Hello, I seem to have a similar problem as I start to bias my right channel. I'm using a Variac [thanks God] and at 50V I quickly get over .222+ in bias with the trimpot set all the way down. Offset works normally.
I'm using:
R8 27.4K
R9 4.75K
P1 5K
P2 500R
I checked all the mossfets for continuity. All the Mossfets were warming up.
I read thru the forum, but can't find something to guide me forward.
Appreciate any thoughts.
Attachments
all the way down
clarify your procedure of establishing "all the way down"
when P1 is set to max resistance, Iq is smallest possible
when P1 is set to minimal resistance, Iq is highest possible
clarify your procedure of establishing "all the way down"
when P1 is set to max resistance, Iq is smallest possible
when P1 is set to minimal resistance, Iq is highest possible
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On one of my FW builds I had a similar problem. After extensive searching, it turned out that while fiddling around with the transistors and screwing down the PCB too hard, I had fractured one of the transistor legs. It was still put but not well enough to give consistence measurements / bias values.
Just a thought. 🙂
Just a thought. 🙂
Chiptech, as ZM wrote, you need P1 at 5K for minimum bias current.
Also, why is your R9 = 4.75K instead of 10K in the schematics? With 4.75K, even
with P1 set at max of 5K, your TL431 will give a min voltage of 9.5V and the Vgs
(and hence the bias) of the mosfets will be quite high.
Also, why is your R9 = 4.75K instead of 10K in the schematics? With 4.75K, even
with P1 set at max of 5K, your TL431 will give a min voltage of 9.5V and the Vgs
(and hence the bias) of the mosfets will be quite high.
Dennis,
The reason it is 4.75K is it looks like I mistook your direction back in post 1712:
"I had a closer look and it seems you have 22.1K for R8? If so, I suggest changing that to 27.4K (as in the latest schematics) and leave R9 at 10K. If you change R9 to 4.75K then even with max value of P1, you will have significant current flow (since you already have 110mV across 0.47 in your current setup)."
My mistake. I will change R9 to 10K and try again.
Thanks,
Chip
The reason it is 4.75K is it looks like I mistook your direction back in post 1712:
"I had a closer look and it seems you have 22.1K for R8? If so, I suggest changing that to 27.4K (as in the latest schematics) and leave R9 at 10K. If you change R9 to 4.75K then even with max value of P1, you will have significant current flow (since you already have 110mV across 0.47 in your current setup)."
My mistake. I will change R9 to 10K and try again.
Thanks,
Chip
I once thought that was the secret to getting out of high school. But, I prefer reading at my own pace, but with error correction built in?
With A Little Help From My Friends
I'm happy to report I've successfully biased my right channel.
All on my own, by researching thru the forum, I figured out I had expertly reversed the trimpots, so that was fixed.
And thanks to Dennis for sorting out my error on R9.
It's all good.
Now on to the left channel.
I can't recommend using a Variac. It really lowers the stress and limits frying parts. I will never leave home without it.
I'm happy to report I've successfully biased my right channel.
All on my own, by researching thru the forum, I figured out I had expertly reversed the trimpots, so that was fixed.
And thanks to Dennis for sorting out my error on R9.
It's all good.
Now on to the left channel.
I can't recommend using a Variac. It really lowers the stress and limits frying parts. I will never leave home without it.
then you either didn't read or understood what I wrote in #2623
it could save you of massive search
I have noticed in prior posts that you often assume the newbies on here know more than we do. In this case my IQ isn't high enough to know what Iq means or why it matters. My guess is Chiptech didn't understand what you meant either 🙂. Sadly, most of us have no idea what we are doing when we build one of these DIY amps.
But we’re her not just to play lego, but to learn, too.
