sreten.it was talked about here.
http://www.diyaudio.com/forums/showthread.php?s=&threadid=26739&highlight=
http://www.diyaudio.com/forums/showthread.php?s=&threadid=26739&highlight=
I also liked mosfets. they are rugged, cheap and sound good. sure, they have lower gain, higher distortion, and etc. But I just had tremendous amount of trouble getting BJTs to work and until my luck runs out on mosfet, I will stay with them.
the P101 is a welcome sign that Rod has finally joined the mosfet crowd.
the P101 is a welcome sign that Rod has finally joined the mosfet crowd.
Good or bad
To Peranders : This amp have low efficiency, 'cos have the same voltage on VAS rails like voltage on output stage. Have wrong current limitation - voltage limitation on gates is with complex load insufficient. Slew rate will be unsymetrical thrue bootstraped VAS. Through current in VAS is too low - distortion on higher frequecy will very rise . PCB - " beauty ". Results : " No glory ".
To Peranders : This amp have low efficiency, 'cos have the same voltage on VAS rails like voltage on output stage. Have wrong current limitation - voltage limitation on gates is with complex load insufficient. Slew rate will be unsymetrical thrue bootstraped VAS. Through current in VAS is too low - distortion on higher frequecy will very rise . PCB - " beauty ". Results : " No glory ".
Actually, having separate and higher voltage rails for the driver/VAS circuitry would make practically no difference because the MOSFET on resistance is so high; at full power the source is automatically dragged down much lower than the gate, thus is fully turned on.
The zeners on the gate are not really intended specifically for current limitation; they are to protect the gate from overvoltage. The fact that they provide rudimentary current limitation is a bonus.
I would have liked to see a CCS VAS, but at the end of the day the amp performs well and is a great project for beginners, easy to get working and relatively simple and cheap. It's not intended to be the last word in design, but it still manages a very respectable effort.
The zeners on the gate are not really intended specifically for current limitation; they are to protect the gate from overvoltage. The fact that they provide rudimentary current limitation is a bonus.
I would have liked to see a CCS VAS, but at the end of the day the amp performs well and is a great project for beginners, easy to get working and relatively simple and cheap. It's not intended to be the last word in design, but it still manages a very respectable effort.
Higher voltage for VAS
is uncoditionaly needed for full opening the fet when peak output voltage is nearly voltage rails. Practicaly in this concrete connection is it about 3 - 4 V higher voltage than main voltage. This voltage must be floating ( PS connected in series with main voltage ). Belive me, I have doing MOSFET amps twenty years. Zeners at gate can be used as current limitation, but only with real load.
is uncoditionaly needed for full opening the fet when peak output voltage is nearly voltage rails. Practicaly in this concrete connection is it about 3 - 4 V higher voltage than main voltage. This voltage must be floating ( PS connected in series with main voltage ). Belive me, I have doing MOSFET amps twenty years. Zeners at gate can be used as current limitation, but only with real load.
Re: Higher voltage for VAS
1 Effeciency, normally not very important
2 Use is home use I'll gather => no need for advanced protection.
I think it's OK, nothing new but why has it to be that? Compare AKSA100. How many of you have seen Hugh's AKSA amps and how many have serious complaints. Soon SonnyA will have AKSA going into battle with his SMD current feedback amp. I'm really interested in the outcome.
Upupa Epops said:
I think you first should identify the needed design features for specific customer. This amp isn't any high-end state of the art. It's a product for a DIY'er and it's a good piece of craftmanship.Upupa Epops said:
1 Effeciency, normally not very important
2 Use is home use I'll gather => no need for advanced protection.
I think it's OK, nothing new but why has it to be that? Compare AKSA100. How many of you have seen Hugh's AKSA amps and how many have serious complaints. Soon SonnyA will have AKSA going into battle with his SMD current feedback amp. I'm really interested in the outcome.
My experience with 2SK135/2SJ50 is that Rdson is much lower than the datasheet tells you.richie00boy said:
My first mosfet amp delivered 285 W at 4 ohms. When I changed to newer mosfets, the same type, the power went up to 480 W! So in this case you really can win with higher driver voltage. In my case 80 volts (driver) and 72-75 V (output stage). Still how many dB's is this? Can you hear it?
PMA said:
that's very much like what I did with my own version of citation 12. Except that I used a pair of mosfets and a Vbe multiplier.
I am also trying out a trimmer for Vbe, like in the above schematic. so far, no sonic difference that i can tell.
the t-driver stage is very important to improving thd specs but sonically it really dont' do a whole lot.
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