Making Transistor switch from audio signal??

[diskoduck]

Hello everybody,
I did some mods on my guvnor including a bright switch. Now Iwant to add a status LED besides other LEDs. Further I'd like to switch the whole thing with a SPST (3 pole) since
it's not necessary to waste a precious true-bypass switch on switching a cap in.
Question:
There must be a way making a transistor switch from a audio-trigger.(small current to source)
But how do I handle the AC audio signal and make it DC for triggering the transistor?
Does anybody have any tips or suggestions?
Thanx

[diskoduck]

Do I have to put a diode rectifier between source and AC signal?
Anyone................................

[R.G.]

1. You have to rectify the signal to DC, then use the DC to trigger the switch.
2. You will need a buffer between the signal and the rectifier to avoid the rectifier causing unwanted distortion in the signal
3. You will have to make the rectifier be an active rectifier with gain if the signal you're sensing is low level, like a guitar.
4. Depending on whether the cap you're switching in is a cap to ground or not, a transistor may not work. You may need a CMOS switch chip. Bipolars and FETs are hard to make floating switches out of.
5. Do yourself a favor and make sure that both ends of the cap you're switching are pulled to the same DC level with resistors. Otherwise you'll be back here complaining that it makes a hige pop when it switches.

Frankly, a true bypass switch may be simpler than the remote switching triggered by audio.

[diskoduck]

R.G. thank you.
Impressive list. What you wrote: true bypass would be easier. I allready had this impression after the third line of your list:-(
Thanx again.

[diskoduck]

Ould a CD 4013 make sense if I want to switch say 3 caps and a status led with one switch??
Could this be an alternative for the ultimate 27 pole switch? :-)

[birt]

i do have a very simple schematic to switch a relay with audio signal, that's probably usefull for you too with some minor modifications.

[diskoduck]

Hey birt,
sure! Allthough the flipflop seems appealing it would be nice if you could mail the relay scheme to:
disko@audiostatement.de

[birt]

[d95err]

I did some mods on my guvnor including a bright switch. Now Iwant to add a status LED besides other LEDs. Further I'd like to switch the whole thing with a SPST (3 pole) since
it's not necessary to waste a precious true-bypass switch on switching a cap in.
Question:
There must be a way making a transistor switch from a audio-trigger.(small current to source)
But how do I handle the AC audio signal and make it DC for triggering the transistor?

I'm a bit confused by this description. There seems to be two completely different issues involved.

First, it seems like you want to use a transistor switch to add or remove a bright cap in or out of the Guvnor circuit.
Second, it seems that you want the bright switch to be triggered by an audio signal.

Is this correct?

[brett]

Hi
the circuit that I was thinking of is similar to birt's.
Differences that I would employ would be:
Drive it with a JFET buffer.  You cannot drive this circuit from most stompbox circuits.
make C5 equal to 1uF
remove T4, and the relay
change R10 to 1k
connect the collector of T3 to 9V via the LED that you want controlled

It works like this:
positive voltages flow via D1 to an uncharged C5
if the voltage is sufficient, C5 takes 0.3 seconds to charge
otherwise the charge flows out through R8
if the signal stays "up" for 0.3 seconds, T3 turns "on" and current flows from the +9V through the LED and T3 and R10 to ground.  R10 controls the current flow.  1K allows about 6mA to flow. 

[diskoduck]

Thanks to everyone,

especially brett and birt.
Yes what I wanted to achieve was to trigger a LED from an audio signal. (signal flow=LED lights up)

[R.G.]

Yes what I wanted to achieve was to trigger a LED from an audio signal. (signal flow=LED lights up)

Oh.

OK, that's easy.

(1) Set up an opamp in a high gain, noninverting fashion by biasing the + input to about 1.2V with resistors and use a 1M feedback resistor, 1K resistor from - input to bias. Um, this is a single supply solution, opamp powered from 0V and +9V.

(2) capacitively couple the line to be watched into the + input.

(3) put an LED to 0V on the output.  All done.

Now when audio comes along, it drives the opamp crazy, with massive swings down to 0V, where it clips, and to +9V where it drives the LED to the current limit of the opamp. The LED is on only on positive swings, but your eye will think it's on all the time.