Switchable Hi-Z input impedance, how ? - Page 3 - diyAudio
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Old 10th September 2011, 07:31 PM   #21
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Quote:
Originally Posted by tinitus View Post
Nigel, your numbers are including active curcuits, pots, etc
my numbers are raw output from the pickup

please note that this is all about trying to get an understanding how things work
I wasn't aware we were butchering a guitar for this discussion

Quote:

like, what do you reckon is max possible input impedance of a 2sk170 buffer ?
why? because I have plenty
Presumably it's far higher than you could possibly need?.
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Old 10th September 2011, 09:12 PM   #22
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Quote:
Originally Posted by Nigel Goodwin View Post
I wasn't aware we were butchering a guitar for this discussion
trying to look at it as a whole

and now looking at mu-follower tube pre
thank you


btw, reading TheValveWizard, there's a mu-follower ecc81 curcuit claimed to have 6M input and 300R output
sounds perfect, and I really like the ecc81
don't know why I didn't see that before
but maybe I wasn't looking fore it
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Old 11th September 2011, 02:58 AM   #23
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searching on mu-follower, reading AlanKimmel describing mu-stage with top penthode, and how to replace it with a mosfet, the hybrid mu-stage
and look what popped up right under....http://www.diyaudio.com/forums/blogs...-follower.html
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Old 11th September 2011, 03:06 AM   #24
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for this mu-follower, I wonder if anyone tried one of those funny tubes with a triode and penthode, all in one.....?
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Old 12th September 2011, 02:00 PM   #25
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I'm surpriced noone have tried a Compactron triode/pentode mu-stage
but I can't find anything
so it will be a bit difficult for me

well, maybe I could 'just' do the easy thing and use a single C3g
those I already have
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Old 12th September 2011, 03:22 PM   #26
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its funny
somethimes, the stuff you failed to find suddenly pops up when not looking fore it

and here it is, straight from our own forum
mind you, I haven't read it yet

Mu-follower with ECL805 and output xformer
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File Type: png ecl85 mu follower.png (12.5 KB, 197 views)
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Old 12th September 2011, 03:35 PM   #27
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just now I read that in a mu follower, the lower triode should be one that works well on lower voltage
and that you basicly want a high mu for the top triode, and a low mu for the bottom triode

some of those among the Compactrons too
but seems a major problem with many of them are the tube bases

hmm, it may become boring to hear about my C3g and 6C19n, but I wonder if they would form a nice mu stage
a 300B driver with D3a mu stage is not hard to find
but can I put in the 6C19n
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Old 12th September 2011, 06:58 PM   #28
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ok, a more direct question

my goal is still Hi-Z input

6C19n data says resistance in grid curcuit 0.5Mohm

does this mean that 500Kohm will be my max possible input
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Old 12th September 2011, 07:14 PM   #29
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Quote:
Originally Posted by tinitus View Post
6C19n data says resistance in grid curcuit 0.5Mohm

does this mean that 500Kohm will be my max possible input
Well, this means the maximum value of the grid resistor is 0.5 Mohm, although there is a note on the datasheet saying it can be pushed higher for at least one application. Isn't your 6S19P on the top of the mu-follower though?

But what is the point of all this? High input input impedance is easily and trivially achieved by using any number of input tubes, a FET, or a FET opamp as is commonly done in commercial amps. Where are you trying to go? Maybe I'm slow but I just can't read that from your posts.
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Old 12th September 2011, 11:02 PM   #30
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Originally Posted by leadbelly View Post
Isn't your 6S19P on the top of the mu-follower though?
ups, you are right
I forgot it has very little gain
not good
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