Got a noisy AKG C451E.

[PepsiFX357]

Hey guys,

I've got an old C451E that's getting a little hissy and crumbly. When my MXL did this, I just replaced every conceivable part I could and it came out sounding pretty good.

Anyway, I opened the C451E, expecting to see a million surface mount components, only to be surprised at how many through hole components they managed to pack into that little tube. Not to mention the microscopic wires coming off of the tiny transformer.

I managed to download a repair manual for it and I was wondering, are these hiss/crumbles cause by worn out caps? If not, what should I be replacing?

Thanks.

[Les]

We make a similar SDC mic.

Hissing, popping and bacon frying sounds are usually moisture/dirt related.
Electrolytic capacitors are suspect too as older ones had mean lifetimes of 1000 hrs or so. Their failure usually does not result in noise though.

If you could pm a schematic i can have a look.

Or drop it by. I'm just up the road a ways.

[Bill@WelcomeHome]

I'm not going to recommend the oven technique which used to be a common fix for the 451, but you might try putting the capsule in a mic bag with some silica gel.

as these mics age, the electronic parts are going to break down, and they are not repair-friendly. At CB,I we had piles of 451s and 460s, and when something went wrong with them the techs whined a lot.

[PepsiFX357]

Originally Posted by Les

We make a similar SDC mic.
If you could pm a schematic i can have a look.

Or drop it by. I'm just up the road a ways.

http://www.akg.com/mediendatenbank2/...4627a7b1f0.pdf

[Les]

Got it.

Pretty standard source follower/emitter follower/transformer circuit.

The electrolytics, particularly C9, are always supect on old gear due to short lifetimes. The FET uses voltage divider bias so if C9 was weak there could be some phantom supply noise transferred to the signal output.

At least it's bypassed with C8.

Most likely is moisture absorbing dirt around the capsule insulator and
FET T1 and it's bias resistor R2 as well as capsule bias resistor R1.

Since those components are mounted on the PCB dirt on the board is suspect as well. For that reason we fly those components...i.e. The high impedance leads are not soldered to the board.

the silica gel thing is fine, but careful cleaning of the components and board mentioned with denatured alcohol might be required.

This early leaded component version looks not so hard to work on unlike later surface mount.

Les

[PepsiFX357]

Thanks for the info. I'll try cleaning the board. Probably with a toothpick...lol j/k I'll find something to clean it with and see if that helps.

Would a hair dryer be something I could use after the alcohol cleaning, to remove moisture?

[kryssound]

Hi, I have a pair of AKG C 451 E for sale. They are used but in best condition. They are in original AKG case and with pair of A 51 adaptor. The price of botha are 400 euro. If you are interested write me on kryssound@email.cz