Meeting Topic: Analog Tape Machines - Basics of Alignment and Calibration
Speaker Name: Gary Louie/Univ. of Wash. and Rick Chinn/Uneeda Audio
Meeting Location: Shoreline Community College, Shoreline WA
The PNW Section March 2014 meeting featured Section officers Rick Chinn and Gary Louie revisiting that age when analog tape ruled the earth, presenting a workshop/demo of an introduction to the analog studio tape machine, and the basics of alignment and calibration. 33 people attended (15 being AES members, including AES Executive Director Bob Moses) at Shoreline Community College, Shoreline WA.
Rick Chinn, PNW AES Committee-at-Large, and is owner of Uneeda Audio. At one point in his past, he got to align five Ampex AG440B and one 3M Model 79 machine every morning, times two studios. He now provides playback and digitizing services for the audio community. As far as recording goes, he now sips the digital kool-aid. Gary Louie, PNW AES secretary, is the audio technician at the University of Washington School of Music, whose fleet of analog 2-tracks still runs tape (playback/digitize) nearly every day. He has a BSEE from the UW, and is co-author of the 3rd ed. of The Audio Dictionary, with Glenn White (UW Press).
While a dim memory and nostalgia trip for many, some have never given up on analog tape, and need to do playbacks of archival material, or wish to record on tape for aesthetic reasons. Yet others know little about tape, but are now interested. This presentation attempted to cover only the basics of what a studio 2-track machine is, and how the "daily" alignment is done. On hand for the demo was an Ampex AG440C 2-track 1/4 inch tape machine, the typical analog test gear of the era (oscilloscope and generator), and various vintage hardware examples.
Gary began with a description of the basic tape transport, and the importance of very precise alignment of all parts. Rick continued with an overview of the electronics of these machines, including signal flow for record, repro and synch playback. Gary showed basics of headblocks, alignment and tools, noting many service manuals give rather poor methods for setting head positions accurately. Precision machine setups such as gage blocks give proper results, or you send it to an expert.
Rick next covered track formats, cleaning of machines and demagnetizing. Then, the basics of reproduce calibration with the calibration tape. Calibration tapes are a huge topic, with the MRL "Choose and Use" document being recommended. Repro head azimuth adjustment using the oscilloscope Lissajous figure display was shown, then the calibration of repro frequency response.
After a cookie break, some door prizes were awarded.
-Speaker patch cord (donated by Uneeda Audio) - Everett Moran
-traveler's toolkit (Bob Moses) - Paul Colvin
-AES papers CDROM (Bob Moses) - Rick Chinn; Ed Gruse
-"Audio Dictionary, 3rd ed." book by White & Louie (Gary Louie) - Dan Charette
-Tape topics CDROM (Uneeda) - Tom Stiles; Greg Mauser
-Booklet on tape topics (Uneeda) - Mike Matesky
-Custom logo CD blanks pkg (Uneeda) - Dan Droz
The next calibration step was the record calibration. Issues with picking a tape and reference fluxivity level were discussed. The sample tape was run, and the record head azimuth adjusted. Bias and methods of bias adjustment were mentioned. Finally, setting record equalization was demonstrated, juggling bias with EQ controls while sweeping through the tones with the oscillator.
It was a fun blast from the past and seemed to interest some newbies as well as amuse the old timers. Certainly the evolution of 50 years of this technology could only be touched on in one evening, but there's some evidence that the technology deserves and needs to be preserved.
Special thanks to Ki Choi for providing machine expertise.