R/E/P > Bruno Putzeys (Designer) - Dave Hecht (Master Tech)

Audio Upgrades mic pre card

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Marcus Black:

Does anyone have experience with the Audio Upgrades mic pre cards ? Here: http://audioupgrades.com/products/products_pre_card.htm

Would I (not a tech but have good soldering skills and some basic common sense when it comes to electronics) be able to build a compact, portable, battery powered stereo mic pre out of these ?

Is it as simple as adding the 9-18V feed, mic iP and line out connectors and a gain pot ? What about +48V phantom, will it provide that although battery powered ?


You should need plus AND minus 9-18Volts (I'd go with plus/minus 18V to avoid the significant headroom penalty), and some means of generating +48V if you plan on using phantom. -This CAN be done using a square-wave oscillator (555 timer IC) and a diode/capacitor voltage multiplier, but beware... I don't recommend doing it that way, since you're building an oscillator near the most delicate of signals; -that's asking for trouble, though kit makers like PIAA do it, I think.

If you'll NEVER use phantom, you can probably take the opportunity to bypass the input capacitors, but Jim Williams will be the person to ask. -I have no idea if the output is balanced or unbalanced... but I'd guess unbalanced.

I have a 9V-battery powered 48V microphone phantom supply, in case you need such a thing.


Jim Williams:
There are 8 wires to it, balanced mic in, unbalanced line out, two wires to the gain pot and + - power and ground.

So it needs a gain pot, XLR inputs, + 48 if you want phantom power, + - 15~18 volts and an output jack. It draws 9 ma idling. Output current is 100 ma and it will drive 150 ohm loads.

Noise is -129.6 EIN with a 150 ohm source. That goes down with a lower input impedance so all noise is from the source. Input impedance is 4 k ohms. Output impedance is 56.2 ohms. Gain will vary from +13 to +60 db with a 2.5k reverse log gain pot.

THD+noise is .0006%. CCIF IMD is .0002%. Bandwidth is -1 db at 200k hz. Slew rate is 3000 v/us.

John Roberts {JR}:
I hope that's fast enough...  


Jim Williams:
I do have faster stuff if interested.  I can load up the High Speed mic preamp (rack version) with TI THS3061 current feedback opamps. Those run at 300 mhz and slew at 7000 v/us.

I also have those parts designed into a custom DAC designed by Michal J. of Mytek and me for Mark Levinson Labs using a BurrBrown PCM1704 DAC chipset, it sounds wonderful and very open and clear. I used the current feedback THS3061 as a current to voltage converter and as a 2 pole Sallen Key low pass bessel filter set to 65k hz.


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