Talking Optical Compression with XQP Audio March 30, 2012 09:48 2 Comments

XQP Audio is a two-man audio company designing new, unique audio gear for the 500-series. Unlike other people I've interviewed, they don't make DIY kits, but they do run their business with more than a hint of DIY ethos--building units by hand, posting schematics on their website, and generally being openhanded with info about their circuits. When I called XQP out of the blue, Product Specialist Dane Tate made good on their slogan "Nice guys. Yes we are." by sending me a Disruptor to try out and walking me through the circuit in the video below. I learned a ton about vactrols, asymmetrical distortion, and how optical compression works. Hope you enjoy our geeky banter! Audio Samples: The following are samples of the 545 Optical Disruptor processing various instruments. Just as Dane says in the interview, this thing is great at making synths more lifelike. All of the samples are in the order of: 1) Clean, original audio 2) Medium disruption 3) All the way up!

DIY Mic Preamp Design: Interview with Mike Mabie of Hairball Audio March 2, 2012 10:38 1 Comment

Sometime this month (March '12), Hairball Audio will drop a totally new mic preamp design called the "Lola." It's rare enough that we see an original design made specifically for the DIY world, so I wanted to talk to Mike about how it came about and what's involved in the design. The Lola is unique in being a fully differential design with input/output transformers and discrete opamps. Don't worry, Mike explains what "fully differential" means in the interview!

The Lola's fully differential design is derived from the "Double Balanced" mic pre design of Graeme Cohen. There's a lot of good stuff about Cohen and his preamp design at Leon Audio's website. Full and partial kits for the Lola will be available from Hairball Audio's website. Many thanks to Mike for granting me this interview!

LINE2AMP Design Journey February 15, 2012 20:14 1 Comment

This all started when my grandfather decided to dissolve his woodworking shop and give me his gorgeous old Sears drill press. I couldn't let a tool like that sit idle in my basement, so I thought, hey why not make a DIY kit? That was last August (2011), and while the The LINE2AMP reamping box is about as simple a piece of gear can get, it's been a rather long and circuitous journey to bring it to fruition. Doubtless, someone more experienced could have whipped the LINE2AMP up in a weekend, but I've learned a ton about electronics, product design, and DIY in the past few months. I'll be using this page to share what I've learned with you, as well as to let you in on the design process of the LINE2AMP as it progress.

 

August 2011: Researching Reamping

My original goals for the LINE2AMP were that it should:

1. Perform as well as any commercially available unit
2. Cost less than $50 to build
3. Be simple enough for newbies to build successfully.

I starting looking around at other reamping designs available on the internet and found three popular schematics: Jensen, Recording Magazine (Scott Dorsey), and NYDave. Looking at schematics the schematics, I realized that all of them shared the same essential topology:

I ordered a couple of transformers from Edcor USA to start experimenting with circuits.

September 2011: Prototyping

Four weeks later transformers arrived and I started soldering. 30 minutes later I had a working reamping box. Huzzah! Goal #3 was in the bag. My first prototype hewed almost exactly to NYDave's design: I used the Edcor PC10k/150 transformer with a volume pot and 200 Ohm terminating resistor. The only variation was that I used a 1M Ohm variable resistor to test different output impedances. Testing the prototype with a variety of amps, pedals, and DIs revealed a few things:

1. The unit was dead quiet and imparted practically nothing on the tone. At first, I had been skeptical about how the unshielded Edcor would perform, as both the Jensen schematic and the Reamp use shielded transformers. While a shielded trafo would certainly be better on paper, in practice the Edcor added no noticeable noise, even when run via DI into a clean preamp.
2. The impedance resistor had no noticeable effect on the sound until it was cranked beyond about 200k Ohms, after which the signal started to lose some high frequencies and become distorted in the bass.
3. In almost all cases, there was less noise when the connection from ground pin of the input jack to the case was disconnected. Only with some pedals did it sound better connected.

Overall, I was really happy with how the circuit worked. I didn't have a commercial reamping box on hand to shoot it out against, but it did everything a reamping box should and without any noise or sonic artifacts of its own. In fact, I was pretty blown away by the transparency of the Edcor transformer. In a blind test between A) a signal sent first to the reamping box, then the DI input of my Hamptone preamps and B) a signal sent right from my interface to the line input of the Hamptones, I couldn't make any conclusive distinction between the reamped and non-reamped signal.

 

Paring Down to Essentials

After playing around with my prototype, I realized that the LINE2AMP could be made even simpler than any of the other reamping designs and do the job just as well. The first thing to go was the impedance knob. From one perspective, it makes sense to have a range of output impedance available to emulate the source impedances of different guitars (typically between 10k-50k Ohms) and pedals (as little as 200 Ohms with a buffered output). However, in testing there was no audible change in tone until about 200k Ohms. From a technical perspective this makes sense, as any source impedance below 100k or so would be easily bridged by most guitar amp and pedal inputs. Goodbye to that pot! Next to go was the volume knob. In theory it's nice to have a tactile way to control the level, but in practice I found myself almost always doing it from the DAW. I also rarely found myself wanting less signal, and without adding active circuitry the volume control can only attenuate, not boost. What's left is the bare essentials of a reamping device: a transformer for impedance/voltage conversion and ground isolation, and a resistor to set the input/output impedances. That's it!

