V475 translation + summing network

So, I know that there are many many threads about passive summing networks out there... but as one of the menbers here posted a link where I found some info on my V475/2C modules, I thought now was the time to start the passive mixer I always wanted to build with those modules. The problem is that I need your help, because I can´t even read the german paper. It´s here:

http://www.audiosonic.de/pdf/V475.pdf

So, could someone translate the important specs for me, like input impedance, gain, etc... I tried to guess, but I wasn´t exactly succesfull, I think.

If you can give me any directions about the summing network to put before this card, it´s very welcome. I´m still studying the many NYDave notes about passive network design and I´m going to try a simple balanced network, input attenuator, then a panpot, then directly to L and R. No inserts, no auxialiars, no nothing.

Thanks for the link, and thanks for any input. :thumb:

Input impedance: 3-4 Ohm

Gain dependent on the R(G)'s:
2xinfinite ohms (not mounted) = +6dB
2x13K = 0dB
2x 0 Ohms (shorted) = -12dB

Table at page 3:

Gain versus R(G)
Signat-to-noise versus mix resistor value

Jakob E.

Thaks Jakob! But... what kind of summing unit is this? inpt impedance 3-4 ohms??? Gain maximum 6dB??? :shock:

Not what I was thinking it was.

So, it seems that it´s not a good candidate for putting a passive network in front. Is that what they call 0ohms input module?

So, in the end, how neumann used this thing as summing card? I will go the original route. If I only could have a glimpse of how it was used back then.

Thanks again!

It's not a gainstage for a passive summer, it is an active summer..!

Yes, and that´s the reason I need info on how to hook this thing up. If it would be worth doing so...

It says in there:

minimaler vorwiderstand : -100ohms (2x50ohm)

Click to expand...

So, is it as simple as that? I just put as many channels I want with the same 50Ohms resistors per phase?

I also thinkthat in this case, if I want pans, I´ll have to make pan buffers before the mixing networks, no?

Sorry to be a dumb, but I´m really is when it comes for active mixers.

Oliver put up a good diagram of how the german units fitted together..
Notice the V86s (valve version of Vx86s) down the bottom acting as mixers for the lines ahead
In addition something to aspire to... the germans units bolted together - look at that patchbay!!!

http://recforums.prosoundweb.com/index.php/t/3432/0

scoll down to the piccies...

JFKsmall.JPG (physical mixer)
Hannoverstudio.jpg (the logical layout of modules)

wrong link :?:

took me a while to sort it out - can;t link to the piccies

scoll down till you see display attachment on those two filenames

edit..
soryy I have got that wrong..

the summing amps are the V75 (4:1 valve summing)
The V86 /V87s are playback/record amps

http://recforums.prosoundweb.com/index.php/fa/566/0
http://recforums.prosoundweb.com/index.php/fa/567/0

Well, it sounds like "forget about it"...

According to the piccies
One path was... (and after a bit of research as well_

N52a Valve Mic PSU -> V76 Mic Pre (12 step gain selector +3dB to +76dB) -> W85 fader -> V74a Line Amp (0, 9, 15db out) -> V75 (4:1 Summing Amp -> W85 Fader -> V74a Line amp -> V75 (4:1 Summing Amp)

It looks like they were daisychaining the summing amps to get more than 4 inputs

In fact those are entirely different things.

The V475 is a solid state active mixer and I think it can sum up much more channels alone... like 48, or maybe more.

OK, at the firt graph of page three, I think I can read something:

A: Für V=0dB, RE = 2 x 1,2 kohms / RG = 2 x 0 ohms
B: Für V=0dB, RE = 2 x 2,4 kohms / RG = 2 x 2,7 kohms
C: Für V=0dB, RE = 2 x 5,1 kohms / RG = 2 x 13 kohms
D: Für V=0dB, RE = 2 x 10 kohms / RG = 2 x oo (infinite?) ohms

Click to expand...

Not really sure about what to do with this. I mean, It gives no info on the number of channel vs RE value I should use. Unless it´s not important in an active mixer???

