#1
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...
#2
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.
Last edited by von Layzonfon at Mar 31, 2014,
#3
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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#4
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.
#6
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.*
#8
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?
#9
Quote by von Layzonfon
Maybe a "hot" out as well, for direct injection into a cabinet?

Oooooh, yes! Great idea.
Squier "VMC" Stratocaster
PRS SE Singlecut
tc electronic polytune
CMAT MODS Signa Drive
Blakemore Effects Deus Ex Machina
DIY gaussmarkov Dr. Boogey
EHX Small Clone
Mooer ShimVerb
DIY Beavis Devolt
T-REX Fuel Tank Chameleon
Ampeg GVT52-112
#10
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.
Last edited by von Layzonfon at Apr 2, 2014,
#11
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.
Gear:

Guitars:
BC Rich Warlock
Dean 88
ME682-In Progress
Amps:
Carvin SX300
Etc:
Clayton 1.0mm picks
Planet Waves cables.
#12
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.
#13
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.
#14
Quote 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 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.
#15
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.
Gear:

Guitars:
BC Rich Warlock
Dean 88
ME682-In Progress
Amps:
Carvin SX300
Etc:
Clayton 1.0mm picks
Planet Waves cables.
#16
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.
#19
This is so cool man.
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Stay classy, pit.
#20
why not recess the speaker into the body, through the pick guard?
Gear:

Guitars:
BC Rich Warlock
Dean 88
ME682-In Progress
Amps:
Carvin SX300
Etc:
Clayton 1.0mm picks
Planet Waves cables.
#21
Despite being off work for a week and having lovely weather, I still didn't get as much done to this as I would have liked. This is partially due to getting distracted and partially due to waiting for the DIY store to get some more paint in.

In the end I gave up waiting (2 coats would have to do) added the jack holes and clear coated it.



I also spent some time converting my wiring schematic into a strip board layout that I can actually work from.



As usual, if anyone spots anything drastically wrong with my electronics I'd be very pleased to hear about it. I think I now have everything I need to finish the job off...except some spare time to do it in.
#22
Last night I got busy with the 1500 grit wet & dry (wet) and T-Cut. I did manage to get a fabulous mirror finish, mostly (hard to do it justice with a photo).



So I'm a lot more confident that I could actually get a fairly professional looking finish from spray cans. But as this is only the second time I've done this - and the first time spraying colour - I've also learned some more things.

Firstly, the two 100ml cans of colour and one 400ml of clear were not enough and I should have put far more layers on. As a result there's a few patches of unintentional relicking where I've sanded through to the primer - that white edge is not a reflection - and some where I seem to have been just plain careless and gouged it on something.



I've also been reminded that, even before you've started spraying, if you think you've sanded enough, you haven't. Do the same amount again. Probably twice. It's hard to believe, looking at that picture, that I could have failed to notice how rough it was in places.

But as far as the actual spraying process goes, I'm a lot more comfortable with it.
#23
That paint looks really nice!

But I'm a little perplexed as to why you need volume, gain, and master volume. I know the LM386 has the gain pins and tweaking them can yield nice sounds, but at least one of the remaining two seems redundant.
#24
Quote by Telecaster7
That paint looks really nice!

I agree, isn't that finish?
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This thread topic is gold. I've been on this website for 8 years and I've never come up with anything like this. So yeah. Great job TS[457undead].
#25
Quote by Telecaster7
But I'm a little perplexed as to why you need volume, gain, and master volume. I know the LM386 has the gain pins and tweaking them can yield nice sounds, but at least one of the remaining two seems redundant.
Here's the way I figured it...

Essentially, the first two columns of my strip layout represent a normal guitar. If I plug into the "dry" socket, the on-board amp is superfluous and I can run into my standard rig, should I so desire.

The first volume pot is to control the input level into the amp. As you know, rolling back the volume at this stage will affect how hard the amp gets driven and when it starts to break up.

The "master" comes post-amp and is intended to control the overall output level. Playing with both my test amp for this project and my old Marshall MS-2 micro amp, if you want maximum crunch you've got to turn the guitar and the gain up to 11, by which time you could feasibly be getting to ASBO volume levels - especially if you take the "wet" output into, say, a 4x12.

That's the theory anyway. It'll be interesting to see how it works in practice.

Quote by 457undead
Quote by Telecaster7
That paint looks really nice!
I agree, isn't that finish?

