Simple Circuit to Pull a Transistor to Ground?

EchoWars · 19th September 2008, 01:01 PM

I have an amp with a reed relay that needs to be opened as soon as power is removed. The relay is actuated through a driver transistor with only about .8V on its base. In Post #11 of this thread, there's a circuit that I've used before to sense the loss of AC, but this won't work in this circuit since it has to discharge through a diode and the base of the driver transistor is at such a low potential.

I need to pull that base to ground potential immediately on power-off, and all I can come up with is a kluge with a SPDT DC reed relay tied to an AC line (with associated circuitry to rectify the voltage for the relay coil) and short the transistor base to ground on power off. Which also makes me realize how great a little 12V AC reed relay would be right about now...would simplify things a lot.

Anything I'm overlooking in my sleep-deprived state?

gain · 22nd September 2008, 08:02 PM

a schematic would be helpful ... perhaps just tie the base to ground through a suitable resistor? then when power is removed the .8V will be discharged quickly through the resistor into ground. or just drive the coil of the reed relay / driver transistor directly from a voltage source that goes away when power is removed. your idea of an additional relay shunting to ground is a good one but seems unnecessarily complex given the situation.

turnA_zpoint · 23rd September 2008, 11:36 AM

Hi !

It introduces it because it was very effective though it is a primitive method for a pop noise when it is on-off by using mechanical SW with standby . It would be greatly appreciated if it helps you even if it is a little. (All You have already thought knowing..... )

SW
maker :Carling
type : DPTTP (3 position)

working
position circuit 1.. circuit2 .. explain
UPPER .....ON ........ON.....AMP(circuit1) & Relay ON (circuit2)
CENTER ...OFF .......ON ....Only Amp ON (circuit1)
LOWER ....OFF .......OFF .....All OFF

(1)When turn ON SW (Lower ---> Center--->Upper),
previously the Cente rposition AMP is on ,but Relay off.
next,Upper position relay on.

(2)When turn OFF SW (Upper --->center--> Lower),
previously the Center position Relay is off,
next,Lower position Amp off.

I had same problem at turn off ,then try some delay circuit,
but there is an experience that the influence of the delay circuit gave tone quality the change through the ground line. (Though it may be only my feeling ...Somehow, it is not possible to know. )
So,I become use this method.

Now I use this SW very good feeling.
(If it is OK that attach maker parts photo ,I can do)

REGARD

turnA_zpoint · 23rd September 2008, 04:42 PM

I'm verry sorry ,I mistake !

bellow I correct

working
...............AMP........Relay
position circuit 1.. circuit2 .. explain
UPPER .....ON ........ON.....AMP(circuit1) & Relay ON (circuit2)
CENTER ...ON .......OFF ....Only Amp ON (circuit1) <<<< Correction!!
LOWER ....OFF ......OFF ....All OFF

Sincerely.

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19th September 2008, 01:01 PM	#1
EchoWars diyAudio Member Join Date: Dec 2002 Location: Left of the Dial	Simple Circuit to Pull a Transistor to Ground? I have an amp with a reed relay that needs to be opened as soon as power is removed. The relay is actuated through a driver transistor with only about .8V on its base. In Post #11 of this thread, there's a circuit that I've used before to sense the loss of AC, but this won't work in this circuit since it has to discharge through a diode and the base of the driver transistor is at such a low potential. I need to pull that base to ground potential immediately on power-off, and all I can come up with is a kluge with a SPDT DC reed relay tied to an AC line (with associated circuitry to rectify the voltage for the relay coil) and short the transistor base to ground on power off. Which also makes me realize how great a little 12V AC reed relay would be right about now...would simplify things a lot. Anything I'm overlooking in my sleep-deprived state?

22nd September 2008, 08:02 PM	#2
gain diyAudio Member Join Date: Apr 2008	a schematic would be helpful ... perhaps just tie the base to ground through a suitable resistor? then when power is removed the .8V will be discharged quickly through the resistor into ground. or just drive the coil of the reed relay / driver transistor directly from a voltage source that goes away when power is removed. your idea of an additional relay shunting to ground is a good one but seems unnecessarily complex given the situation.

23rd September 2008, 11:36 AM	#3
turnA_zpoint diyAudio Member Join Date: Nov 2006	Hi ! It introduces it because it was very effective though it is a primitive method for a pop noise when it is on-off by using mechanical SW with standby . It would be greatly appreciated if it helps you even if it is a little. (All You have already thought knowing..... ) SW maker :Carling type : DPTTP (3 position) working position circuit 1.. circuit2 .. explain UPPER .....ON ........ON.....AMP(circuit1) & Relay ON (circuit2) CENTER ...OFF .......ON ....Only Amp ON (circuit1) LOWER ....OFF .......OFF .....All OFF (1)When turn ON SW (Lower ---> Center--->Upper), previously the Cente rposition AMP is on ,but Relay off. next,Upper position relay on. (2)When turn OFF SW (Upper --->center--> Lower), previously the Center position Relay is off, next,Lower position Amp off. I had same problem at turn off ,then try some delay circuit, but there is an experience that the influence of the delay circuit gave tone quality the change through the ground line. (Though it may be only my feeling ...Somehow, it is not possible to know. ) So,I become use this method. Now I use this SW very good feeling. (If it is OK that attach maker parts photo ,I can do) REGARD

23rd September 2008, 04:42 PM	#4
turnA_zpoint diyAudio Member Join Date: Nov 2006	I'm verry sorry ,I mistake ! bellow I correct working ...............AMP........Relay position circuit 1.. circuit2 .. explain UPPER .....ON ........ON.....AMP(circuit1) & Relay ON (circuit2) CENTER ...ON .......OFF ....Only Amp ON (circuit1) <<<< Correction!! LOWER ....OFF ......OFF ....All OFF Sincerely.

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