Km84 PCB

[titote]

I built a pcb of the micro Km 84, but this one has a lot of background noise, can you help me to validate my circuit.

 

[Migs 31]

I built a pcb of the micro Km 84, but this one has a lot of background noise, can you help me to validate my circuit.

Hi there,

I have built that circuit a couple of times.
Got my PCB's from a fellow GDIY member here.

First describe the "background noise" so people here can help you.
Is it Hiss, is it Humm like 50/60Hz humm?
Is it frying or popcorn type noise (I'm not joking).
Try your best to describe what you hear or post some audio.

If you have not put the microphone sleeve back yet.
Could be that the circuit needs to be shielded (Faraday cage).

My 2 cents.
M

 

[titote]

the background noise is huge and continuous, but it still persists when the -6db pad is engaged. The pcb includes the reduction loop.

 

[Migs 31]

the background noise is huge and continuous, but it still persists when the -6db pad is engaged. The pcb includes the reduction loop.

Have you put the circuit back in its metal casing or sleeve?
Or is the circuit on your work table, being tested?

Is it a ground continuous type of Hum?
Or something else? Describe it please.
High pitched, low pitched, hiss? Etc.

M

 

[titote]

I had the same noise on the table that once mounted, the sound was not very clear

 

[titote]

there are schematics with a 10 ohm resistor (R13) to ground, could this reduce the noise

 

[Chrisfromthepast]

Can you post a photo?
This sounds like a km84 that either has no capsule attached or the circuit is being tested outside of its body tube. Sorry, I couldn’t make the mp3 work.

 

[titote]

I signed the pcb with a cnc 3018 after creating the model on Kikad, the renin did not hold in certain places, the body is a stainless steel tube. the model is without the capsule or the xlr connector, I'm trying to understand where the problem can come from with a new assembly

 

[titote]

you can see it better in this picture

 

[Khron]

Is that supposed to be a double-sided PCB?

If it is, are those component leg holes / vias plated? Can't see any solder on maybe half of those pads.

And the gate of the JFET and both 1G resistors seem to be connected through the PCB traces (as opposed to in-the-air or on Teflon isolation pins).

 

[Chrisfromthepast]

Beyond the sort of last 10% noise optimizations @Khron mentioned, It is possibly working pretty much normally. Close it up in a metal body, connect a capsule, make sure all your body parts connect to pin 1 of your xlr and test again.

 

[titote]

the pcb is double sided, connected as in the diagram

 

[titote]

the faraday cage only works when the microphone is installed in a metal tube?

 

[titote]

Hi there,

I have built that circuit a couple of times.
Got my PCB's from a fellow GDIY member here.

First describe the "background noise" so people here can help you.
Is it Hiss, is it Humm like 50/60Hz humm?
Is it frying or popcorn type noise (I'm not joking).
Try your best to describe what you hear or post some audio.

If you have not put the microphone sleeve back yet.
Could be that the circuit needs to be shielded (Faraday cage).

My 2 cents.
M

I just welded, I have a sound of popcorn !!!

 

[Chrisfromthepast]

Did you thoroughly clean everything near the capsule connection? careful do not subject transformer to solvents.
Tantalum capacitors make the popcorn noise sometimes. Replace C3, C4 first?

 

[titote]

Did you thoroughly clean everything near the capsule connection? careful do not subject transformer to solvents.
Tantalum capacitors make the popcorn noise sometimes. Replace C3, C4 first?

I have intermittent cuts, but less background noise

 

[Chrisfromthepast]

You have cleaned up the solder work? Take your time to flow plenty of solder, and be very still as it cools.
And then clean thoroughly.
Maybe post another photo of the micPCB enclosed in metal and an mp3 hosted offsite?

 

[jean-christophe boussin]

You have cleaned up the solder work? Take your time to flow plenty of solder, and be very still as it cools.
And then clean thoroughly.
Maybe post another photo of the micPCB enclosed in metal and an mp3 hosted offsite?

I will try tomorrow, when the soldering of the wires is finished (22H in Canada), I maintain the wires with hot glue to the pcb, it prevents the wires from being cut, I use AGW22

 

[Khron]

Can we also see the bottom of the PCB?

 

[Migs 31]

Good Morning,

What @Khron & @Chrisfromthepast pointed out, is most likely the cause of your noise.

"And the gate of the JFET and both 1G resistors seem to be connected through the PCB traces (as opposed to in-the-air or on Teflon isolation pins)."

It's good to have Teflon standoffs at the junctions of R1-C9-C2-C1-Capsule and C1-G-R2.
If you don't have Teflon standoffs you can always "lift" the Gate leg to solder "mid air".
All the area in Yellow and Red on schematic attached is susceptible to dirt, moist, residue solder resin.

You need to have neat soldering (by keeping your soldering tip clean with a wet sponge) quick clean soldering without dirt. Clean the residue solder resin and specially parts in Yellow circle with Alcohol.

As Chris said : "Close it up in a metal body, connect a capsule, make sure all your body parts connect to pin 1 of your xlr and test again." Put circuit into metal casing for Faraday cage effect.
Good luck.

M