audio – Page 4 – Engineering Radio

Analog Sauce

A little blast from the past. This was found in a transmitter manual at one of the sites we take care of:

I thought I would scan it and make it available here. As luck would have it, there is also a corresponding piece of equipment to go along with it. I had never seen a “CCA Optomod” (.pdf) before I was working at one of the radio stations in Trenton, Florida. This unit was rescued from under a pile of garbage out in the lawn shed. It was full of mud wasp nests and mouse droppings. Needless to say, it required a bit of TLC to return it to operation. I replaced the electrolytics, cleaned it up, and ran some audio through it. It is probably as good as the day it left the factory. Bob Orban made some really good stuff in his day.

The original Optomod 8000 was an evolutionary design that made FM radio processing what it is today. The idea of combining broadband limiter, AGC and stereo generator in one box was a radical departure from the norm. The audio limiter functioned as a 15 KHz low pass filter and broadband AGC.

Orban Optomod 8000 audio limiter block diagram

The stereo generator used very modest amounts of composite clipping to reduce overshoot and transients. Many people disparage composite clippers. If done correctly, it is transparent to the listener and increases perceived loudness by stripping off modulation product that is non-productive.

Orban Optomod 8000 Stereo Generator block diagram

Some thirty five or so years later, there are still many of these units in service in various stations around the world.

The Raytheon RL10 Limiting Amplifier

Update: Apparently this is quite interesting to a number of people. I have rescanned the manual, properly compressed it and which you may find it here.

Found this manual at one of the older transmitter sites:

Raytheon RL10 limiting amplifier manual cover

The entire manual is available for your reading pleasure here: Raytheon RL10 limiting amplifier

As this is an older design than either the Gates Sta level or the Collins 26U, it may not be as useful to tube audio enthusiasts.

The main issue with the Gates and Collins unit is the GE 6386 remote cutoff triode used, which were great tubes, but very difficult to come by these days. This design calls for a 1612 or 6L7, which is a pentagrid amplifier. Feedback is provided by the screen of the following stage, a 6SJ7GT. Anyway, perhaps it will give somebody some idea of how to make a good tube compressor limiter.

New Studio Project, Part II

The finished product:

This is the finished product from an earlier post. Currently, it is the studio for WAJZ in Albany, but that is not permanent. The SAS studio goes together fairly quickly, as most of the trunking between the TOC and studio is done over the SAS data channel.

The studio monitors (Tanoy Reveal) are set on little posts under the computer screens. I like this setup as the DJs are less likely to rock the house if they decide to crank up the volume on their favorite tune. I am also kind of digging the lack of a tabletop equipment pod. That takes up a lot of countertop space and always seems to be in the way. There are two CD players racks mounted below the counter (lower left), which are almost never used.

New Studio project

It is time, once again, to replace some very old Pacific Recorders BMXII consoles. The Pacific Recorders consoles were very expensive when new, but after 30 years of continuous use, have more than paid for themselves. The replacement console of choice for this installation is a SAS Rubicon. I have installed these units elsewhere and they are the modern equivalent of the PRE BMX.

The heart of the Rubicon system is the 32KD router. Routed audio systems can save a lot of time and effort in a large studio facility installation. Not having to run and terminate multiple analog and digital trunk cables between the rack room and the studio is a huge deal in a six or ten-studio installation project.

The SAS 32KD router and Rubicon console system use a serial TDM bus to communicate and transport audio around. This is a simpler system than packet-switched IP data. Basically, the console surface is a very large, fancy computer control interface. Here are some pictures of the start of the project:

This is the view from the entry door. The furniture was placed last week and the countertop was cut in for the console. The furniture is made by Studio Technology. The pile of yet-to-be-installed equipment:

For monitors, we are using the Tanoy 602p near field monitor placed on the table top above the computer screens. This studio will not have a turret. Turrets used to be necessary to hold things like cart machines and CD players. These days the CD players are used so infrequently that it was decided to put them in the side rack under the counter top. Turrets also take up a lot of counter top space that can be put to better use.

Punch blocks and power connections. The red outlets are isolated ground UPS type, the back outlets are feed by the emergency generator power panel. All electric wiring is inside of the metal conduit. The punch blocks are the inputs to the SAS RIO link unit, one 16-pair analog audio cable and ten category 5e shielded cables. The cat 5e is used for computer and TDM data buss to the router.

The SAS Rubicon console is cut into the counter top and protected by plastic sheets.

Rack room with 32KD routers. This facility has 9 studios total plus a news room with three work areas.

The SAS 32KD router. All audio from the automation systems, satellite feeds and other sources is connected directly to these units. This unit is on line for other studios that have already been converted to the SAS gear.