i just built the thing called hotfet preamp found here
im trying to make the mosfets run hotter and cant seem to do so. so far i've increased r2, added 3 more leds on each side, and lowered the r9 and r10 resistors. i would like to get the bias up to 500ma if possible.
also the thing sounds rather shrill on its own. im thinking of changing the jfet to something better. perhaps 2sk170?
im trying to make the mosfets run hotter and cant seem to do so. so far i've increased r2, added 3 more leds on each side, and lowered the r9 and r10 resistors. i would like to get the bias up to 500ma if possible.
also the thing sounds rather shrill on its own. im thinking of changing the jfet to something better. perhaps 2sk170?
I'm tempted to comment, but there are 12 screens of the design to sift through. Could you post the component values you built here, at least. Maybe a pic or two as well?
Thanks,
Cheers
Thanks,
Cheers
Sorry i had linked the webpage under the word 'here'
HotFET Pre: J-FET audio preamplifier schematics | MyElectrons
HotFET Pre: J-FET audio preamplifier schematics | MyElectrons
Increasing the current thru VT1 and VT3 will cause an increase in the current thru VT2 and VT4 also. The max. on VT2 and VT4 is only 10ma, 500ma will let the magic smoke out of VT2 and VT4 me thinks.
Craig
Craig
That's OK -- I found it -- that was the 12 screens of development details mentioned -- that I'm reluctant to spend the time sifting through, if that wasn't the exact design you built .. or if there are component substitutions .. or aspects to your construction methods .. or, you get the idea.
Actual build component values on your posted schematic, if that's what you built, and maybe a picture or two. Please.
Cheers
edit: Thanks llwhtt. And forgot to ask, 'Why, exactly, does the OP want it to run that hot?' Or, 'What is so special about 500 mA?'
Actual build component values on your posted schematic, if that's what you built, and maybe a picture or two. Please.
Cheers
edit: Thanks llwhtt. And forgot to ask, 'Why, exactly, does the OP want it to run that hot?' Or, 'What is so special about 500 mA?'
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+1 llwhtt -- Yup!
Even if you could get the MOSFETs happy at 500mA, the JFETs can't get anywhere near that. Measure the Idss @ Vgs=0 for your JFETs -- that's more than they can conduct in any related circuit. Plus, it blows the primary design objective of the circuit: Operating the device at the point of its maximum linearlty!(According to the developer on the website.😕😉)
Again, why do you want to conduct 500mA?
Cheers
Even if you could get the MOSFETs happy at 500mA, the JFETs can't get anywhere near that. Measure the Idss @ Vgs=0 for your JFETs -- that's more than they can conduct in any related circuit. Plus, it blows the primary design objective of the circuit: Operating the device at the point of its maximum linearlty!(According to the developer on the website.😕😉)
Again, why do you want to conduct 500mA?
Cheers
Cascodes don't have current bias. So long as the voltage bias is large enough
not to limit the input devices the current is constant, controlled by the input devices. Cascodes just pass current through.
So how do i increase biasing of this circuit? Im thinking of replacing the jfets to metal cans and adding heatsinks to it.
You could parallel J2 with multiple high Idss jfets, it's not the cascodes that control the current.... The bottom current source could then be changed to something else, like a bipolar transistor, or to multiple high Idss jfets....