if i were to omit the Q11 N channel Jfet..to be replace with a 10k resistor, how do connect it.? from R9 to which pin G,S or D.using the original circuit broad from passlabs article.thanks
Tone,
You could also replace the resistor with a current diode. (The fet in the A-40 article is strapped like a current diode). This gives you a 20db improvement in rail rejection.
Failing that you could split the 10k resistor into two 5k resistors and attach a cap to ground (say 200uf), observe polarity.
Jam
You could also replace the resistor with a current diode. (The fet in the A-40 article is strapped like a current diode). This gives you a 20db improvement in rail rejection.
Failing that you could split the 10k resistor into two 5k resistors and attach a cap to ground (say 200uf), observe polarity.
Jam
Hello
I've got another question about the A40. We've just completed the amps and got 'm running. Only 30 mV DC offset, so that looks OK. Maybe in the future a bit of tweaking and we could reach 0 V.
But... the tantalum caps in the amp were replaced with solid aluminium types. It lookes like the amp is a bit more quit in the high frequencies (compared to my amp that is..) Could those caps be responsible for this ???
Has anybody experimented with those caps (C2,3) to improve the sound.
Any suggestions ??? Or are we not patient enough and should we wait till the amp has played for a few days ?
Grtz,
Nick
I've got another question about the A40. We've just completed the amps and got 'm running. Only 30 mV DC offset, so that looks OK. Maybe in the future a bit of tweaking and we could reach 0 V.
But... the tantalum caps in the amp were replaced with solid aluminium types. It lookes like the amp is a bit more quit in the high frequencies (compared to my amp that is..) Could those caps be responsible for this ???
Has anybody experimented with those caps (C2,3) to improve the sound.
Any suggestions ??? Or are we not patient enough and should we wait till the amp has played for a few days ?
Grtz,
Nick
Pass DIY Addict
Joined 2000
Paid Member
Nick: My amp has approx 30mV offset on one channel and closter to 45-50mV offset on the other channel. I don't find that this creates any problem at all. I didn't use the tantalum caps either; instead, I put 220uF 25v BlackGate FK caps in their place. I can't really compare the tants to the BG, but I am very happy thus far with the amp.
I have not yet had the opportunity for a critical comparison between the a-40 and my Marantz MA500 monoblocks that I've been using for years now.
Jam: You've recommended using a current diode in this place before. Since I'm still somewhat of a newbie, could I trouble you for a more detailed account of how to pull this off? Thanks!
My a-40 project - pictures soon.
Eric
I have not yet had the opportunity for a critical comparison between the a-40 and my Marantz MA500 monoblocks that I've been using for years now.
Jam: You've recommended using a current diode in this place before. Since I'm still somewhat of a newbie, could I trouble you for a more detailed account of how to pull this off? Thanks!
My a-40 project - pictures soon.
Eric
Eric,
Look for a 3 to 4 ml current diode. (I believe Motorola makes them). Solder the banded end to the top of the diode stack (base of current source transistor for differential pair) and the other end to ground.
Check
http://www.fosu.edu.cn/fas/Library/chips/1n2n/1N5292.pdf
Jam
Look for a 3 to 4 ml current diode. (I believe Motorola makes them). Solder the banded end to the top of the diode stack (base of current source transistor for differential pair) and the other end to ground.
Check
http://www.fosu.edu.cn/fas/Library/chips/1n2n/1N5292.pdf
Jam
Nick,
I have not noticed much difference between the types of cap used but I have a slight bias (no pun intended) to black gates in that position. 30 to 40 mV offset is not bad and I would not worry about it. If this still bugs you could adjust the current source to null the offset.
Jam
I have not noticed much difference between the types of cap used but I have a slight bias (no pun intended) to black gates in that position. 30 to 40 mV offset is not bad and I would not worry about it. If this still bugs you could adjust the current source to null the offset.
Jam
Pass DIY Addict
Joined 2000
Paid Member
A-40 parts list
The small signal trans are a bit unihqe
would a mps 18 ( higher gain) or a 2n 4401 (general purpose lower voltage) be ok? And how about newer versions for those drivers--Are we working in the 35-100 gain range? (there are some nice linear panasonics@ digikey)
The small signal trans are a bit unihqe
would a mps 18 ( higher gain) or a 2n 4401 (general purpose lower voltage) be ok? And how about newer versions for those drivers--Are we working in the 35-100 gain range? (there are some nice linear panasonics@ digikey)
One more question. Does anyone have a cross for Q11 that has the correct pinout? Can I use an IRF9610?
- Status
- Not open for further replies.