VanguardAudioLabs
Well-known member
Had an Altec M49 set (539a PSU and 29B cardioid capsule with a 195a mic base) in for repair from a client. Had to fix significant resonance on the capsule springs - that's a whole other post! - but thought I'd mention something here. The Microphone input connectors were extremely corroded and cracked and were the source of significant sporadic noise. I tried several rounds of Deoxit, but no dice.
Fortunately switchcraft makes the QG series of XLR inserts, and the QG3F happened to fit perfectly…or nearly so. https://www.switchcraft.com/qg-3-pin-female-xlr-insert-standard-latchlock/qg3f/
I had to mark new holes and tap them to secure it to the PSU frame - chose M2 because that's what i had on hand. Metric threads on an American product - don't tell anyone or I'll get excommunicated from the USA
the other modification was using a rotary tool and slightly enlarging the gap for the release lever on the XLR insert. it was a touch wider and deeper than the original part.
After that it was a perfect fit and noise-free power supplies (they'd been recapped previously by someone else).
Some photos:
Zoom in for the cracked connector plastic. Note the corrosion around it as well, which made plugging in the XLR cable extremely difficult.
You can see how badly rusted the internals are, and the release lever was barely functional and grinding. The screw on the left was also rusted and took some persuasion to get loose. That's also how it was secured.
Replaced and ready to roll. These were a lot of fun to work on - so tiny!
The spring resonance on the capsule plunger was also extremely loud - not a good idea to design a 910Hz tuned spring reverb into your hi-Z section. Got that damped as well in both capsules and now both mics produce a "thunk" when tapped, instead of ringing like wedding bells.
Fortunately switchcraft makes the QG series of XLR inserts, and the QG3F happened to fit perfectly…or nearly so. https://www.switchcraft.com/qg-3-pin-female-xlr-insert-standard-latchlock/qg3f/
I had to mark new holes and tap them to secure it to the PSU frame - chose M2 because that's what i had on hand. Metric threads on an American product - don't tell anyone or I'll get excommunicated from the USA
the other modification was using a rotary tool and slightly enlarging the gap for the release lever on the XLR insert. it was a touch wider and deeper than the original part.
After that it was a perfect fit and noise-free power supplies (they'd been recapped previously by someone else).
Some photos:
Zoom in for the cracked connector plastic. Note the corrosion around it as well, which made plugging in the XLR cable extremely difficult.
You can see how badly rusted the internals are, and the release lever was barely functional and grinding. The screw on the left was also rusted and took some persuasion to get loose. That's also how it was secured.
Replaced and ready to roll. These were a lot of fun to work on - so tiny!
The spring resonance on the capsule plunger was also extremely loud - not a good idea to design a 910Hz tuned spring reverb into your hi-Z section. Got that damped as well in both capsules and now both mics produce a "thunk" when tapped, instead of ringing like wedding bells.
