AKG Perception 420 Mod

[Prahs7]

I find the capsule phenomenal. Coupling is just fine if you ask me. The only further mod i did, which made it realy shine, is custom headbasket which got rid of all internal reflections. I got crazy smooth response from the mic. Without random dips in the high end. I can post measurements later. Sound samples as well. However it left me with very ugly mic. I use it as mono overhead on drums, so the looks are not that important.

Could we possibly get a photo of the custom head basket? - what did you do?

Thanks!

 

[kingkorg]

Could we possibly get a photo of the custom head basket? - what did you do?

Thanks!

Oh, you don't want to see that, it's ugly as %*#$

Not something i would recommend, simply because of the esthetics. Basically replacet the whole headbasket with one piece mesh, no mechanical support anywhere.

 

[kingkorg]

I don't thave that exact one here, but something like this.

 

[sr1200]

Hey, does anyone have the schematic for this mic (perc. 420) or previous iterations of it? Thanks.

 

[Khron]

Could it be any different from the Perception 200 / 220, just with an added pattern switch? The capsule bias generator is the "complete U89" even in the 200/220's (+/-60v, +/-12v).

 

[AUDIO FREQ]

Side B

what does the K30A do here? Can I replace a broken K30A here with a K170A or a 2N3819

 

[micolas]

Hi AUDIO FREQ

As I told you in the case of the cad glx3000, k170 has an input capacitance of about 30pF, much higher than the k30a, so the noise will increase a lot. I understand you have the LSK489, a dual monolithic jFet. Use half of it. (Or use 2n3819). If you readjusted its BIAS you would get good noise and low distortion

 

[micolas]

Could it be any different from the Perception 200 / 220, just with an added pattern switch? The capsule bias generator is the "complete U89" even in the 200/220's (+/-60v, +/-12v).

unfortunately the diagram is only found for the perception 200 series, but the jFET works similarly

 

[kingkorg]

Hi AUDIO FREQ

As I told you in the case of the cad glx3000, k170 has an input capacitance of about 30pF, much higher than the k30a, so the noise will increase a lot. I understand you have the LSK489, a dual monolithic jFet. Use half of it. (Or use 2n3819). If you readjusted its BIAS you would get good noise and low distortion

Nope, it will not. Capsule has passive capacitance that does nothing but create noise in the range of about 60pF, and 120pF in omni. That thing about fet input capacitance is overplayed. Matters more with SDCs.

 

[kingkorg]

what does the K30A do here? Can I replace a broken K30A here with a K170A or a 2N3819

Yes you absolutely can.

 

[micolas]

Yes, almost anything can be used, if you don't mind a bit more noise.
It didn't bother Neumann either, the M49V reissue has quite a lot of noise.
It seems that now I'm used to the Rode style, although in the 70s-80s I was happy to hear the background noise of amplifiers, preamps, guitar effects, AM receivers, etc.
I knew it was working, that it was living…

 

[AUDIO FREQ]

With being so happy with the 420 mod, I decided to buy another one for dirt cheap, but it was listed as broken.

Further inspection, I see it’s got holes in one side of the capsule, and some parts are missing. Can anyone help
Me out?

I know the transistor missing is a K30a. But not sure of the other parts.

Attached is photos.

 

[k brown]

With being so happy with the 420 mod, I decided to buy another one for dirt cheap, but it was listed as broken.

Further inspection, I see it’s got holes in one side of the capsule, and some parts are missing. Can anyone help
Me out?

I know the transistor missing is a K30a. But not sure of the other parts.

Attached is photos.

Sadly appears to be a case of DIY gone bad - the capsule damage looks like classic solder splatter.

 

[AUDIO FREQ]

Sadly appears to be a case of DIY gone bad - the capsule damage looks like classic solder splatter.

Yeah, and I noticed the previous owner took the inner mesh of the headbasket out....but for the price...and some help from my groupdiy friends, I think i'll be happy

 

[micolas]

Hi, AUDIO FREQ

And the other half of the capsule is damaged?
You can only make it cardioid, and the pattern switcher to adjust different Hi-Cut.
Post more detailed pictures of the inside of the mic to see what components are missing or destroyed.
Because you have nothing to lose, you have the opportunity to experiment, to really DIY. You can even choose a different capsule and circuit changes to get other flavors

 

[AUDIO FREQ]

Hi, AUDIO FREQ

And the other half of the capsule is damaged?
You can only make it cardioid, and the pattern switcher to adjust different Hi-Cut.
Post more detailed pictures of the inside of the mic to see what components are missing or destroyed.
Because you have nothing to lose, you have the opportunity to experiment, to really DIY. You can even choose a different capsule and circuit changes to get other flavors

 

[micolas]

AUDIO FREQ

If you want the same kind of sound, you can replace the damaged capsule with Takstar TSC-2 from JLI.

 

[AUDIO FREQ]

AUDIO FREQ

If you want the same kind of sound, you can replace the damaged capsule with Takstar TSC-2 from JLI.

Nice! I ordered one .

Any idea what the K30A does on this board? Or what the value of the capacitor?

 

[Khron]

The 2SK30A is the JFET that amplifies the signal coming from the capsule's front diaphragm. The capacitor (anything between 470pF-1nF) blocks the 60v bias voltage that's applied to the front diaphragm, from reaching the JFET's gate.

 

[micolas]

Audio Freq

If you still have a perfectly functional Perception 420, and an electronics engineer friend, I don't see what the problem is in repairing the defective one.