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

May 15, 2007

I'm still waiting for my recording engineer friend on how it goes, and maybe he'll give me professionally recorded samples this Sunday... I hope, not sure though.

I'm in discussion with a THAT engineer. I did something on my design that has a side-effect of increasing gain at high frequencies (according to him, 1Ghz and beyond), way beyond the bandwidth of the chip. But I said it removes a tremendous amount of RFI, and if it's beyond the chip's bandwidth then shouldn't it not matter because it won't get amplified anyway? I'll probably get his response tomorrow.

tecno, you're not far from your estimates. I computed $921 for an 8-channel DIY SC-1 on a 2u rack. ($115/channel vs. your estimate of $118/channel)

I looked around the Internet asking how much they charge to do testing of my preamp. I got quotes from "Do you want our engineer to come to your facility?"... which means $$$$$$$ to small companies asking $400-$500 per test run. Hmmmm.....

So I bought on evilBay an HP 8903B test equipment, and will just study how to use it myself.

REV4 PCB

Rev4 PCB just got delivered by Fedex to my frontdoor....

So I'll try to build another channel tonight using the new PCB design. See if it's any better.

Here's a photo showing the progression in design from Rev1 to Rev3 to Rev 4. Rev2 didn't got prototyped, it only existed on my computer.

Rev1. - Dumb mistake, selector switch mounted backwards, switch holes too small. Insufficient use of bypass capacitors, some capacitor size dimensions off.

Rev3. - Switch position for ON is downwards instead of upwards. Very useable preamp! A good candidate for manufacturing.

Rev4. - Fixed switch mistake above. And since we're at it anyway, add soft-start phantom power circuitry, and test reduction of popping sound when changing gain at high settings.

If Rev4 comes out good, we're off to mass production of the PCB... with some slight changes and additions, which I'm calling Rev4.3

The "X-Module"

I don't want to talk about it yet, but maybe it's time. There are plans in the works for an add-on to the SC-1. I've already built the schematic for it last March. I'm calling it for now "the X module".

Unlike the INSERT modules that are meant to be "inserted", the X-Module goes at the frontend and backend, i.e. it connects to the input and output of the SC-1.

So it will be:

SC1 ---- "the X Module" ----- XLR Jacks

What will be in the X-Module?

Active-DI guitar input (Hi-Z input), relay-controlled switching between Mic and Guitar inputs, relay-controlled pads, relay-controlled phase reverse, soft-start phantom power (but scratch that since I already included soft-start phantom on the SC-1 unit itself).... Analog VU meter hookups and Output Transformer options!

Yes! You read that right. Output transformer add-on! We're going to marry this clean SC-1 preamp and fortify it with some Iron vitamins!

Right now, I'm already in negotiation deals with a factory to manufacture some output transformers for me (that if this deal goes through, you guys will be pleasantly surprised on the pedigree, and quality and type of transformer that will be used in the X-Module!) I gave the go signal to them to manufacture a very, very small batch for me... and it's going to cost me $600 for a few pieces. But this will be cool!

So just wait and see!!!!

May 16, 2007

I finished building Prototype #005 tonight and did some quick testing on it. This is using the Rev4 PCB design.

All I can say is ..... AWESOME!!!

The RFI fix really works, and according to the THAT engineer is "if it works for me, then use it!" So I'll use it.

So far, I've built 5 prototypes of varying PCB designs, and each revision is better than the last. Prototype #003, #004 and #005 are just great. The latest prototype #005 (using PCB Rev4) is the best of all!

How is the new PCB revision better ???

1. Eliminated popping sound when changing selector switch gain at the lower settings. At the higher settings, it's just a faint "clicking" heard on the speaker... no loud popping sound that sounds like your woofer getting ripped out.

2. The phantom power switch is correctly positioned now. Toggle UP to turn ON phantom power.

3. And the best feature of all... the SOFT-START Phantom Power WORKS! No matter what gain setting you're on, and even if your Volume knob is at Max, you flip the phantom power switch and you nary hear a "POP" or any noise when switching it on. It's like nothing happened. Is it broke? But you can see the LED lit up.

Then you start talking to the mic, and slowly the condenser mic comes to life! First your voice is faint, then getting stronger and stronger. No LOUD POPPING SOUND you normally hear when you activate phantom power and your volume is not set to zero. No sireeee!.... not on the SC-1.

And then the same thing happens when you turn phantom power OFF. Again, NO LOUD POPPING SOUND. Nothing happens. Then slowly, your voice gets fainter and fainter, and the mic dies a slow death.

All I can say is it's beautiful.

I am really, really, really pleased with this new revision. It was worth the wait for another PCB revision. Rev3 was good, but mannnn.... Rev 4 is even better. I'm happy!

May 18, 2007

UPDATE:

Well, I sent the work order to the factory to manufacture a small batch of PCBs for me.

Also placed orders for a couple hundred of IC chips, and more parts, anti-static bags for packing, etc.... Spent $1800 these last (2) days. I feel broke. LOL!

I may get the PCBs in (2) weeks instead of (4) weeks. So it may happen sooner than you think.