A simple mod/fix for Altec lipstick mics / AKG C28s
Nov 21, 2024 14:22:53 GMT -6
ericn, EmRR, and 2 more like this
Post by vanguardaudiolabs on Nov 21, 2024 14:22:53 GMT -6
Had a repair client come in recently with some Altec 195a solid-state "lipstick" mics, aka "The Elvis mic".
They're the cutest little mics you'll ever see, and the inside of the mic itself is insanely simple - 5 whole components.
The complaints were two-fold - noise in the signal (which I tracked down to corroded XLR connectors in the PSU) and also a 900Hz resonance from handling.
Normally when I hear resonance I suspect one of two things - a microphonic electronic component, or the mic chassis itself…but I checked for both, and no dice.
I found the culprit in the spring inside the capsule. It is important - it ensures the capsule contact makes a good connection to the FET inside the microphone.
However, springs resonate (hence spring reverbs).
The fix was quite simple. I got some heatshrink to the proper size around a ballpoint pen with a heat gun. Then I transferred it over to the spring, measured the correct length for an assembled capsule, and put the heatshrink around the spring/contactor. (I also did it to the transistor casing, just because i was already there.)
The result is pretty significant - the handling noise/pinging resonance is completely gone.
Moral of the story - don't build a spring reverb into the high-Z section of your microphone (unless that's what you're going for).
Note that these capsules - the 29B and 28A - are used on the tube Altec lipstick mics as well. AKG actually made the capsules for Altec early on, so the C26/C28 capsules for the AKG C28 mic have a similar spring system.
It's a simple fix that doesn't even require you to fully disassembly the capsule/expose the diaphragm. Just removing the spring clip from the back of the capsule (WITHOUT letting it fly across the room) will get you the access you need. That and some 10mm heatshrink, a pen with the same diameter as the spring, and a hair dryer or heat gun will do the trick and gives you a MASSIVE improvement.
They're the cutest little mics you'll ever see, and the inside of the mic itself is insanely simple - 5 whole components.
The complaints were two-fold - noise in the signal (which I tracked down to corroded XLR connectors in the PSU) and also a 900Hz resonance from handling.
Normally when I hear resonance I suspect one of two things - a microphonic electronic component, or the mic chassis itself…but I checked for both, and no dice.
I found the culprit in the spring inside the capsule. It is important - it ensures the capsule contact makes a good connection to the FET inside the microphone.
However, springs resonate (hence spring reverbs).
The fix was quite simple. I got some heatshrink to the proper size around a ballpoint pen with a heat gun. Then I transferred it over to the spring, measured the correct length for an assembled capsule, and put the heatshrink around the spring/contactor. (I also did it to the transistor casing, just because i was already there.)
The result is pretty significant - the handling noise/pinging resonance is completely gone.
Moral of the story - don't build a spring reverb into the high-Z section of your microphone (unless that's what you're going for).
Note that these capsules - the 29B and 28A - are used on the tube Altec lipstick mics as well. AKG actually made the capsules for Altec early on, so the C26/C28 capsules for the AKG C28 mic have a similar spring system.
It's a simple fix that doesn't even require you to fully disassembly the capsule/expose the diaphragm. Just removing the spring clip from the back of the capsule (WITHOUT letting it fly across the room) will get you the access you need. That and some 10mm heatshrink, a pen with the same diameter as the spring, and a hair dryer or heat gun will do the trick and gives you a MASSIVE improvement.
