Spendor SP2

Rosewood BC1

Rosewood BC1 rewired

Spendor BC1 crossover upgrade


My Introduction to the Spendor sound.

My first pair of Spendors were a pair of SP2's. I thought that they were the
most convincing box speakers I had heard to date. However they were not
a standard pair of Spendor speakers. The crossover had been cleverly
modifed by Amar Bizwas of Eminent Audio. Later I bought a pair of SP2/2's
which were standard. These did not sound anywhere near as good and I was
a little disapointed. Both SP2 units lacked bass so I bought a pair of BC1's.

The BC1's have a real pedigree!

I bid on an ebay auction and won my first BC1's for a bargain price £220.
I was unlucky, I listened to them at the sellers house but when I got them
home the bass unit had moved internally and I found myself with dud spe-
akers. I then bought another pair for spares. Soon afterwards I had my B-
C1's fixed and was enjoying that famous BBC sound. I had enjoyed work-
ing with these old classics whilst fixing them up. They exude a level of....
quality which is uncommon in a modern speaker.

Although the BC1 is a great speaker, I felt that it had problems in some
areas of it's performance. Bloated bass is a common complaint and is
well known about amongst Spendor users. Also I did not feel that the
treble was performing as well as my modified pair of Spendor SP2's.
This seemed a bit strange as I expected the tweeters to be better on
the BC1. At this point I realised that the aging components on the BC1
crossover could be upgraded in the same way as my SP2's. Note:
Subsequent research has turned up various issues with BC1 aging and
performance variability. See BC1 issues for more information.

I knew it would take a lot of development time and as a gradient measure
I decided to start by rewiring the speakers first and modifying crossovers
later. I rewired BC1's and by then I had a pair of SP1's I got good but su-
btle results. At about this time Darren Hackleton approached me as a
result of my posts on the Yahoo Spendor user group. He wanted to have
his BC1's rewired and I was happy to do so. See the work here. The BC1
has poor original wiring. It is an ageing speaker and wiring was not the
craze that we find today within hifi. I now rewire BC1 speakers differently.
The rewire has changed as I now use Silver plated OFC copper wire, this
has evolved over the last year along with the crossover upgrade.

Back to the drawing board!

Sometime later I had refurbed a Rosewood pair of BC1's and put them
up for sale on ebay. I had invited prospective buyers to audition them,
I got an email from Heskett Dawson. He is a Yahoo Spendor group mem-
ber and had been intrigued by my posts on the rewiring subject, he wan-
ted to hear them for himself and compare them to his standard pair of
late model BC1's. We performed a shootout within a couple of days and
the results were not as great as I had hoped. Heskett's speakers were
six years newer and a slightly different version to mine but even so I had
expected mine to perform better. Heskett could easily hear differences
the two speakers but still preferred his. I on the other hand was biased
towards the sound of my speakers. I know that I had improved my BC1's
performance, but not enough to make them stand out against another
good well sorted (within specification) pair of BC1's.

I definitely decided to modify the xover of my next pair of BC1's. I was
sure that there was more performance to be squeezed out of the stand-
dard component of the xvover. I wanted to find if I could achieve an up-
grade for this classic design. I also was beginning to think that there may
be some commercial possibilities. My rosewood pair sold on ebay for an
impressive sum and were exported to Spain. The new owner was and
still is delighted with them. I may have sounded negative about them but
the fact remains that a well sorted pair of BC1's are great speakers.

The next phase of the upgrade.....

I soon had an opportunity to buy another pair of BC1's with Teak cabinets. The pair in question had unfortunately been used for an eighteenth birthday party and reportedly had a blown bass unit. The price offered was adjusted to account for the bass unit repair and I drove to south London to pick them up. When I got them back home I opened them up and stripped them down. with the backs off the speakers I could test them more thoroughly. It was worse than I thought and I found that both (supertweeter) shunt resistors were burnt out this meant that the supertweeters were probably destroyed, a quick test with the multimeter confirmed my fears.

