The March 2014 Issue of audioXpress is Now Online

This month’s audioXpress brings a great article from our regular contributor Thomas Perazella, in which he revisits the art of studio reamping and the different approaches and implications of that two-stage studio process. During the process, we first record a dry or clean track and then re-record the track by sending the clean track back through amplifiers and effects. Naturally, he looks at different Reamp circuits and some implications for the different impedance audio signals and balance to unbalance challenges.

audioXpress March 2014Another highlight is our review of the Rockruepel comp.two tube stereo compressor, hand built by Oliver Gregor in Germany. As Miguel Marques discovers, this is one of the most versatile audio processors on the market, packaged in a simple but impressive design.

Following the first of a two-part article dedicated to Dante audio networks, our Standards Review revisits Audinate from the perspective of those companies who have licensed the technology.

And for our readers who have are interested in the recently introduced loudness standards, Jon Schorah returns with another great article about Loudness Meters and Measurements.

Don’t miss another take from Mike Klasco and Steve Tatarunis on the “Weird Science Woofers,” in which they discuss some market innovations and pure research on unique speaker mechanisms, from huge to ultra-shallow speaker configurations.

In this month’s Sound Control column, Richard Honeycutt explores predictive acoustics and how the results of such evaluations can be highly rewarding.

Certainly an entertaining read is Shannon Becker’s interview this month with Morten Sissener, founder of Tortuga Audio, a DIY-oriented audio company dedicated and committed to audio enjoyment.

On the subject of DIY projects, this month contributor George Ntanavaras explains how to build his MC100 high-quality moving coil RIAA preamplifier. It is a great read for anyone who would like to know more about the phono signal chain.

And for Audio Electronics enthusiasts, Ron Tipton shares a fascinating project on testing a Class-T or Tripath power amplifier. We also discuss the story of Tripath Technology, which was later acquired by Cirrus Logic who discontinued the company operations. We also speculate on reasons why the Tripath ICs are still popular among the DIY audio community.

And for those with a passion for tubes, columnist Richard Honeycutt looks at Tube Guitar Amplifiers and why distortion evolved from an undesirable effect to part of the established guitar amplification industry practice.

Your new issue of audioXpress is now available at www.gotomyxpress.com

Prism Sound Launches New Free Webinar Series

The enormous success of Prism Sound’s Audio Design Workshop LIVE event at the 51st AES Conference in Helsinki has inspired the company to launch a new, free series of 30-minute webinars – Audio Design Workshop: Bitesize. These webinars are ideal to brush up on test and measurement knowledge and techniques.

The Bitesize series delves deeper into the audio engineering and measurement topics already discussed in Prism Sound’s popular Wednesday Webinars series and they are available to download from the Prism Sound website.

The first Bitesize webinar will take place on December 18th 2013 at 14.00 and 18:00 (UTC/GMT) and will cover FFT Fundamentals and discuss the six essential steps in audio test and measurement:

  • Why you need to understand Fourier Theory
  • The significance of the Time-Frequency Relationship
  • DFT/FFT and why they matter
  • How to choose the right window function for your measurement
  • Avoiding the ‘Picket-Fence’ effect and the errors it may bring
  • Make the most of your FFT – special measurement techniques

Each webinar will include live demonstrations and a Q&A session.

Anyone wanting to attend should register at www.prismsound.com/webinars to receive their session login details.

Q&A: Ken Heng Gin Loo – DIY Audio Appeals to Applications Engineer

Ken Heng Gin Loo

Ken created the diy-audio-guide.com website because of his interest in DIY audio, in particular tube amplifiers, Class-T amplifiers, NOS DAC, high-efficiency loudspeakers, and high-quality audio reproduction.

SHANNON BECKER: Tell us about your background and where you live.

KEN HENG GIN LOO: I’m a Malaysian Chinese. I spent a wonderful childhood in a small and peaceful town called Taiping, Perak, up North in Peninsular Malaysia.
I’m fortunate that my father could afford to send me overseas to the United Kingdom to pursue a bachelor’s degree after locally earning my diploma in Electrical and Electronics. Now, I’m a graduate in Electrical and Electronics Engineering (Honors) from the University of Manchester, UK.

