HomeStudioGuide.com - Guide to Home Studio Recording

This is a repost of my SSL Build Thread. Thanks to Gyraf.dk for the schematic plans.

The compressor is a clone based from the SSL4044E desk (1985 era). The SSL mixbus is actually an integrated part of the desk's main quad fader and autofade system. Schematics and mods can be found below the article.

I also did some mods on my unit. Mainly, adding transformers at the output. Originally, the unit uses opamps for balanced outs. I have some MCI 416 output trafos that I used for my SSL unit.

The PCB...



Screenshot of my PCB stuffed with components. A few missing parts but almost there.

Just an update of my build: Click here if your want to read Part 2.

Soldered 90% of the parts, including the Lundahl transformers, JFETS and transistors. I'm awaiting some parts that were "out of stock" from my first order.

Also, I ordered some wire assemblies with male/female jacks. I'll use them for connections between the main board and xlr jacks, pots, switches, etc... that way, if I need to troubleshoot the board, I can just unhook them instead of desoldering the wire from the board.

TIP: Before you complete assembly of your project, have a suitable chassis ready for it. From my experience, if I built a project without finishing the chassis first, that project becomes half-finished, working but not in a case. Laziness I know...

Also, if everything is in a chassis, you can wire everything and not have to worry about your solder connections or wires becoming loose. Everything is already in place, plus it makes it easier to work on it.

You can get your rack chassis, from 1u, 2u, all the way to 4u and 8u at par-metal.com.  They've got good prices and have nice quality racks.

Looking to save some money? Create your own cables! By spending a few dollars on jacks, shielded cables, solder and soldering iron, you can save a ton of money in cables.

It's easy. Here are some step by step photos. 

At the bottom of this article, is a wiring guide for XLR to XLR, XLR to TRS, XLR to TS, and whatever combination you can think of.

On this guide, I'm wiring up an XLR cable.  First, we disassemble the cable by unscrewing the lock screw. Pull out the rubber plug (black thingy) and then you'll be able to push out the 3-pin connection assembly.

Just a continuation of the saga of building my 1176 clone compressor/limiter. Click here for Part 1

Parts arrived a few days ago, and other than the audio input and output transformers and chassis, I think I have enough parts to build (2) units. Here are some pics...

First, we have the output LL5402 Lundahl transformer and the LL1540 input transformer. Made in Sweden.  These things are small.

I've seen the new Zoom H4 Handy Recorder. I think it's a neat little thing! And best of all, it's "cheap" at $299. Of course, "cheap" is a relative word, but compared to other gear out there, this seems to be one of the low priced new entry. It looks good too!

While reading the H4 specs, this caught my eye... "The H4 features 2 studio-quality electret condenser microphones configured in an X/Y pattern for true stereo recording."  The keyword here is "electret microphone." And the picture seems to confirm that it's really just an electret mic.

So I'm thinking, maybe I can DIY my own stereo mic.

I've used an electret microphone on a non-audio project. I made a sound-triggered flash sync for my Canon EOS30D camera. In this case, I just used the audio output from the mic to trigger an SCR, which then triggered the camera flash.

Can we used the same electret mic to create a good enough sounding stereo mic? I think we can.

So I begin adapting my sound-triggered flash sync and while doing some Googling around, I came across this product.
Stereo Super Ear Amplifier Kit

It's a kit made by Velleman and it uses 2 electret mics, and a headphone output jack. Hmmmm.... interesting. So I ordered a kit (hey, it's less than $10 so if it didn't work, it's not too much of a loss). You can use the link above to order your own kit.

The circuit is simple... the Left and Right channel is the same, so the operation of the circuit is identical. Basically, an electret condenser microphone is biased for operation using a single resistor and capacitor. The output of the microphone goes to a potentiometer which acts as the volume control. This is then amplified by the NE5532 opamp, which is then routed to a headphone jack. Since the whole circuit operates from a single supply voltage (4.5Volts), the opamp uses a virtual ground by the use of 2 resistors in it's input pin. This of course, means that each leg of the split power supply will be only Vcc/2, where Vcc=4.5Volts.

I built this kit in less than an hour... while watching TV. And construction isn't hard and it's very simple. So if you're ready to jump into this Electronics hobby and looking for your first audio project, why not try this stereo mic kit? It's only less than $10.

Here are some pics during construction... enjoy.

I haven't DIY'ed for a long time, so to kickstart this hobby again, I decided I'm going to build an 1176 Compressor.

The 1176 is one of the classic compressors in used by almost every recording studio out there. (The other classic compressor is the LA-2A). Bill Putnam designed the 1176, based on the 1108 preamp. Back in 1966, the Field Effect Transistor (FET) was just developed and he's experimenting with the properties of this new device. Basically, think of an FET as a "voltage controlled variable resistor."  The FET has three terminals. Drain, Source, and Gate. The resistance between the Drain and Source can  be varied/controlled by the Gate voltage. So what Mr. Putnam was doing with the FET is using it as a variable resistor to contorl the gain reduction in the circuit.

The output stage of the 1176 is a Class A line level amp, feeding a load of 600 ohms. It's got an output transformer which converts the output from unbalanced to balanced, and also do impedance matching. 

If you don't know or don't want to DIY, you can buy an 1176LN (for Low Noise) compressor for about $1800. Or, you can purchae "virtual" 1176 plugins from $130 to $225 price range. Click here for software plugin versions of the 1176.

Just a work in progress.... using a breadboard. API schematics found on the Internet... just google API 312 schematic. You can see the printout of the schematic on the photo. I'm using a Melcor Discrete opamp instead of the original 2520 opamp (which you can't buy unless you have a broken 2520 to surrender to API). Although there are many substitute opamps you can use like the Jensen 990C, Forsell Technologies 992, John Hardy opamp, etc... or if you're really scraping, just use an NE5534 IC chip.