audio – Page 6 – Engineering Radio

The old humming console

We are starting to work at a new client’s studios. It is a bit like stepping into a 1980s time machine, as the newest console seems to be the Broadcast Audio console in the FM studio. I feel I should wear a wide colorful tie and part my hair in the middle when working there. There is also an older UMC console in the second production room.

A what?

Exactly.

It seems the UMC console (UMC was a Connecticut-based console manufacturer that was later sold to Broadcast Audio) was having an intermittent hum problem on all the audio buses.

After poking around under the hood for a few minutes, I decided I should begin with the basics. Checking the power supply for ripple seemed like as good a place to start as any. This console has a 30-volt and a 12-volt power supply. The 30-volt supply checked out good, but the 12-volt supply, not so much:

2.7 volts AC on the 12-volt DC power supply. That will put some hum on the audio, all right. I tried to replace the power supply main filter capacitor, but it had no effect. The regulator must also be bad and it is a Motorola part number which is likely not made anymore.

This is a pretty standard off the shelf power supply, I should be able to get one from Mouser for about $60.00 or so for a linear unit, which will be cheaper than us trying to trouble shoot and repair the old one. In the meantime, I took the 10 amp 0-30 volt bench supply and pressed it into temporary service. The console is working again, for now.

At some point, all this old, um, stuff needs to be replaced.

The Raytheon RM-10 Monitor Amp

I found this manual from 1946 in the drawer at the WICC transmitter site, which is a sort of time capsule due to its inaccessibility. I figured I would bring it home and scan it, then return it to the file drawer out on the island. Step one is done:

This is a cool little monitor amp, capable of driving line-level or speaker outputs up to about 10 watts or so. It could be used as a front or input stage for a larger audio amp. By the way, 10 watts is a lot more than it seems, if using efficient speakers to convert that power into sound waves. Specs show total harmonic distortion is between 0.6 to 2 percent depending on power and frequency. Lower power output levels net less distortion.

Schematic is pretty simple, a pair of 6L6’s in push-pull for the output. Inverse feedback into the previous stage via the output transformer. Click on image for higher resolution.

Full manual and parts list is available here.

Now I just need to get the manual back out there.

Documentation and labeling wire and cable

There are a myriad of details involved in building a studio, not to mention an entire facility. Getting everything down on paper before a single wire is pulled is one way to ensure that a neat, logical, and orderly product ensues. For wire run documentation, I like to use Excel spreadsheet templates that I came up with.

There are several different types of cable, from 25-pair ATT style to 16 or 24-pair shielded audio cable, to miscellaneous control cable, all of it has different color codes. I found the Belden Technical info website to be an excellent source for various color codes.

Doing neat work is the best way to keep things in order. Notice all the wires are labeled. All the ground conductors have heat shrink, which is required on insulation displacement terminations like 66 blocks, 110 blocks, and ICON terminations.

ADC ICON termination block

Once all the work is done, the wire run sheets are updated with changes and additions (there are always changes and additions) which will keep the documentation accurate.

I made up several templates with the wire color code, pair number, and cable information on each wire. This allows the wire man to quickly enter changes to the wire information on the sheet. At the end of the wiring project, these forms can be saved in several places, printed out, and placed in a book or however, the engineering manager wants to keep the information.

The excel spread sheet for this is here.

For 16 pair Gepco cable on 66 blocks, click here.

For 16/24 pair Gepco cable on ADC ICON Termination blocks, click here.

I say Gepco cable, any audio cable that is color coded with standard resistor color codes will work with these sheets, or the sheets can be adapted for use with other cables.

66 blocks audio and control for nextgen installation

This is a good installation. The company I work for has several wiremen that are artists and do excellent work. Notice there is adequate room and light to work on the wall. A dark, cramped area will lead to hurried work, poor workmanship, and mistakes in wiring.

Automation computer on slide out rack with cable management system — Automation computer on slide-out rack with cable management system

All the cables to the rack mount computers are neatly dressed, which allows easier service.

They do it a little differently in Europe

Old world and all that. I am of the impression that European broadcast engineers are a more studied lot. Their process involves much more deliberation, thoughtful analysis, and planning than ours does. For example, when it comes to station loudness, most programmers and many engineers (myself not included) to do more is better. It is thus that we get the Omina 11 and other audio squashers.

The EBU technical group takes a different approach:

EBU R128 (ed: Loudness Recommendation) is the result of two years of intense work by the audio experts in the EBU PLOUD Group

Aside from the above-mentioned EBU R128, there are four technical papers dealing with implementation, meters, distribution, and so on. The body of work is a recommendation, not a requirement. I can’t imagine the voluntary implementation of something like this in the US. Even so, there are advantages to having a single acceptable level of programming audio. It is interesting reading.