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DIY Sound Mixer

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Posted · Original PosterOP

Hey guys,

 

I want do create an active sound mixer to use with my PC's line in (to connect my PS3, my other PC, my phone, etc.). The thing is, I've searched online for circuits and I've only found passive mixers (and I'd prefer active to reduce attenuation from components inside the circuits and the cables themselves).

 

If there's a cheap mixer around for sale (In the EU, preferably), I'll also consider that.

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There is free ones out there software wise like Voicemeeter which is a very common one that a lot of people use. This might do what you want/need. 


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Posted · Original PosterOP
7 minutes ago, legacy99 said:

There is free ones out there software wise like Voicemeeter which is a very common one that a lot of people use. This might do what you want/need. 

It's something like that but, in my case, I need a hardware mixer, because I want to get the sound from multiple analog inputs (as I stated, my PS3 and phone are some examples) and I only have one line-in

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PSU Tier List Thread

 

"The Angry Cup o` Joe" v2.0

| Ryzen 1800x @ 4.0ghz | Asrock X370 Taichi | MSI GTX 1070 Gaming X | Flare X 14-14-14-34 3200mhz 32gb | Full Custom Water Cooling Loop | 512gb Intel 600p | 

| Samsung 850evo 250gb | 2x 3tb Seagate Drive | Phantex Enthoo Evolv | Custom front cover from mnpctech.com | Custom Top cover from Modmymods.com |

| EVGA G2 750w PSU | 3x Corsair ML140 Pro White LED case fans | 3x Corsair ML120 Pro White LED Case Fans | Cablemod White LED Magnetic strips 2x 60cm |

https://imgur.com/a/WCwxk

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21 hours ago, sup its ya daddy boi said:

t's something like that but, in my case, I need a hardware mixer, because I want to get the sound from multiple analog inputs (as I stated, my PS3 and phone are some examples) and I only have one line-in

Wait, do you need a mixer or a source switch?

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On 2/28/2018 at 11:49 AM, sup its ya daddy boi said:

I want do create an active sound mixer to use with my PC's line in (to connect my PS3, my other PC, my phone, etc.). The thing is, I've searched online for circuits and I've only found passive mixers (and I'd prefer active to reduce attenuation from components inside the circuits and the cables themselves).

How is the audio getting from the sources to the destination? Are you using audio only cables?

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You could build an Op-Amp summer with multiple inputs and use potentiometers to control the gain on a per input basis and at the final output.  Do you have any electronics experience?

The circuit would be fairly simple to build, you'll just have to make sure you select op-amps that have linear-phase for audio frequencies and you may need to build buffer stages to isolate the inputs from each other.  You could also build in peak limiters using diodes.

 

I bet there are off the shelf parts specifically for audio that already a lot this build into an IC.  Another thing you could do is buy a cheap DSP development board with multiple analog inputs and program your own digital mixer.

 

Plenty of ways to get this accomplished.  If you're aiming for quality, it might be easier and cheaper to just purchase a turn-key solution, but this could potentially be a fun project.

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Posted · Original PosterOP
On 12/03/2018 at 4:51 AM, straight_stewie said:

How is the audio getting from the sources to the destination? Are you using audio only cables?

Yes, I'm using the RCA cables from the ps3 and jack cables on my PC and smartphone. The thing is, I want to have them all connected at once and be able to control the volume.

18 hours ago, ShredBird said:

You could build an Op-Amp summer with multiple inputs and use potentiometers to control the gain on a per input basis and at the final output.  Do you have any electronics experience?

The circuit would be fairly simple to build, you'll just have to make sure you select op-amps that have linear-phase for audio frequencies and you may need to build buffer stages to isolate the inputs from each other.  You could also build in peak limiters using diodes.

 

I bet there are off the shelf parts specifically for audio that already a lot this build into an IC.  Another thing you could do is buy a cheap DSP development board with multiple analog inputs and program your own digital mixer.

 

Plenty of ways to get this accomplished.  If you're aiming for quality, it might be easier and cheaper to just purchase a turn-key solution, but this could potentially be a fun project.

I'll try, thanks. And no, I don't have much electronics experience, but I usually do well at creating circuits if I have schematics and guidelines.

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1 hour ago, sup its ya daddy boi said:

Yes, I'm using the RCA cables from the ps3 and jack cables on my PC and smartphone. The thing is, I want to have them all connected at once and be able to control the volume.

There are many boards out there that can do this, but they are usually fairly expensive and geared towards professionals (or atleast, dedicated hobbyists). The cheapest ones I've found are priced at $100, which isn't bad, but you only get stereo, and only a few channels. Also, no software control.

