Volume woes

ActionArnie

Hey guys,

I recently acquired an awesome vintage ernie ball volume here on the forums. Pedal is great looking and sturdy. Had a bit of an issue with it though when I tried it live for the first time. Basically I got virtually no volume dip out of it at all. Only with the pedal held right 'off' did it mute the guitar signal (guitar going straight into the pedal).

Now from my understanding these passive volumes are simply a pot that serves as a voltage divider. I pulled out my trusty multimeter and measured the impedance across the input and output. Output goes from (heel down) 0 - 300k (toe down) and the input goes from (heel down) 5k - 300k (toe down). Now surely this is not right? My simple brain tells me that this is not dividing the voltage at all. I would expect the input impedance to always be 300k and the output to sweep 0 - 300k, or am I missing something?

Gearhead

You're right about the input to ground being a fixed amount and the output to ground to go from said amount (toe down) to 0 (toe up). You could measure between input and output as well, which should vary between 0 (toe down) and said amount (toe up). If the thing is f'ed, it would measure more or less the same regardless of the position.

ActionArnie

Gearhead wrote You're right about the input to ground being a fixed amount and the output to ground to go from said amount (toe down) to 0 (toe up). You could measure between input and output as well, which should vary between 0 (toe down) and said amount (toe up). If the thing is f'ed, it would measure more or less the same regardless of the position.

Yeh the impedance between the input and output is always 0, no matter the position of the pedal.

Failed to mention there is a knob thingy on the pedal too. If I turn it fully counter-clockwise I get the results I mentioned, if I turn it fully clockwise the input impedance is the same, 0-300K, but the output impedance is 140K-300K. In this case when its full ON the input/output impedance is 0, full OFF the input/output impedance is 140K. Unfortunately the 0-300K input impedance is still very much a problem ☹

The passive volume pedal is a fairly simple beast though, not sure exactly how it could be exhibiting the problems I'm seeing.

AlanRatcliffe

Being passive the input impedance does not stay constant - you'd need a buffer circuit on the input for that. I suspect you merely had the "knob thingy" (which limits the minimum volume) turned full up during performance that way the pedal will do very little.

ActionArnie

Alan Ratcliffe wrote Being passive the input impedance does not stay constant - you'd need a buffer circuit on the input for that. I suspect you merely had the "knob thingy" (which limits the minimum volume) turned full up during performance that way the pedal will do very little.

Could've sworn I tried everything to get it to work properly. Tried it again at home into guitar rig (I don't have an amp in my flat) and it seems to work fine though. Had a look at the circuit (which I believe to be the one for my pedal, off the EB site) with my very rusty electronics brain in place and I still can't figure out how its possible that the impedance across the input can go to 0 with the trim pot in any position.

Anyways, will test it again with my full rig tonight. Thanks again for the replies.