The paint is rather snazzy. It's Plastikote Metallic Red. Just a shame I was too impatient to wait for my local DIY stores to get more stock. But it would've been more expense and this "budget" project has already cost more than I anticipated when I started.
#27
Quote by Telecaster7
Ah, that makes good sense!

Yeah, but I guess he could repaint it if he really wanted to, right?

Edit: oh, you were talking about something completely different, oops
Quote by lolmnt
I love to have my vag pounded by guys who make lame threads on the internet!


Quote by snipelfritz
This thread topic is gold. I've been on this website for 8 years and I've never come up with anything like this. So yeah. Great job TS[457undead].
Last edited by 457undead at Apr 25, 2014,
#28
I spent a few hours soldering tonight.



I can't completely finish the job because I don't have mounting screws/springs for the pickup (there's always something).

Anyway, early indications are that something's not quite right. The dry output works as expected, so that's good. However, when I switch the amp on I get a rapid clicking (or a very slow buzzing) from the speaker, but only with the 'master' control on full; if I roll it off a little the noise stops.

Furthermore, I've noticed that with the amp switched off I also get the dry signal from the 'wet' socket. I've looked long and hard at my circuit diagram and I don't think that should be possible, so I guess I've got something wrong somewhere.

It's late now, so it'll have to wait until the next time I get a couple of hours to mess with it.

Update
I had a quick prod with my mulitmeter this morning before I left for work and there's definitely a connection between the two output signals. I've been pondering this, and looking at my layout I think I may have created some sort of ground loop.



I'm thinking that if I remove the earth connection between the tone and master pots (indicated by the pink arrow) that will effectively separate the pre and post circuits and hopefully resolve the issue. I won't get to find out until I get home and try it though.

This is precisely the sort of unforseen issue that leads me to believe I'll never quite "get" electronics.
Last edited by von Layzonfon at May 1, 2014,
#29


Looks pretty cool.

Unfortunately it still doesn't work properly. I thought I'd got it sorted, so I put it all together but the on-board amp still doesn't work. The standard dry output works fine, so I guess that's something, but...

The amp circuit is toast and I've no idea why - which was sort of most of the point of doing this.
For some reason the string tension is now pulling the neck forward. So I added another bolt.
Now the string tension is pulling the bridge forward because the crappy wood is so soft, such that...
The intonation is way off.

All in all, I think I'll put this aside as in interesting learning experience. I may come back to it at some point but right now I'm a little cheesed off with it as my (as it turns) misplaced confidence in what I was doing has led me to invest far more in this than I initially intended.

On the positive side, I think my finishing and soldering skills have improved considerably.
#30
I'm a little curious as to why you would need a "wet" out anyway. If you have the "dry" out to go to an external amp, then you don't really need a wet to amplify an amplified signal. It just seems as if it's overcomplicating things.

Another thing i noticed is most amplifiers have an input impedance resistor of about 1Mohm. Your amp does not. Adding a 1M resistor on pin three of your lm386 might help. attached is a pic

also, in your schematic, should your tone not be in parallel with the volume pot and not in series after the volume?

I would use the stereo switched jack for your dry output, making sure that the amp circuitry is disconnected when that jack is being used. Also a power switch for the battery.

just some thoughts that might be easy enough to try out.
Attachments:
circuit-5.png
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#31
Hey, macgregger, thanks for the input and actually spending some time illustrating your suggestion. It is very much appreciated.

The reason for the wet out was because these little 386 amps can sound pretty awsome when they're fed into a big cab rather than a 2 inch speaker, so the intention wasn't to re-amplify but go directly into a cab.

Most of the 386 amp schematics I came across don't have the input resistor but it's certainly something worth looking into.

The standard volume/tone section works just fine. My grasp of schematics is rather basic so I may well have drawn it out incorrectly.

There actually is a power switch (it's the one with the LED on the lower horn) so I thought it would be enough to turn the amp off if I didn't want it, rather than having to isolate it. I also had it in mind that I could possibly use both outputs at once to create a wet+dry rig.

There are still a few things I could try out - simplify and then recomplicate - but unless I sort out the issue with the bridge (and I do have an idea for that, too) there's not much point.

I do think I need to take a break from messing with guitars for a bit though.
Last edited by von Layzonfon at May 2, 2014,
#32
I reckon it looks pretty cool too and projects like this are never a waste of time. That wood must have been total cheese though, especially if it's tearing at the bridge posts. I guess there must have been enough play around the grub screws for them to eat into the wood under tension too.

I'm sure you'll come back with a clear head and nail it all if you take some time off! It always helps.