Well it looks like I’m going to have to install the OK2s in my amp. I was not happy with sound and just finished with my M2x and put it in the system, so this gave my the opportunity to check the settings on the amp. I just could not get the offset on the left channel to settle down. It just kept on rising no matter what I did. I spent a couple hours with it but the offset would not settle into a range. The right channel did not seem to have a problem. Now going through the instructions (post 1562 thru 1568) preparing to do the surgery on my amp. Where there any changes to what was previously posted?
Hopefully it will be successful in the end.
Hopefully it will be successful in the end.
Well I installed the 6N139 and I’m still not able to adjust the offset on the left channel. The bias is steady, but the offset keeps climbing. Not sure what to try next?
The right channel is behaving and the offset does move, but it is within a small range.
The right channel is behaving and the offset does move, but it is within a small range.
That’s what I was afraid of.
I only bought the pair. Can I used the 2SK182ES since THF-51 is hard to come by now?
Also, can the bad SIT be used in something like the Singing Bush?
I only bought the pair. Can I used the 2SK182ES since THF-51 is hard to come by now?
Also, can the bad SIT be used in something like the Singing Bush?
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without touching setting of other channel ( and obviously - you need to remove it from PSU) - can you borrow good channel's SIT , and test misbehaving channel with it?
there is practically (still) none iteration made to address misbehaving SITs, what for 6N139 iteration was made - to accommodate those SITs being little closer in Ugs to mosfet, so Ugs difference voltage window is little smaller and as bonus getting slightly lesser skate of Iq and offset, generally
I have in the bag iteration thought for further increased stability both for Iq and offset ( in temp./time domain) but I'm damned with constant lack of time ...... and I hope with that iteration slight gate current issues of SIT should be covered
there is practically (still) none iteration made to address misbehaving SITs, what for 6N139 iteration was made - to accommodate those SITs being little closer in Ugs to mosfet, so Ugs difference voltage window is little smaller and as bonus getting slightly lesser skate of Iq and offset, generally
I have in the bag iteration thought for further increased stability both for Iq and offset ( in temp./time domain) but I'm damned with constant lack of time ...... and I hope with that iteration slight gate current issues of SIT should be covered
I swapped the SITs between channels and noticed that hole where the bolt goes in insulation pad on the channel I was having problems with was a little big. I fixed it before installing the SIT. I’m not sure if that was what was causing the offset problem, but now the offset is fairly stable. I can get the offset close to zero with a little drift of about 10mv in one and 5mv in the other. Bias is stable and set at 180mv in both channels.
I rechecked the buffer on both boards. The right was good, but the left needed some adjustment, and was easily set.
Now my problem is that I have no sound in the right channel. Not sure what the problem is. I checked all the usual suspects. Swapped RCAs to make sure it was not the source or cables and music stayed in the left channel. Swapping the speaker cables and music came out of the opposite speaker. Checked continuity between the board and inputs and outputs, and everything checks. I even reseated the jumper.
I’m too tired to do anymore tonight. Will look closer tomorrow. Any suggestions on what to check next?
I rechecked the buffer on both boards. The right was good, but the left needed some adjustment, and was easily set.
Now my problem is that I have no sound in the right channel. Not sure what the problem is. I checked all the usual suspects. Swapped RCAs to make sure it was not the source or cables and music stayed in the left channel. Swapping the speaker cables and music came out of the opposite speaker. Checked continuity between the board and inputs and outputs, and everything checks. I even reseated the jumper.
I’m too tired to do anymore tonight. Will look closer tomorrow. Any suggestions on what to check next?
check jumper - it can go loose when fiddling too much with it ; if needed , use needle or tiny flat screwdriver and tighten contacts of jumper, in case that you don't have spare (good) one
tracing signal with scope is easy, if you have it
you can check buffer function easily - introducing signal after it - say at jumper pin
same with xformer - introducing signal after it - say at R14 (any pin), which is nothing more than shortie - 0R
tracing signal with scope is easy, if you have it
you can check buffer function easily - introducing signal after it - say at jumper pin
same with xformer - introducing signal after it - say at R14 (any pin), which is nothing more than shortie - 0R
ZM,
Thanks. I will try those troubleshooting steps tonight. Hopefully it is just a simple fix.
Brad
Thanks. I will try those troubleshooting steps tonight. Hopefully it is just a simple fix.
Brad
I had one channel that wouldn’t track as well as the other. I found that when I removed the Vfet that I had not removed the sticker on the bottom of the device. I removed it and it tracks fine now. So thermal issues will make all the difference in the dc offset.
