Spare time in the last few days has mainly been spent on researching options for the amp repair. The CI9120 uses four power amp PCBs each carrying three channels; these are independently protected by NAD’s circuitry. Spares are still available via Sevenoaks Sound & Vision but I was informed they were around £230 each and would take one to two weeks to arrive. I have rejected this route therefore in favour of taking it to someone prepared to replace individual components as necessary – after diagnostics of course. Whether it will cost any less remains to be seen…

After reading around my thinking was that whilst the amp is in the workshop it would be an opportunity to reset or even replace all trim pots, and even consider increasing bias to tweak performance. The power amp modules are regarded by NAD as “non user-serviceable”, and annoyingly for this reason the service manual has no info on factory default quiescent current settings. The only channels taking appreciable current will be the woofers so it should be OK running warmer. I intend to discuss these options with the pro to whom I have been recommended. It goes off to him tomorrow.

I had one small final task for the speaker bridges – to protect both bridges and woofer boxes, and to minimise any transmitted vibrations, I cut some self adhesive felt to cover the vertical inside edges of the bridge feet. I also cut four strips of self-adhesive foam and placed these on the sides of the bridges under their tops. If I ever built another pair of LX521s I would incorporate some sort of levelling option for the bridge feet; my build ended up with a slight twist on one of the bridge assemblies due to the solid cherry top so the feet were not absolutely level. My little carpet mats allow for this, so not a huge issue.

In the absence of amplification I have decided to educate myself further on circuits and have begun to work through the Complete Electronics Self-Teaching Guide. Who knows – I may end up building a Hypex multichannel amp as beloved of the LX521 user group fraternity! In the mean time the good lady wife has a plump list of projects for me now the speakers are complete…

OK, so now you will learn why, from the listening point of view, I have time on my hands. A couple of days ago I lugged 36kg of NAD amp in from the garage, connected up the miniDSP and the CD player, and transferred SL’s test files to a memory stick in readiness for a full system test. My new Marantz CD player conveniently has a USB input on the front panel which saved the hassle of burning them to disc.

Before turn-on there was the small matter of affixing 20 banana plugs to the speaker cables. I had bought 24 Nakamichi plugs off e-bay some weeks earlier – nice plugs but affordable. The screwdriver slipped off one and plunged into my index finger – brisk haemorrhage resulted but no severed nerves or tendons…

A few days earlier I had experimented with the miniDSP  remote learning facility, hoping I could use the Marantz remote. Didn’t recognise any key presses, so I retrieved a spare NAD remote, and this programmed with no difficulty, allowing volume control and configuration selection. Turned on DSP, CD player, then amp, ran the alternating pink noise test and cautiously turned up the volume…

Obvious clear difference between speakers, and quickly apparent that the L woofers were doing nothing. I knew the speaker cables were fine as I had performed full polarity checks the day before – but I checked again. Fine. So one of my RCA leads was faulty? (Though I had tested all these too.) Lead swaps did not correct the problem however, and I was puzzled.

So… Was it the amp? Unplugged everything except for one input and a lower midrange driver, and went along the channels one by one using the 100 Hz test signal. Channels 1,2 and 3 dead as a dodo. I then realised  the amp was in protection mode, and had switched off the power amp module supplying 1 – 3. Damn! I had no idea when this fault occurred, having barely used the thing since purchasing it many months earlier.

After I settled down I retrieved my old NAD 2155 amp from the garage, transferred the upper woofer channels to it and tried again. Had to take off four banana plugs (note the blood-stained screwdriver). Pink noise test passed, so (at gentle volume) I christened speakers with a little Bowie in honour of our recently departed hero. Following this with snippets of a Yes favourite track was enough to prove that:

• Everything I have built works as it should
• The sound is very clean and detailed

However, sadly I am going to have to wait before a more thorough evaluation of quality and power. Everything is unplugged and the music room is restored to some order for now. At least it gives me the opportunity to finish this log…

Neglected the log in the last few days, so writing in retrospect (I now have time on my hands… read on to discover the reason). The baffle wiring is complete. Not much to do here; mainly an exercise in managing Techflex and heatshrink, and keeping things neat. I carefully took some photos of the process and later discovered the camera’s SD card was still in the desk PC! – so pics of finished article only. I used the gas ring to “set” the end of the Techflex at a stretched diameter (threaded over a 24mm tube) to fit over the connections on the back of the Speakon mount. I remembered to wire the L and R baffles in mirror image which I feel adds a professional touch! I was very glad I had kept the little Speakon bracket detachable; it would have been impossible to fit the six terminals in the “black hole” otherwise.

