Buffer with Dual N-Ch Jfets and Dual Power Supply - Page 6

vdi_nenna · 11:30 PM

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.

Zen Mod · 7th April 2019, 11:59 PM

use 8R2-10R as lower , use 20R trimpot as upper

vdi_nenna · 8th April 2019, 01:28 AM

Thanks ZM. The target is 10mA?

Zen Mod · 8th April 2019, 11:17 AM

target is , say , 90% of Idss

vdi_nenna · 8th April 2019, 11:41 AM

Ok, to avoid saturation.

vdi_nenna · 02:11 PM

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

Zen Mod · 8th April 2019, 02:41 PM

everything ok , at least in my book

that's just buffer , not critical as some other implementations

EUVL · 8th April 2019, 06:57 PM

> 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

vdi_nenna · 8th April 2019, 07:32 PM

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

vdi_nenna · 05:45 PM

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.

7th April 2019, 11:17 PM	#51
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	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. __________________ 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.

7th April 2019, 11:59 PM	#52
Zen Mod Official Court Jester diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	use 8R2-10R as lower , use 20R trimpot as upper __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

8th April 2019, 01:28 AM	#53
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	Thanks ZM. The target is 10mA? __________________ I build, therefore I am. Do not create problems where there are none.

8th April 2019, 11:17 AM	#54
Zen Mod Official Court Jester diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	target is , say , 90% of Idss __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

8th April 2019, 11:41 AM	#55
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	Ok, to avoid saturation. __________________ I build, therefore I am. Do not create problems where there are none.


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8th April 2019, 01:50 PM	#56
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	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 __________________ 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.

8th April 2019, 02:41 PM	#57
Zen Mod Official Court Jester diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	everything ok , at least in my book that's just buffer , not critical as some other implementations __________________ my Papa is smarter than your Nelson ! clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa...© by Mighty ZM

8th April 2019, 06:57 PM	#58
EUVL diyAudio Member Join Date: Oct 2003	> 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 __________________ xen-audio.com

8th April 2019, 07:32 PM	#59
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	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 __________________ I build, therefore I am. Do not create problems where there are none.

22nd April 2019, 05:35 PM	#60
vdi_nenna diyAudio Member Join Date: Oct 2000 Location: PA, USA	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. __________________ 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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