Tube Buffer for CD-PRO2M (6922) - diyAudio
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Old 24th February 2005, 02:20 PM   #1
Rarkov is offline Rarkov  England
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Default Tube Buffer for CD-PRO2M (6922)

Hi,
I have tried to pick out a bit of the Tube Buffered gainclone to make an output buffer for a CD-PRO2M. I want try it to see the difference in sound.

I was hoping someone would check to see if this is OK, or if I have left out any thing I'd need.

Thanks,
Gaz
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Old 24th February 2005, 02:21 PM   #2
Rarkov is offline Rarkov  England
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This is the original version.

Regards,
Gaz
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Old 24th February 2005, 09:46 PM   #3
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Hi,

Quote:
I want try it to see the difference in sound.
Not sure what you expect to hear from a cathode follower, probably just the sum of fingerprints of the components used but here goes:

As for the circuit, if you put a 50 to 100K gridleak resistor "en lieu" of the volpot it should work.
Plus add a bleeder resistor of roughly 100 to 470K behind the coupling cap too.

Cheers,
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Old 24th February 2005, 10:10 PM   #4
Rarkov is offline Rarkov  England
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Well, the buffer is supposed to give the Gainclone a hint of "Tube" sound. Since I've rarely heard tubes (in fact, only the buffered Gainclone - with a buzz) I'm not sure what Im listening for. However, I'd like to see what the impact is on the output of the CD Player.

Is this revised schematic correct?

Kind Regards,
Gaz
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Old 24th February 2005, 10:30 PM   #5
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Hi,

Quote:
Well, the buffer is supposed to give the Gainclone a hint of "Tube" sound.
I doubt that's the main purpose but nevermind.

Quote:
Is this revised schematic correct?
Yes.
You can safely reduce the 3K9 gridstopper (gatestopper in semi lingo) to 1K or lower.

Cheers,
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Old 24th February 2005, 11:00 PM   #6
Sheldon is offline Sheldon  United States
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Or, if you don't mind a little higher voltage, this full implementation of Joe R's buffer:

http://www.diyaudio.com/forums/showt...300#post546300

I think Steve Eddy showed a buffer in the same thread, with lower B+/- too.

sheldon
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Old 24th February 2005, 11:05 PM   #7
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Rarkov,

If you don't mind opinions, I would keep looking around for a better tube linestage to try out. The 6922 buffered GC is an elegant design in that you have 1 tube which handles 2 channels plus it runs off the same rails as the chip, so it is really a minimalist change. But I'm guessing you will have to add a +35V, -35V, and 6V for the heater to add it to your CDP....why? Seems like there are better choices if you look for them.
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Old 25th February 2005, 12:36 AM   #8
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Hi,

Sorry to say so but 90% of what I read on that page is absolute nonsense.

Heater polarity, cascode stuff that has nothing, nothing whatsoever to do with the circuit shown.

Forget it.

BTW, why would anyone want to put a tube buffer behind a couple of stinkin' opamp buffers anyway?

If you want to work with valves then start on page one of the book, don't jump right in.

Sorry, had to get it off my chest,
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Old 25th February 2005, 01:56 AM   #9
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Hi,

I have built Joe's VBIGC so many times now and it works great (for me at least), if I remember it right, Joe's reason for using a tube buffer is to isolate the feedback circuit of the GC amp from being affected by the position of the volume pot. Oh, and if you'll follow the schematic, the valve section has a separate trafo for psu and heater.

I was going to build that buffer in Sheldon's link, but a friend here told me to listen to an MF x10D tube buffer instead. Well I like it's sound, I think someone posted a similar schematic here but I can't find it even with local search. Or maybe it's somewhere else on the net.

As always, YMMV.

Jojo
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Old 25th February 2005, 02:09 AM   #10
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Hi,

Quote:
Well I like it's sound, I think someone posted a similar schematic here but I can't find it even with local search.
Local search engine will dig up everything but that....
But indeed I recall that little buffer being discussed here maybe a year or two ago....
I should have that circuit in my archives somewhere too.

I'll stress once again the importance of understanding what you want to do here, if it's a certain sonic signature you're after and don't have a clue about what's inside you CDP then leave it as it is, it probably already has a buffered output. No need to add insult to injury...

If you just want a volctrl and a buffer to drive the IC running to the amp then a cicrcuit such as the 12BH7A I submitted here some time back would do the trick just fine.

Cheers,
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