At this point I mounted the baffles on the bridges before taking my first snaps of the finished speakers. I knew I had created the same “design fault” as Bill Schneider described in that I had to take the baffles off the supports to allow the front pivot bolt to drop into its hole! Texted this pic to eldest daughter on her birthday (making it clear these were NOT birthday presents for her – she has already told me she wants them…) She was still gracious enough to reply that they “looked amazing”. They ain’t bad.

On to the speaker cables. Again this is an exercise in careful measuring, and labelling, to ensure the Speakon plugs are wired correctly. Threading the Techflex over five double wires requires staged pushing on rather like a caterpillar walking. I used heatshrink at the joint where the three baffle wires leave the woofer wires, and at the plug ends. I also found it helpful to use insulating tape to hold the cable ends together whilst wrestling with the Techflex. I’m leaving the amp ends battoned down with a cable tie for now until I know how much play I need to plug them all in.

The pic shows the first cable approaching completion with the baffle Speakon wired in. I had not used Speakons before, and the first time I finished screwing the 6 wires onto the plug mount I discovered that I had not only slid the blue back cover upstream on the cable (correct) but also the male insert element as well (definitely incorrect – you cannot remove it without taking all the wires out again!). After this little learning curve the other three plugs went on without a hitch.

EDIT: For my records, the wiring for the 8 way Speakons is:

• T+ to 4-
• T- to 1-
• UM+ to 2-
• UM- to 3-
• LM+ to 4+
• LM- to 2+

Maybe a wire up and test tomorrow?

Well, I finally managed to eradicate the end grain to the point where you have to strain to see it in strong light – it is not noticeable otherwise. Another coat of matt black and the painting is done.

My original plan was to finish with the soft satin, however I have had second thoughts for two reasons. Firstly, it’s difficult to obtain a really smooth finish with the brush (one can see the brushwork on

the tweeter baffles and baffle supports) but the matt finish is much more forgiving. Secondly, the wood finish is quite a gentle satin and I don’t want any gloss on the woofers to draw the eye away from the wood.  They do look really good in matt – wife says they look as if I had bought them, so that’ll do for me!

Next task was to prepare the woofer wiring. It proved impossible to locate any female 8mm push-on spade connectors in the UK so I soldered the wires to the drivers before installing them (upper woofer reverse polarity). I’m using  Maplin 79/0.18mm speaker cable  (equivalent to AWG 14) for the woofer boxes and the main speaker cables. This project needs plenty of wire – I needed three drums to allow 12 foot speaker leads.

Mounting the woofers is made straightforward by leaning the boxes against a sofa edge. The operation was extended however by a brain failure… I mounted an upper driver first. SL advises mounting the lower ones first. There is an excellent reason for this – you can’t get the lower one in if you start with an upper one! Unscrew everything and start again. Access to some of the bolts, washers and screws is somewhat restricted but not impossible – once a couple of bolts are secure you can turn the box round to work, but you do need decent light. At this point you realise how seriously heavy these bass units are…

On to the wiring up. I had ordered a reel of Techflex clean cut 12mm from Kustom PCs, together with two sizes of black heatshrink, to keep both the woofer box wiring and the speaker leads tidy. Clean-cut it is, but it soon frays out, and I quickly learned that once threaded over the wires it is wise to secure free ends with a temporary draw-tight cable tie before final fixing. Ends can be sealed by wafting them near a flame; I used a gas ring.  I secured the wiring run with some nylon P-clips I found on e-bay – my last online order for this project!

Before soldering the Neutrik spade terminals and attaching the 4-way Speakon panel mount I labelled the wires UW and LW to keep track. During the wiring up a good light helps enormously; our music room “father and son” flexible lamp lit up the dim interior of the black boxes well.

Woofer boxes done! My remaining tasks are to finish wiring the baffles and make up the speaker leads – only a few more days!

The woofer boxes had their second full primer coat several weeks ago now; it was with a mixture of relief and apprehension that I picked up where I had left off with them – relief that the end of the project was in sight, but apprehension about achieving a reasonable quality finish – especially round the corners of the front / top. That stubborn end grain persists in showing through despite much sanding already.