The best I can tell you to do is to google "source mixer". If you want anything more than stereo, or if you want software control, get ready to spend $$$.

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On 2/28/2018 at 6:49 PM, sup its ya daddy boi said:

Hey guys,

 

I want do create an active sound mixer to use with my PC's line in (to connect my PS3, my other PC, my phone, etc.). The thing is, I've searched online for circuits and I've only found passive mixers (and I'd prefer active to reduce attenuation from components inside the circuits and the cables themselves).

 

If there's a cheap mixer around for sale (In the EU, preferably), I'll also consider that.

It depends on how picky you are. A simple active mixer with a opamp like the NE5532 should work pretty well...

pNc4H.gif

 

But probably won't satisfy audiophiles.

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7 hours ago, Unimportant said:

It depends on how picky you are. A simple active mixer with a opamp like the NE5532 should work pretty well...

pNc4H.gif

 

But probably won't satisfy audiophiles.

Yeah, this is inline with what I was thinking.  There is a lot you can do to improve a circuit like this if you want even more fidelity, like building input buffers, current buffered output.  You could do matched potentiometers or even digital pots for precise control.

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Posted · Original PosterOP
On 13/03/2018 at 2:56 PM, straight_stewie said:

There are many boards out there that can do this, but they are usually fairly expensive and geared towards professionals (or atleast, dedicated hobbyists). The cheapest ones I've found are priced at $100, which isn't bad, but you only get stereo, and only a few channels. Also, no software control.

The best I can tell you to do is to google "source mixer". If you want anything more than stereo, or if you want software control, get ready to spend $$$.

My objective is simply clean sound, I don't need any amplification or effects (so, I don't want any EQ's) and yes, it's stereo.

On 13/03/2018 at 6:00 PM, Unimportant said:

It depends on how picky you are. A simple active mixer with a opamp like the NE5532 should work pretty well...

pNc4H.gif

 

But probably won't satisfy audiophiles.

That seems nice, I'll try it out, thanks! :)

On 14/03/2018 at 2:01 AM, ShredBird said:

Yeah, this is inline with what I was thinking.  There is a lot you can do to improve a circuit like this if you want even more fidelity, like building input buffers, current buffered output.  You could do matched potentiometers or even digital pots for precise control.

Do input buffers increase sound volume or are they used to mantain quality?

And I'll check the pots part out, thanks! :) 

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14 hours ago, sup its ya daddy boi said:

Do input buffers increase sound volume or are they used to mantain quality?

They make the input impedance independent of the volume setting on the input potentiometers. In the unbuffered circuit above, the input impedance will be a function of the potentiometer setting and it's accompanying series resistor to virtual ground (R1, R2, R3). A non-inverting opamp buffer circuit would pose such a high input impedance that you can ignore it and the input impedance of the mixer would effectively always be the pot's resistance to ground value.

 

That *could* have a effect on audio quality, depending on volume pot setting, if the device outputting the audio has some averse reaction to a changing input impedance of whatever it is driving (unlikely).

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@sup its ya daddy boi, just some things to keep in mind when building this: 

  • The more resistance there is in the circuit, the more thermal noise there will be.  Usually you need a ratio of resistance to determine the gain (this will effectively set your volume).  If you're aiming for a gain of 10, you could do something like 10k Ohm / 1 Ohm, or 100 Ohm / 10 Ohm.  Both of these ratios equal 10 and will result in the same gain, however the first ratio will be noisier.  The second ratio will be less noisy, but more power hungry.
  • You can choose any op-amp for this task as long as the datasheet says it has "linear phase" for audio frequencies.  Each frequency has a delay as it passes through the amp, linear phase just means it's the same for all frequencies.  This will make sure you don't have any temporal distortion.  If the op-amp says it's specifically for audio then that it's likely taken that into account in its design.  You will also have to pay attention to the maximum output current as this will limit the total amount of power your amplifier can put out.  If it's not sufficient you can build a current buffer or try another op-amp.  I would breadboard this before committing a design.
  • The design above is an inverting design, which means you will have to pay attention to how you wire up your headphone jack, otherwise your drivers will be pushing when they're supposed to pull and vice versa.  It's possible to build another version of this circuit using a non-inverting amp which has better input impedance, but if you use an input buffer it won't matter.
  • Noise in your power source will bleed into your amp.  Most op-amps will list a "power supply rejection ratio".  You'll want a good PSRR and a clean power source.  If you're planning to run this from a DC transformer, you'll want to consider using a "floating ground" to get your voltage to swing both positive and negative.  What I mean by this is, for example, if you have a 12 V supply, you would split it and use 6 V as ground, then feed 12 V and 0 V as your positive and negative voltages to your op-amp.  You would set 6 V as your "ground" (better called common than ground in this case) for your headphone jack as well.

