Noisy Cricket combo amp questions

[tatou]

(Long time lurker, first time poster!)

I've built a few stompboxes now and want to try my hand at a simple amp. In particular, I want to "upcycle" a vintage train case I was given by installing a 6" speaker and making it a little practice combo amp. I'm planning to stripboard the circuit using one of these layouts.

However, from what I've seen most people just build this in a stompbox enclosure and treat it at a "head." Since I'm such a n00b, I have a couple of questions about this build and implementing some features I want:

• Should I put the circuit itself in a shielded enclosure *inside* the suitcase frame? My impression is yes, so as to cut down on radio interference. If so, any advice on what do use for the chassis (a regular die-cast stompbox enclosure seems like overkill here).
  
• I want to add a 1/4" optional jack such that, when nothing is plugged in, the amp just powers the 6" speaker. But when you plug in a cabinet/etc it cuts off the speaker and goes to the external unit instead. Is this what a "switching output jack" is for? If so, can you refer me to a part and how to wire it up for this kind of application? My googling has failed me. I might want both an output jack and a headphone jack that has this property, but it might depend on how involved this is...
  
• On a related note, the standard stereo-input/DC/9v battery wiring trick would work for this little guy too, yes?
  

Any advice is appreciated, thanks!

[bluebunny]

Welcome!

You could just build it and see if it's noisy?  If it is, then line the case with aluminium tape, or something similar.  And you could use something like this for your speaker connection:



This has two terminals.  The two nearest to you in this picture are the ones that connect to the jack, if there's one inserted.  So these connect to the output from the amp circuit.  The other two terminals on the far side connect to your internal speaker.  The insertion of the jack disconnects the internal speaker.  If you're including the headphone driver mod, then things are a little more involved, but similar.

Using a stereo input jack can indeed be used to turn the power on and off.  But if the amp volume is high, it might thump!  I would choose a switched volume pot so that there's zero volume when the power is applied.

[tatou]

Thanks bluebunny!

EDITED: So would these be appropriate jacks for the sort of thing you're talking about?

• Mono (cab): http://smallbear-electronics.mybigcommerce.com/jack-mono-pc-pins-e-h/
• Stereo (phones): http://smallbear-electronics.mybigcommerce.com/jack-stereo-pc-pins-e-h/

I realize now that the stereo input isn't necessary: I'll definitely have a power switch on this.

[davent]

Another option for the speaker jack would be the Switchcraft 12A if you prefer the open frame.

http://www.switchcraft.com/Drawings/12A_CD.pdf