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On a previous post, I posted a schematic of a passive direct box using Jensen Transformers.

I have a ROLLS DB25 passive direct box in my studio so I decided to open it up to see it's "guts".

The ROLLS DB25 is an inexpensive direct box using all passive components. That's right, no need for a 9V battery or wall wart to use this thing. Plus, it's got a transformer inside that takes care of converting from an unbalanced Hi-Z connection (from a guitar) to a balanced Lo-Z connection for connection to your mixer or preamp via XLR jacks.

In addition, it has a -20dB and -40dB pad, and a ground lift switch for "stubborn hum" reduction.

We did an unbalanced to balanced converter using dual opamp chips, the NE5532 opamp previously. While the previous circuit works, it uses a lot of components.... which means, more chances that something could go wrong.

Picture of old unbalanced to balanced converter

New Design

This new unbalanced to balanced converter uses a single chip and only 2 capacitors. We're using the Burr-Brown DRV134/135 chip. I got some DRV135 which comes in an SOIC package. There is a DRV134 which comes in an 8-pin DIP package.

This is a schematic plan for building a passive, transformer-based DI Box (Direct Box) from Jensen-Transformers.com. View the original PDF here.

You plug your hi-Z (or high impedance) guitar to jack J1. From here, it goes to a pad on/off switch. You also have 2 pad choices... -10dB and -20dB depending on the position of switch S2.

S3 is a hi-cut filter switch. If S1a (i.e. the pad switch) is switched ON, and the hi-cut filter is ON, the high frequencies are shunted to ground via C3.

The signal going back to your guitar amp via jack J2 is unaffected by the pad and hi-cut switches.

Transformer T1 is a JT-DB-E transformer. This takes care of matching impedance between your guitar and the mic preamp of your mixer. It also converts the guitar signal from unbalanced to balanced connection.  The red-brwn wires of the transformer goes to pin 2 and 3 of the XLR which forms the HOT (+) and COLD (-) connections.

Ground is connected to Pin 1 of the XLR. A ground lift switch is provided, S5, which isolates the pin 1 ground of the mixer from the rest of the circuit.



If you don't want to build one, here are some passive DI boxes.

ART ZDirect Passive DI View more products from ART The Zdirect is a high-quality, totally passive interface that lets you connect instrument-, line-, or speaker-level signals to a mixer or other balanced input through a high-performance audio isolation transformer. The high impedance single-ended 1/4 in. input is converted by the transformer into an isolated balanced low impedance signal source. Read Reviews... List Price: $30 Click for Sale price   Shipping cost: $4.99

Radial JDI Duplex Stereo Passive DI Box View more products from Radial A stereo version of the Radial JDI. Ideal for recording, broadcast, and live sound where extreme dynamics such as those produced by digital sampling devices and keyboards are encountered. Completely passive, the JD4 employs two Jensen JT-DBE transformers for 100% isolation and low phase distortion. Read Reviews... List Price: $350 Click for Sale price   FREE SHIPPING!

Radial JDI MK3 Passive Direct Box View more products from Radial The Radial JDI is considered by many to be the world’s finest direct box. It is a passive DI that employs a Jensen isolation transformer for optimum audio performance offering outstanding linearity at all frequencies, combined with extraordinary level handling without introducing distortion. Read Reviews... List Price: $200 Click for Sale price   FREE SHIPPING!

Radial Pro DI Passive Direct Box View more products from Radial The Radial ProDIs are high-quality, full-range passive direct boxes equipped with custom-made audio transformers for exceptional signal handling without saturation and with extremely low phase distortion in the critical bass and mid regions. The result is exceptional clarity and definition at an attractive price point. Read Reviews... List Price: $100 Click for Sale price   Shipping cost: $4.99

Just an update of my build: Click here 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.

Oscilloscopes are indispensable tools for anyone designing, manufacturing or repairing electronic equipment. In today’s fast-paced world, engineers need the best tools available to solve their measurement challenges quickly and accurately. As the eyes of the engineer, oscilloscopes are the key to meeting today’s demanding measurement challenges.

