Simple line mixer designs

[Jean-Yvan Fradet]

I have very basic knowledge in electronics.

I am currently looking to build myself a passive simple line mixer. This
is why I read carefully the two pages from Tomi Engdhal at
http://www.tkk.fi/Misc/Electronics/circuits/linesum.html and
http://www.tkk.fi/Misc/Electronics/circuits/linemixer.html. These were
of great interest.

But it raised a few questions. In the section titled "Can I mix more
than two outputs with this kind of circuit ?", Mr Engdhal wrote : "You
you can expand this circuit to more channels if you add one resistor and
one input connector for each new output. Connect them to the circuit in
the same way as the existing inputs.".

If I understood well, a simple line mixer with 3 inputs and 2 outputs
should then look like this :

INPUT 1 -------\/\/\/\---+
---+ R1 10K +------------ OUTPUT 1
| | +----
INPUT 2 -------\/\/\/\---+ |
---+ R2 10K +------------ OUTPUT 2
| | +----
INPUT 3 -------\/\/\/\---+ |
---+ R3 10K |
| |
| (shields) |
+---------------------+

Since my project is to create a passive simple line mixer with 3 inputs
and 3 outputs, I assumed it should look like this :

INPUT 1 -------\/\/\/\---+
---+ R1 10K +------------ OUTPUT 1
| | +----
INPUT 2 -------\/\/\/\---+ |
---+ R2 10K +------------ OUTPUT 2
| | +----
INPUT 3 -------\/\/\/\---+ |
---+ R3 10K +------------ OUTPUT 3
| +----
| (shields) |
+---------------------+

But after reading a few other articles, I guessed it could also look
like this :

INPUT 1 -------\/\/\/\---+
---+ R1 10K +---\/\/\/\-------- OUTPUT 1
| | R4 10K +----
INPUT 2 -------\/\/\/\---+ |
---+ R2 10K +---\/\/\/\-------- OUTPUT 2
| | R5 10K +----
INPUT 3 -------\/\/\/\---+ |
---+ R3 10K +---\/\/\/\-------- OUTPUT 3
| R6 10K +----
| (shields) |
+---------------------------+

My goal is to be able to select to which output a signal would be sent
to. Should it then look like the image below (where -./_- is a switch to
select an output) or with additional resistances before each outputs ?

+--./_--------+
| |
INPUT 1 -------\/\/\/\--+--./_-----+ |
---+ R2 10K | | |
| +--./_--+ | +------ OUTPUT 1
| | | | +---
| | | | | |
| +--./_--------+ |
| | | | | |
INPUT 2 -------\/\/\/\--+--./_-----+ | |
---+ R2 10K | | | | |
| +--./_--+ +--------- OUTPUT 2
| | | | +---
| | | | | |
| +--./_--------+ |
| | | | |
INPUT 3 -------\/\/\/\--+--./_-----+ |
---+ R3 10K | | |
| +--./_--+------------ OUTPUT 3
| +---
| (shields) |
+-----------------------------+

Thanks in advance for your help. And please remember in your responses
that I have very little knowledge in electronics.

Jean-Yvan

 

[BobG]

I am currently looking to build myself a passive simple line mixer.

===================================================
The 'mixing resistors' keep the low output impedance sources from
'loading down'
the adjacent output channel. Usually a mixer has a volume control to
be able
to actually control the mix. Are you mixing mono or stereo sources?
This design
is a 'passive' mixer. Next level up would use opamps to make a
lossless 'active'
mixer with master output level controls and some gain.

 

[Jean-Yvan Fradet]

BobG a écrit :

===================================================
The 'mixing resistors' keep the low output impedance sources from
'loading down'
the adjacent output channel. Usually a mixer has a volume control to
be able
to actually control the mix. Are you mixing mono or stereo sources?
This design
is a 'passive' mixer. Next level up would use opamps to make a
lossless 'active'
mixer with master output level controls and some gain.

The original design is mono. But I intend to double the design to make
it stereo. I would simply double the channels and link all grounds
together. Buttons and eventual potentiometers would be double-channel
for that purpose.

