Omnimaga
General Discussion => Technology and Development => Other => Topic started by: Sorunome on October 14, 2014, 01:51:30 pm
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Yup, i'm making a sound mixer. Most of you probably know already anyways due to chat :P
Also, keoni helped me a lot with it so far.
(http://img.ourl.ca/CIMG4314-small.jpg)
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Looking good :) I see there are 3 pots on there. 2 channels and 1 master I assume?
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Looking good :) I see there are 3 pots on there. 2 channels and 1 master I assume?
Yep!
By now there are 4 pots, as i already wired up all but a pot for channel 3.
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It reminds me of one of Keoni's builds. Looks like some mad scientist stuff going on there. ;D
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It reminds me of one of Keoni's builds. Looks like some mad scientist stuff going on there. ;D
But that isn't much, only some amps, resistors and pottys :P
Anyways, thanks ^.^
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My brother is into audio electronics, and he was wondering what precisely is it doing to mix the channels? Are the ICs just for amping or something? Also if you have a schematic that'd be cool :D
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This looks really cool (and complicated :P)! Good work :)
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My brother is into audio electronics, and he was wondering what precisely is it doing to mix the channels? Are the ICs just for amping or something? Also if you have a schematic that'd be cool :D
the ICs are indeed just amps. The key to mixing the channels is to prevent the input of one "going" into the input of another, you can do that by simply putting in resistors before merging them.
And I have a schematic.....ok, keoni made that schematic :P http://img.ourl.ca/schematic1.pngThis looks really cool (and complicated :P)! Good work :)
Thanks!
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It's basically a bunch of inverting amps with an ajustable resistor in the feedback loop. The outputs of those are then summed by an inverting summing amplifier. The result is all of the channels coming out non-inverted again. (Not that it matters most of the time though.)
The amps make sure there is no crosstalk between channels. I should have made that schematic in CAD software. It looks so ugly
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Haha, but it serves purpose ;)
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I completely missed this due to being sick around when this got posted, but it's cool to see you're into sound hardware stuff too. :)
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Hehe :P
I'm waiting for parts from china.....
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You can also do this digitally, without pots, by using some analog multiplexers and digital pots.
I built a preamp consisting of a TDA7439 and TEA6420, it sounds pretty impressive, although it's not complex in any way.
You could easily combine it with some PT2257 and control the whole thing over I²C with a MCU with the added bonus of remote control and you can also save/restore some settings.
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well i wanted to be able to control that thing without the need of a computer ;)
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That looks pretty cool. Reminds me I have an electronics project to post here as well.
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well i wanted to be able to control that thing without the need of a computer ;)
I can only recommend that you read a bit about MCUs, they're really useful for this kind of stuff ;)
(MCU = Micro Controller Unit = Mikrocontroller, in case that wasn't clear)
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I have stereo now!
And and better handling of wiring to the potentiometers!
And a cinch port thingy!
Images:
This is the back side of the cinch port thingy:
(https://img.ourl.ca/CIMG4365.JPG)
And now with plugs:
(https://img.ourl.ca/CIMG4366-small.jpg)
And the top:
(https://img.ourl.ca/CIMG4367-small.jpg)
Trust me, soldering those headers was a PITA
The boardy-ness:
(https://img.ourl.ca/CIMG4368-small.jpg)
And the volume regulators integrated into my knex desk stand my monitor is standing on:
(https://img.ourl.ca/CIMG4370-small.jpg)
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Cool beans! Those hama cables are fancy :3
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I got them for free, just like all my other cinch cables :P
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Sooooo, i just noticed a little issue that makes no sense to me:
Input A is my raspberry pi
Input B is my laptop
If I connect only input A then everything is fine
If I connect only input B then everything is fine
If I connect A and B then I get static noise on B, but not on A
Is it a issue that I just connect all the grounds? But if I split grounds I get even greater static noise, perhaps they need resistors or something?
EDIT: I mean connecting the grounds in such a way, would that help to prevent static noise?
(https://img.ourl.ca/grounds.png)
If so, which value should the resistors have? 10k?
EDIT2: Also, when regulating the channels, the static noise also gets louder/quieter, which is actually weird as the volume control only effects the signal.
EDIT3: so now I connected the ground with a power socket ground and the static decreased a lot, but now there is still some, but the weird thing is that the static increases if i decrease the volume, that makes absolutely no sense!
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This is probably caused by a ground loop somewhere in your system.
http://en.wikipedia.org/wiki/Ground_loop_(electricity)
You cannot isolate grounds using resistors. The grounds are still electrically connected this way. Instead you could try using audio transformers or optocouplers to electrically isolate the signals. This technique is commonly used to get rid of ground loop interference.
Instead of isolating grounds you could also use differential inputs for the amplifiers. This requires an extra feedback loop on all input amplifiers.
http://en.wikipedia.org/wiki/Differential_amplifier#Operational_amplifier_as_differential_amplifier
With this method the voltage reference is no longer common ground, but the signal ground. You no longer need to connect all signal grounds together. Edit: They're not completely electrically isolated but you can set a very high input impedance, so they can barely affect eachother.
