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i'd like to build my own simple mixer, but i don't know where to start!
i'd like to build my own simple mixer, but i don't know where to start!
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Old 12th September 2017, 10:15 PM   #1
aae is offline aae  United States
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Default i'd like to build my own simple mixer, but i don't know where to start!

Hello,

First post!

I'd like to build myself an audio device but i really don't know where to start.

It would be a powered mixer in both directions.

Ultimately i'm envisioning an altoids tin with nothing but power (not sure what's needed here) and 5 TRRS for devices and 1 TRRS for speaker/microphone...

i'd like to be able to hook up (for example) 3 computers, an iphone, and a tablet up to this thing (the computers might require splitters, not a problem) to the same set of speakers/headphones and microphone, i don't need level control on it, they can all be handled on device...

i don't mind getting my hands dirty and am comfortable with soldering, but i'm not sure what parts to buy (besides the obvious connectors), i'd like the levels to remain standard, so i don't know what sort of circuitry that would require, if i need buttons to enable/disable the different device ports

not sure where to start, any tips?
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Old 12th September 2017, 10:42 PM   #2
MAAC0 is offline MAAC0  Portugal
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Oh dear..
Some resistors do it.


Start here from the beginning to get some ideas:


Elliott Sound Products - The Audio Pages (Main Index)
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Old 12th September 2017, 10:44 PM   #3
aae is offline aae  United States
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hmm, resistors even for the microphone portion?
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Old 12th September 2017, 10:48 PM   #4
rayma is offline rayma  United States
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Quote:
Originally Posted by MAAC0 View Post
Some resistors do it.
Each channel looks like this, use resistors of 5k to 10k value.
https://upload.wikimedia.org/wikiped...mixer_1000.jpg
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Old 12th September 2017, 10:50 PM   #5
scottjoplin is offline scottjoplin  Wales
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Audio Signal Mixing
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Old 12th September 2017, 10:52 PM   #6
aae is offline aae  United States
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this is great... so once i decide what type of mixing i want to do, do i just do the same in reverse for the microphone?
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Old 12th September 2017, 10:56 PM   #7
MAAC0 is offline MAAC0  Portugal
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I remember building some years ago a ELEKTOR magazine mixer project. It worked quite well with 4 LINE /Phono inputs, VU and PFL...when I was at high school.


Come on, with 100€ You buy a YAMAHA or a Behringer working ready made mixer.
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Old 13th September 2017, 03:23 PM   #8
indianajo is offline indianajo  United States
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What kind of microphone? crystal? dynamic? electret condensor which needs phantom power? Different gain levels for each one and the condensor needs 36-50 vdc at low current.
line level inputs like radio phone or computer need no DC on the input.
Many cheap commercial mixers switch the phantom power to all the inputs, or none.
Line level inputs can use just an attenuator pot, not a gain device, but dynamic & condensor mikes will need a gain device like an op amp.
The mixing is done by a number of 10 k typically resistors going to a final gain device. This separates the source voltages from damaging each other.
Buying a ****y used mixer with bad pots is a good way to start, but not a Behringer, they have no schematics and the pots are unique.
I bought a hissy hummy Herald RA-88a (nineties kit) with good pots and spent a year modifying it so it didn't hiss or hum. It uses op amps 33078 or NJM2068 and sounds quite good now. The older the better used mixer the better, as leaded components are a lot cheaper to solder than SMC. NE5532 is another op amp which gives good results although it draws more power. You want something using DIP duals which gives you a lot of choices. SIP IC limits you to 4558 which is hissy, but very widely used commercially.
So project board for op amps is useful. I don't like the velleman one it had a pinout for 741 which is hissy. When I looked at it. MPJA used to sell PC board kits but has gone out of that business. Ted's audio e-bay store or something, I can't quite remember. Op amp boards as an e-bay search item gets a number of answers, no experience with any of them.
Earphone drive takes more voltage & current than the input devices. Successful ones will have a heat sink attached. Various earphone drive IC go in and out of fashion, the currently available stocked ICs require sweating the IC body to the huge pad on the custom made circuit board with some special soldering device. That is for factories, not a newby with a $40 iron. I'd say a LM386 or LM1875 with a TO220 heat tab are the best stocked devices, although they have more power than necessary for earphone. For earphone you can also drive two output transistors with an op amp, see various projects on solid state.
One trick to cut your expense is to buy all your components at once from a distributor so you don't pay 10 or 15 freight bills. Keeps you above the minimum buy at distributors too, else a handling charge.
I'd say an altoid tin for all those inputs is undersized. May be just doable if the power supplies are external. The cables would tend to drag it around off the table. I'd use a kid steel pencil box, just gone off the shelves at the discount stores as the school supplies were thrown away. I replaced the ****y clasp which broke the third use with velcro strips glued on.
Have fun shopping. And maybe building.
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Last edited by indianajo; 13th September 2017 at 03:31 PM.
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Old 13th September 2017, 11:32 PM   #9
MAAC0 is offline MAAC0  Portugal
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I have two of them and also have the schematics. Cheap just 63€ .
The only mod I did on them was replacing the "S-video like" power connector and replaced the tiny power regulator heatsinks with a 2mm aluminium plate covering the bottom of the mixer.


Behringer Xenyx 802 - Thomann UK
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Old 14th September 2017, 02:33 PM   #10
aae is offline aae  United States
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Quote:
Originally Posted by indianajo View Post
What kind of microphone? <snip>
i was just thinking like the type of mic used with 1/8" jacks, like a PC microphone, since i was thinking about the TRRS form factor, just like a standard mobile phone headset

Amazon.com: Professional Condenser Microphone, Venoro Plug & Play Home Studio Condenser Microphone with Tripod for PC , Computer, Phone for Studio Recording, Skype, Games, Podcast, Broadcasting (Black-C): Musical Instruments

or something like that with the included breakout adapter...

i need to keep reading through the document on mixer design, but wouldn't just simple resistors on all the inputs make the output REALLY low? i want the output of the unit to basically be the same as what they would be on input, maybe i don't understand enough about audio design to know if that's possible...

for example, i'd want one source to be plugged into this device and for it to act like nothing more than a passthrough...

then add a 2nd device and have all the levels remain the same

i'm not hellbent on an altoids tin, even if i stay with an external power source, i could definitely get a project box

the main limitations with an off the shelf mixer is that 1, i don't need/want the gain levels for each input, and of course none of them would support what i'm trying to do with the microphone side of things
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