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Old 22nd July 2012, 02:02 PM   #211
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Quote:
Originally Posted by Antoinel View Post
Silk
You should have been into capacitor designing, instead of tanning leather strings.
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Old 22nd July 2012, 02:09 PM   #212
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Quote:
Originally Posted by Nelson Pass View Post
...But it's more complicated than that. The Mu follower current source on
top of the circuit also contributes to gain, adding maybe 5 dB. So now we estimate that with infinite Drain resistance the gain is 29 dB, which is
28X.

OK so far?
We have 2 sources of gain totalling 29db loaded with 8 ohms. We have at this point neglected the Drain impeadance and the Mu follower contibution to the impeadance the drain see's. And the feedback.
Quote:
Originally Posted by Nelson Pass View Post
But we actually experience 23 dB gain due to the finite Drain resistance(s) and the contribution of the DC feedback loop. This 5 dB drop is a factor of 0.56X, and is equivalent to our high Drain resistance example driving 8 X 0.56, which is 4.5 ohms
So now we have an apparent Drain resistance which is equivalent to that value which paralleled with 8 ohms gives us 4.5 ohms. That resistor is close to 10 ohms.
So the impeadance value of the Mu follower can be calculated to exhibit 10 ohms of paralell load to the 8 ohms?
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Originally Posted by Nelson Pass View Post
Without the R12/R11 loop, the output impedance of the amplifier is 10
ohms...
Wait a minute, The -5db that reduced our theoritical gain from 29-23 included feedback and Drain resistance(s) and was used to determine the actual Drain load was 10 ohms?
I'm missing something here. There are a few to many "DC"s and "Drain"s maybe?
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Old 22nd July 2012, 02:23 PM   #213
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Regarding FET Drain resitance/impeadance; Is'nt it possible to use the Vds/Ids graph such as buzzforb's from post #230 of the SS 120R085 Depletion Mode Jfet thread, and choose 1 Vgs line to select 2 points. Subtract the Voltage at point 1 from 2 and currents from point 1 and 2, and V/I = Drain Resistance?
This seems similar to the way you figure output Z across the load range in a power supply?
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Old 22nd July 2012, 02:33 PM   #214
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Quote:
Originally Posted by jacco vermeulen View Post
You should have been into capacitor designing, instead of tanning leather strings.
Thanks for making the connection to my previous employer Rohm and Haas. This pair of entreupreuners started selling chemicals to the leather industry in 1907. I am still chasing new tanning agents. Collagen [skin fiber] is a poor eco-dielectric. It has the dreaded zwitter ions which ironically are needed for tanning. Amine groups for aldehyde and carboxylic for chrome tannages. I may be able to get the dielectric properties of silk [or better] with leather as we know it. Food for my thought.
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Old 22nd July 2012, 03:41 PM   #215
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Quote:
Originally Posted by flg View Post
So the impeadance value of the Mu follower can be calculated to exhibit 10 ohms of paralell load to the 8 ohms?
The open loop output impedance is a function of the Drain resistance of the
gain Mosfet, the output resistance of the Mu follower, and the DC feedback
loop circuit. Taken together, the value is 10 ohms. as calculated by the
measured open loop gain into 8 ohms vs the expected open loop gain.

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Old 22nd July 2012, 07:58 PM   #216
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Thnaks for pushing on this FLG. I must admit to not understanding how to derive many of the numbers being tossed around. In relation to the R085, Rds was the point of interest based on current experiments.
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Old 22nd July 2012, 08:00 PM   #217
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Quote:
Originally Posted by buzzforb View Post
I must admit to not understanding how to derive many of the numbers being tossed around.
The important thing is to be able to visualize the concepts. If you want
really accurate information, build the thing and measure it.

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Old 22nd July 2012, 08:06 PM   #218
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The SE version has been built and listened to but not measured. I am knee deep in a crossover. ADHD really hurts in audio building.
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Old 22nd July 2012, 10:29 PM   #219
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Yea, I was trying to get pretty close without building first. It's just that from your graph buzz, the R085 looks very similar to the Sony Sit?
Regarding R085 Drain impeadance, in one post N.P. says its lower than the R100 but the Sony Sit is much lower??? he also mentions it is dependant on your op point, but, the op point we're looking at is almost the same?
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Old 22nd July 2012, 10:47 PM   #220
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Look at the slope of the curve at OP.
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