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Audio Testing of new SC-1 Solo prototype.... SUCCESS!!!
DIY DC-DC Converter PSU working!

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SC-1mk2 and SC-1mk500 Mic Preamp Kits



SC-1mk2 Preamp Kit  SC-1mk500 Lunchbox Preamp Kit 
 Thursday, June 05, 2008
Thursday, June 05, 2008 11:11:54 PM (Central Daylight Time, UTC-05:00) ( )



Finally finished wiring the preamp to XLR jacks. Connected to my RP8 active monitor, hooked up a 150-ohm terminated XLR at the inputs to simulate a mic connected, then crank up the gain and volume to max.... and listened....

No hum, no RF buzz... even at 72dB gain setting, and even though it's running and powered by a DC-DC converter PSU and wall wart. Smile

As you can see from the photo, the XLR jacks are right beside the DC-DC converter PSU, and the wires are LAID ON TOP of it!

I am so pleased and happy with this... I can now breathe easily. Oh this is going to be great!!!!

Connected the SC-1 Solo prototype to Channel 1 of my MOTU 828mk2, set the SC-1 Mic Pre gain to 72db max, volume to max, input XLR terminated with 150-ohm (to simulate a mic) and recorded the resulting audio in DP 5.

LISTEN TO THE AUDIO SAMPLE
http://www.fivefishstudios.com/audio/SC1Solo-NoiseTest.mp3

Okay... that noise you're hearing is with the preamp set to 72dB gain.. 72!!!! And volume at max. This is not "hiss" recorded with shorted inputs, or minimum gain...

And to make it even more mind-boggling... all this powered from a WallWart PSU... and a DC-DC converter.

And to visualize what you're hearing...





I am personally amazed. Smile


UPDATE: The spike you see up is most probably 15.734 Khz.... i.e. TV Horizontal Scan Frequency interference. (I do have a 20" TV a few feet away, yeah the old CRT kind of TV).


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 Wednesday, June 04, 2008
Wednesday, June 04, 2008 11:08:43 PM (Central Daylight Time, UTC-05:00) ( )


Oh yea!!! working sweet.

A few misadventures while building it... was in too much of a hurry... I inserted a diode backwards in the 48V section, which effectively shorted the thing... the IC chip and board got a little warm... but no damage.

Desoldered it, and put in a new one, (made sure to install it properly) and now the 48V section works perfectly!

Found a little error in my header jumper... my original intention was using a jumper to activate or deactivate the 48V section (in case the user doesn't need it, will also conserve battery power)... but I miswired it so now the 48V section is always available and it's the split psu section that can be disabled or enabled... dumb backwards! I'll fix this on the next PCB revision.

Connected the 12VDC wall wart... measured 27Volts on the 48V section, adjust the onboard trimmer for 48.05 Volts... and now we have a working +/- voltage rails plus 48Volts output.

But yea, everything is working great. See the little LED lit up? It's a sign that the future looks bright.

I just need to continue to populate the board and complete the testing.

UPDATE:



Finally finished building the first SC-1 Solo prototype using the latest PCB design, and latest DC-DC Converter PSU design.

I haven't passed audio through it yet, but I did some power up testing, measuring voltages, etc... everything looks perfect!

I need to get some sleep. Will do audio testing later.



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