I bought a Thump15a and plan to use a focusrite scarlett solo with it. My brother plays bass and has a bass amp, and so I was wondering if I could take the output of the thump15a and plug into the input of the bass amp, while setting the mode of the thump15a to sub (this takes out the low end from the loudspeaker and lets the bass amp handle it instead). The only danger I see is that the output is line level whereas the input to the amp is instrument level. What do you guys think?

I am not using a stereo setup (as I only have one loudspeaker), so I could also hook up the scarlett solo directly to the bass amp (but again I believe the output on the scarlett solo is line level). What is the difference between these two setups?

2 Answers 2


The usual way to connect a line output to an instrument input is using a DI (typically passive) with an attenuation switch and a ground lift switch. That's comparatively advisable since instrument inputs tend to be rather sensitive to ground loop hum.

The Thump15A already has a 15" bass speaker. The typical bass amp will not really offer to move much more air. Its specified range starts at 32Hz and in the images and instructions I see nothing that would point towards a ported design (that uses a resonance port for lowering the specified bass response while giving higher rolloff below it at the cost of a more sluggish phase response).

A compact subwoofer tends to give more "oomph" at the cost of an even more sluggish phase response. A typical bass amp, however, is supposed to deliver a very precise onset at the cost of considerably coloring the signal and partly adding its own characteristics. That makes it an instrument amplifier and implies, among other things, that it will become locatable as the source of sound due to the characteristics of its nonharmonic distortions. Good for an instrument amp, bad for a PA component.

Mackie's dedicated subwoofer uses an 18" speaker. That can move more air than a 15" speaker without overly relying on resonance trickery. If you want to project a really big bass drum (like when working with electronic drums) or a church organ, this can make a difference compared to the unadorned Thump15A. For most other purposes, I am skeptical that using this functionality with a separate bass speaker cabinet is going to buy you much of an improvement. And I am particularly skeptical that using a bass guitar amp will make any reasonable sense as part of a setup in connection with a Thump15A.


This may work. If there is any level mismatch you should be able to adjust it with the gain knob on the bass amp (make sure the amp doesn't clip at large volumes). But...

  • Thump15a manual says sub mode rolls off low frequencies on the speaker, but it doesn't roll off high frequencies on the output (you want to connect to an amp), so you'll need to do it by yourself. A proper way is to use a crossover. Maybe turning high and mid knobs on the amp all way down will suffice, maybe not. You risk having the bass amp sound interfering with Mackie's sound.
  • Why do you want to add a subwoofer in the first place? For stage monitoring you perhaps don't want a subwoofer at all. For PA you may have trouble to get good sound without a proper crossover.
  • Bass amp and cab might not be as good in reproducing very low frequencies as you may naively think. And very likely it is not reproducing the input sound neutrally.

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