I currently live on a beautiful tropical island named Pulau Pinang (aka Penang) in Malaysia. It is an urbanized and industrialized state that houses several the multinational corporations (e.g., Intel, Agilent, Motorola, Altera, National Instruments, etc.). Yet, it retains its historical heritage and it is one of the UNESCO World Heritage sites. Downtown is filled with historical sites, excellent local delicacies and seafood, and many beachside resorts.

I live in a terrace house with my lovely wife Brenda and 3-month-old baby girl Ember. In the past, I worked as an engineer for several multinational corporations. Now I work at Intel (for more than eight years) as an applications engineer. I focus on customer-enabling team program management, working with high-speed electronics applied in tablets, notebooks, and PCs.

SHANNON: How did you become interested in audio electronics?

KEN: I was “trained” in hi-fi very early, way back in my primary school years. I’m fortunate to have a hi-fi enthusiast as a father. He plays vinyl, and previously used cassettes before moving to CDs in the 1990s. I was brought up (or spoiled?) with high-quality stereos since I was a youngster.

I started to like tube equipment when I heard the combination of a Unison Research Simply 2 and a B&W 601S2 speaker in a shop in Hsinchu, Taiwan. I seriously started to create DIY audio projects when
I was working in Taiwan in early 2000. A friend, who was also a tube dealer, introduced me to his DIY 300B tube amplifier that was driving a pair of vintage Tannoy 15” dual-concentric speakers. It was the Tannoy GFR, if memory serves me right. The sound they produced was made in heaven and no setup that I’d encountered at that time was close to producing what I heard that day.

I was hooked on the glowing tubes. I started reading about vacuum tubes online, in books, and in magazines (e.g., Sound Practices, Audio Amateur, audioXpress, etc.). I wanted to learn more about vacuum tubes so that I could build a sound system of my own. I also started “wasting” money collecting NOS tubes for my future projects. Now, I have more tubes than I will ever need in my entire lifetime. Maybe if my daughter inherits my interest in audio technology, she will find a use for them. Who knows?

Among his many projects, Ken built a 2A3 amplifier. However, instead of a 2A3 tube, he used the double plate NOS 6B4G because it has the same electrical characteristics as a 2A3 tube. The main difference is that the filament uses 6.3 instead of 2.5 V.

Among his many projects, Ken built a 2A3 amplifier. However, instead of a 2A3 tube, he used the double plate NOS 6B4G because it has the same electrical characteristics as a 2A3 tube. The main difference is that the filament uses 6.3 instead of 2.5 V.

SHANNON: Describe your first personal project. Why did you build it? Is it still in use?

KEN: Tube amplifiers were still uncommon in those days and purchasing one was costly. It was definitely out of my budget when I was a young engineer. Back then, an ordinary tube amplifier alone was two or three times my monthly pay. Since I have knowledge in electrical engineering and electronics (well, sort of, since I studied all solid-state electronics), I thought I would attempt to build a tube amplifier. I thought making a tube amplifier from scratch certainly would not be difficult for me. So, I started building tube amplifiers because the DIY methods made them accessible to me.

A Taiwanese friend assisted me with my first build. He did most of the design work and I did all the soldering since I was still very new to DIY tube amplifier construction. It was a two-stage all triode amplifier with a 300-B direct heat triode driven by a 5842 miniature triode. The sound was sweet and warm even though it was (un?)matched with a small B&W 601S2 bookshelf speaker. (I still have this pair of speakers today!) They are definitely 10 times (exaggerated!) better than all the entry solid states I owned or bought when I was in the UK.

My true first 100% built-by-myself project was an all Russian Reflektor 6C45PI with a 6C33CB triode mono-block tube amplifier. I read an article about a 15-W SE 6C33C-B amplifier that Erno Borbely published in Glass Audio magazine. His article sparked the idea for my own project. I used his design to build my own 6C33C-B amplifier circuit.

“I’m a mischievous youngster! I’m an engineer! I can do much better than him!” So I thought. Well, it didn’t go that well.

SHANNON: What kinds of audio projects do you build? Can you share some of the challenges involved with the designs?

