just saw that i mounted the 100R Pots counter clockwise to your PCB silksreen, so screw is on other side.
But pots are symmetrical, wiper in the middle, shoud be ok, right?
But pots are symmetrical, wiper in the middle, shoud be ok, right?
I'm always saying - I don't care for CCW or CW or whatever , regarding orientation of trimpots ......... sole thing I believe in is - reading of DMM
so , if I wrote max value , I believe you did right thing - measuring across parallel resistor
point is , praxis acquired from years of service work , in majority of situations even without any service documentation , even if I remember/chose what is "normal orientation" of trimpot , I'm already confused first time when I rotate anything for 180deg - either entire apparatus , or just my head
so , yes , solder trimpot whichever way you want ... even on other side of pcb ..... electrically that's irrelevant 🙂
so , if I wrote max value , I believe you did right thing - measuring across parallel resistor
point is , praxis acquired from years of service work , in majority of situations even without any service documentation , even if I remember/chose what is "normal orientation" of trimpot , I'm already confused first time when I rotate anything for 180deg - either entire apparatus , or just my head
so , yes , solder trimpot whichever way you want ... even on other side of pcb ..... electrically that's irrelevant 🙂
hey, guess i got it, me numbhead, dunno for what reason, LEFT OUT R3.. (100 R for regular buffer)
It is of course stupid and i cannot explain, will put it in an try another start?
It is of course stupid and i cannot explain, will put it in an try another start?
recheck everything , complete what you didn't made and wait for me
you made me slightly hysteric , so I need few hours to check some things in vivo
even if I just few days ago assembled complete Babelfish M25 , too much snakes did bite me so I'm slightly nervous even when I see a Lizard
and - of course that missing R3 is stupid thing ..... cross your fingers that you didn't scorched them
but relax - that's just electronic , not life support .....even if broken , it can be repaired
you made me slightly hysteric , so I need few hours to check some things in vivo
even if I just few days ago assembled complete Babelfish M25 , too much snakes did bite me so I'm slightly nervous even when I see a Lizard
and - of course that missing R3 is stupid thing ..... cross your fingers that you didn't scorched them
but relax - that's just electronic , not life support .....even if broken , it can be repaired
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just checked , had second coffee of the day , and conclusion is that your problem , logically and obviously to properly caffein-ed mind , was exactly because gates of lower group of JFets are floating , due to absence of gate resistor (R3)
point is - gate being floating , D-S of JFet is nothing else than silly resistor of some low value ....... there is nothing to establish any limiting effect
so , now , presuming that you trice checked all parts and positions , and that you soldered R3 in place (or you inserted them in 1-pin sockets, whatever) , try entire procedure again.
as I didn't get (in my edits of post #1) to part of output critters mounting and necessary insertion of 0R1 in negative rail (Iq monitoring), it would be clever to do whatever you're doing - without output critters even mounted on pcb
keep me informed .... my fingers are crossed that tiny bugs survived
point is - gate being floating , D-S of JFet is nothing else than silly resistor of some low value ....... there is nothing to establish any limiting effect
so , now , presuming that you trice checked all parts and positions , and that you soldered R3 in place (or you inserted them in 1-pin sockets, whatever) , try entire procedure again.
as I didn't get (in my edits of post #1) to part of output critters mounting and necessary insertion of 0R1 in negative rail (Iq monitoring), it would be clever to do whatever you're doing - without output critters even mounted on pcb
keep me informed .... my fingers are crossed that tiny bugs survived
half good news,
i can´t get lower than 21.5mV aross R8 and R6 pot has very little influence on Iq. Several turns do just about 0.2 mV difference on R8, but vary offset for about 3.5 mV for example.
offset pot reacts supergood, no problem to adjust 0mV.
i´ll send you coffee : )
i can´t get lower than 21.5mV aross R8 and R6 pot has very little influence on Iq. Several turns do just about 0.2 mV difference on R8, but vary offset for about 3.5 mV for example.
offset pot reacts supergood, no problem to adjust 0mV.
i´ll send you coffee : )
some musings and some questions :
looking at schematic , if you had 0R for source resistor of upper group , you could get only Idss through entire group , even if lower group of JFets you had them acting as silly resistor ...... so current through entire chain (from pos to negative rail) couldn't be 200+mA
so , I'm still puzzled how you get , supposedly , more than 200mV across R8?
check (powered off) - what you can get as min and as max value of source resistance for both groups , just to be sure that trimpots are still in good shape
also , I hope you didn't had both input xformers in place and JP closed ..... as clearly written on schematic , JP closing only after you finish entire procedure with input buffers
generally - you can set JFets Iq anywhere between , say 18mA to 25mA , without any change in performance ...... I chose 20mA as convenient value from several reasons ,, but it isn't carved in stone
we just need to find is everything in working condition , then just blame JFets Idss span for not being able to get less mA with 100R ll 27R as source resistor
no big deal
looking at schematic , if you had 0R for source resistor of upper group , you could get only Idss through entire group , even if lower group of JFets you had them acting as silly resistor ...... so current through entire chain (from pos to negative rail) couldn't be 200+mA
so , I'm still puzzled how you get , supposedly , more than 200mV across R8?
check (powered off) - what you can get as min and as max value of source resistance for both groups , just to be sure that trimpots are still in good shape
also , I hope you didn't had both input xformers in place and JP closed ..... as clearly written on schematic , JP closing only after you finish entire procedure with input buffers
generally - you can set JFets Iq anywhere between , say 18mA to 25mA , without any change in performance ...... I chose 20mA as convenient value from several reasons ,, but it isn't carved in stone
we just need to find is everything in working condition , then just blame JFets Idss span for not being able to get less mA with 100R ll 27R as source resistor
no big deal
JP was open all the time.
