I've whipped up a layout for a very small but very useful power amp using the TDA2003A 5-pin amp chip.
This chip was originally designed for use in car radios, so it lends itself very well to small guitar-amp use operating from a single voltage DC supply (e.g., 9-volt battery or small DC wall-wart), following your guitar pedals and driving speakers down to 2-ohm load.
It uses minimal extra parts, while including short-circuit protection, current overload protection, and thermal overload protection (none of which you should encounter when using this with a battery or wall-wart DC power supply for guitar use).
Although the TDA2003A 5-pin chipamp is discontinued, literally millions of the things were manufactured, and they are readily available for around $0.40 each in quantities of around 10 on Amazon and eBay. (They're pretty ubiquitous and can be found in many commercial solid-state guitar amps.)
I've built it and tested it, and it works perfectly. I built it with two less columns than the final design, which I lengthened to provide more room for the 1000uF output capacitor. With the datasheet circuit it has a bandwidth out to around 18.5kHz. I substituted a 47-ohm resistor and 47nF cap for Rx and Cx because that's what I had on-hand, which gives a bandwidth of around 15.4kHz, which I don't think makes a significant difference for guitar use. I also twisted together in series a pair of 1-ohm resistors for R2. Other than that I stuck to the datasheet circuit and it works perfectly on this very tiny stripboard layout, operating from a single 9-volt battery. I haven't measure the quiescent current draw yet. It should also work nicely from a decent regulated 9 to 18 volt DC wall-wart supply. You could always use a larger stripboard and include filter caps and a regulator to use a cheapie DC wall-wart. Not shown in the photo: the signal input ground, signal output ground, and power supply grounds are all tied together, wired from jack to jack and finally to the stripboard. I tested this driving an 8" 8-ohm Jensen Vintage Alnico P8R in a small semi-open-back cabinet, and it sounded just fine. With an 8-ohm speaker the amp is capable of delivering around 2.5 watts, which was plenty for a pocket-sized battery-driven power amp. It should have no problem driving 4 or 2 ohm loads, if you provide it with sufficient power supply juice. I plugged my guitar directly into it and it played fine off a 9-volt battery. It has a 40dB gain of 100 with the combination of 220-ohm and 2.2-ohm resistors R1 and R2.
I also made use of the fact that these 2-row chipamps fit perfectly on stripboard when you mount them at an angle. (One trace cut is needed between pins 1 and 4 since they land on the same row.) I used a small TO-220 heatsink. No insulating washer is needed with the TDA2003 chip. (I also made the stripboard layout so that the corner of the stripboard behind the amp chip can be broken off if one wants to fasten the chip directly to a metal cabinet as its heatsink.)
My intention is to put together this and similar small stripboard power amp circuits as options to throw on the end of various pedal effects circuits for a compact solid-state amp-head with effects. My goals are to be inexpensive, have low parts count, and have a simple stripboard layout so anybody can whip one together in a spare hour without needing a custom PC board. This amp fits the bill.
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