LU1014 will get you there much easier - 2 pairs per channel, Vds=10V and about 0.5A through each JFET. In that case I would not use the Rs to bias the JFETs but the battery emulating PSUs for -Vgs (something like the one in F6 circuit)
Gate leakage is a concern with BF862 only when you want to have an extremely high input resistance and higher Vds. For almost all practical purposes 47k-100k is enough and then you don't have to worry about it...
I'd say it's wrong because LSKpre's gain can be set in wide range, from less than 0 to 20db or more.
You can attach "flag" type sinks to keep the device temperatures down due to average operational conditions. That leaves a bigger margin for transient temperature fluctuations.
Running a 600mW device at 200mW will require some temperature de-rating.
Running it at 300mW will require significant temperature de-rating.
Running a 600mW device at 200mW will require some temperature de-rating.
Running it at 300mW will require significant temperature de-rating.
Where would a volume pot (10k) best be placed in the LSKpre circuit when used with a F5? Will I need the buffer section and/or would the pot best go before or after the buffer, or even before the pre
Impedance matching always confuses me
I believe it should go before the preamp, and you should choose the impedance of the pot according to your sources' output impedance.
Just don't ask me for the math side of things!
Of course I neglected to mention that a simple pair of self-biased
complementary followers for this circuit will take the output impedance
down to something like 20 ohms.
Of course we would want to use the same LS parts...
wonder how this would work with the bjt version Juma presented in post #25
edit ...ahh, yes ofcourse, the LSK preamp
Where would a volume pot (10k) best be placed in the LSKpre circuit when used with a F5? Will I need the buffer section and/or would the pot best go before or after the buffer, or even before the pre
Impedance matching always confuses me
If you build the LSKpre with Zout low enough (say 1k5) it can be used to drive F5 (Zin=101k) wihout a buffer. Just don't forget to add serial 15-22R at the preamp's output, to isolate the cable's capacitance.
In any case pot goes at the preamp's input.
I like 100:1 more. Capacitance and inductance play the role too so the drive capability is important regardless of resistances' ratio. Pure thermogenic resistance will just bring the level of the signal down so no big deal, but the reactive resistances will change the frequency and phase response. Either way, it's better to have enough current handy...
1:10 is a good ratio that works well.
I try to exceed 1:20, but much more important is cable and parasitic capacitance driving capability.
That is what Juma is referring to.
An example to show what can easily be achieved.
Zin of Receiver: 100k || 47pF || 1k+680pF
required Zout of Vol pot Source <= 100k/20 <= 5k
Use a 10k or 20k volume pot.
Required Zout of Audio Source <= 10k/20 <= 500r
Two stages of 1:20 work with virtually all DIY equipment.
Two stages of 1:100 can be made to work with most DIY equipment, if you build your own low output impedance buffers. B1 and DCB1 don't meet this criteria.
I try to exceed 1:20, but much more important is cable and parasitic capacitance driving capability.
That is what Juma is referring to.
An example to show what can easily be achieved.
Zin of Receiver: 100k || 47pF || 1k+680pF
required Zout of Vol pot Source <= 100k/20 <= 5k
Use a 10k or 20k volume pot.
Required Zout of Audio Source <= 10k/20 <= 500r
Two stages of 1:20 work with virtually all DIY equipment.
Two stages of 1:100 can be made to work with most DIY equipment, if you build your own low output impedance buffers. B1 and DCB1 don't meet this criteria.