DB25 summing PCB - MK2??

ruffrecords

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Audioman said:
Hi Ian,
I think the new version of the db25 needs :
Thank you for taking the time to respond. Here are my thoughts on what you have asked for:
- Pan switch (L C R)
usually the DB25 board is at the back of the enclosure and the LCR switches will be on the front. The idea of adding an extra connector was so you could connect in a ribbon cable from the DB25 to the front panel and wire in your pan switches. The connector on the DB25 would be a 32 way IDC ribbon connector. Maybe we need a new board for the other end of this with the LCR switches on it?
- balanced insert (send/return) option in every channel
If you use 25 way audio connectors then there is no need to change the DB25 board. You would come in on a regular 25 way connector at the back of the unit and wire this 1:1 to another 25 way connector which would be the send. The connector on the DB25 board is then the return. You simply connect your patch bay to the send and return. Or were you thinking of something more complicated?
-  another good improvement is the possibility to have a balanced inserts on the master of the summer

This cannot be done at the DB25 output because the signal level is too small. It needs to be done after the gain make up stage.
if you change the side of the board (more bigger) Theres no problem for me.

You can raise also the number of channels for pcb
( eg 16 instead of 8 ) a good summing mixer needs at least 16 channels
You would be surprised how many people buy a single board for just 8 channels. Also, many people want 24 channels which is easy with three boards
This is my Thoughts for my little experience.

P.S. during reading of the thread i know that the shunt resistors are needed only on the last pcb (eg i have mount the shunt resistor on every four DB25 pcb on my summer) i understand ?
This is correct.
i also read that if you use the neumann V475 you don't need the shunt resistor is it right ?
This is also correct.

Cheers

Ian
 

Audioman

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Q- usually the DB25 board is at the back of the enclosure and the LCR switches will be on the front. The idea of adding an extra connector was so you could connect in a ribbon cable from the DB25 to the front panel and wire in your pan switches. The connector on the DB25 would be a 32 way IDC ribbon connector. Maybe we need a new board for the other end of this with the LCR switches on it?

A- Yes a new board for place the switch is necessary.

Q- If you use 25 way audio connectors then there is no need to change the DB25 board. You would come in on a regular 25 way connector at the back of the unit and wire this 1:1 to another 25 way connector which would be the send. The connector on the DB25 board is then the return. You simply connect your patch bay to the send and return. Or were you thinking of something more complicated?

A- I'm thinking this way for a more clean and easy wiring (not everybody have patch bay in the studio) and if you need to insert a compressor o an EQ in a single channel you can do it straight with two cable and without to use the computer sound card (latency) or the patch bay. off course is necessary redesign the pcb with the new features.
if you want i can send you in PM some sheet for ideas


Q-This cannot be done at the DB25 output because the signal level is too small. It needs to be done after the gain make up stage.

A- If in the future you may want to redesign the twin line amp you can add this feature to the new design (balanced inserts)


Q- About the shuth resistor how it affect the signal if i not remove them on the first three card on my summing mixer (32 channels) ??

Q-And in the case of the neumann V475 design ??

Thank you
Fabio

P.S. in attached a picture of the passive resistor bus the last 8 channels are on the left and only this card have the shunt resistors i hope is correct :) :) :) :)
 

ruffrecords

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Hi Fabio,

I am not sure I understand how you are planning to do inserts. Post your ideas here rather than in a pm.

The Twin Line Amp normally drives a transformer which provides a balanced output.  Adding an insert is just a matter of adding a couple of TRS sockets for each channel. If nyou want a relay switched insert there are already boards available  for this.

You only need to add the shunt resistors to one board. It does not matter which one you add them to.

Most versions of the V475 are virtual earth balanced mixers. For these you do not need shunt resistors.

Cheers

Ian
 

andow

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Can somebody recommend a good quality connector for the boards? There are just so many to choose from at mouser...
 

znjamznjam

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Hy Ian
Can these boards been used with classic 2-aca-bo summing boards for 24 chanels?
If wel can I order 3 boards?

Thanks
 

ruffrecords

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znjamznjam said:
Hy Ian
Can these boards been used with classic 2-aca-bo summing boards for 24 chanels?
If wel can I order 3 boards?

