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

May 12, 2007

Well... this thread hasn't been updated in a long time. Don't think that I've neglected this project... rather, I'm nit-picking and wanting so bad to get rid of every bit of noise.

I'm just obsessed with getting rid of it.

Problem: Noise is almost non-existent at 60dB and below. Noise floor shows excellent figures. But at the 66dB and 72dB settings, (2000x and 4000x amplification) every tiny ounce of noise will get amplified by a lot.

Tonight, I did some noise troubleshooting by connecting a 20ft long cable on the input XLR, leaving it UNTERMINATED and hanging, coiling it and putting it near the PSU of my external firewire drive, running it on top of an AC cord. Then I switch the gain selector all the way to the right, maximum gain, and turn the preamp's volume knob all the way up at 100%. Guess what? I heard nasty RF sound... hissing, popping, some slight radio signal, humming. Sounds real nasty. This is to simulate the environment on where this preamp will be used. i.e. near computers, cables laying on the floor, home studio, near other gear, etc.

I looked at the resulting spectrum.

Again, note the slider knob on the left... I had to add another 40dB on the plugin to bring up the noise floor and see it on the graph. Otherwise, you won't see anything... just the very tip of the waveforms.

GOOD NEWS! I found the fix for this! Again, just to remind you... this is with 20ft unterminated cable at the inputs, near AC cords, maximum gain, maximum volume, and the plugin gain boosted.

I connected the outputs straight to a KRK RP8 monitor to listen for any "frying, popping, AM radio, nasty" noise.... and I hear nothing! Just your average hissing white noise.

I'm pretty happy about it. So if you can see what the noise reduction is at 66/72dB, imagine how much even lower it will be at the lower gain settings of 60dB and below.

Also, that small bump around 15khz you see above... I think that's caused by my patchbay. Because even without the preamp connected, I have a slight bump there that's made even worse when you connect a long cable (like 20ft in this case) to it. (A THAT engineer told me they had that problem before and they traced it to their LCD monitors.)

But not anymore... as you can see from the second photo. It's very nice looking and hearing tests also shows a dramatic improvement in quietness... even with all the RF junk I threw at it.

COOL!

The Rev4 prototype PCBs will be arriving either Monday or Tuesday, then I'll build prototype #005 and then we're off to mass production of PCBs.

I've been bulk-buying parts slowly and have spent $3K to $4K already, (including R&D costs, making prototypes, etc.) and need another $3+K to buy the rest of the parts and pay for mass PCB manufacturing before I can sell the 1st kit!

So I really hope you guys will buy some kits when it goes on sale.... Otherwise, I've dug myself in a deep hole. Wife is very supportive but getting worried about the thou$and$ I've spent so far.