Meeting Topic: Development of a Low Cost Programmable Microphone Preamp Gain Control IC for Pro Audio Applications
Speaker Name: Gary K. Hebert, THAT Corporation
Other business or activities at the meeting:
Annual PNW business meeting/election held.
Discussion of a field trip to see LP pressing/mastering in Portland OR.
Discussion of participating in a gear swap meet with Antique Radio Society.
Meeting Location: Shoreline Community College Music Building, Shoreline, WA
The PNW Section held its season closing and Annual Business Meeting June 29, 2016, and hosted Gary Hebert, CTO of THAT Corp, who spoke about his company's development of a lower cost digital gain control IC for microphone preamps.
PNW chair Chris Deckard made opening remarks, then Rick Chinn talked about a pending July field trip to Milwaukie OR to see a mastering and disc pressing plant. Date TBA and people would provide their own transportation and expenses. Dan Mortensen then talked about the upcoming Aug. 21 Antique Radio Society swap meet at the SCC parking lot and the PNW AES Section participating. Dan also mentioned the AES world elections and encouraged voting.
The PNW election was then conducted.
Rene Jaeger then introduced Gary Hebert, a former co-worker. Mr. Hebert is a co-founder of THAT Corporation and a longtime audio-electronics enthusiast. He currently serves as THAT's Chief Technology Officer, spending the majority of his time defining and supervising the design of analog and mixed-signal integrated circuits intended for use in the professional audio industry. He is credited with creating many of THAT's high-performance audio ICs, including the popular 218x series of VCAs, the 2162 Dual VCA, the 4320/4315/4305 Analog Engines®, the 1646/1606 Balanced Floating Line Drivers, and the 5171 and 5173 Preamplifier Controllers. He also continues to serve as an executive advisor to THAT's dbx-tv business unit.
Prior to founding THAT Corporation, Mr. Hebert was with dbx, Inc. from 1981 through 1989, where he held several positions, the last being Electrical Engineering Manager. He was responsible for a number of audio product designs marketed under the dbx, ADC, and Audio Dynamics brands. He also worked with semiconductor manufacturers on ICs used in the dbx Noise Reduction licensing program. He began his career at automated test equipment manufacturer Teradyne.
Mr. Hebert holds seven patents in the audio electronics field. He has authored and presented several papers for the Audio Engineering Society. He earned a BSEE from the Massachusetts Institute of Technology in 1979.
Gary began with a history of THAT Corp - founded in 1989, spun off from dbx, and the name is from the founders (Paul Travaline, Gary Hebert, And Les Tyler).
Next, he described characteristics of modern analog microphone preamps, and how digitally controlling their gain is used in modern products. He showed a typical mic preamp circuit, and how the gain is adjusted with feedback resistors. A digitally controlled array of resistors in the feedback circuit is the essence of their first controller ICs. He also talked about characteristics of doing resistors and switches in silicon, and using tapped strings of resistors for large gain changes and paralleling resistors for small steps.
He noted that this approach was somewhat expensive. Gary described several things that were done to reduce costs, and talked about the tradeoffs:
-make gain steps 3dB instead of 1 dB
-make the IC dual channel
-eliminate the on-chip servo output offset circuit, at the expense of needing a largish external capacitor.
-design a different feedback circuit to use the switchable resistor arrays, with less max gain (51dB). This turns out NOT to be so bad with typical preamps and A/D converters, although the THD can be a bit more. Noise ends up actually better at most gains.
-Fudge some LSBs (least significant bits) in the resistor array control to get better lower gain accuracy.
-scale down the size of resistors on the silicon die. While bigger is better, smaller is cheaper.
All in all, the new part is a 55% cost reduction from their premier products.
A refreshment break was held, then some door prizes were awarded:
-THAT logo thermal bottles: Rene Jaeger, Paul Colvin, Chris Deckard
-THAT gift certificates for IC samples: Tom Stiles, Steve Malott, Larry Aamodt
-Book, "Sony Book of Digital Audio Technologies" 1st ed, donated by Steve Malott, won by Kai Scheer
After the prizes, a general Q&A session was held, covering topics such as:
-Can he talk about any products using this part? He can't talk, except about a new Zoom device. Several major names use THAT products, perhaps an open secret.
-comments about parts taking a long time (years) to develop.
-discussion of noise specs and their derivation.
-discussion of different manufacturers using either or both THAT preamp ICs and/or THAT controllers. A customer may ask for the ability to add "color" to their preamp.
-VCA market discussion
Written By: Gary Louie