Analog Summing

[Michael1]

Hey Guys,
I'd like to build a analog summing amplifier. Perfect would be with tubes. I want to get the typical tube sound, if it's possible.

So I want to know if it's possible to built a summer like the Neumann 475 or LAWO DV975 by myself.

I've searched for some "open source" projects like SymAsym which is about building a mono power amplifier but theres nothing like this about building a summing amplifier.

I studie electrical Engineering so I know what the summer does but not how to built it.

Thanks for your help

 

[kevinkr]

Of course it is, and I feel this belongs in the tube forum so I am going to move it there.

 

[DavesNotHere]

do you want to balance control so you can have an adjustable ratio or straight 50/50.

take a look at the 2 channel mixer (summer) from this rca manual:

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VACUUM TUBE MANUAL​

Two-Channel Audio Mixer Schematic
Electronic Vacuum Tube Circuit

 

[AndreasS]

... Perfect would be with tubes.

Hello Michael,

pls. look here:

Tube summing amp

Regards Andreas

 

[ChrisA]

Hey Guys,
I'd like to build a analog summing amplifier. Perfect would be with tubes. I want to get the typical tube sound, if it's possible.

There is a range of solutions from simple and cheap to complex and not cheap.

The most simple tube mixer is just a simple passive resistor mixer followed by a simple gain stage to make up for the los in the mixer.

A better but more complex design uses one triode for each input channel. Then the outputs are summed as above. Having one tube per input means the inputs don't interact nearly as much. If you want a "tube sound" this is what you want as it has some gain.

To this you can add improvements. (1) the input triode can be followed by a cathode follower. Now you can better drive the resistors (2) you can add a line driver to the resistor mixing network. (3) mix tube types using 12au7 for the followers and 12ax7 for the common cathode gain stages. (4) regulated DC heaters. (5) transformers in inputs and output to handle balanced interconnects for pro-audio use. (6) mu-metal shields on the transformers and shielded coax hookup wires in the signal path.

It depends on if this is a simple home use box or if you are using this for recording how many of the improvements you want. The passive mixer folloed by a gain stag might be good enough and it only takes one tube for a stereo mixer. So decide on how this will be used and what you need.

One thing. that "tube sound" requires gain. a unitiy gain buffer does not give you much.

 

[Chris Hornbeck]

How many channels do you need to sum? This question is critical because it determines what kind of summing junction you'll need to make. Power levels escalate rapidly with number of sources because of noise factors.

All good fortune,
Chris

 

[Michael1]

Thank you first for the links and schematics.
I need only 16 mono channels.

I found this PDF file about the LAWO DV975.

http://audio.kubarth.com/rundfunk/g...97-T+VQA=V]?1%8Y-S4M,RTT7U-C:&5M871I8RYP9&8`

I don't know if it's a good way to recreate this?!?!

Is anyone here who has experience with such a schematic? Is it possible to apply this part "step by step"

 

[Frank Berry]

Are these microphone levels or line levels?

 

[Michael1]

Line Levels....

 

[Chris Hornbeck]

Paul Stamler published an excellent overview of mixer design requirements in _Audio Amateur_ in about 1995, that I haven't seen bettered - might be worth finding.

Link doesn't work, so I can't see your reference, but 16 channels is enough to require some serious thought to dynamic range in the summing amp. Its output must drive a feedback resistor 1/16 as large as the source resistors (more or less) and they must be kept to a reasonably small size because they *all* add noise to the output.

Thanks,
Chris

 

[Michael1]

Sorry, the correct link is Vintage german modules (Neumann, Siemens, TAB, IRT, Lawo, ANT, Eckmiller, Adis, Monitora and Telefunken modules and Braunbuch scans)
and search for LAWO DV975 (Strg + f) and take the schematic.

 

[ThorstenL]

Hi,

I'd like to build a analog summing amplifier. Perfect would be with tubes. I want to get the typical tube sound, if it's possible.

So I want to know if it's possible to built a summer like the Neumann 475 or LAWO DV975 by myself.

I think it would be help if you could elaborate a bit more on your intended application.

The Neumann and Lawo are designed as parts of modular mixing desks specifically for the German Public Radio/TV System which is a bit of a law onto itself. There many areas of performance/operation that may not be needed.

If for example you simply wanted to have a system to downmix eight channels of outputs from a Pro-Audio Sound Box attached to a DAW (e.g. Protools) into a stereo mix and give this a health dash of tube sound before looping it back into the AD converter, the circuit can be very much simpler than LAWO.

If on the other hand you have a project for your classes you may need to list the precise requirements set out in the project brief.

And so on.

Ciao T

 

[Michael1]

Hey,
the purpose for this analog summer is to summarize the digital to analog converted signals of my mixer.

I want the tubes inside, to give the mix a warm touch.

Maybe I transform my "studio" to a analog studio, because I dislike the synthetic, "perfect" digital sound.
My DAW has only the function to record the tracks and in my opinion, my DAW delivers not the quality I wanted after summing the signals.

regards, Michael

 

[ruffrecords]

If you want to sum 16 channels with tubes then there is little point or benefit in thinking about active summing. Passive summing will be more than adequate for your needs and the summing network will not be a noise issue.

Cheers

Ian