Gsoz-t

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I've been working to improve the SOZ and ZV7-T design. So, to that end, I've come up with the idea pictured below. Let me first protect myself somewhat... No, it's not something new, maybe just several old valuable ideas put into one. I like to call it Grand Son Of Zen T.
:att'n: This is still a Work In Progress :att'n:
But, I was wondering if some of you would be interested in helping along the design process. The values pictured are of coarse "ThumbNail" as N.P. would say. But, I beleive it to be a funtional idea. And, I hope a good sounding one.
Any thoughts or comments would be greatly appreciated:smash: :smash: :smash:
Thanks.
 

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Babowana, mostly the 1 ohm R between the sources. Like PaPa SOZ:D
I think the gain may be higher than I expect though. That being the case, a little larger cross coupling resister value might be appropriate???
I don't think my Pspice model is good enough for the JFET yet, but I will try a simulation soon. I've been playing around with a version that only has an IRFP244 as a gain device. It seems to be a small improvement over the ZV7-T. Also, I'm having trouble actually sim'ing a real xfmr. Inductors work O.K. but when I try to use a real Xfmr, I get the dreaded, Does Not Converge!
Hey, maybe you could help me with somethin... I would like to convert my OrCad Capture Pic to something the Forum accepts that is of better visual quality. I havent been to sucsessful at figuring that out:confused: They look O.K. on all my graphic apps:confused:
 
The one and only
Joined 2001
Paid Member
Very likely you can eliminate the 0.6 ohms and couple the
cascode reference to the other side of the 1 ohm, or even
make the 1 ohm into an optimal value based on distortion.

Also, note that while the cascode modulation straightens out
the 2nd harmonic, so does the differential, and you may find
that entirely different values for cascode modulation are called
for. This means a distortion analyzer.

:cool:
 
Thanks:D About the Inductors, I just figured getting this big should get the response down pretty low. At least a few octives above the 8 ohm point would be nice. I have a little help from the experts. They should get back to me in a few day's. I asked for matched windings of 270mH at less than 1 ohm DCR and >3A Isat. 2 samples is all they'll go for... But, that's all I need...
Nelson, thank you for the suggestions. But, do you mean a form of cross coupling the cascode refrence??? "to the other side of the 1 ohm"???
Yes, my MOSFET version seems to have mostly 3rd harmonic in the simulation. I have not been successful simulating with the cascoded JFET yet.
Well, I have access to an HP339 now but, Hmmm, I was hoping to get a new job soon and I don't know if I will have that benifit much longer...:smash: :smash: :smash:
 
I finally got a model for the JFET working nicely in the ZV8 circuit:D So, I tried it in the GSOZ-T and all I get is some switch mode looking output (Oscillation City). So, I replaced the Inductors with R's. 35 ohm R's and 100V +V. I still could not get a decent output until I used a 220p from D-G on the cascode transistors. Lots of gain and low THD levels. But, that's not the answer. Especially with an inductor back in there. Caps cannot be used in this position with the Inductors, without creating an oscilator:confused: :confused: :confused:
I took Nelson's suggestion of removing the .6 ohm Source R's. It also did not seem to like the cascode refrence on the other side of the cross coupling 1 ohm???
I Also noticed a mistake in the way the I Sources are fed by the bootstrap. I split them into two seperate voltage sources:smash: :smash: :smash:
 
I worked on the oscilation issue but in doing so I ended up with a simpler design. The simulated performance is better. I was able to use a real transformer model as the load, rather than just inductors. And, I have adapted 1 of Nelson's suggestions with good results also.:D :D :D
I'm not sure the Pspice jfet model will actually produce the "Triode Character". So, this may be the reason the cross couppling of the cascode refrence is still not showing a benifit :confused: :confused: :confused:
I guess I can improve the model :confused: or build this thing and play with the distortion analyzer and the 1.2 ohm resistor :smash: :smash: :smash:
 

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Formerly "jh6you". R.I.P.
Joined 2006
Looking simpler and nice.
I have thought about Papa's suggestion from the first reading . . .
Probably, the reason of the cascode reference to the opposite side of the 1.2 ohms . . . mmm . . . is for a better harmony of the two different transconductance curves between MOSFET and JFET . . . ? Whatever . . . very intersting . . .
 
