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Old 16th January 2013, 01:06 PM   #3491
generg is offline generg  Germany
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Quote:
Originally Posted by Botte View Post
@botte: how much db did you choose k2 over k3, please?


~10dB at 1 watt, is where it's at with no trimming.
thank you Botte!

I can get this value also without using degeneration by choosing the right pair....!

But first I want to play the distortion tango!
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Old 16th January 2013, 03:21 PM   #3492
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thanks generg for the information. Working with the F6 is like doing experiments in the lab. Control those variables
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Old 17th January 2013, 05:48 PM   #3493
lhquam is offline lhquam  United States
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I tried just matching transconductance but some other parameter(s) that was not being measured was also important. I suspect that it is the internal source resistance of the SS-R100.

Quote:
Originally Posted by generg View Post
O.K......

it took me some hours to find out of my 8 R125 the two pairs that gave me around 0,012% THD and a distortion spectra where k2 and k3 are at the same level.
I wanted this position to go later more easily for negative and positive phase.

If it is possible to find the pairs only by measuring the transconductance of the parts outside of the circuit then I am an idiot.....not to build the circuit Nelson suggested 1993...!

So buzzforb and tea-bag can measure the transconductance, so it would be very interesting to see, if they get a predictable distortion picture.

Tea-bag please insert in your F6 two pairs of SS with same transconductance and let us see the distortion picture. k2 should be reduced, shouldn't it?

Buzzforb can you see distortion?

and of course Ihquam did you see a correspondence between equal transconduction and a reduced k2 compared to k3?

when my 10 Ohm pots are coming I will continue....

because changing the source resistors changes as well the bias, as the offset values...... ! Too much work! Am I correct to suppose that using the pots the bias and the offset is not changed?

Gute Nacht!
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Old 18th January 2013, 01:43 PM   #3494
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Here is a paper I haev had for a while. It may be of interest to some.

http://socrates.berkeley.edu/~phylab...Files/bsc4.pdf

If I get a chance, i am going to measure each of my 8 SS using both the curve tracer and the meothod above to see what we get. According to the paper above, both simple test should yield similar results.

The theory put forward so far is, that a jfet with lower yfs(transconductance) up top compared to bottom fet, should yield higher k2 to k3. With the same yfs for both top and bottom, cancellation of 2k is ecpected, as well as lower overall distortion. If this proves true, then it should be easy enough to work things out for higher K2 to K3, even using no degeneration(which I like best), if we put lower yfs fet up top. To get higher K2 up top should be easy if we add source degeneration, as we can alter the yfs of the top fet, yielding higher K2 even with perfectly matched pairs. There is some question as to whether the aforementioned threory is actually proving valid or if there is something else at work. We shall see.

Oh yeah.
This may take a while.
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Old 18th January 2013, 03:51 PM   #3495
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thanks for the UCB lab reference
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Old 18th January 2013, 04:13 PM   #3496
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Originally Posted by flocchini View Post
thanks for the UCB lab reference
Something screwey about it. Saw front page only[out of 23], and it froze the computer requiring a restart; twice.
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Old 18th January 2013, 04:15 PM   #3497
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Loaded perfectly for me.
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Old 18th January 2013, 04:17 PM   #3498
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also loaded for me
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Old 18th January 2013, 04:56 PM   #3499
flg is offline flg  United States
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Well, I'm an impatient type when it comes to putors. It just took a minute A MINUTE!!!
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Old 18th January 2013, 05:00 PM   #3500
Zen Mod is offline Zen Mod  Serbia
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lazy greedy boyz ...........

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