KEN: I build speakers, pre- and power amplifiers, DACs, subwoofers, mains filters, and almost any kind of audio-related gadget. Some of the projects I have built over the years include: Class-D amplifiers with Philips and Tripath integrated circuits, Gain Clone clones (LM3886 and LM1875), Fostex FE167E bass reflex bookshelf speakers out of real wood, a Fostex FE167E in TQWT enclosure, an Altec 640D in Altec 620D cabinet, several 300B SE amplifier variations, 45 SE amplifiers, 6B4G amplifiers, an 1H4G preamplifier, a 6SN7 preamplifier, a 5687 preamplifier, a 6C45PI SPUD, a 5842 SPUD, an EL34 single-ended amplifier, a Tannoy HPD385A active crossover, and many more that I can no longer remember.

I still have some of the completed projects. I’ve also posted a few of them on my website (www.diy-audio-guide.com). DIY audio is challenging in many aspects, especially if you want your designs to sound really good and be reliable. To get something to work is easy. To master it is rather difficult.

Ken used this chassis for a hybrid amplifier design. The front plate and heatsinks are made of aluminum. All the holes are pre-drilled and the chassis accessories are supplied as a package.

Ken used this chassis for a hybrid amplifier design. The front plate and heatsinks are made of aluminum. All the holes are pre-drilled and the chassis accessories are supplied as a package.

Some of the most challenging areas include:

  • Aesthetics—I admit this is one of the challenges I always face. I do see that there are a lot of DIY designs online that look fantastic, almost as good as commercial designs. But for the projects to look good, you need to spend significant time, effort, and money from the design’s start until the end. However, my bias would lean more toward sound than looks. For my projects, I definitely spend more time on the design and the components rather than the finished look.
  • Test and Measurement—This is something I find really challenging on financial and knowledge terms. My daily job includes testing and measuring computer motherboards for power, signal integrity, compliance, eye diagram, and so forth. I use a lot of test and measurement equipment (e.g., multimeters, LCR meters, oscilloscopes, spectrum analyzers, and various other meters). This equipment is expensive and not something an ordinary DIY guy can afford to purchase for personal use. An oscilloscope can cost more than a house in Penang.
  • Measurement Methodology—This is a topic on its own. A different methodology or setup yields different results and that is sometimes misused because end users occasionally deviate from the figures/specifications that matters the most. Audio design is an art. Or perhaps it is better to say audio design is a black art? When I was a young graduate, I thought that if I got the circuit right, good sound would follow. It is not that easy! Everything matters, from component selection to the layout.
    I’m often amazed that some people think tidy wiring equals good sound. This will not guarantee good sound, but it does help future troubleshooting.
  • Separating Truth from Fiction—One thing I personally do not like is trying to differentiate among the hype or claims with hidden/personal agendas. I was, and sometimes I still am, tricked into buying something (DIY parts/components) that does not perform as claimed. There are many out there. So, beware!
  • Last but not least, the biggest challenge for all DIY audio hobbyists is that DIY audio projects often involve carpentry and electrical/electronic, which can sometimes be dangerous. You must work with sharp objects, live electrical connections, and tools. Take precautions and be safe.
Siegfried (Sigi) Maiwald of Wuppertal, Germany, shared his multi-cellular horn project on Ken’s DIY website.

Siegfried (Sigi) Maiwald of Wuppertal, Germany, shared his multi-cellular horn project on Ken’s DIY website.

SHANNON: What has been the most creative project you’ve received on your website?

KEN: I received these two amazing DIY speaker and DIY tube amplifier projects from Siegfried (Sigi) Maiwald of Wuppertal, Germany. One day, I met Sigi via the website’s feedback form and we became good friends due to our DIY audio hobby.

Sigi’s approach to DIY audio, his attention to detail and workmanship, not to mention his energy (and strength to manage such a humongous speaker), and spirit are simply outstanding.
In terms of creativity, he used a broom as the support/stand for a multi-cellular horn! In addition, he used the “УO186” as an inexpensive substitute for the ultra-rare and ultra-expensive RE604, which is definitely cool. I would not have known you could do that. Too bad the project suffered at the end due to a mishap.

