AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )

[Khron]

Between this:

http://cdn.recordinghacks.com/images//mic_extras/akg/perception-420-circuit.jpg

and what i've seen in my own Perception 200's, it's gonna be on that horizontal board that also carries the switches.

I've also annotated Henry Spragens' Perception 220 schematic with the values i measured on my 200's (i didn't bother measuring the pad cap on mine - that's the only difference between the _00's and the _20's) - see attachment.

It'll be an 0805 ceramic capacitor, on the bottom of the input/switch board. It may very well be easily accessible even without removing the board(s) from the chassis, i think it's near the edge.

So where would the smd cap be located on a perception 400 version? please help,

 

[Khron]

[Disclaimer] Due to the one-attachment-per-post limitation here, i'm forced to double-post.

You're in luck, i found some documentation photos i took while modding my 200's (multipattern'ed them, with dual-diaphragm capsules).

That high-frequency-attenuation cap will be nearest to the front edge, right in the middle there - the silver-looking styroflex cap, in this photo.

 

[rockinrob86]

I'm a bit confused...

AKG perception would be similar to U87 if not for the biasing  OR Perception needs higher cap value and then to be correctly biased?  or it needs new FET/biasing and the capacitor?

If these are similar it would be significantly cheaper than a scratch build u87 - I've been thinking about building another because I use my DU87 build all the time.  It's my go to, "uh, let's do this, where's a mic?" mic because it always works and sounds good!  May have to pick up a couple P420s...

 

[Khron]

It's got nothing to do with biasing, but with the compensating EQ / filtering

http://audioimprov.com/AudioImprov/Mics/Entries/2014/2/7_Mic_Electronic_Eq_Pt.1.html

In the linked article, the capacitor this thread is (mostly) about is that 120pF C10.

Or rather, to be more specific, it needs a larger value cap with the stock biasing to reach  a U87-ish response

OR

(perhaps) The stock cap makes reaching that same curve possible by altering the bias.

I stand to be corrected on the 2nd option, though The 1st one is what kingkorg did, so it's quite literally "tried and tested" ;D

 

[joelgurule]

wherenis this 220pf cap on a 400, its not the same as a p200

 

[Khron]

Could you maybe attach a photo of the underside of that switch / input board (in case you're not able to trace out the circuit yourself)?

wherenis this 220pf cap on a 400, its not the same as a p200

 

[JulesP]

Hi, all. I am fresh member.

As I am already stuck with a pair of P420, I would beg any of you  to the very confusing cap location change, as it is very clear on the PERCEPTION 420 , but rather perilous to identify on the completely surface mount of the P420 version, I would beg for a clear picture and identification of the location of the cap needed to be changed, in the simple mod already discussed with a 680 polystyrene cap swap.
I can't find any reference pic anywhere that points the one in need to be changed,
I am far from being an electronic wizard, but can handle pretty delicate soldering operation.

As they are pretty useless as now ( Very peaky and harsh on all acoustic instruments), I would live very happy at any simple amelioration and improvement.

I hope someone can post the exact location on the P420.

Cheers.
And thanks in advance, if ever someone can,

 

[Khron]

See my last post here

Hi, all. I am fresh member.

As I am already stuck with a pair of P420, I would beg any of you  to the very confusing cap location change, as it is very clear on the PERCEPTION 420 , but rather perilous to identify on the completely surface mount of the P420 version, I would beg for a clear picture and identification of the location of the cap needed to be changed, in the simple mod already discussed with a 680 polystyrene cap swap.
I can't find any reference pic anywhere that points the one in need to be changed,
I am far from being an electronic wizard, but can handle pretty delicate soldering operation.

As they are pretty useless as now ( Very peaky and harsh on all acoustic instruments), I would live very happy at any simple amelioration and improvement.

I hope someone can post the exact location on the P420.

Cheers.
And thanks in advance, if ever someone can,

 

[abbey road d enfer]

As they are pretty useless as now ( Very peaky and harsh on all acoustic instruments), I would live very happy at any simple amelioration and improvement.

Why don't you just EQ out the excess treble? Contrary to what some seem to believe, the result is the same, as long as your EQ is flexible enough.

 

[22evan]

Hi all, im new to this world of modding. I was wondering if this mod could work with the new akg p120, it says in recordinghacks that the new one has a true condenser capsule...

 

[kingkorg]

No way of knowing unless we see some guts pics, or schematic.

 

[22evan]

Thanks for the reply, in the future i will get one and post pictures here, who knows... maybe  it work maybe not hehehehe,

Have a great weekend and happy recordings!

 

[mjrippe]

Updating this with pics of a P420 I modded for a client.  First photo shows location of the cap.

 

[mjrippe]

Second photo shows how I tagged a 470pf cap across it.  Client thought it made the mic go from useless to useable.

 

[mateus]

Indeed, you could really hurt someone with those chunky bodies, i have three 200's myself (and neither cost me more than 100eu ).

Two i've re-capped (replaced the ceramics with film / styroflex caps, and the tantalums with electrolytics), slipped in dual-diaphragm K67's (out of a pair of Devine / iSK BM600's), and included a pattern switch.

Haven't gotten around to applying those mods / upgrades to the third one, but this EQ mod is a welcome addition to the "to do"-list! Especially with the franken-K67 i made from the active halves of the capsules left over from the above-mentioned ones ;D

PS: For completing the title, the mics that share that "platform" are the 100, 200, 400, 220, 420 and 820. The 820 is a tube mic, so it's not 100% certain it has the same tone-shaping feedback circuitry there, and the 120 has an electret capsule.

Heyas, I was reading tru the thread again and got curious about the switching of the tantalums for electrolytics, could someone educate me in this matter?

Cheers!

 

[Khron]

Unless it can't be helped, i would. For peace of (my) mind, if not for longevity or reliability. "Sound" has zero influence over that decision, for me.

 

[abbey road d enfer]

Second photo shows how I tagged a 470pf cap across it. Client thought it made the mic go from useless to useable.

IINM, this cap just crudely rolls off treble. So, your satisfied customers don't use EQ?

 

[mjrippe]

IINM, this cap just crudely rolls off treble. So, your satisfied customers don't use EQ?

My client asked me to perform the mod they read about here. I did not tell them to "just use EQ" and they did not tell me how to do my job.

 

[James-F]

Matija, to be clear - one thing is that unbiased fet makes a nasty repsonse - other thing is that the whole bias circuit don't fit deemphasis network - that's why it only works with higher capacitance.
If you will change biasing to the same as in U87, then it will work with 220pF.
Left - chinese biasing, right - U87

Thank you @ln76d !

Yep, first thing to be done in chinese clones of U87i or U87Ai is to remove the castration resistor that elevates the JFET and cuts 6-10db of gain from the feedback loop and changes the correct EQ operation, I'd do that before changing any feedback components.
And of course rebias the JFET Drain to VDD/2.

Why did they put that resistor in the first place?
Why reduce gain in that stage?

 

[Khron]

Why did they put that resistor in the first place?
Why reduce gain in that stage?

I may very well be wrong, but my hunch is to not end up with too high a sensitivity.

Keep in mind, the original uses a 10:1 step-down transformer on the output. These JFET+PNP circuits use a 2:1 or lower ratio output transformer, resulting in a higher output for the same physical SPL seen by the capsule.