VFS2A VOX footswitch question.

[aienco]

Hello all from down under once again... I have a Vox amp and only posted here once before. Been informed this is as good a forum as any other for Vox stuff?

I have been battling with, what I thought would be a simple issue, for some time.

I have built a Vox VFS2A footswitch. For those unfamiliar with these, it is a simple two button foot switch with LEDs. One turns reverb on and off, the other tremlo.

Tremolo works fine with LED and all. However the Reverb will only work if I disconect the negative of the LED. I am using a switched stereo jack and a sp footswitch. The amp supplies voltage to the output of the foot switch. It is around 16V. The tremolo works because when you plug the footswitch in, it is in the open state. So the ground and signal are not making contact. So when switched, they make contact and I just connect the LED through a resistor to the same points.

The REVERB when you first plug in, is in a closed state. So the signal and ground are making contact and when I switch to open the contacts the reverb works fine. UNTILL I connect the LED. The led is connected to the signal of the reverb and the sheild. Reverb does not work, but led does. Disconnect the Shield and the Reverb works, but the LED doesn't?? I know I can do this with a battery. But I know this is NOT how vox do it. All the diagrams and schematics for the vox footswitch do NOT work properly. All links I find to the schematic do not work.

I have been trying for a while to find a way of separating the sheild into two so the one that goes to the reverb LED is not connected to any other sheild.

Any guidance would be gratefully appreciated. I have invested so much time and money in this, that I would have been far better off just buying a new vox footswitch to start with.
The first image is what I started with. The 2nd is where I am at now.

 

[Jon Snell]

A clue to the model number and type of your VOX amd would help as there are subtle differences in the foot switches.
Here is the only available schematic from Korg. We can tell it is from Korg, check out the STERED Plug

 

[PelliX]

The REVERB when you first plug in, is in a closed state. So the signal and ground are making contact and when I switch to open the contacts the reverb works fine. UNTILL I connect the LED. The led is connected to the signal of the reverb and the sheild. Reverb does not work, but led does. Disconnect the Shield and the Reverb works, but the LED doesn't?? I know I can do this with a battery. But I know this is NOT how vox do it. All the diagrams and schematics for the vox footswitch do NOT work properly. All links I find to the schematic do not work.

Could you confirm the values of the resistors you used? I don't actually have the footswitch for either of my VOX amps, otherwise I'd gladly inspect its guts. Have you tried increasing the resistor on the Reverb switch side?

I have been trying for a while to find a way of separating the sheild into two so the one that goes to the reverb LED is not connected to any other sheild.

No point in splitting, the shield is connected to the chassis, aka common ground in the amp itself.

Any guidance would be gratefully appreciated. I have invested so much time and money in this, that I would have been far better off just buying a new vox footswitch to start with.
The first image is what I started with. The 2nd is where I am at now.

Depends, if you learn something this way, it may still be a better deal in the end, right?

I gather you're quite new to making these sort of devices - welcome aboard! That said, I would either 'omit' the shrinktube until you have a working layout (no shame in putting this together on a breadboard first if you feel more comfortable that way), and when you do install the shrinktube - heat it

Quick afterthought:

I am using a switched stereo jack and a sp footswitch.

I can't make it out on the pics, but I presume you've got the right contacts for the switched jack? No need to use a switched one here, but it won't hurt either - provided it's wired correctly.

 

[aienco]

Sorry its an ac15 and the ac 30 is the same.

 

[aienco]

The resistors play no part in it. They just limit the voltage to the leds and they work. 470 ohm.
The shield in this case is actually not attached to the case as the socket is an insulated socket.

I really hope I learn somthing. So far I have learned that this is expensive and time consuming if you are not sure what you are doing.

 

[Jon Snell]

The AC15 uses a 3k3 pull up resistor from the +15v supply.
The pedal resistors need to be more than 3k3 to allow the pedal to work.

 

[PelliX]

The resistors play no part in it. They just limit the voltage to the leds and they work. 470 ohm.
The shield in this case is actually not attached to the case as the socket is an insulated socket.

I really hope I learn somthing. So far I have learned that this is expensive and time consuming if you are not sure what you are doing.

Uhm, I'd be looking at a higher value there, maybe 1K5, maybe 2K2. Sure, you can have an insulated socket, but it's a TRS connector on the amp side - so S(hield) will always be shield unless you put in a TRRS jack or something else with an extra conductor - but even then, they would be bound at the amp. Long story short: that's not your problem.

The AC15 uses a 3k3 pull up resistor from the +15v supply.
The pedal resistors need to be more than 3k3 to allow the pedal to work.

I think Jon has a point here. Would you care to try this?

 

[aienco]

Where are you suggesting a pull up resistor? The only resistors are on the Anode of the LED to lower the voltage from 16V to 2V. A 3k3 resistor in its place, would render the LED in active?

 

[Jon Snell]

R39 and R70 are pull up resistors.
Ths is why I suggested the value;
It's not rocket science to know that the base of the switching transistors require at least 0.7v to make them work.
Could work as low as 1k8 as there is an LED to help with the voltage drop.

 

[aienco]

Sorry for my ignorance, It works fine for the Tremlo, however for the reverb it doesn't. I only assumed it is because the Reverb is in the closed state when off and open when on. The LED Ground Cable on the reverb is what stops it working. If I disconnect the ground, it works but no led. So I have been going about this all wrong. I just by chance right now came across this diagram attached. It wasn't there the last few days nor earlier today.
Does this seem to be the way it should work?

 

[Jon Snell]

That is correct. I would choose 1k8 though but only through preference when using ultrabright LEDs.

 

[LAAF]

Looking at the design of the amp, the LED is causing an issue because it clamps the voltage way too low for the transistors to operate normally. I would recommend a larger series resistor on the LED or use a zener diode (~12V or so) to allow enought current to flow into the transistors. Remember on the NPN, the Vbe (base to emitter voiltage) is ~0.7V, but it's the current into the base that determines the max collector current needed for proper operation. Dropping this too much and you may have issues. The LED with no resistor causes this base current to be <<0.2mA when it normally is >2mA. I verified that the two voltages on the pedal are 28V and 21V when open, which is normal.

 

[sputnick007]

I too am having lots of problems with vox footswitch vfs2 using the vox vx1 practice amp.
I have had conflicting replies from vox
One says I should use the vfs2 which I have and another says I should use vfs2a
Apart from the leds and associated resistors etc What is the difference
I assume both are latching switches
I presume the footswitch somehow triggers the components in the amp.
Where does the vfs2a get voltage to power the leds

 

[sputnick007]

I'm still.uncertain how the vox vfs2 works with the vx1 amp.im told that sw 2 turns the tremelo on and off but on mine sw1 only selects bank A
and sw2 selects bank 2
I'm also told that I can change how the switch can be used by holding down the manual button on the amp, but my amp dosent have a manual button.
For such a simple switch it doesnt seem to work how it should