First thing was to set up shop with dust sheets etc in the music room; temperatures have plummeted to -4 deg C overnight in the last few days. Woofer boxes and paint now ensconced indoors – WAF surprisingly compliant.  I was planning to give the boxes an initial coat of matt black to assess finish to date, and almost forgot that I hadn’t made the Speakon brackets! Back out to the garage, well layered up… Quick job though – pics show these in place. Again, I am not gluing these to make wiring up easier later.

On with the matt black – and they look really good. However on closer inspection the problems with visible joints and end grain around the top front flap remain considerable, especially the box on the right in the pic. The flash photography is merciless here, and makes the problem look even worse than is apparent in real life. At this point one voice in my head was telling me “no-one will notice – get the woofers in!” whilst the other (OCD) voice said “you’ve got this far – a few more days is a small price to pay…”.

It was a close thing, but the OCD came out on top, and a radical sandpaper attack on the top fronts followed. To get the joint lines clean I had to go back down to bare wood in places. Stress. It also meant lugging the boxes repeatedly between house and garage for the sanding. Back to the primer, and three coats later (fine sanding between coats) one box was good – I now cannot see any wood grain even in strong light. The other box however is putting up more of a fight, and despite another coat and sand the end grain STILL keeps popping up. So back to the filler again… hopefully after a gentle sand-off tomorrow and yet more primer it will capitulate. The back corners can look after themselves however – the OCD lost this one!

I took several more photos of this miserable process, but, you know, they are so boring, so I am sparing my readers…

After a further sand down and more primer, this looked practically the same!

Whilst all this was going on I had been mulling over floor protection, and remembered we had some small rolls of carpet offcuts. Better still, I discovered a local carpet edging company only 15 mins away (had thought about, er, learning another skill, but some quick research made it clear that acquiring the necessary kit would cost a lot more than their charges). I now have two custom mini-rugs for my speakers!

The bridges are done – the final coat of wax-oil was applied in the music room to speed up drying time. I am increasingly trying to find reasons to avoid venturing out to the garage as the temperature is dropping fast; we are forecast the first really cold spell this winter. All that remained was to screw the brass inserts back in to their previously prepared holes in the underside of the tops.

What I should be doing next is returning to the woofer boxes… in the garage… Instead I decided to dispatch the tedious job of making up the phono leads that will run between the MiniDSP and my NAD CI9120 12-channel power amp – in the warmth of the kitchen. Sadly, NAD have discontinued this amp, but I was fortunate in picking one up second hand on E-bay. Ten of the twelve channels are needed for the LX521.4 setup. Decent phono leads go for silly prices in the shops, so some weeks earlier I had ordered from Canford a quantity of Rean heavy-duty plugs and several metres of their good quality HSS screened cable.

It took me the best part of four hours to solder and assemble the 24 connectors – but they are thankfully now all ready (see photo – note the fourth lead for L and R needs a splitter as upper and lower woofers share MiniDSP output but each have their own power amp channel).

A much quicker (and easier) task was to cut some self-adhesive black felt to stick onto the bases of the baffle supports before giving them a trial fit onto the bridges. With the front M5 bolts in place the rear ones lined up perfectly with the toe-in holes – relief!

My last LX521 job of the day was to order some Techflex sheathing and heatshrink in anticipation of making up the speaker leads. This should be my last on-line order for this project – a cause for celebration in itself as it certainly all adds up…

Progress has been slowed by various domestic mechanical and electrical failures; New Years Day was the day when a bulb failure blew an obscurely sited fuse, the girls’ power shower gave up, and the washing machine decided to just keep washing and not bother with rinsing or spinning – the rule of 3’s is live and well. I now know how to change a Bosch washing machine heater element and door seal (but it’s still washing ad infinitum; a new thermostat is now in the post… esperons).

In a way these distractions have helped conquer any impatience with the bridge finishing. It is tempting to rush in with the second wax-oil coat before the first has thoroughly dried – the first paint-on application really needs a good 36 hours to dry and harden up (more if panels left in a cold garage) before any light fine sanding and the second rub-off coat. I finished the side panels before glueing but left the feet and tops until the bridges were assembled.

I was concerned about how to ensure the bridges were glued accurately so the sides ended up parallel to the woofer boxes. The feet take care of the bottom end, but not the top. My method was to assemble them around a woofer box, taping some hardboard and sticky-backed foam spacers onto the upper sides of the latter to ensure the bridge sides were held exactly the right distance from the woofer boxes (see photos). I cut some spare shelving to act as a base I could clamp from, and this worked very well – I was surprised how solid the resulting 8-dowel joints between top and sides turned out. I had purchased some small metal right-angle brackets but now I don’t think I need them. I am equally pleased that the mild bowing in the bridge tops has been completely eradicated by the clamp glueing onto the sides as I had hoped.

