The modification of my Tannoy:
The dual-concentric patent, (HPD version)
The Tannoy Monitor Gold LSU/15/8 (with serial #115760 and #129969) units were produced in 1970 and 1971 and purchased without cabinets in the same years. The modified cabinets were built after York designs by Tannoy (see elswere on this site) in 1971/2. Also the cross-over filters were modified in 2001 as you can see below.
Here the original schematic of the Monitor Gold crossover unit.*
The schematic diagram of my modified crossover filter below.*
As you can see the switches are gone and the resistor of 50 Ohms was put out of action, and later reconnected again. The capacitors were tested and some of them were replaced by high quality parts. The coils stayed unchanged in the circuit and the capacitor of 3.3 uF and the one of 1.5 uF were not changed. The 6.8 uF and the 16 uF capacitors were replaced. All remaining components stayed the same value. The wiring was modified at the terminal board and in the cross over unit, but stayed unchanged at the speaker side. Good quality copper wire was used.
Below pictures of the old capacitors.
Right speaker (right picture): 16 uF (15.1 uF) 20V electrolytic bipolar cap. and 6.8 uF (7 uF) 100V cap. Left speaker (left picture): 16 uF (16.7 uF) 20V electrolytic bipolar cap. and 6.8 uF (6.5 uF) 250V cap. The values in (...) are actual measured values in december 2000 (+/- 1% at 5 KHz). These parts are high quality capacitors considering that they are made before 1970. The electrolytic caps were made by Plessey in England, the 6.8 uF 250V cap. was made in Germany by ITT and the tiny 6.8 uF 100V cap. was made by ARCO in USA.
Here the new capacitors of type MKS for polyester, MKP for polypropylene made by Wima Germany:
Type MKS SC HD (special quality) 16 uF (17 uF) 100V, 2.2 uF (2.2 uF) 250V + MKP SC (special quality) 4.7 uF (4.55 uF) 250V giving a total of 6.75 uF. The gray 2.2 uF is a general purpose polyester made by Siemens (ROE).
The values in (...) are actual measured values in december 2000 (+/- 1% at 5 KHz). The combination of the 2 caps, 2.2 uF and 4.7uF of different brand and type, are used to avoid possible frequency dependency of a single cap (other combinations may give slightly better results).
All caps were hot-glued in the crossover unit to avoid acoustic resonances, the huge 16 uF capacitor just fits in the crossover unit.
The modified crossover filter in final situation. As you can see all other components were left as is, they are of good quality and do not need replacement.
Bottom view, the wiring is partly replaced and extended.
As an extra example: at the right one of the quite big polypropylene capacitors I used in my crossover unit. At the left a polyester capacitor of well known brand with printed on it as you can see: 'Film Capacitor' and on the other side: 'high quality capacitor for professional speaker crossover networks' used by a very well known speaker manufacturer, selling high end speaker systems all over the world.
Both caps are 4.7 uF and 250 V.
I want to thank the members of the Tannoy-eGroup for their contribution to this modification. You can join our TANNOY eGroup: firstname.lastname@example.org and http://www.egroups.com or email@example.com
You can also join our LUXMAN eGroup: firstname.lastname@example.org or http://www.egroups.com or email@example.com
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© Hans Hilberink PE1MMK ® last update: 06-04-2017.