build basic audio mixer (4 channels to 1)?

[janklug]

hi,

i'm new to this forum (and basically to audio electronics, too, so please forgive any newbie mistakes ;-) )

(the first one was to post the same question to the digital forum, but apparently not all things containing IC's are digital - so once again..)

i'm planning to build a very basic audio mixer, that should combine 4 channels (2 dynamic mics, 2 line level instruments) to 1 line level channel.

the level of the in's should be set individually, and i'd like to have a master fader, too.

i've searched the internet & found several designs that (more or less) seem to fulfil these wishes; unfortunately, i don't know the used amplification methods & their pros/cons, so i can't decide what solution would sound & work best...

does anybody have any idea wich of the following schematics to prefer, and/or answers to the related questions on that design?
any help greatly appreciated!

http://www.redcircuits.com//Page53.htm (looks like the best choice to me)
(question 1: do i need the full 'input module' also for the line level inputs?
question 2: what can be omitted to make it just a mono out?)

http://www-fa.upc.es/websfa/lab/111/audio/audmixer.txt
(question on this: Audio Taper pots - are that just logarithmic pots?)

http://home.maine.rr.com/randylinscott/may20.htm
(- question 1: does it need 9V power, or is that +9V / -9V symmetrical power? just heard of the existance of symmetrical power today ;-)
-question 2: what kind of caps are those? the 100uf seem to be polarized, but what about the 10uf at the outputs?!)

http://www.zen22142.zen.co.uk/Circuits/Audio/6ipmix.htm
(question 1: what are those opAmps? which model to choose for that?
question 2: this actually USES a symmetrical 9V power source, right?)

well, i found more, but these seemed to be fitting best.

thanks & greetings,

jan

[paulb]

Originally posted by janklug
http://www.redcircuits.com//Page53.htm (looks like the best choice to me)
(question 1: do i need the full 'input module' also for the line level inputs?
> No.
question 2: what can be omitted to make it just a mono out?)
> The pan pots and either the left or right channel mixer amps.

http://www-fa.upc.es/websfa/lab/111/audio/audmixer.txt
(question on this: Audio Taper pots - are that just logarithmic pots?)
> audio taper = logarithmic taper

http://home.maine.rr.com/randylinscott/may20.htm
(- question 1: does it need 9V power, or is that +9V / -9V symmetrical power? just heard of the existance of symmetrical power today ;-)
> +/-9V. Two 9V batteries will do it.

-question 2: what kind of caps are those? the 100uf seem to be polarized, but what about the 10uf at the outputs?!)
> 10 uF non-polarized electrolytics would be best, but normal polarized electrolytics will also work. If the input impedance of whatever it is feeding is higher than 2K, you can reduce the capacitor size accordingly.
> Careful with this circuit. There is no such thing as an LM353, it's actually an LF353 which could be replaced by a TL072.

http://www.zen22142.zen.co.uk/Circuits/Audio/6ipmix.htm
(question 1: what are those opAmps? which model to choose for that?
> TL072 will work. You will need bypass capacitors close to each IC, one each on the +ve and -ve supplies. 0.1uF (100nF) will work.

question 2: this actually USES a symmetrical 9V power source, right?)
> Yes.
well, i found more, but these seemed to be fitting best.

thanks & greetings,

jan

Also see http://headwize.com/projects/showfil...=opamp_prj.htm

[janklug]

thanks for having a look into this, paulb!

i think i'll go for the modular version at http://www.redcircuits.com//Page53.htm.

> The pan pots and either the left or right channel mixer amps.

ok!
i wondered though if for example R1, C1 and R2 should stay in there, or if they should be skipped together with the pan pot..

thans again & greetings,

Jan

[lulu]

you can skip the pan pot but if you want both channels to have only one output, then perhaps you could skip one half of that circuit (without pan pot both outputs would be the same)

[paulb]

Originally posted by janklug
thanks for having a look into this, paulb!

i think i'll go for the modular version at http://www.redcircuits.com//Page53.htm.

> The pan pots and either the left or right channel mixer amps.

ok!
i wondered though if for example R1, C1 and R2 should stay in there, or if they should be skipped together with the pan pot..

thans again & greetings,

Jan

R1, R2 and P1 can be skipped. You need to keep C1, connected directly to the wiper of P1.

[janklug]

R1, R2 and P1 can be skipped.

ah, that'll save me lots of money!

- but seriously: thanks a lot, paulb & lulu!
i'll order parts today.
i guess it will be a bit tricky to connect everything on bread board, but it's probably even more tricky to design a pcb without experience & software...
anyway, looking forward to it!

greetings,

jan

[Havoc]

without experience & software...

Cannot help with experience, but software you can find free at: http://www.cadsoft.de/ Take your choice of windows or linux. The free version is limited to 2 layers and 1/2 of a eurocard. But with one for the psu and another for the rest you should be able to do it. (or you could put the headphone amp on a third pcb and stack them)

[janklug]

Take your choice of windows or linux

thanks for the tip!
unfortunately, i'm macintosh only...
many nice free programs for designing pcb's, front covers, pic programs etc are win/linux only; starting to get used to it

greetings,

jan

[Havoc]

Sorry Jan, but I didn't tought about that. The good news is, they have a version for OS X. And it is just as free

[janklug]

yep, got the eagle flying!

now i'll have to see what will be faster - learning to work with eagle or puzzling with about 150 electronic parts..

just ordered them, so i'll find out soon!

greetings,

jan