TO-126: 2SA1209 is a very good transistor for VAS or driver
The NPN complement to 2SA1209 is 2SC2911
Here's my version 
Very easy and only Mosfets:
LT-Spice, FFT:
And square 500Hz, 8ohm, 1uF parallel:
Very easy and only Mosfets:
An externally hosted image should be here but it was not working when we last tested it.
LT-Spice, FFT:
An externally hosted image should be here but it was not working when we last tested it.
And square 500Hz, 8ohm, 1uF parallel:
An externally hosted image should be here but it was not working when we last tested it.
Yes, KSA1381 (and KSC3503) are at least just as good.
And if they are easier to buy, then they should be a great choice.
Ostripper is in love with KSA1381/KSC3503, for example
Great circuit.Here's my version
Very easy and only Mosfets:
Different.
But in the spirit of this topic with FET, MOSFET etc.
Will you or have you built it, moschfet?
Thanks lineup. I will try to get the jfet version built tonight - but I'm running out of parts so it might be difficult.
To answer your question I'm 31 years old. I've been interested in amplifiers for a long time but it is only in the last year that I have had enough time, space and money to really experiment. Happy 60th birthday! Your guidance, experience and willingness to give advice on these forums are most appreciated and you are an asset to this DIY community. Here's to many more years of amplifier construction!
To answer your question I'm 31 years old. I've been interested in amplifiers for a long time but it is only in the last year that I have had enough time, space and money to really experiment. Happy 60th birthday! Your guidance, experience and willingness to give advice on these forums are most appreciated and you are an asset to this DIY community. Here's to many more years of amplifier construction!
The ksa1381 has much higher early voltage which will make this part outperform the 2sa1209 at low and medium frequencies.
No problem.Yes, sorry, it does not really fits to the theme.
I think it is an interesting circuit with all mosfet.
And it fits very well here in this topic.
Hello all,
Good news. JFET version is built. Schematic is the same as MOSFET version, with some small differences made to the dc offset adjust to provide a slightly negative gate bias at the input fet. I will post a full schematic over the next day or two.
The amp seems as stable as before. The only difference is there is a bit more ringing on the square wave, but I think this is a layout issue - despite the fact that this is my 4th version of this amplifier it is my worst layout yet. Also I only had 390nf caps for PS bypassing.
As it is 2:00 in the morning and my other half is asleep, I have only been able to try some very low volume listening tests. Initial impressions suggest that the JFET has done everything they are known for, and sound quality has improved in every way possible. Voices have taken on a really "airy" character and it sounds like an amp you would pay many thousands of dollars for. I'm impressed to say the least. I will write more tomorrow after I have been able to have a proper listen, but I think it's easily going to live up to expectations. The JFET front end looks to be the icing on the cake.
Who would have thought you could get such a nice sound from only 5 active devices?
Going to start on a pcb design over the coming days.
Oh, by the way, thanks to everyone who posted options fo VAS transistors. I'm looking in to those now.
Greg.
Good news. JFET version is built. Schematic is the same as MOSFET version, with some small differences made to the dc offset adjust to provide a slightly negative gate bias at the input fet. I will post a full schematic over the next day or two.
The amp seems as stable as before. The only difference is there is a bit more ringing on the square wave, but I think this is a layout issue - despite the fact that this is my 4th version of this amplifier it is my worst layout yet. Also I only had 390nf caps for PS bypassing.
As it is 2:00 in the morning and my other half is asleep, I have only been able to try some very low volume listening tests. Initial impressions suggest that the JFET has done everything they are known for, and sound quality has improved in every way possible. Voices have taken on a really "airy" character and it sounds like an amp you would pay many thousands of dollars for. I'm impressed to say the least. I will write more tomorrow after I have been able to have a proper listen, but I think it's easily going to live up to expectations. The JFET front end looks to be the icing on the cake.
Who would have thought you could get such a nice sound from only 5 active devices?
Going to start on a pcb design over the coming days.
Oh, by the way, thanks to everyone who posted options fo VAS transistors. I'm looking in to those now.
Greg.
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SWF,
Gudonya!
Does this mean both input and VAS are both JFETs? What jfet are you using for the VAS?
For the input filter, a very necessary gizmo with extended FR, you need a 1K series resistor after the input point, then a 1nF to ground, then the blocking cap, then the input jfet gate. An amp without an input filter is a disaster waiting to happen....
Lineup, I too had my birthday a couple of weeks back, happy birthday to both of us!
Personally, I feel that people who design with more than 10 transistors for a simple power amp should be heavily fined to teach them the error of their ways.....
Hugh
Gudonya!
Does this mean both input and VAS are both JFETs? What jfet are you using for the VAS?
For the input filter, a very necessary gizmo with extended FR, you need a 1K series resistor after the input point, then a 1nF to ground, then the blocking cap, then the input jfet gate. An amp without an input filter is a disaster waiting to happen....
Lineup, I too had my birthday a couple of weeks back, happy birthday to both of us!
Personally, I feel that people who design with more than 10 transistors for a simple power amp should be heavily fined to teach them the error of their ways.....
Hugh
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I have already said that in post #358:
"...Are you sure your input filter with C2 from post #336 circuit is really effective.... ...maybe if your input V3 has a hi output impedance."
Maybe the message was not so obvious after all...
Fab,
I saw your post and I did reply in the very next post I made.
Unfortunately as you did not suggest an alternative and I was distracted by other aspects of the circuit I had not have not gotten around to trying anything different.
Hugh, thanks for your filter description. Are you suggesting I don't use a gate stopper or did you just assume I would use one anyway?
Oh, by the way, the vas is still the BJT version.
I saw your post and I did reply in the very next post I made.
Unfortunately as you did not suggest an alternative and I was distracted by other aspects of the circuit I had not have not gotten around to trying anything different.
Hugh, thanks for your filter description. Are you suggesting I don't use a gate stopper or did you just assume I would use one anyway?
Oh, by the way, the vas is still the BJT version.
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