I ordered the supertweeters from Falcon Acoustics and stripped out the bass units and crossovers. I replaced all the resistors on the crossovers and fitted two spare bass units for testing purposes. One really positive thing was that the original bass units that came with the speakers were Spendor replacements. A quick consultation with the previous owner confirmed that he had overdriven the BC1's on an earlier occasion and had made a day trip to the Spendor factory where two brand new drivers had been installed only seven or so years earlier. This meant that I had two units that were as new as I was ever likely to get. The bass unit that was blown was sent to a London reconer to be repaired. The second unit was tested and found to have survived it's ordeal without damage.

The work got started firstly I rewired the speakers and installed new binding posts. The wiring loom was composed of a mix of silver plated OFC (PTFE) with standard copper (PVC). I wanted to create a balance of sound similar to the original wiring whilst allowing more detail to flow through.

click here for larger imageNext bass port tubes were installed. These are 50mm diameter ports which are available from Maplins. The ports are cut to 3.75 inches in length and simply push into the existing hole in the baffle. The information for the ideal port tube length was consulting with the members of the Yahoo Spendor users group. I should say thanks specifically to HifiWizz and Derek Hughes. There are various diameters and port lengths that can be tried. This is what I used and it has worked well. Finally the bass port tubes were glued to ensure no movement.

Next I stripped every capacitor off the crossovers and replaced them with exotic paper in oil types made by Ampohm capacitors in the UK. Paper in oils allow very smooth and even flow of signal and are particularly good for curing sibilant vocals. However they are expensive and one 3.0 uF cap costs £10 alone. The original capacitor would only cost 65 pence or so. The crossover on the left is made up of £48 worth of high grade caps. On the bass section I knew from previous experimentation that paper in oils would not sound good. I spoke to Glenn Croft (Eminent Audio) and he advised that he had got good bass results with use of cheap Electrolytics in B&W DM2's. Electrolytics were duely installed.

By now my supertweeters had arrived from Falcon and were fitted. The first time I heard this pair of BC1's was a mixture of pleasure and dismay. I liked the bass in some respects and could hear that the port mod had created some improvements. However there was some flabbiness at the bottom end but not as bad as some early BC1's that I have heard. Also the midrange was not as it should be. At this point I was not sure whether or not the top end of the bass unit was off or the bottom end of the Hf1300. This is the problem with developing sound by ear. The midrange sounded too soft (drum hits were not percussive enough) I decided to change the crossover caps on the Hf1300. I made up the 3.3uF value on the main cap by soldering a 1uF paper in oil with a 2.2uF polypropelene cap in parallel. This improved things slightly but I was still not sure that I had got it right. There were lots of variables and I was beginning to feel confused. I needed a reference point........

I decided that I needed to have a side by side shootout with a standard pair of BC1's. In this way I could get a real idea of where I was with the development. I phoned up Heskett Dawson and explained my problem. Thankfully he was happy to help and within a few days the speakers were in the boot of my car and I was driving down to see him for a shootout. Heskett was lucky enough to find his speakers in a charity shop. They are a very late pair with the factory port modification and have seen very little use. I woud say that they are the best standard pair of BC1's I have heard and this is the reason I was keen to use his speakers as a point of reference.

The moment of truth.........

click to enlarge

We spent a good few hours running both sets of speakers with various diferent styles of music on Heskett's Naim system, also we listened to his pair of Harbeth HL 3PES's. I don't like anything about the small monitor speakers except for the midrange which was very good. In general I have no time for any of the LS3/5a type variants. Small boxes don't do anything for me. All in all I was quite pleased with the fact that my speakers were still very much Spendor BC1's despite the fact I had made so many modifications. My fears about the percussive element of the midrange were confirmed. In many ways my speakers were more detailed and precise but there were balance issues which the standard speakers did not have. The bottom end of the bass on my speakers was still flabby despite the port modification. I began to suspect the electrolytic cap to be a bad move. One of my test bass units had previously repaired by the same company where I had just posted my latest blown unit.This was unfortunate as It was now clear to me that this unit had been repaired badly. I had to hope for the best and be optimistic that the next one would come back in better condition.

