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Old 14th January 2019, 03:09 PM   #1
HerrFlick is offline HerrFlick  Netherlands
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Location: Apeldoorn
Default Elektor AXL V2 with Lateral MOSFET's

More then 30 years ago (1985) I build the Elektor AXL class A/AB amplifier, time to upgrade this amplifier using new (= better)components.
My main goal was to replace the power mosfets 2SK134/2SJ49 with Exicon ECF10N20/ECF10P20. Also the medium power transistor BF469/BF470 changed to MJE340G/MJE350G.
Extra power supply filter capacitors where used and placed on the PCB.
The two capacitors for the 15V zener diodes where increased to 100uF 25V
and the capacitor parallel to the quiescent current potentiometer (1k) is increased to 220 F (Single-Ended Conductive Polymer Aluminum Solid Electrolytic Capacitors)plus extra 47nF WIMA MKP.
The two source resistors (0,22 Ohm) are no longer needed.
The input capacitor (C1,C2,C3-820 nF) is replaced by a high end capacitor 2,7 uF Clarity Cap ESA.
The Exicon Application notes told me to decrease the inductance in the output line to 1H (1mm Cu wire inner diameter 8 mm, 15 windings). Due to different gate input capacitance of the mosfets the gate resistors are also different, 330 Ohm for ECF10N20 and 220 Ohm for ECF10P20.
The power supply for each channel (2x25V AC 2,4A 120 VA) is filtered by 4 x 10.000 F rectifier (Ebay) so that results in 2 x 38V DC output voltage.
It is still very important to set the quiescent current potentiometer to zero Ohm before switching on the amplifier for the first time.
I tried to use the same component labels but did not 100 percent succeed.
On my old (same as me) but still working oscilloscope (Philips PM3226) I saw a maximum error free waveform of about 60 Volt peak-peak with a 8 Ohm resistor load.
No oscillation what so ever, 60 Volt peak to peak over 8 Ohm i.e. 30 : 1,4 = 22 Watt output power with a quiescent current 0,1 A.
The calculated damping factor is more then 200.
I am using a Rasberry Pi in combination with the HiFiBerry DAC plus and a home made power supply (5V 3A), controlled by Volumio software, NAS. The loudspeakers: Acoustic Energy AE1.
Attached Images
File Type: jpg AXL-v2-schema.jpg (303.4 KB, 73 views)
File Type: jpg AXL-v2-assambled.jpg (701.0 KB, 73 views)
File Type: jpg AXL-v2-PCB-scl.jpg (588.1 KB, 66 views)
File Type: jpg AXL-v2-PCB-bcl.jpg (536.3 KB, 59 views)
File Type: jpg AXL-v2.jpg (707.9 KB, 61 views)

Last edited by HerrFlick; Yesterday at 12:58 PM.
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Old 14th January 2019, 04:49 PM   #2
mlloyd1 is offline mlloyd1  United States
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Location: Northern Iliinois
Elektor AXL V2 with Lateral MOSFET's
are you sure there are no errors in that schematic?
some things around the drive for t11 and t12 looks a bit strange ...

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Old 14th January 2019, 08:00 PM   #3
Herr Flick is offline Herr Flick  Netherlands
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Location: The Netherlands
Thanks for your reply -mlloyd1-.
I checked again my schema with the original one from march 1985 but I asure you there is no difference at all. I also check the pcb layout again and came to the same conclusion. If there is a problem then my amplifier could probably not produce such a clear sound at all I think.
Herr Flick
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