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Old 14th January 2019, 02:09 PM   #1
HerrFlick is offline HerrFlick  Netherlands
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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, 330 views)
File Type: jpg AXL-v2-assambled.jpg (701.0 KB, 328 views)
File Type: jpg AXL-v2-PCB-scl.jpg (588.1 KB, 310 views)
File Type: jpg AXL-v2-PCB-bcl.jpg (536.3 KB, 281 views)
File Type: jpg AXL-v2.jpg (707.9 KB, 273 views)

Last edited by HerrFlick; 19th February 2019 at 11:58 AM.
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Old 14th January 2019, 03:49 PM   #2
mlloyd1 is offline mlloyd1  United States
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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 ...

mlloyd1
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Old 14th January 2019, 07:00 PM   #3
Herr Flick is offline Herr Flick  Netherlands
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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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Old 27th February 2019, 11:37 PM   #4
nigelwright7557 is offline nigelwright7557  United Kingdom
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Completely over engineered for very little improvement, if any.

Newer doesn't always mean better, could be just "different" or even "the same"
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Old 28th February 2019, 12:36 AM   #5
johnego is online now johnego  Indonesia
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Herr Flick,
How would you compare the sound quality of this new version with the old one? And with other amplifiers?
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Old 28th February 2019, 02:30 PM   #6
HerrFlick is offline HerrFlick  Netherlands
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It is always difficult to find the right words to descripe the difference between two amplifiers -jonnego-, escpecially when you are not a native english speaker. The first thing we (my wife and I) said to each other when we listen to my upgraded amplifier was: much more details and a lower bass. A couple of weeks ago I went to a friend and made comparision with his amplifier NAD C352, Bowers and Wilkens 804S loudspeakers and -van den Hul D-101 III interlinks.
All three of us came to the conclusion that the Elektor AXL V2 was slighty "better" i.e. more details. Later on I invited another friend, HiFi freak as well, at home and he was impressed by the sound. Another big improvement was earlier made due to the use of the Raspberry Pi and the HiFiBerry DAC, thatswhy I sold my Arcam Alpha 7 CD player.
I will try to make more comparings with other Hi-End amplifiers and let you know by that time, but it is hard to find people who uses Hi-End stereo equipment nowadays.
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Old 1st March 2019, 05:51 AM   #7
johnego is online now johnego  Indonesia
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Quote:
Originally Posted by HerrFlick View Post
it is hard to find people who uses Hi-End stereo equipment nowadays.
thanks herr flick. seems like you are new with diy. nowadays, if we are selective we can build amp that rivals commercial amps many times the price of the NAD
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Old 4th March 2019, 02:19 AM   #8
sariwangi2008 is offline sariwangi2008
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What amp do you recommended?
With latfet 2SK176/2SJ56.
Its worthed if I build AXL mosfet now?
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Old 4th March 2019, 02:05 PM   #9
HerrFlick is offline HerrFlick  Netherlands
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The 2SK176/2SJ56 is a good replacement for the original 2SK134/2SJ49, but you have to use the old Elektor schema (1985). I.e. you have to insert two source resistors (0,22 Ohm low inductance) and lower the gate resistor R25 330 Ohm in 220 Ohm. The output coil L1 must be changed back in 2 H. Because of the source resistors you need a new PCB layout and last but not least, I think the the sound of the lateral mosfets ECF10N20/ECF10P20 is better but I cannot confirm that.
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Old 25th March 2019, 03:04 AM   #10
phri is offline phri  Australia
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Default upgrade AXL

Quote:
Originally Posted by HerrFlick View Post
The 2SK176/2SJ56 is a good replacement for the original 2SK134/2SJ49, but you have to use the old Elektor schema (1985). I.e. you have to insert two source resistors (0,22 Ohm low inductance) and lower the gate resistor R25 330 Ohm in 220 Ohm. The output coil L1 must be changed back in 2 H. Because of the source resistors you need a new PCB layout and last but not least, I think the the sound of the lateral mosfets ECF10N20/ECF10P20 is better but I cannot confirm that.

What was the motivation to replace the mosfets? In your opinion which upgrade improved sound quality most?

I build 8 versions of the AXL back in the 80's, and still have them, stored in the shed (next to fancy also unused electrostatic speakers), as they have been replaced with a modern Yamaha AV-receiver. However I have some time for the Audio hobby again and look at options to use these again.
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