the circuit of a KM84 in the body of a Chinese TLM103

[titote]

I used the body of a Chinese microphone with the KM84 circuit on a one-sided PCB, the capsule lacks bass because it is that of the Chinese microphone

 

[Khron]

Maybe..?

 

[rock soderstrom]

This can have many causes. Correct transformer with suitable impedance matching and sufficient inductance? Have you tried the circuit with different capsules? Does anything change? Which FET with which biasing? Matching coupling capacitors with sufficient capacitance?

Did you test the circuit for linearity without capsule (with a small C as dummy capsule)?

 

[titote]

the transformer is a T13 and the capsule is 25mm, the fet is polarized at 10V, it is good in the medium and treble.

 

[rock soderstrom]

Have you tried the circuit with different capsules?

Did you test the circuit for linearity without capsule (with a small C as dummy capsule)?

 

[titote]

I polarized with the capsule mounted, for the moment I only have a single capsule which has a grid on the surface, I do not know the technique to simulate a capsule

 

[rock soderstrom]

I do not know the technique to simulate a capsule

It is quite easy, replace the capsule with a small capacitor. The original schematic says 36pF/50V is right for that circuit. Some pF more or less will work as well. Than insert a small test signal and check the output of your mic. This will test the frequency response (and THD if you want) of the circuit and transformer without the capsule signal. The small cap simulates for the circuit the capsule.

 

[rock soderstrom]

I polarized with the capsule mounted, for the moment I only have a single capsule which has a grid on the surface,

I don't understand this part. "Grid on the surface"?

Is this a electret capsule?

Photos?

 

[titote]

 

[rock soderstrom]

These are electret capsules, I like them, I use them myself.(I call them KK12, named after member @kingkorg ) These do not need external polarization voltage, no experience how they behave with it. Maybe someone else can say something about it.

I would just disconnect the polarization voltage and see what happens. Normally, if the rest is right, you have a good sounding microphone for the little money these capsules cost. There are of course better, but not in this price range...

Edit: Small addendum, these capsules are definitely not bass shy when you get close.

 

[titote]

the microphone works very well, it lacks a little gain but I think it's the T13 transformer, I ordered another 25mm capsule

 

[rock soderstrom]

These are good capsules, too. They are a bit slimmer in the bass region. Check this thread
https://groupdiy.com/threads/lookin...nufacturer-recommendations.80083/post-1097514

 

[titote]

I have a version of the Km84 with a small capsule mounted in a Tlm103 and a version with a large capsule mounted in a U87, one is good in the mids and highs the other in the bass and mids