OK,
The resistor error is quite likely, but puzzles me a bit :
An error on one side should not allow to adjust properly the rel offset.
Assuming your trimmers are OK (right values), check the cascode voltage divider resistors.
Check also (measure) the resistance between the wiper of the 50R pot and one of its end. It should measure quite close to 25R. If you're far from this half value, then a resistor on one side can be the cause of the problem.
Let's hear some news soon
The resistor error is quite likely, but puzzles me a bit :
An error on one side should not allow to adjust properly the rel offset.
Assuming your trimmers are OK (right values), check the cascode voltage divider resistors.
Check also (measure) the resistance between the wiper of the 50R pot and one of its end. It should measure quite close to 25R. If you're far from this half value, then a resistor on one side can be the cause of the problem.
Let's hear some news soon
Hi Cheff,
Checked and rechecked...no resistor mistake.....so:
Took the other route...built 2 new UGS modules...it works. it sings!!!
now i'll debug the other 2, it seems that the RH UGS module is a dud...values were all a little higher than the LH one but it was plausible...and offsets were ok...yet it was a dud.
guess that if i mached the ZTXs i would not have this problem...i know it is not necessary, in your opinion, but it would make me check all the transistors.
now i have two new, very similar and very nicely aligned modules singing with my AYA II DAC........gorgeous.
Pots it seems come from production essentially at 50% so offset alignment was a few turns and...bingo!
These two modules will serve as my reference for the debuging of the other 2.
thanks Cheff.....and Nelson !!!
First step in a long road...i hope.
Checked and rechecked...no resistor mistake.....so:
Took the other route...built 2 new UGS modules...it works. it sings!!!
now i'll debug the other 2, it seems that the RH UGS module is a dud...values were all a little higher than the LH one but it was plausible...and offsets were ok...yet it was a dud.
guess that if i mached the ZTXs i would not have this problem...i know it is not necessary, in your opinion, but it would make me check all the transistors.
now i have two new, very similar and very nicely aligned modules singing with my AYA II DAC........gorgeous.
Pots it seems come from production essentially at 50% so offset alignment was a few turns and...bingo!
These two modules will serve as my reference for the debuging of the other 2.
thanks Cheff.....and Nelson !!!
First step in a long road...i hope.
Hi Maousse,
I was in cloud 9 yesterday so i don't know yet what the problems are with my first 2 modules but soldering is not very probable....i'm very good at that...and modest....but if i can change an ATmega and recover a display....i'm not all bad.
Anyway overheating is not likely...i'm just as curious to find out what is going on as you guys....the offset issue is curious in the Lh module and the complete failure of the Rh module.....well i have even thought about fake jfets !!! but these two new modules have jfets from same source/lot.
I'll post some pictures today
...while i listen to it....I'm using an Alesis 300 at the moment...nothing to write home about but quite nice....don't have an UP yet
I was in cloud 9 yesterday so i don't know yet what the problems are with my first 2 modules but soldering is not very probable....i'm very good at that...and modest....but if i can change an ATmega and recover a display....i'm not all bad.
Anyway overheating is not likely...i'm just as curious to find out what is going on as you guys....the offset issue is curious in the Lh module and the complete failure of the Rh module.....well i have even thought about fake jfets !!! but these two new modules have jfets from same source/lot.
I'll post some pictures today
...while i listen to it....I'm using an Alesis 300 at the moment...nothing to write home about but quite nice....don't have an UP yet
Sorry to ask, now I know you are a soldering god 
If I have a display to mend, I'll ask you
The first soldering party we organized for soldering noobs (16 UGS modules) was with a 100% good result. So was the second.
The main source of failure was with the µC board, it's very ESD sensitive...
In all the errors I heard about, some were with bad/swapped resistors, one was with swapped ZTX.
Two DIYers plugged the module reversed, with no damage... !!
Overheating occured for 2 DIYers on the BS170 of the µC board.
Talking about fake JFETs, those may be rebadged BL.
As said CheffDeGaar, try playing around with the degeneration resistors (higher and lower values) to see what it does.
If I have a display to mend, I'll ask you
The first soldering party we organized for soldering noobs (16 UGS modules) was with a 100% good result. So was the second.
The main source of failure was with the µC board, it's very ESD sensitive...
In all the errors I heard about, some were with bad/swapped resistors, one was with swapped ZTX.
Two DIYers plugged the module reversed, with no damage... !!
Overheating occured for 2 DIYers on the BS170 of the µC board.
Talking about fake JFETs, those may be rebadged BL.
As said CheffDeGaar, try playing around with the degeneration resistors (higher and lower values) to see what it does.
Hi Maousse...
No need to be sorry, it's how we get to know each other here, by asking questions !
No i'm not a god in soldering...but competent enough...I work at Tech services in Air Traffic Control and as such have been doing engineering work for 25 years....audio is my hobby for as long as i can remember, although the DIY part was on hold for about 15 years...restarted now with UGS....nicest possible restart, i think.
