Condenser mic broken: no sound

pinksoir

Howdy,

My T-Bone SCT800 condenser mic has stopped working. I've had it maybe about 5 years at this point but it hasn't had that much use.

What happened is the volume coming from it dropped very low yesterday. If I turned up the input channel on my audio interface I could still hear microphonics coming from the mic if I tapped the casing, but there was nothing coming from the actual diaphragm. After a while, and for no reason at all, it started working again, though with peaks and troughs in the volume and eventually cutting out altogether.

Today I fired it up again and the same thing happened. When I leave it for a while it outputs volume, but after a while it cuts out but remains microphonic if I tap it etc.

I opened it up and all the solder connections are good. It runs on a 12AX7B and I don't really know much about tubes, but it looks like there is only one filament (I have no idea how many filaments there should be...) glowing when it's connected to power (phantom). Does this sound like it could be a problem with the tube? Or is it a problem elsewhere?

Thanks in advance.

madtheory

Impossible to say from here (on the internet). Easiest thing to do is borrow a working 12AX7 from something and see if that solves the problem. Second easiest thing is inspect the capacitors- you might have a leaking one, especially near the tube (due to the heat). Would be an idea to phone Thomann, see if the nice man knows there's an issue with these mics.

pinksoir

Cheers, I'll send them an email alright. I don't really have access to any tooobs to check if that's the issue. Caps look alright. It's just weird how it happens, a gradual volume drop until nothing... Weirder is that it comes back and then happens again.

madtheory

Waste of time emailing them. They do answer the phone though!

I could maybe have a look at it and see if i can fix it for ya if you want to send it to clare..

pinksoir

Thanks a million CQD. I might just do that depending on how I get on with Thomann.

@madtheory: I see... I'll try ringing them if I haven't gotten a reply by tomorrow evening.

pinksoir

They replied! Only to say it's out of warranty so I'll have to pay for shipping, repair and return shipping. Twas only 169 new so it' not really worth my time.

I did have another look inside though. It looks like there is some white residue where the tube socket is soldered onto the PCB. It also looks like the solder is not joined properly and looks burned. Sort of like it has become heated, melted and misshapen. Possibly the connection was not right to begin with. The caps all look good to me. This is really the only spot that looks questionable...

madtheory

I'd hazard a guess that the socket is not up to the heat the valve produces, hence the residue and the lifted solder joint. See if you can replace the socket (@valve mic experts-is there such a thing as a heatsink that would fit in there?) This is caused by a lack of stress testing by the manufacturer. That sort of QC is what you pay for with a more expensive mic.