Vox Valvenergy help for "always on"

[Esppse]

Hey guys,

I plan on rackmount some Valvenergy pedals. When I got them, I realized that when power is introduced, they default to a bypass state, regardless of its position during the last power off. Very much like digitech pedals. Is there anyway to mod them to be permanently on?

[ElectricDruid]

Have you got a schematic?

Without it, we're just guessing...

[amptramp]

It sounds like they have an initialize circuit or at least different component values in a flip-flop that determines whether it is bypassed or not.  We need to see a schematic to figure out what has to be changed.

[Esppse]

Ah I couldn't find a schematic unfortunately. It's mostly SMD stuff in there too. Here's what a Copperhead Drive looks like in there.

[anotherjim]

If SW1 is the bypass switch, what happens if you power on while the switch is operated? I suppose it's momentary? It looks like it's SPDT but you can confirm that with a continuity test.

[Rob Strand]

From these two pics it looks like the switch is a simple push button (SPST momentary).

https://postimg.cc/NyKDjj0w
https://postimg.cc/dLF5jF58

I can only assume the ground wire going to the switch *PCB* for added shielding.  Without a schematic it's impossible to work out how the switch is wired to the rest of the circuit.  The switch could be floating, wired to +V, or wired to ground at the CPU end.

There's many different scenarious depending if the switching is processed by a microprocessor or by a separate footswitch circuit.   If there's only one chip for the whole pedal then it's likely to be DSP.

If the switch is handled by a microprocessor, it's highly likely the software forces the code to power-up in the bypassed state.       For a digital circuit to remember the last state it needs to have code to save and restore the state and the hardware to store the setting - that's usually done some with form of non-volatile memory.   Given you can't modify the code the only work around is to fake a switch pulse on power-up with a separate circuit.   To come with such a circuit you need to know exactly how it interfaces to the processor.

If the pedal has a separate switching circuit with a flip-flop what you often find is the power-up state is random from *unit-to-unit* but it might be consistent on your particular unit.   What you can do in this case is tweak the part valuyes to coax it into power-up in the state you want.   This method isn't 100% reliable but is often good enough that it takes the chore of changing the state manually.

Bottom line is you will need to trace the circuit or find a schematic someone else had done for that series of pedals (assuming they are all based on the same design for the switching).

Unfortunately no easy way out without doing some work.

[GibsonGM]

What would happen if one replaced the SPST with a relay that has a simply-made, brief delay at power on to allow the circuit to stabilize, and then is pulsed to blip its contact, simulating a 'foot press' of the foot switch?  R-C based - I've seen some things like this in power supplies that keep a relay closed with a R in-circuit to allow empty caps to charge safely and then the time constant ending opens the relay for normal use.  Something a little like that, but in reverse... 

It's a rudimentary idea, but maybe it would allow the OP to do what he wants without having to really crack open (and ruin) the PCB.  Just a thought, maybe it isn't feasible... 

[Esppse]

If SW1 is the bypass switch, what happens if you power on while the switch is operated? I suppose it's momentary? It looks like it's SPDT but you can confirm that with a continuity test.

I remember trying this a few months ago when I got them.

When power is applied to a switch being held down, it goes into some sort of setup mode, which means a micro controller is involved.

[Esppse]

What would happen if one replaced the SPST with a relay that has a simply-made, brief delay at power on to allow the circuit to stabilize, and then is pulsed to blip its contact, simulating a 'foot press' of the foot switch?  R-C based - I've seen some things like this in power supplies that keep a relay closed with a R in-circuit to allow empty caps to charge safely and then the time constant ending opens the relay for normal use.  Something a little like that, but in reverse... 

It's a rudimentary idea, but maybe it would allow the OP to do what he wants without having to really crack open (and ruin) the PCB.  Just a thought, maybe it isn't feasible...

That seems like a really good idea wow, is there any drawback of this method?

[GibsonGM]

Clunky 'configuration' for one - wires trailing out of the orig. unit enclosure to a relay box of some sort. Could accidentally rip out the wires (use a jack?) or lose the 'patch cord' that is only for this purpose.   This goes back to my 'more mechanical than electrical' background lol.  This is 70s tech.

If you tapped power from the unit's jack, there is the 'signal' that it was powered on, starting whatever R-C or IC time circuit counting til steady-state, then triggering the relay.   Seems like 4 wires would be needed ('a cable').   I can picture a small 2x2 box housing a 555 and relay very easily.

Others with actual design experience will have better advice regarding what pitfalls you could encounter with this idea!   

[Esppse]

Is it possible to put this in the same Vox pedal? Could we do a small Arduino controllers to jog the switch after power is introduced?

Do arduino controllers like the ItsyBitsy have some sort of relay feature?

[Rob Strand]

If you can power-up the pedal with the footswitch held down then release it a little later and the device flips state then it simplifies the timing and circuit.   It might flip state at power-up or when you release the button.  You don't really care.

You need to make sure the pedal works like before you can see if a simple circuit will work.

If the pedal doesn't work like this then you need a more complicated circuit.  Something that does the following:
- power-up
- wait delay
- output *pulse* on relay

Anyway here's the simple version using a NE555:

You can use a Mute circuit like this (section 3.7 - 555 Relay Mute Circuit, Figure 14),

https://sound-au.com/articles/555-timer.htm

To speed up recovery between power-ups or if the power glitches quickly put 1N914 diodes across R1 and R2, especially R1.  Cathode to +ve.

In the circuit as shown, the relay activates when pin 3 goes low.  Pin 3 remains high for the first 4.7 seconds so the relay is off.  After the delay the relay is on and the mute contacts are released.   With this circuit idles with the relay powered.

If you put C1 = 10uF the output on pin 3 will remain high for about 1 second. 

If you connect the relay like this the relay will be active during the first 1 second then the relay is turned off.    That way the relay doesn't take power while the pedal is running/idle.

https://www.zorgeffects.com/index.php/en/blog/143-true-relay-bypass-with-ne555-flip-flop

You need to connect the normally-open relay contacts across the footswitch.    So the idea is it holds the footswitch down for 1 second after power up.   You need to test the circuit to the pedal doesn't respond to any glitches at power up.  If the relay glitches are a problem then you might have to use the previous method where the relay idles on and connect the normally-closed relay contacts across the footswitch - in which case when the relay turns on the contacts are opened.

[PRR]

I has to be simpler to find the switching element and wire around it.

[Rob Strand]

I has to be simpler to find the switching element and wire around it.

Someone has to trace it out.  That was the original problem.

[anotherjim]

If it's the part I think it is, the bypass switch even has a plug-in connector to the main PCB.

If that's the stomp switch operating shaft with the spring and the button-like thing on the little PCB is the electrical switch it acts on.

A start would be to identify the switch common, normally open and normally closed wires by continuity testing and with it unplugged, see what voltages are present on the mainboard connector and with it plugged in, what the voltages are and what pressing the switch does to those voltages.
As holding the switch on during power-up causes the controller to enter an engineering mode, it's a good chance we are dealing with simple logic levels but it would help to know if it is 5v or 3v3 logic.