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Old 8th July 2010, 06:32 AM   #211
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If you can set BIAS to 200mA, replace R17 (1k) with 470R.
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Old 8th July 2010, 07:43 AM   #212
BV is offline BV  Slovakia
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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.
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Old 8th July 2010, 08:13 AM   #213
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Quote:
Originally Posted by BV View Post
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.
For 100W/8R you need 80Vpp (28v RMS), if you have +/-56V rail voltage you don't need drive MOSFETs to saturation to get that, this is HI-Fi amp extra eficiency is not important.
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Last edited by apexaudio; 8th July 2010 at 08:16 AM.
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Old 8th July 2010, 10:19 AM   #214
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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.

Last edited by apexaudio; 8th July 2010 at 10:28 AM.
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Old 8th July 2010, 10:26 AM   #215
BV is offline BV  Slovakia
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Quote:
just disconnect R18,R19 (220R) from rails and connect to +/-75V DC stabilised if is posible, and you can drive MOSFETs to the saturation.
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?
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Old 8th July 2010, 10:38 AM   #216
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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.
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Last edited by apexaudio; 8th July 2010 at 10:58 AM.
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Old 8th July 2010, 01:43 PM   #217
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I don't want to convince diyers to build this amplifier. Who recognise some adventage of this schematic be welcome.
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Old 8th July 2010, 01:46 PM   #218
balaboo is offline balaboo  United States
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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 :-(.
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Old 8th July 2010, 02:26 PM   #219
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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 :-(.
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.
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Old 8th July 2010, 02:59 PM   #220
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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.
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