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Erno Borbely "Milennium" All Fet Class A Power amp 75W RMS
Erno Borbely "Milennium" All Fet Class A Power amp 75W RMS
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Old 20th April 2019, 12:42 AM   #31
ticknpop is offline ticknpop  Canada
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Erno Borbely "Milennium" All Fet Class A Power amp 75W RMS
I have 11 millenniums, the offset means you still have a problem, not using the servo does’t remove it. What front end jfets do you have 389/109 Or 170/74?
The 170/74,s need to be thermally coupled to reduce offset. You have tried turning the 50 ohm trimpot yes?
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Old 20th April 2019, 09:24 AM   #32
merlin el mago is offline merlin el mago  Europe
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I have 389/109.
Yes I have tried turning the 50 ohm trimpot.
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Old 20th April 2019, 10:33 PM   #33
alweit is offline alweit  Israel
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If you have -6V offset with AD820 it means: or AD820 is damaged, or one of its power (+/- 10V, regulated by shunts LM4040) is wrong - I saw few millivolts offset during driver setup after inserting servo opamp. Another issue: how did you connect chassis ground? When I connected it to ground point of driver board I had self-oscillation, I connected ground to chassis only at amplifier input - but I did not use original Borbely PCBs (he already closed his business that time), I designed them myself.
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Old 20th April 2019, 10:45 PM   #34
merlin el mago is offline merlin el mago  Europe
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I will check if the socket of AD820AN measure +10V pin 7 & -10V pin 4. When I tested the LM4040 was ok. I connect the chassis ground only from the PSU board. Your stereo amp looks superb and you have all my admiration if you do it yourself.
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Old 20th April 2019, 10:50 PM   #35
merlin el mago is offline merlin el mago  Europe
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AD820 is damaged, I measure at the socket +-10V
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Old 22nd April 2019, 03:56 PM   #36
merlin el mago is offline merlin el mago  Europe
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Well managed to measure the K982 & J148 in place Idss I have to measure like mosfets, I guess to input mosfet using 2K2 resistor Transistor matching

I need for the minus rail regulator Q21 K982, Q22 & Q23 both J148

And for the driver minus said Q5 & Q6 both J148

Have VGS
K982 J148
2.69 2.75
2.75 2.76
2.81 2.78
2.83 2.79
2.85 2.82
2.89 2.83
2.91 2.84
2.92 2.85
3.05 x 2 3.03
----- 3.06 x 2
----- 3.08 x 2
----- 3.12
----- 3.16

Wich one to use in each position?

Last edited by merlin el mago; 22nd April 2019 at 03:58 PM.
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