Just to muddy the waters for you further still4given - nelson pass indicates that the fail voltage for the jfet is around 43v in practice (in the f5 turbo article), and I seem to recall that the power dissipation on that part in the sim is fairly low as well. Real life may be different though!
Hi Still4given - AndrewT is talking about the Vds across the Jfet (the K170). The magic smoke voltage is rated to 40V for a k170 according to the datasheet. Pass says 43V is the upper limit, but I suspect he was talking about the SJ74 complementary jfet as well which is only rated to 25V...
You can more easily measure the jfet Vds from where R8 connects to the trace going to the Jfet, and from where R10 connects to the trace going to the jfet.
Whether there's much point is another question - but I would defer to those who've actually built one as opposed to myself browsing datasheets... 🙂
You can more easily measure the jfet Vds from where R8 connects to the trace going to the Jfet, and from where R10 connects to the trace going to the jfet.
Whether there's much point is another question - but I would defer to those who've actually built one as opposed to myself browsing datasheets... 🙂
Clear Communication
I can be blunt, so I hope it's taken constructively
It appears that Andrew T knows a lot
Maybe he's much more short of time than most people here?
But I recall from lots of his posts in several threads he's so succinct they read as terse.
Regardless of their brevity, they invariably assume a level of knowledge that is well out of whack with half the likely readers
Frankly my perception is, it often reads like point scoring
I can be blunt, so I hope it's taken constructively
It appears that Andrew T knows a lot
Maybe he's much more short of time than most people here?
But I recall from lots of his posts in several threads he's so succinct they read as terse.
Regardless of their brevity, they invariably assume a level of knowledge that is well out of whack with half the likely readers
Frankly my perception is, it often reads like point scoring
aspringv
When I catch up with you, I will re-read that logical sounding advice
Much appreciated 🙂
When I catch up with you, I will re-read that logical sounding advice
Much appreciated 🙂
Andrew was perhaps assuming that I know what Vds and Vdg mean. I don't. Perhaps my first question should have been that rather than how to measure.
No matter, it is a simple thing to dial down the SMPS to +-36V. Two volts on the rail can't be heard.
No matter, it is a simple thing to dial down the SMPS to +-36V. Two volts on the rail can't be heard.
Ah. Vds is the voltage across the Jfet - ie V(drain)(source) and Vgs is the voltage from gate to source - the voltage that controls the jfet.
http://www.firstwatt.com/pdf/prod_f5_man.pdf has a good quick intro to using FET's - scroll down a bit and there you have it.
I'm still not sure whether Meanman's advice is to protect the jfet or because it sounds worse at that operating point... Meanman, would you be kind enough to clarify?
I look forward to the building and generating my own questions 🙂
http://www.firstwatt.com/pdf/prod_f5_man.pdf has a good quick intro to using FET's - scroll down a bit and there you have it.
I'm still not sure whether Meanman's advice is to protect the jfet or because it sounds worse at that operating point... Meanman, would you be kind enough to clarify?
I look forward to the building and generating my own questions 🙂
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It has nothing to do with sound it's only to protect the jfet.Don't know in what thread it was but I did get the advice not to take a toroid with higher rating than 2x25Vac when you use a single SK170 due heat dissipation of the fet.I think in was in the SymaSym thread of Rudi Ratlos
Ok, I haven't read that thread I'm afraid so I can't really make any comment on that advice. I just had a bit of a mess around with LTSpice though, and it's indicating about 3.5mA through the Jfet, and a dissipation of about 60mW for Still4givens setup. Does this line up with real life measurements?
The datasheet rates the part to 400mW (for how long I wonder 🙂 ) and I'd consider half that comfortable. If 60mW or so is the real dissipation, I reckon there'd be no real reason for still4given to change his setup at all... Just crank the bias to wherever he likes it best. That said, I for one would like to see a photo or two or none of what he's said really happened 🙂
I might have to rethink my plan to use a bf862 instead of the sk170 though! 3.5mA might be a bit low for a 10mA Idss part...
The datasheet rates the part to 400mW (for how long I wonder 🙂 ) and I'd consider half that comfortable. If 60mW or so is the real dissipation, I reckon there'd be no real reason for still4given to change his setup at all... Just crank the bias to wherever he likes it best. That said, I for one would like to see a photo or two or none of what he's said really happened 🙂
I might have to rethink my plan to use a bf862 instead of the sk170 though! 3.5mA might be a bit low for a 10mA Idss part...
I'm missing some addresses and or nickname linked to the address.So please all that have payed the shipping cost mail me at 1964Roovers@gmail.com and write down your address and nickname please.
I like it. Very nice, non-fatiguing. I'm only waiting for some smaller heatsinks and then I'll put it in a case. I believe this will this will an amp I listen to often.
Blessings, Terry
Blessings, Terry
There is something with this amp just can't put my finger on it. When you compair it with others amps it can lose with soundstage or resolution but when it comes to sound WOW total different face.It's as you say you keep listening to this amp and with the right speakers just awesome.Keeps one of my favorite amps
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