After the invention of the transistor in 1947, semiconductors began rapidly supplanting the electron tube for all but the most specialized uses (yes, like in some of your favorite analog gear). Today’s high-powered computing ICs incorporate transistor counts besting a million per square millimeter. Individual transistors and their integrated circuit brethren form the building blocks of most of today’s audio devices, be they analog or digital, simple amplifier stages or processing blocks.
Each year, Pro Sound News queries audio design engineers about their semiconductor usage. This year’s respondents are B.J. Buchalter, VP R&D at Metric Halo; David Eltzroth, president and CEO of ROX Electronics; Tony Gambacurta, senior engineer at Whirlwind Music Distributors; Rob Jenkins, director of product strategy for Focusrite; Patrick Quilter, senior audio designer at QSC Audio Products; David Thibodeau, VP at Daking Audio; and Paul Wolff, president at Tonelux Designs.
Analog Audio Building Blocks
For analog design, these designers are largely using familiar components though, as Buchalter says, “The components of the types that we have been using continue to evolve, and we continually evaluate new products to see if they fit with upgrades or new designs.” Our designers are finding some new favorites; Eltzroth gives a nod to chipsets from THAT Corp—the 1200 InGenius balanced line receiver, the 1646 balanced line driver and the 4301 dynamics processor. THAT was also endorsed by Buchalter, who mentions the 1570 and 1571 single chip, digitally controlled mic preamplifiers. Thibodeau adds the THAT 5171 digital preamp control chip, which pairs nicely with the 1570 and 1571. Wolff includes Texas Instruments chips on the list, noting its new OPA1642 dual op amp (operational amplifier; common ICs used in analog circuitry) “sounds really great and has low noise.” Gambacurta adds the THAT 4315—a low-power version of its dynamics engine for use with battery-powered devices, as well as the TI OPA2211 (single) and TLC2272 (dual) 8-pin op amps. Whirlwind designs, he notes, are increasingly using ICs as opposed to discrete devices, for both high performance and low cost.
THAT Corp’s 1570 audio preamplifier and 5171 digital preamplifier controller make short work of designing and controlling circuits like microphone preamps.
As illustrated by the devices cited, our panelists will use special-purpose analog ICs (like single-chip mic pres, dynamics processors or volume controllers), though Quilter cautions that such devices are “generally too expensive for value-based, higher-volume products.” Thibodeau says that Daking has been “using the THAT Corp balanced drivers and receivers for a couple of years now, and we are pleased with the results. Customers who compare the new units with the old units using transformers are reporting little to no difference.” ROX’s Eltzroth says he’s adopted THAT Corp chips because of “a big improvement in sonic and lower noise performance, as well as stability.” He attributes these quality improvements to “the ability of the chip manufacturer to laser-trim on-chip components [ICs employ components such as resistors and capacitors in their substrate, in addition to transistors], which greatly improves performance of the on-chip circuits and, in turn, improvement of the overall product.”
Buchalter also cites noise and distortion performance as motivators in new part selection, though cautioning that, “Unfortunately, this is always in competition with quiescent power, which is a real issue for the sorts of high-density designs we do.” While “there are a lot of choices for specialized audio ICs both high performance and low cost,” according to Gambacurta, he adds that, “Discrete component choices continue to narrow.” Wolff says that he will “always use my discrete op-amp for mic preamp, summing and input/outputs,” though he will employ chips in circuits “where the signature tone of the TX-240 (Tonelux’s proprietary op amp built from individual components) isn’t desired or required.”
Wolff says that even in this increasingly digital world, the higher-end analog IC market “has actually grown quite a bit; as the resolution and noise floor improves with the market, these IC products are becoming better and more available.” Current audio circuit board designs are increasingly using surfacemount components as opposed to devices with leads that pass through holes in a circuit board to be soldered down on the backside. Wolff continues, “Some older chips are slowly becoming surface mount only, so if you aren’t prepared for that, you might be screwed.” Eltzroth says that trend applies to components besides semiconductors: “It appears that distributors are carrying less through hole-capacitor types and values. In many cases, we have had to take what we consider second best.” Thibodeau adds, “Some of the film caps are never stocked. Suppliers seem to be stocking less of the low-volume parts.” Gambacurta sees a shortage in the “parts used in vintage guitar effects products.” Quilter states, “‘Common’ parts may be discontinued by old suppliers, but someone still makes them.” Jenkins says, “Currently most silicon [‘silicon’ used here as a synonym for semiconductor devices] is difficult to source. We have lead times for common parts that were originally on a 6-week lead time now have extended out to 6- to 9-month lead times...We expect another year of problems before it gets back to normal. Now, of course, there is an inflationary pressure too, with the demand outstripping supply once again.”
Quilter says that QSC has adapted to limited availability by finding new suppliers, while Eltzroth says his company has been “buying larger quantities when available,” as does Metric Halo and Daking. Gambacurta cites “functional block replacement” as a coping strategy, along with “buying new-old stock.” Jenkins sums up the situation this way: “The old pre-2008 model was very hands off with vendor supply chain management. However, these days, we have had to become more focused on accurate production forecasting and to manage the component supply-chain issues more closely if we want to maintain supply, avoid surprises and protect profit margin.”
