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History Files: Tycobrahe Sound Company And “The California Jam”
54,000 watts of audio power... 105 dB SPL at one mile... 200,000 satisfied rock fans...
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The SM57’s were chosen because, according to Jim Chase, Tycobrahe’s director of operations, “You have to use a real close-pattern cardioid dynamic microphone on any instrument that is going to be put through the monitor system. Other people use a lot of wide-pattern stuff, even good cardioid patterns, but no good enough. There’s only one mike that works for us and that’s a Shure SM57.”

Everything on stage was miked except the bass, which was also taken direct, so as to deliver through the system the distortion and other effects created in the guitar amplifiers. As Chase points out, “We don’t much get into studio techniques in terms of miking or direct instrument feeds. The groups are looking for a sound and they want to be in control of that sound. They don’t want us to color it or change it. We’d make it clean if we had our choice. If we were to take the instruments direct we wouldn’t get the musician’s tube amplifier mushing and his power supply saturating and the speakers moving to maximum excursion, and all the other things that create the particular noises that you can get out of a guitar amplifier. The talent wants that and they want us to simply reinforce it.”

At the Jam the signal from each mike on stage had to feed four separate and distinctly different entities: the main Tycobrahe sound system, the Tycobrahe monitor system, the Wally Heider 24-track recording vans and the ABC-TV videotape trucks.

Two vans were use by Wally Heider, one for each stage, and it was determined that the Heider mixers would feed the signal to the ABC-TV mix.

From the early planning stages the interfacing of the four systems was considered one of the primary potential trouble areas. As Ralph Morris stated it, “The equipment was all different and the concepts were all different. And, of course, each group of engineers had different points of view. We anticipated ground problems as with any interconnected system so we left plenty of time to work them out. Sure enough, when we plugged it all in, it hummed!”

In considering how to isolate the various signal feeds from each microphone any resistive method was quickly discarded because of the substantial gain loss that would occur. Instead, each microphone fed a separate four-winding transformer. The transformers were special-ordered from Sescom and mounted in boxes with ground-release switches.

The installation of equipment began on the Tuesday before the Jam with Wednesday and Thursday devoted to the set-up of speakers and electronic hardware and the check-out of each individual system. On Friday morning the main system, monitor system, recording and TV systems were interconnected for the first time. It was then a question of methodically going through the systems and eliminating the ground loops. Ralph Morris told the story of one potential area:

“At one point we found we were still picking up an additional ground on some channels which was then no an overall problem. So we started going through them and found one connector with the shell wired to ground. Some manufacturers make them that way and they have to be disconnected. At that time our chief engineer said, ‘Oh, my God, we’re going to have to go through 180 connectors and clip the grounds on all the shell connections!’ But most professional audio engineers will remove the case ground if they use that brand of connector so as it turned out that was the only connector in the system that was causing the problem.

“Our MX2404 mixers are wired with all internal grounds returned directly to the center tap of the power supply secondary. If a mike cable with the connector shell wired to the shield is plugged in, this creates an exaggerated ground loop and a lot of hum, even if the input is turned down. We did this on purpose so we could instantly recognize an improperly wired cable.”

Another interesting point was the special attention paid to the delivery of power to the site. Separate mains were run to accommodate the Tycobrahe equipment and isolate it from the power source feeding the on-stage equipment of the groups. Otherwise, as Jim Gamble pointed out, “We’d have had the whole band playing and sucking up the A.C., especially on the bass notes. The power gets eaten up by the low end instruments. Consequently the AC starts dropping on every low note. It can drop from 120 volts down to as low as 90 volts. Instead of more power when you need it most, we’d get less.”

All-in-all the problems involved with bringing 12 hours of an ultra high level of audio entertainment to a potentially volatile audience of over 200,000 supercharged rock fans seemed to be very few… Very few, indeed, as typified by the comparative brevity of what the producers and their sound contractor had to say about problems.

Perhaps a statement from one of the producers summed it all up: “We were delighted to do without any lurid post concert headlines.”

Our sincerest thanks to Mark Gander and the gang at JBL Professional for supplying these materials.

Source: Live Sound International

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Comment (1)
Posted by Scott Lifshine  on  07/31/10  at  10:01 AM
Awesome! Great to see this once again.
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