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V-fet pre amp

totem

totem

Addicted Member
On the heals of Ecowars post regarding the blown V-fet on his 4650 integrated,
I am wondering about a pre amp that also uses V-fets with a channel that drops
out. The description given to me is one channel will come on then off again, because this is a pre amp & not a power amp should there be a better chance
that the V-fets are ok, & the problem lies in another direction, cold solder etc.
 
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Well as ByrdWings has informed me, the preamp in question is not a V-fet. Every day I continue to learn a little more.
 
Nakdoc - Any chance you could post the VFET device number for the C-1 output stages you mention? The TA-5650 has a baby VFET in the preamp, but was my understanding that it is the only use of a VFET in a preamp. The one is the TA-5650 is a 2SK63 and we (VFET followers) didn't realize it was a small VFET until about a year, or so, ago (http://audiokarma.org/forums/showthread.php?t=51718&highlight=2SK63 - see posts #3 & 5). Guess we were blinded by the larger VFETs in the amp(s). And, perhaps by the misnomer of 'vertical' FETs (like Halcro states in their advertising today).
 
VFETS where else?

Yamaha B-2- being new to the VFET world & reading your post re the TA-5650 & 2SK63
small VFET, does it then follow that the tae series pre amps would then also use small VFETS ?
 
Definitely not. Need to look at each preamp schematic to see what is there. We were quite surprised when I discovered the 2SK63 last year. And there were several folks (Axel, etc.) who have been into VFETs much longer than I who had not noticed it, either. Perhaps EW will see this thread and cast his eye on the TAE-8450 schematic (he has mine in for a refurb).
 
As previously mentioned the only known dedicated preamplifier using V-Fets is the Yamaha C-1 ! It uses two 2SK75 (C grade) medium power V-Fets as voltage followers of the output stage. The circuit used for this application is nearly identically to the rumble filter amplifier stage of the B-1.

The only candidate, which remains, is the JP-S7 preamplifier from Victor, which probably used the 2SK69/2SJ19 complementary pair. The high supply voltage of +-59 V (see k.nisi website) doesn´t allow J-Fets to be used (ordinary J-Fets range up to 50V, some types up to 100V, but with very high internal resistances).

A service manual for these rare Victor V-Fet units would help a lot !
 
Perhaps EW will see this thread and cast his eye on the TAE-8450 schematic (he has mine in for a refurb).
Click to expand...
The schematic won't tell me much...there's no special schematic for a VFET since a VFET is just a big JFET. I'd need the datasheet for the part, and finding it will be an exercise in futility.
 
Several of the vintage Sony schematics have the transistor part numbers on the schematic. Like the TA-5650, for instance. Some are near the transistor symbol in the circuit and others are in a box listing the active devices somewhere near the edge of the schematic, identified by the schematic part number (Q101, for instance) and the device part number (2SK63, etc.). But, not having seen the TAE-8450 schematic, it may well be different.

BTW - just received the owner's manual for the TAE-8450.

Unda Maris said:
The only candidate, which remains, is the JP-S7 preamplifier from Victor, which probably used the 2SK69/2SJ19 complementary pair. The high supply voltage of +-59 V (see k.nisi website) doesn´t allow J-Fets to be used (ordinary J-Fets range up to 50V, some types up to 100V, but with very high internal resistances).

A service manual for these rare Victor V-Fet units would help a lot !
Click to expand...
Would this be the one? http://www.manuals-in-pdf.com/advanced_search_result.php?keywords=JP-S7
 
Device number (2SK-whatever) doesn't tell me if it's a FET or a VFET or MOSFET, unless you have a list of such devices.

The driver FET's at the output of the 8450 are 2SK43.
 
Info used to be available on the Vintage Knob VFET site. Now listed as 'Soon Available'. Google resources give 2SK43 as an N-channel JFET. So, not a VFET. But, Mirko seems to all ready know this.

the-real-mandak said:
Unda I thought the C-2 was the same as the C-1, but without all the fancy adjusting?
Click to expand...
A quick look at the C-2 schematic shows no FETs of any sort in the preamp, other than a couple in the power supply. Everything else is a few ICs (probably the Yamaha specific modules) and discrete BJTs.
 
Every year, just before christmas a nice (but more or less senseless) V-Fet discussion starts. I´d like to have more V-Fet discussions all over the year !

EW:

I wished shipping from Germany to the U.S. would be easier, then I could send you your 2SK60.
 
To ship a VFET to here would cost a Euro or maybe two at the most. I sent a whole bunch of ceramic IF filters to a AK'er in Germany a year or so ago, and I think I spent about $1.75 US to do it.
 
Unda Maris said:
Every year, just before christmas a nice (but more or less senseless) V-Fet discussion starts. I´d like to have more V-Fet discussions all over the year!

EW: I wished shipping from Germany to the U.S. would be easier, then I could send you your 2SK60.
Click to expand...
Maybe they don't have a postal service in Germany. Or, if they do, it doesn't go out of the country. :D
 
Since Germany is the country with the highest export rate in the world, this would be very strange ... :lmao:

I´ll check ...
 
Unda Maris said:
As previously mentioned the only known dedicated preamplifier using V-Fets is the Yamaha C-1 ! It uses two 2SK75 (C grade) medium power V-Fets as voltage followers of the output stage. The circuit used for this application is nearly identically to the rumble filter amplifier stage of the B-1.

The only candidate, which remains, is the JP-S7 preamplifier from Victor, which probably used the 2SK69/2SJ19 complementary pair. The high supply voltage of +-59 V (see k.nisi website) doesn´t allow J-Fets to be used (ordinary J-Fets range up to 50V, some types up to 100V, but with very high internal resistances).

A service manual for these rare Victor V-Fet units would help a lot !
Click to expand...
Yup, Nakdoc and Unda Maris know their stuff. Take off the cover of the C-1
and the 2SK-75's are staring you in the face. I had the C-1 on the closet shelf
while dabbing around with the likes of tube pre-amps, Parasound Fet preamp
and having fun just changing stuff around. I put the C-1 back in, driving
the B-1 and B-2's(two main preouts and one switchable pre-out makes this
easy) and Wow, I'm not straying again. Maybe there's a reason the C-1 cost
$1800.00 way back then. Maybe it's the super smooth sterling sound, Ya
think? Ssuperrob, grabbed the latest one on Ebay, Congrats! Long live
V-fets. :yes:
picture005-1.jpg

picture004-1.jpg

picture003-2.jpg
 
Klipschornman said:
I had the C-1 on the closet shelf
while dabbing around with the likes of tube pre-amps, Parasound Fet preamp
and having fun just changing stuff around. I put the C-1 back in, driving
the B-1 and B-2's(two main preouts and one switchable pre-out makes this
easy) and Wow, I'm not straying again. Maybe there's a reason the C-1 cost
$1800.00 way back then. Maybe it's the super smooth sterling sound, Ya
think? Ssuperrob, grabbed the latest one on Ebay, Congrats! Long live
V-fets. :yes:
Click to expand...
Very nice system Klipschornman!
 
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