(I still haven’t understood Iq though [emoji16] )
(I still haven’t understood Iq though [emoji16] )
I'm practically using small number of abbreviations, and those I'm using are worthy of becoming every DIY-er common knowledge ....... they're so important;
further , when technical matters are in case, I'm really trying to be responsible ( not serious, not same thing), so always investing some energy to be concise and clear
exactly because of that - I'm not objecting nor having difficulty to answer any further question, leading to things being more and fully clarified
that's also why I'm always insisting to call things with right name - bias is not Iq , bias is ( in most cases) voltage which is controlling Iq
while Iq is nothing else than quiescent current
I'm not having problems differentiating these two, but novices can have problem, and in most cases difference between is crucial , not just for understanding , but also for not-emptiness of someone's wallet
so - Ask And Ye Shall Receive.......
at least, that was and still is my policy, and it works 🙂
What Choky is saying here, is that - regardless of inverse or correct orientation, the resistance provides IQ. I have no God damn clue about the physics, but I understood what he meant. I never care extremely much about pot orientation, simply measuring voltage drops and turning the pot the way that avoids blow-ups, is enough. So I don’t agree that Choky assumes too much knowledge. On the contrary, I regard him as quite patient with people like me (complete novice).
Of course, he sometimes makes it clear he is running out of patience, and remarks when lack of knowledge stops further progress. But he is never rude, and most of the time, he is very funny.
I have learned that a fair share of self-irony is good to have meeting some of Chokys advice. But he is «never» wrong. But sometimes he makes us have to think ourselves. And he absolutely ALWAYS helps us.
He is what he is, and I like it.
Like Zardos, unbeatable.
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Taking in account what Pa is doing to me all these years, I'm little Kitten, comparing to him.
whenever I had some question to him, best I got ( in 99% of cases) was one-liner
and then, after my tremendous struggle, some time after, I always realized that he gave me direct answer to third or fourth next logical question.
go figure
that's exact reason why I'm often writing something and asking just one question - expecting direct answer, so we can proceed further
why I'm not blasting with tirade is from various reasons - one of them is that I respect someone's lack of mileage, and want to give him right to breathe and take one thing at a time
second ( less important reason) is that I have no patience for long tirades ; longer it lasts, greater lag between my brain and what I managed to type
though - Papaway is best - you want to learn? glue sandpaper on the bench, put your elbows on ........
relax Boyz , feel free to ask, whatever you're not sure of
if residents see that you really care, they will always reply
whenever I had some question to him, best I got ( in 99% of cases) was one-liner
and then, after my tremendous struggle, some time after, I always realized that he gave me direct answer to third or fourth next logical question.
go figure
that's exact reason why I'm often writing something and asking just one question - expecting direct answer, so we can proceed further
why I'm not blasting with tirade is from various reasons - one of them is that I respect someone's lack of mileage, and want to give him right to breathe and take one thing at a time
second ( less important reason) is that I have no patience for long tirades ; longer it lasts, greater lag between my brain and what I managed to type
though - Papaway is best - you want to learn? glue sandpaper on the bench, put your elbows on ........
relax Boyz , feel free to ask, whatever you're not sure of
if residents see that you really care, they will always reply
Watch it, Mighty! With that attitude you might be adopted by force to California 😀
Smooth sailing. Might pop you a question or two about my XS300 clones, hoping for one liners two or three steps down the logical path from the original question
Smooth sailing. Might pop you a question or two about my XS300 clones, hoping for one liners two or three steps down the logical path from the original question
you nutz, two reasons:
-I'm in eternal Potential Adoptee status, never to be resolved
-XS300; even in case that you know exact schematic (crumbs around, say that I can guess at least 90%, rest is always Babelfishing area), sheer amount of hardware is frightening ......... not even taking in account that powering up The Beasts is justified only when you want your Sauna functional ......
even XS30 is way above my head.... and needs
-I'm in eternal Potential Adoptee status, never to be resolved
-XS300; even in case that you know exact schematic (crumbs around, say that I can guess at least 90%, rest is always Babelfishing area), sheer amount of hardware is frightening ......... not even taking in account that powering up The Beasts is justified only when you want your Sauna functional ......
even XS30 is way above my head.... and needs
I always wanted a sauna of my own. To be clear: the XS300 clone-thing was purely a joke. I barely have a single project that hasn’t gone wrong at some point or another. I’d say that amp is maybe the one closest to impossibility of the bunch, but willing to stand corrected of course. You might have forgotten, but the joke is a reference to a joke you yourself made one time a guy -presumably a newbie - asked what was the best Papa amp to build. One of your better jokes imho
I’ll stick with my ACP+ and finishing that BA-3 reiteration 😀
I’ll stick with my ACP+ and finishing that BA-3 reiteration 😀
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I remember very well what you're building
but , simply couldn't resist when you mentioned XS300, second or third time
but , simply couldn't resist when you mentioned XS300, second or third time