Build stompbox from solid state amp?

[ericohman]

Hi!

What modifications is needed to turn a solid state amp into a overdrive stompbox?
Has anyone here done it?

For example the Marshall MS-4:

[Johan]

that one?..just rehouse the pcb and add a footswitch for bypass..it'll double as a tiny amp plugged directly into your 4x12 too (and probably sound better than today)
j

[Paul Marossy]

My question is it really going to sound any good? I have my doubts. It's probably just ye old LM386 audio amplifier circuit in there anyway. You could build one for far less than buying that, tearing it apart and then buying everything to rehouse it into some sort of stompbox. Check out the Little Gem at www.runoffgroove.com - just add a tone control onto it. Or build Aron's "Smash Drive".

[Brymus]

Yeah or search here I have found more than 30 different LM386 distortion circuits in the gallery.
Most by accident.
And I thought the one I made was original...
My favorites are the Burning Crunch by D Shwartz and the Jade practice amp by Mac,those are the two best sounding 386 circits IMO.

[meffcio]

That tiny marshall isn't based on lm386. i had the scheme, and there was an other chip. I forgot what was that xd

[EDIT]
Here's the MS-2 scheme.
http://www.tremolo.pl/Firmowe/MARSHALL/Marshall%20ms2%20-%20wzmak.gif

[Paul Marossy]

That tiny marshall isn't based on lm386. i had the scheme, and there was an other chip. I forgot what was that xd

[EDIT]
Here's the MS-2 scheme.
http://www.tremolo.pl/Firmowe/MARSHALL/Marshall%20ms2%20-%20wzmak.gif

Well, gee, what a surprise. It's still an audio opamp, though. The KIA6213 is a 0.5W audio opamp, looks to be basically a Korean version of the LM386. Conceptually, the circuit looks similar to a Little Gem with an input buffer and tone control added.

[meffcio]

Conceptually yes, with a booster at the input ;p

[Paul Marossy]

I rest my case. 

[ericohman]

What would I do with the speaker connections if I would rehouse it and try it as a stompbox, just for fun...

Should I take the audio OUT from the phones output or from where the speaker was?

[Johan]

What would I do with the speaker connections if I would rehouse it and try it as a stompbox, just for fun...

Should I take the audio OUT from the phones output or from where the speaker was?

before you start, try just pluging the cable going to your amp "halfway in" into the headphone jack..that will tell you if it sounds like what you think it will sound like and if it'll be worth your trouble
j

[ericohman]

didn't sound too good. but maybe I'll try some modding just to learn a few things. I never use it anyway...

In a solid state amp, are there any things that is different from an ordinary boost/overdrive stompbox? I mean, I don't need to worry about output transformers and speaker load etc do I? When looking at the  schematic, to me, it seems like I can just take the speaker out completely. Or do I need to add 8 ohm resistor in place of the speaker or how does it work?

schematic again:
http://www.tremolo.pl/Firmowe/MARSHALL/Marshall%20ms2%20-%20wzmak.gif

[petemoore]

  It looks like a couple circuit fragments between the 1k and the 50klin.
 A transistor with 560 emitter R and 10k collector...boosts the input signal, then some shaping prior to the chip input.
 These could be built on a perfboard, tested, perhaps 'improved, within' a small number of hours, very low cost for what is shown on the schematic.
 You could have two of these seriesed fragment circuits, I would suggest something else for the Q1 circuit, something perhaps with 2 transistors and...
  Look at this, man do I get to rambling OT, breadboard and speaker searches is what I'd recommend, this other stuff is kinda dangerous.
 Skip the amp for the present purposes of discussion, this chip can be though of as an addendum to it's power supply, I'm sure it is capable of amplifying output cleanly at 1/2 volume...if not then start studying, looking for those power supply parts that you will need so you can hook a chip to in a matter of nearly minutes, such as already in a bigger amp if you want bigger volumes.
 nuff about the chipamps and their easy of use, amazing abilities...and power supply requirements [ugh].
 Here's the other day's excellent results from simple speaker experiment
 starting with:
 a very vintage, patched 6x9'', and a Jensen 2-way 6x9''.
 A tube 12'' diameter, 48'' tall [5.88 at the hardware store].
 A board 12'' x 48'', some carpet padding.
 Tube cut in 1/2, re-inforced, padded inner diameter.
 Speaker put in board, wired, board put on the end of the glued tube rim, another board and weights placed on that [if your tube cut wasn't so great, use gorilla glue, go around it with paper or string mache', plenty of glue, some salt...set it on a rug, listen to the amazing bass response from the effecient little alnico and the Jensen ceramic 2-way.
 The 2-way's designed nice w/extra highs which can be aimed offset from straight, just great for speech/vocals, listening in the bathroom...big bass/small footprint !
 The Alnico won't handle as much as the Jensen, but sounds better for guitar use.
 The little cabinets ship good and market well "Powerful little package" [lol] but will never allow the speaker to demonstrate the bass extension a larger cabinet can easily afford. Even including the new Skil jigsaw and blades the whole shebang put free speakers in cabinets for under 60 buxx.
 Reinforcing is a bit more time consuming, but the tube shape lends itself perfectly to performing pretty loudly with near 0 output, with good padding and minimal reinforcing.
 Weighting and stiffening around and at the front board tube joint also optional. Plug the other end option of course, but a long-ish tube with padded back is pretty good sound !
 Can't say this technique is recommendable until a better ''circle forms a C wrestling jig'' can be designed.
 I wrestled together a 2x8'' tube/board. I split the tube to make a C, then put the board on the front of the Cl<...about like that, then mounted a 2x4 to go down the length of the tube [past the backs of the speakers], and capped the ends with carpet and just boards pinning the 'can shut', long screws grab the 2x4 I sent down the tube [and built the end so the screws could find grain-meat to grab...sucked both ends in, with the carpet gasket ! This one got the double-C-wall treatment, the second layer was easy, getting the first C to open and accept the baffle board was a wrestling match, even with the pin-down jigs...boards, screws, clamps, uumphhh, and I didn't even know If I'd get it into shape by the time the glue dried...A-1 enclosure hafta say though, worth every bit of the effort. Will recieve the kings royal red carpet [added mass 'n damping] and finished/shaped oak ends of course .