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2W Electric Guitar Amplifier
I designed this 2W electric guitar amplifier to have handy so I could practice guitar at a whim. I wanted to build it as a head for storage reasons, and to have the option to swap speaker cabs if I so desire.
Many commercial chassis options are pretty lame looking in my opinion. I wanted a rugged "industrial chic" look and decided die-cast aluminum electronics boxes would probably work out nicely. With a rough idea, I went ahead and put together some design goals...
The finished 2W electric guitar amplifier. Notice the guitar pick for size comparison.Design Goals for 2W Electric Guitar Amplifier
- Similar circuit as Fender Tweed Princeton
- 12AX7 Input Tube
- 12L8GT Output Tube for low output => smaller transformers => smaller amp
- Full wave diode rectifier bridge
- Single Ended Class A
- Single input, volume, tone and power switch on front
- Quiet (High Signal-to-Noise Ratio)
- Built Point-to-Point
- IEC connector w/ fuse drawer and output on back For power entry
- Built as a head
- Diecast boxes for chassis
- Diecast boxes also as covers for the open-frame transformers
- As compact as possible
- Inexpensive to build
Schematic
2W Guitar Tube Amp SchematicI have a PDF file with schematic and download available. The file also contain a bill of material (BOM) and can be downloaded here: Electric guitar amplifier schematic.
Circuit
For a more technical explanation of the circuit, see 2W Tube Guitar Amp Schematic.
The challenges
A high signal-to-noise ratio is important when playing at low levels. I wanted to use this amp at night when the younger member of the family may be sleeping, and therefore need low noise at a really low volume. Most commercial amps just won't cut it as they are simply too loud or too noisy, or both.
Here is a picture inside the chassis. The power supply to the left, tubes in the middle.The circuit is simple, so the building this amp in a "normal" size enclosure wouldn't have posed much of a problem. However, Shoehorning it into a box 7 1/4 x 4 1/2 x 2 1/4 inches turned out to be tricky.
Here are the two power transformers. High voltage to the left and 12.6VAC for the heaters to the right.To save cost, I decided to use inexpensive circuit-board mounted transformers and mount them to 1/8" phenolic board. The connection points have eyelets staked to the board. Boards built this way can withstand a nuclear disaster.
Finished amp on top of a speaker cab.Conclusions
It has turned out to be an awesome little amp. I hit all of my design targets. It has a nice bluesy growl when over-driven. In fact, it was a little too prone to overdrive, so I added some local negative feedback. It did the trick. Now it stays clean to about 12 o'clock.
There is no audible hum when no instrument is plugged in. I mean nada, zero...It blew my mind. The reason, I believe, is due to the encased transformers and an old trick to elevate the relative DC voltage level of the heaters to about 1/2 of B+. This is something I will always do from now on.
The few downsides are pretty minor. For instance, it's a little awkward to transport as it doesn't have a handle. It's small enough to easily get a grip of the chassis though, and it's light as a feather for a tube amp. I also found the tone control somewhat limiting. The upside is that I practice playing more, rather than fiddling with knobs. See, there is an upside to everything.
A very exciting little guitar amp for sure!
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Speaker Plans
Feb 04, 18 05:23 PM
Speaker plans for download - free pdfs for DIY builders and tire kickers