Well, Nelson has said that a "modulation" of 600mV per Amp is about what we are looking for. At idle the resistor has no current in it and both Sources are at the same potential. Let's say an arbitrary differential input signal causes an increase of 1 Amp in the left side and a decrese of 1 Amp in the right. The right and left side current sources just keep cooking along at 2.5 Amps but 1 of them goes through the cross coupled resistor and adds to the other sides current. Now we have a voltage differential across the Sources of 1.2V. I'm thinking effectively, that is a shift of 600mV per side :confused::confused: :confused:
It may be of interest that the simulated distortion, without the cross coupled cascode connection, but like the first picture, is about 0.02% @ 1kHz with 1V in (2V diff) and 13V out. It clips just before 20V out.
 
Formerly "jh6you". R.I.P.
Joined 2006
flg said:
"modulation" of 600mV


I see.
I revisited ZV9 and read: "Because we want to cancel two nonlinear characteristics, the optimal Vds across Q1 will be DC plus a finite AC voltage at around -600 mV per amp, which was determined by testing at 1 watt."

Thanks for your explanation. Now, I got it. So, the target is finding the optimal Vds across Q1.
I have few LU1014s. I hope I could have chance to use them soon . . . :)
 
Well, looking at the Vds vs. Ids curve of the -1V G-S condition, shows a gain change. No gain change would be a strait line. If we had more data we might see that a shift of 600mV Vds over a 1 Amp swing, would make the line a strait one:D :D :D Nelson has so gracously contributed this tidbit and that's what I'm working from. I might also point out, all the parameters I'm working with and putting on the "Work In Progress" schematic, are 25 degrees and mostly ideal. But, I think it's easier at this point and will be a good starting point. :smash:
I'm not in a position to build anything for a while. :bawling:
I would be interested in more comments or suggestions :confused: I'm certainly no expert at this stuff. Nelson's comments did not suggest my thinking was out there a little to far or anything so that was certainly rewarding. :D
I'm happy to spark your interest Babowana. Maybe you will be the first to build a Grand Son Of Zen T. Carpenter, has built a T type amp that he liked. I expect him to jump in here soon :cool: Maybe he could try to convert his amp :bigeyes: :bigeyes: :bigeyes:
 
I went through the excersise of trying to Pspice model the Vds vs Ids curves. I could replicate the "pentode" looking curves. That is, Vgs above -.5V. I could not produce anything that fit the datasheet for the "Triode" looking operating area :bawling: :bawling: :bawling:
So much for my modeling abilities :smash: :smash: :smash:
Does anyone have a clue how to deal with this other than at the bench :confused: :confused: :confused:
I can try to squeze some of the intelect from my partners at work :cool:
:D :D :D
 
Yes, I think your right. :bigeyes: It's really very simple. If I can get the .4 ohm resistors to set the right current, and the 14.5K to be a pot for setting the cascode voltage, the only other questionable componant to play with is the cross coupling 1.2 ohm.:D :D :D
 
The one and only
Joined 2001
Paid Member
A couple of things:

The oscillation with inductive loads is often the result of no
damping to ground off the Drains of the outputs. I usually use
something like 47 ohms (see the F1 manual).

As I alluded before, with a differential system I would not expect
to see as much benefit with cascode modulation (of this sort)
as the 2nd harmonic is already being cancelled by the differential.

:cool:
 
Wow, Thanks Nelson. Please excuse my Wow:D , I am flatered by your interest with my attempt at one of the 100's of ZEN "Variations". I remember you mentioning the R's to GND in ZV7. As ussual, I need to carefully ponder your suggestions :bigeyes: :bigeyes: :bigeyes: And the "while the cascode modulation straightens out the 2nd harmonic, so does the differential, and you may find that entirely different values for cascode modulation are called for." is still one of them :smash:
Is it not true though that I am improving linearity with this configuration? And maintainig reliability of the JFET operating point? And, therefore, I should continue with the basic configuration? But now there is "(of this sort)", Hmmm...
What I think needs more work and thought, is the level of third harmonic I see in the simulation :confused: Although I have found my JFET model to be inaccurate at these levels, I'm not sure it is the culprit :confused: I also had high 3rd in the MOSFET version I was working on. I have also noticed, on the way to finding a useable operating point, a crossover looking distortion in the output waveform :confused: :confused: :confused: I'm thinking although not "visable" anymore, the mV level of third harmonic has a source, possibly the funny waveform, I don't understand, yet :D :D :D
Another direction would be to abandon the cross coupling and exploit the extra gain with a susy F.B. approach :bigeyes: Ala ZV7.
Thanks again! :smash: :smash: :smash:
 
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