Can anyone tell me what's causing this problem? Volume ramp up when switching on

[Otbaudio]

Hoping someone might be able to tell me what's causing this:

Currently working on a drive circuit & im having this issue when I switch it on where it takes a few second for the effect to kick in/the volume slowly ramps up when I switch it on. Sounds like when you switch the power on on a tube amp & it takes a few seconds to warm up.

It's  true bypass, and no I haven't connected the power supply via the switch or anything stupid like that.  The circuit involves several BJT's and FET's, 6 in total so I've been wondering if maybe it's taking a while for the signal to get all the transistors operating. Anyone got an idea what could be going on to cause this?

[duck_arse]

we might be able to offer theories if we could see the schematic diagram of what you are building. izz it on the breadboard or soldered?

[Prehistoricman]

Sounds like you're missing a coupling cap somewhere so the output/input has to charge up before your pedal starts receiving/sending the signal.

[R.G.]

Both comments are correct.

We can't help much without a schematic, and it's almost certainly a missing or oddly connected capacitor that has to charge up to get the circuit into operation.

Expounding on that last point, if the bias of an active device is not held somewhere in the middle of its amplifying range, signal will push it into the active range if it's big enough. This is responsible for the every-so-often question here asking why a circuit sounds "gated" and distorted, only letting signal through on loud peaks. In addition, if a circuit is biased to an inactive portion of its operating range, sometimes a signal can push it to not only let signal through, but modify its self-biasing by charging up a cap so it stays relatively well-biased while there is a signal. When signal vanishes, the biasing relaxes back to the condition that lets signal not pass.

Having signal "pump" the circuit into operation is relatively rarer than just gating, but it happens. One commercial pedal of some years back even used this effect as a backwards-tape fade in effect. It was caused by a missing input coupling cap letting the circuit pump up an emitter bypass cap when signal was present. The "fade in" was caused by the fact that most transistors have lower gain when they're almost off, so turning the transistor on slowlyl increased its signal gain for a fade-in.

It would probably be interesting for you to put a meter on some point in the circuit ( try a collector first ) and watch the voltage change as you whack the circuit with signal.

But this is about all we can do without a schematic.

[Otbaudio]

Thanks for these answers! I haven't drawn up a schematic yet unfortunately, but these points make sense.

It's definitely not missing any coupling caps, unless one of them is faulty & shorted. Could it be that one or two caps are too large? Or possibly there's too many in series throughout the circuit?

I'm confident it's not the signal pumping an active component into its operating range as it only happens immediately when turning it on. If I leave it on without passing a signal through it, and then come back to it and start playing it plays fine.

[amptramp]

Some circuits use a "noiseless bias" network which is the other side of the resistor going to the base of a transistor connected to the junction of two resistors, one connected to ground and one connected to the supply line.  To limit noise coming from the power supply, this junction has a big electrolytic cap connected to ground.  During power application, the voltage at this junction rises slowly and no signal passes until it is in the active range.

[R.G.]

If it's not signal pumping, it's probably some issue with your bypass switching mucking with the bias.

Again, we can't really tell anything without a schematic.

[pinkjimiphoton]

reverse polarity electro input cap and a board input shorting footswitching setup?
def a cap charging somewhere

i've had this kind of issue with some fuzzes if i ground the input of the board in bypass. its kinda cool in an annoying kinda way.