USB mic to XLR/phantom?

[k brown]

Anyone ever mod a USB mic to XLR phantom power operation?

Just comitted to a Samson C03 on eBay and didn't notice it was the USB version.

I was planning on replacing the capsules with better ones.

 

[Khron]

Looks like the USB version has the same features as the "normal" one. Best case, it has all the same circuitry, and just an additional board with the ADC/USB interface, and maybe a boost-converter to power the analog stuff?

If not, it will entirely depend what the analog circuitry is. You might get away with just a couple resistors and a zener, or it might need more involved modding, or a new circuit altogether.

 

[k brown]

It will be very interesting to see what's in there . . .

 

[Khron]

Looking forward to photos!

 

[k brown]

Gurr-on-teed!

 

[k brown]

Looking forward to photos!

As expected, two TSB160A in there. That's an '072 in between the 1G resistors; no FETs.

The top board under the capsules has only the switches, no other components.

The third chip, in the middle of the mic board is a quad analog switch (HEF4066BT).

Audio out to the digital board is from MC33178 op amp.

Would appear that all the USB/AD stuff is on the separate board, and what looks like only gnd, V+ and audio connection to the mic board via that 4-pin connector.

Exhibits none of the 'extra-crispy-ness' of the 160A, so must have some simple EQ in there. The audio sounds good, but there's lots of digital chirpies and random hash going on low in the BG. Probably poor filtering on the digital board.

 

[rock soderstrom]

Interesting, I would have expected it to be a similar design to the T.bone SC450 USB, but it's not.

Inside the t.bone SC450 USB - Gutting party for mic DIYer?

It is also stupid that you can not simply replace the USB by an XLR plug.

It is quite dusty in the microphone.

 

[k brown]

Yeah, the internal casting is shaped for the USB jack, and can't accept an XLR.

Good news is, the audio out op amp is rated for 600 ohm loads, so should be able to drive a decent length of cable with impedance balanced out. The USB board is feeding the mic board with 4.5v, so should be able to just connect to a small box containing three 1.5v batteries, and the phantom blocking caps and impedance balancing parts.

Yes I could build a 48v > 4.5v dropping circuit in there, but I'm too lazy; especially since this mic isn't likely get very frequent use.

 

[Khron]

... Or an 18650 lithium cell (or even 21700 if it fits), and a small powerbank board (5V output, battery supervision/protection/charging)

 

[k brown]

... Or an 18650 lithium cell (or even 21700 if it fits), and a small powerbank board (5V output, battery supervision/protection/charging)

I'm afraid of over-volt; doesn't look like any regulation on the mic board. All three chips can handle up to 15v, but I don't know about all the passives; smallest electro is 10v, but the chip caps? Probably worrying about nothing.

Would probably have to use 'C' batts; AA might not last long enough to be practical.

 

[Khron]

Overvolting of what, and from what? Powerbanks are those doohickeys with one or several lithium cells, and circuitry that puts out 5V out one or several USB connectors, to charge your phone or whatever.

An ("oversized") example:
https://khronscave.blogspot.com/2021/09/78-focusrite-saffire-6-usb-20-modding.html?m=0
And a much more low-tech and brute-force approach (which was actually the very first post on my blog ):
https://khronscave.blogspot.com/2017/04/m-audio-fast-track-mk1-gain-and-18650.html?m=0
Both still working fine to this day

 

[k brown]

Dumpstered.

Getting the audio out before all the USB junk was easy as pie, but even with much better capsules in place the sound was crap; not exactly sure why.

 

[Khron]

"Crap" is a bit vague...?

 

[k brown]

OK -

Like shellaced cardboard.

Though I didn't trace the circuit out fully, I suspect there's some EQ tailored for the TSB160As used, so better capules are getting mangled by it.