OK, back to the monologue.

What really bothers me is that RE is always listed as 2x5k1 or 2x 10k or 2x1k2, but in the last page it´s really clear that I can feed as many channels I want, so, should the value of RE be the same disreguard the number of inputs used ? Take a look at the last page...

Or should the resulting resistance be equal to the value of RE (5,1k, 10k, etc) depending on the gain I want...???

All and all, I´ve been reading about active summing mixers on other threads and there is a very interesting point from IJR:

Ugh..."node" in hebrew...FOLKS, quiet! )))
Well, for me, inverting v.g. amplifier is _makeup_amplifier_ 'cause it amplify, or brings up, bus loss; active or passive, is another thing.
Just terminology.
There was gigatone of good reading here, let's not concentrate on this subject.
Putting trafo into _active_bus_, ot before v.g. inverting
makeup amp, is stupid thing.
Trafo is NEVER mathematically ideal....
You actually need bring feedback to separate winding of trafo to compensate its non-linearity, then stuff like oscillations,
you cut freqresp, ending up with crappy sound.&etc.
Or... another attempt to build Tele' v672.
But hey, trafo used here
is a bit specific. And 672 aren't very good as summing amps.

Click to expand...

I think this is exactly what goes in V475. I got the schem from another menber here in the forum (as well as lot better, readable manual) and it seems that it´s esactly what goes on in he V475. The secondary of the input tranfsormer has two windings. One goes to the amps, and the other is there for feedback purposes. It also has a strange filter card after the first balanced dual 5534 amp card. Is there a schematic online already? Other wise, I think I can post it...

Now I should stop writing alone :grin:

[quote author="rafafredd"]Is there a schematic online already?[/quote]
http://www.silentarts.de/lab/studiotechnik/neumann/V475-2B_Schematic.pdf

some minor changes, but essentially the same thing. I´ll post the 475-2C later today...

I'm curious to hear how you like the sound of this 475/2 when your mixer is finished. I was thinking of using one of these for my 4 (stereo) channel dj mixer project......

Erik

If I ever have it done, I will post results.

I always thought that a virtual ground active mixer had to be inverting, so, I don´t really know what´s going on on those modules.I´m afraid I´ll need some more help to have it hooked up as a mixer, so if you can tell me something about my last posts, it would be cool... I have been looking at active mixer schems and reading what I can find about it, but those are all transformerless, single ended, inverting devices, so I´m pretty confused. :?

Hi,
i will try to answer your questions.
My english is not so good, so I hope you will understand me...

You need a 5,11 kOhm Resistor on EVERY "+" & "-" Phase. Thats your RE´s.

For example: When you want to sum 24 Channels you need 48 * 5,11 KOhm Resistors :grin:

With RG (the feedback resistor) you can control the Gain of this summingamp.

When you don´t connect RG, you have +6db. If you put a 13kOhm Resistor in, you have 0db, and if you connect the pins without a resistor, you have -12db Output. (but all only if RE=5,11 KOhm)

For your understanding:

1. You can see the entire V475 as a single OP!
2. It is current driven!
3. So the input current directly depends on RE!
4. So there is no crosstalk between your -for example- 24 inputs,
because there is "only" a "current addition".
5. It has a 0 Ohm Input (not realy but nearly).
6. So your Input impedance of each channel you connect is 2 * Re.

If you want to change the input Level, you can calculate Re like this
for example:

if you want to have only one Input of this 24 Inputs at -3db and all others at 0db use RE 2 * 7,15 KOhm Resistors (5,11 KOhm * 1,4142135623730950488016 :grin: ) for this one Input ...

This little "filter board" is a highcut, because in the past the german broadcast studios used a 19KHz "pilot tone" Signal.
Normaly the highcut is around 15 KHz. But its a gentle cut.

Try to adjust C5/C7 & C6/C8 to bring the amp flat to 20 or more KHz....
You can also leave the whole "Highcut PCB" out if you want....

Damn, I Hope you understand me....

Leslie