The Universal Pad PCBThe universal pad board provides a simple and convenient way to make and use single-value attenuator pads. The board accommodates most of the common fixed attenuator topologies: H, T, L, U, O, Pi, Bridged Tee. The wiring layout is flexible enough to be used with either balanced or unbalanced configurations.
The board is small: 2.062 x 0.85 inches, and it is made on a piece of FR4 epoxy-glass material, double sided, and thru-hole plated. A ground plane surrounds the circuitry. It is laid out for 1/4-watt resistors, but half-watt units will fit. The board does not fit inside a Switchcraft S3FM XLR tube. There is a hole provided for a single swage spacer (supplied). You can purchase the board several different ways. You can get the Universal Pad Board Manual here. Click the link for a short article describing how to calculate resistor values.
Prices and Options
One Small DetailIf you are ordering a complete kit, with resistors, delivery could take at least two weeks, possibly more. Why? Because if I don't have the resistors on hand, I have to order them. Here's the problem:
1% resistors use the e-96 series of preferred numbers for their values. This means that there are 96 values for every decade. There are 5 decades between 10-ohms and 1-megaohm. There are 480 1% values between 10-ohms and 10-Meg. That's a lot of resistors. As much as I'd like to, I don't stock every e-96 value between 10-ohms and 1-megaohm. It's just too many (nearly 500 resistor values x 100 resistors/value).I stock many of the e-96 values, and I stock all of the e-24 (5%) values. If you request a value that I don't have, I'll have to order it, which takes time. There's no way to forsee which values I have and which ones I don't. I charge a small premium for this service. I'm willing to buy 100 at a time. Are you? If you need this in a giant hurry, then I can have the parts shipped next-day-air, but you get to pay for that privilege. You could also just order the raw (unstuffed) PCBs from me, and order your resistors from Mouser. They're fast, and they don't have minimums.
Resistor ChoiceI'm into buying good parts, but I refuse to buy pedigreed parts. If that's your game, be my guest, but don't ask me to be your purchasing agent. My 5% parts are all carbon film resistors, with varying sources, mostly Asian.
My 1% parts are a mix of US and Asian parts. Some are Vishay-Dale, but newer parts are made by Koa-Speer.
If you want to buy pedigreed parts, then you're on your own.
Design ServiceIf you can't make heads or tails out of the calculations, I'm happy to do them for you... For a Price. Design time is $75 per hour. Most designs take 15-minutes. The design process is supposed to be simple, so this should be a learning experience for you. Whatever... Send me your problem, and its application, and I'll tell you how many 15-minute blocks this represents.
If you order the pad board kits from me, calculating the resistor values is included in the price. (within reason, my interpretation). Of course, you're welcome to do it yourself.
Copyright © 2008 by Rick Chinn. All rights reserved.
Last modified 03/08/2012.