Is it feasible to modify a combo-amp so the line-out doesn't silence the speaker?

Question

I'm considering this small bass amp, primarily for practising at home: http://www.amazon.co.uk/Vox-PATHFINDER-Combo-Bulldog-Speakers/dp/B002YC36ZI

A few people have said it's also capable for small venues, or on-stage, but it has the common practice feature that plugging in to the line-out silences the main speaker. This is unhelpful for using it on-stage, where you would perhaps like to use the amp for stage sound and feed the line-out into the mixing desk. Of course you could mic it but we tend not to do that for bass amps.

I'm sure this will vary from amp to amp but can someone give an informed opinion/educated guess whether these type of amps lend themselves to simple modifications, such as disabling the silent practice mode? Is it likely to be a very simple circuit (disconnect a wire) or some computer-controlled chip/circuit-board that makes this impracticable?

Answer 1

Many bass amps have a DI output (XLR jack), which, unlike a line out, is actually intended for routing into a live mixing console. For bass amps which don't have this, it's actually often best to use an external DI, entirely before the amp. You also lose preamp sound shaping then, but whether the Pathfinder actually does anything useful to the sound there... I'd have my doubts. – In fact, some live engineers prefer putting their own DI in front of even a high-quality bass amp, because this way they have better control of how the bass will sit in the mix.
For bass you don't need a top-notch DI, but a decent active one would be a good investment.

That said, this kind of plug-in-mute switch is indeed a very simple circuit that you can easily disable yourself^†. It is usually implemented as an extra contact which doesn't contact the plug, but the T contact – but only if no cable is plugged in.

To disable, simply make this contact permanent.

Be aware that using the line-out to go into a mixing console may not work well anyway. This output doesn't really have the right impedance for a mic input, and it's not balanced, so you'll probably get mains hum. This can be avoided with a DI, but... as I said, you'd probably best use a DI entirely before the amp, then the issue doesn't arise in the first place.

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^†_{Voids warranty, of course.}