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Old 28th September 2011, 07:01 PM   #1
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Question Novice needs advice: building a suitcase amp

I'm working on building a suitcase instrument amplifier and I need some advice about the actual amplification circuitry. Here's the deal:

The amp will be built into an old suitcase I found at a flea market. The design I'm thinking of is a front panel that folds up from the inside and catches on the lid, not unlike one of those travel alarm clocks. the front panel will have two 8" speakers, right now I'm looking at Jensen's C8R (25 watts each, 4/8 ohms) and a VU meter or two for good looks. I'm attaching a diagram.

For the amplification component itself, I'd like something that will put out 40 watts, at 4 or 8 ohms. Probably mains-powered (is that the right term?), not battery. For cost and space effectiveness, tubes are out. For a while I was tempted by Electro-Harmonix's 22 Caliber or44 Magnum, since they'd really keep things simple. However, I feel like I can do better with an amp kit of some sort that I can actually attach to the back of the panel. Plus DIY is so much more awesome!

I should say, at this stage, that I know next to nothing about electronics. I'm learning as I go, but I'm still completely new to this stuff. I'd probably need a kit, as opposed to designing my own circuit and finding the right components. I've been browsing these forums for a while now and it's all a bit intimidating...still, I'm optimistic!

Budget-wise, I'd like to keep it under $100. So no tubes, probably.

Application: I'll be playing clean electric guitar and mandolin through this amp. I want the sound to stay clean at higher volume. I currently play a Roland Micro-Cube at gigs and it doesn't have quite enough oomph to stand alone without distorting, so I usually have to mic it. I'd like my suitcase amplifier to pack some more power than that (playing small clubs and backyard gigs).

Any suggestions will be greatly appreciated. Thanks in advance,

Noam
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File Type: jpg SuitcaseAmpDiagram.jpg (35.8 KB, 84 views)
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Old 28th September 2011, 09:20 PM   #2
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interesting idea. if your keeping it clean you wont need much of a preamp, a TL072/TL082 opamp would work fine. you can do plenty including EQ and volume with that. as for power stages ive only ever used a TDA2030 (around 10 watts) but theres probably a few push pull power stages using darlington transistors or MOSFETs. Theres some schematics around for some solid state marshall amps with these stages. as for mains power, a 15-0-15 2A transformer should be plenty. Im not sure about the speaker being completely open when flipped up. it will have a similar effect of not being mounted in a cab at all. not only that, wouldnt the open design leave the electronics out in the open? might be a bit risky if someone drops a pick in there and accidentally grabs some mains voltage...
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Old 28th September 2011, 11:24 PM   #3
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No, you want to keep the suitcase closed or at least mounted on the bottom of the case if the lid is opened up any. If you wanted tilted have the amp sit open with the lid and the box siting on the ground, this will give you an idea of what I mean.

http://i42.photobucket.com/albums/e3...standP6276.jpg

Might not be a bad little speaker but it only has a dB rating of 93dB. Something like this one

10? G10C - 75 watts | Warehouse Guitar Speakers

which has a 99dB rating it would be like having an amp with four times the power. (you need to double the power for every 3dB increase in loudness). It would probably cost you as much as two 8" speakers but give you more clean output. I have not used this one but am impressed with the 10" and the 12" of theirs I bought.

The 10"

Ten inch speaker comparison in a Fender Custom Vibrolux Reverb amp-part 2 - YouTube

As far as an amplifier I do not have any suggestions other than go for a chip amp, they probably have more info on them in the SS forum.
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Old 29th September 2011, 09:39 AM   #4
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Quote:
Originally Posted by Exfish View Post
I'm working on building a suitcase instrument amplifier and I need some advice about the actual amplification circuitry.
Interestingly I built a valve amplifier in a suitcase back in the late 60's, both the suitcase and almost all the components came from a local rubbish tip

I was about 14 at the time, and the circuit was designed for me by a local electronics university student (who later on worked at the BBC I believe), and he gave me a mains transformer for it. Everything else came from the tip, and it used a 6BW6 output pentode, an EF80 pentode as a preamp, and a metal rectifier - all from old TV's, as was the speaker and grill mounted through the lid of the suitcase.

Bear in mind this was a 'no money at all' project, and I built it on a piece of hardboard (again from the tip), drilling holes through the hardboard and pushing component wires through, then wiring underneath.

It takes me back, I hadn't thought about it for decades
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Old 29th September 2011, 11:55 AM   #5
Trout is offline Trout  United States
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Hey, you might think about going the guitar case amp route, one less thing to carry.

Click the image to open in full size.

These are still floating around since they were sold by sears in the thousands back in the 60's.
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Old 29th September 2011, 12:54 PM   #6
Cassiel is offline Cassiel  Libya
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LOL!
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Old 29th September 2011, 12:56 PM   #7
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Originally Posted by Cassiel View Post
LOL!
I sure hope you're LOLing at that guitar case amp and not at my query
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Old 30th September 2011, 04:22 AM   #8
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I like the idea of mounting the speakers on a baffle that folds into the suitcase - I plan to steal that for a project someday! To keep it cheap, you might browse Ebay for solid state amps with trashed cabinets or without cabs. I would suggest looking for something that has a decent sound to begin with - maybe a Yamaha GS or Peavey Bandit. Most DIY solid state guitar amp designs tend to be kinda crappy for anything other than squeaky clean amplification (think acoustic or some jazz) - the trick to a good sounding guitar amp is introducing at least small amounts of "desirable" types of distortion to the signal. Another thing you might try is to use a clean DIY power amp driven by a distortion "stompbox" - maybe a Bad Monkey or Boss DS-1 (both good sounding and cheap).
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Old 30th September 2011, 04:28 AM   #9
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A trick used by a friend in Silicon Valley was to make a small Nuvistor tube based front end to give solid state amps "that tube sound". Nuvistors are rare now, but a small one tube preamp might fit just this application.
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