Very good question. The weakest aspect of simulations is usually the device models. Unless you can accurately model the devices you are actually using, the simulations will be imprecise. But, you can derive useful understanding by observing how the simulations behave as various circuit parameters are changed.
I did both...
I changed the 10R source resistors to 10R pots I had from F6 output Zen Pot idea and changed the pot values till I got the lowest distortion, mostly k3 dominant
I put Nelson's 100R pot F5 like over the 10Rs and turned it to lowest distortion....
Or the k2 value and phase I wanted....it is really easy ....on this level...I can do...
No simulation, the distortion analyser was hooked on the amp.
I changed the 10R source resistors to 10R pots I had from F6 output Zen Pot idea and changed the pot values till I got the lowest distortion, mostly k3 dominant
I put Nelson's 100R pot F5 like over the 10Rs and turned it to lowest distortion....
Or the k2 value and phase I wanted....it is really easy ....on this level...I can do...
No simulation, the distortion analyser was hooked on the amp.
I suggested a USB soundcard, the EMU0404, I believe.
re the distortion testing, I still think the behringer usb card is value for money.....full write up is still here:
Vitalstates- Amplifiers
Vitalstates- Amplifiers
I installed an 10R pot in place of the source resistors and ran distortion tests. Apparently the distortion due to the JFET follower FE is so low that the pot adjustment makes no measurable difference. The entire amp channel is around THD=0.0045% with H2=0.0027% H3=0.0035% at 1 Watt ,1 kHz into 8 ohms.
IT is not cheap, but can be had for about $100, but heck, if laptop pinut will work, its perfect. Had no idea they were capable. Like I said, dont listen to me.
if nelson is listening - think a small simple soundcard interface would be a great summer project + a little article around it and so many people would then feel comfortable to join the harmonics party for next to no money .... kind of like his seminal (love that word) mosfet testing and mosfet matching articles from way back. Pete's design is really excellent but not simple.
Hi LHQUAM,
astonishing ...
My input stage was the known j74/k170 combo, xformer 1:5 and combined with a F4 outputstage, but only one pair.
Measurement was not after the input stage, but after the output stage.
The same effect, that I could manipulate K2 was possible with the BA-3 inputstage and the same F4 outputstage (no xformer, no j-FETs)
In the first case the THD was around 0.03%, a value that Nelson's M2 shows also. Turning the pot for higher k2 gave of course considerable more THD.
With the BA-3 input stage and crippled F4 and K2 minimum, the distortion values we're around 0.015%.
I think trying to make k2 higher to get the k2 sound is only recommended in this case, when you have some "headroom". With 0.015% as a starting point you cab screw up k2 around 12db over k3 and you still have only around 0.025% THD.
Why can't you mistune to higher THD or k2, real surprise!
But of course fine .....and these measurements were done with the real amp?
How do you measure distortion? Better system than sound card, I suppose....
Hi LHQUAM,
astonishing ...
My input stage was the known j74/k170 combo, xformer 1:5 and combined with a F4 outputstage, but only one pair.
Measurement was not after the input stage, but after the output stage.
The same effect, that I could manipulate K2 was possible with the BA-3 inputstage and the same F4 outputstage (no xformer, no j-FETs)
In the first case the THD was around 0.03%, a value that Nelson's M2 shows also. Turning the pot for higher k2 gave of course considerable more THD.
With the BA-3 input stage and crippled F4 and K2 minimum, the distortion values we're around 0.015%.
I think trying to make k2 higher to get the k2 sound is only recommended in this case, when you have some "headroom". With 0.015% as a starting point you cab screw up k2 around 12db over k3 and you still have only around 0.025% THD.
Why can't you mistune to higher THD or k2, real surprise!
But of course fine .....and these measurements were done with the real amp?
How do you measure distortion? Better system than sound card, I suppose....
is it because you dont have loop feedback that encompass the front end JFET ?