NX14 on test biased with 200mA have DC offset 6mV without any adjust and matching transistors. There is no any click from speakers when powered on.
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200mA bias decrease to 120mA when amp was hot, I considering to put two 1N4148 diode or LED in series with BD139 to prevent bias decrease.
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When amp (NX14) was warm (very loud home listening) bias was 180mA, offset didn't changed 6mV with any temperature.
Yes that will be DC offset adjust, but I mean on reff GND for diff input, if amplifier have not input GND offset will be about 15V. Amplifier without offset adjust have only 6mV on output, 1k trimpot can oxsydate in time, and than you have higher offset than 6mV.
Regards
![APEX 20NX14[1].jpg](/community/data/attachments/172/172144-06e37107f4245acd33a8d7d5521e5882.jpg?hash=BuNxB_QkWs)
Sorry, but how will You drive output Mosfets near limitation? Saturation voltage will be about 6-9V (Ugs needed for Id about 8A, You can not reach full output swing.
Upgrade with separate rail voltage for VAS can be done (only for FX14, for NX14 you need boostrep in positive rail), just disconnect R18,R19 (220R) from rails and connect to +/-75V DC stabilised if is posible, and you can drive MOSFETs to the saturation. I give simpliest version with available parts, but amp without upgrades and best quality parts still is Ultimate Fidelity with high performanse.
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It is impossible to do it so simply in this schematic, look at driver transistors (quasicomplementary output..) Maybe with complemetary (N and P) Mosfets, but drivers must be conected to higher rails, too.
Are any measurements available?
That is problem with upgrades, when you started never ending, and at the end you get new amp. You are right for drivers, but who want to upgrade amp know all that very well. Who want just to built this amp better don't change anything. I want to give ordinary diyers chance to build simple but high performance amp, that is not easy, some compromise must be done without lose sound quality. Compare with brands, and be better. Most diy amps just work, and not realy better than Pioneer, Technics, Sony... exsept for people who build it and love it becouse of that.
Regards
Regards
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I don't want to convince diyers to build this amplifier. Who recognise some adventage of this schematic be welcome.
Mile;
You are being far too generous with the questions/comments being thrown your way - just make it clear that the designs you are sharing will work AS-IS. Anybody who wants mo-power, etc. can do their own work...
Otherwhise you will find yourself defending your upgrades/suggestions forever :-(.
You are being far too generous with the questions/comments being thrown your way - just make it clear that the designs you are sharing will work AS-IS. Anybody who wants mo-power, etc. can do their own work...
Otherwhise you will find yourself defending your upgrades/suggestions forever :-(.
Yes amplifiers will work, as you are useing suggested design and pcb, upgrades are not for begginers, and if someone do some improvments, and share, I want just comment not mentored.
Regards
AX14 is 'Ultimate Fidelity Amp', FX14 and NX14 are MOSFET and QUASI (NMOS) variation with same VAS, all work great. In many threads people argue BJT vs MOSFET or vs QUASI, but with different VAS, speakers... I build and test AX14,FX14 and NX14 listen and compare sound on same speakers with same PSU, and I don't want share expiriance about that, it's your own to find.
Regards
Regards