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 ARCHIVED TOPIC: Installing an amplifier & speaker into an acoustic guitar


Please note this is an archived topic, so it is locked and unable to be replied to. You may, however, start a new topic and refer to this topic with a link: http://www.banjohangout.org/archive/264780

jpiperson2002 - Posted - 06/14/2013:  06:06:49


I don't play the banjo very often any more but have a couple of guitars with 5 string banjo necks that I still take to jams regularly. Also have a lot of fun playing a ukulele tuned to open C with finger picks and an old Vega Little Wonder mandolin banjo with 4 nylon strings. A few years ago I took a few luthier classes at the Chicago School of Guitar Making specimenproducts.com/chicago-s...r-making/ and since then I've modified most of my instruments to personalize them.



I picked up a small Pignose PGG-200 electric travel guitar with a built in amp and speaker recently, replaced the pickup with a Seymour Duncan Little 59 humbucker and upgraded the 4" speaker and now it sounds pretty good. So when my son brought back an old Voyage-air acoustic folding neck guitar from college recently I decided to install an amplifier in it to see what would happen.  



Getting a speaker to work correctly in an acoustic guitar is a difficult project because an internal speaker is usually going to vibrate the body of a guitar so much that it will cause feedback at low volumes. And the control cards on some of the small amps I've seen which have good sound effects and 5 to 6 inch speakers are too large to mount easily inside a guitar. In the end though this project worked out pretty well and now we have an acoustic  guitar that does double duty as an amplified electric with a built in speaker.

 

First I got a couple of of small 7 watt Fender Mustang mini amps with 6.5 inch speakers in them. fender.com/series/mustang/mustang-mini/ I'd done some other projects using Roland micro cube amps with the single 5 inch speaker but prefer the bigger sound sound and better effects and from the lower cost 7 watt Mustang mini. The single control card on the mustang is only about 4x8 inches so it will fit inside an acoustic guitar.



To reduce the feedback problem I completely wrapped the rear of the speaker in a couple of layers of 1/4 inch soundproof foam to force all of the sound  through the front grill. And added a layer of 1/4 inch foam around the edge of the speaker grill where it touches/exits the body of the guitar. A project like this just won't work correctly without major feedback problems unless the vibrations from the speaker are effectively isolated from the guitar itself.



The guitar still gets some feedback at higher volumes on some of the distortion settings when the gain is turned up, but it's plenty loud for my purposes and can go to volume 10 on clean settings and low gain. It easily overpowers a room full of acoustic instruments and can hold it's own with other electric guitars in a casual jam.



Here's a picture is the completed guitar and the 2nd, now modified Mustang amplifier with an extra speaker (more on that mini-project below). It has a Baggs M-1 sound hole pickup, these have fantastic sound similar to a microphone. The 6.5 inch speaker which came with the amp was a too large to install easily in the guitar. It could have been used with some extra effort but instead I used a 5 inch speaker which I'd removed from a Roland micro cube amp for a different project.



       



The hole for the control panel was big enough to fit the speaker through when I was mounting it. The 6x C cell battery pack is mounted with Velcro inside the guitar. Since the guitar has a hinge at the base of the neck I can fold down the neck to remove the battery pack through the sound hole without removing the strings.



Since I had purchased two of the same Mustang amplifiers and had an extra speaker I decided to add the spare speaker to the remaining amp to get a bigger sound. I cut the face off the amp which didn't have the control card in it and mounted it, with speaker attached, on the rear of the other amp. That gave me an amp with 2 speakers, one facing front and one rear.



It doesn't look very different from the original amp but didn't sound as good as I'd hoped since the sound from the rear speaker was going in the wrong direction. So I put small hinges on the top corners of the rear speaker frame so the rear speaker can be swung up until the rear speaker is facing forward in a sort of 'dual stack' arrangement.



The carrying strap holds the top speaker securely in place when it's open, and a couple of neodymium magnets hold the rear speaker panel closed when it's swung back down. I'm very happy with they way the amp turned out even though it wasn't planned, it just sort of evolved this way when I was working on the guitar.



   



So that's it. I don't really recommend a guitar project like this unless you have a spare guitar you're willing to chop large holes in and are willing to accept the possibility that it won't live up to your expectations. The guitar sounds somewhat better when played through the external amp because I can crank it up louder that way without worrying about feedback. But it you like to experiment and want to be the person who shows up at jams with a one-of-a-kind instrument which you've modified yourself, this might do it.



JP


mike gregory - Posted - 06/14/2013:  06:34:34


Looks like a complicated project, and looks like you did it well.
Any chance you'll post a sound file or a video?

5B-Ranch - Posted - 06/14/2013:  07:24:52


Got a cheesy name for it Frankentar Guitstien.:-) Please post a sound file. Looks like you know your way around amps and stuff.

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