"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.

David Looser wrote:


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.

Sorry. As I said, I'm not an expert, I'm here to learn.

In that case you can't use the virtual-ground method.


As I feared. Comment noted.


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


Extra bus is OK. But that would require a separate unit where audio
transfers from the mixer bus to the distribution bus. I wanted to make the
system modular with all units identical. However, it is looking like I need
to provide a "master unit" for my idea to work out.

Your comments/suggestions *are* helpful, BTW.



..

In article ,
TonyL wrote:
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 add two identical signals the level doubles. With non identical
ones it could be anything.

To design a system where you add non identical signals with no apparent
change in level sounds like the Holy Grail...

--
*Men are from Earth, women are from Earth. Deal with it.

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:

If you add two identical signals the level doubles. With non identical
ones it could be anything.

To design a system where you add non identical signals with no
apparent change in level sounds like the Holy Grail...


As others have said, a virtual ground mixer would do the trick but see
David's comments on that.

On Tue, 27 Jan 2009 14:00:41 -0000, "TonyL"
wrote:

Dave Plowman (News) wrote:

If you add two identical signals the level doubles. With non identical
ones it could be anything.

To design a system where you add non identical signals with no
apparent change in level sounds like the Holy Grail...


As others have said, a virtual ground mixer would do the trick but see
David's comments on that.


I think Dave was talking about the overall level changing by virtue of
more channels being added - not the loudness of the individual
channels themselves changing.

d

In article ,
TonyL wrote:
If you add two identical signals the level doubles. With non identical
ones it could be anything.

To design a system where you add non identical signals with no
apparent change in level sounds like the Holy Grail...


As others have said, a virtual ground mixer would do the trick but see
David's comments on that.

Not really. A poorly designed mixer can mean the level on one channel is
effected by the addition of another - regardless of the signal on the
second one. But that's not the same thing.

--
*Lottery: A tax on people who are bad at math.

Dave Plowman London SW
To e-mail, change noise into sound.

"Dave Plowman (News)"


If you add two identical signals the level doubles. With non identical
ones it could be anything.

To design a system where you add non identical signals with no apparent
change in level sounds like the Holy Grail...


** Finally someone ELSE has heard the ****ing penny drop !!!!

The ****wit OP has asked for something obviously impossible.


BTW:

He has totally changed his story in a recent post.



........ Phil

TonyL wrote:

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

You're not kidding !

Graham

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.


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.

Graham

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.