have 6C33, 6336,
6AS7, 6C19. If another is better I will use this.

I know the Rozenblit Book, think I have it, but I
am still looking for a reliable, full symmetrical design, circlotron? Donīt like the asymmetrical futterman designs, because they are only working with a lot of feedback.

Thanks for your answers.

Ah, I donīt need much power, 10 Watt with some slam in the bass region is ok.

Reinhard
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Old 23rd October 2002, 11:03 AM   #5
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Default OTL

Hello Reinhard,

With OTL designs you inevitably have to use a certain number of output tubes to get low output impedance after applying global NFB.
So you inevitably end up in the 20 to 40 Watt range if you want to get good bass response into an 8 Ohm speaker.
As in Germany a lot of the speakers have a 4 Ohm impedance you would then need at least twice as much power.

If you need to stick to the Circlotron types of OTL then the only ones currently made (to my knowledge) are Atmasphere.
They have a good support group at this site:

http://www.otlamp.com

Other possibilties exist: Bruce Rozenblitts' design appeared in Glass Audio and I've built a few based around that with twice the power.
It sounds very good and is pretty straightforward to build.
Maybe he published the circuit in his book as well.

As far as Croft goes you will not find any circuit diagrams drawn by himself but I can tell you that the principles are the same as used in the Rosenblitt design.
His latest designs even add HT regulation (with tubes) for the output stages.
I think Klimo used sweep tubes for the output.The Diefenbacher OTL I'm not familiar with.

Cheers,

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Old 8th November 2002, 07:52 AM   #6
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Bruce Rosenblit DOES publish the complete schematic in his book Audio Reality. I own the Transcendent Stereo T8 OTL and it is the finest amp I've heard. The only drawback is that I'd like more power for one of my several pairs of speakers. Still, at 25 watts it acquits itself quite well at moderate volumes. Highly recommended.

Andy
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Old 8th November 2002, 11:27 AM   #7
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Hi,

Andy,

Best thing for you seems to get another stereo amp and have both bridged for twice the power?
Does the book describe the circuit with the EL509/6KG6 or the one that was published in GA with the 6AS7s'?

Reinhard,

For a fully symmetrical approach only the Atmasphere do that according to the Wiggins Circlotron principles.

Another candidate for OTL use is the 6528 if you can find it at reasonable price and quantities.

Cheers,
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Old 8th November 2002, 12:43 PM   #8
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Hi Frank and Andy,

I've got bruces book as well..but instinctively don't fancy the complexity...(for diy that is...don't mean to imply the effect on the sound)

Are there some good (and simple) OTL designs out there...not necessarily from the well known manufacturers..

Regards,
Bas
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Old 8th November 2002, 01:20 PM   #9
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Default my otl!

Hello friends,
have build my own in the meantime, looks like the atmasphere, 2*6N1 as diff.cascode amplifier, cap coupled to a 6H30 Cathode followers, direct coupled to 12*6C19 triodes. Some 60 Watt into 8 Ohms.

Use a servo to correct the output DC, an idea of tubecadīs John Broskie, thanks for it.

Have a plus minus of 310 Volts for the driver and
two 180 Volt for the output stage.

At the time I have made first lissening sessions with great pleasure. I am more impressed about the bass than any other thing.

Reinhard
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Old 8th November 2002, 01:29 PM   #10
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Reinhard,

Congratulations!

Quote:
Have a plus minus of 310 Volts for the driver and two 180 Volt for the output stage
Is your amp PP or SE?

Re:the output stage: you didn't use a B+ and B- on anode and cathode on either side of the output tubes.



Quote:
Use a servo to correct the output DC, an idea of tubecadīs John Broskie, thanks for it.
If you use the B+ and - Ht rails as described any DC is automatically nulled at the output if you take it between the tubes.
It makes me wonder if this wouldn't degrade the performace of the amp.

In the 16 years I use my OTL amps I never had any DC on the output even when pulling tubes out live.

The above is assuming your design is PP.

Can you tell us some more,how does it sound?

Thx,
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