You lucked out , I just did the cascoded Jfet version , I will also include the original (the one I'm listening to now).
Anyone please comment , I did notice the jfet's doubled the THD20
to .014% max (up from .007%) I used 2N4393 , mouser still has them at $1.84 apiece !! these devices do not have the gain of the KSC's so less degeneration was in order. (22r instead of 100r).
In the .zip is the original and the new cascoded version , make sure
all 3 files are in the same folder.
OS
Anyone please comment , I did notice the jfet's doubled the THD20
to .014% max (up from .007%) I used 2N4393 , mouser still has them at $1.84 apiece !! these devices do not have the gain of the KSC's so less degeneration was in order. (22r instead of 100r).
In the .zip is the original and the new cascoded version , make sure
all 3 files are in the same folder.
OS
Hi ostripper,
Everything looks like you are on the right track, even if someone wants to use mosfets.
2SK170 are still floating around out there, you can also use a surface mount dual jfet pair, or just two singles. These could be mounted on an adapter PCB to make life easier.
Have a look at J201 ~ J203 and J210 ~ J212. LS846 might be good. I have a short list of current devices around here somewhere. There are more devices available as surface mount parts, but that might actually work to our advantage. It's a good excuse to mount these parts in the diff pair for better heat sharing and freedom from air currents across the leads. Additional shielding can also be applied.
The reduction in gm may not be a huge problem at all. In fact, you may end up with lower order effects, and the current could be increased some to raise the gm. Remember, no base bias currents to worry about with Jfets. That may also mean that the feedback network can have a higher impedance. Remember that the 2SK170 still has lower noise than many BJTs do...
So, it looks like you have options still.
-Chris
Everything looks like you are on the right track, even if someone wants to use mosfets.
2SK170 are still floating around out there, you can also use a surface mount dual jfet pair, or just two singles. These could be mounted on an adapter PCB to make life easier.
Have a look at J201 ~ J203 and J210 ~ J212. LS846 might be good. I have a short list of current devices around here somewhere. There are more devices available as surface mount parts, but that might actually work to our advantage. It's a good excuse to mount these parts in the diff pair for better heat sharing and freedom from air currents across the leads. Additional shielding can also be applied.
The reduction in gm may not be a huge problem at all. In fact, you may end up with lower order effects, and the current could be increased some to raise the gm. Remember, no base bias currents to worry about with Jfets. That may also mean that the feedback network can have a higher impedance. Remember that the 2SK170 still has lower noise than many BJTs do...
So, it looks like you have options still.
-Chris
They are in the supersym.txt , the supersym.asc will automatically
include those models when you run the sim. OR , you could copy/paste to your standard.BJT file in LT.
That is what I originally thought , simulation at a 2R load and real life use with 3R loads have shown almost no loading of the VAS.
But feel free to run this VAS at 7-10mA (47R - R16), it is not the symasym one.
.007% at 60v p-p 20khz
@ at a nuclear 120v p-p... .012% (3v input)
Red ..1.6 - 1.8V Vf
And so shall the constructor , on the one PCB , it shall be easy.. in a neat and professional way , to go 1. plain jane BJT , 2. cascoded BJT , or 3. cascoded JFET . All with documented support (jumpers and component changes).
OS
Just to show an unrealistic output and load, (2R and 120v p-p)and how this loads the VAS at 4ma, the (attached) file shows (top plot)
current through driver basestoppers and (bottom plot) total Ic of the Mje15032/33 , not even close to their SOA , even at 100 C.
I would not want to be the speaker or touch the wire at this level..
OS
Attachments
Cdom question
Was simulating the loop gain with middlebrook probe and found the amp stable without C7, C8. The gain plot didnt move up in freq. very much at all. Am I doing something wrong, is this amp that stable? And if it is why not use lower cdoms? Heres the plot.
Was simulating the loop gain with middlebrook probe and found the amp stable without C7, C8. The gain plot didnt move up in freq. very much at all. Am I doing something wrong, is this amp that stable? And if it is why not use lower cdoms? Heres the plot.
Attachments
Re: Cascode arrangement
.
After countless versions of SymAsym in lots of setups, it is still among the best amplifiers I have ever heard.
This one seems to be a good chance to scale things up a little (my original ones are a little bit weak to drive the current 103 dB/2,83V/1m bass units).
Piersma, mind telling something more? Rail voltages? How's sonic performance?
I am very much interested in this SymAsym version. Even if Roender doesn't like the roots of this design any more, me doesPiersma said:
.After countless versions of SymAsym in lots of setups, it is still among the best amplifiers I have ever heard.
This one seems to be a good chance to scale things up a little (my original ones are a little bit weak to drive the current 103 dB/2,83V/1m bass units).
Piersma, mind telling something more? Rail voltages? How's sonic performance?
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