You can check out his projects (write-up and photos) at www.diy-audio-guide.com/sigi-audio-setup.html and at www.diy-audio-guide.com/RE604-tube-amplifier.html.

The DIY 300B amplifier circuit design and components use a Tung-Sol 5687WA military tube as the pre-amplifier and driver stage. The power tube is JJ 300B and the power supply uses a RCA 5U4GB full wave rectifier tube.

The DIY 300B amplifier circuit design and components use a Tung-Sol 5687WA military tube as the pre-amplifier and driver stage. The power tube is JJ 300B and the power supply uses a RCA 5U4GB full wave rectifier tube.

SHANNON: With all the products that are available, why do you think audiophiles continue to experiment and build their own equipment?

KEN: DIY audio is one of those continuing trends. Fanned by the increasing price of audio equipment, it remains popular among the DIY-audiophiles. Everyone wants a piece of high-end equipment but the disproportionate price vs. performance and the return of investment places many high-end products out of reach for the general community.

Cost aside (DIY is not inexpensive either!), I’m sure DIY audiophiles will continue to design and build because of the satisfaction and enjoyment they receive when listening to their own creations and masterpieces! I am proud to say that I made most of my home audio gear!

TurboCal Provides a Low-Cost Solution

HAA’s TurboCal Suite is designed for quick acoustic calibrations.

HAA’s TurboCal Suite is designed for quick acoustic calibrations.

Home Acoustics Alliance (HAA) now offers an audio TurboCal package. This kit is designed for quick acoustic calibrations you suitable for every job. AVPro 2.0 will even walk you through the process. With this setup, you only need to add the AVPro iMux 4 and you will have the complete professional kit. Just add an iPad and a few apps.

The kit includes an iAudioInterface2 preamp/generator, an HAA-approved Type 2 measurement microphone, AVPro 2.0 audio reporting software, and a SC05 sound-level calibrator. The TurboCal package costs $1,150.

For more information, visit www.avproalliance.com.

B&K Precision Expands Waveform Generator Series

B&K Precision’s 4050 Series offers several modulation schemes and the display functions are clearly labeled (a). The back panels are universal for all the 4050 Series units (b).

B&K Precision’s 4050 Series offers several modulation schemes and the display functions are clearly labeled (a). The back panels are universal for all the 4050 Series units (b).

B&K Precision announced the launch of its 4050 Series, a line of four dual-channel function/arbitrary waveform generators. These instruments can generate waveforms up to 50 MHz for use in education and applications requiring stable and precise sine, square, triangle, and pulse waveforms with modulation and arbitrary waveform capabilities.

All models are dual-channel and provide a main output voltage that can be varied from 0 to 10 VPP into 50 Ω. A secondary output can be varied from 0 to 3 VPP into 50 Ω. Large 3.5” color LCDs, rotary control knobs, and numeric keypads with dedicated waveform keys and output buttons make waveform adjustments quick and effortless.

Equipped with a 14-bit, 125 MSa/s, 16k point arbitrary waveform generator, the 4050 Series provides users 48 built-in arbitrary waveforms and the ability to create and load up to 10 custom 16 kpt waveforms using the included waveform editing software via a standard USB interface. An optional USB-to-GPIB adapter is available for GPIB connectivity.

The 4050 Series offers: amplitude and frequency modulation (AM/FM), double sideband amplitude modulation (DSB-AM), amplitude and frequency shift keying (ASK/FSK), phase modulation (PM), and pulse width modulation (PWM). Other standard features include linear and logarithmic sweep function, built-in counter, Sync output, trigger I/O terminal, and USB host port on the front panel to save and recall instrument settings and waveforms. A standard external 10- MHz reference clock input is provided for synchronization of the instrument to another generator, a feature not typically found in generators at this price point.

B&K Precision’s 4050 Series products are backed by a standard three-year warranty. The 4052 (5 MHz) costs $499. The 4053 (10 MHz) costs $599. The 4054 (25 MHz) costs $850. The 4055 (50 MHz) costs $1,050.

B&K Precision is offering a 10% discount until November 30, 2013. Visit www.bkprecision.com for details.

