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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 15th April 2019, 03:09 PM   #11
alweit is offline alweit  Israel
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Yes, it should work - replace R11, R12: instead of 75R put 50R and use 100R trimmer.
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Old 15th April 2019, 03:37 PM   #12
merlin el mago is offline merlin el mago  Europe
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I don't have an50 ohm resistort, still can't set the offset voltage to 0V with P3.

Last edited by merlin el mago; 15th April 2019 at 03:39 PM.
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Old 15th April 2019, 03:50 PM   #13
Osvaldo de Banfield is offline Osvaldo de Banfield  Argentina
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For a better precision, you can put the pot in parallel of a resistance that bot give the original pot value required.
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Old 15th April 2019, 04:09 PM   #14
alweit is offline alweit  Israel
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If you look at schematic, you can see that it is symmetrical, resistors R8, R9 - 100 Ohm,
R11, R12 - 75 Ohm, P3 - 50 Ohm, so R8 + R9 = 200 Ohm, R11 + P3 + R12 - also = 200 Ohm, you cat put 200 Ohm pot instead of 50 Ohm (P3) and short R11 and R12, or, as I offer, put 100 Ohm instead of P3 and replace R11 and R12 with 50 Ohm (closest 49.9 Ohm) resistors - it will keep symmetry. If you put 25 Ohm instead of 50 Ohm trimmer,
you should use R11, R12 value 175 / 2 = 87,5R (closest 86.6 Ohm), in my amp the P3 is almost in the center, so I think 25 ohm will be enough - I selected all components very carefully with curve tracer - but I do not know about yours.
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Old 15th April 2019, 08:28 PM   #15
merlin el mago is offline merlin el mago  Europe
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Quote:
Originally Posted by Osvaldo de Banfield View Post
For a better precision, you can put the pot in parallel of a resistance that bot give the original pot value required.
That's a good idea, I will try P3 trimpot 100 ohms + parallel 100 ohm fixed resistor.

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Originally Posted by alweit View Post
If you look at schematic, you can see that it is symmetrical, resistors R8, R9 - 100 Ohm,
R11, R12 - 75 Ohm, P3 - 50 Ohm, so R8 + R9 = 200 Ohm, R11 + P3 + R12 - also = 200 Ohm, you cat put 200 Ohm pot instead of 50 Ohm (P3) and short R11 and R12, or, as I offer, put 100 Ohm instead of P3 and replace R11 and R12 with 50 Ohm (closest 49.9 Ohm) resistors - it will keep symmetry. If you put 25 Ohm instead of 50 Ohm trimmer,
you should use R11, R12 value 175 / 2 = 87,5R (closest 86.6 Ohm), in my amp the P3 is almost in the center, so I think 25 ohm will be enough - I selected all components very carefully with curve tracer - but I do not know about yours.
If Osvaldo idea doesn't work I will try P3 200 ohm shorting R11 R12.

Thanks for support guys.

Good night
Felip
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Old 17th April 2019, 02:50 PM   #16
merlin el mago is offline merlin el mago  Europe
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I have problems now with the regulator, in the plus side I'm measuring -5Vout, the regulator input is OK +55V but when I measure voltage across D17 is 0V in place 6.9-7V, I desoldered the voltage reference diode from the PCB and measured with DC75 and says is OK

The measuring is done connecting both rails positive and negative (+Vs2 & -Vs2) to the driver, SGND to PGND (Driver) and PGND from PSU PCB to PGND (Driver) so only disconnected from output section: FB, +D & D-

I guess wasn't necessary to connect the output section to the driver?

I desoldered all diodes & FETS of the plus side of regulator and all the devices are OK. Can be P5 damaged?
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File Type: jpg Millenium All-Fet Regulators EB-2000-342 001.jpg (379.9 KB, 122 views)

Last edited by merlin el mago; 17th April 2019 at 03:09 PM.
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Old 17th April 2019, 03:20 PM   #17
merlin el mago is offline merlin el mago  Europe
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P5 is OK
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Old 17th April 2019, 03:23 PM   #18
merlin el mago is offline merlin el mago  Europe
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Quote:
Originally Posted by Osvaldo de Banfield View Post
For a better precision, you can put the pot in parallel of a resistance that bot give the original pot value required.
Done paralleled the pot with a 100 ohm but I have now problems setting the regulator to +50V
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Old 17th April 2019, 07:29 PM   #19
merlin el mago is offline merlin el mago  Europe
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Ref. diode D17 is OK 6.9V

Voltage across D15 0,7V, the other power amp D15 2.7V
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Old 17th April 2019, 09:35 PM   #20
alweit is offline alweit  Israel
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Is it possible that D16 is damaged - this is current regulator diode (J508 2 mA). You can remove it from the board and easily check - connect milliampermeter in serial with it and apply ~10V - (of course take care about diode polarity) - milliampermeter should show 2-2.5 mA, if not - the diode is damaged. If you do not have spare one, it is possible to replace it with ~22K resistor, but in this case you should connect electrolytic capacitor 22-47 uF in parallel to C27 to protect voltage reference (LM329) at start point - I offer to to it only fo test, you still need to find J508, if it is damaged.
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