Building a Hairball Audio 1176
Hairball Audio 1176
One piece of gear I’ve always loved the sound of is the famed Urei 1176.You can get a wide variety of types of compression, from fast, clean, and smooth to slammed, pumpy, and dirty tones, as well as anywhere in between. This makes it an extremely versatile compressor, it sounds great on about any source, but I particularly like it for vocals, snare, bass, room, or really just about anything. It’s classic for a reason, and it’s sound has been featured on countless records. There are several great options of 1176s currently in production. Hairball Audio 1176, Universal Audio 1176, Purple Audio, Warm Audio, etc, are great options. We decided to go with the Hairball Audio 1176 Revision D for a few reasons. Firstly we love doing things the DIY route when it is an option, you have a better understanding of how our gear works and to fix it if it stops working, not to mention the serious price breaks you get by building it yourself. The build quality on Hairball Audio’s products are unparalleled; Always overbuilt, with the highest quality components available. I have already built two of their Lola Mic Preamp, which simply put it my favorite preamp I’ve ever heard, and can’t imagine using anything else for vocals in the foreseeable future.
Before We Begin:
Once our Hairball Audio 1176 kit arrived, we also had to order all the components for our kit. Fortunately, Hairball Audio is nice enough to have a link to an entire bill of materials. Unfortunately depending when you order (like us), not all of the parts we needed may be in stock, or even manufactured anymore. Thus we had to source and replace a few suitable resistors, capacitors, and a potentiometer.
Now that all our parts have arrived, it’s time to gather all the tools and supplies you will need to start assembly. Here is a list of all the tools I used to complete my Hairball Audio 1176 FET Compressor:
Soldering Iron
Solder
Digital Multimeter
Side Cutters
Needle Nose Pliers
Wire Strippers
Hex Keys
Nut Drivers
Wire
etc
Let’s Get Started:
Now that we are all set to build, lets start by assembling the most basic part of the compressor, the enclosure. To do this I took each of the side panels and screwed them to the front. Then I attached the rear panel and two PCB rails. I found my dremel tool, and ground off the paint from any surface where critical components were going to be mounted. The reason I did this is to ensure everything is properly grounded, so no one gets electrocuted, as well as ensure everything is properly shielded. This included the power transformer mounting hole, XLR jack mounting hole, input and output transformer mounting holes, etc. I then soldered a terminal to two ground wires and those wires to the incoming ground on the IEC connector. Having the second wire in there helps protect you and your equipment before the fuse blows in case of a short circuit. Mount the IEC socket in your enclosure and screw the ground to the section where you removed the paint.
Next step is to find your meter switch, meter switch PCB, 3.6k Ω resistor and 8.2k Ω resistor. Start by mounting the two resistors in your PCB, then flip it over, solder the leads, and clip off any excess in the lead with a pair of side cutters. take your meter switches and mount the switches flush against the meter PCB, and solder those on, taking care not to put too much heat into adjacent pins. There is a metal mounting bracket that you then screw the switch assembly onto, and mount that to the enclosure.
The Power Section:
Let’s start by mounting the power transformer, run a bolt through a washer, the case, a foam washer, the transformer, another foam washer, a metal plate, and finally cap it off with a nut to hold it all together. Understanding how to read transformer diagrams, as well as interpret how to wire it for your application is essential. There is no standard for transformer color codes, so you really have to refer to the diagram usually printed on the transformer itself or it’s documents. I identified that I needed to run my two primary windings in parallel since I live in Cleveland, and I have 120 volts here. If I were wiring it for someone who lived outside the states in an area with 240 volts, I would have wired it in series. On the secondary side there are 4 wires, the two center wires in the coil will be tied together to form a center tap. Between the center tap and either leg you should be able to pull about 30 volts, and about 60 volts between the two outer ones.
The next step is to populate the power supply side. To understand the basics of how a power supply works, first you use a transformer to get the voltage to an appropriate level. The next components it enters is four diodes setup in a configuration to act as a bridge rectifier. Diodes simply put, restrict electron flow to one direction. With four diodes, you can split the AC sine wave fluctuating back and forth between positive and negative to two separate half sine waves. From there, it hits our filter capacitors, these smooth out the sine wave pattern into a smooth consistent voltage. The AC has now been converted to DC. There are a few more parts located in our power supply that helps you maintain clean even power, as well as regulates the voltage. It’s pretty straight forward design, and is fairly easy to build. I recommend starting with smaller parts, and gradually moving bigger until you have installed the largest (the filter capacitors). After all the components have been installed, it’s important to test your power supply, a malfunctioning power supply can damage components down the line. To test a power supply, take your digital multimeter and measure from the center tap to two points on the PCB. If you look close, there is a +30v and -10v silkscreened on the board. If you are off more than ±5%, then check for mistakes. Do not move on until you have verified that the power supply is functioning correctly, I cannot stress this enough!
