Ruby amp circuit mods....

[lezdyxsia]

   Hello, this is my first posting here, though I have been reading through the forum for a while and am blown away by the talent and knowledge contained here... The photos pages alone is humbling and surely some kind of shrine to tone hey... I have some rudimentary electronics knowledge, but am not capable of designing circuits myself. However, like the guitar, every time I pick it up, I learn something and what better way than an amp project I'm thinking...

   My question here is in regard to the little Ruby style amplifier circuit using the LM386 chip. I am wondering if it is possible to incorporate multiple inputs, much like many guitar amps? I have searched through this forum and Googled various times but can't quite dig up what I'm looking for. Rather than say, "bright" or "rhythm" etc style inputs though I am envisioning having the standard guitar input as it is designed, together with another 3.5mm stereo(looped) input which could be used in conjunction with, or stand alone from, the instrument input.
    i.e., I can plug in and just play guitar, I can feed in a second input simultaneously such as a backing track or drum machine/metronome or thirdly just use output "2" maybe with an ipod/iphone or hard drive recording etc. The reason is just versatility- if I'm making the thing from scratch, I figure try and get it right, and the idea of a super portable little device which can cover a few bases seems logical. Maybe the electronic characteristics of the input buffer stage makes this not a viable option? Could  parallel inputs and the associated impedance  be calculated, or would it maybe have to have two buffer stages with dual Vol pot? I am kinda out of my depth here and wondering if anybody has some ideas..
    I'm sure there are more things that will stump me, but maybe one basic question per post is the way to go...? Thanking everyone in advance. Cheers.

[JKowalski]

Its easy - use a op amp mixer.

Look here:

http://www.all-electric.com/schematic/simp_mix.htm

Notice how there are two op amp stages, you only really need the first one.

[lezdyxsia]

Hey thanks there... OK, wow- op amps open up a can of worms hey...? Will be doing some reading there. Funny how when you make things less simple, they become more complicated...Mmm, maybe I should apply the K.I.S.S. principle and just get a working project first- I aim to make it pretty modular, and if I allow the room for future additions, it can be a plug-and-play kind of set up with different amp builds. Cheers.

[CynicalMan]

Its easy - use a op amp mixer.

Look here:

http://www.all-electric.com/schematic/simp_mix.htm

Notice how there are two op amp stages, you only really need the first one.

That circuit only has a 10k input impedance so you might have to change the input resistor values or buffer the inputs, especially if you plan to run guitars directly into it.

[teemuk]

There's no need for OpAmp mixer.

The biggest problem is that amps like Ruby are made to be overdriven heavily. When you feed such amps with signals of backing track, metronome etc. these signals get heavily overdriven as well and sound horrendous. The distortions of these signals will also "mush up" the guitar's tone.

[lezdyxsia]

The biggest problem is that amps like Ruby are made to be overdriven heavily. When you feed such amps with signals of backing track, metronome etc. these signals get heavily overdriven as well and sound horrendous. The distortions of these signals will also "mush up" the guitar's tone.The biggest problem is that amps like Ruby are made to be overdriven heavily. When you feed such amps with signals of backing track, metronome etc. these signals get heavily overdriven as well and sound horrendous. The distortions of these signals will also "mush up" the guitar's tone.

- yeah, I think at my level that I will build the circuit as designed first. Listen to it then if I do some mods, I will have a reference point. Baby steps ya know... Bit embarrassing- I probably should be starting out 101 with an egg timer or L.E.D. dice, but this looked about the same complexity and is so much more useful and organic kind of project... Anyways, I've got most of the parts gathered, so will give it a go. Cheers.