Tektronix presents the XYZs of Oscilloscopes. Learn about the different types of oscilloscopes, systems and controls, measurement, and how to operate an oscilloscope including measurement techniques.

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.

For more money saving tips for your home studio, like building your own Neve preamps, SSL compressors, Yamaha "old-school" type preamps, MIDI controllers, check out my other projects.

Back to building your own cable...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.




Since an XLR cable is a balanced cabel, we need a 3-wire cable. Also, make sure it is shielded to provide RF interference protection. 




Now, let's take a look at the XLR jack itself.  It's got 3 pins. Pin 1, 3 and 3. 

The convention is Pin 1 is the GROUND.
Pin 2 is the HOT (+) wire.
and Pin 3 is the COLD (-) wire.

Note: The COLD wire (-) is not the same as the GROUND wire. Don't short these two wires together!

Here's a closeup of the 3-pin assembly and you can see it's labeled for us. Great!  For this, I'm going to make my RED wire my HOT (+) wire and the WHITE wire as my COLD (-) wire.  (If you're wiring a headphone, the RED wire is usually designed for the RIGHT channel, and the WHITE wire for the LEFT channel)



Strip off a few millimeters of insulator, coat it with solder and solder it to the XLR jack terminals.



When you're done soldering the 3 wires, crimp the jack around the cable. This will provide support to the cable... i.e. when you yank off the jack, your wires wouldn't disconnect from your solder points.



Here, you can see the metal teeth crimped around the cable's jacket. Use a long-nose pliers to crimp it close. But don't crimp it too much that you mess up the cable.

Do the same procedure for the other end of the cable. This time using a Female XLR jack.  And here's our finished XLR cable.



If you need to DIY a different kind of cable, say a TRS jack or RCA, use the table below as a guide. This guide has been provided by Rane in their Technical Library section. Visit Rane website.

Credits: Rane

Visi the RANE website for more information about grounding, shielding, ground loops, etc.

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 got most of the capacitors and the power transformer at digikey.com. They have good prices for these components.




The rest of the parts like the pots, resistors, and ceramic/mylar parts came from Mouser.com. It's a big pile!







I'll clear up my work area and maybe this Christmas break, I'll be able to start construction.  Oh yeah, need to order some 2u case from Par-Metal.com.  I only have spare 1u cases in my workshop at the moment.

We're ready to build the 1176!

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.



There are assembly instructions and schematics on the box. Very easy to follow.

The Art of Electronics
Price: $55.79

People have asked me what is a good book to read to start DIYing... On this page, I'll compile books that I have, read, or know will be good for the DIYer or electronics buff.

The following books are not expensive... the most expensive of the bunch is $55. But considering the knowledge you'll have (priceless), and the savings you'll realize when you build that super-duper preamp for a few hundred dollars rather than buying one and spending $1400, these books are a bargain.

These books link to Amazon.com. I'd appreciate it if you can buy your books by clicking on the links below :)

This site takes a lot of time, effort and money. My latest addition is a new bookstore with products and reviews from Amazon.com.  If you like this site, please consider buying books or stuff via my Amazon link. You'll get great prices and it won't cost you anything extra. In return, I get a little commission that I can use to pay for hosting of this site.

Check it out.  Buy from Amazon.com

It's that time of the year... here are some gift ideas for your home studio.

Furman PL8II Rackmount Power Conditioner with Lights
So you have thousands of dollars in gear and you're plugging it "naked" to your wall outlet or with a $5 Walmart power strip? I recommend you buy this power conditioner that will give you added protection to your gear. All your gear plugs to the back and you have a single switch to turn on all your gear. The lights are very handy too illuminating your rack gear so you can see what you're doing.



Korg MA-30 Metronome
Keeping time is important. And this little device from KORG packs a lot of sophisticated features at a small size. You can do rythms such as triplets and quadruplets with inner beats removed.