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Old 4th December 2006, 09:50 PM   #1
Fuling is offline Fuling  Sweden
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Default LPT with low triodes?

Good evening!

Since Im soon to be finished with my X-Son of Zen I need a good preamp that converts the unbalanced signal from my CDP to a balanced one which is capable of driving an horribly low input impedance (470 ohms!).
For various reasons I dont want to build a BZLS, so Im looking into tube/hybrid territory instead.

To get straight to my question: Does LPTs work good with low triodes like 12B4A?
Im thinking 6k8 or so on the plates, CCS in the tail and Mosfet buffers on the outputs.
Would I be better of with higher triodes and some feedback to get the gain down?
I like the 12B4A very much and I happen to have a good number of them (quality brands) but Im a little hesitant since I believe Ive read somewhere that LPTs works best with high triodes.

Best regards,

Daniel
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Old 4th December 2006, 09:54 PM   #2
Zen Mod is offline Zen Mod  Serbia
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Default Re: LPT with low triodes?

Quote:
Originally posted by Fuling
Good evening!

Since Im soon to be finished with my X-Son of Zen I need a good preamp that converts the unbalanced signal from my CDP to a balanced one which is capable of driving an horribly low input impedance (470 ohms!).
For various reasons I dont want to build a BZLS, so Im looking into tube/hybrid territory instead.

To get straight to my question: Does LPTs work good with low triodes like 12B4A?
Im thinking 6k8 or so on the plates, CCS in the tail and Mosfet buffers on the outputs.
Would I be better of with higher triodes and some feedback to get the gain down?
I like the 12B4A very much and I happen to have a good number of them (quality brands) but Im a little hesitant since I believe Ive read somewhere that LPTs works best with high triodes.

Best regards,

Daniel

since you want to use CCS in tail,I don't see why you can't use 12B4 in LPT............
in that configuration length of tail is always critical........and with CCS your is biggest
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Old 4th December 2006, 10:25 PM   #3
Fuling is offline Fuling  Sweden
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Im thinking the same way, with a CCS in the tail the "balancing act" shouldnt suffer due to the lack of .
I guess building a breadboard is the best way to find out!
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Old 4th December 2006, 10:32 PM   #4
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Default Re: LPT with low triodes?

Quote:
Originally posted by Fuling
but Im a little hesitant since I believe Ive read somewhere that LPTs works best with high triodes.
That's because the common mode noise rejection increases with increasing mu.
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Old 4th December 2006, 10:38 PM   #5
Fuling is offline Fuling  Sweden
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So with a quiet PSU the low is no longer an issue? Sounds good! Thanks!
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Old 4th December 2006, 10:56 PM   #6
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Quote:
Originally posted by Fuling
So with a quiet PSU .......................

conditio sine qua non
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Old 4th December 2006, 11:03 PM   #7
Fuling is offline Fuling  Sweden
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Quote:
conditio sine qua non
I feel stupid, I dont have a clue what that means...
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Old 4th December 2006, 11:07 PM   #8
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Fuling


I feel stupid, I dont have a clue what that means...

you know me -I mean everything
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Old 4th December 2006, 11:16 PM   #9
Fuling is offline Fuling  Sweden
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Quote:
I mean everything
Well, Im still not getting any wiser

But after all it seems that Ive had my original question answered, thanks!
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Old 4th December 2006, 11:48 PM   #10
Zen Mod is offline Zen Mod  Serbia
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Quote:
Originally posted by Fuling


Well, Im still not getting any wiser

But after all it seems that Ive had my original question answered, thanks!

http://www.google.com/url?sa=t&ct=re...6q2Wmpk36anY2Q
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