audio – Page 6 – Engineering Radio

The Audioarts Air-4 Console

Aside from everything else, we have been working at WSBS, Great Barrington, MA installing a new Audioarts Air-4 console. WSBS is a small AM station (860 KHz, 2,500 watts day, 4 watts night) serving the Great Barrington area. They also have a 35-watt FM translator (W231AK) on 94.1 MHz which is highly directional. During the day, the AM station has a much better signal than the translator. After dark, the translator covers the downtown area fairly well. WSBS has been on the air since December 24th, 1957 (Happy 55th anniversary!), broadcasting from a non-directional tower just east of town on US Route 7.

The format could be termed full service, in the old tradition. Music, professional sports, local news, network news, and weather with coverage of special events like election night and so on. The station does local very well, and as such, is profitable and has a great community presence.

The air studio console was this rather tired-out Broadcast Audio unit from the early 1980s. It had certainly served its station well, but change was in the air, so to speak. Actually, we were getting worried about continuing to service this unit, as parts had become scarce about ten years ago.

Thus, we moved the air studio to the production room temporarily and removed all the old equipment and furniture. We installed an Audioarts AIR-4, which is a pretty cool little console. The AIR-4 has four built in microphone preamps, a telco mix minus feed, two program busses selectable VU meters and so on. The control room rebuild project included a new counter top, adding extra microphones, headphone amplifiers, cleaning up wiring rat’s nests, installing new monitor antennas, rewiring a good bit of the rack room and so forth.

It was a little more involved than we first thought, however, it came out pretty well:

The carpenter will be back next week, after Christmas to install the sides on the studio furniture under the counter top. It is a small operation in a small market in Western Massachusetts, but they have a real, live station staff including two news reporters. Hey, what a concept! To be honest with you, it is a joy all its own to work at a real radio station, if only for a short while.

AES X192

There is a lot of buzz about converged technologies and what not. I have always been a wee bit leery of bleeding edge technology, lots of money and time can be wasted there. Incompatibility between different manufactures equipment and protocols can cause major heartburn in all equipment life stages. See also: VHS vs Betamax. Thus, when many disparate standards are homogenized into one acceptable system for everyone, we all benefit and technology moves forward.

Audio over IP (AOIP) is moving into the general acceptance of broadcasters as a reliable system for studio construction. As with anything, there are pluses and minus to this development: First of all, packet switched data is more efficient and flexible than circuit switched data. For the purposes of clarity, an AES3 signal within a broadcast facility going from one piece of equipment to another can be defined as circuit switched data. Once the data is segmented, packetized and framed, it can be sent anywhere, over any LAN or WAN. This allows for greater connectivity between facilities and greatly increased delivery methods and redundancy.

The downsides are increased complexity in transmission, greater reliance software and delicate operating systems to process audio into data and deliver it, and Quality of Service (QoS) issues. Additionally, there are many different AOIP protocols and applications currently in use. To date, this is the current list AOIP standards that are used by various manufactures:

Wheatnet – Wheatstone, inc
Livewire – Telos
Ravenna – ALC Networkx (Open source)
Dante – Audinate
CobraNet – Peak Audio
EtherSound – Digigram
N/ACIP – EBU
Q LAN – QSC Audio Products
AVB – IEEE, AVnu

Each system has different characteristics. A Livewire system will not talk with a Wheatnet system and so forth. This is because of differences in the transport layer encoding schemes. Some use UDP, some use RTP, some use a propriety transport protocol, and some may even use TCP (remember the 7 layer OSI model). It would be similar to having an analog Wheatstone console unable to send audio to an analog Optimod which would be unable to modulate a BE transmitter.

AES X192 is an effort by the Audio Engineering Society to set an Audio over IP interoperability standard. This is the direction that studio audio equipment is moving and indeed, broadcasting in general.

The X192 project endeavors to identify the region of intersection between these technologies and to define an interoperability mode within that region. The initiative will focus on defining how existing protocols may be used to create an interoperable system. No new protocols will be developed to achieve this. Developing interoperability is therefore a relatively small investment with potentially huge return for users, audio equipment manufacturers and network equipment providers.

More here.

Eventually, broadcast audio consoles will plug into a WAN and be able to source audio from all over the place, not just the local physical studio structure. This lends itself to the evolving wired or wireless IP delivery method in place of the current terrestrial radio broadcasting currently used. As such, I will be diving into the fascinating world of AOIP more in future posts.

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.