Help for understanding a Chinese U87 fake microphone schematics
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Voyager10
Well-known member
In the schematic, Q2 C, Q3 C, and one terminal of each of Q4 and Q5 are all connected together. How are they reading different voltages?
Q2 C (1.29V) is the least likely.
This hurts my head. Floating bases and gates make no sense. Does this even work?
The capsule, if it's just a capsule with nothing can't drive the sources or drains on the 2N5457s.
Look up the basing on the transistors, check and double check that.
I suggest you start over with this schematic and draw this so the signal travels left to right, which is the usual convention.
Good luck. Over and out.
The capsule, if it's just a capsule with nothing can't drive the sources or drains on the 2N5457s.
Look up the basing on the transistors, check and double check that.
I suggest you start over with this schematic and draw this so the signal travels left to right, which is the usual convention.
Good luck. Over and out.
@Mr. Moscode : If you have a headache, take paracetamol 
-Yes, it works. Did you read the whole post?
As mentioned, I am not an electronics "specialist". It is precisely people like you who can help me. Thanks in advance.
I know my schematic is terrible, I've spent several hours on it already. I don't claim to be a schematic drawing champion, I do what I can...
-Yes, it works. Did you read the whole post?
As mentioned, I am not an electronics "specialist". It is precisely people like you who can help me. Thanks in advance.
I know my schematic is terrible, I've spent several hours on it already. I don't claim to be a schematic drawing champion, I do what I can...
I know my schematic is terrible, I've spent several hours on it already. I don't claim to be a schematic drawing champion, I do what I can...
Voyager10
Well-known member
If you'll forgive the hasty artwork, here's how I think the FETs are connected:
The 1G resistor must go to a Gate terminal, nothing will work otherwise.
The 1G resistor must go to a Gate terminal, nothing will work otherwise.
Cqwet Dbdfte
Well-known member
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Use LTspice for schematic capture.
Fast, easy, free, and works great.
Posting the bottom view is a bit confusing. Top view with the ref designations reading correctly would make it easier.
You have the pinout wrong on the 2N5457s:
This is the correct one. Pin 3 is the gate.
Look this stuff up in Google to be sure of details like this when you do this work. Don't ask me why I know to do that. If you're dyslexic like me, check it 3 times.
You have the pinout wrong on the 2N5457s:
This is the correct one. Pin 3 is the gate.
Look this stuff up in Google to be sure of details like this when you do this work. Don't ask me why I know to do that. If you're dyslexic like me, check it 3 times.
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Cqwet Dbdfte
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That could be it. That circuit will works and is easy to follow.
FWIW, Grasshopper* - Schematic conventions you should follow:
The signal path is left to right.
The Positive voltage supply is at the top.
Ground is on the bottom.
If there was a negative voltage referenced to ground it would generally be drawn below the ground.
AS for the circuit analysis - the 2 jfets are in a cascode configuration feeding Q3, a PNP xstor.
Q4 is a constant current source, or load for that circuit. Q1-4 form a follower circuit (the voltage gain is 1, it's a current amplifier) that takes the capsule voltage and adds current to drive the output. NOTE that this is a single ended circuit, only 1 phase output.
The positive output is off the emitter of Q3 & collector of Q4 and is in phase with the capsule voltage. It is known as the positive phase. The negative phase is AC ground, with phantom positive DC power isolated from ground and audio ground goes through C4.
It acts as a pseudo balanced AC circuit for the signal for noise immunity.
This allows the all the current from the phantom PS to be routed to the positive supply at the top thru R3 & 6 with the supply voltage for the step up DC converter for the capsule's 60V coming through R4,5.
Since the + 60 V supply is not drawn I assume the +15 V 4 supplies the 60 v supply (V1 & V2). The way that it's drawn as 2 separate entities (V1, V2) is, IMHO, not correct. It should be 15 V in and 60V out in one symbol, usually shown as a box with a ground.
I hope this helps you learn good schematic practices, and understand the circuit, no charge.
*Kung Foo TV series.
FWIW, Grasshopper* - Schematic conventions you should follow:
The signal path is left to right.
The Positive voltage supply is at the top.
Ground is on the bottom.
If there was a negative voltage referenced to ground it would generally be drawn below the ground.
AS for the circuit analysis - the 2 jfets are in a cascode configuration feeding Q3, a PNP xstor.
Q4 is a constant current source, or load for that circuit. Q1-4 form a follower circuit (the voltage gain is 1, it's a current amplifier) that takes the capsule voltage and adds current to drive the output. NOTE that this is a single ended circuit, only 1 phase output.
The positive output is off the emitter of Q3 & collector of Q4 and is in phase with the capsule voltage. It is known as the positive phase. The negative phase is AC ground, with phantom positive DC power isolated from ground and audio ground goes through C4.
It acts as a pseudo balanced AC circuit for the signal for noise immunity.
This allows the all the current from the phantom PS to be routed to the positive supply at the top thru R3 & 6 with the supply voltage for the step up DC converter for the capsule's 60V coming through R4,5.
Since the + 60 V supply is not drawn I assume the +15 V 4 supplies the 60 v supply (V1 & V2). The way that it's drawn as 2 separate entities (V1, V2) is, IMHO, not correct. It should be 15 V in and 60V out in one symbol, usually shown as a box with a ground.
I hope this helps you learn good schematic practices, and understand the circuit, no charge.
*Kung Foo TV series.
Great, Sunsplash!
Your work has come a long way. Way to go.
An oscillator feeding a voltage quadrupler! And the mysteries disappear!
If you would, add the pins for the XLR socket. Pin 2 is usually + phase.
Then you should have it.
Happy Soldering Everyone!
Your work has come a long way. Way to go.
An oscillator feeding a voltage quadrupler! And the mysteries disappear!
If you would, add the pins for the XLR socket. Pin 2 is usually + phase.
Then you should have it.
Happy Soldering Everyone!
Cqwet Dbdfte
Well-known member
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- Oct 2, 2023
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- 633
Not sure the oscillator is correct. Nothing from simulation. Take another look.
@Cqwet Dbdfte
It works well, I tested it.
This is a really quick build, but it works.
I just added a variable capacitor to adjust the oscillator, which changes the output voltage and I put a 100uH choke.
It works well, I tested it.
This is a really quick build, but it works.
I just added a variable capacitor to adjust the oscillator, which changes the output voltage and I put a 100uH choke.
Екатерина
Active member
Good day, this circuit is not U87, it comes from ISK in China. It was originally placed in ISK3000 and JZ also used this circuit. This circuit is already considered sophisticated and not simple, with heavier coloring and a warmer type
I have the mic lying around for a while now, but haven't got around doing anything with it yet. But I'd expect the circuit to be way more linear and less coloring than a real U87 circuit having a single JFET with low feedback and a transformer output. Which one is the better sounding circuit, I cannot tell and I guess will depend on personal taste, source material etc.
I plan on using this mic for experiments with the circuit as is and compare with ORS87 and a transformer output circuit that I designed myself. Just for fun and learning.
Jan
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