AKG C3000B 5 min mod - Awesome mic!

[kingkorg]

Another great mic ruined by stupid internal EQ implementation. About 5db boost at 15k.

This mic appeared in my local adds for 50 bucks and I just had to give it a go. Measured, tested, bright - OK.

Opened, circuit measured, and it revealed this stupid eq curve by injecting signal.  Found capacitor guilty of this, removed it, and now it sounds beautifully! I got about +5db output as well.

I am kind of surprised as this mic was modded before, by Scot Dorsey, whole circuit changed I believe. It got me puzzled, no one discovered that it was this simple? Otherwise I see no need for changing the circuit, works fine, clean, low thd. Beautifully sounding capsule by the way. No sign of 10k+ hype. Since c214 has the same capsule, and boost above 10k i suspect similar bull is done to it as well.

This is the cap that should be removed.

 

[kingkorg]

Frequency response of the circuit (not acoustic microphone mesurement) before mod. Now it's flat.

 

[kingkorg]

And acoustic frequency response before and after, taken in my controll room, 0.5m from the speaker.  Not perfect but shows exactly what is achieved.

Peaks and dips in modded look suspiciously similar to graphs published on Recording Hacks for c414 XL series. The capsule itself even being single sided electret looks remarkably similar to XL II model. How it's terminated, and tension ring having hole at exactly same spot.

Looks exactly like this one, only single sided. And it is ''teflon'' capsule.

http://www.saturn-sound.com/Curio%27s/akg%27s%202072%20z%200009%20capsule.htm

 

[kingkorg]

Here's schematic. If i am not mistaking i removed C303. It says +9db at 6-20k!!!

 

[kingkorg]

Reading articles about Dorsey's mod i can not help but think that he didn't even realize this was an electret. I can imagine he opened it, and saw SMD and just decided to rip the guts out. He applied additional polarization voltage to the capsule and according  to answer from AKG to Rossi's question in another topic, the capsule got stiffer, changed resonant peak and became another sort of peaky capsule. Could be why Dorsey described it still bright after mod. Damn, is it possible?

Another thing about this mic is that it has magnificent low end, so he either messed it up with this mic, or the capsule/microphone he was modding was way different.

I asked AKG about applying an external voltage to an electret capsule. They were very friendly (Austrians) and gave me a surprisingly detailed answer from their mic developers. The gist of it is that an external voltage (of the same polarity)...
- adds to the electret voltage and thus
- increases the sensitivity;
- the diaphragm tension increases, thus
- the resonance frequency will be higher
- sound change also occurs due to some other effects relating to friction, increased stiffness and deformation of the diaphragm.
- some loss in low frequency response if the surrounding environment (I suppose that means the inner resistance of the voltage source + resistors) becomes lower than 10 Gohms

The AKG guys found Dorsey's approach quite interesting and innovative and said they were pleased with this kind of customer input.

I still wonder about the very high FET voltage, though.

I also wonder how much sound change could be had by just applying the phantom voltage to the capsule. That would be a very cheap and easy mod except for sourcing a gigohm resistor.

 

[john12ax7]

Would this be the same for the original c3000 (not b)?

 

[kingkorg]

The one with pattern switch?

If so, you would have to open it and check it out. Quite easy to disassemble.  If that cap is there, just remove it. I can't see how one could benefit from that kind of curve baked in with any kind of capsule.

Service manual says its the same thing with or without B at the end. However C2000b has the same pcb but  that capacitor is missing stock.

 

[ln76d]

Nice catch

It's C303 on the schematic.

There's more things to change

All AKG LDC from 90's to current production can be modified and can sound pretty decent.
All have bugs inside the circuits. Solidtube, C414's, C214, C314, C2000-C4500, Perception seriec etc.
In each one circuit sucks. "Teflon" capsules permanently polarised or electret are really great but need to work with proper circuit.
Devil's in the details.

C3000 is a differnt circuit than C3000B. First was only discrete, second use opamp,

 

[kingkorg]

Investigating AKG documents i found out that C4500 used this same capsule but without  EQ circuit. So i used my Photoshop skills to overlay flat circuit response of this capsule in C4500 (modded c3000b in furter text) over published C414 XL II frequency response chart. They are scary similar.  Having in mind body/grille differences...

Red curve is c414, blue is C4500 (modded c3000B)

 

[kingkorg]

And published curves of stock C3000B(blue) vs C414 (Red)

 

[john12ax7]

Another common mod seems to be the windscreen which also supposedly helps the sound.

 

[kingkorg]

Some more pics of the capsule. I am really excited about how the mic sounds now. It is very rich in low mids. I can't recommend it enough.

Measured thd and it is very, very low. With 300mv injected its 0.01 @1khz and it's all second harmonic. Best of all stock mics i ever owned.

It is more quiet than my Shure ksm44 which is really quiet. I wonder if i just got lucky with this mic, or if they upgraded it at some point.

I had very bad luck with Akg 535 for example, and it had totaly different circuit than specified in any schematic. FR was terrible.

I have four Røde nt3s and oldest one i have used heavily as main mic for 10 years has 5db more low end and way warmer high end. Same exact capsule, they simply change during time. A lot of screaming, spitting into it, blowing.

I had a Neumann u87 with back membrane punctured last week. It had better low end response than two other Neumanns i had before, other stuff being the same. Same age, models. All come from Norwegian state TV. And it was not subtle 3-5 db.

Baybe i just got lucky with this one, but i am desperate to find another one to make a pair.

 

[kingkorg]

Back.

 

[tzu]

Hey Kingkong thanks so much for posting this.

I am very new to this kind of thing so was wondering is it just getting rid of c303? do you need to bridge it or anything like that (excuse me if that is the wrong terminology)

cheers

 

[kingkorg]

Nope. Just remove it. It disables eq circuit, and that's it.

 

[tzu]

Thanks so much for confirming and once again for sharing this knowledge!

 

[micro1_de]

Hi Kingkorg,

I have a AKG 4500. You wrote: " All have bugs inside the circuits. Solidtube, C414's, C214, C314, C2000-C4500, Perception seriec etc.
In each one circuit sucks. "Teflon" capsules permanently polarised or electret are really great but need to work with proper circuit.
Devil's in the details. "

What do you recommand for this mico?

Thanks for your answer.

Regards Reiner

 

[kingkorg]

Hi.

It wasn't me who wrote that, it was ln76d.

I didn't find anything else that bothers me in c3000b i even bought one more. Could be diferend editions, but these i have work awesome. IC is Burr Brown btw.

 

[micro1_de]

Hi 

sorry!

My mistake.
Reiner

 

[MagnetoSound]

Useful info on the (4!) different variants of C3000 (B) ...

http://www.silentway.com/recording-tricks-akg-c-3000-mic