Switchable Hi-Z input impedance, how ? - Page 32 - diyAudio
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Old 21st September 2012, 10:23 AM   #311
tinitus is offline tinitus  Europe
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a few small changes

LED/bleeder
resistor was mounted on the cathode/ground side
shifting the resistor to the anode/supply side lowered hum a bit

input-Z was set by a 1M5
changing it to 9K resulted in further improvement

connected as high-Z input on my head amp hum is almost acceptable now
dont know why, but the gain also seem to be more controlled now
and the sound is quite good

things to try, a regulated supply, and 2-channel output
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Old 21st September 2012, 12:13 PM   #312
shanx is offline shanx  Canada
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Hi Tinitus, The tube heater circuit could be giving you hum. What type of heater supply setup are you using?
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Old 21st September 2012, 12:15 PM   #313
shanx is offline shanx  Canada
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By the way, great that you got it up and running!
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Old 21st September 2012, 12:32 PM   #314
tinitus is offline tinitus  Europe
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hey, shanx
patience my friend, its so far only a small proto with a single 2sk170
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Old 21st September 2012, 01:33 PM   #315
shanx is offline shanx  Canada
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Ah OK!
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Old 21st September 2012, 02:15 PM   #316
tinitus is offline tinitus  Europe
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just fooling around, practicing, and testing

strangely, after inserting a hifi stereo preamp its now close to noise free
and just for the record, a describtion of this setup

bass guitar is plugged into a compressor effetc/'pedal' unit
and mostly because of its 12db gain and level control

signal then goes to the new jfet 'booster' proto
now with 2 channels out
and from there the signal goes to a hifi stereo preamp-buffer
originally built especially to drive the power amp I use

this setup sounds really great, and my best yet
now thinking about how to move on from here
I have a suspicion the jfet boz may not be the ideal high-Z input
but with some help it might become a great booster
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Old 21st September 2012, 03:11 PM   #317
shanx is offline shanx  Canada
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On my first stage jfet, I am putting a 10uF bypass cap,and a second 10uF across that with a switch. This to try different roll-off (should give a bottom end boost when switched in)
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Old 21st September 2012, 03:32 PM   #318
tinitus is offline tinitus  Europe
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lets know how it goes

did you consider to try with just a smaller film cap bypass, to 'boost' highs, and limit the lows, when/if needed
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Old 21st September 2012, 05:40 PM   #319
shanx is offline shanx  Canada
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I can give that a try, for sure
Thanks
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Old 21st September 2012, 07:58 PM   #320
tinitus is offline tinitus  Europe
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no doubt, this little 'simple jfet boz' is good
need to think about how/where to use it

and why the noise almost goes away with the stereo hifi preamp driving the output
but I guess it also indicate theres nothing wrong with my jfet power supply
must be something other problem elsewhere
I have had problems with noise when not touching the strings
could be related to something on the instrument
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