Evening gentlemen 🙂
So i stuffed up my second channel, and gave it power.
Everything seems at first to be okay, so i set bias and offset to near the same as the other working channel. -No problem so far.
Then i tried to attach my cheap pc-speakers; and my source and gave it some music (excatly as i did on first channel).
What i noticed right away, when i powered it up, was some humming (no music) and right after that the source resister R19 at Q8 gave some "magic" smoke 😱
I ofcause powered it off imidiatly, and after that it cooled a little of, i shorted the input again and powered it on. -I think everything is okay at this point, i am not sure but maybee the Q8 heats up faster than it did before? Bias + offset is allright (allthrough offset is a bit jumpy)
So it looks as the amp. fails, only when a source is connected. If i connect speakers and still have input shorted, everything seems okay still.
Well, i can ofcause plugin the working channel and take some meassurements there. But before i do that i really would like to understand what is happening here? -Can anyone here help with some meassurement? -Or maybee explain how the circuit works, making me understand better what happens when source is connected and music applied! -I feel i could be better prepared for this fault clearance if i now better how circuit is working.
thanks in advance.
Jesper.
So i stuffed up my second channel, and gave it power.
Everything seems at first to be okay, so i set bias and offset to near the same as the other working channel. -No problem so far.
Then i tried to attach my cheap pc-speakers; and my source and gave it some music (excatly as i did on first channel).
What i noticed right away, when i powered it up, was some humming (no music) and right after that the source resister R19 at Q8 gave some "magic" smoke 😱
I ofcause powered it off imidiatly, and after that it cooled a little of, i shorted the input again and powered it on. -I think everything is okay at this point, i am not sure but maybee the Q8 heats up faster than it did before? Bias + offset is allright (allthrough offset is a bit jumpy)
So it looks as the amp. fails, only when a source is connected. If i connect speakers and still have input shorted, everything seems okay still.
Well, i can ofcause plugin the working channel and take some meassurements there. But before i do that i really would like to understand what is happening here? -Can anyone here help with some meassurement? -Or maybee explain how the circuit works, making me understand better what happens when source is connected and music applied! -I feel i could be better prepared for this fault clearance if i now better how circuit is working.
thanks in advance.
Jesper.
Attachments
power up with inputs shorted , no load
check Iq and offset , in temp equilibrium
power of
connect one input cable , power on , recheck values , connect speaker , check functionality
power of
connect second input , power on , recheck values , connect speaker , check functionality
if some problem persists , post detailed pictures and measured values
check Iq and offset , in temp equilibrium
power of
connect one input cable , power on , recheck values , connect speaker , check functionality
power of
connect second input , power on , recheck values , connect speaker , check functionality
if some problem persists , post detailed pictures and measured values
power up with inputs shorted , no load
check Iq and offset , in temp equilibrium
power of
connect one input cable , power on , recheck values , connect speaker , check functionality
power of
connect second input , power on , recheck values , connect speaker , check functionality
if some problem persists , post detailed pictures and measured values
I will do sir. Zm. 😄
Is it possible that you write a little explanatio, what Q8 does in this circuit? I cant figure it all out...
Jesper
Q8 is no more no less than singing link in chain
signal goes to Q1a , amplifies at drain , arrives at gate of Q8 , amplifies at drain , arrives to speaker
signal goes to Q1a , amplifies at drain , arrives at gate of Q8 , amplifies at drain , arrives to speaker
Q8 is no more no less than singing link in chain
signal goes to Q1a , amplifies at drain , arrives at gate of Q8 , amplifies at drain , arrives to speaker
🙂 So practically speaking lower half is music, upper part is aleph current ?
Thanks...
Jesper.
well ......... sort of .......... but not exactly
remember - in A class , where both halves are active , they're working together all the time
remember - in A class , where both halves are active , they're working together all the time
So it looks as the amp. fails, only when a source is connected. If i connect speakers and still have input shorted, everything seems okay still.
Jesper.
A scenario
Oscillation burst when an input interconnect is present. At power on until the bias settles gives R19 a fast massage and then goes away.
well ......... sort of .......... but not exactly
remember - in A class , where both halves are active , they're working together all the time
A scenario
Oscillation burst when an input interconnect is present. At power on until the bias settles gives R19 a fast massage and then goes away.
If i just think, i would replace the two bjt's (bc550+bc560), and the Q8 mosfet + its source resistor (R19) .. I hope not the 2sj109 is gone (this one has been working in another circuit i know, but could have been damaged desoldering?)
Salas about the oscillation, do you think it's a damaged part?
Thanks for helping both!
Jesper.
do not replace anything , yet
what is result of tests I wrote few posts above?
what source you're using?
what is result of tests I wrote few posts above?
what source you're using?
Salas about the oscillation, do you think it's a damaged part?
Thanks for helping both!
Jesper.
Most probably not. Gate stoppers at Q1 instead of jumpers could help testing?
do not replace anything , yet
what is result of tests I wrote few posts above?
what source you're using?
Okay then... fair enough... I see meassuring good channel and compare with bad is good fault clearance.
I am still at work, will write back when i got time and space for this testing ZM.
Jesper.
Most probably not. Gate stoppers at Q1 instead of jumpers could help testing?
Will also be doable! -There are jumpers installed -perfect 🙂
Jesper.
Attachments
Btw: Is there some meassurements i especially have to carefully test/write down on good channel ?
Anyway i will set it up, so both channels are "working" at same time.
What will be the minimum bias for the aleph current to be working ?
Jesper.
Anyway i will set it up, so both channels are "working" at same time.
What will be the minimum bias for the aleph current to be working ?
Jesper.
recheck all solder joints , all connections , mosfets mounting (both tightness and non-connection with heatsink)
all resistor values
replace those jumpers at gates with 470R-1K resistors
that,as first step
all resistor values
replace those jumpers at gates with 470R-1K resistors
that,as first step
recheck all solder joints , all connections , mosfets mounting (both tightness and non-connection with heatsink)
all resistor values
replace those jumpers at gates with 470R-1K resistors
that,as first step
Cool (or hot)
Resistorvalues checked, mosfet connection checked
I unfortunately haven't much time this evening, but i tried firing it up again, and set the bias at 0.5vdc. The Meassurement is the same on both R19 and R16. R19 and R16 are sourceresistors for Q8/Q5.
I then clipped on my DMM on sourceresistor R19(Q8), and plugged in my Ipad, which i use for source on testbench. Now i meassure 0,5vdc here. When powering up, the voltage imidiatly raised to 1,8-1,9vdc (3,8A/72watt

