© 2013 Benden Sound Technology

Made by Serif

Refurbishment

The first three units I worked on were in poor shape. They had been acquired from a service centre, had no known history and had clearly seen a lot of action. The strong suspicion was that they were loaded with all the bad parts which had accumulated over a period, so I expected multiple faults and was not disappointed.

Some of the many issues overcome were:

- physical damage including bent panels, broken switches and connectors.

- liquid spillage into chassis (!)

- shorted diodes in power supply.

- failed electrolytic capacitors in power supply and elsewhere.

- numerous failed ICs, both analogue and digital.

- an intermittent internal ribbon cable.

- NiCd backup battery leakage.

- partly-erased EPROMs.

- dirty connectors and IC sockets.

However, in keeping with their overall high standard of engineering, Lexicon built into their firmware some very comprehensive self-diagnostics routines which do their best to direct an engineer to the location of a fault. These proved invaluable, as did the modular, cardframe-based design which allowed card-swapping between units.

Less helpful is the fact that the chassis is entirely welded together with no removable panels, hence servicing anything other than the removable cards can require some complex disassembly.

Once the units were operational again, attention was given to making them reliable for years to come. My recommendations for work that should be done proactively on any 224/224X are as follows, and these were all carried out:

1. Re-cap the power supply.

The 224/224X uses a large, multiple-output linear power supply in which the electrolytic capacitors have to work quite hard. Electrolytic capacitors have a finite lifespan (they use a semi-liquid paste which eventually dries out) and these parts are now at an age where problems can be expected.

2. Clean the card edge connectors.

Many problems can be traced to poor contacts between the cards and cardframe. IC sockets can also be problematic.

3. Replace the NiCd memory backup batteries.

These are located on the NVS card (fitted to units with firmware above v4.4) and can leak with messy consequences for the card. They should be replaced if this has not already been done.

4. Recalibrate the ADC and DAC.

This minimises distortion for optimal audio performance.

5. (optional) Re-cap the remaining circuitry.

A further few electrolytic capacitors are present elsewhere in the unit along with a large number of tantalum caps. These don't degrade in an age-related way, but parts of this vintage have been known to occasionally fail completely and short the power supply until replaced. However, it is by no means inevitable that this will happen, so it is ultimately a personal decision about how keen you are to eradicate all sources of unreliability.

Many 224s suffer from broken power switches because, unless support is provided when removing the front panel, all its weight hangs on the plastic shaft of the power button and casualties are inevitable. The original switch is a Schadow type N30X-2U, but more modern parts can be grafted in and I have some of the original "magic eye" caps in stock.

Sound

A lot has been said about the sound of the 224 and I was keen to try one out. I hooked up my Yamaha electronic piano and A/B'd the Lexicons with both the Yamaha's internal reverbs and an E-Mu software reverb. The Lexicon sound was clearly superior, being much more spacious and less artificial than the other two.

Being a send/return effect (as opposed to an insert device), the limited bandwidth of the 224 wasn't particularly noticeable. Neither did the extra bandwidth of the 224X make as much difference as might have been expected - in fact, some argue that the algorithms contained in the earlier units/versions of firmware are superior to the later ones. Unfortunately I did not have simultaneous access to both a 224 and a 224X for comparison, so my impressions are separated by some time.

The extra non-reverb patches in the 224X are great fun, though - I particularly liked the resonant chords program, which uses the input signal to excite several tunable, resonant vibrators.

The interesting question is: what makes the 224 sound so good? The quality of the algorithms is the obvious answer, though aficionados claim that the later Lexicon effects units (which presumably possess equal or better algorithms) lack the same "mojo".

We can rule out the purely digital circuitry, the characteristics of which are defined wholly by the algorithm.

Perhaps it is the analogue-to-digital conversion. When designing nowadays, one would not choose a 12-bit successive-approximation converter when 24-bit delta-sigma audio codecs are available ten-a-penny, yet the significant architectural differences seem certain to affect the sound.

I would offer one last possibility. Very few more modern/lower-end pieces of equipment use transformer isolation for their analogue audio signals because users can't stomach the cost. Yet passing the signal through a soft iron core can give similar subtle distortion as analogue tape (which is assigned similar "mojo") - perhaps it's as simple as that!

The Future?

I now possess extensive documentation and EPROM images for the 224 and 224X as well as a full set of known-good cards which can be used for debugging. With sensible precautionary work, there is no reason why these pioneering units cannot be kept operational for many years to come.

Of course, the temptation to assemble those spare cards into a working unit is strong. I possess a suitable cardframe (though an original Lexicon frame would be better) and aim to replicate the ancillary parts as time allows. The 224 also seems to be a prime target for emulation on a modern FPGA, but that is a project for after-hours...keep an eye on my workshop pages.

Inside the chassis of the Lexicon 224 - mains transformer, PSU, output transformers and card backplane.

Lexicon 224 power supply before overhaul.

Lexicon 224 power supply after overhaul. Modern electrolytic caps are much smaller and no longer need support bracket.