oh you meant ON
lololol
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Neumann Vintage U87 Clone : Build Thread.
- Thread starter poctop
- Start date
Help Support GroupDIY Audio Forum:
lololol
Ricardus
WILL SOLDER FOR FOOD
I feel like that someone posted that info in this thread somewhere. But I don't recall where.
The SSL9000 preamps use these switches, which I recall are similar to the ones Dany provides, from when I built my U87 clones, but I don't know if they're compatible.
https://www.mouser.com/ProductDetail/Mountain-Switch/108-2AS1T2627-EVX?qs=ELBlAjflrFIddurRblxThw==
Possibly this:
https://www.mouser.com/ProductDetail/Apem/TL36P000000?qs=/g/CUlbiKFAxztkNXLd4yA==
So I am getting 15v on the 24v zener.... which is not good as per the first few pages of this thread.
I don't have my capsule connected but have the transformer connected. I cannot see how this would make a difference but wanted to make your guys.
The Idss of the fet is 6.26ma and I thinking this might be too low??
So my options (correct me if wrong) are to swap out the jfet with a higher idss jfet or drop down the 56kohms of R17?
Dropping R17 seems like a more viable option to me.
I assume I could do this with all my low idss jfets as I have a lot....lol??
If I did remove r17 to bring up the zener, what resistor values would do the step downs until you got the right one?
Thanks gang!
I don't have my capsule connected but have the transformer connected. I cannot see how this would make a difference but wanted to make your guys.
The Idss of the fet is 6.26ma and I thinking this might be too low??
So my options (correct me if wrong) are to swap out the jfet with a higher idss jfet or drop down the 56kohms of R17?
Dropping R17 seems like a more viable option to me.
I assume I could do this with all my low idss jfets as I have a lot....lol??
If I did remove r17 to bring up the zener, what resistor values would do the step downs until you got the right one?
Thanks gang!
fsalter
Well-known member
I'm not sure what the problem is, but i can assure you an idss of 6.26ma is fine. Your fet is not to blame.
Does it make a difference if the transformer is connected when measuring the circuit?
Drosselmeier
Well-known member
So can someone please help me.
I am not sure if this forum is still active like it once was.
It would be nice to get some of the creators active on this as I am lost!
So if I set my drain on the fet between 11-15vish, I get the required voltage at the zener accounting for the 5%, its 22.8v to 25.2 v.
However if I connect the ocilloscope to the circuit, the sine wave is not balanced. So if I turn the pot and to balance the sine wave, I now have 15v at the zener??
I have check all my parts and they are correct.
I even check the 48v supply and its working fine.
The current is 47.7 right up the 2k2 resistors and drops one volt after them 47.6.
Any thoughts????
It would be nice to hear from Dany or Matador or anyone who really understands this circuit.
I tested this with the transformer in and no capsule................does this make a difference??
I am not sure if this forum is still active like it once was.
It would be nice to get some of the creators active on this as I am lost!
So if I set my drain on the fet between 11-15vish, I get the required voltage at the zener accounting for the 5%, its 22.8v to 25.2 v.
However if I connect the ocilloscope to the circuit, the sine wave is not balanced. So if I turn the pot and to balance the sine wave, I now have 15v at the zener??
I have check all my parts and they are correct.
I even check the 48v supply and its working fine.
The current is 47.7 right up the 2k2 resistors and drops one volt after them 47.6.
Any thoughts????
It would be nice to hear from Dany or Matador or anyone who really understands this circuit.
I tested this with the transformer in and no capsule................does this make a difference??
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I'm sure more people would try to help you if we had a proper schematic. We can't possibly know all schematics of the projects in this group.
The schematic.
I will post some dmm measurements. Schematics at the beginning of this form I know.
I have completed the build and not able to get the 24vish number on the diode.
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So here are my voltages I am reading from the DMM to help paint the situation gang....
L1 and L2 = 47.78v
R18 = 47.78v
R19 = 47.78v
R17 = 22.91v
Zener Diode is reading 22.91v
Fet Drain is 16.88v
Fet Source is 17.60v
R12 = 21.85v
R13 = 45.15v
R14 = 22.91v
R8 = 45.15v
Clearly something wonky is going on here
As per previous post....
So can someone please help me.
I am not sure if this forum is still active like it once was.
It would be nice to get some of the creators active on this as I am lost!
So if I set my drain on the fet between 11-15vish, I get the required voltage at the zener accounting for the 5%, its 22.8v to 25.2 v.
However if I connect the ocilloscope to the circuit, the sine wave is not balanced. So if I turn the pot and to balance the sine wave, I now have 15v at the zener??
I have check all my parts and they are correct.
I even check the 48v supply and its working fine.
The current is 47.7 right up the 2k2 resistors and drops one volt after them 47.6.
Any thoughts????
It would be nice to hear from Dany or Matador or anyone who really understands this circuit.
I tested this with the transformer in and no capsule................does this make a difference??
Ricardus
WILL SOLDER FOR FOOD
D87 schematics.
i have provided dmm measurements....hope that helps
Do you mean you have 47V on one side ( junction of R18/R19/R17) and 22.91V on the other side?
That means the FET is drawing about 0.4mA, which is not enough; OTOH R17, at 56k, cannot deliver much. Do you realize you power the FET via a total of 114 kiloohms? that's a lot.
I would seriously decrease the value of R17. Maybe 5.6k?
Which leaves the FET with 0.72V to operate. It should see about 10V.
Ricardus
WILL SOLDER FOR FOOD
Well, for what it's worth, I built two with basically the same BOM and the same values and they worked fine right out of the gate.
ok let me try that man... thanks
l wish I had that luck
lol
Probably, but the tolerance on FET's is so wide it may explain why some work and some others don't.
In this circuit, the current available for the FET is quite low. Not all FET's are suitable.
Ricardus
WILL SOLDER FOR FOOD
At this point he should just change the FET and see what happens.
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