Timed killswitch stompbox

[SeneX225]

Hi!
I've got this peculiar idea of a killswitch pedal that can cut the signal for a certain amount of time after pressing a switch. After a bit of looking around I found that a 555-based Off Delay would be exactly what needed. I also found (and slightly modified for particular instance) this schematic:



Combination of 10k potentiometer and 10nF capacitor will give signal off time of 11 seconds on maximum pot value and also, I think, will work as a usual killswitch on minimum.

There's a vero I transcribed from the schematic:



Please verify if everything is in order. I'm quite new to the whole thing and most like made a blunder somewhere.

Thanks!

[ElectricDruid]

The mute transistor is connected to ground? That's not right, is it?

I think I need to see better how the in/out jacks are connected up. I don't get what it's trying to do at the moment.

[antonis]

The mute transistor is connected to ground? That's not right, is it?

It depends on the way of grounding, Tom..

Should IN/OUT jack GND be "open" (floating), like in IN jack Ring/Sleeve configuration, it should work..
(but with a significant DC offset due to BJT V_CEsat - about 250mV for a Collector current of 10mA..)

edit: Just realized that OP deals with signal delayed cut off so IN/OUT jack hot should definatelly be connected directly to Q1 Collector..

[GibsonGM]

Cool idea.  If you used a 556, I bet you could add to this and make it a 'gated', stutter effect. 

[SeneX225]

The mute transistor is connected to ground? That's not right, is it?

I think I need to see better how the in/out jacks are connected up. I don't get what it's trying to do at the moment.

I thought that these two leads it will close the circuit the way a regular killswitch does. Now I see my mistake. In original schematic there was a relay between jack hot and jack ground, so that's what confused me.

Thank you for the correction! This way, if I understand it right, the circuit will actually close between jack's hot and ground, doing exactly as I want it to.

Here's the updated vero:



Is everything alright now (besides my very space-inefficient vero design, but corrections on that are welcome as well)?

[antonis]

Beware of BC547B pin-out..!!
(it's C-B-E)

Also, you have plenty or board room so place all resistor in horizontal position..

P.S.
Your board layout is tremendously wrong..!!
(e.g. Jack hot is wired on power supply ..)

edit: Actually, your initial circuit is wrong..
You need a cut (discontinuity) between D1 Cathode and CLR..

[ElectricDruid]

The jack ground is going to need connecting to the circuit ground too, otherwise the transistor isn't shorting the signal.

Also D1 looks like a left-over from a relay driver. I don't see what it's for in this circuit.

[antonis]

The jack ground is going to need connecting to the circuit ground too, otherwise the transistor isn't shorting the signal.

Of course, but not on timer GND..

Something like this:

[ElectricDruid]

Antonis makes a good point - the details of the grounding are going to be significant in this circuit. He's shown it taken right back to the power supply, so that the 555 circuit and the audio part don't share any wiring. That's a good idea.

Using the low power ICM7555 rather than the standard version would help a lot too. The 555 is famous for the spikes it puts on the supply rails, which comes out in audio circuits as unwanted clicks or thumps.

[SeneX225]

Beware of BC547B pin-out..!!
(it's C-B-E)

These three-legged tricksters confuse me all the time!

P.S.
Your board layout is tremendously wrong..!!
(e.g. Jack hot is wired on power supply ..)

edit: Actually, your initial circuit is wrong..
You need a cut (discontinuity) between D1 Cathode and CLR..

The jack ground is going to need connecting to the circuit ground too, otherwise the transistor isn't shorting the signal.

Of course, but not on timer GND..

Something like this:

I see, without that cut the circuit would close on powering up.

Antonis makes a good point - the details of the grounding are going to be significant in this circuit. He's shown it taken right back to the power supply, so that the 555 circuit and the audio part don't share any wiring. That's a good idea.

Can you please explain why is it better to separate 555 and jack grounds?

Using the low power ICM7555 rather than the standard version would help a lot too. The 555 is famous for the spikes it puts on the supply rails, which comes out in audio circuits as unwanted clicks or thumps.

Noted, thanks!

Now, yet another vero attempt:

[garcho]

Can you please explain why is it better to separate 555 and jack grounds?

For the same reason Tom suggested using the low-power version of the 555. The holy trinity of electronics - voltage, current & resistance - work together to do useful stuff. That useful work can also produce non-useful reactions in the circuitry. The current spikes the 555 produces to do work can also produce audible pops in your signal.

Think if you slap your strings and then mute them right away. You're sending a current "spike", pushed by voltage, to your amp, which then does amp-y stuff to it so you can hear it with your human ear.  The current spikes from the 555 do the same thing. The only difference is that those spikes are "in" the ground instead of "in" your signal. But since we're talking about circuitry, as in circle, it ALL matters. So, it's usually always important to know where your return current is routed. If those spikes return in a direct fashion to the power supply, hopefully they bypass your signal and your audio remains spike-free. It's not always that easy...

