I followed your advice and now everything works perfectly. "For 5 hours I listened to the different music, it sounds very special - neutral, no fatigue, totally silent. I like the sounds and the bass sounds great, I'm sure it will be one of my reference preamplifiers. All respect and thanks a lot, Aleksandar!
well , never measured it alone (why would I ?) but on paper it is something like :
each JFet declared having 15mS xconductance at 10V and 0 Ugs ; there 20mA is shared to 6pcs , so from graph at 20/6=3.33mA , xconductance is at least 12mS (conservative)
so , 12mS x 6= 72mS combined
Rout of cell is 1/Yfs = 1/72mS = 13R9
add to that whatever value of source resistance is there ( 39R // 100R trimpot ), never more than ,say , 20R ....... that's resulting Rout of 13R9+20R= 33R9
when connected to autoformer , overall Rout is multiplied with square of output tap
for 0db output tap , overall Rout is same as buffer cell Rout
for +6db tap out , where A=2V/V , overall Rout is cell Rout x A^2 = Rout x 4 = 33R9 x 4 = 135R
for -6db tap out , where A=0.5V/V , overall Rout is cell Rout x A^-2 = Rout x 1/4 = 33R9 x 1/4 = 8R475
all that ignoring Rdc of autoformer winding , which is under 100R per phase
of course , we all know that xformers are live thingies , so we usually ignore Rdc , when no actual currents are involved
each JFet declared having 15mS xconductance at 10V and 0 Ugs ; there 20mA is shared to 6pcs , so from graph at 20/6=3.33mA , xconductance is at least 12mS (conservative)
so , 12mS x 6= 72mS combined
Rout of cell is 1/Yfs = 1/72mS = 13R9
add to that whatever value of source resistance is there ( 39R // 100R trimpot ), never more than ,say , 20R ....... that's resulting Rout of 13R9+20R= 33R9
when connected to autoformer , overall Rout is multiplied with square of output tap
for 0db output tap , overall Rout is same as buffer cell Rout
for +6db tap out , where A=2V/V , overall Rout is cell Rout x A^2 = Rout x 4 = 33R9 x 4 = 135R
for -6db tap out , where A=0.5V/V , overall Rout is cell Rout x A^-2 = Rout x 1/4 = 33R9 x 1/4 = 8R475
all that ignoring Rdc of autoformer winding , which is under 100R per phase
of course , we all know that xformers are live thingies , so we usually ignore Rdc , when no actual currents are involved
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Thanks for the super clear explanation. Looks like two 2SK2145 in // would substitute very nicely for one 2sk170 with lower dissipation since in //. Is that what led you to choose these(readily available) opposed to 2SK170(not available easily)? I asked the buffer Rout question since I remember you explaining for 170 same sex buffer is around 50R while 170/74 is around 25R? Why not same 2145 buffer cell for Iron Pre?
Has the pricing for just the balanced AVC pumpkin boards changed or same as in the thread detailing the pricing, still measly 160euro?
Thanks. nash
Has the pricing for just the balanced AVC pumpkin boards changed or same as in the thread detailing the pricing, still measly 160euro?
Thanks. nash
well , even two boxes of original Toshiba 2SK170BL/2SJ74BL (1K pcs/box) , which I snatched from Pa together with 2SK77B , they aren't enough to build a pair of my own Beasts ..... so I needed to resort to some other solution , when speaking of buffers I want to make
so that explains why I'm using 2SK2145BL buffer cell in musings of mine........ while Iron Pre - can't remember how that happened (probably 6L6 simply asked) is my Gift to Store , so it's logical that LSK Jfets are going to be part of it - Store already have them , more the Store is selling them , longer LS is going to deal with us Greedy Boyz ...... not even mentioning the fact that matching small critters is bothersome , same as soldering them on pcb could be bothersome for regular Greedy Boy
pricing ....... yes , still measly ..... and to remind you - this is what you get for that :
so that explains why I'm using 2SK2145BL buffer cell in musings of mine........ while Iron Pre - can't remember how that happened (probably 6L6 simply asked) is my Gift to Store , so it's logical that LSK Jfets are going to be part of it - Store already have them , more the Store is selling them , longer LS is going to deal with us Greedy Boyz ...... not even mentioning the fact that matching small critters is bothersome , same as soldering them on pcb could be bothersome for regular Greedy Boy
pricing ....... yes , still measly ..... and to remind you - this is what you get for that :
Turtle was sent eons ago
channel pcbs I got with me , then we had few days fun , how to box it or plank it , in fastest possible way
btw. these are smallest Donuts Pa had around ...... they're radiating stronger than Hafler DH200 xformer
...... "no , Pa - we can't use your favorite switchers with this preamp ............ no, Pa - I really insist on dual mono ......... "
channel pcbs I got with me , then we had few days fun , how to box it or plank it , in fastest possible way
btw. these are smallest Donuts Pa had around ...... they're radiating stronger than Hafler DH200 xformer
...... "no , Pa - we can't use your favorite switchers with this preamp ............ no, Pa - I really insist on dual mono ......... "
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Here's Bubba Uncle Bob's
it's finished...... now we are waiting to hear that Flying Pony Express is working again
pics 1/3
it's finished...... now we are waiting to hear that Flying Pony Express is working again
pics 1/3
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