If the led string is on when G-S of Q6 is shorted. With the power off, is the source of Q6 about 260 ohms to -36v?
Not a red herring, thats important information.
From your test results, I would say that Q8 is faulty.
Amusing bit, shorting G-S of Q6 or Q8 would create a low impedance path for the 5mA of the JFET CCS to the minus rail, ~500 Ohm.
(5mA times 500 Ohm makes 2.5 V, which is less than the ~12V drop across the LED string).
Shorting G-S of Q8 should kill the LED string, kill Q9, and turn all of ampy into dead duck.
Shorting G-S of Q6, but greeny Xmas tree remains burning : apparantly busy traffic at R(oute) 12 & 26 .
(5mA times 500 Ohm makes 2.5 V, which is less than the ~12V drop across the LED string).
Shorting G-S of Q8 should kill the LED string, kill Q9, and turn all of ampy into dead duck.
Shorting G-S of Q6, but greeny Xmas tree remains burning : apparantly busy traffic at R(oute) 12 & 26 .
Yea shorting G-S of Q8 or Q6 throws all the voltages out of whack. I think Q11 is the only one that would be working, it's set for 5ma and don't care where it gets it.
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Sorry lads.
I didn't have my glasses on when I put the short across Q6.
With R8 shorted and Q6 g-s shorted the LEDs are OUT and the amplifier has NO oscillation.
Back to the drawing board ????
I didn't have my glasses on when I put the short across Q6.
With R8 shorted and Q6 g-s shorted the LEDs are OUT and the amplifier has NO oscillation.
Back to the drawing board ????
I still think we are all missing a point here.
BOTH Pumpkins are exactly the SAME. Only one is being subjected to fault finding.
Alexander says that it is probably a component choice somewhere.
The resistors are all 1% Low Noise Metal Film.
C1 and C2 are Silvered Mica
C3 is an Orange Drop
C4 and C5 are Metalised Polypropylene
C6 is a WIMA MKS4
C7,C9 are Orange Drops
C8,C10,C13 and C14 are Rubycon
C11 and C12 are Orange Drops
All semis are matched - actually supplied by Alexander himself.
BOTH Pumpkins are exactly the SAME. Only one is being subjected to fault finding.
Alexander says that it is probably a component choice somewhere.
The resistors are all 1% Low Noise Metal Film.
C1 and C2 are Silvered Mica
C3 is an Orange Drop
C4 and C5 are Metalised Polypropylene
C6 is a WIMA MKS4
C7,C9 are Orange Drops
C8,C10,C13 and C14 are Rubycon
C11 and C12 are Orange Drops
All semis are matched - actually supplied by Alexander himself.
Unlikely unless there is a design issue.
I've been buidling electronic circuits for over 30 years and have NEVER yet fried anything.
Including working in strict ESD environment and soldering CMOS components.
I've given up. I'm offering the 2 x Shuntky (Perfectly working) with the 2 x Pumpkin (Oscillating) on SWAP MEET for £50 plus P&P.
Common, this build has been short circuited from day one years ago till yesterday, one comprimise after another, faulty wire connections (XLR's), etcetera.
Oops !
Papa's DIY designs from Alephs to the latest FW ones are fairly fool proof, basically an idiot can assemble them, which also makes them rather elegant.
Point is that fully balanced designs require a lot of "seasoning", and attention to every single detail.
Example is the Aleph-X, few have managed to get it working properly : sticking two halves together transforms an amp that anyone can build into a completely different animal.
Comments such as : "As we are reducing the frequency, the amplitude is increasing", implies you're way over your head, despite 30 years of building circuits.
Following Itsmee's suggestion of shorting Gate to Source of the current sinks again suggests one definitely does not have the basics covered.
In such cases, one should follow the assembly manual by the letter.
Example : a youngster overhere was hell bent on having a big flat screen, despite my advice not to, he got the biggest Samsung TV his pig saving account could handle.
When it shut down after a water accident, the screen had to be opened.
Inspection turned up a fried resistor and a couple terminated MOSFETs in the high voltage section.
Second glance also showed a couple of cheap azz electrolytic caps, which were half way en route to heaven, and would have terminated the screen anyway within a year or so.
That's 30 years electronics experience, and attention to detail.
Little reminder : you entered the BS, not Brag, and keep the savvy to yourself bar.
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I am sorry KatieandDad that you did not find the problem....
on the other side I am happy that the "drama" is over.....
good luck with the search of a new pre....
😀
on the other side I am happy that the "drama" is over.....
good luck with the search of a new pre....
😀
The B1 is working perfectly. It is SILENT in operation and does its job impecably.
The Pumpkin is horrible. It is difficult to use and is only suitable for the experts.
Lots of us have Pumpkins, and very well sounding ones I might add.
That you failed to build a kit, says nothing about the kit in question.......
Magura 🙂
That you failed to build a kit, says nothing about the kit in question.......
Magura 🙂
I would have hoped that buying PCBs from ZenMod would have made the job easier. But No.
I've used over 30 years experience in this trade to get the boards working. I've had NO LUCK.
Buy these with CARE. They probably wont work. If you are lucky they might.
I've used over 30 years experience in this trade to get the boards working. I've had NO LUCK.
Buy these with CARE. They probably wont work. If you are lucky they might.
So far I have seen quite a few Pumpkins that work, and none that didn't.
So to claim that they probably don't work, is gonna be on your own account.
Magura 🙂