Interspace Industries Audio Puck

The Audio Puck control unit and loom, pictured here with the forthcoming TAP‑CAT box that supports audio over Cat6/7 cables.

Does this box of tricks live up to its billing as the Swiss Army Knife of audio cables?

We’ve all needed some form of special ‘bodge cable’ to link one device to another because of non‑standard connections or incompatible interfacing, and most of us will have built up an assortment of adaptors and special cables. Interspace Industries aim to tackle this perennial issue with their new Audio Puck, which they claim can be configured into more than 90 different connection formats.

Achieved with just one compact switch box and a detachable connector loom, it also has options for balanced‑to‑unbalanced interfacing, stereo splitting, insert breakout, phantom‑power blocking, ground lifting, and more besides. It’s entirely passive, with no transformers: just wires, switches, and connectors. The Audio Puck was designed by a live‑sound engineer primarily for solving everyday live‑sound interfacing problems, but it’s obviously of use to anyone working with analogue audio who has a regular need to interconnect devices that aren’t directly compatible.

Overview

The control unit’s configuration switches are located in a protective recess, while the loom attaches securely to it using a DB25 D‑Sub connector.Housed in a strong metal case, the Audio Puck control unit measures roughly 82 x 79 x 42mm and weighs 200 grams, making it smaller and lighter than a typical DI box. The front panel carries a pair of combi XLRs and a pair of RCA phono connectors, while the rear has a 25‑pin D‑Sub connector for attaching the supplied cable loom (see ‘Loom Wiring Arrangements’ box).

A recessed trough on the top protects a trio of switches and a 3.5mm mini‑jack socket. Two of these switches are miniature toggles and select an Iso/Mono mode (of which more later) and a ground‑lift function. A larger, three‑way toggle configures the system for balanced, unbalanced, or stereo/insert modes. Most of the switch labelling is black on a white background, for easy legibility in dark situations, while the sockets and Iso switch have colour‑coded markings that indicate which cable groups and sockets carry which signals.

Supplied with the Audio Puck is a short (about 45cm) cable loom weighing around 460 grams. There are a lot of connectors in this loom, most being Neutrik types, and the control box end is terminated robustly in a 25‑pin male D‑Sub connector. The loom itself fans out into nine separate tails, each with a different connector, and with three different cable colours. There are two tails in the blue group, two in the green, and five in the red. The D‑Sub is wired to the AES59 (Tascam) standard, with each tail’s connection on its own channel. The only exception is that the left and right RCA phono connectors in the red group share a channel (there’s more about that in the box).

All connectors in the same colour group are essentially wired in parallel, but the different groups are linked (or not) to each other in various ways, depending on the mode setting on the control unit. The blue cable group is designated as carrying the left‑channel or insert‑send signals, while the green group conveys right‑channel or insert‑return signals. The corresponding combi XLR sockets on the control unit have the same coloured labels. In most modes, the larger red group effectively serves as the input or output connection set.

Obviously, colour coding is essential in identifying the different connector groups, and the designer told me he assigned the red, green and blue colours for “no rhyme or reason”. I’m sure regular use will bring familiarity but it has the potential to confuse some users: in the consumer world, the CEA standard uses white for the left channel and red for right, and my BBC training means I always associate red with left and green with right (as with navigation lights on planes and ships), so coping with blue and green felt a little unnatural. The control unit sockets being colour coded helps a lot, though, and if all else fails then a QR code printed on the base of the unit links directly to the full user manual online, which is a very thoughtful touch.

While we’re on the subject of the manual, it has 18 pages in total, though only seven are needed to explain the multitude of configuration options and functions — and that’s quite an achievement given that there are over 90 variations! There are also clear and useful block diagrams to illustrate the signal routing in different modes, for those who prefer images to words.

Blue & Green Group Connections

In terms of loom connectivity, the two blue (left/send) and two green (right/return) tails each terminate in a Neutrik ConvertCon and a quarter‑inch TRS plug. For anyone unfamiliar with the ConvertCon, it’s an ingenious XLR connector which transforms from female to male forms just by sliding the outer sleeve forward or back.

When connected to the control unit, the XLR and TRS connectors in each colour group are wired directly in parallel, along with their corresponding combi XLRs and RCA phono plugs on the control unit. Both RCA phono sockets are wired with their sleeves connected to the green (right/return) channel only — rarely of significance in practice, but worth noting. The left RCA phono socket signal connection is wired to the blue (left/send) hot line (pin 2/tip), while the right RCA phono socket signal connection is wired to the green (right/return) hot line. Both RCA phono signal lines are protected with phantom‑power blocking capacitors, which is very useful.

Most of the loom’s plug connectors are provided with natty little isolating ‘jackette’ covers, secured to their cables by wire tethers so they can’t be lost.

With multiple loom connectors wired in parallel and many with exposed contact points, there’s a real risk of signals being lost should a stray connector accidentally touch something it shouldn’t. To combat this, most of the loom’s plug connectors are provided with natty little isolating ‘jackette’ covers, secured to their cables by wire tethers so they can’t be lost. These were designed and 3D‑printed by the manufacturer and fit snugly over their associated plug type — it’s a very neat solution.

