Hi people,

As we all know Perception circuits are pure ripoff of u87, but don't sound like one because of the capsule. A fellow musician sent me vintage u87 to clean super dirty capsule, and two AKG P220 to try to match the sound to Neumann.

I found out by comparing and measuring the two, for some reason AKG has weaker HF attenuation, and brighter capsule. I just wanted to report that Neumann u87's C6 capacitor responsible for HF de emphasis network is super easy to reach and change.

By measuring frequency responses of u87 and P220 i came to conclusion that it needs to be changed to an 680pF capacitor, instead of original 220pF.  You get incredible replica in minutes. It's just that Perception has better bass response , because i t's bass roll off is weaker as well. I didn't want to touch that. I sent files of the shootout to the owner, he picked wrong one to be Neumann. Probably due to AKG's better bass response. Akg is louder, and has less noise. Modded even less due to more HF attenuation.  By googling i found that people report this cap to have up to 870pF in some Neumanns. This value gave me u67 kind of response.

No need to disassemble any boards, it's right in front of you when you open the mic. This should work for other Perception mics as well. Might be tricky for newbies to remove smd cap. 

One thing to add, AKG is built like a tank!

I'll upload audio files and frequency response graphs tomorrow.
Here is the cap we are talking about.
« Last Edit: November 16, 2017, 06:12:17 PM by kingkorg »


Khron

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

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.
« Last Edit: November 16, 2017, 06:31:20 PM by Khron »
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Great, i might suggest those to him as well. It's just that i finally i got my hands on an  u87 i can play with, and get some real world takes in my environment.

One thing that shocked me the most is that k67 is not that bright at all. Too many reported that it's actually brighter than most chinese copies, but nowhere near. I tried 797 capsule in u87, sounds just like stock Perception. Tried Neumann capsule in flat S circuit, totally fine to use without attenuation, and  not as bright as any replica i heard so far.  Now i get K.H. who gets rid of de emphasis, and his customers praise that mic. Neumann k67 is one amazing capsule.  So i was kind of chasing my tail the whole time.  The good thing is that when EQ is matched, curves, and other parameters follow pretty much the same path.

Roughly, i need -10db at 20.000KHz with 797 capsule to match stock u87 which has attenuation about -3.5db at 20.000khz. This is all with my setup, in my non calibrated, but consistent conditions. 

So i would sum up, that anyone building a clone blindly by the specs, and using any OEM capsule i have encountered (797, Alctron, AKG, Feilo)  without having the real deal to compare and re-adjust the circuit is way off specs.

MP guy claims his k67 is darker, but looking at his own graphs it's still about 3-4db hotter in high end than Neumann.
« Last Edit: November 16, 2017, 08:49:11 PM by kingkorg »

Khron

I'm so glad there still ARE people who are capable of reason and a modicum of science, and at least trying to stick to the scientific method :D As opposed to using vague mumbo-jumbo terms to describe all sorts of "intangible" qualities etc...
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Where's that like button?   :D

Khron

Without having a "classic" to use as a reference, i just went with my calibrated measurement mic, when i took some plots of my trio of CK12-equipped BM800's, and they looked remarkably flat, if maybe a bit bass-shy (but then again, the reference mic is -1dB around 12Hz or so :D )

PS: Back on topic, have you bothered with removing the internal layer of (finer) mesh? I remember that being pleasantly-surprisingly easy to remove.
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Gus

have you read this thread from 2012?
https://groupdiy.com/index.php?topic=47569.0


Hi Gus,

Yes i have, several times actually. Very helpful, although a bit confusing, as it was kind of tricky to figure out what was the point of the mod for very average modding hobbyist. I wasn't familiar with original schematic either. I get it now though. I think :)

 


ln76d

Hi people,

As we all know Perception circuits are pure ripoff of u87, but don't sound like one because of the capsule. A fellow musician sent me vintage u87 to clean super dirty capsule, and two AKG P220 to try to match the sound to Neumann.

I found out by comparing and measuring the two, for some reason AKG has weaker HF attenuation, and brighter capsule. I just wanted to report that Neumann u87's C6 capacitor responsible for HF de emphasis network is super easy to reach and change.

By measuring frequency responses of u87 and P220 i came to conclusion that it needs to be changed to an 680pF capacitor, instead of original 220pF.  You get incredible replica in minutes. It's just that Perception has better bass response , because i t's bass roll off is weaker as well. I didn't want to touch that. I sent files of the shootout to the owner, he picked wrong one to be Neumann. Probably due to AKG's better bass response. Akg is louder, and has less noise. Modded even less due to more HF attenuation.  By googling i found that people report this cap to have up to 870pF in some Neumanns. This value gave me u67 kind of response.

No need to disassemble any boards, it's right in front of you when you open the mic. This should work for other Perception mics as well. Might be tricky for newbies to remove smd cap. 

One thing to add, AKG is built like a tank!

I'll upload audio files and frequency response graphs tomorrow.
Here is the cap we are talking about.

