In 2018 we decided to standardise our amplifier racks that house our Lab Gruppen PLM12k44 amplifiers.
We wanted to create a new standard for all our amp racks and work from the ground up. As part of this article, we will give a complete overview of our the re-design process to create our flexible amp rack solution.
To start the process we need to understand the amplifer in question. The Lab Gruppen PLM12k44 is an industry leading standard in amplifier technology allowing for high power output over all 4 channels. As a DSP amplifier, it has the capability to route many different inputs to a variety of different outputs – in the simplest terms, the amplifier has an input stage, the 4 amplifier modules and the output stage.
The input stage comprises of 3 different audio formats – Dante, AES and Analogue. There are a total of 4 Analogue input lines, 4 AES input lines and 8 Dante inputs.
The amplifier modules are where all the processing occurs with amplifier presets available for a wide variety of speakers.
Finally there are 4 speaker outputs send down a single NL8 connector (or 2 NL4 connectors). There are also Dante outputs to allow route through connectivity to any other Dante device.
You can route any input to any module, and any module to any output.
In terms of physical connectors, this relates to:
- 4 x Analogue XLR connectors
- 2 x AES XLR connectors
- 2 x Neutrik Ethercon connectors
- 1 x NL8 connector output (or 2 x NL4 connectors)
- 1 x 32A Powercon input for mains power
Power Distribution
Our first stage was to develop the power distribution. As we primarily use 3phase supply on site and the power connector supplied on the amplifier is 32A, the logical route was to use a 32A 3phase input. This also led to the very straight forward decision to mount 3 amplifiers per rack – one per phase. We also knew we would need some 13A internal power inside the rack to power the network switches we would need (discussed later on).
We also decided we wanted to mount a courtesy 16A and 13A to be mounted to the power distribution. This would allow simple connector for an additional amplifier if needed or plug a laptop in for configuring the amplifiers.
We chose to use our friends at SES Electrical Services who specialise in electrical power distribution. They created a power distribution with 32A 3phase input, 32A 3phase link out, 16A and 13A courtesy sockets on the front, 3 6mm 3 core tails and 3 x 13A outlets internal to the rack. This maxed out at 3U high.
Rack Case
The next stage was designing the case itself. For easy use and durability we wanted to use a slam lock lid style case. With the high value of equipment in the case we also wanted this to be a suspended rack case to reduce unnecessary vibration through the equipment.
In terms of size, we new we needed to fit 3 amplifiers at 2U each, a 3U power distribution unit and 2 network switches at 1U each which totals 11U. As such we chose to give a bit more space and make the rack 12U tall. We opted for 600mm depth between rack strip to allow for wiring the rear of the rack.
Connectivity
We wanted to provide a flexible and easy to use system for connectivity into the rack to enable the units to be easily configurable.
Networking
As the amplifiers are controlled and edited over network and also operate through Dante audio networking we needed to ensure the networking is easily accessible. Dante can operate with dual redundancy with a primary and secondary network – hence mounting 2 network switches in the amp rack – if one switch was to go down or the primary network would fail somewhere else down the line, the network would instantly switch to the secondary network and remain functional. As we already have a stock of the very reliable Level One GSW-0841 we chose to use these.
These switches have 3 vital advantages in this scenario. Firstly, they are 1U rack mount format with power and networking connectivity on the rear and indicator lights on the front, making for a clean and easily connectable unit. Secondly, they are a bit old to have a lot of the energy saving settings that a lot of modern routers have which can be detrimental to Dante. Finally, they come with an SFP fibre port which means we can make the amp racks usable at great distances.
In order to gain this connectivity, we designed a standard 1U rack panel to be mounted in the rear of the rack. This custom panel, designed and wired in house, included 4 CAT5 Ethercon connectors and 1 Neutrik Opticalcon fibre connector each for both the primary and secondary network. With the ports on the amplifiers themselves, this means that every port of the network switches is accessible.
Analogue Connectivity
The next most regularly used connector will be the Analogue stage. However this proved to be more challenging to develop. These amp racks will primarily have 2 different uses – as a FOH system amp rack or as a monitor system amp rack – which changes the analogue input needs of the rack. In FOH mode we primarily run the system as “Left, Right, Sub, Fill” over the 4 inputs, sending all 4 inputs into each amplifier, whereas if monitor mode, we want 12 individual inputs, 4 per amplifier.
So, this became the only swappable panel we have created for these racks – one panel for FOH mode and another panel for monitor mode.
For the FOH panel, we need to input the same 4 XLR feeds to each amplifier analogue input. We wanted to ensure we could access link outs on the analogue inputs to link through to other racks and for speed, we wanted multipin input and output available on each rack.
In-house, we only use 8, 16 or 32 pair cable in rack designs to allow continuity throughout all our panels and racks. As such, for this panel we opted to modify a standard design we have for an 8 way XLR panel from 25pin VEAM multipin. This allows us a 25pin VEAM input connector, with a link out VEAM connector, and 8 XLR inputs and outputs. Internally, the first 4 XLR inputs of this panel are each wired to 3 XLR connectors in parallel – one for each amplifier.
While we rarely use the additional 4 XLR inputs, however if we need an extra feed internally or similar we are able to provide this over the multipin and alter a patch internally.
For the monitor panel we chose to use a 54pin input VEAM paralleled with 16 XLR inputs. This is another modification of a standard 54pin VEAM to 16 XLR panel we have where we have altered the labelling and some connectivity. In this case, the first 12 XLR lines are connected into the 12 analogue inputs over the 3 amplifiers. The remaining 4 XLR feeds are connected with link outs to enable an additional amplifier to be connected simply and still run over the say 54pin VEAM input.
As these 2 panels are able to be hot swapped, the rear of the amp rack has been fitted with a 5U vented door for easy access.
AES Input
With 6 AES input connectors across the 3 amps, in order to keep with our standard 8way or 16way format, we chose to fit a 1U panel with VEAM multipin input and link out and 8 XLR inputs. We have included more custom labelling to show that its only the first 6 connectors that are connected to amplifiers.
The design of all these panels has been made so that we keep within our own internal standards and allow flexibility of use throughout our events.
Output Stage
The final panel is the 2U output panel. This panel needed to provide easy connectivity to both NL4 and NL8 as well as socapex. On this panel, each amplifier has its own section with 4 NL4s – 1 for each amplifier output – and an NL8 connector to route all 4 output feeds. Output 1 also contains output 2 on pins 2+/2- to allow for a biamp feed here – the same can be said of output 3 containing output 4 on pins 2+/2-.
Finally we mounted a socapex connector to the far right. This contains 8 amp feeds – all 4 from both amp 1 and 2 – to allow for easy cabling to line array hangs etc.
We may well ungrade the socapex to an LP25 connector to allow all 3 amplifier outputs (12 in total) to be routed down a single multicore speaker cable however at the moment, the socapex version works well for us.
We have used lacing bars internally to keep cabling in place and neat for easy maintenance.
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