Tube sources always come up slowly. This means there can be a very low frequency component (typical <1Hz) present at the output of stages like tube ouput CD-players, preamplifiers, RIAA prepre amplifiers, etc. A wide band power amplifier can amplify this and blow out the bassdrivers. Also most of the time there are warming up noises, etc. This can sound really nasty and you don't want (and need) to hear this. When there is a power failure, it is also possible preamps give a very nasty peak, resulting in damage of other equipment, speakers or your ears.

This simple delay and protection circuit takes care the outputs of your source are shorted the first 30 second the equipment is on. Also the relais shorts the outputs in case of a power failure. This reduces the chance of damage to the rest of the equipment. Please note that the relais is not in the signal, and therefore the circuit does not give any reduction in sound quality. When using this protection, please take care the output of your device van handle shortcircuiting. Tube output stages always do.

Features:

• Configurable startup delay, immediate reset (and new delay) after powerdrop
• Output is short-circuited with a relay during startup and realesed after the delay
• Works on 5-20 Vdc, easy to extract from any power supply or tube heather supply
• Delay is 35 seconds, but can easily set to other values
• Available in stereo and 6 channel version
• The delay circuit is completely isolated from the signal and signal ground

Price list:

Kit	Price kit	Price fully build
Stereo Delay	12.50	22.50
6 Channel Delay	22.50	34.50
+5V regulted power supply, including transformer and all other parts	17.50	32.50

Building and using the delay circuit:

Before you start, read this article about soldering and the disclaimers. If you have questions about the manual, about the kit, about your configuration, or anything else, please do not hesitate to ask us. We will do all we can to help you getting the best out or our DIY kits.

The below description is for application of the stereo version of the delay. For the 6 channel version some values have to be changed, please ask me.

1. Mount the parts like you see in the picture. The colour codes of the resistors are noted in the partslist. Connect the plus of the capacitors the plus symbol on the PCB (printed circuit board). Take care the the ring on the diodes is in the same direction as the ring on the PCB. The transistor case should match the shape on the PCB, round and flat side.
2. For power supply voltages of 5Vdc to 10Vdc, a resistor has to be used in the place of the 7805 regulator. It has to be soldered between the in and out pin (picture). The value of the resistor should be Rdrop=(Vinput-5V)/40mA, the power of the resistor should be 40mA*40mA*5*Rdrop. For example, for 6.3V, you will need a 27 Ohm/0.25W resistor, for 9V input a 100R/1W resistor.
3. For power supply voltages of 10-20Vdc the 7805 has to be installed.
4. Input voltage has to be applied between the +V and-V pins.
5. The protected outputs must be connected to L and R on the print, the signal ground to GND.
6. The PCB comes standard with the delay ground and signal ground connected. If you want them isolated (for example in case of a floating input voltage), you have to scratch the little connection between the ground planes of both grounds (picture).
7. To test the print apply an input voltage and wait for 35 seconds. You should hear a clear click sound when the relais get activated. The outputs are shortcircuited between the output pins and signal ground for the first 35 seconds, after that all outputs are seperated and have no connection (infinite resistance) with one each other.