Speaker Related Projects

   Vector2
(A T-line and ribbon tweeter 2-way. August-2012)

   Polaris
(A tall, thin, upwards firing omnidirectional speaker. May-2010)

   Shiva_PR15
(A powered subwoofer using a 12" driver and 15" passive radiator. Jan-2010)

   Can-Less
(A computer speaker; redux. December-2005)

   Can-Can
(A computer speaker in a light canister. Jan-2005)

   Sonosub
(10" vented subwoofer in a cardboard tube, powered by a Parapix amp. May-1999)

   MTM Center Channel Speaker
(A Madisound design. Nov-1997)

   2-way Surround Speakers
(5" woofer and 1" tweeter. July 1997)

   3-piece mini system
(6" DVC bass module mated to 4" car speaker. June 1997)

   3-way Vented Floorstanding Speaker
(vented 10" woofer, 5" mid and 1" tweeter in a 4 ft tower. Summer 1995)

   NHT1259 Subwoofer
(A 12" woofer in a sealed architectural pedestal. Winter 1994-95)

   Inexpensive Speaker Stands
(Particle board, sand and spray paint. Fall 1994)

   2-way satellite
(6.5" woofer and 1" tweeter. Summer/Fall 1994)

Electronics Related Projects

  900 MHz Audio Receiver
(Better use for bad headphones. Jan-2008)

  Buster - A Simple Guitar Amp
(Perfect for the beginner. Jan-2010)

  A PC-based Audio Console
(Use a PC to play tunes. Jan-2010)

  LM-12 Amp
(Bridged LM-12 opamps. Aug-2003)

   CeeDeePee
(A CD player and FM tuner from spare computer parts. Oct-2002)

   Quad 2000 4-Channel Amp
(Premade modules by Marantz. May-1998)

   Zen Amp and Bride of Zen Preamp
(by Nelson Pass. Apr-1997)

Articles

  Backing-up LPs to CD-R
(Whiningdog.net 10-Dec-2002)

  Using Wood in Speakers FAQ
(Work in progress)

   MDF FAQ for speaker builders

   Woodworking Tools for the DYIer
(HomeTheaterHiFi.com Oct-1998)

  Some Thoughts on Cabinet Finished for DIY Speakers

   Large Grills Made Easy

   Some Parts Suppliers
(Outdated)

Other Useful Stuff

   DIY Audio Related URLs

  Veneering Primer
(by Keith Lahteine)

   How to get a Black Piano Finish
(by DYI Loudspeaker List members)

   Sonotube FAQ
(by Gordon McGill)

   Excerpts from the Bass List
(Oldies but Goodies)

DIY Loudspeaker List

   Current DIY Loudspeaker Forum Home

   Former DIY Loudspeaker List Subscription Page

  DIY Loudspeaker List Archives

Buster

A cheap guitar speaker and amplifier that's perfect for the beginner

Introduction

The good news - got a free electric guitar - a Gibson Epiphone Junior.

The bad news - no one plays the guitar in my house and I really don't want to spend the money on equipment that may end up not being used.

The solution? Build something cheap that can bridge the learning curve gap. If nothing comes of it, it's no big loss. If someone (me?) ends up loving the guitar, we can always upgrade the amp.

After a little hunting on the internet, and a little shopping in my spare parts bin, the solution became obvious. Here are the basic components that make up my guitar speaker and amp.

  • The Noisy Cricket preamp. This little gem is easy to assemble and is powerful enough to drive a speaker directly for low-volume (personal space) use.
  • Since I wanted a little more volume, I'm going to use a spare JBL PC speaker amplifer from my parts bin. This is the same amplifier I previously used on my CanCan project. There are many other possible choices here. Any amp from an old PC speaker would work; as would any of the chip amps on the market. I took the path of least resistance.
  • For the speaker, I'm going to use a 5 inch Peerless 831990 driver. I have 4 of these collecting dust so I might as well put one into service. I also have a Lineaum monopole driver sitting around so I'll combine the two. The result will should give more range than the guitar needs.
  • To house everything, a simple plywood box will do. It's covered with heavy duty fabric and metal corners. My only concern is with the cat - will she use the fabric like a scratching post?

