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Tube preamplifier with PCC88

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I found this circuit with PCC88. Opinion, please :)
 

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IMO, the biggest problem with the 6922, et al in line stage service is its "high" mu of 33. A simple common cathode block has too much gain.

What sort of a source is the line stage going to be used with? If it's a CDP, no gain at all is needed and a tricked out cathode follower buffering the level control will be just fine.
 
r!sc!,

Herr Stein's circuit uses RC coupled, cascaded, common cathode blocks DC coupled to a cathode follower. Negative feedback is taken from the cathode follower back to the 1st gain block.

If you decide to build that circuit, be sure to place 1 KOhm Carbon composition "stopper" resistors at each triode's grid. The 6922 is QUITE vulnerable to parasitic oscillation.
 
The ECC88 is so linear it doesn't need feedback. It makes a great mu-follower but then you get the whole 33x gain out of it.

Should you decide to use HS's circuit, do drop the bypass caps in the cathode. The reduction of loop gain is made up for by the better linearity of the second stage. The output impedance of the cathode follower is low enough (S=12.5mmhos, 1/12.5=80 ohms) such as not to require much help.
Your ears will thank you.
 
diyAudio Senior Member
Joined 2002
Hi,

The circuit will have way too much gain for a CDP source and most other common line sources bar, perhaps, a very weak tuner.

If you want to remove the bypass caps, remove C2 : two electrolytics back to back and a film bypass cap.
You'll have some current feedback from the unbypassed cathode,
followed by a 100% NFB loop in the CF and a global loop going from output cathode to the input node on the cathode of the first stage.
Definetely not something I'd build for my own use but YMMV.

Actually, the last two stages will do very well on their own already but with one minor disadvantage; it wil invert absolute polarity.

If you'd let us know what you want to do with this stage, I'm sure there are plenty of people with suggestions around.

Cheers,;)
 
If you'd let us know what you want to do with this stage, I'm sure there are plenty of people with suggestions around.

Hi,

the reason way I want use this preamp is that I can found localy PCC88 tubes (very cheap) . This preamp will be used with Hiraga 20W and there will be only one line input (CD or DAC).

The tubes is new to me. Most of suggestions I don't understund. Help is welcome. Just want to make good preamp, nothing else :).

Thanks, Boban
 
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