As for the rebadged Jfets...it's a possibility, i got these from Criklewood
couple of years back and from the Irish guys selling them for outrageous prices now.
I do have some BLs from Serjac GB which should be genuine.
I used resistor values for BL and the resulting bias current : 3,3mA in both cases ( k389Bl and J109BL ) is correct as expected so this should indicate a genuine BL i think ( 22R and 47 R ), it they were GR rebaged as BL it would probably be lower.
All this does not eliminate the fact that it was surely a stupid mistake of mine....but i will try the sugestion you and Cheff make of course, it's great to have such strong and friendly support from you guys.
No need to be sorry, it's how we get to know each other here, by asking questions !
No i'm not a god in soldering...but competent enough...I work at Tech services in Air Traffic Control and as such have been doing engineering work for 25 years....audio is my hobby for as long as i can remember, although the DIY part was on hold for about 15 years...restarted now with UGS....nicest possible restart, i think.
As for the rebadged Jfets...it's a possibility, i got these from Criklewood
couple of years back and from the Irish guys selling them for outrageous prices now.
I do have some BLs from Serjac GB which should be genuine.
I used resistor values for BL and the resulting bias current : 3,3mA in both cases ( k389Bl and J109BL ) is correct as expected so this should indicate a genuine BL i think ( 22R and 47 R ), it they were GR rebaged as BL it would probably be lower.
All this does not eliminate the fact that it was surely a stupid mistake of mine....but i will try the sugestion you and Cheff make of course, it's great to have such strong and friendly support from you guys.
Ok i promised some pictures today, so here goes;
Solved the "dud" issue.
After measuring the whole board it became quite clear something odd was going on arround the K389.
Taking a closer look at what i thought i had looked at many times, i saw that there was a cut track connecting the fb resistor to the connector.
Fixed that, tested and put it playing after aligning the offsets....it sings.
This just goes to show that one can look and not see what is in front of us .
Tomorrow, more pictures and some results, i hope of the tests Cheff and Maousse sugested.
Solved the "dud" issue.
After measuring the whole board it became quite clear something odd was going on arround the K389.
Taking a closer look at what i thought i had looked at many times, i saw that there was a cut track connecting the fb resistor to the connector.
Fixed that, tested and put it playing after aligning the offsets....it sings.
This just goes to show that one can look and not see what is in front of us .
Tomorrow, more pictures and some results, i hope of the tests Cheff and Maousse sugested.
Attachments
CeeVee said:
Thanks for reporting.
And thanks for having had this issue
- so to speak ...Half serious : Its always very interesting ... Thats sharing experiences ... which is precious.
I suppose you did the first tests with the FB res not implemented. And all readings were OK. So you couldn't see the problem.
So I think it could be usefull in the future to test the boards a 2nd time with the FB res in to be sure...
BTW Which is the value of Rin you choose?
Manu
Hi Manu,
Yes the document published by François is very thourough but as he states near the end...it does not cover everything.
The feedback resistor is only put in at the end before offset adjustment, odd thing with this board was that the offsets adjusted ok before but what was clear after a complete check on all the bias points was that the gate values were crazy.
This is the clearest sign that the feedback resistor was not ok but this was a test that was not included in the paper...we can include it now i guess
Now i will try to debug the other board, wich plays but does not adjust absolute offset.
Yes the document published by François is very thourough but as he states near the end...it does not cover everything.
The feedback resistor is only put in at the end before offset adjustment, odd thing with this board was that the offsets adjusted ok before but what was clear after a complete check on all the bias points was that the gate values were crazy.
This is the clearest sign that the feedback resistor was not ok but this was a test that was not included in the paper...we can include it now i guess
Now i will try to debug the other board, wich plays but does not adjust absolute offset.
Yesterday had no time for debugging....life !
But there is an issue i'd like to share, in the past few days i've been doing A/B comparison tests with DACs, using the UGS ie: input 1 - my Shanling CD, input 2 Shanling but with diferent DACs.
Should be easy just swapping between input 1 and 2 ...but i notice that not always does the switching occur, sometimes i need to repeat the procedure for the relays to actually switch...there seems to be some lag, have any of you experienced this ?
But there is an issue i'd like to share, in the past few days i've been doing A/B comparison tests with DACs, using the UGS ie: input 1 - my Shanling CD, input 2 Shanling but with diferent DACs.
Should be easy just swapping between input 1 and 2 ...but i notice that not always does the switching occur, sometimes i need to repeat the procedure for the relays to actually switch...there seems to be some lag, have any of you experienced this ?
CeeVee said:
Hi Calrlos,
Never encountered your problem...
Normal sequence of relays when switching from input A to B :
1) Mute relay on (muted output)
2) Signal relay for A off
3) Ground relay A off
4) Ground relay B on
5) Signal relay B on
6) mute relay off to get sound again.
All of this within 2 seconds
Does your problem happen both when using the switches or the remote ?
Same symptoms with input 3 & 4, or 1 & 3 for instance ?
The two channels show the same behaviour ?
You've checked your ribbon cables/connectors ?
Sorry to see you collecting so much probelms....