Holger

Summing again: V475 box / pics
« on: February 26, 2010, 10:01:35 AM »
Since a couple of people are still interested in summing boxes, I'd like to post my latest (and last) summing device here:



It's a 18 channel (2x8 per sub-d plus two additional rear inputs) summing box with a Neuman V 475 2C summing amp.
I used Volker's POSPSU.



I've designed a little PCB that holds the resistors for channel 3-8 plus the 'daisy-chain' connectors.
One can connect as much 8-channel PCBs as wanted.



The resistors for the swichable first two channels of each PCB are soldered directly to the switches.



Some details:








radiance

Re: Summing again: V475 box / pics
« Reply #1 on: February 26, 2010, 10:19:38 AM »
 Very nice!.
Those pcb's surely saved you a lot of tedious soldering....
"Knowing that you are dreaming, however, does not automatically guarantee full rationality.
Then again, being awake doesn't ensure good thinking, either." -  Lynne Levitan

Autophase

Re: Summing again: V475 box / pics
« Reply #2 on: February 26, 2010, 10:26:27 AM »
looks amazing,
I;m currently building mine, I have a design for the PCB's which i will etch at college next month.
I'm going to have 8 stereo pairs on mine, rather than D-Subs, Just waiting for Volkers psu board to arrive.

Yours looks great, I really like it.
amazing job.

toffifee

Re: Summing again: V475 box / pics
« Reply #3 on: February 26, 2010, 03:31:19 PM »
As always: Very good work! Thumbs up!
Cheers, Toff

eskimo

Re: Summing again: V475 box / pics
« Reply #4 on: February 26, 2010, 03:44:32 PM »
Flawless typography and choice of colour! Also like you using your native tounge. Nice :)

Audioman

Re: Summing again: V475 box / pics
« Reply #5 on: November 16, 2011, 06:38:08 AM »
Hi All ,
I though to build mine neumann summing box but i dont know nothing about volker psu and how to build resistor network for the neumann card
Anyone can post the information
Thank you all
Fabio

Re: Summing again: V475 box / pics
« Reply #6 on: April 19, 2016, 08:08:45 PM »
I hope nobody minds me reviving this old thread.   I am embarking on a V475-2a  summimg project and I really like the economical approach of mono/left or right channel assignment Holger used for this project since I would assume that one could use a 4PDT toggle switch insead of 4P3T rotary shown in NYDave's schematic.

I was hopping someone could help me size the parallel resistors for mono channel assignment.  I assume they would be different since the summimg resistors are 5K11 and the V475 is an active summing device instead of passive? 

I will be using this mixer primarily for recording live to stereo instead of mixing so adjusting preamp gain/output for any potential signal loss would not be problem but I am unsure if different load impedance would be a problem.

Any help is appreciated.


PRR

Re: Summing again: V475 box / pics
« Reply #7 on: April 19, 2016, 11:39:54 PM »
> use a 4PDT toggle switch

No center (mono) position.

Unless it is an on-off-on type toggle.

Re: Summing again: V475 box / pics
« Reply #8 on: April 20, 2016, 08:12:06 AM »
Thanks PRR, I may be misunderstanding your reply but, if you look at Holger's front panel photos, four of the channels have toggle switches that allow for switching between center (mono) and left OR right.   I think since it is not a full L/C/R switch only a 4PDT switch is needed (on, on).

Re: Summing again: V475 box / pics
« Reply #9 on: April 20, 2016, 02:43:09 PM »
OK,  I did a little more looking around and hopefully answered my (admittedly very electronics 101) question.  Perhaps some sage and kind person could check my math and assumptions.  Attached is a schematic of the V475-2A from Kubarth for reference. 

Assumption #1:  From what I understand, the value of Rk (called Re on the official Neumann schems)  is 5K11 for all Nuemann summing cards, regardless of number of inputs.  I will be starting with a 8x2 summing box - perhaps to expand to 16 some day.
Assumption#2:  If I use -3dB pan law for center (3dB = 1.4), 5,110x1.4 = 7,154.  So, I would need to add 2K resistor in series for each leg for mono channel assignment to get  to -3dB +/-.
Assumption#3:  Adding a resistor between high and low to minimize crosstalk is not necessary for Neumann active summing card.


 

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