SWCAD III
I've briefly tried the above but wouldn't go as far as saying that I anything like evaluated it. I admit I didn't get along with it too well but then I didn't persevere either. Perhaps I'll give it another try sometime.
Sonny, thanks for the offer of help. I'll keep it in mind for when I have time to try SWCAD again.
I think we are getting a little off topic here - perhaps someone would like to start a new thread on Spice simulators? Come to that I seem to recall having seen something like this before on another of the forums.
Ian.
I've briefly tried the above but wouldn't go as far as saying that I anything like evaluated it. I admit I didn't get along with it too well but then I didn't persevere either. Perhaps I'll give it another try sometime.
Sonny, thanks for the offer of help. I'll keep it in mind for when I have time to try SWCAD again.
I think we are getting a little off topic here - perhaps someone would like to start a new thread on Spice simulators? Come to that I seem to recall having seen something like this before on another of the forums.
Ian.
JFET Output Impedance
Harry, just made some measurments of the above that seem to confirm your theory about the JFET front end reducing open loop gain. Using constant current sources (as opposed to Aleph) for the output stage, I measured the output impedance of the stock circuit (IRF9610 front end) as approx 0.4R. Substituting J109 increases this to around 2R. This always assuming I did my measuring right! Presumably distortion will also rise though I am unable to verify this by simulation.
Ian.
Harry, just made some measurments of the above that seem to confirm your theory about the JFET front end reducing open loop gain. Using constant current sources (as opposed to Aleph) for the output stage, I measured the output impedance of the stock circuit (IRF9610 front end) as approx 0.4R. Substituting J109 increases this to around 2R. This always assuming I did my measuring right! Presumably distortion will also rise though I am unable to verify this by simulation.
Ian.
JFET front end
Referenced to each drain resistor I get a voltage gain of 7 with the Jfets for 784 ohms load and 5 mA in each fet. For the mosfet pair with 392 ohm drain resistors I a gain of about 20. Not really theory but more based on experience. Nelson makes this amp design stuff look a little easier that it really is. I suspect that the mosfet front end for this amp was a well thought out choice on his part.
H.H.
Referenced to each drain resistor I get a voltage gain of 7 with the Jfets for 784 ohms load and 5 mA in each fet. For the mosfet pair with 392 ohm drain resistors I a gain of about 20. Not really theory but more based on experience. Nelson makes this amp design stuff look a little easier that it really is. I suspect that the mosfet front end for this amp was a well thought out choice on his part.
H.H.
Current Source Reference
Harry, thanks for the information regarding voltage gain of JFET vs MOSTFET. Interesting - I had not appreciated the magnitude of the difference (haven't really thought about it to tell the truth).
I note you haven't passed comment on my previous question (see quote below). Is there some reason? Perhaps it has already been covered in another thread?
Ian.
Harry, thanks for the information regarding voltage gain of JFET vs MOSTFET. Interesting - I had not appreciated the magnitude of the difference (haven't really thought about it to tell the truth).
I note you haven't passed comment on my previous question (see quote below). Is there some reason? Perhaps it has already been covered in another thread?
Ian.
"Am I correct in assuming your primary focus here is DC (static) stability in the face of temperature and/or supply voltage variations?"
Yes
Do you see the latter as a problem or is there another reason to prefer the single device current source?
No but the mosfet CCS with a solid voltage reference looked fine to me.
I believe the Aleph P 1.7 preamp uses a current source like what you have in mind . I guess one could compare this in simlation. I don't know how quiet or stable the supply for the collector resistor would need to be for the same performance, but I will include it as an option for the curious.
http://www.passlabs.com/pdf/aleph/apserv17.pdf
H.H.
Yes
Do you see the latter as a problem or is there another reason to prefer the single device current source?
No but the mosfet CCS with a solid voltage reference looked fine to me.
I believe the Aleph P 1.7 preamp uses a current source like what you have in mind . I guess one could compare this in simlation. I don't know how quiet or stable the supply for the collector resistor would need to be for the same performance, but I will include it as an option for the curious.
http://www.passlabs.com/pdf/aleph/apserv17.pdf
H.H.
Attachments
Current Source
Thanks Harry. As usual you are correct about what I had in mind. I was really just wondering whether you had any opinion on the relative advantages and disadvantages of the two types (and I do appreciate that there are a great many other variations too).
Ian.
Thanks Harry. As usual you are correct about what I had in mind. I was really just wondering whether you had any opinion on the relative advantages and disadvantages of the two types (and I do appreciate that there are a great many other variations too).
Ian.
