that would be completely another amp , considering changes needed
however , there are few M. Rothacher's amps with VFets where you can easily implement your SJDP
however , there are few M. Rothacher's amps with VFets where you can easily implement your SJDP
first - amp is made for enhanced type of devices , which means biasing voltage at gate of mosfet is positive ref. to source , while D in SJDP means that part is depletion type , demanding exactly oposite polarity of biasing voltage - negative at gate ref. to source
for that you'll need additional voltage source , based either on separate winding on xformer or on few other Papa's tricks (pulled from RDH era)
as I said - look for M. Rothacher's amps , there is at least one fulfilling your desires
principally very close to F2 , but optimized exactly for depletion devices
to conclude - that is exactly answer you needed for your question
sorry - I'm lazy to search and look for exact thread ........ just find M. Rothacher in member list and look for threads he started
or go to his site : AudioMaker | DIY Audio Projects & More
for that you'll need additional voltage source , based either on separate winding on xformer or on few other Papa's tricks (pulled from RDH era)
as I said - look for M. Rothacher's amps , there is at least one fulfilling your desires
principally very close to F2 , but optimized exactly for depletion devices
to conclude - that is exactly answer you needed for your question
sorry - I'm lazy to search and look for exact thread ........ just find M. Rothacher in member list and look for threads he started
or go to his site : AudioMaker | DIY Audio Projects & More
of course that you can ....... but in this case SJDP is taking role of invisible part , while mosfet is still governing one .......... and entire circuit would remain (almost) same in sound character
practically - same as if you cascode mosfet with same type of mosfet
btw. you can always try to swap your SJDP for someone's SJEP , then no more complications
practically - same as if you cascode mosfet with same type of mosfet
btw. you can always try to swap your SJDP for someone's SJEP , then no more complications
I am not acting as an expert but I was reading that when baliga cascode is used ,MOSFET is practically transparent in switching because of low resistance and capacitance.😕
If you're lucky enough to have some of the Semisouth depletion parts you might want to save them for building Nelson's DEF amp. 🙂
I imagine there are plenty of obtainable enhancement parts for making an F2 sort of amp.
I imagine there are plenty of obtainable enhancement parts for making an F2 sort of amp.
in switching ...... yes ...... just because switching is sole purpose of cascoded stage
in amplification use , part which gate is directly driven with signal is dominating while cascoding device is pretty much irrelevant , without adding much of his own to stage character
go to firstwatt.com , search for Cascode article
I know few ppl around found some Cree and whatnot , but I didn't bookmarked that .
Probably Mr. M.R. knows
Probably Mr. M.R. knows
I can recall seeing a few CREE parts last year that looked like they'd work, lowish capacitance, lowish threshold voltage. The Wolfspeed C2M0280120D springs to mind. They're like five bucks at Mouser so, you can try them out pretty cheaply. There is no "drop-in" replacement as far as I know, you're going to have to fiddle with the bias knob a little. 🙂
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Thanks Michael. Can you please help me with the Bias adjustment details. Will I need separate power supply etc?
Will it affect the distortion though? What I mean is the THD figures comparable to Jfet version by Pass ?
Will it affect the distortion though? What I mean is the THD figures comparable to Jfet version by Pass ?
1. I simply mean you'll have to adjust P1 for the desired bias.
2. With the enhancement part you will not need a separate supply.
3. I haven't built one, so I couldn't really say. If I had to venture a guess, I think it will get you within spitting distance.
Experimentation is required (and also fun I might add). If you want perfectly predictable results then you have to stick to the charted waters. 🙂
Michael , what should be the selection criteria for replacement Jfets. What specifications will make Jfet suitable replacement for SJEP used in original design. I assume normally off is one?
The SJEP could be thought of as an enhancement mode JFET, hence the "E" in SJEP. Since there aren't a lot of affordable power JFETs in production, you'll be probably looking for a SiC mosfet. Have a look at the part you're replacing and try to find something with similar (or lower) capacitance, Vgs, and transconductance. The F2 isn't a super fussy circuit. Try some stuff.
The Cree C2M0280120 is a MOSFET and not a jfet.Why to use this MOSFET when original version F2 uses mosfets itself?
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Because you can probably do a little better than the old IR parts. There's nothing especially magical about the SJEP. It's basically like a really good mosfet operationally speaking. If you want a JFET, go find some. It is not a VFET.
Exit, pursued by a bear 🙂
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