DIY Hero: Old Thai Street Performer April 8, 2011 20:11 1 Comment

When I first visited Thailand in 2007, I was blown away by old man busking in the midst of massive street market in Chiang Mai. He plucked single notes from a squarish, wooden-fretted guitar and sang in that melismatic head voice that issues so effortlessly from Thai vocal chords.  But what really made me stop to stare was that his whole setup--from the small speaker-turned-microphone he sang into to the PA system mounted on his motorized cart--appeared to be hand made. I didn't have a camera on me at the time, so I vowed to come back as soon as I could and prayed I would be able to find him again when I did. "As soon as I could" turned out to be last December (2010) and I was thrilled to find the man in the same exact spot, this time playing amplified violin. Although I felt a little like a paparazzo circling him and his contraptions taking photos, I overcame my reluctance enough to get a few good shots. So, here is my photo tribute to the incredible ingenuity and skill of a man who, for lack of a better name, I must refer to as "Old Man DIY."

DIY Profile: Artur Fisher of DIY Audio Components March 29, 2011 12:07 1 Comment

RM-5 Assembly Manual

Artur Fisher does some cool stuff with aluminum foil. Since last year, he has created a hand-made ribbon motor for DIY projects, the RE-154 and the RM-5, a microphone of his own design based on the RE-154. What makes the RM-5 really unique, besides being hand made by Artur in Latvia, is that Artur has made all of the details of its design and construction "open source" via his Designer's Diaries blog. I'm glad to have Artur as the first "DIY Profile."

What's your backround? How did you get into DIY and designing gear? I got into DIY electronics about two years later then I got into pro audio business. I started hanging around the industry when I was 17, started getting occasional payed jobs when I was 18 and got my first full-time employment when I was 19, so I am in the business for 10 years yet. My first job was in the theater as a member of stage sound crew and this was the period when I got into audio DIY. We have had a senior technician who was an engineer in electronics, so he was not just a sound guy, but was also responsible for equipment maintenance and servicing. All the electronics stuff seemed something like a black magic to me that time, but I was very curious about how is it that all these small things inside the amp do factually make sound... So I was hanging around his laboratory when he was doing some stuff and got my first basic understanding on how things work from him. After about half year I have built my first tube amp (home audio), which I still have assembled, but it wasn't what you call "designing" yet, as I have just cloned a schematic I found on the web. Then there were few attempts to make a tube guitar amp, that were marginally successful - well, they did make sound, but it wasn't exactly what I had expected, so I have understood that simple schematic cloning is not likely to work if you don't have a clear idea of what You are doing. So, I started digging old books, internet, following around people who had knowledge and skills, and after about two years after my first tube amp was built, I came to my first design - a tube guitar combo that I have calculated entirely myself from scratch, designed the chassis and made a body. It was my first small success, as some of my fellow musicians got quite excited after trying the amp, so I managed to produce and sell few pieces. I suppose that this was the moment when audio DIY culture became a major part of my life.

Why ribbon mics? Well, because they are a major trend in recording fashion right now - I just fell for ribbon mics once, but I couldn't afford to buy a Royer that time, while cheap ribbons performed way to badly to be seriously used in recording sessions. That was the moment when I asked myself a question - can't I make my own? And the long way started. Research, material sourcing and basic design works took about half-year. From the moment I had my first motor working (read, producing sound) it took another year till I brought a fully assembled good sounding microphone to my studio. I suppose that there wasn't a single session from that moment when I wouldn't use at least one of my microphones some way. In general, from a DIY point of view ribbons are very rewarding, as it is one of the rare situations when you can make something out of nothing. You can make a good condenser microphone using a pre-made chinese capsule, but nothing comes close to the feeling when you have made a working transducer out of raw materials with your own hands - and it is possible, while making your own condenser capsule is way beyond the abilities and skills of a regular DIYer, not even talking about precision machinery that You are not likely to have easily accessible in your neighborhood. There is one guy I know on the web who managed to make a condenser capsule, but from his words, it took him about 10 years to make it sound good.

Tell us about the RM-5. Is it based on anything in particular? If there is something it is based on - it is my design philosophy. I wanted to keep the microphone as simple as possible, as with all of my other designs. I wanted it to be fundamentally classical - no ribbon offsetting, no ultra-extended frequency response - pure old-school warm ribbon sound. I could easily go about 1500 - 2000 Hz up in response, but I didn't find it necessary after testing. I would rather design another model with completely different sonic signature, but I want this one to sound the way it does - conservatively charming. Advantages of modern materials provide elegant shape, compact size and quite high signal output level - these mics are absolutely usable when I just plug them into my Mackie 1640 console without any additional preamps.

On your website, you mention the RM-5 is an "open source" project. What does that mean in terms of a microphone? With "open-source" I mean that all the information about my approach to design is revealed on the site for free (and I will keep updating with more articles, when I have more time), all the materials are easily available on the web and I am open to answer any technical questions people ask me - no secrets. Feel free to make your own microphone and I will help if my advice is needed.

After you fill the current preorder for RM-5s, what's next for you and DIY Audio Components? Next - as always - is to keep working. As I can already see, there is a big interest to my pre-order offer, so I will do my best to keep providing the microphones to people who are eager for a good yet reasonably affordable ribbon sound. I have also started designing a microphone preamp. It is going to be a high-end full-tube transformer-coupled design, but I can't tell You right now when it is going to be released, hopefully by the end of the summer. Most likely it is going to be available as both - DIY kit and a ready to use assembled unit. Join the DIY Audio Components page on Facebook - all the updates are posted there. Thanks a lot to Artur Fisher of DIY Audio Components for doing this interview.