UGS adventures

[Maousse]

Hey ! People ! He's got stock !

So do I, chhhhhhhht...

[CeeVee]

....but he's also got plans for 'em.....Cheff and Papa have other beautifull things for me to make.

[CheffDeGaar]

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

[CeeVee]

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.

[Maousse]

None of the DiYers I know (a few dozens) did matched their ZTX.
If the resistors are all of the good value, try change the ZTX if you have some spare, they may be overheated at the soldering step (I don't know your soldering skill).

[CeeVee]

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

[Maousse]

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.

[CeeVee]

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.

[Maousse]

What about the pictures I asked ?
Did you remembered to take some ? At best, taken from 3 different orientations

[Manu]

Originally posted by CeeVee
...built 2 new UGS modules...it works. it sings!!!

That is great news ...


I am also very interested if you can find out the reason why the former two modules failed ... keep us informed....

Manu