newprotest.org: LITTLE GEM

LITTLE GEM

November 03, 2007
by: jovial_cynic
In the previous post, I mentioned my 5-string electric violin, and since most people with whom I've talked have no clue what such an instrument looks like, I took a picture.



Electric violins come in many shapes, some of which are actually shaped like a true violin, only the "body" of the instrument doesn't actually do anything. On a traditional violin, the body serves as an echoing chamber, giving the instrument its resonance. On an electric violin, such resonance unnecessary, and on my particular violin, the body wasn't even included on the design. For that reason, I refer to my violin as "the stick." And what does a stick sound like? With effects pedals, it sounds like anything I want it to sound like.

Anyhow, the first of my DIY audio projects is, as previously mentioned, the little gem. This is the starting point for a lot of people who want to break into DIY audio. Consequently, lots of people have written fine tutorials and included pictures of this very project. The most handy picture I've found for the build-up is on flickr (click for big):



After studying the diagram and running through it with pen and paper (re-writing the diagram on your own is a good way to make sure you understand what's going on), I went ahead with the buildup.



The first thing I did was actually stick everything into the blank circuit board. I don't think people typically do it this way, since it makes for a forest of wires underneath, and soldering through such a forest can be difficult. However, with only a few components, I didn't figure it'd be a problem.



After getting everything in place, I soldered it all up. This was my first time soldering, and as you can see by the few bird-crap globs of solder, it wasn't perfect. However, all the connections looked secure without any unwanted overlap, and that's all that matters.



Since I didn't have an enclosure yet (I experimented with an Altoids tin -- too small, and with a mini-tub of Play-doh -- too pliable) I just laid it out on my counter and twisted some wires in place. I connected my violin, a volume-control potentiometer, and a little speaker that came with a kit I purchased.

It works. The kit's speaker is terrible, and the sound is barely audible, but it does work as expected -- the sound of my violin is going through the system. I now plan to swing by my local Goodwill and pick up a speaker that I can use to get a better idea of the potential of the little gem. As small as the circuit is, I can probably carve out a space in a speaker box and run the amp and speaker as a single unit. Alternatively, I might make a mini-enclosure and wire in a headphone jack, so I can play my violin privately when my kids are napping and not wake them up.

Enclosure


I went to my local Goodwill and picked up a set of speakers for $5.99. It worked out better than I planned, since I thought the speakers were individually tagged at that price, but upon getting to the register, I was told that they came in a set for the same price. Fantastic.



I brought the two speakers home and opened one of them up, discovering to my surprise that the speaker enclosure actually only held a little 4" speaker.



I guess that's what you get for $5.99. Since the little gem is supposed to be able to power a 2x12 cabinet (that's two 12" speakers), I feel like I'm short-changing the potential of the amp.

I could double-up the speakers by mounting both of them into a single box -- there's plenty of room in there. However, I don't know enough about the math of the relationship between multiple speakers and amps (serial? parallel?), and since I don't want to stress out my amp, maybe I'll not double up. Hrm. Perhaps I'll just keep my eyes open for some larger speakers, and plan to swap in the future. That said, I should probably connect everything in a way that makes it easy for me to disconnect it again when I'm ready.

I carved out the back of the enclosure where the panel will go, and cut up a piece of sheet metal for the panel itself.



On another note, I've intentionally left out one of the items on the circuit board - another potentiometer used to control the gain on the amp. The potentiometer goes between the 1 and 8 points on the LM386 chip; the less resistance there is between the two points, the greater the gain. By leaving the spot open (ie., 100% resistance), the sound coming through the speaker was very quiet. By adding a wire between the two points (no resistance), the gain was turned up all the way, and the sound coming through the speakers was perfect. Since I prefer the gain all the way up on this amp, I've soldered in a wire between the two points, shown in red in the picture below.



I soldered all the wires to the circuit board, and to the volume-control potentiometer and input jack, and here you can see them all sticking out of the back of the enclosure.



And since I couldn't resist using an Altoids tin for something on this project, I decided that it would be perfect for housing the 9-volt battery.



Putting it in


As far as the minimum requirements, my little gem buildup is done. The volume-control potentiometer and the input jack are securely housed on the rear panel, and everything is properly secured.

Here's the shot of the front. The circuit board is zip-tied through a hole I drilled out.



Here's a shot of the rear.



And here's my new amp and violin in a shot together.



Although I'm technically done, I've got a few ideas for some additions. Namely, I want to build in a DC-in jack so I can plug the amp in and bypass the 9v when available. No sense in needlessly draining all my 9v batteries.

I picked up a glass clock at work that I think would look clever on the side of the amp. I'll have to bore out a 4" hole and mount the clock. It won't really serve a purpose other than look kind of interesting. And who knows what else. Maybe I'll mount a cup-holder on it or something.

First Clip


Fun fact: Playing an electric violin is a little more difficult than playing an acoustic violin.

This is because when you play a note that has an accompanying open string (not being played), the matching open string reverberates, causing the whole violin to "ring." This is noticeable on an acoustic violin, because the chamber reverberates enough to feel. That's how a violinist knows the note being played is in tune.

With an electric violin, you don't get that ring. Unless you have perfect pitch, you can't tell if you're playing the note in tune or not. You have to use a little bit of reverb to make the instrument sound like a proper violin. The reverb effect seems to capture the tiny amount of natural reverb that the violin produces, making it easier to find the right pitch.

Now that I've effectively blamed my horrible playing on lack of reverb, here's an audio clip from my little gem amp. The gain is at 100%, but I'm not playing aggressively enough to cause much clipping.

Audio Clip (ZIP)

Also - I wired in a switch. I didn't feel like trying to make room for it on the rear panel, so I attached the switch to the Altoids tin.


COMMENTS for LITTLE GEM


sublmnl said:
hah, awesome man! :)
so... i wonder how the design of this little amp compares to the Smokey guitar amp design... the smokey is able to power a 4x12 cabinet with enough volume to record with a mic properly, all from a 9v battery... so, i wonder what yours will end up being capable of.

i installed my smokey inside my guitar, by the way.

November 04, 2007


jovial_cynic said:
The plans say this is supposed to be able to support a 2x12 cabinet at speaking-volume. When I get it done, I'll record some audio clips and see what happens.
November 04, 2007


add comments. you are limited to 5,000 characters:

<< your name
<< your email (won't be displayed)
<< your website / location
<< type these numbers: 645412 (plus 0NE)

(html -enabled- / no scripts)

<< Comments temporarily disabled >>

Rules: Don't spam. Don't harrass. Don't be a jerk. Your IP address (54.145.51.250) will be logged.