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Old 03-30-2014, 06:37 AM   #1
von Layzonfon
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UK DIY Travel Guitar Project

I was looking around for an electric travel guitar solution and very much enamoured with the Pignose PGG-200 but I really didn't fancy spending 180 on a "novelty" item that won't see massive use, however cool it may be.

I figured I'd be able to mash up a cheap guitar and a micro amp (something like a Marshall MS-2) for way less than that.

I also had a good look around at other travel guitar solutions and found some interesting (and excruciatingly expensive) solutions.

So now I'm embarking on putting a few of those ideas together into my own DIY travel guitar project.

The first thing I did was pick up a Jay Turser strat off ebay for 25. It's a perfectly nice guitar, has been set up decently and plays nicely (although I've never had a yearning for a 'vanilla' strat).



While waiting for a suitable micro amp to turn up I got started on phase 1 of the plan. Having come across theBone guitar I thought, "If they can just unbolt the neck like that then why can't I?" and I devised a plan.



Replace the four screws with a single bolt and a couple of grub screws to act as locating points. So here we go...



The first task is to get the neck plate out of the way so I can drill a new hole for the bolt. I temporarily replace the plate with penny washers.



Using the drill guide, I drill down until the hole penetrates the neck by about 10mm.



A knock-in threaded insert is...well...knocked in, and the two upper screw holes enlarged slightly to clear the grub screws.



The grub screw "locating pins" are screwed into the body. You'll note that I haven't removed the strings throughout the procedure.





Now I can just locate the neck in the pocket, flip the guitar and tighten the bolt, just like theBone guitar works, and by some small miracle after some very minor tuning we're back in business. The action is unchanged.

Result!

On to phase 2...
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Old 03-30-2014, 06:39 AM   #2
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Phase 2 is amplification.

While I was scouting about for tiny amplifiers that might be persuaded to fit inside a guitar body I came across numerous schematics for "smokey"-style amps. As even second-hand micro amps are going for around 20 on ebay and I can get the components for one of these projects for less than a fiver I thought it must be worth a shot. I chose a random schematic and went shopping.



Rather than going straight for butchering the guitar I though it wise to make a stand-alone version first - given how ham-fisted I tend to be with electronics. So in addition to the perf board, IC, 2 capacitors and battery clip I actually needed I picked up a jack socket, speaker and project box.



And after what seemed like far too long I ended up with this.

At first I thought it didn't work but then I noticed that it was actually working and if I pressed it right up to my ear I could just about hear it.

I checked my rather slap-dash soldering and it all appeared fine. Nothing grounded that shouldn't be. I wondered if I'd chosen the wrong capacitors and started tinkering. I found that if I bypassed C2 (see linked schematic above) then I suddenly get decent volume out of it. But only for about 10 seconds before it fades. If I unplug the battery for a while and reconnect I get another 10 seconds of proper amplification.

I confess, I know what a capacitor does on a fundamental level but I have no idea what it's doing in this circuit. Did I get duff caps? Will different ones solve the problem. I've found other schematics that are pretty much identical but specify 220uF caps rather than 47uF.

In fact, looking at my shopping list, it's possible I managed to pick up 0.047uF caps. I'm thinking that might be the problem.

All input gratefully received.
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Old 03-30-2014, 12:08 PM   #3
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I can't help you with the capacitor question, but this is an interesting project. I want to see the final result.
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Old 03-31-2014, 07:44 AM   #4
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I did some research and found a good description of the Smokey amp circuit.

Of course, on a fundamental level I know that capacitors are used for filtering frequencies; that's how they work on the tone pot - they only allow the high frequencies to leak to ground. So you'd think I would've worked that out for myself.

Working with this knowledge; if larger value caps allow lower frequencies through then it's possible that the caps I used are so small that they're not letting any of the guitar's range past. It doesn't really explain why I get signal fade when I bypass it but I'll replace the caps this evening and see how it goes.
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Old 03-31-2014, 10:01 AM   #5
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Are they meant to be 47uf? Because the ones in there look too small and too non-polarised to be that high a value.
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Old 03-31-2014, 10:19 AM   #6
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There's two common options: 47uF and 220uF. Having just picked up some 220s which are the nice chunky cylindrical ones I'm guessing the guy who was working in the store on Saturday had as much of a clue as I do about them.

This is my first foray into home electronics so there'll be much floundering about.

*Goes to do some reading.*
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Old 03-31-2014, 02:23 PM   #7
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I am gonna be following this. If it comes out good I might just try this myself at some point.
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Old 03-31-2014, 05:02 PM   #8
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That looks better. Quality workmanship on the speaker grille, I'm sure you'll agree.



While I was in there I also moved the battery earth from the common ground rail to the jack socket ring so removing the plug isolates the battery.

It's amazing what a difference using the right components makes. Here's an audio sample of me messing about with my lovely Vintage VH51, recorded with my phone about 8 inches from the speaker.

Now I've just got to decide how I'm going to implement this internally. I definitely want to add a couple of refinements like maybe a gain control and master volume. And I'll have to see about making the jack socket isolate the amp section so it could potentially be used as a normal guitar. Maybe a "hot" out as well, for direct injection into a cabinet?
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Old 03-31-2014, 05:07 PM   #9
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Quote:
Originally Posted by von Layzonfon
Maybe a "hot" out as well, for direct injection into a cabinet?

