Phil Allison wrote:


** I take it you want a mixer whose gain is a function of the number
of inputs actually connected.


I want to add/remove inputs without having to adjust levels.

So forget using the "virtual earth" summing method.

Feed each input to a high impedance summing point via a suitable
resistor ( like 10k ohms) and the job is done.


Tried that....

As each new source is connected, the gain will drop in proportion to
the number.


...and the level fell as each new input was added. Which was why I was
looking at a virtual ground input instead.

Folks, I seem to be having problems communicating what I'm trying to do.
Here's the requirements:

I have a single audio conductor (+ground), length from 6 feet upwards.

A variable number of inputs are to be fed *to* the conductor at different
points along its length.

A variable number of outputs are to be taken *from* the conductor at
different points along it's length.

Level changes on the outputs to be zero, or small, as inputs/outputs
added/removed.

How would you do it ?

Eeyore wrote:
TonyL wrote:

Here's a problem that is causing me some grief. I'm rusty with
electronics these days, perhaps the experts in here can give me some
pointers ?

I want to combine the audio outputs of an unspecified number of
op-amps, say 2-20. A simple mixer would do the trick...except I need
the resulting summed audio level to be constant as outputs are
connected to and disconnected from the system.

Absolutely constant ? You need a thing called a hard limiter on the
mixer output.


Not absolutely...reasonably. Limiting has occurred to me but I wanted to
explore other options before I looked at active limiting. Hoping there was
some clever trick that would keep the levels constant such as an adaptation
of the virtual ground idea.


I know a virtual ground is the standard method to mix audio but
there's another wrinkle here. I also need to send the summed audio
signal to an unspecified number of outputs, between 2 and 20.

You need a distribution amplifier for that.

All readily available off the shelf for a price.


A DA would work if all of the outputs were to branch from a single location.
In the proposed setup, outputs were to be taken from various locations along
a single conductor.

The unexpected difficulties may force me to reconsider the "daisy chain"
configuration (which had lots of practical advantages) and go for a central
mixer/distribution amp instead.

"TonyL"


Folks, I seem to be having problems communicating what I'm trying to do.


** Only cos you are a complete mental retard.


Here's the requirements:

I have a single audio conductor (+ground), length from 6 feet upwards.

A variable number of inputs ....



** You have to specify the NATURE of the input signals !!!

EVERYTHING depends on that and you have not supplied ONE tiny clue !

----------------------------------------------------------------------------------------



A variable number of outputs are to be taken *from* the conductor at
different points along it's length.

Level changes on the outputs to be zero, or small, as inputs/outputs
added/removed.


** The question is totally meaningless without a description of what these
input signals are like.

Are they tones, music, voices or what ??

Do they vary in level over time or not ?

Are the signals correlated - ie originate from a common source ?





...... Phil

Phil Allison wrote:

** You have to specify the NATURE of the input signals !!!


Speech

"Tony the Total Lummox "

Phil Allison wrote:

** You have to specify the NATURE of the input signals !!!


Speech


** Huh - you snipped my post like a rabid maniac and posted just one word
in reply when you are asked for proper details ?


What about the other questions - eh ???

" Do they vary in level over time or not ? "

" Are the signals correlated - ie originate from a common source ? "

PLUS:

Do you expect there to be NO level change when a new source is connected
even when that source is silent at the time ?
---------------------------------------------------------------------------------------------------------------------------------------


The problem is, ****ing RETARDS like YOU are totally INCAPABLE of
specifying a technical problem in technical terms.

Sooooooo, for ** ****'S SAKE **

TELL US what are YOU trying to achieve !!

Then WE can figure out the requirements.





...... Phil

On Tue, 27 Jan 2009 11:22:30 -0000, "TonyL"
wrote:

Phil Allison wrote:


** I take it you want a mixer whose gain is a function of the number
of inputs actually connected.


I want to add/remove inputs without having to adjust levels.

So forget using the "virtual earth" summing method.

Feed each input to a high impedance summing point via a suitable
resistor ( like 10k ohms) and the job is done.


Tried that....

As each new source is connected, the gain will drop in proportion to
the number.


..and the level fell as each new input was added. Which was why I was
looking at a virtual ground input instead.

