Ciao ciccio!
Where are you supposed to connect the power supply to the amplifier? From the diagram it's not clear.
I think you should connect the positive end of the power supply (maybe 20-25Vdc) to the drain of the upper power transistor, and the negative end to the drain of the lower power transistor.
Also make sure about the pinout of the power mosfets and the operational amplifier. Just for testing, you can also put a 1000uF 50V capacitor in series with the load (the 8ohm power resistor or a loudspeaker), just in case there is serious voltage offset at the output due to a wiring error.
BTW, I don't think it's a great design. You can't drive power mosfets with an output impedance of 10k (between the output of the opamp and the power mosfet's gate).
Where are you supposed to connect the power supply to the amplifier? From the diagram it's not clear.
I think you should connect the positive end of the power supply (maybe 20-25Vdc) to the drain of the upper power transistor, and the negative end to the drain of the lower power transistor.
Also make sure about the pinout of the power mosfets and the operational amplifier. Just for testing, you can also put a 1000uF 50V capacitor in series with the load (the 8ohm power resistor or a loudspeaker), just in case there is serious voltage offset at the output due to a wiring error.
BTW, I don't think it's a great design. You can't drive power mosfets with an output impedance of 10k (between the output of the opamp and the power mosfet's gate).
I agree, the mosfets are too much of a load for the opamp. There is probably some oscillation there.
Maybe you should look at http://www.wnaudio.com/amos100.pdf
Maybe you should look at http://www.wnaudio.com/amos100.pdf
Giaime said:
ciao, yes, the power supply is 22,5v from a torroidal transformer and 2 caps 4700mF/63vl
I have only a tester...
the pinout of the mosfet are correct.... about the design; I dont know! you think is not good???
thanks
ciccio.
jaycee said:
ok I agree... and for this reason I want change all my project with a new one!!!
I think the "classic" project are always the best!
any suggestion are welcome.
Giaime said:
Ciao Giaime
The Mosfet output stage is drived by the open loop output impedance of the TL 071 Op amp, usually around 100 Ohms, in series with the 100 uF capacitors.
As the Mosfets at DC and low frequencies have a near infinite input impedance , the 10 K Ohms are perfectly adequate , at high frequencies when the input capacitance come into play , the 100 uF capacitor bypass the 10 K resistor.
But certanly, the circuit maybe upgraded with a bipolar driver before the output Mos-Fets.
Arrivederci
Tube_Dude said:
Uhm... you're right, I didn't think about capacitors.
Ciccio, you should also check the pinout of the TL431, just in case the drawing was wrong. Did you set the 47k trimmer? How much quiescent current you wanted to pass in the output stage? I hope you're using big heatsinks if you plan deep class A.
Why don't you take a look at Elliott's site, for projects?
http://sound.westhost.com/projects-1.htm
Giaime said:
ciao Giaime, the pinout of TL431 is ok! I have only read the volt...
is about 2.3v and -12v
the current? still not cheked...
the heatsinks... 🙄 mhhh... I made the test without....
maibe for this reason the mosfet always burn!
anyway maybe is better the new solution!!!
what you think?!?!
ciao.
The FETs will burn up if the bias is not set.
Without a heatsink, the FETs will burn up even if the bias is set.
The design of this amp looks marginal.
Without a heatsink, the FETs will burn up even if the bias is set.
The design of this amp looks marginal.
ciccio9000 said:
If you didn't check the current, you could have 1-2A in the power mosfets. And without heatsinks, you fry them immediately, not even having the time to reach the trimmer to put down the current...
Don't waste money on mosfets before getting a good schematic, and some basic notions of electronics building 😉
Giaime said:
If you didn't check the current, you could have 1-2A in the power mosfets. And without heatsinks, you fry them immediately, not even having the time to reach the trimmer to put down the current...
Don't waste money on mosfets before getting a good schematic, and some basic notions of electronics building 😉
ok thanks for your suggestion... I burned about 8 mosfet...
but Im booring to change mosfet and do experiment!
I want listeng music
I posted a new design I think is better!!!
and also this is a pcb!!!
ciao
Attachments
That PCB must be double sided?
Before embarking on a new project, why not just put new MOSFETs in and add a heatsink to what you have already? Just set the trimmer to measure most resistance before power is applied.
Before embarking on a new project, why not just put new MOSFETs in and add a heatsink to what you have already? Just set the trimmer to measure most resistance before power is applied.
richie00boy said:
no the pcb is a single side!
Hi, also your suggestion is a good idea.... but im lazy try again....
but I want do a new test!!!
in another worlds, connect the mosfet on a big heatsink with isolation of course! and without power on turn the trimmer for maximum resistance??? rigth?
thanks
ciccio.
Then that layout is wrong as one MOSFET on each side is shorted out across all 3 pins, and 2 pins on the other.
edit: no now I see the black lines are just the MOSFET outlines. It is alright.
If you are too lazy to finish this project how can you not be too lazy to start another? Also that new schematic uses different MOSFETs that are harder to get and expensive.
edit: no now I see the black lines are just the MOSFET outlines. It is alright.
If you are too lazy to finish this project how can you not be too lazy to start another? Also that new schematic uses different MOSFETs that are harder to get and expensive.
richie00boy said:
for a simple reason; if the design is mistaken why I must finish??? and lose more money??? 😡
and above all begin a new project is always a new experience!!!
for a new (4) mosfet I can buy from ebay for just 25€
its not better a new design like what I have posted??? 😀
ciccio
Well to be honest, I don't think the first schematic is that bad. I've built similar before. I can't think why people are being so negative about it, it's very similar to a classic school lab circuit.
My only recommendation would be to remove the 1.8k resistors in the supply to the op-amp and remove the zeners. Then just run the amp off +/- 15 volt supply. As it is shown it's totally pointless having the higher rails for the output stage, it merely creates excess heat.
My only recommendation would be to remove the 1.8k resistors in the supply to the op-amp and remove the zeners. Then just run the amp off +/- 15 volt supply. As it is shown it's totally pointless having the higher rails for the output stage, it merely creates excess heat.
richie00boy said:
you are very right richie
nothing bad with it
.. schematic in Post #1
I agree 100% - a good circuit for set up
and then maybe try variations and improvements - go from there.
- like try a couple of other op-amps
- some other mosfets
- experiment a bit with how much bias in output IRFxxx
- try what power Supply works best
Also amplifier in Post #7 looks very good!
And not too difficult to build.
Regards lineup 🙂
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