Condenser Mic Innards?

ashcat_lt

Well-known member
Anybody know if/where I might find a fully assembled circuit board for a condenser mic at a reasonable price. It seems like the kind of thing I'd be able to find on amazon for like $5, but I can't seem to find the right search terms. Everything I come up with is for electret elements expecting like 5V power. I don't actually need to polarize an element, but I do need a small amplifier that can power from 48V phantom without exploding and preferably with a balanced output. It is for a DIY project, but I really don't want to DIY the circuit itself. Any hints or help would be appreciated.
 

Tadpui

Well-known member
Would one of the BM800/BM700 mics that sell for under $20 do the trick? Then you'd have the board and a body and a capsule to play with.

I can verify that the Neewer NW800 works on 3v through 48v, and it comes in at about $19. And given its sound quality, you'd be doing it a favor by destroying it and harvesting it for parts.
 

ashcat_lt

Well-known member
I appreciate the suggestion. I actually had looked at those, but honestly it's a bit more than I want to spend. I'm not sure the body itself will actually work for me, the element is useless and that PCB is a heck off a lot bigger than I really want or need. I was also kind of unsure if it was really a balanced output. They are cheaper than what I'm seeing for transformer alternatives, though...
 

ashcat_lt

Well-known member
Yeah, it's a moving coil dynamic, but the element needs some gain, and I'd rather get that at the short end of the cable, and I want real balanced output, and I'd rather stay away from transformer, and I don't want to deal with any special power supply or batteries.
 

arcaxis

Active member
Not sure how it would work out using an amp from a condenser mic. The frontend is usually a FET and biased with 1Gohm resistors, but you might be able tap into the next stage after the FET.

Something close to the image below is what you want...
 

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ecc83

Well-known member
Sorry Mark but TL072s are going to be as noisy as frick with a dynamic capsule.

In fact there are very few op amps that are quiet enough. The NE5534 or the LM4562 (dual amp) might just about be ok but usually you need a very low rb transistor stage afront the op amp. As ever, seek out Duggy Self's Small Signal Audio Design and adapt one of his circuits but you will struggle I think to find all the bits much under 20 quid?

Dave.
 

ashcat_lt

Well-known member
And if I value my time...

I have a couple borked condensers I'm going to run some tests with before I actually buy anything. It's actually pretty cool just raw, "pseudo balanced" across an XLR cable, but it needs the preamp cranked, so the noise creeps in. If the circuit in the mic and "proper" balancing isn't significantly better, it's maybe not worth it, though an active stage is perfect isolation from preamp impedance so we can know the mic itself will sound the same no matter what it's plugged into.
 

arcaxis

Active member
Sorry Mark but TL072s are going to be as noisy as frick with a dynamic capsule.

In fact there are very few op amps that are quiet enough. The NE5534 or the LM4562 (dual amp) might just about be ok but usually you need a very low rb transistor stage afront the op amp. As ever, seek out Duggy Self's Small Signal Audio Design and adapt one of his circuits but you will struggle I think to find all the bits much under 20 quid?

Dave.

Wasn't suggesting to use specific components, simply that the design would be similar to get from unbalanced to balanced and function off phantom without getting into a transformer on the output to couple and balance.
 

Ponder5

Member
It's my understanding that more than a few condensors require nothing like 48V to operate. Of course, buying the mic, they'll require phantom power, but that's standardized, so they're built for it.

Besides, you're only really looking for a little bit of biasing voltage with nearly-trivial current with that tiny of a job, if you're dealing in solid state and not tubes. (a moment of silence <LOL>)

So sure, it could be the elements you've found are rated for 5V (minimum) but will easily handle 48V because that's what the designer/manufacturer knows that they'll see. Drawing next to no current, it's easy to live in a higher voltage environment.

Well.. unless they're specifically for USB mics, i guess.
 

ecc83

Well-known member
Wasn't suggesting to use specific components, simply that the design would be similar to get from unbalanced to balanced and function off phantom without getting into a transformer on the output to couple and balance.

Ah, right. Well yes the circuit is fine for balanced drive. Use an LM4562 and a couple of suitable transistors and it could be fine. Capacitor mic amplifiers are of course optimized for a very high source impedance and an input 10-20dB or more above a dynamic capsule.

Dave.
 

Toastedgoat

New member
Would the assembled board of a MXL990 work? I’ve replaced all the innards of these mics, the original boards are all intact.
 

ashcat_lt

Well-known member
Well I sure do appreciate it. I still haven't gotten around to trying with the one I already have. If that one works, I'd imagine about any one would. I'm kind of looking to make more that a couple, though, and was hoping for a more reliable source than just donations and scavanged components. That's not saying I might not hit you up in a while. :)
 
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