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

May 2, 2007

I received PCB Rev3 from the manufacturer, built prototype #003, hooked-up the wires, Power on, and there ya go!.... it works again!

I may be biased, but this kit is SO EASY to assemble!!! I'm not kidding. The only time consuming part is putting in all the resistors (lots of it... 25pcs), but as soon as you're over that hump, it's just easy going after that.

The other thing that needs some care, is soldering the Red Grayhill switch. The pins are pretty close together. Need a sharp tip soldering iron, and a magnifying glass (if you're like me with an old man eyesight)!

I am real pleased with Rev3 PCB. All the pots and switches fit perfectly.

Now, this may just be quibbling, but the the Phantom Power ON position (if the PCB is installed vertically) is pointed downwards. If the PCB is installed horizontally, then the phantom power on position is pointed to the right (which seems to be right). So Rev3 is recommended for horizontal mounting.

I'm now wondering if I should correct this on Rev4. i.e. phantom power On position will be UP or LEFT (depending if vertical or horizontal mounting).

Photo of the finished Rev3 KIT. (IC chips not inserted yet, and LED not soldered yet)

The additional bypass capacitors used in Rev3 PCB design is well worth it. I also added jumper headers (kinda like the jumper in motherboards) so you don't have to solder "jumper" wires in.

JP1 is a jumper if you don't want to use DC Servo and instead want capacitor coupling. If you want to use DC SERVO, keep the jumper in.

JP2 is a jumper if you don't want to use any INSERTS. If using an INSERT jack, remove jumper JP2.

The blue potentiometer is conductive plastic in a sealed box. Unlike carbon potentiometers, these won't fade easily and become scratchy.

The Grayhill (red selector switch) has a nice, heavy, solid feel to it. Unlike the plastic rotary switches. Well worth the money spent here.

TIP: I found out that the quality of your regulated PSU is highly critical to the performance of the SC-1 preamp. I tried my bench PSU (which was a commercial kit) and found it to be extremely noisy when used with the SC-1.

On the other hand, my custom designed 18-0-18 PSU is very quiet when used with the SC-1. So don't skimp on the PSU when building your preamp... otherwise, you may be greeted with a noisy preamp.

May 3, 2007

I made Rev4, and sent it out today for prototype manufacturing. Wait another 5 days, and then we'll see how it performs:

Rev4 adds

a) Soft-start phantom power... think of it as a gentle start up of 48V, instead of slamming 48V directly to your expensive mic.

b) INSERT JACK - SEND protection (If you short the output to ground, it won't blow up your delicate mic preamp).

c) Design change in gain selector for less/minimized/elimination of pops and clicks when changing gain settings.

Today, I tried playing with the Rev1 design and comparing it with the Rev3 design. I'm learning and discovering new things.

All I can say is the Rev3 is a well worth change. And the upcoming Rev4 should be even better.

1. Rev3 is RF resistant. This could be because of the Grayhill on-board selector switch compared to the clumpy wiring of Rev1 (using off board selector switch). There is also output RF protection using JWMiller inductors. Shunt those RF to ground. Result? Cleaner signal, very miniscule RF noise.
RECOMMENDATION: DO NOT BE CHEAP and use an off board selector switch. Use the Grayhill switch I will recommend in the parts list.

2. I noticed that using a cheap mic like the Behringer C-2 and turning on phantom power in Rev1 generates LOTS OF HUM... 120Hz, and multiples of it (240Hz, 360Hz etc.) Using a better mic like an MXL 991 does not generate hum in Rev1 design.

However, Rev3 design is hum free even with phantom power ON on both the cheap Behringer C-2 and the better MXL991 mic.

RECOMMENDATION: BEHRINGER IS REALLY CRAPPOLA. But Rev3 design still allows you to use this cheap mic and get the most use out of it, and make it sound clean (no hum). Of course, using any better mic with the Rev3 design is just over-the-top sweet.

3. Great care has been taken to make this preamp RF/hum and noise free. But all this can go to waste if you use a crappy power supply. Not all regulated power supply are created equal. I've tried the SC-1 on (2) different regulated power supplies. It was noisy using my bench regulated PSU, and clean and noise-free using my custom designed PSU.

RECOMMENDATION: Don't skimp on the PSU that will power your SC-1, don't skimp on cheap power transformers, or cheaply built power supply (breadboards, point-to-point wiring, etc). Use my PSU-1848 for your SC-1. :)

That's all for now....