Problem of perception series isn't the capsule brightness.
Except dc converter it's almost the same circuit as many other chinese "u87 with emitter follower".
Main problem is biasing circuit. Also these microphones have not properly set bias.
If you want to keep 2sk30, then use 5k trim pot (if i remember correctly) and connect 1G from gate to ground.
Now you should be able to use lower capacitance for de-emphasis circuit.
Changing most of smd caps makes huge improvement. Removing input capacitor also. Going step by step you can make really good mike ;) Internal mesh isn't the best for response but note that these capsules are truly fragile for any moisture and dirt.

So that was the reason for weaker attenuation. Thanks, great as always.

Here are the links:

Neumann u87:
https://app.box.com/s/qyfzrlfrbdphef5p2tylhcxun855u36g

Modded p220:
https://app.box.com/s/zrbpd1vd8mc0xpu4v3ig0id6d5prvx0s

Stock p220:
https://app.box.com/s/nrgajqonp29e16q38k70c159zvnt3g81
« Last Edit: November 17, 2017, 02:08:36 PM by kingkorg »


Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #10 on: November 17, 2017, 08:55:21 PM »
I guess i am done with this one. I sent bunch of files to the owner, side by side comparison, blind test, he picked AKG every time to be Neumann. AKG being flat in low end made him believe it had to be Neumann as it was ''more fluent in the low end'' translated from Norwegian. Now that characteristic high end from AKG disappeared,  he couldn't pick it easily out. And he is full time mastering engineer ;)

Now i am not pretending i turned this AKG into Neumann, as he managed to follow AKG in every example there is obviously a difference, and we can hear it. But to achieve this by changing that little bugger without spending 2 x 164 dollars for something like this and still not reach that curve, i'd say it's pretty cool.

https://microphone-parts.com/products/akg-perception-mod-kit   

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #11 on: November 17, 2017, 09:06:52 PM »
Dude, I agree. It's kinda blowing my mind.

Khron

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #12 on: November 17, 2017, 09:11:48 PM »
Well, if you have a product to sell, you've gotta create that demand SOMEhow ::)

You don't think they could've charged that much for replacing that one diddy little cap, do you? ;D Or that they could've been bothered with looking into the "why and how"s...
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #13 on: November 17, 2017, 10:17:45 PM »
Well if that 680pf is vintage, nos, egyptian paper in virgins blood, only two left in universe type of capacitor...

Khron

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #14 on: November 17, 2017, 10:36:49 PM »
Maybe it's just my sick and twisted imagination, but that sounds strikingly close to a (used) tampon or something... ;D ;D ;D

Well if that 680pf is vintage, nos, egyptian paper in virgins blood, only two left in universe type of capacitor...
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

Gus

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #15 on: November 18, 2017, 10:53:32 AM »
Hi Gus,

Yes i have, several times actually. Very helpful, although a bit confusing, as it was kind of tricky to figure out what was the point of the mod for very average modding hobbyist. I wasn't familiar with original schematic either. I get it now though. I think :)

first post is the adjusted v67, 2001 type schematic with easy changes using some of the same parts.
One can "improve" on this set of basic adjustments.
This was posted at a "adjustment starting point"to get people thinking about this type circuit.

reply 27 shows the LT spice sim of the circuit note the high end EQ section with the 220pf

I find it is useful to sim the circuit to adjust the EQ there are interactions with the selection of resistors and caps.

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #16 on: November 18, 2017, 12:05:29 PM »
Is there any place one can download mic LT Spice projects? Maybe you are willing to share? 

Khron

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #17 on: November 18, 2017, 12:16:33 PM »
Surely it's not THAT difficult to just throw a handful of parts into a schematic... ;)
Khron's Cave - Electronics - Audio - Teardowns - Mods - Repairs - Projects - Music - Rants - Shenanigans

abbey road d enfer

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #18 on: November 18, 2017, 01:06:31 PM »
... i came to conclusion that it needs to be changed to an 680pF capacitor, instead of original 220pF. 
That raises two questions:
  • Since the action of the capacitor is 1st-order, it should be very easy to compensate with basic EQ in the mixer/DAW; wouldn't it be a quicker (and more tunable) fix?
  • It would cost nothing to the manufacturer to change this cap; then, why don't they do it? I guess there are enough people who like the added sizzle...
Who's right or wrong is irrelevant. What matters is what's right or wrong.
Star ground is for electricians.

Re: AKG Perception P220 to Neumann u87 5 min mod ( p200, p100, p400, p420? )
« Reply #19 on: November 18, 2017, 03:46:33 PM »
That raises two questions:
  • Since the action of the capacitor is 1st-order, it should be very easy to compensate with basic EQ in the mixer/DAW; wouldn't it be a quicker (and more tunable) fix?
  • It would cost nothing to the manufacturer to change this cap; then, why don't they do it? I guess there are enough people who like the added sizzle...

1. I use mics i mod personaly a lot for live sound. Analog EQ curve doesn't match always this curve. In live situations i often have 3 or 4 band EQ with one parametric band, and i use it rather to be creative than to fix problems. If i use that one for deessing, i dont have much left.

2. In this case they just followed blindly u87 schematics, even with some blank spots. Like Piotr said, didnt even bother to bias the fet, so even with 220pF doesnt work as it should.