Solid State Guitar Amp Forum | DIY Guitar Amplifiers

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

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

Guitar straight in.

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

Why not buy a graphics EQ pedal?

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

Quote from: Tassieviking on December 05, 2024, 11:06:33 PM...
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.

Actually an eq pedal or other pedals with tone controls work well but I'd like to make it standalone. I know there is an impedance mismatch but I find the treble end  acceptable. Going to try just the capacitor on the input as a starting point.

Well having messed around with input caps I've decided to proceed as follows.
1. Turn the guitar down so it doesnt distort. Its loud enough anyway for living room jamming.
3. Use the preamp and EQ pedals which I already have.

Quote from: edvard on December 08, 2024, 01:38:34 AM

Quote from: Tassieviking on December 05, 2024, 11:06:33 PM...
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

That is the *preamp* datasheet.

The power amp itself does not state any input impedance but it suggests using a 10k input volume pot.

IF it has a TDA2030 or similar inside (most probable) they often have 22k input impedance but it *might* be 50k.

I would NOT use the 10k volume pot IF straight fed Guitar , lowers impedance way too much, just use guitar own controls, and add a Bass limiting cap in series with input.

Try 4700pF or .01 uF, this would approach "VOX EQ" as in simplest AC15/30 where they cut everything below 600-700Hz or so.
Crazy as it sounds, it works fine in the Guitar World  :duh

You can use almost  any pedal (except, say, a FUZZ one or an old Wah) you currently have as a Preamp, even if set to minimum or no effect, it will work as a Buffer.

Back in the day, it was common to use a simple pedal such as an MXR Distortion+ as a Preamp, go figure.

Volume set to 10, Distortion turned to Minimum or almost, just enough to provide some boost.
Still needing to cut Bass at your power amp input, back in the day it went straight into any Fender or Marshall amp.

Not applicable to true bypass pedals, which route Guitar straight through when turned OFF

PS: you may use 2 input jacks in your powered cabinet: a straight/flat one to listen to Music; the other through the Bass cutting cap for Guitar use only.

Most probably it has this inside, the datasheet example:

(https://tronicspro.com/wp-content/uploads/2023/04/3a-TDA2030-Power-Amplifier-Single-Supply-Circuit-Diagram.jpg)