Wharfedale Active Diamond Plus loudspeakers
There are occasionally products in hifi which are true bargains. In my mind, the original Wharfedale Diamond speakers of the early 1980s were just this. They were extremely successful on launch in the UK. They offered a great quality of sound from diminutive size boxes, just 186 mm wide, 240 mm high and 204 mm deep and at a very good price.
After the Diamonds had been around for a few years, an active version was launched. These are not true active speakers as they use passive crossovers after one amplifier per channel rather than a line level crossover driving separate amplifiers per driver, but they do have a built in amplifier which makes them convenient for many purposes. The amplifier used is a good quality "chipamp", used nearly 20 years before they came into fashion.
My Active Diamonds were manufactured in April 1989 by Wharfedale for Ferguson and have a Ferguson badge on the front. The idea was for them to be sold to accompany NICAM televisions and video recorders. It seems that not many of them were sold this way, as I ended up picking them up a year or so later for just £50 instead of the usual price of around £150.
At the time I bought these, I was working as a software contractor. This sometimes involved travelling from place to place and setting up home temporarily in hotel rooms. Combined with the Sony WM-D6C professional walkman as a source, these speakers gave me a creditable hifi away from home.
The speakers come in a very useful box with a handle on top, and are themselves quite non-descript black vinyl wrap boxes. Wharfedale diamonds were also available for a time in several different bright gloss colours.
The speakers with and without grills. Note how the Ferguson badge is only on the outside of the grill. On the inside they are genuine Wharfedale.
Note that the tweeter seems to be the improved model fitted to the Diamond III rather than that fitted to the very first versions of the speakers, and that the bass driver is a paper cone instead of the polypropylene cone which the original version of the speakers had.
The bass driver measures a mere 110 mm, while the treble dome is 20 mm in size.
The backs of the two speakers are different. The powered one having a volume control and three cables. A mains cable, and two flying leads. One is terminated with phono plugs for a line level source and the other is unterminated to use with the clips on the back of the passive speaker.
Inside the speakers
Inside the passive (left) speaker there is a simple first order crossover using a 2.2uF capacitor and a resistor to match efficiency for the tweeter and a coil of unknown value for the woofer. The small physical size of the coil could mean this is prone to saturation at higher volumes and hence some level of distortion.
The crossover is claimed to be at 5 kHz, so I guess the impedance of the tweeter must be around 16 ohms to approximate a 5 kHz crossover frequency.
Inside the powered (right) speaker there is a power supply and a stereo power amp built around the TDA2040 IC power amp chip. The crossover circuit for this speaker is also on the PCB. The metal plate on the back of the speakers is used as a heatsink.
The TDA2040 is a good power op-amp chip. It is rated for an output of 36 W into 4 ohms, which is more than adequate for these speakers. It was also amongst those reviewed by Ben Duncan in his 1993 article for Wireless World "Spectrally Challenged" it was demonstrated that not only does this cheap have low distortion, but that it has monotonically descending distortion. i.e. the 2nd harmonic is greater than the 3rd which is greater than the 4th - this being generally understood to sound better than other distortion patterns and "more pleasing to the ear, and more like the harmonics in euphoric musical instruments", and also that it is reasonably benign in overload. Not at all a bad set of features in an audio amplifier.
I'm a big fan of these speakers. They actually sound really good, and have a surprising amount of bottom end too if positioned close to the wall (as is recommended by the manufacturer). The manufacturer claims a frequency response when wall mounted of 50Hz to 20kHz. However, they don't give the level at these frequencies. Some other sources claim that bass response has "all but disappeared" by 75 Hz. Nevertheless, the speakers sound well balanced and are fun to listen to, which is a good start. I found them more pleasing than some larger and more expensive speakers.
A good match for computers (keep them away from CRT monitors because of the magnetic field from the drivers) or other line level sources.
A cheap minimal setup could be made with speakers like this and a Chinese MP3 player.
If you're looking for a review of later versions of the Wharfedale Diamond, so far as I remember the speakers were quite similar up until the Diamond III. However, later "Wharfedale Diamonds" are often completely unrelated designs which I have not heard.
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