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Thanks, I found another ground loop - either my laptop or my desktop sound card is designed badly: you can create a static noise on line out if they have a common mic on line in.
EDIT: But how would I merge then? As I have multiple signal grounds instead of one common ground
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Thanks, I found another ground loop - either my laptop or my desktop sound card is designed badly: you can create a static noise on line out if they have a common mic on line in.
So you have essentially a T-connector for your microphone? That's not really a good idea, noise won't be the only issue here. You can try capacitive coupling, around 330n should be enough.
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Thanks, I found another ground loop - either my laptop or my desktop sound card is designed badly: you can create a static noise on line out if they have a common mic on line in.
So you have essentially a T-connector for your microphone? That's not really a good idea, noise won't be the only issue here. You can try capacitive coupling, around 330n should be enough.
That only reduces any DC offset and other low frequency interference. The signal grounds should be isolated from the power supply's ground and most importantly from eachother.
Here is some more reading material:
http://books.google.nl/books?id=PvKPEFu2PVkC&pg=PA344&redir_esc=y#v=onepage&q&f=false
This differential input also rejects any common mode noise: Static noise introduced in the cable. Because the difference between the two signal wires is amplified any noise common to the wires is not amplified.
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Thanks, I found another ground loop - either my laptop or my desktop sound card is designed badly: you can create a static noise on line out if they have a common mic on line in.
So you have essentially a T-connector for your microphone? That's not really a good idea, noise won't be the only issue here. You can try capacitive coupling, around 330n should be enough.
That only reduces any DC offset and other low frequency interference. The signal grounds should be isolated from the power supply's ground and most importantly from eachother.
Here is some more reading material:
http://books.google.nl/books?id=PvKPEFu2PVkC&pg=PA344&redir_esc=y#v=onepage&q&f=false
This differential input also rejects any common mode noise: Static noise introduced in the cable. Because the difference between the two signal wires is amplified any noise common to the wires is not amplified.
If you design it correctly, you won't need a differential signal for audio. Just make sure that not more than one device is earthed.
You definitely need to connet all signal grounds together, otherwise the shielding becomes useless and will in fact introduce even more noise.
The decoupling is needed to make sure that both input devices don't interfere with each other, to get the best signal out of it you'd even have to calculate some resistors in series with the caps for impedance matching (audio is normally about 200 or 400 Ohms).
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Shielding ground and signal ground are not the same thing. They are typically connected to eachother with an inductor, so the current is limited and high-frequency noise is rejected.
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PCB GOGOGO!!!
(https://img.ourl.ca/P1020883-small.jpg)
I know it looks like crap but it is my first PCB.
Also I just noticed that my 10K stereo potentiometers are freaking crap.......anyone know good ones to recommend?
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Congrats on soldering your first board!
This looks a lot better than our project group's preamplifier. That thing had long airwires going all over the place.
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Congrats on soldering your first board!
This looks a lot better than our project group's preamplifier. That thing had long airwires going all over the place.
Thanks! The back is even more messy, though :P
Edit: here it is!
(https://img.ourl.ca/P1020889-small.jpg)
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That's not bad for a first. You haven't seen my early work yet :P
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So I just ordered some digital potentiometers for some dark magic
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Make sure that they can deal with the +12 -12v supply before you hook them up.
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That sounds fun :3 I need to build an amp board for my pc at somepoint. But I will probably use digital pots and make it a USB HID controllable device ;) So I do not have to fiddle with manual pots :D
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Make sure that they can deal with the +12 -12v supply before you hook them up.
Couldn't I power them only between the 0 and +12V or something? That sounds fun :3 I need to build an amp board for my pc at somepoint. But I will probably use digital pots and make it a USB HID controllable device ;) So I do not have to fiddle with manual pots :D
Yeah the main reason why i got digital pots is that my manual ones are so shitty that the resistance randomly increases by more than double from time to time x.x
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You can clean potentiometers by spraying some wd40 in the little hole at the top.
You need digital potentiometers with a dual power supply because the signal voltage may drop below 0V. The potentiometer will cut off the signal and might even get damaged. You could use +6 and -6v supply across the device. It's effectively 12v but the center is shifted. For this you need additional regulators. You could also make the entire system run from a single supply, but it requires some trickery.
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You can clean potentiometers by spraying some wd40 in the little hole at the top.
You need digital potentiometers with a dual power supply because the input voltage may drop below 0V. You could also use +6 and -6. For this you need additional regulators. You could also make the entire system run from a single supply, but it requires some trickery.
The issue is something mechanical, that the little metal nob thingy is detaching from the resistor part thingy, i blame china quality :P
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Hmm I have tons of china quality pots and they seem to hold up fine (after cleaning)
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Ok, I got some trouble now, my Digital Potentiometers arrived and i set them to the exact same resistance value as the master channel of my sound mixer, i measured the resistance to make absolutely sure it matches the one of the analog resistor. And when using the digital one there is no sound coming out at all! D:
the digital pots are MCP42010
The power supply of the controlling unit (arduino + digital potentiometers) and the sound mixer (OP-Amps) is a different one.