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PAIR LARGE 1970s BBC/ROGERS LS3/7 ACTIVE STUDIO MONITORS
IN GOOD WORKING ORDER
GOOD VINTAGE CONDITION, WITH SOME SMALL COSMETIC IMPERFECTIONS
[INCLUDED ARE TWO AM8/15 ACTIVE X-OVER BOARDS – *FOR REPAIR*]
ALL BBC DOCS/MANUALS
TWO 4-PIN XLR INPUT PLUGS
*SHIPPING AVAILABLE to UK, and to EU countries*
*Shipping costs given below are generally correct, but may vary for some locations, please request accurate shipping cost to your location.*
BACKGROUND INFO:
First introduced by the BBC in 1977 as “high sound level” (104dB @1.5 metres) monitors for OB units (Outside Broadcast vehicles). A slightly modified active-crossover followed in 1978 (AM8/15).
Designed to monitor national BBC broadcasts of music at higher volume than previous OB monitor systems in order to satisfy demands of louder shows, such as Radio One Roadshow, etc.
There were no further modifications made until the LS3/7 was itself superseded in the early 2000s, after approximately quarter of a century service.
At that point, BBC maintenance schedules for this unit were withdrawn, and it was therefore seen by the BBC as no longer viable for the critical job of national broadcast monitoring.
In the early 2000s, some LS3/7 were then redeployed for non-critical work within the BBC, and some made available for sale outside the BBC.
SPECIFICATION:
Input impedance: 15 Ohms
Axial frequency response: 35Hz – 20kHz
Max Sound level : 104dB w.r.t. at 1.5 metres
2-way driver configuration
Spendor/Rogers 10 bass/mid driver (with 8-inch Bextrene inner cone)
Audax SD 12 x 9 D 25 25mm tweeter
Similar to the Tannoy’s dual-concentric system, the tweeter is mounted over the main driver (woofer), in order to enable “accurate near-field monitoring from as close as 0.5 metres”.
Cabinet finish: Teak veneer with black Tygan cloth_________________________________________
Photo 9 shows main driver, with the tweeter mounting removed and turned 180 degrees showing the rear of the Audax tweeter.
These are active monitors (ie no passive crossover inside the speaker).
Although the speakers themselves are fully working, they rely on active crossovers in order to function as intended.
A pair of the specified BBC AM8/15 active crossover boards are included, *The crossovers are sold as not-working, they are untested and will require maintenance and 47V DC power supply, and ideally mounting in a rack unit or similar box.*
Some refurbishment/component testing has already been done:
Both transformer/coils have been tested for resistance, and give good matching readings.
Some caps have been replaced, including one large cap. A new spare large cap is included for the other board, although the original tests OK.
Research shows the boards will typically need some transistors replacing. Even the vintage (best) replacements are inexpensive, only 20 to replace the entire set of 14 transistors (7 per board = 14 transistors). Online links for these available if requested.
The crossovers were originally mounted underneath Quad 303 amplifiers, to BBC design.
However, mounting the crossover units in their own box means they can be used in conjunction with any pair of good stereo amplifiers of suitable output.
Originally designed to be powered by the 47V DC tap of the Quad 303, they could be powered from a suitable 48V phantom power source.
Full set of relevant BBC documents with diagrams and parts lists.
Original cast alloy handles included.
Each speaker is designed to be driven by 2 x 100W of amplification, one channel for low frequency, one for high.
With the crossovers now separated from the amps, they can be wired through the amplifiers in a more natural configuration: one stereo amp for low frequencies, and one stereo amp for high frequencies, if desired.
Dimensions – approx 770mm high; 470mm wide; 330mm deep;
weight: approx. 32kg each.
Shipping is expensive due to weight and size.
Please see large photos.
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Category: Musical Instruments:Pro Audio Equipment:Speakers and Monitors
Location: Mid Somerset