Au fait, des améliorations qu'on peut apporter à ce kit :
Velleman K4700
C11 Velleman's K4700 Loudspeaker protection kit provides for turn-on delay and output DC protection.
Specs
6-10s turn-on delay
DC protection (activates at 1V DC)
Manual turn-off option (short to V-)
Relays spec'd for 28VDC @ 10A, 125VAC @ 15A
Two-channel protection
This inexpensive Velleman kit provides reliable speaker protection at low cost. It is quick and easy to assemble. Although there are other protection circuits available, the Velleman kit may allow constructors to spend more time on audio projects and less on building blocks.
Improvements
Add Zener
Replace D9 with a back-to-back diode and 12V zener. (Diode retains original direction) This will greatly speed relay release time. If the 30V BC517 switching transistor (T4) is replaced with a higher-rated one, a 24V zener may be used.
Connect ground
An important improvement is connecting the "unused" relay contact solidly to ground. The pads for R23/24 and R25/26 may be used for this purpose. This ensures the relay switches the load to ground in a fault state.
Remove AC supply
Many constructors may not like the idea of mains leads or a transformer near their audio outputs. One may eliminate the tranfo and four power diodes by supplying +-7.5V to the marked pads (symmetric supply). The stock supply is rated for only 100mA per rail, so little power is required.
Replace relays
The K4700 will safely supply quite a bit of current, especially if the AC power supply is replaced. T4 is rated for 500mA, quite enough to power larger, higher rated relays.
The stock relays may be insufficient for some amplifiers. If the amp can supply >10A into the load in a fault condition, the relays will arc and weld. Some knowledgable builders suggest derating the relay's current specs by at least 50% to ensure that welding will not occur. Choosing the correct relays is of great importance.
Alter timing
The turn-on delay timing will be dependent on the supply voltages. By altering the value of C11, the delay time may be adjusted.
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http://www.anidian.com/audio/deconstruct/k4700.shtml
J'ai deja prévu de mettre le transfo dans un compartiment réservé aux autres transfos.
Hervé
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