Wiring non-powered basic line-level mixer

[tomhop]

Hey guys, this is my first post and im only 15 so be nice xD

a while ago i got my hands on a basic powered mixer that had blown up and was beyond repair, so i wanted to convert it into a passive mixer without buying loads of extra bits and bobs, im not sure if i can do this though. inputs and outputs are all going to be line-level but the variable resistors are 500k . what other components am i going to need if this is possible?

i know this question isn't really bout mains electrical like most posts but i hope that someone can help

Thanks,
Tom

 

[Adam W]

What kind of mixer is it and what are you going to be using it for, eg a disco mixer for cd players, studio type mixer for guitar inputs etc?

If it is possible I imagine you would need to take most of the electronic gubbins out of the equation and pretty much just use the level pots in the live path, and probably put all the screens together, then combine them at the output.

I suggest you prepare yourself for the worst - personally I would just buy a mixer, although saying that when i was your age money was an issue so i had to cobble together whatever kit I could beg/borrow/steal. If electronics is your bag you could do what me and some of the other cool kids did and set up an electronics club under the supervision of one of the physics teachers - then you would have access to soldering irons, components, advice etc, just don't do what one of my mates did and try to work on a mixer when it is plugged into the mains - he nearly killed himself doing that.

 

[tomhop]

Hello NovusSparkus,

thanks for you reply, i was beginning to think i wasn't going to get one
Anyway i ripped apart all the insides today and wired it up how i originally planed too, the same way you suggested.
its a very basic little mixer a sure scm262

Shure - Mixers and DSP - SCM262 Stereo Microphone Mixer

(2 mic 3aux inputs) that i am going to setup in my room to run my tv, computer and maybe my mp3 player or other little gadgets through and then into an amp (computer speakers ) then out to some speakers around the room. its kind of worked, the problem is i get no control over the volume until the pot is just about till the end so you don't have to much control over the volume, what value pots would you suggest for line level audio?

the club is a good idea but i think im the only one that's really into electronics that i know of i have a soldering iron and tubs of random bits and bobs that i collect and as for working on things while there live i don't tend t do that yet anyway

Thanks,
Tom

 

[Adam W]

Hi Tom,
Personally I have my tv and computer connected to my receiver (combined tuner/amp) via one of these:
BEHRINGER: VMX100
which I bought ex-demo from a local disco shop. It's not ideal but i had it left over from my DJ days, and it does the job.
I'm afraid i can't really recommend a specific value for replacement pots as i've never done anything like that myself, but at a guess i would just try something lower, eg 100k, although the danger is you may not be able to cut the unwanted channels right down to zero - obviously it needs to be a stereo pot.
The closest thing I've found seems to be these which are 80p each so you could try one and if it doesn't work you haven't lost much:
Dual Miniature Potentiometers : Potentiometers : Maplin
Apparently they don't have a flat on the shaft so you may have to file one down to get the knob on.

Remember you won't be able to match the output you get from your tv or pc, only attenuate it, so you'll have to crank up the volume on your pc speakers unless you add a preamp at the output, which will need some kind of power supply.
I managed to build (after a few attempts) a very small preamp from components on veroboard powered by a 9v battery but could use a mains powered external transformer. I did that at 'Electronics club' so it didn't cost me a penny.
If you wanted to set up your own I'm sure there are other people interested, you'd just need to get a physics or technology teacher interested, then advertise for members via poster/assembly.

Regarding working live (230v), as an electrician and "responsible adult" I would urge you not to try this - ordinarily it is actually illegal under part 14 of the Electricity at Work Regulations 1989.

Please let me know how you get on - I'm intrigued now.
Good luck,
Adam.

 

[tomhop]

Hello again Adam,

Today i started putting it together as it is, i already tried 100k pots but no good .
iv got my system up and running with a different 2ch mixer that i wasn't going to use because it was battery powered, so all i did is put a dc jack on it and run it on a low voltage adapter
i now have 6 speakers and 1 sub running

I haven't given up on the mixer as i plan to put a little amp out of some computer speakers inside it and have have a DC jack on it for power and some bare cable speaker connectors on the back. i was thinking about putting a little power led and a switch on it too and maybe change the pots if i can find some of a better value

I don't plan too work on anything live for a few years anyway

Thanks for all the help and advise ,
Tom.