stereo ruby

[drk]

Hi, im thinking about building a stereo ruby, with 2 lm386 and a dual-opamp as the buffer for both. I also want to be able to use both IN in a single lm386(when i just have one speaker, i want to be able to ear both the right and left). Im planning on using it to listen to music from the PC.

Here's the schematic(if you see any mistake please let me know):


Now the doubts 
About the switch(to use both IN in a single lm386), will this approach works?
Another thing, i'm not 100% sure, but i think it's ok to have the lm386 not connected to a speaker? or when i want just to use one of them, i have to disconnect the other?

thanks 

[drk]

i started breadboarding it yesterday just one side, the buffer worked well, but the lm386 didn't, so maybe i have some mistake in the schematic..
anyway, could anyone anwers the questions above?

[Thomeeque]

 Connecting directly those two preamp opamp outputs (for MONO mode) does not look very healthy to me.. you should probably put some resistors between opamp outputs and the rest of circuit (something like 1-10k?).. plus there's no need for those two 100k pull-down resistors, 560R+vol pot will do the pull-down as well..?

Yep, and I see missing bias resistor for second preamp opamp (1M between pin 5 and V_ref)..

Another thing, i'm not 100% sure, but i think it's ok to have the lm386 not connected to a speaker? or when i want just to use one of them, i have to disconnect the other?

Since input remains grounded by pot (no signal), speakerless LM386 should be OK.. or if you want to be really calm, yuo can use output jack with switches which would put same fake load resistor (10R?) to output when no jack is inside.

[drk]

Ok, i've changed the switch so that it is after the 10k resistor and the cap.

About the bias resistor, im not sure i need to put another resistor. i think the bias current is already set with one resistor, and i think it can be shared for both opamps(but i could be wrong..)

The jack switch is a nice idea, but 10R sounds a bit small no?? maybe it's better an higher resistor?
thanks 

[Thomeeque]

Ok, i've changed the switch so that it is after the 10k resistor and the cap.

Yep, it looks better now

About the bias resistor, im not sure i need to put another resistor. i think the bias current is already set with one resistor, and i think it can be shared for both opamps(but i could be wrong..)

OK, now I look at the schematic again really closely and.. are really both inputs (pins 3 & 5) connected together??? This would mix your two input signals into one and kill stereo already at the beginning

But you know what, you don't need input buffers for PC audio output at all - remove buffers part, put input jack where you have buffer outputs now and that's it, PC audio output is strong enough to feed it.

The jack switch is a nice idea, but 10R sounds a bit small no?? maybe it's better an higher resistor?
thanks 

OK, this resistor should simulate load of speaker, so it should match with speaker impedance (what speaker impedance is it designed for? 4, 8, 16.. ohms?).

[drk]

hmm ...
ok, gonna try with just the lm386.

I got a 8ohm and a 16ohm, so it's gonna be connected to either one. I guess then a 10/12ohm resistor is a good middle point?

[drk]

hey, I'm back with this project(this last month i didn't spend much time doing diy stuff ).

Anyway, i breadboard the circuit(there's some mistakes in the above schematic, when i finish the breadboard part i'll post the correct one), but in the end, i decided i wasn't gonna use that much 2 speakers(for the stereo), so i'm currently with just one lm386(with the two channels on it).

The thing works great when i use my mp3 player, but when i connect the computer on the input to play music, it has some noise, that doesn't appear with the mp3 player. Don't really know why this happens, but it seems it only comes from the computer. Apart from the noise it works nice.

Anyone knows how to minimize this noise from the computer?

[drk]

ok, 3 months after starting this, it's done! (better late than never right? )

as usual it ended up different from what i initially thought. It can be used for music(as was the idea), but i decided to used it too for the guitar, so i added a 741chip for the distortion part, added a switch to switch that part off when i was listening to music(that part of the circuit added a lot of noise when playing music). That switch also switches indirectly from stereo(music) to mono(guitar).
After that it's a single lm386 chip and that's it!

Later i will post the schematic, still have to pass it to the computer, too lazy to do it now

As a overall it was very challenging for me building this, because i spend a lot of time in the breadboard testing several versions, which i learn a lot from.

some pics:


I just painted some days ago and i already let it fall and some of the paint came of... gotta be more careful