Help with Mini-Amp Guitar

[maxcalibur]

A few months ago I posted about a guitar modification involving putting an Orange Micro Crush mini amp and speaker inside a guitar. I thought I had finished all the wiring and it would just work but some weird things happen when I try to use it. Firstly, I can turn the mini amp on but then no sound will be produced from the pickups until I plug a lead into the jack of the amp. The lead doesn't have to be plugged into anything at the other end and then if I remove it the guitar and amp then continue to function as normal. Secondly, I have wired in the normal output of the guitar as normal so when the mini amp is not in use I can plug the guitar into my normal Marshall amp. However, nothing happens until I turn the mini amp on and then plug something into its input jack too! For clarification I have included the modified wiring diagram I have used. Very grateful for any help.

[newey]

Max Calber-

I have an Orange Micro Crush amp. It's set up such that a plug must be inserted into the input jack before it powers up.

I'm assuming that the box shown in your diagram means that you took the guts of the amp, intact, and just wired it in? If so, that explains why you have to insert a jack for the amp to work.

As far as your passive setup is concerned, inserting a plug in the jack labelled "output should (I think) do the trick, I'm not sure why you're having that problem.

But I also don't understand why you have retained the input jack on the amp in any event. I think you'd be better off just using a switch, maybe a P/P pot, to switch the amp in and out of the circuit, using a second pole to disconnect the battery at the same time. In one position, you'd have normal output to an amp, in the other, you'd engage the onboard amp, using just a single jack.

(BTW, "Max Calber" is a joke only diehard fans of 007 will get . . .)

[maxcalibur]

I had noticed that you had to have a jack plugged in to make the amp power up before I dismantled it and stuck it in the guitar. However I wasn't sure whether this was due to an electrical or mechanical switch inside the jack. What I did was simply to solder the two wires to the tip and sleeve inside the jack.

As I said, it works when I plug a jack in even if I then remove it. I may in that case remove that jack altogether as you suggested, the reason I kept it in was simply to have an easy way to merge the circuits but evidently this hasn't worked out. I could of course just run a short lead between the amp and guitar jacks but I would rather have everything working internally.

The other thought I had is that somehow, the active circuit being wired directly to the ground of the guitar may be interferring with the passive circuit but I believe that's how it would be grounded anyway.

I will post up a picture of work so far a bit later today.

[newey]

As I said, it works when I plug a jack in even if I then remove it.

OK, I didn't understand that from your first post. That, frankly, has me stumped.

Some photos may help.

Is the amp jack a regular mono jack, or is it a TRS or switched type of jack?

[maxcalibur]

Yeah, it is a normal mono jack. What I think may be happening is that a mechanical switch inside the jack must be triggered to allow the amp to switch on but after that it only needs the circuit to be closed (in this case soldered straight into the guitar output wires) to remain on. If this is the case then I will remove the jack on the amp altogether.

That does leave me with the problem of a loose metal plate though as the nut of the jack secures the faceplate of the amp down.

Also this still doesn't solve the question of why the passive circuit doesn't work on its own! Really confused about that.

[sumgai]

Feb 12, 2010 8:49:30 GMT -5 maxcalibur said:

Also this still doesn't solve the question of why the passive circuit doesn't work on its own! Really confused about that.

Because you simply connected 'hot' to 'hot' and ground to ground, one jack to the other. What you didn't realize is that when the amp is off, it shorts its jack 'hot' to ground. to prevent any possible "loud" thumps or other noises when the amp is first turned on.

The cure is as newey suggests: remove the jack, and use a switch to control the amp's power. This will have the desirable side-effect of giving you "passive" output when the amp is not on.


HTH




sumgai

[maxcalibur]

Yeah, I can see it now. Will try wiring a switch in tomorrow morning. Is this what you meant? I can use one DPDT switch to do both switching jobs at once I think.

[newey]

Max-

A DPDT will do it, but your diagram doesn't show one, you show a SP switch.

