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Resistive pad vs Gate stopper for JFET inputs.
Resistive pad vs Gate stopper for JFET inputs.
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Old 5th February 2018, 09:01 PM   #1
Botte is offline Botte  United States
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Default Resistive pad vs Gate stopper for JFET inputs.

I'm looking for some pros and cons about when to use the resistive pad versus the gate stopper for JFET inputs.

Thanks,
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Old 5th February 2018, 09:36 PM   #2
MarcelvdG is offline MarcelvdG  Netherlands
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The resistive pad attenuates the signal a bit, while the gate stopper doesn't. With the gate stopper version, you can easily give each JFET its own resistor right next to its gate, which minimizes the chances of parasitic oscillation. Both versions add some noise, which is negligible for line level signals, but not for amplifiers for microphones or phonograph cartridges.
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Old 5th February 2018, 09:58 PM   #3
Botte is offline Botte  United States
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I have seen Nelson use both methods. I'm wondering why he chooses one over the other for the first watt amps?
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Old 5th February 2018, 10:04 PM   #4
Nelson Pass is offline Nelson Pass  United States
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Resistive pad vs Gate stopper for JFET inputs.
No particular reason. In some precision gain circuits it balances out
the resistor ratios of another part
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Old 5th February 2018, 10:11 PM   #5
Botte is offline Botte  United States
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So it's like, whatever drawing you started with when you are doing a new schematic.
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Old 6th February 2018, 12:10 PM   #6
AndrewT is offline AndrewT  Scotland
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I usually move any Gate Stopper resistor to attach directly to the Gate lead.
In this close relationship, the stopper does it's best to ensure the gate never sees a negative impedance and thus usually is a fool proof method of avoiding gate inductance oscillation/instability.

Resistor/s located some distance away from the Gate leadout with long traces/leads will add some inductance to the Gate lead and can make de-bugging of problems later in the build more difficult to find/analyse.
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