Plenty of space on the DiyVfet pcb
Only C3 is little close to resistors if you use biger diameter capacitor
but ok if resistors diameter is like dale RN55C model or similar
ps . capacitor example are 10 mm diameter
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Variac,
"A" type for the TL431 should be the correct type. From http://www.diyaudio.com/forums/group-buys/285823-gb-pass-sony-vfet-version-2-al-boards-tea-bag.html on recommended parts:
"TL431ACLPR - Buy extra, if something will short, it will likely be these that die. The TL431B were found not to work well. Use "A" type."
"A" type for the TL431 should be the correct type. From http://www.diyaudio.com/forums/group-buys/285823-gb-pass-sony-vfet-version-2-al-boards-tea-bag.html on recommended parts:
"TL431ACLPR - Buy extra, if something will short, it will likely be these that die. The TL431B were found not to work well. Use "A" type."
Looking at the datasheet of the texas instruments ones the B grade has a reference tolerance voltage at 25C of .5% vs the A grades 1%. I already have the B grade to install and now I find out to some are saying get the A grades. What would be the consequences of using the B grade when actually they have better numbers.
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What 1 ohm resistor is that? Can you describe the test a little more?
The attached image is the test setup I used to measure my VFets. I then used the following protocol to measure them:
1) Connect first meter across 1R0 3w resistor, connect second meter across Gate and Source pins of transistor
2) Connect the VFET to a 20V bench supply, limited in current at 1A for protection
3) Attach 18v battery supply across the pot
4) Start with pot at full CCW and increase the Vgate until you measure 0.5v across the 1R0 resistor
5) Record Vgs reading from transistor
6) Disconnect battery and PSU
The two Vfets that measured 11 & 12v also got hotter than the other Vfets during the few seconds it took to test them.
Any insights would be appreciated.
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Plenty of space on the DiyVfet pcb
Only C3 is little close to resistors if you use biger diameter capacitor
but ok if resistors diameter is like dale RN55C model or similar
ps . capacitor example are 10 mm diameter
Great pic! I'm still a bit uneasy about the resistor proximity. There is a corresponding 47uF 25V Silmic II that has the right lead spacing and is 6mm diameter. What's a healthy cap voltage spec for this part - is 25V enough?
Are any locations actually better suited for a good non-audio grade cap such as Panasonic FC?? I get a warm fuzzy whenever I see long-life 105C caps with lots of voltage headroom...
BK
Looking at the schematic a 25V should be adequate. Test point T19 shows +14. Using a larger cap is no problem for me. Caps have long leads to suspend the cap away from everything and from what I have read it is not a good idea to put a cap directly on a board because of contracting and expansion pulling the leads of a cap. Probably never happen but.
Thanks. I'm going to guess that it's the current limiting circuit on your supply.
Nothing to worry about as long as it settles to the values you need.
somebody made some oockup (or just had ooked part) , and suddenly part grade is responsible
that's same as saying that 2SJ74V is wrong part for Aleph J , just because BL is on schematic ....... and someone rotate it on pcb
Attached (borrowed from TI data sheet) graph of stability vs conditions
for the B part which is a little less stable than the A part.
I have personally seen oscillation in the regulator with this amp for high
bypass values, so the maximum cap value I used was 220uF.
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Also one can plan ahead with the resistors adjacent to the caps and put them a tiny bit off to the side. So will 25v work at all positions of the caps?
However that is EXACTLY what I'm asking you guys to check. Mechanical stuff, wrong resistor values, something ignored entirely,etc.
As far as the caps go I've also heard the opposite. That its its better to have caps tight to the board so they don't move and fatigue their leads. I actually agree that for caps that size it doesn't matter...
However that is EXACTLY what I'm asking you guys to check. Mechanical stuff, wrong resistor values, something ignored entirely,etc.
As far as the caps go I've also heard the opposite. That its its better to have caps tight to the board so they don't move and fatigue their leads. I actually agree that for caps that size it doesn't matter...
Attached (borrowed from TI data sheet) graph of stability vs conditions
for the B part which is a little less stable than the A part.
I have personally seen oscillation in the regulator with this amp for high
bypass values, so the maximum cap value I used was 220uF.
Is it possible to determine if the part is oscillating without the use of an oscilloscope?
In Vfet Part 1 CSX1 psu output is +/- 24 V and Mr Pass write with schematic all electrochemical caps are + 35 V.
If Diy Vfet Part 2 psu work around +/- 28 V i do stay on the same safe 35 V side of the moon
Only experiments with caps on breadboard can tell you witch caps you like it
Package received in perfect condition to The Netherlands. Looking forward to join/build this unique project. I heard the VFET's in a CSX1 from another dutch member, and the 2SK160/2SJ18 VFET's in an ancient TA-4650 (preamp bypassed); makes me long in anticipation for the finished VFET2 amp!
Thanks to Nelson Pass for making the project possible, and to the DIYA people (special mention for Jason...) for their great service.
Thanks to Nelson Pass for making the project possible, and to the DIYA people (special mention for Jason...) for their great service.
From my very limited understanding of electronics I assume from Zen Mod's and Nelson's statements that the A's are best but the B's are good enough the way they are used in this circuit. Someone with more knowledgeable correct me if I am wrong.
To answer your question, again from my limited understanding, if there is oscillation you will not need an oscilloscope to know something is wrong. You may need one to find where it is coming from.
Eric, thought about it some more, and I think you want to apply the bias voltage
before the main supply.
The symptom I saw was motor-boating, so if you have the right voltage
and it remains constant, I wouldn't worry about it.
For all I know, the larger caps I tried had some other issue with high
frequency impedance.
Trying using the caps as specified, and I don't think you will have any
problems.
