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SparkFun Breakout Boards

DIY Balanced Interface Modules
By Hugh Robjohns

The SparkFun balanced input receiver is seen here fitted to the author's vintage Powertran delay unit — the breakout boards are the red ones in the top-left of the picure.The SparkFun balanced input receiver is seen here fitted to the author's vintage Powertran delay unit — the breakout boards are the red ones in the top-left of the picure.

I was rummaging about in my 'man cave' recently and came across an old Powertran Digital Delay Line, which I built as a kit in the very early 1980s while I was at university. By modern standards, it's a fairly crude mono, 12-bit, digital delay... but it has some good memories associated with it, it still works, and it actually has quite an appealing sound in a grungy kind of way. So I thought I should give it a new lease of life and reinstall it in my current studio setup. The only challenge was that its input and output are unbalanced, and leaving it that way would make patching messy — so I started to ponder the options for providing it with a balanced I/O. There are lots of ways it could be done, of course, with the simplest being an external transformer balancing box like my favourite problem-solving ART DTI, but I really wanted a neater, integrated solution, and ideally one that didn't require too much re-engineering of such an old unit.

They can be powered from any dual DC supply in the range ±5 to ±20 Volts — so installing these modules into most equipment is very straightforward.

For the sake of simplicity, I rather favoured the idea of using the very good THAT 1600 and 1200 series balanced interfacing chips, which are employed in a great deal of professional and semi-pro audio equipment today. However, while surfing for the THAT spec sheets I stumbled across American manufacturers SparkFun, who make all manner of interesting DIY electronics kits and modules, including two very neat and simple boards carrying the THAT 1646 balanced line driver and 1206 differential receiver (along with all the associated protection components) — and each was very inexpensive.

The balanced line drivers, installed in the same device.The balanced line drivers, installed in the same device.Better still for me, these boards were also available in the UK from a company called Cool Components, who also sell a wide variety of DIY electronic kits (mainly Arduinos, Raspberry Pis and that kind of thing) alongside the whole SparkFun range. These audio interface boards come complete with a TRS socket directly on the board, which makes mounting them a complete doddle, and they can be powered from any dual DC supply in the range ±5 to ±20 Volts — so installing these modules into most equipment is very straightforward. There's even a thoughtful option to separate the TRS connector's sleeve ground (which should go straight to the chassis metalwork) from the audio reference ground (direct from the power supply), to ensure optimal RF interference and ground-loop suppression.

My Powertran operates with a ±12V supply for the audio circuitry, making the boards a perfect option, and two quarter-inch holes later, with some new wiring to pick up the power, ground and audio input and output connections, the work was done. Now, my Powertran has fully balanced inputs and outputs on the back panel to supplement the original unbalanced ones on the front!

The build quality of these little SparkFun boards is excellent — as are the technical specs and sound quality — and they're very easy and convenient to work with. If you're considering updating some old equipment with a balanced I/O, I can definitely recommend them.

information

£14.94 each including VAT.

coolcomponents.co.uk

www.sparkfun.com

$14.95 each.

www.sparkfun.com

Published December 2019