NTi XL2-TA Receives Type Approval

The XL2-TA Sound Level Meter has received Class 1 approval.

The XL2-TA Sound Level Meter has received Class 1 approval.

The XL2-TA sound level meter has received Class 1 type-approval from the Physikalisch-Technische Bundesanstalt (PTB) in Germany. The XL2-TA in combination with the M2230 measurement microphone, is officially listed as a type-approved Class 1 sound level meter. The XL2-TA is suitable for environmental noise, occupational health, and sound insulation applications where the measurements require certification.

Receipt of the type-approval certificate confirms the XL2-TA (in combination with the M2230 measurement microphone and the ASD cable) offers full compliance with the Class 1 sound level meter requirements in accordance with the International Electrotechnical Commission (IEC) standards 61672 and 61260 and meets the American National Standards Institute (ANSI) S1.4 Type 1 performance. The XL2-TA offers certified spectral measurements in octave and third-octave resolution, which further comply with Class 0 filter specifications.

The M2230 measurement microphone connected to the XL2-TA via the ASD cable configuration enables the user to monitor the level readings on the instrument display while Class 1 measurements are taken. The NTi Audio Precision Calibrator completes the portable measurement kit offered in the compact system case.

Customers may upgrade their XL2 analyzers to a type-approved XL2-TA by adding a retrofit kit. Contact your local NTi Audio partner for the upgrade. For more information about the XL2 Analyzer and obtaining the type-approval 0ption, visit www.nti-audio.com/XL2.

ADLINK Introduces a Signal-Acquisition Module

Adlink-USB-2405

ADLINK’s USB-2405 supports four analog input channels.

ADLINK Technology now offers the USB-2405, a four-channel USB 2.0 dynamic signal-acquisition module. The module’s built-in IEPE excitation current source provides 2 mA on each AI channel. BNC connectors enable the USB-2405 to provide high accuracy and excellent dynamic performance for microphone and accelerometer measurement in vibration and acoustic applications.

The USB-2405 offers a portable solution for time-frequency analysis and research that includes accuracy with low temperature drift, built-in anti-aliasing filters, support for flexible trigger mode, and a USB power.

The USB-2405 supports four analog input channels simultaneously sampling up to 128 kS/s. It delivers 100-dB dynamic range and –94-dB THD of dynamic performance. Built-in anti-aliasing filters enable the filter cutoff frequency to be automatically adjusted to the sampling rate, suppressing out-of-band noise and avoiding measurement distortion.

ADLINK’s USB-2405 also supports auto-calibration for ensured accuracy and minimizes temperature drift in the field. The USB-2405’s low DC measurement drift, along with temperature deviation, optimizes accuracy in spite of the environment.

The USB-2405 provides a lockable USB to enhance connectivity. The included multi-functional stand fully supports desktop, rail, or wall mounting. ADLINK’s easy-to-use U-Test software is included at no extra charge. With no programming required, the USB-2405 delivers fast, easy instrument setup and quality data acquisition. The USB-2405 supports Windows 8, Windows 7, and Windows XP OSes and is fully compatible with third-party software (e.g., LabVIEW, MATLAB, and Visual Studio.NET).

For more information, visit www.adlinktech.com.

A Workspace for Radio & Metrology Projects

Ralph Berres, a television technician in Germany, created an exemplary design space in his house for working on projects relating to his two main technical interests: amateur radio and metrology (the science of measurement). He even builds his own measurement equipment for his bench.

Ralph Berres built this workspace for his radio and metrology projects

Ralph Berres built this workspace for his radio and metrology projects

“I am a licensed radio amateur with the call sign DF6WU… My hobby is high-frequency and low-frequency metrology,” Berres wrote in his submission.

Amateur radio is popular among Circuit Cellar readers. Countless electrical engineers and technical DIYers I’ve met or worked with during the past few years are amateur radio operators. Some got involved in radio during childhood. Others obtained radio licenses more recently. For instance, Rebecca Yang of Tymkrs.com chronicled the process in late 2011. Check it out: http://youtu.be/9HfmyiHTWZI and http://tymkrs.tumblr.com/.

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