My two cents.
My two cents.
well, I can proudly say that that mistake is almost on level of Mighty ZM stupidity
but, my throne still undisputed ....
name it
funny, and not funny anecdotes of ZM being Omnistupid and Omniclumsy are numberless
random list:
-mixed N and P mosfets in complementary OS
-both N mosfets in complementary OS
-both P mosfets in complementary OS
-same, input JFets
-same, input bjts
-same, OS bjts
-K instead of R
-R instead of K, ouch
-damn tube amp dead silent, everything in DC domain perfect ............ who did forgot to solder signal caps to OS?
-wrong Keratherms installed, mosfets exactly 20C hotter ....... made by order Babelfish M25 amp - result - Dynaudio bass units scorched
and list goes on and on .....
though, as I;m often saying, my probably biggest mistake was refusing offer to work in Paris as Lady of the Night, I was so smart thinking - it's better earning as electronic tech. in Balkan Country, out of EU, eternally in, oh yeah, Transition state
funny, and not funny anecdotes of ZM being Omnistupid and Omniclumsy are numberless
random list:
-mixed N and P mosfets in complementary OS
-both N mosfets in complementary OS
-both P mosfets in complementary OS
-same, input JFets
-same, input bjts
-same, OS bjts
-K instead of R
-R instead of K, ouch
-damn tube amp dead silent, everything in DC domain perfect ............ who did forgot to solder signal caps to OS?
-wrong Keratherms installed, mosfets exactly 20C hotter ....... made by order Babelfish M25 amp - result - Dynaudio bass units scorched
and list goes on and on .....
though, as I;m often saying, my probably biggest mistake was refusing offer to work in Paris as Lady of the Night, I was so smart thinking - it's better earning as electronic tech. in Balkan Country, out of EU, eternally in, oh yeah, Transition state
"though, as I;m often saying, my probably biggest mistake was refusing offer to work in Paris as Lady of the Night, I was so smart thinking - it's better earning as electronic tech. in Balkan Country, out of EU, eternally in, oh yeah, Transition state
"
😀 😀 😀
"
😀 😀 😀
had Dodo battery in my (then) main DMM, so switched it Off and took another one
after approx. 1.5hrs of useless and messy troubleshooting of an amp, I simply stopped and abandoned work for that day - nothing, absolutely nothing is measuring according to my (irrelevant how low) knowledge
tomorrow, when I took from where I stopped yesterday, I realized that second DMM is having separate buzzer and diode test (function switch) positions, while my main DMM is having them together
I was poking through amp for 1.5hrs,looking at display when I'm expecting something PN, while not looking at all when checking for continuity, expecting to hear a buzz
damn, nothing is conducting where I'm expecting
go figure
never made same mistake again
and yes - I also hate today's auto standby meters
after approx. 1.5hrs of useless and messy troubleshooting of an amp, I simply stopped and abandoned work for that day - nothing, absolutely nothing is measuring according to my (irrelevant how low) knowledge
tomorrow, when I took from where I stopped yesterday, I realized that second DMM is having separate buzzer and diode test (function switch) positions, while my main DMM is having them together
I was poking through amp for 1.5hrs,looking at display when I'm expecting something PN, while not looking at all when checking for continuity, expecting to hear a buzz
damn, nothing is conducting where I'm expecting
go figure
never made same mistake again
and yes - I also hate today's auto standby meters
Oh mighty Zen Mod 
I've built up a SissySIT R2.
I ended up with THF-51N parts. Gate voltage with your test circuit at 2.0A is 4.5V
I'm getting way too much bias current - 2.5Amps with the IQ pot at its lowest setting.
Is there a value change that will put them in the correct 1.8A range?
I've built up a SissySIT R2.
I ended up with THF-51N parts. Gate voltage with your test circuit at 2.0A is 4.5V
I'm getting way too much bias current - 2.5Amps with the IQ pot at its lowest setting.
Is there a value change that will put them in the correct 1.8A range?
no way that you are going to squeeze 4V5 specimens in that circuit, having Iq on sane enough level to keep IRFP alive and well
so, either find another pair with lower Ugs (buy, swap with someone - they're perfect for Singing Bush), or sell populated pcbs and wait some time for even crazier iteration of Sissy, hopefully working, where any Ugs value should be OK
so, either find another pair with lower Ugs (buy, swap with someone - they're perfect for Singing Bush), or sell populated pcbs and wait some time for even crazier iteration of Sissy, hopefully working, where any Ugs value should be OK