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Buffer with Dual N-Ch Jfets and Dual Power Supply
Buffer with Dual N-Ch Jfets and Dual Power Supply
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Old 7th April 2019, 11:17 PM   #51
vdi_nenna is online now vdi_nenna  United States
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Buffer with Dual N-Ch Jfets and Dual Power Supply
106.6mV across 18 ohm source resistor on current source jfet and same across buffer jfet source resistor.
I figure that's just under 6mA.
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Old 7th April 2019, 11:59 PM   #52
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Buffer with Dual N-Ch Jfets and Dual Power Supply
use 8R2-10R as lower , use 20R trimpot as upper
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Old 8th April 2019, 01:28 AM   #53
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Buffer with Dual N-Ch Jfets and Dual Power Supply
Thanks ZM. The target is 10mA?
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Old 8th April 2019, 11:17 AM   #54
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Buffer with Dual N-Ch Jfets and Dual Power Supply
target is , say , 90% of Idss
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Old 8th April 2019, 11:41 AM   #55
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Buffer with Dual N-Ch Jfets and Dual Power Supply
Ok, to avoid saturation.
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Old 8th April 2019, 01:50 PM   #56
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Buffer with Dual N-Ch Jfets and Dual Power Supply
One more question. I'm not trying to state the obvious here, but not sure of the impact of needing matched quads.

For example, I have a well matched pair of sk170s at 9.76mA for channel 1 and another set at 10.50 and 10.52mA for channel 2.
Will there be, let's call it, a "balance" issue between channels?
I want to assume- Yes they should be quad matched, because they are technically biased at different currents,
but if that's what they require to be at 90% of their Idss, then does it matter if both channels have quad matched JFETs?

Thanks,

Vince
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Old 8th April 2019, 02:41 PM   #57
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Buffer with Dual N-Ch Jfets and Dual Power Supply
everything ok , at least in my book

that's just buffer , not critical as some other implementations
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Old 8th April 2019, 06:57 PM   #58
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> but if that's what they require to be at 90% of their Idss, then does it matter if both channels have quad matched JFETs?

Yes, because the transconductance (and hence Zout) at 9.7mA is slightly lower than 10.5mA.
So the DC will be low for both, but they are not 100% identical.


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Old 8th April 2019, 07:32 PM   #59
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Buffer with Dual N-Ch Jfets and Dual Power Supply
All very interesting. Now that I understand the parameters a little better, I can play around with the different jfets I have available.

Thanks for everyone's help!

Vince
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Old 22nd April 2019, 05:35 PM   #60
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Buffer with Dual N-Ch Jfets and Dual Power Supply
What do you think about some resistance on the input?
Mr Pass uses 1k in some buffers.
Right now using a 1M to ground.
Is it needed or help prevent issues?
Using schematic 15c on first page.
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