Less Bass

[flester]

Im using one of these built into a bookshelf speaker as a practice amp. It works great with electric mandolin and harmonica but the speaker gets overwhelmed with guitar turned up loud. I was wondering if there was
a way to filter out some of the bass?

https://www.ebay.ie/itm/374178708497?mkcid=16&mkevt=1&mkrid=5282-175127-2357-0&ssspo=YI5yZF5vTzy&sssrc=4429486&ssuid=5dZ_imPdR-i&var=&widget_ver=artemis&media=COPY

[Tassieviking]

Are you plugging the guitar straight into it? No other preamp with tone controls at all or is there a pedal inbetween.

[flester]

Guitar straight in.

[saturated]

That's really cool looks like it would fit in the palm of your hand 

[Jazz P Bass]

Why not buy a graphics EQ pedal?

[Tassieviking]

You could place a HP filter on it, or a preamp with tone controls.
A simple High Pass filter with a drop off slope of 6dB is just a capacitor and a resistor, I have read somewhere that those small amps have an input impedance of 50k ohms so just a capacitor on the input might be enough.

Try placing a 22nF capacitor between the guitar and the amp and see what happens, you will have to find a value you like by experimenting.
The smaller the capacitor the more bass you cut off.

Try using this simple calculator to work out different values:
http://www.learningaboutelectronics.com/Articles/High-pass-filter-calculator.php#answer1

[edvard]

...
I have read somewhere that those small amps have an input impedance of 50k ohms so just a capacitor on the input might be enough.
...

Yep, the manual says so: https://www.farnell.com/datasheets/1712767.pdf

I'd dare say that input impedance that low is actually chopping off a bunch of treble, which translates to more bass when you turn things up.  I'd build a small simple buffer to put in front of it; FET Source follower or non-inverting op-amp circuit powered by 9V, then see what happens.  Or if you have an overdrive pedal around, turn the gain down and the volume up, adjust to taste.