Current Source
I would probably prefer a mosfet CS with a fixed voltage reference
since it would have greater source degeneration and be free of the bipolar transistor and feedback loop. I think simpler circuits are better, even for current sources.
H.H.
I would probably prefer a mosfet CS with a fixed voltage reference
since it would have greater source degeneration and be free of the bipolar transistor and feedback loop. I think simpler circuits are better, even for current sources.
H.H.
Nelson's Prize
Just thought some of you might like to know that I did receive a prize from Nelson, just as promised. Thank you Mr. Pass!
Ian.
Just thought some of you might like to know that I did receive a prize from Nelson, just as promised. Thank you Mr. Pass!
Ian.
Ian's fast asleep by now but hopefully will have responded by our morning.
Ian? Ian? Wake up, man!
Ian? Ian? Wake up, man!
Prize
Oh, alright - I didn't think it would take long before folks started asking...
Well I am now awake and can report that I received a signed pin-up of Nelson Pass in his prime, standing next to some sort of edifice. The latter would be some sort of curious prototype panel type speaker without a diagphram (ion discharge) from the days of Threshold. I doubt somehow that it ever saw the light of day as a commercial product but then again, I could easily be wrong.
So, an interesting and collectable prize if not quite what I was expecting. To tell the truth I didn't know what to expect, I half wondered if it wouldn't be two resistors of precisely the right value for an XA.
Ian.
Oh, alright - I didn't think it would take long before folks started asking...
Well I am now awake and can report that I received a signed pin-up of Nelson Pass in his prime, standing next to some sort of edifice. The latter would be some sort of curious prototype panel type speaker without a diagphram (ion discharge) from the days of Threshold. I doubt somehow that it ever saw the light of day as a commercial product but then again, I could easily be wrong.
So, an interesting and collectable prize if not quite what I was expecting. To tell the truth I didn't know what to expect, I half wondered if it wouldn't be two resistors of precisely the right value for an XA.
Ian.
Ian... that sounds interesting..Now I believe that I've seen that pin-up before somewhere in the forum...but of course...minus the moniker....😉
O.K. Has someone finished and listened to their Aleph-X as yet? Could someone post the final schematic of the Aleph-X with the Servo/DC offset correction circuit as finally accepted in this forum? Many might begin to try their own versions; I for one definitely. Thanks.
Sorry, Joe took them home and won't bring them back.
The very first proof-of-concept pieces were slightly rewired
Aleph 2's, and subsequently I built a pair from Aleph 60's.
They all worked just Jake. Currently I'm waiting production
PC boards, expected at the end of the month. When I
get them, I'll post a photo.
The very first proof-of-concept pieces were slightly rewired
Aleph 2's, and subsequently I built a pair from Aleph 60's.
They all worked just Jake. Currently I'm waiting production
PC boards, expected at the end of the month. When I
get them, I'll post a photo.
A funny idea?
Hello Everybody and Nelson in particular!
I like Elliot with his projects, ESP, Elliot Sound Projects.
Although not the absolute HIGH END,
there are many things to learn and discover there,
as well as useful circuits in different areas of audio.
http://sound.westhost.com/
I have also enjoyed reading your, Nelson,
article no DIY OP-amplifier.
I read it with great interest.
Now when I first saw the name Death of Zener
I was surprised. That would for me be to cross the line,
to say that Another human beeing's work
is deserving to die.
Your amplifiers might have their drawbacks, but on the other hand
they have other qualities that are valuable.
I assume this was a provocative way of Elliot,
a trick to draw attention to what he has to offer.
Now my idea. Why not name some of your constructions
"Death of DOZ"!!!!!!
Would give us the smile of the day!!!!
gromamswe
not dead serious about audio
but it is a nice interest to give us new friends
Hello Everybody and Nelson in particular!
I like Elliot with his projects, ESP, Elliot Sound Projects.
Although not the absolute HIGH END,
there are many things to learn and discover there,
as well as useful circuits in different areas of audio.
http://sound.westhost.com/
I have also enjoyed reading your, Nelson,
article no DIY OP-amplifier.
I read it with great interest.
Now when I first saw the name Death of Zener
I was surprised. That would for me be to cross the line,
to say that Another human beeing's work
is deserving to die.
Your amplifiers might have their drawbacks, but on the other hand
they have other qualities that are valuable.
I assume this was a provocative way of Elliot,
a trick to draw attention to what he has to offer.
Now my idea. Why not name some of your constructions
"Death of DOZ"!!!!!!
Would give us the smile of the day!!!!
gromamswe
not dead serious about audio
but it is a nice interest to give us new friends