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Old 18th July 2009, 11:40 AM   #1
Dxvideo is offline Dxvideo  Turkey
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Lightbulb Cavalli OCL Buffer

Hi all,

As a group of Turkish DIY ers, we started a common project that a clone of Cavalli OCL Buffer with DC servo;
http://www.cavalliaudio.com/oclbuffer/main.php?page=diy
With my PSU design, the total application schematic will be like that;
Click the image to open in full size.
And the PCB design I made;
Click the image to open in full size.
Now I am waiting for your precious comments on this..
Thanks a lot for your advices in advance..

PS: Were using Russian 6N6P instead of ECC99 tube.
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Old 18th July 2009, 12:16 PM   #2
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not as complain but more as reminding - draw on schematic grid to gnd resistor , to prevent possible confuse .

beside that - having grid resistor is always good , in case that anything goes wrong with pot contact ; not of much importance here , where triode is biased with CCS , but anyway ....

also - grid stopper is good thing to have

on link you gave - bootstrapped (cascoded) version is certainly better ( not just in test , but soundwise too) ; then it's real SLCF , as Alan Wright like to call it , and you squeeze all quality possible in that stage .
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Old 18th July 2009, 12:30 PM   #3
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Actually I was thinking about to put a grid resistor too! Thanks for reminding.
And concerning the bootstrapping issue;
I have tried a bootstrap like in this application with Pedja Rogic's famous JFET buffer stage however I found its sound a bit dull. Then I've removed the bootstrap and connect the input JFET directly to the Vcc (like this application) then the trebles came back again. May be the bootstraped version was more musical and the non-bootstraped was more boring...
Anyway, I can add a space for bootstrap to the PCB, who wants to add bootstrap just solder a MOSFET to here..
Thanks for your comments again.
More?
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Old 18th July 2009, 02:50 PM   #4
Gordy is offline Gordy  United Kingdom
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An interesting project for you. However my guess is that your power supply with just CRC will give too much ripple. I suggest more RCRC, or even better to use a TL783 for a regulator.
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Old 18th July 2009, 02:51 PM   #5
Gordy is offline Gordy  United Kingdom
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C14 and C15 are close to V1, so will they get too hot?
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Old 18th July 2009, 07:04 PM   #6
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Allan Wright claims that every mosfet replaced by a valve brings sonic benefits. My experience says I am inclined to agree with him. Unfortunately it makes the voltages a lot higher and the need for two twin triodes for a full SLCF.

Its possible to achieve a decent CCS in the tail by using a voltage divider from +B down to about 20V and then referencing a triodes grid to that. This then allows you to include a much bigger cathode resistor. This impedance is multiplied by the triodes mu and you have a decent and adequate impedance CCS. I did the same thing but with a pentode as the CCS element for a much higher output impedance. I used a simple mosfet regulator for the screen and the same resistive reference chain raised the grid to 30V. Works a treat.

This is not meant as criticism of your circuit, just passing on my experience

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Old 19th July 2009, 12:11 PM   #7
Dxvideo is offline Dxvideo  Turkey
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Thanks a lot for your comments.

Dear Gordy,
- I will move C14 and C15 more distance place against the tubes heat.
- About the CRC filter for B+.... I am confused about that because in the simulation I saw -40dB @100Hz. Isn't it enough you think?

And Dear Shoog,
I think I am not good at tube designing. And this is not my design. So I think I cannot make a critical modification the on design.
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Old 19th July 2009, 02:52 PM   #8
Gordy is offline Gordy  United Kingdom
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Quote:
Originally posted by Dxvideo


- About the CRC filter for B+.... I am confused about that because in the simulation I saw -40dB @100Hz. Isn't it enough you think?

Perhaps reality will match the simulation.
In my own Cathode Follower I used a regulator (TL783) and it was fine. Maybe I worry too much? Maybe your CRC will be enough when combined with the PSRR of the CF.
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Old 19th July 2009, 07:01 PM   #9
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Maybe I´m missing something here, but wouldn´t it be very beneficial replacing the CRC with Salas´ very exciting regulator?

Karsten
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Old 20th July 2009, 08:38 AM   #10
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What benefits should we expect with adding a regulator to B+ , do you think?
And whats "Salas' very exciting regulator", is it a special thing?
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