414 EB with brass capsule. Poor bass response and now it's making noise

[Double G]

I recently purchased a brass capsule 414 EB off Reverb.

For a week or so before I made the purchase, I was loaned an original EB to make sure I really liked it.

When I received mine and compared it to the loaner, mine was considerably lacking in bass response. Also, when setting the low pass filter to 75Hz, it caused an ugly bump in the low end. The 150Hz position didn't cause a bump and the loaner EB did not exhibit the same behavior regarding its roll off.

I had it checked by a reputable tech and it checks out. The capsule is legit and has never been taken apart. The components are also original, aside from the switches, which must have been replaced at some point because they're black instead of white.

The tech did a visual inspection of the capsule and the electronics. The diaphragms have spit stains on them and the rear diaphragm has a little bit of gold missing around the center and the edge is rippled a little in one spot. I could see the missing gold but the rippling could only be seen with a magnifying lens. The loaner EB had near identical levels of spit stains. Both were fairly dusty and the tech cleaned the capsules with a very soft brush. That was the extent of the inspection.

A few days later, I brought my EB to the studio and compared it to their nylon capsule EB. Theirs too had a noticeably better bass response. The studio's techs were kind enough to check it out. While having the mic plugged up in their shop, to demonstrate the roll off bass bump, the mic started to make popping and scratching noises. I left it with them and the next day they told me the roll off switch was the reason for the noise and it needed to be replaced. I asked them if they could take the roll offs out of the circuit because I'm never gonna use them anyway. They said they could do it and it would have no ill effect on the mic.

They removed the roll offs and we checked it against their nylon EB. Their EB still had more bass and had considerably more output than mine, which I thought was odd because my EB had slightly more output than the loaner. One of them also did the hot breath test on the capsule and it passed. So I went home and checked it on my preamp, that I had used it on for many hours. The output was the same as before but I noticed there was a little bit more low end coming out of the mic, compared to my last test recording.

Then the mic started to make the popping and scratching noises again. I switched the polar patterns around. That didn't stop the noises. Then I engaged the pad, and not only did the noises not stop, they also stayed at the same level. I imagine that if the capsule was causing the noise, engaging the pad should've lowered the noise, right?

What I'm wondering is, could the lack of bass be the result of there being something wrong with the electronics? And even though the pad didn't lower the noise, does that necessarily mean that it couldn't be the result of the capsule starting to fail completely?

 

[pasarski]

I would check the 33uF tantalum coupling cap first. I'm not sure but it indeed seems like it's not the capsule failing, which would be nice because it's by far the most valuable part in the mic.

 

[Voyager10]

I would start by connecting a signal generator to the preamp input (R1/C1 junction, on this schematic) and measuring the response. Just comparing the output levels at 1KHz vs 30Hz will do initially, if there's more than 1-2dB drop the electronics is probably at fault, and it will be much easier to debug on the test bench rather than via listening tests.

(It won't hurt the capsule to inject a small signal, e.g. 100mV, at this point).

 

[Double G]

The techs at the studio replaced a diode and a capacitor. The low end improved and the noise (largely) went away. But the next day, with the mic being in use for about 5 hours, it made a popping sound twice within that time.

I ended up sending the mic to Richard Land, certified AKG repair specialist. I've had it back for a week or so. Over the phone, he told me exactly what he did but I didn't write it down so I don't remember specifically what components he replaced.

He replaced both the pad and roll off switches. He also replaced some of the capacitors and the diode that the studio techs put in.

He completely fixed it. No noise at all and I've used it for a collective 15 or so hours so far. The frequency response is remarkably full and balanced now. It sounds better than the loaner that I had because that one had a dip in the mid range, it wasn't bad per se, but it wasn't ideal.

It's hard to believe a capsule this old can sound so good, considering it's said to not age well, and likely wasn't handled with the greatest care over its lifetime. I am very familiar with real C12s that are in great working order as well as real 251s. This is my first venture into 414 brass capsule land, and I'm beyond impressed.

Too bad AKG doesn't make them like this anymore.

 

[garp]

AKG , is not for sure, but Group DIY did it ! For a ridiculous fraction of the price of the original you can build a wonderfull clone that sounds as good (if not better !) than the original ones on the market.