Red Group Connections

The red group has five separate tails. The first two are terminated in an XLR ConvertCon and a quarter‑inch TRS plug, as with the green and blue groups. Once again, these two plugs are wired in parallel via the control box, as well as being linked directly to the 3.5mm TRS socket in the control box switch recess. The third tail carries a 3.5mm TRS mini‑jack plug, while the fourth and fifth have RCA phono plugs. The left RCA plug is wired to the pin 2/tip hot line, while the right RCA plug is wired to the pin 3/ring cold line. All three are again protected by DC‑blocking capacitors to protect from phantom power, and all have protective jackettes.

Another point worth noting is that while the red group mini‑jack plug is protected against phantom power, the 3.5mm socket on the control box is not. This is to allow the passage of plug‑in power to electret microphones and the like if an alternative cable is being used.

Operating Modes

The simplest configuration mode is Balanced, where all three cable groups are wired directly in parallel, essentially with the red group as the input and the blue and green groups as the outputs. Consequently, this mode allows balanced XLR‑jack conversions in either direction, signal splits or mults, and even balanced connections over mini‑jacks. For example, by plugging the red quarter‑inch TRS plug into a balanced output, a signal can be shared across combinations of three male XLRs, five female XLRs, two more jack plugs, or two jack sockets. Or, if a signal is plugged into one of the combi XLR quarter‑inch sockets on the control unit, it can be split to feed three male XLRs or four females XLRs, and three more jack plugs. It’s also possible to create gender reversers with female to female or male to male XLR connections.

By operating the ground‑lift switch, the sleeve/pin 1 connection is broken between the three different colour groups — but the grounding is maintained within each colour group; all of the red connectors remain grounded to each other, but that ground is not shared with the green or blue group connectors.

Selecting the Unbalanced mode shares signals between connectors in the same way, except that the ‘cold’ side of each balanced connector is shorted to the screen/ground within each colour group. That’s to say, XLR pin 3 is linked to pin 1, and the TRS ring to the sleeve. This allows unbalanced signals to be passed over balanced connectors and cabling in a straightforward way, as well as for connecting unbalanced outputs to balanced inputs or balanced outputs to unbalanced inputs.

Although shorting the cold side to ground works in many situations, it can cause problems with some types of balanced output. It works correctly with transformer outputs and cross‑coupled electronic outputs, but it can sometimes cause problems with simpler electronic balanced outputs. In these cases, the cold‑side output device might not like being shorted to ground, and can introduce peak or transient distortion as a result; if in doubt, always check the manufacturer’s recommendation when unbalancing a balanced output!

Instigating the Stereo/Insert mode assigns the red cable group as the unbalanced stereo or insert connector, routing two unbalanced audio channels separately to/from the blue and green groups. So, for example, if the red TRS plug was inserted into a stereo headphone output or a mixer’s insert socket, the blue group connectors will carry the unbalanced left channel or send signal, while the green group connectors carry the unbalanced right or return signals. This mode also allows conversion from stereo mini‑jack to dual‑XLR/TRS, or dual‑RCAs to dual‑XLR/TRS, for example.

The final switch selects Iso/Mono modes. In the stereo/insert mode, activating the switch means the blue and green groups both receive an unbalanced mono sum from the (red group) mini‑jack plug’s left and right channels, mixed via 100Ω resistors. In balanced mode, the Iso switch disconnects the blue and green groups from each other, allowing the blue group to handle one signal, and the green group another. The blue and green group grounds are still shared unless the ground‑lift switch is operated. (When using this Iso mode in the balanced or unbalanced configurations, the red group is not used.)

Looming Large

As you can see, there’s lots of capability and flexibility in the Audio Puck, and the claim of it being configurable “into over 90 different cable types” is genuine: there are 93 explicitly different setups! In practical applications, all of the most commonly required configurations are quick and easy to set up: balanced signal splitting/distribution in mono or stereo, ground lifting, unbalanced insert or stereo breakouts, and balanced/unbalanced connections. Moreover, all of the most common connector types are available here, too — and, importantly, most of the unbalanced ones are protected from phantom power, which is a very nice feature.

On the down side, with no isolating transformers in the Audio Puck it’s not possible to create a balanced signal from an unbalanced source, or to provide genuine galvanic isolation. The shorted‑cold side issue I mentioned earlier wouldn’t happen with transformer unbalancing, either, and it’s partly for these reasons that I’ve relied heavily on ART Pro DTI transformer isolation boxes for a lot of my interfacing needs — and these boxes feature paralleled XLR, TRS and RCA phono connections. However, the Audio Puck can do things my DTI boxes can’t and it’s genuinely worthy of the Swiss Army Knife moniker: it’s a tool for fast and efficient problem solving in the vast majority of commonly encountered situations. It works very well, is easy to set up and use, and is a nicely integrated solution.