Is that good or bad?
AKG Perception 420 Mod
- Thread starter Gbout2
- Start date
Help Support GroupDIY Audio Forum:
There you have jFETs with values between
Idss = 2.7...3 mA
It depends on which circuit you will use them.
Should I use them on the top board (fet board), or the bottom big board (oscillator board).
Am I correct to assume Idss = noise? So id want the lowest Idss on the fet board right?
what exact model is the microphone?
AKG Perception 200
for the input circuit you use a small Idss and for dc/dc it doesn't matter, I also go with a large value
If that is the case, I am thinking about ordering some R-type for the fet board.
IDSS for R-type seems to be the lowest according to the datasheet.
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No, low Idss means higher gain, lower headroom
Higher Idss results in lower gain but higher headroom
For noise I select them, I use a temporary socket.
what you have now will work
They send you what they want anyway
I ordered group Y and they sent me GR
And you too
In addition, jFETs have a very large dispersion of parameters, that's why I ordered 60 pieces.
Others also ordered 1000 pieces of 2N3819. (I only ordered 100, but I was lucky with a good batch)
You have taught me a lot in this little bit of time, thank you.
Audio FREQ,
I want to warn you that the FNIRSI DSO-TC3 is a very good and accurate multimeter for BJT transistors, resistors, capacitors, inductances, etc., but it won't help you measure jFETs.
For example, he measured me
Idss=4.7mA for a jFET which in reality has 8.1mA.
My advice is to manually measure ALL the jFETs you have, by the method described before, put labels, so you can quickly test them in various circuits. Test them ALL in Perception200, you might be pleasantly surprised and select for low noise. Use a temporary socket that accepts any combination of pins.
Did you measure the 2n3819 by manual method? I'm curious how much it indicates.
I want to warn you that the FNIRSI DSO-TC3 is a very good and accurate multimeter for BJT transistors, resistors, capacitors, inductances, etc., but it won't help you measure jFETs.
For example, he measured me
Idss=4.7mA for a jFET which in reality has 8.1mA.
My advice is to manually measure ALL the jFETs you have, by the method described before, put labels, so you can quickly test them in various circuits. Test them ALL in Perception200, you might be pleasantly surprised and select for low noise. Use a temporary socket that accepts any combination of pins.
Did you measure the 2n3819 by manual method? I'm curious how much it indicates.
Thank you.Audio FREQ,
I want to warn you that the FNIRSI DSO-TC3 is a very good and accurate multimeter for BJT transistors, resistors, capacitors, inductances, etc., but it won't help you measure jFETs.
For example, he measured me
Idss=4.7mA for a jFET which in reality has 8.1mA.
My advice is to manually measure ALL the jFETs you have, by the method described before, put labels, so you can quickly test them in various circuits. Test them ALL in Perception200, you might be pleasantly surprised and select for low noise. Use a temporary socket that accepts any combination of pins.
Did you measure the 2n3819 by manual method? I'm curious how much it indicates.
I will do as you say, I will create a tiny circuit with a perf board to manually test JFETS with your method. I was thinking about installed a temporary socket on the Perception 200 jfet socket like you said. Not sure where to buy them.
I have not measure the 2n3819 yet, but I will when I get home.
You build the Idss measuring circuit in the AIR, not on pcb or perfboard, because it gets contaminated, we have high impedances and microcurrents. Pay attention to fat, sweat, other substances on the fingers during measurements.
Tens of years ago, we kept FETs, MosFETs, etc. on metal foils to short-circuit the pins, or in anti-static bags, they could be destroyed by the static electricity of the hand, packaging elements, etc.
You make the socket for the jFET from an IC socket, cut (or not). You need to use 4 pins to be able to measure any jFET, having the pins arranged differently as I have drawn for you.
You will use the same type of socket in the microphone.
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WOW! I did not know that! I will wear gloves next time I handle the JFETS. This is amazing information micolas, thank you very much. When I get home, ill make sure to clean all the JFETS I handled during the test with 99% Isopropyl Alcohol.
After permanently installing on the microphone, should I apply conformal coating to protect it?
Let's not even exaggerate. You don't need to clean every jFET, but you will need to clean the board well in the end. Applying a protective layer would be ideal
but it requires more special conditions, just clean the area well with isopropyl alcohol.
It is difficult to work with gloves, but the hands must be very clean. It's everyone's choice.
The same precautions must be strictly followed in the case of high-value resistors, hundreds of mohms, gohms.
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I made sure to clean off the solder joints before I applied liquid tape. I’m ready to measure again!
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That cleaning advice was for the mic PCB, rather than the JFET test jig.
Oohhh man!
Are you sure the liquid tape has good insulation resistivity or is it not behaving like a parasite capacitor at the gate?I didn't recommend protecting the socket pins in the test jig, you have no way of knowing what dielectric properties the liquid tape has, I specified that electrical protection by coating is pretentious, complicated, at the amateur level.
I specified: in the AIR, and not on perfboard, pcb, because air is a good dielectric if you don't have excessive atmospheric/environmental humidity.
You noticed that in microphones built with through-hole parts, the Gate pin of the first jFET in the input circuit does not touch the PCB.
(I want to buy a Victor 88c multimeter
which can measure up to 2Gohms)
Anyway, let us know how this insulating substance does, we're curious.
(I think Khron had a lot of fun. Me too
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