Thanks

The 2-aca-bo summing boards are really intended for summing unbalanced signals inside a mixer. My DB25 board is intended for summing balanced inputs but is can be used for unbalanced summing.

Exactly what is it you are trying to build?

Cheers

Ian
 

znjamznjam

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Hy Ian

Thanks for fast response.
I need summing mixer with 24 Chanels.
8 mono and the rest normal stereo
1 x send/return stereo
With vu meter and stereo pot for master.
Thats all.
I think if i combine 3 pcb boards from you and combine with aca 2 board as gain amp wil be nice summing mixer for my setup

Regarders

Nenad from NL
 

ruffrecords

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znjamznjam said:
Hy Ian

Thanks for fast response.
I need summing mixer with 24 Chanels.
8 mono and the rest normal stereo
1 x send/return stereo
With vu meter and stereo pot for master.
Thats all.
I think if i combine 3 pcb boards from you and combine with aca 2 board as gain amp wil be nice summing mixer for my setup

Regarders

Nenad from NL

OK, that begins to make sense. The send/return, is this on the stereo mix in  other words is it an insert rather than an aux send.

Are you inputs balanced? If they are then I am not sure how the aca 2 board can be used.

Cheers

ian
 

znjamznjam

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Yes send return is on the main mix stereo.
Yes  my  inputs are balanced (outputs from DAW via RME fireface to summing mixer)
 

znjamznjam

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Folgens jsteiger this can be  done. Its kinda depends on the interface. The cold leg will likely need to be grounded. Some electronic devices don't like this, some don't care.
 

ruffrecords

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znjamznjam said:
Folgens jsteiger this can be  done. Its kinda depends on the interface. The cold leg will likely need to be grounded. Some electronic devices don't like this, some don't care.
Grounding the cold leg really defeats the whole point of having balanced signals and removes all their beneficial properties. There has to be a better way of interfacing balanced signals to the aca-2.

Cheers

Ian
 

znjamznjam

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Hy Ian
Can you help me for beter solution from you db25 cards to aca?
Also i will order 3 cards


 

ruffrecords

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znjamznjam said:
Hy Ian
Can you help me for beter solution from you db25 cards to aca?
Also i will order 3 cards

Basically my DB25 cards, like any passive  balanced summing mixer, takes line level signal in and produces a mic level signal out. So yiu really need to fiollow it with a mic pre. I know API used their discrete op amps as mic pres. So I think you need to feed the output of the DB25 cards into a 1:1 mic input transformer and then into a single DOA which you can probably fit on the aca card you already have.

Cheers

Ian
 

znjamznjam

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Hy Ian
Thanks for info.
If I good understand signal from you passive summing cards is to low for direct connecting to aca board.
Between you board and aca board must be mic line level preamp for the aca board.
Thanks in advance
 

ruffrecords

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znjamznjam said:
Hy Ian
Thanks for info.
If I good understand signal from you passive summing cards is to low for direct connecting to aca board.
Between you board and aca board must be mic line level preamp for the aca board.
Thanks in advance

What I meant is that the aca is a virtual earth summing amp. The DB25 is a passive summing board so it needs a different type of gain make up amplifier. However, the op amps on the aca card should be able to be configured to do this. Check out the schematic for the API mic pre using the 2520.

Cheers

ian
 

andre tchmil

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I'm trying to get my grip on that passive summing fashion.
Ther's one thing I don't understand. With the calculated input resistors does this mean that all channels need to be loaded all time ? Let's say we have a 16x2 mixer and my DA outputs are devided over 3 interfaces, do  they have to be all the time connected to match the correct input impedance, even if I only use a few channels ?
 

PRR

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> do  they have to be all the time connected

That's another reason we use a "mike preamp". A bunch of sources through 10k mix resistors has large loss but not all the way to mike level. So we have a bunch of 10k sources and put a 500 Ohm on the end. Now it hardly matters (much) how many sources are connected. One source is -26dB and ten sources is -30dB. You would not un-plug nine sources in the middle of a steady-level passage; normally you'd leave the setup alone for a whole track. A 4dB change is not large. Also it "goes the right way": more sources is more signal but also more loss.
 

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