Folks, I seem to be having problems communicating what I'm trying to do.
Here's the requirements:

I have a single audio conductor (+ground), length from 6 feet upwards.

A variable number of inputs are to be fed *to* the conductor at different
points along its length.

A variable number of outputs are to be taken *from* the conductor at
different points along it's length.

Level changes on the outputs to be zero, or small, as inputs/outputs
added/removed.

How would you do it ?







If you know the maximum number of inputs you will need, you can do
this by putting an op-amp buffer on each input, then putting a
resistor in series with each output to feed the common inner of the
coax. Set the gain of the buffer so it cancels the loss caused by all
those commoning resistors that appear in parallel with each other. As
long as the outputs feed a high impedance, you can connect as many of
those as you like.

d

"TonyL" wrote in message
...

Folks, I seem to be having problems communicating what I'm trying to do.
Here's the requirements:

I have a single audio conductor (+ground), length from 6 feet upwards.

A variable number of inputs are to be fed *to* the conductor at different
points along its length.

A variable number of outputs are to be taken *from* the conductor at
different points along it's length.

Ah!, you are trying to use the same conductor as an input mixing bus *and*
as an output distribution bus at the same time, you didn't make that clear.
In that case you can't use the virtual-ground method.

Level changes on the outputs to be zero, or small, as inputs/outputs
added/removed.

How would you do it ?

I'd forget about using the same conductor for both purposes. Have a
virtual-ground input mixing bus and a separate output bus.

David.

Don Pearce Pommy Retard


If you know the maximum number of inputs you will need, you can do
this by putting an op-amp buffer on each input, then putting a
resistor in series with each output to feed the common inner of the
coax. Set the gain of the buffer so it cancels the loss caused by all
those commoning resistors that appear in parallel with each other. As
long as the outputs feed a high impedance, you can connect as many of
those as you like.


** TOTAL ******** !!

The geriatric **** has no clue whatever what the question is about.

Cos the COMPLETELY ASININE OP does not wanna say.





....... Phil

On Tue, 27 Jan 2009 12:26:40 GMT, (Don Pearce) wrote:

On Tue, 27 Jan 2009 11:22:30 -0000, "TonyL"
wrote:

Phil Allison wrote:


** I take it you want a mixer whose gain is a function of the number
of inputs actually connected.


I want to add/remove inputs without having to adjust levels.

So forget using the "virtual earth" summing method.

Feed each input to a high impedance summing point via a suitable
resistor ( like 10k ohms) and the job is done.


Tried that....

As each new source is connected, the gain will drop in proportion to
the number.


..and the level fell as each new input was added. Which was why I was
looking at a virtual ground input instead.

Folks, I seem to be having problems communicating what I'm trying to do.
Here's the requirements:

I have a single audio conductor (+ground), length from 6 feet upwards.

A variable number of inputs are to be fed *to* the conductor at different
points along its length.

A variable number of outputs are to be taken *from* the conductor at
different points along it's length.

Level changes on the outputs to be zero, or small, as inputs/outputs
added/removed.

How would you do it ?







If you know the maximum number of inputs you will need, you can do
this by putting an op-amp buffer on each input, then putting a
resistor in series with each output to feed the common inner of the
coax. Set the gain of the buffer so it cancels the loss caused by all
those commoning resistors that appear in parallel with each other. As
long as the outputs feed a high impedance, you can connect as many of
those as you like.

d


Circuit diagram here - it doesn't matter how many inputs you plug in
as long as the op amps are all there. The gain will stay constant.

http://81.174.169.10/odds/multi_cable.pdf

As usual, ignore the Australian.

d

Don Pearce wrote in message news:498105de.430631890@localhost...

Circuit diagram here - it doesn't matter how many inputs you plug in
as long as the op amps are all there. The gain will stay constant.

http://81.174.169.10/odds/multi_cable.pdf

The best solution to the OPs problem so far. But he does need to know in
advance how many inputs he wants. I got the impression he wanted to be able
to add, or subtract, inputs at will without causing any change in gain,
which, of course, he can't do with that topology.

As usual, ignore the Australian.

Absolutely!

David.