Introduction: Frankenstein Guitar Amp Build

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This is called the "Frankenstein Amplifier" because I had a couple of amp cabinets with speakers and no working amplifiers, plus some other bits and pieces that were just waiting to be reduced and combined.

I wired a Crate GX15 into 3 separate speakers instead of 1, and turned a pair of old computer speakers into an overdriven 2nd channel.

Step 1: Gluing and Compressing the Plywood Speaker Panel

Picture of Gluing and Compressing the Plywood Speaker Panel

I had plenty of 3 ply wood lying around, but this wasn't quite up to the task of handling 5 speakers with heavy magnets in them.

So I cut identically sized pieces, spread a thin layer of wood glue between them, and (as you can see in the pic) clamped the hell out of them! Once dry and trimmed to size, the profile was seamless.

Step 2: Components Used for the Build

Picture of Components Used for the Build

1. Creative SBS20 Computer Speakers and amp
2. Crate GX15 amplifier and speaker
3. Speaker from a Champion 600 amp
4. Other 4" speaker

Step 3:

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The holes that were cut for the cabinets the speakers original were housed in served as great templates to stencil and cut the new holes.

Holes were cut with an electric drill and jigsaw.

Step 4:

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These are the controls from the computer speakers being mocked up for housing fabrication - I used an angle grinder to cut the basic shape out of the Fender Champion housing, then used cobalt drill bits to make the holes for the potentiometers.

Lucky the potentiometers were threaded, so I was able to firmly attach the whole circuit board to the housing.

Step 5:

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Here the housing is trimmed to size - I used the pre-existing holes to screw the housing in vertically to the cabinet, but needed a horizontal fastening point to make it a bit more stable.

I don't have any metal bending equipment, so I put the faceplate in my bench vise, then attached my vise grips to the tab hanging out, and bent it 90 degrees - it wasn't a bad way to do it...

Step 6: Completed Housing Fabrication

Picture of Completed Housing Fabrication

The crystal-looking thing is the chopped-of end of a christmas light - the existing LED light from the computer speakers was affixed to the inside of the christmas light with hot glue, and it now glows a soothing verdant hue when switched on.

Step 7: Jumping the Signal Off the Headphone Out

Picture of Jumping the Signal Off the Headphone Out

The Crate amplifier turns it's main speaker output off when you plug in headphones. To bypass this, I soldered output leads directly to the contact points on the headphone jack. These went into the computer speaker input, so now I could control whether or not I wanted to engage the (very distorted and nasty) computer speakers or keep it with a cleaner tone.


Step 8: Re-use and ReDecorate!

Picture of Re-use and ReDecorate!

I used the framed grill cloth from a different amplifier, which as a bit on the small side. So I filled in the gaps with some green pen carcasses I had hung onto after they bit the dust as writing implements.

Attached it all using hot glue.

Step 9: The Finished Product in Action!

Comments

yudithkarimi (author)2010-12-10

its very hard

JuCo (author)2010-08-13

dang... i was working on this exact instructable, but my soldering iron broke. (cheap little piece of junk) mine has a 6" pignose speaker from one of those 7-100's, the amp and a 6" from some cheapy practice amp and 2 little radio speakers that give a nice ratty overdrive. the only difference was that i was gonna give an on/off for each circuit, though, (pignose speaker, no name speaker, and radio speakers.) because they each had an interesting tone and then i could mix them however i wanted or play them individually. you did great job, though.

IronManMC (author)JuCo2010-12-08

I've never broken a soldering iron. I own both cheapies and a pro soldering station (Weller WTCPL 60 watt controlled output) that I bought CHEAP.). My favorite is a plain vanilla iron (blue handle) I bought at Heathkit. I've used this for decades, and the tip just won't tarnish.

I buy soldering irons for specific purposes, such as microtip very low wattage for surface mount, etc. that's the trick to good soldering. Use JUST enough wattage.

I keep all of my soldering tools so clean, my Mom the clean freak could eat off it. Keep a small wet sponge nearby, and wipe the tip frequently. I'm not that concerned about the irons. A clean iron makes much better joints.


-Mike Curtis

kyismaster (author)JuCo2010-09-30

might as well buy a 50- 100 dollar solder, little 10 dollar ones are worthless, mines is $300 +, works like a champ.

IronManMC (author)2010-12-08

I'm an electronics engineer, and I smell SMOKE!

Solid state amplifiers (I didn't see any tubes) have a specific output impedance. If your speakers are LESS than this, the power amp will overheat and destroy itself. If you wired your speakers in parallel, they're probably too low, unless they're unusually high impedance (16 ohms). The formula for parallel impedance is 1/((1/sp1)+ (1/sp2)+(1/sp3)).

If any (or all) are 4 ohms, wire them in series.

to amps (-)---(-)-sp1-(+)---(-)-sp2-(+)---(-)-sp3-(+)----to amp's (+)

The impedance of series wired speakers is the sum of all (sp1+sp2+sp3)

If your amp output is tube, then you MUST use the specified impedance OR LOWER. Too high and you'll arc the power tubes, and probably the plate transformer.

You can also use series-parallel. connect 2 speaker pairs in parallel, then connect the two sets in series. Four 8 ohm speakers connected thusly have a total combined impedance of 8 ohms.

I generally don't recommend mixing speaker impedances. The lower impedance receives WAYYY more power. And yes speakers blow out, too.

-Mike Curtis

maxkracht (author)2010-09-28

How did you wire up the speakers? If memory serves, the champ runs at 4 ohms, the crate speaker says 4 ohms, and the other speaker?? I could be missing something, but I don't see how you could have matched the amps impedance with that setup. Sorry if I am underestimating you, but if you didn't get the impedance right your setup is either going to be inefficient/weak or on the verge of blowing a transformer or the voicecoil on a speaker. If i'm right, i would recommend just using one of those speakers and leave the rest in there for appearance... no one would know the difference and your amp will probably sound better/louder/etc.

J3PPiSH (author)2010-08-08

Nice!

iamtoats (author)2010-08-03

Nice. I have a Crate MX15R. Even though I have other nice amps, I will never give this up because of it's awesome spring reverb, and pedal friendlyness.

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Bio: A chronicle of ideas and projects from a designer and thinker in repurposing obsolete technology and discarded materials. Professional Musician, Grad student at NYU's ... More »
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