The picture above shows the front and back of the finished amp. You can see all of the controls and features (through I have not labeled them). Items worth noting are:

  • A top mounted handle - collapes down when not in use. From PartsExpress.com
  • Heavy duty fabric and metal corners - from PartsExpress.com
  • A 10 inch metal grill to cover the 2 drivers underneath - from PartsExpress.com
  • A 1/4 inch input jack for the guitar cord
  • A gain knob. This goes to the Noisy Cricket circuitry.
  • A tone control know. This goes to the Noisy Cricket circuitry.
  • A "grit" switch for the Noisy Cricket circuitry.
  • A green power LED.
  • A red pushbutton power switch on the back.
  • A power cord.

Construction

There are two parts to the build process - a 5-sided box and the front baffle. The front baffle containts almost everything. The only thing that's part of the 5-sided box is the power transformer and power switch. Components such as the knobs can't be mounted onto 1/2 inch plywood (too thick) so they are mounted on a piece of hardboard. The hardboard is then mounted into the cutout on the baffle. This structure has the added benefit of allowing the controls to be recessed and thus less likely to he damaged.

The pictures below show the 5-sided box. Note that the original plan called for the case to have square edges. After I received the metal corners, I realized that I had to round over the edges with a 3/8 inch radius. This forced me to remove the screws and reinforce the interior edges. The roundover was applied after everything was assembled and is not reflected in the pictures below.

The power switch is recessed in the rear for two reasons - (1) to avoid running 110VAC to the front panel near the other components and injecting noise and (2) to keep it out of the way. The switch is also mounted on a piece of hardboard which is in turn glued and screwed into the plywood.

The transformer is a wall-wart that's been kept intact. An old extension cord was hacked so that the wall wart could be plugged into it. Should I ever decide to scrapt this guitar amp, I can recycle the transformer easily.

The front baffle holds the drivers, the crossover, and the electronics. This setup allows me to test everything before assembling the box. Once assembly is done, there's really no good way to open up the box again so it's important that everything is tested before assembly.

To mount the electronics, a piece of plywood is mounted at right angle to the baffle. The picture on the left shows the various components and the wiring mess. The two small boards on the left and center are the power supply and Noisy Cricket. The main transformer delives low voltage AC to the JBL amp which converts it to DC and filters it. The power supply on the left takes DC power from the JBL amp board to regulates it to about 9.5v to power the Noisy Cricket. It uses a LM317 variable regulator to do the job. The JBL amp has its volume control set to close to maximum. The tone control is set to the middle position. These will remain unchanged and inaccessible once the unit is assembled.

The JBL board is mounted vertically because that's the easiest way for me to mount this particular assembly. It comes with its own metal heat sink. I used a small right angle bracket to connect the heat sink to the plywood.

I don't have pictures of the crossover boards. There are two of them, one for the woofer and one for the tweeter. The are mounted behind the baffle, adjacent to the tweeter on either side. The woofer network is a 4th order low pass with a corner at about 2KHz. The tweeter is a second order high pass at about 1400Hz. Tweeter response is padded with a 4.7 ohm resistor. The summed response is pretty good as measured with LAUD. With an estimated internal volume of about 0.7 cubic feet, the predicted low end response is F3=67Hz, F10=38Hz. Not bad. The upper end is a little soft as the monopole has a slight droop in its response. But the treble is fairly clean and pleasant to listen to.

Once everything has been tested and the unit is assembled, the last step is to roundover the edges and apply the fabric. I used 3M #77 spray adhesive to glue one continuous piece of fabric to the box. Holes were cut for all openings on-the-fly and trimmed with a sharp pair of scissors. The drivers were mounted over the fabric. The corners and grill were installed last.

Conclusion

I am very pleased with the results. The amp plays loud enough to be annoying yet can be turned down for quiet playing. The unit is solid and best of all, was cheap enough given the number of spare parts I already had on-hand. The only bad thing is that the cat has indeed found the fabric to her liking but it's really tough stuff and so far, there's been no damage... yet.

 

03-January-2010


Note: The contents in these pages are provided without any guarantee, written or implied. Readers are free to use them at their own risk, for personal use only. No commercial use is allowed without prior written consent from the author.