I mount the bridges onto individual heatsink as well an they are at 54 degees C. These are 35V bridges.
then call it good and enjoy
output offset , in temp. equilibrium , is good if under +/-50mV
from cold , it can be even 350-400mV , depending of actual physical amp layout , what's normal for Aleph amps , at least to my experience
output offset , in temp. equilibrium , is good if under +/-50mV
from cold , it can be even 350-400mV , depending of actual physical amp layout , what's normal for Aleph amps , at least to my experience
Thank you. I am relieved by the words you said. I have check the offset again and it is now at 17 degrees. I have turn the amp off but noticed the the test speaker moved out....quite a bit.
let amp cool , then recheck it - offset from cold and again in temp equilibrium
take a look at enclosed pic - relocate gate resistors for all output mosfets ot their daughter boards
btw. - your pictures take eternity to upload , because they're too big
anything bigger then 130K for 1200pix pic is waste of time and bandwidth
take a look at enclosed pic - relocate gate resistors for all output mosfets ot their daughter boards
btw. - your pictures take eternity to upload , because they're too big
anything bigger then 130K for 1200pix pic is waste of time and bandwidth
Attachments
Thanks Zen. Your help is greatly appreciated. The gate resistor is on the daughter board. I'll test the amp again tomorrow morning. It's almost midnight now. Have a nice day over there....
Attachments
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sorry - I meant that these green thingies on daughter board were source resistors ...... both size of them and combo of my old eyes and brain mislead me 
so - just ignore that sketch
so - just ignore that sketch
Thanks, Zen.
I powered up the amp this morning. The offset shoots to 50mV then drops down to 25mV. After 15minutes, it goes up to 30mV and then it slowly goes back down. After 45 minutes, the offset drops back down to 25mV and at 1hour, the offset is at 20mV.
The heatsinks measurement are consistent with last night's measurement. After 1 hour.....all the heatsinks are between 50-52 degrees C except Q8's heatsink which is at 55 degrees C.
At 1 hour 15 minutes, offset is at 18mV. I turned the amp off.
Thank you.
I powered up the amp this morning. The offset shoots to 50mV then drops down to 25mV. After 15minutes, it goes up to 30mV and then it slowly goes back down. After 45 minutes, the offset drops back down to 25mV and at 1hour, the offset is at 20mV.
The heatsinks measurement are consistent with last night's measurement. After 1 hour.....all the heatsinks are between 50-52 degrees C except Q8's heatsink which is at 55 degrees C.
At 1 hour 15 minutes, offset is at 18mV. I turned the amp off.
Thank you.
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PM,
IMHO, 50mV is nothing for a power amp.
The F5X protection board e.g. trips in at only +/-2V.
If you wish to have the academic 0V, then use a servo.
But aggressive servos also affect the sound.
So pick your poison.
Patrick
IMHO, 50mV is nothing for a power amp.
The F5X protection board e.g. trips in at only +/-2V.
If you wish to have the academic 0V, then use a servo.
But aggressive servos also affect the sound.
So pick your poison.
Patrick
sorry - I meant that these green thingies on daughter board were source resistors ...... both size of them and combo of my old eyes and brain mislead me
so - just ignore that sketch
Don't worry Choky. I came to the same wrong conclusion before reading through the thread to the end. The mind is a powerful instrument! 😀
This morning my wife gave me tea in bed instead of the usuall coffee (coffee was finished). First few sips I could swear tasted like coffee.
Thanks Patrick. But I think I'll stick with my 20mV offset. It just puzzled me that the DC offset goes up and down and that it take such a long time for it to return to 20mV offset.
I wiould still consider switching the fets, as terrible as that sounds. Better current sharing should result in lower distortion.....I think. Perhaps Zen or Patrick can comment. It might be overkill. Zen's idea of a heta spreader is also good in that the fets will "track" each other to a certain degree.
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Is the airflow the same to all sinks? A little difference could make a temperature difference.
Have you measured the voltage across all source resistors as well as the resistance of each? It could be the source resistor is an outlier if the mosfets were tightly matched.
I've noticed the same type of offset drift in other amps. It's probably just the amp coming to thermal equilibrium. As different parts heat up they influence the offset in different directions.
Have you measured the voltage across all source resistors as well as the resistance of each? It could be the source resistor is an outlier if the mosfets were tightly matched.
I've noticed the same type of offset drift in other amps. It's probably just the amp coming to thermal equilibrium. As different parts heat up they influence the offset in different directions.
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I measured the source resistors today and the results are attached in the pdf file. The R19, which is the Q8 is just a bit too high. maybe the mosfets are not matched.
FETs do not seem to be well matched.
Most probably matched at room temperature and not at your bias current and voltage.
There is no short cut in matching if you want best results.
Patrick
Most probably matched at room temperature and not at your bias current and voltage.
There is no short cut in matching if you want best results.
Patrick
Yup.......it's been delayed for too long...😡.
I still haven't get past the protection board yet 😱
I still haven't get past the protection board yet 😱
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