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#51 |
diyAudio Member
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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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I build, therefore I am. Do not create problems where there are none. Last edited by vdi_nenna; 7th April 2019 at 11:30 PM. |
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#52 |
Official Court Jester
diyAudio Member
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use 8R2-10R as lower , use 20R trimpot as upper
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#53 |
diyAudio Member
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Thanks ZM. The target is 10mA?
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I build, therefore I am. Do not create problems where there are none. |
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#54 |
Official Court Jester
diyAudio Member
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target is , say , 90% of Idss
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#55 |
diyAudio Member
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Ok, to avoid saturation.
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I build, therefore I am. Do not create problems where there are none. |
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#56 |
diyAudio Member
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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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I build, therefore I am. Do not create problems where there are none. Last edited by vdi_nenna; 8th April 2019 at 02:11 PM. |
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#57 |
Official Court Jester
diyAudio Member
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everything ok , at least in my book
that's just buffer , not critical as some other implementations
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#58 |
diyAudio Member
Join Date: Oct 2003
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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. Patrick
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#59 |
diyAudio Member
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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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#60 |
diyAudio Member
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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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I build, therefore I am. Do not create problems where there are none. Last edited by vdi_nenna; 22nd April 2019 at 05:45 PM. |
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