When unplugging the source, the voltage goes back to 0,5vdc.
So long story short.
Q8 and R19 goes high as soon source is connected, and therefore i saw some smoke from that sourceresistor yesterday.
Jesper.
Attachments
FAULT Clearance for dummies aka' me

I solved it...
There was no fault at pcb, the fault was the cable connected from the ipad 🙂
The first channel, which worked right away, i used another cable for testing. So while i was scratching my head i throught it could be no harm trying the "old" cable.
Everything is working now, and it plays music like the first channel.
I take this cable to work friday, to figure out what the problem could be with this cable???
Anyway thanks alot for helping me out ZenMod and Salas; wish we was closer, i would then buy a "stupidity
cake
So next important thing today is picking up our daughter, which have been for a highschool trip to Hamburg, Germany! -We miss her a little i guess
Jesper.

I solved it...
There was no fault at pcb, the fault was the cable connected from the ipad 🙂
The first channel, which worked right away, i used another cable for testing. So while i was scratching my head i throught it could be no harm trying the "old" cable.
Everything is working now, and it plays music like the first channel.
I take this cable to work friday, to figure out what the problem could be with this cable???
Anyway thanks alot for helping me out ZenMod and Salas; wish we was closer, i would then buy a "stupidity

So next important thing today is picking up our daughter, which have been for a highschool trip to Hamburg, Germany! -We miss her a little i guess
Jesper.
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