Switchable Hi-Z input impedance, how ? - Page 36 - diyAudio
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Old 11th October 2012, 11:30 AM   #351
tinitus is offline tinitus  Europe
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found a perfect trafo, 20-0-20V, 0-6V
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Old 11th October 2012, 11:45 AM   #352
juma is offline juma  Germany
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Tinitus, as I see it - you want a gain stage before the buffer, right ?

If so, please tell how much gain you need ?

What's the amplitude of the input signal ?

What is the preferred Zin ?
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Old 11th October 2012, 11:57 AM   #353
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hi juma

yes, gain stage-att-buffer
input signal ? Im not sure
but in any case it will end with having multiple gain stages

the jfet boz I use now is more than enough
but will also be attenuated at input

maybe 12db will do
and maybe even the output 'buffer' could have moderate 6db gain, and still have low impedance
I dont think it have to be a unity gain buffer

whatever will be convenient too

z-in ? about 1Mohm at first input stage
at other places through the amp, Im not sure

attached a couple of my messy ideas, just to show where I might be heading
and btw, its basicly the jfet related curcuits I want to look at right now
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Old 11th October 2012, 01:16 PM   #354
juma is offline juma  Germany
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Yes, you should be OK with JBOZ - for less gain there is a J310 version...
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Old 11th October 2012, 04:41 PM   #355
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found it
yes, might be a good idea with lower gain

how is output impedance/drive for the j310 ?
if good I could just use that all the way, and forget about buffers... or ?
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Old 11th October 2012, 05:57 PM   #356
juma is offline juma  Germany
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The Zout of J310 JBOZ is practically equal to Rd (680 R) which is OK to drive the Zin of the next stage of 47k or more. The usable voltage swing at the output of J310 JBOZ iz 5-6V peak (with more than that distortion becomes noticeable which might be acceptable in a guitar amp).
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Old 11th October 2012, 06:38 PM   #357
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passive baxandall load impedance seems to be something like 1Mohm, and falling to 80K above 1khz
should be ok then

need to get hold of some veroboard, and more components

thanks juma
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Old 11th October 2012, 06:57 PM   #358
tinitus is offline tinitus  Europe
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a few more bits and pieces that might work ok for a proto
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Old 11th October 2012, 09:12 PM   #359
tinitus is offline tinitus  Europe
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Quote:
Originally Posted by tinitus View Post
need to get hold of some veroboard, and more components
and to remind myself, remember to get some BS170 to try your sit trioda
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Old 11th October 2012, 10:13 PM   #360
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hey btw, just wondered....

like using two 2sk170 instead of the complementary pair

would the trick work for combining j310 with BS170 ?
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