But I (of course 😀) have to ask how to measure source resistance? Or just measure again across Pots themselves?
tnx
But I (of course 😀) have to ask how to measure source resistance? Or just measure again across Pots themselves?
tnx
yes , across 27R resistors
if trimpots are still in well shape , you'll get from 0 to approx. 21-22R
if trimpots are still in well shape , you'll get from 0 to approx. 21-22R
they seem to be ok, can trim both for 21.3 R across the 27R Resistors. While Iq-pot is in endposition, offset around 9.2R across the 27R resistor.
..puhh, sweat (your thinking, my fear : )
Have to leave workbench for today, i´m the cook for Kässpätzle 🙂 you are heavily invited!
..puhh, sweat (your thinking, my fear : )
Have to leave workbench for today, i´m the cook for Kässpätzle 🙂 you are heavily invited!
if you're eager to get strictly 20mA though buffer , replace lower 27R with , say , 39R
hope they didn't Berserked with that episode
btw. in all these posts , you didn't tell - you had same issues with both channels , or you stopped after first one ?
anyway , I intend tonight to further edit post #1 , so you can proceed with playing ...... mounting outputs and everything , and preparing for first important powering up 🙂
hope they didn't Berserked with that episode
btw. in all these posts , you didn't tell - you had same issues with both channels , or you stopped after first one ?
anyway , I intend tonight to further edit post #1 , so you can proceed with playing ...... mounting outputs and everything , and preparing for first important powering up 🙂
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I just hooked up left channel (frontend). The other one has still some drilling to do.. so it will come in few days.
Maybe i change R4 (27R) to 39R. And letz hope for da buffer to have survived.
i owe you a day : ), mnytnx! maybe you´ll hear a hurayy behind the Alps tomorrow, but i´ll give ok anyway,
best
st.
Maybe i change R4 (27R) to 39R. And letz hope for da buffer to have survived.
i owe you a day : ), mnytnx! maybe you´ll hear a hurayy behind the Alps tomorrow, but i´ll give ok anyway,
best
st.
outing as "noelectrix " again 😀
for bias via the temporary 0.1R Resistor i have to measure 180mV- to 200mV across it for 1.8A- 2.0A?
better save than sorry as ZM says..
for bias via the temporary 0.1R Resistor i have to measure 180mV- to 200mV across it for 1.8A- 2.0A?
better save than sorry as ZM says..
oh yes
yesterday , after checking things for you in my workshop , I needed to go out of town and came back late , so I didn't made that promised editing of post #1 , nor I posted list of already sent kit packages
will do that today , after ........ everything 🙂
I believe everything is clear from notes on schematics and few pictures bellow , but still better to wait for SuperSlow ZM , to type few sentences more
procedure is slow but safe and easy ........
yesterday , after checking things for you in my workshop , I needed to go out of town and came back late , so I didn't made that promised editing of post #1 , nor I posted list of already sent kit packages
will do that today , after ........ everything 🙂
I believe everything is clear from notes on schematics and few pictures bellow , but still better to wait for SuperSlow ZM , to type few sentences more
procedure is slow but safe and easy ........
🙂 quite sure you had to give yourself a drink somewhere, because of me numb guy, triggering your adrenaline : )
its up an running (left channel), a cheap speaker, good sound : )
now listening and coffee,
soon,
st
no porn , no glory!
Iq , offset ?
after being in temp equilibrium for 10 mins at least , with cover closed , and everything set - then you can connect the speaker and enjoy .....
🙂 i´ll wait for porn, first got the other channel running. and as usual, forgot camera.
Iq is about 1.83
offset, wait...lookie...about 30mV, but maybe i´ll get it better, i´ll let it run for another hour.
Iq is about 1.83
offset, wait...lookie...about 30mV, but maybe i´ll get it better, i´ll let it run for another hour.
pulling out the (bias) 0.1R Resistor rised my offset to around 130mV. I than turned offset down via pot to under 10mV. But don´t know what that did to bias. Will check the next days.
Heatsinks, (double mono) are easy warm, ready for hot summers.
Gain is of course not so much. But driven directly from i-pod (don´t have others in studio) on 90 dB papers it´s ok listening level, laptop is even louder : )
Heatsinks, (double mono) are easy warm, ready for hot summers.
Gain is of course not so much. But driven directly from i-pod (don´t have others in studio) on 90 dB papers it´s ok listening level, laptop is even louder : )