Next job is to wax-oil the top and feet. One has its first coat so far (see photo). Once the remaining wax-oiling is done I will then need to screw in all the brass inserts, stick some protective felt onto the feet and the bridges will be done. Then it’s back to the woofer boxes for final sanding and black paint. The end of this project is definitely in sight!

Reviewing the post, I realise the penultimate pic has a somewhat “Wolf Hall” feel to the lighting. Pity it wasn’t a candle in the background…

Bridge tops and feet are now planed up, and essentially complete bar sanding and finishing. I decided to bevel all edges of the bridge tops to the same angle as the baffle support bases for the sake of design continuity.

Planing the cross grain on the bridge tops required the usual degree of care to prevent end grain splitting – I purposely left 3/8″ of waste along the back edge and planed the sides from front to back before trimming this back to the line. Whilst bevelling the edges I also used my trusty aluminium clamps across the work to further support the end grain. The photos show all finished hardwood elements (one bridge top is upside down) with feet detail, dowel holes drilled.

Time to start on the veneered side panels. These were supplied by SL Hardwoods with an “A” and “B” side; the grain on the “A” side has interesting swirls, and I am looking forward to seeing how these come up with the oil. Following the marking out and drilling of the dowel holes in the four sides I was able to do a trial assembly of the bridges over their woofer boxes. All fitted well and looks great. You can see the slight bow on the bridge tops – the clamps will sort that when glueing up. I am planning to glue the bridge parts using the woofer boxes as jigs / guides to ensure the side gaps and angles are true. Regrettably, much sanding is ahead before then!

Not posted for a while – the small matter of Christmas intervening… however I have been chipping away at the woodwork (ho ho) now and then. Work on the bridges is now well under way – I have decided to press on with these prior to finishing the woofer boxes to get the remainder of the woodwork out of the way.

The bridge tops are solid cherry made from glueing three boards together as with the baffles. The assembled boards were reasonably flat, although there was a slight warp which had developed in the boards before glueing which I was able to reduce with the plane. I’m reckoning on eliminating any residual bowing when clamping  and glueing the tops to the sides.

I mentioned in an earlier post that from reading both SL’s material and that of other LX521 owners I realised that including a toe-in facility was an essential element in the design if using these speakers in smaller rooms. My solution was to sink five extra brass inserts into each bridge, as alternative placements for the rear baffle support bolts, along an arc at 5 degree intervals, thus allowing a maximum toe-in of 25 degrees for each baffle. The photos show the marking out for these. I am setting the baffle supports slightly further back on the bridge so that the bases do not protrude over the bridge top when set at maximum toe-in.

My earlier experience with sinking brass inserts was less than satisfactory because of the difficulty avoiding the grain lifting and splitting, so I experimented with using some 10mm ply to act both as a guide and to apply support pressure to the wood around the counterbore recesses. I cut two holes, one smaller and threaded to start the holes in the bridge, the second larger (ie the diameter of the top of the inserts) as a guide when screwing the inserts home. The ply was positioned carefully over each hole and clamped down onto the cherry. It worked well, with much cleaner results. None of this will be seen anyway as the inserts are on the underside of the bridge tops.

Next task: cutting and planing bridge tops and feet to final size… and then a lot of hand sanding – ugh.

The baffle supports have now been given their final coat of satin black and are finished bar the Speakon mounts.

I was keen to position the midrange units and see how the baffles looked with the supports, but before this, taking another leaf from Bill Schneider’s book, I masked up the midrange units and gave the rear metallic surfaces a spray of satin black from a tin of…. I was somewhat nervous of using spray paint, never having used it and not having the proper kit for more substantial surfaces, but I was pleasantly surprised by the finish one coat achieved. The occasional little bubbly imperfection, but more than adequate for the job. Although described as satin, the finish is towards the gloss end. A voice in my head is now questioning whether I should spray the final coat on the woofer boxes…

Having given the spray 24 hrs to dry I took everything inside and assembled the baffles. I used a small amount of grease on all mounting screws and bolts this time which abolished the stiffness noted previously. Stuck ’em on the kitchen table for a photo; there is little natural light at present during a particularly dingy December, but they look good. Definite sense of progress!