Yes, I might add potentiometers before the R1 to R3 resistors to control
input level. The design for a passive stereo mixer with pots would then
look like the image at the following link :

http://www.geocities.com/jyfradet/images/Mixer2.png

Note that there is an error on this image. The potentiometers input
connections should be on pin 3 and output on pin 2. Ground remains on pin 1.

Still, I need to know if I must add additional resistors or if this
design would be safe.

By the way, if you have a simple design for a do it yourself mixer with
opamps, I might as well go towards that solution.

But the idea behind my initial goal was to avoid adding power supplies
in the first place. It's ok if I lose signal level a bit or if noise is
generated from the resistors. The environment where the device will be
used is noisy anyways...

Jean-Yvan

 

[Jean-Yvan Fradet]

BobG a écrit :

===================================================
The 'mixing resistors' keep the low output impedance sources from
'loading down'
the adjacent output channel. Usually a mixer has a volume control to
be able
to actually control the mix. Are you mixing mono or stereo sources?
This design
is a 'passive' mixer. Next level up would use opamps to make a
lossless 'active'
mixer with master output level controls and some gain.

The original design is mono. But I intend to double the design to make
it stereo. I would simply double the channels and link all grounds
together. Buttons and eventual potentiometers would be double-channel
for that purpose.

Yes, I might add potentiometers before the R1 to R3 resistors to control
input level. The design for a passive stereo mixer with pots would then
look like the image at the following link :

http://www.geocities.com/jyfradet/images/Mixer2.png

Note that there is an error on this image. The potentiometers input
connections should be on pin 3 and output on pin 2. Ground remains on pin 1.

Also, I put a resistor after the switches. It would probably be better
to put only one resitor before the divide to each output selection
buttons...

Still, I need to know if I must add additional resistors or how this
design would be safe.

By the way, if you have a simple design for a do it yourself mixer with
opamps, I might as well go towards that solution.

But the idea behind my initial goal was to avoid adding power supplies
in the first place. It's ok if I lose signal level a bit or if noise is
generated from the resistors. The environment where the device will be
used is noisy anyways...

Jean-Yvan

 

[John Popelish]

BobG a écrit :
The original design is mono. But I intend to double the design to make
it stereo. I would simply double the channels and link all grounds
together. Buttons and eventual potentiometers would be double-channel
for that purpose.

Yes, I might add potentiometers before the R1 to R3 resistors to control
input level. The design for a passive stereo mixer with pots would then
look like the image at the following link :

http://www.geocities.com/jyfradet/images/Mixer2.png

Note that there is an error on this image. The potentiometers input
connections should be on pin 3 and output on pin 2. Ground remains on
pin 1.

Glad to hear it. i don't like volume controls that short
the inputs to ground as you turn the volume down. This can
alter the frequency response of the signal sources. But 1k
resistors are pretty low resistance loads for many signal
sources.

Also, I put a resistor after the switches. It would probably be better
to put only one resitor before the divide to each output selection
buttons...
Yes.

Still, I need to know if I must add additional resistors or how this
design would be safe.

By the way, if you have a simple design for a do it yourself mixer with
opamps, I might as well go towards that solution.

The beauty of opamps is that they unload all sources and
make that loading independent of settings.

 

[Jean-Yvan Fradet]

BobG a écrit :

===================================================
The 'mixing resistors' keep the low output impedance sources from
'loading down'
the adjacent output channel. Usually a mixer has a volume control to
be able
to actually control the mix. Are you mixing mono or stereo sources?
This design
is a 'passive' mixer. Next level up would use opamps to make a
lossless 'active'
mixer with master output level controls and some gain.

The original design is mono. But I intend to double the design to make
it stereo. I would simply double the channels and link all grounds
together. Buttons and eventual potentiometers would be double-channel
for that purpose.

Yes, I might add potentiometers before the R1 to R3 resistors to control
input level. The design for a passive stereo mixer with pots would then
look like the image at the following link :

http://www.geocities.com/jyfradet/images/Mixer3.png

I need to know if I must add additional resistors or if this
design would be safe.

By the way, if you have a simple design for a do it yourself mixer with
opamps, I might as well go towards that solution.

But the idea behind my initial goal was to avoid adding power supplies
in the first place. It's ok if I lose signal level a bit or if noise is
generated from the resistors. The environment where the device will be
used is noisy anyways...

