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NEW!!! SC-1 Mic Preamp Kit
Status: Under Development:

Rev1.00 PCB Prototype #001 Testing

Stuffing parts on the prototype #1 PCB, i.e. the PCB with the backwards selector switch. I want to get this working first, before I order another prototype for the REV 3.00 design.

Here's a photo I took of a partially stuffed PCB. I'm waiting for my 8-pin IC sockets to come in on Monday, then I'll be able to stuff the IC chips and get it working!

The switch shown on the photo is not the actual switch I spec'd in the parts list. But I don't want to use a $6-$8 switch for testing, so I jury rigged a $1 switch. It's not bad... and very stable and secure.

Did some changes on the Rev3.00 board... fixed the width of capacitors, aligned some components and some routing changes.

Signal Gen/Oscilloscope Testing

Soldered the IC sockets, applied 18-0-18 voltages, measure if the correct voltages are present in the correct pins... so far so good....

Insert all 3 IC chips....

Turn on power.... wait for any popping sound... None... Sniff for burnt smell.... None.... touch IC parts for hotness.... None. Everything is cool!

Proceeded to adjust knobs on my oscilloscope for a steady waveform, set my signal generator, and first I test the balanced driver circuit.

Here's a photo of my test rig/prototype.

I soldered some XLR jacks to make testing easier.

Checked the balanced driver stage....

Looks good!!!! I set the signal generator to sweep to a higher frequency... higher... higher... higher.... IN CASE YOU DIDNT NOTICE... That's 60Khz coming in and out of the balanced driver stage!!!! I'm pretty pleased.

Waveform looks pretty clean even at 60khz! WOW!

Since I don't have a selector switch, I just used a jumper to simulate a selector switch adjusting the dB gain selector. I then tapped from the output of the servo... which is after the mic pre. So in this waveform, the balanced driver isn't connected. I want to test each section of the preamp individually first.

So it works... I'm very pleased.