Aleguitarpro

(SOLVED) Neumann V475 summing mixer: Frequencies problem!
« on: February 17, 2012, 05:34:15 AM »
Hi!
I've just finished a 24 input/2 out summing mixer, built with a Neumann V475-2b.
I've remove the mo-12 filter board (and bypassed with jumpers) and I put in each input a 5k1 resistor.

The summing mixer works perfecly with a great stereo image, but I notice by ear a lack in 350-450hz.

So, I've check this with a frequency sweep and a analyzer: is true, those frequencies get lost in the summing...
about 1,5dB of cut, from 350 and 450. Also, from 1.5/2.5 khz I see a light decrease of frequency response, like a very little shelving put from 1.5/2.5khz to 20khz.

The only thing I haven't done, is to recap the Neumann board...

Any ideas?

Here you can listen the tests, with LOGIC PRO internal summing (not a bounce) and with NEUMANN summing mixer:

http://soundcloud.com/aleguitarpro/sets/neumann-summing-mixer-tests

« Last Edit: February 18, 2012, 12:21:52 PM by Aleguitarpro »


radiance

Re: Neumann V475 summing mixer: Frequencies problem!
« Reply #1 on: February 17, 2012, 05:41:58 AM »
recap the board :-)
"Knowing that you are dreaming, however, does not automatically guarantee full rationality.
Then again, being awake doesn't ensure good thinking, either." -  Lynne Levitan

SKJGProject

Re: Neumann V475 summing mixer: Frequencies problem!
« Reply #2 on: February 17, 2012, 05:42:15 AM »
i have no idea what the problem is, but listening to your soundcloud clip on mbp speakers i can't agree with:

The summing mixer works perfecly with a great stereo image

you can even see in the waveform preview that there is something really wrong, it sounds totally out of phase and filtered

edit: quick check with a scope....phase totally messed up
« Last Edit: February 17, 2012, 05:48:56 AM by SKJGProject »
I used to date a blind girl. Her name was ::… ..:.: .:::. .::.. ….: .:.::

Aleguitarpro

Re: Neumann V475 summing mixer: Frequencies problem!
« Reply #3 on: February 17, 2012, 06:01:06 AM »
...and what can I do to solve the phase problem??

[silent:arts]

Re: Neumann V475 summing mixer: Frequencies problem!
« Reply #4 on: February 17, 2012, 06:18:18 AM »
SKJGProject is totally right.
my RTW correlation meter goes far to the left, deep red, -1.
listening in mono, no drums left.
phase flipping one side, they are there.

check your wiring. if you are lucky only either the input or the output of one side regarding the V475 is out of phase.
but if your wiring reversed random channels before the summing resistors, or your summing network reverses randomly: have fun ;)

SKJGProject

Re: Neumann V475 summing mixer: Frequencies problem!
« Reply #5 on: February 17, 2012, 06:19:23 AM »
build it properly? did you test the neumann module? otherwise it must be some mistake in the connections
I used to date a blind girl. Her name was ::… ..:.: .:::. .::.. ….: .:.::

Aleguitarpro

Re: Neumann V475 summing mixer: Frequencies problem!
« Reply #6 on: February 17, 2012, 06:27:07 AM »
O H     M  Y     G   O   D!

Yes, it's out of phase: I've checked it now.
Ok, thanks! :)

I'll try to check all the wiring, but I'm quite shure they're ok: I've test each of that with a tester, before closing the box.

I've follow neumann's scheme of V475-2b for wiring, but I'll check it again.

Thanks for now!
But, only to know: the old cap on the board could change a freq response? Only in case I'd to do also this thing, however...

[silent:arts]

Re: Neumann V475 summing mixer: Frequencies problem!
« Reply #7 on: February 17, 2012, 06:39:59 AM »
But, only to know: the old cap on the board could change a freq response? Only in case I'd to do also this thing, however...
there is no electrolytic in the signal path.
however, change them.

Aleguitarpro

Re: Neumann V475 summing mixer: Frequencies problem!
« Reply #8 on: February 18, 2012, 05:01:13 AM »
Thanks for your help: I've solved my problem.
Now all works correctly: no phase problems, flat frequency response.

The problem was in the wiring: I've used 24 closed jack plug and before wiring I've tested them to wire the resistor board.
After the resistor board I've used 2 balanced cables and 1 channel has a different wire colour... (!!!!)
This was the problem. I've re-checked all the wires and found the mistake.

Here you can listen the beast at work:
http://soundcloud.com/aleguitarpro/sets/neumann-new-summing-tests

The "pushed" file is a sum obtained with an higher value of amplification of the V475 board (+6db), keeping the input channels low. I like very much this result: letting the board working in an higher amplification level, it puts out its attitude in a very beautiful way...

It's difficult to stop listen to!

Thanks, thanks, thanks for help!

r2d2

Re: (SOLVED) Neumann V475 summing mixer: Frequencies problem!
« Reply #9 on: February 18, 2012, 03:51:45 PM »
nice beast !

there is some way to fit a volume pot at any ch input ?

peace
r2d2
..... Cracking D.Vader Firewall ...  II-)


Aleguitarpro

Re: (SOLVED) Neumann V475 summing mixer: Frequencies problem!
« Reply #10 on: February 18, 2012, 09:22:12 PM »
No, the only way to regulate the gain (volume) is to put 2 different 2-way switch (one for each channel, with stepped gain and with different value resistor) or one 4-way switch for the stereo gain regulation.

If you take a look at the scheme, you see Rg referred at 2a/2c and 4a/4c pins of first channel and Rg referred at 30a/30c and 32a/32c pins: these are the pins that you have to connect to your switch.

No way to put a pot. Only with stepped gain.

In Neumann scheme you can see, also, that the fixed value for +6db, 0, -12 corresponds to a 13k resistor, short circuit, open circuit.

I used a 6 position 2 way switch to obtain -12, -6, 0, +1, +3, +6 db with different value resistor.

I hope this can help you.


 

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