analog summing box - active or passive ??

hi,

I'm planning to build an analog summing box...

a passive unit would be much more easier to build as a passive box...
for gain-makeup I could use a tube preamp (g9) or whatever I want, depending on the sound..

so what are the (technical/audible) advantages of an active unit with opamps and input buffers??

Isn't a design with less parts the best way ??

thanks,
mat

[quote author="matthias"]so what are the (technical/audible) advantages of an active unit with opamps and input buffers??[/quote]

Best isolation between inputs, least loading of sources. Notice I didn't give the expected answer "noise", because anyone who understands "noise gain" of an inverting summing amplifier can sort out that active summing is not necessarily quietest. Like so many other things, the quality of the result is as much or more dependent on the skill and understanding of the designer than on the topology chosen.

Isn't a design with less parts the best way ??

Click to expand...

Not always.

[quote author="rf"] .... (identical outputs) the passive method can work very well especially when followed by a killer preamp for make-up gain. [/quote]

oh yes
:thumb:
and this is where the very simple layouts can really shine. Experiment with resistor values and perhaps even throw away the test gear and calculator ... just use your ears in your method of working with your interfaces.

can be quite a tweak fest

Better still: use the test gear, the calculator, and your ears.

Experimentation that is guided by understanding is a better use of time and energy than blind, random tweaking. Your ears can play tricks on you, too; you will hear a difference when you expect to hear a difference. And whether you realize it consciously or not, you do indeed expect to hear some kind of change when you make a tweak. That's the placebo effect, and the reason why I put little value on uncontrolled "listening tests."

thank you...


I just want to mix 16 audiochannels from my 2 converters
together to one stereo track... no more, no less...

so the best solution for me would be a total simple design of a few summing resistors...???

what do you think...??


mat

http://www.forsselltech.com/summing_buss_schematics.htm

I am going to be building the balanced summing mixer for all of my outboard :wink:

Also:

http://www.forsselltech.com/schematics/Summing%20Buss2.pdf

and

http://www.forsselltech.com/summing%20buss.htm

God bless Fred. :guinness: :sam:

Roll your own with this handy chart.

http://electronicdave.myhosting.net/miscimages/mixnetwork.gif

[quote author="NewYorkDave"]Experimentation that is guided by understanding is a better use of time and energy than blind, random tweaking. [/quote]

I see nothing wrong with you and a mate spending some time just drawing on experience and your ears.
Whether it be a stomp box or a passive speaker x-over ... some inch by inch component replacing can lead to good results.

Then, in the cold hard light of day come back and prove what you think, you discovered the day before.

This is your DIY, enjoy it.
When you come to show other people and substantiate your results is when you have to adhere to rules and call apples ... apples

> anyone who understands "noise gain" of an inverting summing amplifier can sort out that active summing is not necessarily quietest.

It is actually noisier. 6dB for the absurd case of a 1-input "summer". The disadvantage lessens with number of channels, less than 1dB difference at 10 channels.

But as others here have noted: a practical passive summer leaks from one input to any other. If you want to take one source out for processing, you can hear all other sources in that feed. Active summing will leak much less. (Or use "zero impedance" buffers between sources and mixer; you lose simplicity but can gain many advantages.)

Wanted to share some results. I built a passive summing box based on calculations from NYD's chart posted in this thread. 8 stereo pairs, no switching or any such fanciness. 10k load resistors and (I think) 250ohms hung across each output, the calulation was like 281 so that's the closest I could get with the values I had on hand.

Edit: Someone pointed out to me that this picture doesn't show the resistors, which were installed after it was taken. (Thanks Snowbird!)



I just did a listening test using only my MOTU 896. No additional processing, just out of the box, through the passive summer and back to the built-in mic preamps. I then compared the in-the-box mix with the out-of-the-box mix. No changes were made between the two, except the summing method.

The difference was very noticeable and positive on this mix. The seperation between instruments was better and high frequencies extended and clearer. The drumkit, cymbals esp., sounded more realistic and much closer to the original tracks. More air in the vocal tracks. Everything sounded {Insert additional audiophool adjectives here}.

Really happy with these results and excited to try this with all my outboard gear and better preamps. Thanks Dave!

The difference was very noticeable and positive on this mix.

Click to expand...

Any samples for us?

Samuel