Everything has resistance, which means conductors, aka wires and leads and tracks and traces on your board, create voltage. Ground is a reference voltage - the more stable the reference, the more true the work. Routing matters!

[SeneX225]

Can you please explain why is it better to separate 555 and jack grounds?

For the same reason Tom suggested using the low-power version of the 555. The holy trinity of electronics - voltage, current & resistance - work together to do useful stuff. That useful work can also produce non-useful reactions in the circuitry. The current spikes the 555 produces to do work can also produce audible pops in your signal.

Think if you slap your strings and then mute them right away. You're sending a current "spike", pushed by voltage, to your amp, which then does amp-y stuff to it so you can hear it with your human ear.  The current spikes from the 555 do the same thing. The only difference is that those spikes are "in" the ground instead of "in" your signal. But since we're talking about circuitry, as in circle, it ALL matters. So, it's usually always important to know where your return current is routed. If those spikes return in a direct fashion to the power supply, hopefully they bypass your signal and your audio remains spike-free. It's not always that easy...

Everything has resistance, which means conductors, aka wires and leads and tracks and traces on your board, create voltage. Ground is a reference voltage - the more stable the reference, the more true the work. Routing matters!

Thank you very much!

[Ripthorn]

I have a box that does this type of thing along with patterns and tap tempo using a microcontroller. Schematics, Gerbers, and code are provided if you want to build one.
https://scientificguitarist.wixsite.com/home/kill-box

[antonis]

I have a box that does this type of thing along with patterns and tap tempo using a microcontroller.

Concerning the pull-up resistor..

Brian, I can't figure out how Kill Box signal Path could work without that resistor (or a diode, at least)..
As far as I know, 7805 regulator output resistance is considered practically zero and C5 is also considered AC short to GND..
So, signal path should be effectively grounded for either T1 state..

or am I missing something..??

[Ripthorn]

I have a box that does this type of thing along with patterns and tap tempo using a microcontroller.

Concerning the pull-up resistor..

Brian, I can't figure out how Kill Box signal Path could work without that resistor (or a diode, at least)..
As far as I know, 7805 regulator output resistance is considered practically zero and C5 is also considered AC short to GND..
So, signal path should be effectively grounded for either T1 state..

or am I missing something..??

C5 is just a smoothing/reservoir cap for the +5V line. The signal path works because the microcontroller turns the transistor base high, causing it to shunt the audio signal to ground.

[antonis]

C5 is just a smoothing/reservoir cap for the +5V line. The signal path works because the microcontroller turns the transistor base high, causing it to shunt the audio signal to ground.

Maybe you didn't get me..

I'm talking about the case of pull-down resistor abscence..
(you said that there was some attenuation but not a complete one..)

To me, both transistor base high (signal mute) and low (signal pass) states seem equivalent due to signal effective grounding via C5 and regulator output..

To make long story short, without pull-up resistor you should have a permanent signal kill regardless CV TIP Hi/Low state..

[Ripthorn]

C5 is just a smoothing/reservoir cap for the +5V line. The signal path works because the microcontroller turns the transistor base high, causing it to shunt the audio signal to ground.

Maybe you didn't get me..

I'm talking about the case of pull-down resistor abscence..
(you said that there was some attenuation but not a complete one..)

To me, both transistor base high (signal mute) and low (signal pass) states seem equivalent due to signal effective grounding via C5 and regulator output..

To make long story short, without pull-up resistor you should have a permanent signal kill regardless CV TIP Hi/Low state..

My remark about not having a pullup resistor was regarding a previous schematic I had briefly published where there was no connection to collector and +5V. So what happened is that when the base was energized, there wasn't sufficient Vce to cause the transistor to fully conduct, thus resulting in incomplete attenuation. The addition of the pullup resistor to +5V biases up the audio so that Vce is sufficiently high to fully conduct. I actually have a second version of the circuit in the works that adds some features and improvements.

[antonis]

@SeneX225:It's been a long time since I've dealt with vero/strip-board so check below layout for flaws..

[SeneX225]

@SeneX225:It's been a long time since I've dealt with vero/strip-board so check below layout for flaws..

This is wonderful, thank you so much!

[SeneX225]

Hi, me again.
While looking for the components I've stumbled upon an issue that had gone completely over my head until now:
Between pin 5 and the ground there's a 0.1F (100,000uF!) film capacitor. The issue is that I cannot find one such capacitor is any electronics store around. I've checked out other similar 555 delay schematics and found out that most of them use capacitors from 0.001uf to 0.01uf, which is quite strange to me.

Can I, then, substitute that 0.1F with something of a smaller value?