The Scrap Mini Amp
Introduction
On my 20th birthday my father gave me enough money to buy an old rusty electric guitar, But after asking for an amp for it i didnt get any, so i saved some money collected some scraps and hacked together a bedroom level guitar amp.
On my summer break in 2024 i was home, and I went to my uncles for something and asked him if he had a speaker lying around he said i dont have a speaker BUT an old home theatre. I was like thats even better.
I brought it to me dorm in pune and started making this, at firat i just hooked the guitar directly to the home theatre, it was very quiet but the sound was great
So i researched abput it and found out there is a signal mismatch, the amp expects a line level signal but the guitar outputs a instrument level signal
But the sound was very warm and i loved it, i found out later after i opened the amp after it got fried and found out on the main board there was a tube simulator circuit used as the preamp for all the signals coming in the. so all i needed was a overdrive circxuit to go with it and i was pretty much done but as i was going to order the parts the piece got fried.
The overdrive circuit
I found this brilliant article by Wampler Pedals that walks through designing a basic overdrive pedal circuit. I used their schematic as the starting point and made some modifications to fit the components I had lying around.
here's the original schematic I based mine on >
and here's what my actual board looks like ā hand-soldered on a perfboard >
the back is a proper rat's nest of solder joints and wire bridges, but it works >
The power amp
The original plan was to use an old home theatre system for both the speakers and the power amplification. It worked for a while, but eventually the circuit got fried. So I replaced the internals with a TPA3118 PBTL Class D power amp module I had bought online.
For power, I used an old laptop charger. It outputs around 19V which is more than enough for a tiny bedroom amp.
How it sounds
It's messy, it's not that loud, but it actually sounds pretty cool for something made of trash.
Clean tone
Overdrive
What I learned
- reading schematics and actually building them on a perfboard are very different skills
- soldering is surprisingly meditative once you get the hang of it
- constraint breeds creativity ā not having money for a real amp forced me to actually understand how amps work
Conclusion
Total cost? about ā¹500. I learned a lot about electronics and guitar amps while building this. It was a fun project and i would recommend it to anyone who is interested in electronics and music.
"Constraint breeds creativity"
- Circuit Reference: Wampler Pedals ā How to Design a Basic Overdrive Pedal Circuit