Here's what I was thinking. Now, before you go wiring it, let's let someone else give it the A-OK. I'm wondering if it doesn't need a resistor of some sort somewhere to stop it from "popping" when you switch to the amp. I'm also wondering whether it matters whether one switches the 9V + vs. the -. I randomly picked the negative lead, it just "seemed right" to do so but I could be wrong.

Actually, as I think about it, it probably isn't really necessary to switch the battery at all, since the amp has a separate power switch anyway. This design does allow for switching between the 2 "on the fly" but I don't imagine you'll be doing a lot of that!

[sumgai]

newey,

max had the second pole shown, but it was 'closed', so if you weren't looking for it.....


~!~!~!~
max,

newey shows the right wires to control. You were switching the ground wire for the signal, and that's not gonna work. Plus, didn't you say that you were going to remove the amp's input jack entirely?

HTH




sumgai

[maxcalibur]

Yeah, sorry for the unclear picture. Thanks, I will wire it into ground now then. Think I will leave out the switch for the battery as it will only mean there are two switches to power up the amp and of course leaves me with less wiring to do! I found a way to wire it without taking the jack out which is good too.

Luckily there was already a DPDT switch built into the scratchplate of this guitar for reasons unkown to me.

Will upload a picture in an hour or so.

[maxcalibur]

Sorry, no photos yet as I was working on rewiring my Strat all day and putting lights into it too. Here's the results!



Will be working on the guitar with the Micro Crush built in tomorrow and should have it finished. I wired in a switch as suggested but havent quite found the right wiring into the amp and havent built in my bypass to the mechanical switch inside the amp yet.

Also, the guitar pictured is making a clicking noise when I touch any metal part but only with my hands that were sweaty at the time. When I used the back of my hands which were dry, no click happened. Just wondering if anyone had any thoughts on that.

[JohnH]

Cool picture! Id be interested to know what your toggle switching scheme is - we have a few around here!

John

[maxcalibur]

Thanks, I'm really pleased with how it turned out. I'm using the Wolf Wire Ultra Strat Mod which I've had in there for quite a long time. The other single toggle switch is just for the lights.

[maxcalibur]

Here's some pictures of the work in progress:

[maxcalibur]

Its more or less finished now. Can only use each pickup individually at the moment, desperately needs painting and a grill over the speaker but will sort all that in due time.

[steveb]

My Silver Tone (not to be confused with Silvertone) with a built-in amp & speaker.
The original transistor amp died and I was unsuccessful in replacing the power transistors, so I took the guts out of a small Radio Shack amp. This thing is a feedback machine when turned up and plugged into an amp.

[ashcatlt]

So, you're not having any trouble with the internal amp, but when plugged into an external amp you get feedback?

1) does the internal amp turn off when you plug it into the external?

2) (more importantly) please describe the feedback. There are generally two types of feedback possible w/a guitar: resonant string feedback where the strings themselves vibrate in sympathy with the sound coming from the amp, or microphonic feedback - usually a high pitched squealing caused when the pickups act like a mic. Some folks, though, will also use the word "feedback" to describe what is actually just noise - a buzz or hum or hissing sound. Which of these are you getting?

[steveb]

^sorry, I wasn't saying it's a problem, it's just feedback as in the infinite sustain you get when standing in front of an amp. By adjusting the gain, it goes from clean to mildly boosted to howling UFO noises.

It generates feedback by the built-in speaker making the strings vibrate and also can overdrive the input of the amp when plugged in, like a distortion box.

The built-in amp can be switched on or off when plugged into an external amp with the switch on the upper right of the pickguard.

[ashcatlt]

I call that a plus!

So if that's not a problem for you, for what help are you asking?

[newey]

Steveb-

Nice guitar, particularly with the David Lindley autograph!

Presumptious of me, but I'll answer Ash for you- you don't have a problem, you're just showing off your axe!