Jean-Yvan

 

[John Popelish]

Jean-Yvan Fradet wrote:
(snip)

Yes, I might add potentiometers before the R1 to R3 resistors to control
input level. The design for a passive stereo mixer with pots would then
look like the image at the following link :

http://www.geocities.com/jyfradet/images/Mixer3.png

I need to know if I must add additional resistors or if this
design would be safe.

By the way, if you have a simple design for a do it yourself mixer with
opamps, I might as well go towards that solution.

But the idea behind my initial goal was to avoid adding power supplies
in the first place. It's ok if I lose signal level a bit or if noise is
generated from the resistors. The environment where the device will be
used is noisy anyways...

I am assuming that you want to cross connect various
patterns of inputs to various patterns of outputs. This
design will cross connect a pair of inputs, if that pair is
selected to go to one output. Then if either of those
inputs is selected for another output, you will have both of
them go there, since they are connected together by the
first output setup. Is that effect okay with you?

 

[Jean-Yvan Fradet]

John Popelish a écrit :

Jean-Yvan Fradet wrote:
(snip)

I am assuming that you want to cross connect various patterns of inputs
to various patterns of outputs. This design will cross connect a pair
of inputs, if that pair is selected to go to one output. Then if either
of those inputs is selected for another output, you will have both of
them go there, since they are connected together by the first output
setup. Is that effect okay with you?

I am not sure I understand your question since I am not that fluid in
English. So I will explain a bit more my idea. Tell me if that answers
your question.

If there is a signal in any inputs, I want it to be sent to any one or
many outputs.

Let's say I have 2 cd players connected to input 1 and 2. I may want cd
1 to play only on output 1, 2 or 3. I may as well want cd 1 to play on
two of the outputs or to all 3 of them.

Now let's say I use cd 2 as well. Cd 1 can be sent to output 1 and 2 and
cd 2 to output 2 and 3. Output 2 would have a mix of cd 1 and cd 2 while
output 1 only plays cd 1 and output 3 only plays cd 2.

The three inputs would very rarely be sent simultaneously to the same
outputs. Also, I see almost no occasions on my setup where two or three
inputs would be sent to all three outputs simultaneously. But I want to
make sure that if one or both scenario happens (probably by accident)
nothing bad would result.

 

[Jean-Yvan Fradet]

Jean-Yvan Fradet a écrit :

John Popelish a écrit :

I am not sure I understand your question since I am not that fluid in
English. So I will explain a bit more my idea. Tell me if that answers
your question.

If there is a signal in any inputs, I want it to be sent to any one or
many outputs.

Let's say I have 2 cd players connected to input 1 and 2. I may want cd
1 to play only on output 1, 2 or 3. I may as well want cd 1 to play on
two of the outputs or to all 3 of them.

Now let's say I use cd 2 as well. Cd 1 can be sent to output 1 and 2 and
cd 2 to output 2 and 3. Output 2 would have a mix of cd 1 and cd 2 while
output 1 only plays cd 1 and output 3 only plays cd 2.

The three inputs would very rarely be sent simultaneously to the same
outputs. Also, I see almost no occasions on my setup where two or three
inputs would be sent to all three outputs simultaneously. But I want to
make sure that if one or both scenario happens (probably by accident)
nothing bad would result.

Anyone else can help me ? I still have no answer to my question about my
passive audio mixer...

 

[John Popelish]

Jean-Yvan Fradet a écrit :
Anyone else can help me ? I still have no answer to my question about my
passive audio mixer...

The case that worries me is:

Output 1 is combination of inputs 1 and 2.

Output 2 is just input 1.

But selecting both input 1 and input 2 for output 1 connects
those two inputs together. So selecting only one of them
for output 2 provides the pair of them, not just one of them
as output 2. Once inputs are mixed (connected together) to
provide a mixed output, they cannot be unmixed and used
separately, also.

Adding resistors between the volume control outputs and
selector switches helps a bit, Using a pair of inputs
together for one output then allows a less mixed version of
the mixed inputs to be available for other outputs.

A purely resistive network does not allow both mixed and
unmixed versions of the input signals at two different
outputs. Mixing is not isolated.