The shootout had been a great learning experience. I had learned that I still needed to find a suitable capacitor for the bass section of the crossover. Also I had lost some detail in the midrange by putting the polyprop cap in parallel with the paper in oil on the HF1300. I needed to change that back to original or change the configuration (I later found another more suitable pair of caps which gave me the detail and sonic aggression I was looking for). The main problem here was that I realised I would make no further progress unless I had two good "on spec" bass units to put into the boxes. As it happened I did have two good bass units but they were rated at differing sensitivities so I couldn't use them toghether as a pair. For now I was stuck I had to wait for my bass units to come back from repair or hope that a good NOS pair came up on ebay (no hope basically).

The SP1's get the treatment while we are waiting.......

Sp1 xover development. Click to enlarge image.In the meanwhile I had my SP1's to experiment with and they were stripped down and put back together several times whilst I tried different capacitors on the bass section and the HF1300 section of that crossover. Eventually I found a good radial polyester cap that gave excellent bass and an excellent (but expensive) polyprop cap (the yellow one in the picture) to use in parallel with the 3.0 uF paper in oil (final configuration 3.0 uF PIO and 0.33 uF polyprop to make a composite value of 3.33 uF). The first time I tested the rebuilt SP1's was a real revelation. They were and still are amazing. Recently Arthur Khoubesserian (former co-owner of Pink Triangle now trading as The Funk Firm) came by to visit. His first comment was that "the treble is just dreamy". I thought this was high praise coming from someone who is a legend in the recent history of British audio. As it happens Arthur is a BBC loudspeaker fan and owns four pairs of BC1's, he is particularly fond of his Rogers LS3/6's which he recently used as part of an unconventional system in his "Funk" room at this years HiFi News Heathrow show. I can't say too much at this time but I think I can safely reveal that Arthur intends a project in the future which involves doing more work with loudspeakers. If you are a vinyl junky check out the new Funk V deck which is currently receiving rave reviews.

After the success with the SP1 rebuild I replicated the work in the BC1 xover using the caps that I discovered working best with the bass unit and hf1300. My second bass unit eventually came back from the London based reconer I was using at that time. With anticipation I installed it (and also its matching counterpart in the other box), it performed well until I drove it at higher volume levels where once again I discovered that I had been let down. The bass unit was distorting but only at high volume. I have created a separeate page called BC1 issues to explain this and other problems associated with buying and running vintage Spendor BC1's. Immediately I decided that the bass unit would be coming out again and was eventually sent to Audioheritage who have the expertise and also the neccessary parts to properly rebuild the unit. This service costs a little more than standard reconers but you essentially get a brand new bass unit with all new moving parts.

Click to enlargeFor the moment I decided that the performance was good enough to get a fair idea of what the crossover was now doing. It was certainly much better than before. As far as the crossover was concerned I was now extremely happy. The bass was now detailed and fairly tight (any small issues were now attributed to the faulty driver). The midrange was now very good indeed and I had achieved the best of both worlds with increased detail and great tone. The drums were now as percussive as I needed. The upper end of the treble was very sweet with female vocals coming accross with clarity and lacking the usual sibilance. I could go on about sound staging etc but I assume that you get the idea.

It was time once again to phone up Heskett and arrange a final shootout. I wanted to ensure that my bias was not colouring my perception of the latest performance of this pair. Very soon I was sat in Heskett's living room and soon we were intensively switching between speakers eagerly comparing notes on the two differing sonic qualities of the BC1 models. Essentially I modify only the wiring, binding posts and capacitors. The vast majority is still standard BC1 hardware. Overall my BC1's could be described as an evolution utilising electronic components which were not available twenty five years ago at the time when the bulk of BC1 production occurred. Heskett readily conceded that he now preferred the sound of my units over his own there was only one area where he preferred the orignal BC1's and that was the the soundstage on my pair had moved back in the room wheras the standard pair projected sound forward. Heskett remarked "They seem to be slightly less romantic/musical".

