AKG Perception 200 / 220 mod & upgrade

[Khron]

Several motivations for this:

1) i had two K67-type dual-sided capsules left over from my pair of Devine BM600's
2) the Perception 200 has a U87A-type front-end and DC-DC converter (even the -60v rail, despite it being cardioid-only; i guess they use the same converter for the multipattern 400 / 420)
3) i had replaced all the ceramic and tantalum caps in two of my 200s at some point last year, with styroflex / polyester / poly-whatever caps
4) admittedly, Henry Spragen's audioimprov.com also served as inspiration 

I didn't want to give up the pad option (unlike Henry), so i took the idea of the pattern selection switch being on the back, as i've seen on some other cheapo mics. Fortunately, there was some room on the input pcb to shoehorn in a tiny 3-position switch
Yeah, i had to saw off a threaded stand-off for a screw, that was part of the chassis casting, but that screw needed to go anyway - the switch was gonna be there. It wasn't exactly structurally essential, anyway  :

I went with the switching arrangement as per the U87A schematic, adding in the series 1G resistor (scavenged from modding a couple of Rode NT1s) for the -60v, before the switch.

Admittedly, making the cutout for the pattern switch was the biggest headache. But between my Proxxon drill (think Dremel), a 25-30mm cutting disc and a 3mm cone-shaped solid tungsten carbide burr i got the other week, i managed  ;D Plus some elbow-grease (cleaning up the "finer details" with some small files)...

Also, since i was doing major rework, i pulled out the inner, finer mesh layer from the headbasket. I couldn't be bothered to dig out the piece on / inside the top dome, though 

Photo 1: input board, top view

 

[Khron]

Photo 2: input board, bottom view

The pattern select switch had two holes drilled underneith it, for the two "mounting tab" legs. I recycled some used desoldering braid, to hold the switch well-enough in place. It won't be fiddled with 24/7 anyway  ;D

 

[Khron]

Photo 3: new capsule wired to the input board

I used a resistor leg "in air", between the post-1G 60v rail and the pattern select switch.

 

[Khron]

Photo 4: DC-DC board, with the extra wire for the -60v

 

[Khron]

Photo 5: output board / front view

 

[Khron]

Photo 6: rear view, fully assembled

 

[ln76d]

Nice

I would change FET for 2n3819 or at least set bias for 2sk30a.
You could think about 10:1 transformer (3Uaudio would be good for this) - it's  much more usable for loud sources.
Note that this bastard only have polarisation voltage around 44-46V.

 

[ln76d]

BTW.

you didn't have to change most of tantals, because most aren't in audio path and works ok.
This one above transformer is output cap, much better would be use MKT cap from 1-4.7uF range than electrolytic, otherwise it doesn't have sense to change it.

 

[Khron]

Actually, i measured  about +/-55v, before the 1M series resistors

Tantalums, i only replaced the "main power filter" 10u one (stuck in a Panasonic FR 100u/63v),  and the transformer coupling cap (4.7u -> FR 18u/63v). Didn't bother with the source-bypass 22u one

I have four NTE10/3's (for now), but two of them i plan to use to KM84-ize a pair of my t.bone SC140s, and the other two, maybe with some groupbuy CK12s in BM800s

Anyway, the idea was that, since the U87-ish feedback / "tone control" was already implemented, as well as the full U87A DC-DC converter, i figured i'd increase the feature set of these, by reusing those two double-sided K67 capsules i had ;D

 

[rankot]

I have really enjoyed this thread, and, since I have P420, was wandering if I could upgrade my mike!

 

[Khron]

I don't see why not. I believe the circuitry is largely identical, apart from the pattern switching.

 

[rankot]

Any tutorial how to disassemble it?

 

[Khron]

I used a pair of needle nose pliers to undo the nut that's around the "pipe" containing the XLR connector.

Look up the website i mentioned in the first post.

 

[AUDIO FREQ]

Hey Khron, I don't think the images are loading anymore. Would love to check this mod you did out.

 

[Khron]

Hey Khron, I don't think the images are loading anymore. Would love to check this mod you did out.

Duly noted, I'll have to see where i might still have those photos. If not, I'll open one up and see if i can get some decent shots without complete disassembly.

 

[kingkorg]

Damn it, I miss In76d

 

[AUDIO FREQ]

Damn it, I miss In76d

What happened to him?

Thank you Khron! I will be waiting patiently

 

[kingkorg]

What happened to him?

Thank you Khron! I will be waiting patiently

No one really knows, but doesn't seem to be good saddly.

 

[AUDIO FREQ]

No one really knows, nut doesn't seem to be good saddly.

Nut?

 

[Khron]

Nut?

*But