John Curl's Blowtorch preamplifier part II - Page 451 - diyAudio
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Old 1st June 2010, 05:10 PM   #4501
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Quote:
Originally Posted by bear View Post
Hi Allen, 6DJ8 might have suitable technical specs but they sound hard and gritty to me no matter when they have been in a circuit... so no go<<

Then, to be blunt, you are not using them right. Check out this review of our RTP3D preamp, using (only) 12 x 6DJ8/6922:

http://www.sixmoons.com/audioreviews...te/preamp.html

He, and no other RTP client reports gritty sound.

>>Now what about those RESISTORS??<<

Which resistors? Not a topicI've brought up.

Regards, Allen

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Old 1st June 2010, 09:06 PM   #4502
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Allen, dunno, I place zero credence in reviews... otoh you may have figured something out. That has not been my experience with this tube. Others may have other experiences and my experience the sound of this toobe differently (and apparently do).

Resistors - not aimed at you - the rest of them! We were discussing resistors and the thread went elsewhere suddenly without notice.

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Old 1st June 2010, 10:18 PM   #4503
SY is offline SY  United States
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Quote:
Originally Posted by bear View Post
Allen, dunno, I place zero credence in reviews...
Wise, especially where 6Moons is concerned. Nonetheless, I have heard (and built) plenty of 6DJ8/ECC88 designs that had no trace of "grittiness," including Allen's. Most bad experiences with that tube are either due to VHF oscillation (most common) or relabeled remote cutoff triodes sold as 6DJ8. The transconductance and low capacitance can be a deadly combination uless handled carefully.

BTW, I'm glad to see that discussion of no-holds-barred preamplification has finally settled on the right devices to use...
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Old 1st June 2010, 10:41 PM   #4504
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Quote:
Originally Posted by bear View Post
Allen, dunno, I place zero credence in reviews... otoh you may have figured something out. That has not been my experience with this tube. Others may have other experiences and my experience the sound of this toobe differently (and apparently do).

Resistors - not aimed at you - the rest of them! We were discussing resistors and the thread went elsewhere suddenly without notice.

_-_-
Bear
The guys were not say 12ax7 sound bad but that certain precautions needed to be taken when using it .
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Old 1st June 2010, 11:00 PM   #4505
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I have worked with both the 12AX7 and the 6DJ8, in virtually the same topology of phono stage. I can live with the 6DJ8, but the tubes have to sorted and listened to. Rejects are expected.
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Old 2nd June 2010, 06:18 AM   #4506
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I know we are getting off topic, but out of curiosity: Which topology of phono stage this happened to be ?
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Old 2nd June 2010, 06:58 AM   #4507
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Originally Posted by gk7 View Post
I know we are getting off topic, but out of curiosity: Which topology of phono stage this happened to be ?
GK7

People spend a lot of time with valve types and circuit topologies but what is also of worthy mention is what circuits are used to power up the individual valves , both high voltage (plate supply) and low voltage (heater supply) as typical valve circuits have very poor power supply rejection and they have a big influence on sound.

So asking John Curl about his circuit is almost pointless without knowing everything else.
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Old 2nd June 2010, 08:54 AM   #4508
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Quote:
Originally Posted by PHEONIX View Post
GK7
typical valve circuits have very poor power supply rejection and they have a big influence on sound.
Have to disagree. As with solid state circuits, there's a wide, wide range of PSR. Taking two good phono preamps, for example, you've got Allen's cascode transistor/ECC88 that has exquisite power supply sensitivity and MUST be used with a top-quality, low noise regulator, and there's mine, which has very high PSR and can be powered off very simple regulators. They're both tube-based, both perform well, and span the alpha-omega of power supply rejection.

I'll guess that John was playing with a Marantz/ARC sort of topology with moderate PSR. It would be interesting to see what he'd do with tubes today.
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Old 2nd June 2010, 03:30 PM   #4509
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Quote:
Originally Posted by SY View Post
I have heard (and built) plenty of 6DJ8/ECC88 designs that had no trace of "grittiness," including Allen's. Most bad experiences with that tube are either due to VHF oscillation (most common) or relabeled remote cutoff triodes sold as 6DJ8<<

Exactly. Also running them at low current in a "12AX7ish" circuit just doesn't sound good.

>>BTW, I'm glad to see that discussion of no-holds-barred preamplification has finally settled on the right devices to use...
Again, exactly!

Regards, Allen
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Old 2nd June 2010, 03:33 PM   #4510
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Quote:
Originally Posted by PHEONIX View Post
GK7

People spend a lot of time with valve types and circuit topologies but what is also of worthy mention is what circuits are used to power up the individual valves.
You are correct here, and that's why my schematics all INSIST on the use of my current sourced shunt regulator to work and sound as they should.

Regards, Allen
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