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Old 23rd June 2013, 07:39 PM   #4681
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Woudl this work?
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Old 23rd June 2013, 08:00 PM   #4682
lhquam is offline lhquam  United States
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Originally Posted by Nelson Pass View Post
And there you have it. Probably the next issue you might want to think about
is the increased capacitance of the gain devices operated at 3 volts.

I was hoping that with cascoded outputs that the increased capacitances of the drive MOSFETs would a relatively minor issue. Perhaps I have a serious gap in my knowledge about cascoded stages. I haven't seen discussions of the capacitance effects due to the cascode devices or parameters of them that should be optimized.

Other than increasing Vds of the drive MOSFETs or using a lower impedance driver circuit, what can be done to reduce the effects due to these capacitances?
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Old 23rd June 2013, 08:17 PM   #4683
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Originally Posted by lhquam View Post
The F5 does not have the output offset problem because it is entirely DC coupled, thus the negative feedback applies to output offset as well as to AC voltage.

Here is the schematic with some voltages added.
lhquam. Thank you for the data. What is the average Gate-Source voltage; not shown in the latest schematic.
With all due respect, the proposed circuit [feedforward] is DC coupled like diyF5. I will use your data to generate a "functional" schematic to analyze its feasibility.

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Old 23rd June 2013, 08:21 PM   #4684
6L6 is online now 6L6  United States
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Originally Posted by Antoinel
I expected a 6L6 tube for scale
Lol... You are right, I should have done that!!


Last edited by 6L6; 23rd June 2013 at 08:36 PM.
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Old 23rd June 2013, 08:26 PM   #4685
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Originally Posted by 6L6 View Post
Lol... You are right, I should have done that!!

Your diyF6 build is great, and professional.
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Old 23rd June 2013, 08:31 PM   #4686
Zen Mod is offline Zen Mod  Serbia
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Originally Posted by buzzforb View Post
Woudl this work?
Q2 is having nuttin' to open it (remember enhanced vs. depletion ) ...... and - even if it have summetin' , it's current will have nowhere to go

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Old 23rd June 2013, 08:35 PM   #4687
6L6 is online now 6L6  United States
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Quote:
Originally Posted by Antoinel
Your diyF6 build is great, and professional.
Thanks! Can you tell me how it looks? I am also still not sure how much space I should have in-between the chassis halves - What did I decide on? You must be Antoinel from the future... I haven't done the F6 yet...

All kidding aside, thanks for the comments, you are probably meaning to have typed F5 or F4.

The F6 is on the docket and a little different than the others - I am going to have the PSU and the amp in 2 chassis. (For modularity, and more amps in the future, cheaper.)
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Old 23rd June 2013, 08:42 PM   #4688
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Originally Posted by 6L6 View Post
I am going to have the PSU and the amp in 2 chassis. (For modularity, and more amps in the future, cheaper.)
Exactly my thoughts about my F6
Plus it should be safer with the trafos...
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Old 23rd June 2013, 08:58 PM   #4689
lhquam is offline lhquam  United States
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Here are frequency sweeps at 1 watt and 10 watts into 8 ohms. Cascode voltages are adjusted for Vds of approximately 3 volts on the drive MOSFETs.
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Old 23rd June 2013, 10:20 PM   #4690
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Originally Posted by lhquam View Post
I was hoping that with cascoded outputs that the increased capacitances of the drive MOSFETs would a relatively minor issue. Perhaps I have a serious gap in my knowledge about cascoded stages. I haven't seen discussions of the capacitance effects due to the cascode devices or parameters of them that should be optimized.

Other than increasing Vds of the drive MOSFETs or using a lower impedance driver circuit, what can be done to reduce the effects due to these capacitances?
Maybe best of all worlds. A proposed buffer circuit is attached. Complementary enhancement JFETs or bjts; your choice.
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