Lots of things to think about, if you're just learning electronics for the first time, best to start with a breadboard, some resistors and some LM741s and play around with with building op-amp circuits to start.

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5 hours ago, ShredBird said:
  • The design above is an inverting design, which means you will have to pay attention to how you wire up your headphone jack, otherwise your drivers will be pushing when they're supposed to pull and vice versa.  It's possible to build another version of this circuit using a non-inverting amp which has better input impedance, but if you use an input buffer it won't matter.

That does not matter. Your ears can't distinguish sound from inverted sound. One just needs to make sure all channels are in phase, in a stereo system for example. So you can invert none of the channels or all of the channels. In fact, many amplifiers invert because it can make implementing negative feedback simpler.

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18 hours ago, Unimportant said:

That does not matter. Your ears can't distinguish sound from inverted sound. One just needs to make sure all channels are in phase, in a stereo system for example. So you can invert none of the channels or all of the channels. In fact, many amplifiers invert because it can make implementing negative feedback simpler.

You're right, although said detail could be interesting from an educational perspective if just learning about op-amps in general.  Maybe OP wants to build a noise cancellation circuit next. :P

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Posted · Original PosterOP
On 3/26/2018 at 3:27 AM, ShredBird said:

@sup its ya daddy boi, just some things to keep in mind when building this: 

  • The more resistance there is in the circuit, the more thermal noise there will be.  Usually you need a ratio of resistance to determine the gain (this will effectively set your volume).  If you're aiming for a gain of 10, you could do something like 10k Ohm / 1 Ohm, or 100 Ohm / 10 Ohm.  Both of these ratios equal 10 and will result in the same gain, however the first ratio will be noisier.  The second ratio will be less noisy, but more power hungry.
  • You can choose any op-amp for this task as long as the datasheet says it has "linear phase" for audio frequencies.  Each frequency has a delay as it passes through the amp, linear phase just means it's the same for all frequencies.  This will make sure you don't have any temporal distortion.  If the op-amp says it's specifically for audio then that it's likely taken that into account in its design.  You will also have to pay attention to the maximum output current as this will limit the total amount of power your amplifier can put out.  If it's not sufficient you can build a current buffer or try another op-amp.  I would breadboard this before committing a design.
  • The design above is an inverting design, which means you will have to pay attention to how you wire up your headphone jack, otherwise your drivers will be pushing when they're supposed to pull and vice versa.  It's possible to build another version of this circuit using a non-inverting amp which has better input impedance, but if you use an input buffer it won't matter.
  • Noise in your power source will bleed into your amp.  Most op-amps will list a "power supply rejection ratio".  You'll want a good PSRR and a clean power source.  If you're planning to run this from a DC transformer, you'll want to consider using a "floating ground" to get your voltage to swing both positive and negative.  What I mean by this is, for example, if you have a 12 V supply, you would split it and use 6 V as ground, then feed 12 V and 0 V as your positive and negative voltages to your op-amp.  You would set 6 V as your "ground" (better called common than ground in this case) for your headphone jack as well.

Lots of things to think about, if you're just learning electronics for the first time, best to start with a breadboard, some resistors and some LM741s and play around with with building op-amp circuits to start.

Thanks, I'll dive into it. It was very exhaustive (in a good way) and informative.

On 3/26/2018 at 9:19 AM, Unimportant said:

That does not matter. Your ears can't distinguish sound from inverted sound. One just needs to make sure all channels are in phase, in a stereo system for example. So you can invert none of the channels or all of the channels. In fact, many amplifiers invert because it can make implementing negative feedback simpler.

I don't know much about inverted sound but I'll dive deeper on how that works when I get the chance.

18 hours ago, ShredBird said:

You're right, although said detail could be interesting from an educational perspective if just learning about op-amps in general.  Maybe OP wants to build a noise cancellation circuit next. :P

Same goes to that reply

 

On 3/18/2018 at 5:09 PM, Unimportant said:

They make the input impedance independent of the volume setting on the input potentiometers. In the unbuffered circuit above, the input impedance will be a function of the potentiometer setting and it's accompanying series resistor to virtual ground (R1, R2, R3). A non-inverting opamp buffer circuit would pose such a high input impedance that you can ignore it and the input impedance of the mixer would effectively always be the pot's resistance to ground value.

 

That *could* have a effect on audio quality, depending on volume pot setting, if the device outputting the audio has some averse reaction to a changing input impedance of whatever it is driving (unlikely).

Thanks for the info for that as well

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