Here are some measurements: (7V on PSU)
R25 3.8 V
Q5
g-s 1,25V
g-d 9,5 V
d-s 10,8 V
R23 0V
Q3
g-s 3,6V
g-d 3,45 V
d-s 6,7 V
R25 3.8 V
Q5
g-s 1,25V
g-d 9,5 V
d-s 10,8 V
R23 0V
Q3
g-s 3,6V
g-d 3,45 V
d-s 6,7 V
To early to tell. I’m not sure I will move the CD-player and the preamplifier before the values are ok.
This problem is for the second channel. The first one which I had problem with is ok. I just need to set DC and AC for that one. Thanks Netlist for helping me with that one.
This problem is for the second channel. The first one which I had problem with is ok. I just need to set DC and AC for that one. Thanks Netlist for helping me with that one.
But with the full voltage applied, there is not that much of a difference between Q2 and Q11. I mean, Q11 should be working with 4V.
I'd apply an old speaker and see if you can get any sound out of it. Just make sure the DC voltage between +out and -out is not too high.
/Hugo 🙂
I'd apply an old speaker and see if you can get any sound out of it. Just make sure the DC voltage between +out and -out is not too high.
/Hugo 🙂
Q2 has 4.6V and Q11 has about 3.8V (if I remeber correctly) when turning on fully. Are you sure this is ok?
Measure the DC between the outputs and if that is OK, give it a try. Doesn’t have to play for hours but if you can hear some music, you know at least the amp works and only needs tuning.
I'll be back tomorrow. 🙂
/Hugo
I'll be back tomorrow. 🙂
/Hugo
When you say measure DC between ouputs do you mean measure between + and - or + and earth and - and earth?
I did some measurements.
Measuring DC full voltage
+ side 1,5 V 🙂
- side 14 V 😱
Between + and - 13 V
Measuring DC full voltage
+ side 1,5 V 🙂
- side 14 V 😱
Between + and - 13 V
So, it looks like one side of the amp is working.
I suspect one of the diffpair mosfets.
No matter what you do, the voltage over R23 and R25 must be there and fairly equal. Take out and check Q9. You can even leave it out for the time being.
/Hugo
I suspect one of the diffpair mosfets.
No matter what you do, the voltage over R23 and R25 must be there and fairly equal. Take out and check Q9. You can even leave it out for the time being.
/Hugo
Check every gate resistor. When you measure any voltage across them you know the corresponding mosfet is bad.
/Hugo
/Hugo
I have 0V on R9 (gate resistor for Q2), R38 (Q11 problem side), R22 (Q5), R27 (Q7).
Voltage on R10,R13 (Q4), R35,R39 (Q9)
Voltage on R10,R13 (Q4), R35,R39 (Q9)
Q4 and Q9 together with R10, R13, R35 and R39 are of no importance at the moment.
Their sole purpose is protection.
What about the voltage over R7 and R36, and every other mosfet in the circuit?
Note that Q3 and Q8 are not mosfets, no need to measure these.
As stated before, I believe the one side (Q2 side) of your amp is working fine.
Try to take these components and their voltages as a reference to find out what is wrong with the other side. With power supply caps fully discharged or disconnected, compare every resistor value on the good side with the bad side.
I’m sure you’ll succeed. 🙂
/Hugo
Their sole purpose is protection.
What about the voltage over R7 and R36, and every other mosfet in the circuit?
Note that Q3 and Q8 are not mosfets, no need to measure these.
As stated before, I believe the one side (Q2 side) of your amp is working fine.
Try to take these components and their voltages as a reference to find out what is wrong with the other side. With power supply caps fully discharged or disconnected, compare every resistor value on the good side with the bad side.
I’m sure you’ll succeed. 🙂
/Hugo
Netlist thanks.
The problem was a bad resistor. I don't remember which. Sorry.
My next problem is setting absolute DC. Relative DC is fine never higher than 0.05V and I can easy set it for 0.00V.
But when firing it up initially the absolute DC starts about 7.5V and 6.5V for each channel. My 200 ohm trimpot is set for 0V. Turning it up to 200 ohm gives me 3.5V (for the 7,5V) and the other 2,5V. After an hour or so both channels goes down about 1V but never lower. So the 3.5V goes down to 2.5V and the 2.5V getting 1.5. I know I shouldn’t worry about 1-2 V but as the voltage only changes about 1 V when the heat sinks is getting hot there shouldn’t be a problem getting a DC offset around 0V.
So the question is where do I start?
Do I get a bigger trimpot?
Or do I change R1, R4, R44, R45. Bigger or smaller?
What would be the easiest solution?
The problem was a bad resistor. I don't remember which. Sorry.
My next problem is setting absolute DC. Relative DC is fine never higher than 0.05V and I can easy set it for 0.00V.
But when firing it up initially the absolute DC starts about 7.5V and 6.5V for each channel. My 200 ohm trimpot is set for 0V. Turning it up to 200 ohm gives me 3.5V (for the 7,5V) and the other 2,5V. After an hour or so both channels goes down about 1V but never lower. So the 3.5V goes down to 2.5V and the 2.5V getting 1.5. I know I shouldn’t worry about 1-2 V but as the voltage only changes about 1 V when the heat sinks is getting hot there shouldn’t be a problem getting a DC offset around 0V.
So the question is where do I start?
Do I get a bigger trimpot?
Or do I change R1, R4, R44, R45. Bigger or smaller?
What would be the easiest solution?
Glad you made it.
You will want to try fiddling with R24. A bit higher or lower in value, depending if the offset is positive or negative. 390 or 560 ohm will do the job.
The output to ground R's are fine if you used the given values, 30 to 100ohm.
Did you add the Macmillan resistors from diff-pair sources to outputs? Something like 3 to 5k seems to be in the ballpark for most people.
/Hugo 🙂
You will want to try fiddling with R24. A bit higher or lower in value, depending if the offset is positive or negative. 390 or 560 ohm will do the job.
The output to ground R's are fine if you used the given values, 30 to 100ohm.
Did you add the Macmillan resistors from diff-pair sources to outputs? Something like 3 to 5k seems to be in the ballpark for most people.
/Hugo 🙂
Hi
Problems, problems. This board is really annoying.
Top transistors (Q1, Q10) have Vgs of 4.7V.
Bottom (Q2, Q11) starts about 4,5V and quickly goes down under 4V. After that I have to turn it of not burn anything. V over source resistors R5,R40 0,55V R6,R26 0,48V.
Not ok I think.
Problems, problems. This board is really annoying.
Top transistors (Q1, Q10) have Vgs of 4.7V.
Bottom (Q2, Q11) starts about 4,5V and quickly goes down under 4V. After that I have to turn it of not burn anything. V over source resistors R5,R40 0,55V R6,R26 0,48V.
Not ok I think.
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