Oooooh, yes! Great idea.
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Old 04-02-2014, 07:16 PM   #10
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Tonight I've been looking at the built-in amp. Although I could quite easily go and find another schematic that includes the features I'm after I want to see if I can work it out for myself. That way I'm more likely to understand what's going on and learn something in the process. That's the theory anyway.

Here's the circuit as it is now.



I've opted to use a more literal representation of the IC simply because it makes more sense to me and might make the actual build slightly easier. Apologies to any schematic purists.

The first thing to do is to add a gain control. The connection between pins 1 and 8 determines the gain, so a variable resistor (potentiometer) in there should allow it to be dialled down.



Now I confess I am not just plucking stuff out of thin air. Not entirely anyway. I'm coming up with an idea and then doing a sanity check - usually by looking stuff op on RunOffGroove.com or BeavisAudio.com. In this case I wanted to know what value pot was required. It seems various 386-based amp projects use a 1k pot for this application.

Next step is to add volume and tone controls. In the external version these are in the guitar so all I really need to do is put them in the input line before the IC. I'm planning on swapping out the stock singles with a Szechuan-special rail I picked up a while ago (I figure a humbucker should help keep the noise down) so I've just used the values I would in a humbucker guitar.



Now I want a Master Volume control, post-amplification. I figure this should be another straightforward pot in between the IC and speker. I'm currently not sure what value I need to use for this. I guess I should look it up. I've put a nominal 10k in for now.



In theory that could be the end of it. The input will be the hot from the pickup. But it would be nice to have the option of using an external amplifier or an external speaker (these small amps are supposed to be pretty cool when run through big cabs). For the dry signal I should be able to just tap into the input line. Can it really be that simple?



Getting the "wet" signal could be just as easy, but ideally I'd like taking that signal to mute the speaker. It seems I'll need a switched stereo jack in the line that will disconnect the speaker when a jack is plugged in.



And that really is it. Because I can't isolate the battery with the input jack it'll need an actual on/off switch but that should be all. So now I just have to try and fit 4 pots, two jacks and a switch into a compact guitar body. And a speaker of course.

If anyone who actually understands all this has any input - glaring omissions, obvious stupidity, helpful suggestions - it will, as always, be gratefully received.
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Old 04-03-2014, 02:00 AM   #11
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I'm frankly amazed that this is getting done. I'm jealous, too, because I'm itching to do one myself; twice as hard at this point.
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Old 04-06-2014, 05:24 PM   #12
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So here's what happened this weekend:



The Pignose guitar is standard scale length but a smaller body so I figured I'd do the same...but different. It should also help save some weight. I needn't have worried about the weight - this body is like balsa.



I'm also hardtailing it. As you can see, there's some plugging up to be done. At least the crappy wood is really easy to carve and shape.



And finally for this installment, I re-styled the headstock, which saves a couple of inches.





The other experiment I did this weekend was to add a gain control to my little amp prototype. I really like the sound at low gain. The pot I had spare was a 500k so there is a short region where all the change happens. Hopefully a 1k will sort this out.

That's it for now. Waiting on parts for the next stage.
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Old 04-06-2014, 07:20 PM   #13
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Oh dear, what about all of the TONE you've lost by cutting the body and headstock? Tone, sustain, resonance, etc, etc.

On a serious note, it looks like you're going to have a very successful travel project on your hands! I'd also been looking at some of those wood inserts, so it's cool to see them in action.
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Old 04-07-2014, 07:11 AM   #14
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Quote:
Originally Posted by -MintSauce-
Oh dear, what about all of the TONE you've lost by cutting the body and headstock? Tone, sustain, resonance, etc, etc.
No worries there - although the body is more like a bath sponge than a guitar body, putting a speaker under the strings should be like having a built-in Sustaniac(TM).
Actually, I am mildly concerned about the feedback issue but I'll deal with that if and when necessary.

Quote:
Originally Posted by -MintSauce-
On a serious note, it looks like you're going to have a very successful travel project on your hands! I'd also been looking at some of those wood inserts, so it's cool to see them in action.
You mean these?



If you look at that last body picture you'll note a circular depression in the neck pocket. The wood is actually so soft that tightening the bolt was pulling the insert out of the neck and sinking it into the body, so I'm putting another penny washer on the inside to help distribute the load. I may also try a bit of glue around the insert too - just to be sure.
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Old 04-07-2014, 08:28 AM   #15
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On my first act discovery travel guitar I have (that has now been cannibalized, and is being painted (for over a year now...)) I didn't have any feedback issues, but at the same time i didn't have a distortion channel on the bugger.
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Old 04-07-2014, 03:11 PM   #16
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You see, this is why modelling things up is invaluable. I thought I was quite clever when I found a rather nice surface mount speaker on ebay. It just arrived in the post today so I was able to model it up properly. Can anyone spot the problem?



I guess I won't be surface mounting it on the pickguard after all.
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Old 04-07-2014, 05:12 PM   #17
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Thats a shame.
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Old 04-13-2014, 05:29 AM   #18
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I made a start on the pickguard yesterday.



But spent most of it tweaking the body routs.



I should be able to start painting today.
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Old 04-13-2014, 11:21 PM   #19
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This is so cool man.
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Old 04-13-2014, 11:59 PM   #20
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why not recess the speaker into the body, through the pick guard?
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