If you’re a gear geek like I am — and since you’re reading FOH, I’ll bet that you are — you may have noticed that signal processing has been steadily migrating into power amplifiers. This is nothing terribly new: For years amplifier manufacturers have offered add-on processing. I can remember when I was a teenager (late 1700s) trying to lift a Peavey CS800 — the original CS800, many of which caused herniated disks and are still in service today — and seeing a weird circular socket on the rear panel. I was afraid to touch that socket, thinking I’d get electrocuted even when the amp was unplugged.
Turns out that was an octal socket intended to accommodate some sort of audio circuit such as an isolation transformer or a crossover. Other manufacturers offered octal sockets for similar purposes. Definitely Crest Audio’s 8001 (and similar amps in that series) employed octal expansion, and some of the QSC amps of the same era come to mind. I clearly remember an install where single Crest amps (model 7301?) were used to biamp monitor mixes. A crossover module plugged into the octal socket, enabling the amp to run low-frequency audio from one amp channel (for the LF driver) and high frequency audio on the other channel (for the horn). If I recall correctly, the 7301 was built with this purpose in mind and provided higher output capability on one channel compared to the other so that you could have more power for the LF driver. Back in the day, I think a lot of engineers didn’t “get it” and stuck with their outboard crossovers. Or maybe that was just me.
The Next Level
Crown Audio took the concept to another level with PIP modules (Plug-In Processing), circuit cards that fit into rear-panel slots of certain Crown amps providing similar functions. Somewhere along the way this processing went from analog to digital domain, opening up the portal to external control via proprietary networks or even commonplace Ethernet. The introduction of amps like the Lab.gruppen PLM 10000Q and Crown’s iTech series raises onboard processing to a new level.
The PLM 10000Q, which literally can deliver enough power to run a moderately sized refrigerator, incorporates something that no other power amp currently in production can offer: Dolby Lake Processing. If you are not familiar with DLP, you should be (see Larry Hall’s review in the February 2008 issue). Among the features that DLP provides are Raised Cosine EQ, linear phase and classic crossover types, LimiterMax loudspeaker protection, and Iso-Float ground isolation [that last item, Iso-Float, is nothing short of pure genius. It allows you to easily make or break an audio ground connection at the rear panel of the device, negating the need to screw around making cables with unterminated grounds in an effort to eliminate a ground loop in the system. Iso-Float should be licensed to every manufacturer who produces a power amplifier, EQ, crossover or system controller].
If we look around at other manufacturers, we’ll find Dynacord’s new PowerH Series of high-end power amps. In addition to delivering peak voltage outputs from 180 to 200, PowerH amps accept Dyncord’s RCM-26 expansion card, a dual-channel digital controller module. Adding an RCM-26 to a PowerH amplifier provides a variety of signal processing functions, including EQ, crossover, delay, compression, linear phase FIR filters, zero-latency FIR filters and digital loudspeaker protection algorithms. It also provides digital (AES-3) I/O, RS-232 and RJ-type ports, allowing the amp to hook into Dynacord’s IRIS-Net- network. That’s an incredible amount of processing muscle for a device that traditionally has done no more that boost the gain of an audio signal.
Other manufacturers are addressing the integration of system control and power amplification. For example, Yamaha’s TXn Series of power amps not only offers the ability to safely drive two-ohm loads, but also incorporates onboard DSP accessible from a front-panel interface. TXn amps incorporate EQ, delay and limiting and have a rear-panel slot for Yamaha mini-YGDAI interface cards enabling a lot of I/O options including EtherSound and CobraNet.
What Does It Mean?
Well, for one thing it means less wiring and smaller racks, both of which translate into systems with smaller footprints (clients love that). Building DSP into power amps can ultimately mean that we won’t need any external crossovers, limiters or EQ in our drive rack — though I still want 31 sliders to grab without paging menus during the show. We can eliminate the wiring that goes along with those outboard devices, and maybe some of the ground issues that crop up as well. Devices with this type of DSP typically include a library for preset and user settings, facilitating setup for touring systems, and I expect we’ll see that in power amps too.
While integration of system processing into power amps means a reduction in the complexity of advanced PA systems in terms of hardware, it means increased complexity in terms of software. You’ll need to learn an operating system to program the amp from the front panel and probably will be able to (or need to) use a PC for programming and monitoring of the amplifier’s status. Oh yeah, and don’t forget to brush up on your networking skills because you’ll need them in audio…
A trade-off of placing DSP in the power amplifier is that you have less physical access to system control. Power amps are rarely if ever located at front of house, with good reason: They occupy a lot of space and make a lot of noise (or at least their fans do). Unfortunately, we’re accustomed to having our drive racks right next to the mixing desk at front-of-house, so having a computer with access to the amp network will become a necessity and not just something that impresses the audience. I imagine that we’ll need some sort of redundancy for these systems because if you lose the processor, you’ll probably lose the amp (and vice-versa). The thing that really scares me, though, is the idea of leaving computers in an amp rack, collecting dust and cooking in the hot summer sun of an outdoor festival. Maybe we can have the amp racks hermetically sealed…
Steve “Woody” La Cerra is the front-of-house engineer and tour manager for Blue Öyster Cult. He can be reached via email at Woody@fohonline.com