This is essentially a matter of preference as I actually do prefer this quality in a loudspeaker. As an example some people love Quad II's but I loathe the bloody things. There are fundamental design issues with many items of vintage audio kit. In many instances sonic colouration has become synonymous with "that vintage magic" For me colouration is unwanted and if a loudspeaker can image "further back" in a room sometimes even behind itself and the wall that is berhind it, then this indicates that I am listening to a real quality "uncoloured" (or less coloured) system. Very few loudspeakers have the ability to achieve this level of soundstage (imaging). I was very pleased with my latest visit to Heskett, I had achieved greater bass control with better imaging, more detail and less sibilance. The differences are subtle but nonetheless very noticeable. At one point during the shootout Heskett put me one the spot and asked me to turn my back whilst he switched between the two pairs of BC1's and also his Harbeths. In this sudden blind test I was required to report which speakers were playing and in what order. It was easy for me to diffentiate my speakers from the Harbeths and the standard BC1's. It would have been embarrssing if I had gotten it wrong and I felt less guilty at the end of the shootout when I announced to Heskett that one of my bass units was still knackered (a fact which had not been noticed throuhout).


Click on image to enlargeThe final chapter......

I have had an expensive summer so it wasn't until months later that I finally got around to sending the faulty bass unit to Audioheritage to be properly sorted. Including postage the final cost of the repair was £90 gbp. Accounting for its previous unsuccessful trip to London this bass unit has cost me £135 gbp. Some people don't pay that for a complete pair of BC1's (yes Heskett I mean you)!

All the strife was eventually worth it. It came back better than new after finally finding a craftsman who really is an artist. Click on the image left to take a look at how good this unit has been rebuilt. Now that my modded BC1's have two perfect bass units the sound has been transformed once again. This will only get better as the new driver runs in. Currently the sound is noticably better than they were at the final shootout with Heskett. In many aspects I now prefer these to the sound of my rebuilt SP1's (which I have always rated as better than the BC1). The SP1's still have the edge but is is now very very very close. I guess ultimately I need the extra sound pressure that an SP1 will provide. I just like my music loud and I don't know that I will ever grow out of this particular abberration. Luckily I have very good neighbours.

For me this has been a very enjoyable project which is essentially at an end. I have really enjoyed everything I have learned, both technically and historically about our audio heritage a such institutions such as Spendor Audio and the BBC research dept. In the future I may experiment with a complete crossover rebuild and find some great sounding inductors which may possibly outperform the standard ones. It all depends upon how much interest this page generates. I would appreciate any comments and you are all welcome to email me via my email page.

I would like to thank my neighbours (fortunately they appreciate my taste in music), Glenn Croft (Eminent Audio), Amar Bizwas (Eminent Audio), Arthur Khoubesserian (The Funk Firm), Heskett Dawson (a patient man who wore out a set of banana plugs with constant switching), the HiFiWizz (you know who you are), Dave Fagan, and Derek Hugues (Spendor) for all of their help and advice both directly and via the Spendor users group. Thanks also to all of the other Spendor group members who offered help, information and advice. Finally I would like to acknowledge the brilliance of Spencer Hughes who designed an absolutely fantastic series of loudspeakers which have stood the test of time and continues to shame modern audio technology. Click here to go to the Spendor site.

If you have read this page and don't own a pair of Spendor BC1's........

Then you are missing out and you should buy some! Be prepared to part with some cash for a good pair. Even the dogs sound good but the sorted ones are sonically hypnotic and should be coveted!

Thanks for reading this far.....

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© mats-enterprise.co.uk december 2005