ROX has avoided the move to surfacemount components. “We are a small, boutique manufacturer and having to convert to surface mount would require us to outsource our circuit board manufacturing. At this time, outsourcing is not a good fit for our company.” Surfacemount design has been embraced by the rest of the surveyed designers except, as Jenkins says, “Where the choice of a non-surface-mount component will positively enhance the audio performance; this is generally true for certain capacitor types and values.” Quilter cites surfacemount design as “routine” and “preferred for compactness and signal integrity (smaller loops) although certain parts remain thru-hole.” Buchalter adds, “SMT [Surface Mount Technology] parts are easier to source these days, generally easier to rework/service and allow for (much) higher-density designs.”
Wolfson’s new WM8912 illustrates how compact sophisticated devices are becoming. The 4x4mm package houses DAC and headphone amp for portable consumer applications, with “ultra-low” power consumption.Wolff says, “In the early days, many of the [SMT] components were not of good quality. Nowadays, the materials used in surface-mounted parts are the same, though some of the higher-current transistors don’t sound the same, as the die design is different, which affects the sonics a bit. The biggest factor in surfacemount products is the ability to service parts, so many manufacturers resist doing it…One other factor is that some companies are claiming that ‘we don’t use any surface-mount parts’ as a ploy to instill fear into customers, implying that they are inferior parts. I think the truth is that you have to build a larger quantity, so they may not be able to afford a larger build.”
In the Digital Domain
Transitioning between analog and digital circuits requires conversion, the historical weak link in many audio circuits. “Subjective sound quality” is the primary determining factor by which Buchalter says Metric Halo judges conversion components, followed by noise and distortion specs, then latency. Dynamic range is the most important spec for Focusrite: “We find that maximum dynamic range is often traded off against distortion so that the art to get both figures low is where most of the hard design work comes in, with close detail having to be taken on the subtle PCB [Printed Circuit Board] layout requirements and key component choices and values.” Quilter adds “long expected life cycles” as a concern for QSC Audio.
AKM converter parts were those most often cited by those of our panel that incorporate converters in their products, “because they sound so good,” says Buchalter. Jenkins gave a nod to a new chip maker: “We have been working with a company called ARDA Technologies. They are relatively new into the audio market, and they have some interesting, well performing, new components, which we are planning to use in some products that will be released in the near future.”
Outside the signal chain, semiconductors are also employed for user interface (UI), control of a device’s parameters and display of settings and status. “Soft” controls or computer-based control often replace the mechanical switches and potentiometers of legacy designs. Buchalter says, “We utilize DSP + FPGA for system and UI control. The DSP does FireWire transport and system control, and the FPGA implements lower-level UI functions like display controller, encoder decoding, de-bouncing and message formatting. Our newest product implements a large-scale, multichannel PWM controller to allow color and brightness control of the 495 bi-color LEDs that are on the front panel of the device. This allows software control over the usage of the indicators and has allowed us a great deal of flexibility in implementation and UI functionality. Future products are likely to utilize newer micro silicon that is C-programmable (ARM or PPC), as this will simply make it easier to write the support code faster.”
Thibodeau answers, “I use several different microchip processors for this, depending on the complexity. I really like the PIC18F6310 because it is really low cost and runs fast enough to scan quite a few switches, and it has lots of communication options. The negative is that it has no EEPROM on board, but for front-panel designs, it is not needed or I just use an external EEPROM. These devices cost around $3 in modest quantities!” Gambacurta adds, “I have used low-cost, 8-bit processors for UI. For the right product, using a single processor for UI, control and DSP makes sense, too.” Quilter says that power amp designs “traditionally have simple needs, but the trend is towards more DSP functionality and graphic interfaces.”
Let the Buyer Be Aware
Does component selection actually affect the end-user experience? Yes and no, says Buchalter. “Two designers can utilize the same basic components and come up with designs that have dramatically different performance characteristics,” he explains. Quilter laments a lack of attention to the basics of design, commenting, “You kind of expect cheap stuff to be a gamble, but even ‘step-up’ gear seems to be the same cheesy guts with a prettier face.”
Buchalter advises: “My takeaway: Trust measurements over parts lists, and learn to correlate subjective experience with measurements. This will allow you to get a good feeling about a device before you evaluate it subjectively— but it does not obviate the need for you to evaluate it subjectively.” Gambacurta also advocates testing: “Test the equipment you plan to use. Learn its limits, so you aren’t surprised during the show. Learn about which manufacturers you can trust and provide the best customer service.” Thibodeau cautions against uneducated opinions, saying, “Get a demo unit, listen to it, use it and make your own opinions.” Eltzroth cautions, “I would suggest that digital versus analog should be carefully evaluated before arbitrarily converting everything to digital. There are some areas in audio where analog is still a better solution.”
Buchalter provides our summation: “Processors keep getting faster and cheaper, serial communications are the future, our audio devices will continue to get smarter, and audio quality has become extremely good at reasonable prices. This doesn’t mean that you can get world-class quality and functionality for a few hundred bucks, but you definitely can without having to spend tens or hundreds of thousands of dollars these days. These are all good things.”
For the full transcript of our survey results, including more detail on the questions above as well as discussions of buspowered designs, DSP components and design tools, FPGA and native processing, and sample rate conversion, visit the blog section of prosoundnews.com.