Spendor BC1 Upgrade kit

The Spendor BC1 was designed in the late 1960s by Spencer Hughes who worked at the BBC. Along with co-designer Dudley Harwood, they used Bextrene (originally used for making egg cartons) which, when covered in gunk, became suitable for making loudspeaker diaphragms. The resulting 3-way design used an 8 inch Bextrene mid-bass driver, a Celestion tweeter and a Coles supertweeter. The drive units are mounted in a thin-walled reflex enclosure and at the time gave impressive stereo imaging and detail, sounding smooth, clear and with low distortion.

The BC1 was part of the system I assembled of the ‘best’ Hi-Fi available in 1973. I was one of the first British Hi-Fi dealers to be allowed to sell it (I remember that Spendor took some persuading to allow non-professional studio users to buy them in the very early days). This was the system that so disappointed me for its lack of musicality, it was just so boringly ‘Hi-Fi’. I now know how to overcome this limitation with all parts of that system (and any other).

The main problem with the BC1 is the rather complex crossover network. The efforts to deliver consistency and response ‘accuracy’ make it low on efficiency and limits dynamic range, softening bass and making the treble rather ‘hard’ in character.

My answer is in two steps.
The conventional approach – Type A – is to upgrade crossover components, rewire with Kimber 4TC speaker cable, remove the foam rubber sheets that line the inside of the cabinet and replace it with Acousti-Wool. The result is a very big step towards giving the sound more life and dynamics and tightening the bass.

The more unconventional solution – Type B – is to remove the crossover completely, wire the mid/bass direct to the input, then feed the treble with a 2uF Kimber Kap and the Supertweeter with a 0.33uF Kimber Kap. The result of this is revelatory. You usefully gain around 6dBs in sensitivity, a sweeter, clearer treble and a tight, clean and deep bass. The music becomes truly involving, detailed and dynamic, yet still smooth and ‘tidy’. And it plays rock and roll! Interestingly, the frequency response graphs are very similar and the modified one is arguably flatter. I have applied this solution to dozens of speakers now and had very consistent results. Interestingly, much of the ‘characteristic’ distortion I associate with dome tweeters turned out to be an artefact of the crossover networks used; specifically the use of inductors.

If you have a pair of BC1s and want to have a more modern, expressive and involving experience with your music, give Type B upgrade a go; you can easily put the old crossover back if you don’t like it. I think you will fall in love with them all over again.

Fact file
Date launched: 1969
Date discontinued: 1994
Type: 3 way
Sensitivity: 84dB / 1W / 1m
Nominal impedance: 8 O
Frequency response: 50Hz – 15kHz
later to 45kHz – 25kHz
Power handling: 20W RMS later 55W
Weight: 14Kg
Dimensions: 635mm x 300mm x 300mm HWD

Please note: The Torlyte Speaker stands shown, are not included as part of the upgrade.

There are two approaches to the upgrades: if you are technically minded, you can purchase an upgrade kit from us and do the upgrade yourself or you can deliver the speakers to us so that we can upgrade them for you.

Tools required
Soldering iron (recommended 60w)
Wire cutters
Wire strippers

Upgrade kits and guide
If you have some experience with electronics, you may find it cost-effective to do the upgrades yourself. Our upgrade kit contains full instructions and all the components you need to complete the upgrade. The instructions do not assume a high level of technical knowledge, just common sense, practicality and native cunning. The instructions are illustrated with line drawings showing what goes where.

Early/Late DIY Kit - Know your speakers!
These kits are for those who want to undertake a conventional upgrade, retaining the BC1's crossover but upgrading the component quality. There were a few changes made to the BC1 during its production. Most literature claims 55W power handling, but this only applies to the later versions. Up until about 1977, I am certain the power handling remained at 20W. Later model BC1s contain fewer components in the crossover and it’s important to know which type you have if you are going to upgrade them. Finding out which one you have can be done with a component count:

Early crossovers have 15 components

Later ones have 12.

Both Early and Late upgrade kits retain the original crossover board, upgrading only the components on it.

Each kit contains:
Kimber Kaps
Inductors
4TC
Acousti-wool
Wonder Solder
Instructions

RA DIY Kit
The Russ Andrews upgrade goes for a far more simple crossover circuit, allowing the bass/mid driver to operate full range and using Kimber capacitors to roll on the higher frequencies.

Kit contains;
4 x Kimber Kaps
4 x pre-prepared lengths of Kimber 4TC
2 x pre-prepared lengths of Kimber TCX cable
Acousti-wool
Wonder Solder
Instructions

Upgrade Service
For those who have neither the facilities, time or courage to do the work themselves, we offer a complete upgrade service. To do the work, you must have adequate means to get the speakers to us safely; we recommend delivering the speakers to us to ensure they arrive to us undamaged. With prior arrangement you could A/B our upgraded pair against yours before you make a decision; we can provide a before and after frequency response graph for you to keep. Contact us for details.