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Old 16th November 2004, 07:05 AM   #1
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Default tubecad is back

hello,

"golden brain" John Broskie is back on tubecad.com with blog entries every day.

A real good source to learn more about tubes and amp variations.

Congradulations John

Reinhard
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Old 16th November 2004, 08:10 AM   #2
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Great news! One of the only places out there free from audio-voodoo!

Oh, and for lazy people out ther (like me) here is a link http://www.tubecad.com/
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Old 16th November 2004, 08:35 AM   #3
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Many people consider the use of tubes to be audio-voodoo
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Old 16th November 2004, 08:40 AM   #4
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Quote:
Originally posted by analog_sa
Many people consider the use of tubes to be audio-voodoo

True. Still it's no reason to embellish it, which John Broskie does not.
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Old 16th November 2004, 01:52 PM   #5
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I learned electronics while growing up (my father was a physicist).

I learned how to compute and calculate in school.

I learned good design practices by experience.

However, I learned how to THINK about electronics by reading John Broskie and Nelson Pass.

I've matured a lot. First, it was building some Pass amps. Now, I'm busy buying and building with tubes. There's a lot of "design maturity" that can be demonstrated when your starting point is Broskie or Pass.
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Old 17th November 2004, 02:29 AM   #6
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Hi,

Thanks for bringing it to our attention, Reinhard.

I'm no big fan of blogs but the November inputs struck me; the Aikido, Gomez circuits immediately struck a chord.
While I'm familiar with the Gomez amplifier, I've never heard of the Aikido circuit before but guess what:

Here's one of the designs I did for a Japanese firm well over ten years ago, have a good look:

Cheers,


EDIT: Don't know what you guys think about it but despite of what's said about the SRPP and its derivative circuits, there's nothing push-pull about it that I can detect....
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Old 17th November 2004, 03:58 AM   #7
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Quote:
Originally posted by fdegrove
Hi,

Thanks for bringing it to our attention, Reinhard.

I'm no big fan of blogs but the November inputs struck me; the Aikido, Gomez circuits immediately struck a chord.
While I'm familiar with the Gomez amplifier, I've never heard of the Aikido circuit before but guess what:

Here's one of the designs I did for a Japanese firm well over ten years ago, have a good look:

Cheers,


EDIT: Don't know what you guys think about it but despite of what's said about the SRPP and its derivative circuits, there's nothing push-pull about it that I can detect....

What about the voltage divider to the grid of the second bottom triode? Isn't that important for the noise performance?

Sheldon
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Old 17th November 2004, 04:55 AM   #8
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Hi,

Quote:
Isn't that important for the noise performance?
If it's the PSRR alone you want to improve, then yes it is in fact the essence of the Aikido trickery.

Note that in the circuit I've shown a regulated PS is used (mandatory) even though it doesn't actually say so on the diagram.
J.B.'s point however is to show how you can use the properties of the feedback mechanism within the WCF to not just reduce the distortion of the previous stage (whether that distortion is generated within the stage or injected into the grid at the input) but by balancing the two stages and reinjecting a well chosen amount of noise into the WCF's grid most of the PS noise is cancelled out, increasing the PSRR of the otherwise poor figure for the SRPP to such a degree that PS requirements can be greatly relaxed.

By doing so, the circuit acts not much different from a classic series regulator or, for that matter, the so called "ripple killer".

Personally I'd rather use as clean a PS as possible to start with as I do not want audio and PS noise to mix but that may just as well be anal retentiveness on my part....

Another advantage of cascading an SRPP into a WCF is that the output is capable of producing a much cleaner full (PP) sine wave than any other cascade that I know of into almost any load.
Something the SRPP alone just can't achieve, which is one reason why I've presented one of my designs.
Please note also that, if you'd care to analyse the feedback mechanism of the WCF, a cascade using a WCF at the tail will invariably improve the PSRR of any preceding stage to some extend anyhow IMHO.

The other is just to show that, contrary to popular belief when the SRPP seemed to be the cure all, the SRPP really works best into a well defined load.
Something I think Mike Van Severs once demonstrated quite clearly in an old SP article even though the reason why this occurs wasn't really explained IIRC.

Cheers,
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