Question about Neve summing - Modding my other vintage Neve desk

Since i finished restoring one of my vintage Neve desks (which i documented in a thread here) i have had some much needed rest.
But now its time to start on my other Neve which is a 12 channel extension which was custom made in 1973 to go with a larger 36 channel custom desk that was ordered by Yorkshire TV.

So, this extension was made to be tagged on to the larger desk if more inputs were needed.
It have its on summing aboard with seventeen 1272 amps but there are no echo send/returns or any monitor section, nor faders for the groups etc etc.

So to make this desk more usable i have been thinking about adding another small unit that i would load up with eight Neve 1943 routing modules with faders to handle the buss routing and Echo returns.
I might also make space for a monitor section of some kind and possibly space for a compressor on each bus.

I dont want to take on another project where i am expanding an exsisting frame, its just to much work to adapt to the old and will be much easier and quicker to build something new.

But since all the summing sits in the main unit there is a problem of course with routing all the sends from the new unit to the bus feeds of the old one.

My idea is to have a internal passive summing which will then be routed to the main buss of the main unit, much like how the passive monitor/tape return panels work in the old desks, and which are often modded to go to the main busses of the desk to have more inputs at mix.
The good thing about doing it this way is that you would only have to run one cable per feed instead of multiple cables from each send in the new unit.

The main problem i see is to run the bussfeeds at all between the desks and i am not even sure if its possible to do without noise problems?
But possibly with sheilded and properly grounded cabling there would not be problem?

I did a basic drawing of what i want to do, so please hit me with any comments you might have.
And if you see this Ian i would love to hear what you have to say

What beautiful consoles!!!!!!
Best,
Bruno2000

I would do an active summing amp but to each his own. That's gorgeous! Your efforts seem to be paying off well

We certainly did side cars at Neve. I visited Pete Townsend at his Eel Pie studio to discuss a side car for his existing Neve desk which he subsequently purchased. In this case the side car was literally bolted on to the existing desk. The woodwork and buffer was changed so it just looked wider. In this case the buses wire wired directly together. What you want to to is a little different. I need to think about it some more.

Cheers

Ian

Thanks for your reply Ian.
Yes, i am sure that Neve built several, small custom consoles over the years.
I could of course do an add-on to the exsisting desk, but it would be even more work i believe, and i like the flexibility with two separate units.
I think what i want to do is the same as dropping the 8-track tape return section from say a 8014 into the mixbux, but cant say for sure.

Buildafriend, there is already all the summing in the main desk, i just want to add all the outputs from the group routingmodules into the summing bars.
It would be easy to do if i built out the main desk and added longer busbars, but i would want to do internal summing in the new desk which then would go to the busbars of the main/old desk.

We often added direct inputs to a custom design. Simply a 31267 wired 10K:600 and 15K feed resistor to each bus. Would that do you?

Cheers

ian

Yes, Ian, that is how this small desk was connected via Hypertac connectors to the main desks according to the original paperwork i have.
But i think you maybe misunderstood my main question so i will rephrase:

Do you think its possible to run unbalanced busfeeds across a multicable between the two desks?
Of course you would need to shield them at one end but still not sure if it would be to "unstable" for lacking of a better word.

I am pretty sure that "submixing" the busfeeds internally in the new desk/unit will work, but just not sure how to connect the two desks together.
But maybe using transformers at each end would be needed?

API said:

Do you think its possible to run unbalanced busfeeds across a multicable between the two desks?

Click to expand...

There is no reason why it shouldn't work, as long as the connections are well shielded. But the major issue is the possible voltage difference between the respective "grounds". A very strong connection between these two "grounds" is essential.

But maybe using transformers at each end would be needed?

Click to expand...

That is a good way of eliminating this longitudinal noise issue.

API said:

Yes, Ian, that is how this small desk was connected via Hypertac connectors to the main desks according to the original paperwork i have.
But i think you maybe misunderstood my main question so i will rephrase:

Do you think its possible to run unbalanced busfeeds across a multicable between the two desks?
Of course you would need to shield them at one end but still not sure if it would be to "unstable" for lacking of a better word.

Click to expand...

It works fine on paper, but in real life sum buses are running at high noise gain so small noise voltages at the wrong place get amplified  by the noise gain.

I am pretty sure that "submixing" the busfeeds internally in the new desk/unit will work, but just not sure how to connect the two desks together.
But maybe using transformers at each end would be needed?

Click to expand...

Transformers work but can be expensive to not degrade performance. A sub bus sum amp, then feeding the local sum at line level for injection into the main bus. A differential at the receiver end can reduce ground potential errors between the two chassis and operating with a line level signal and unity gain will also minimize error potential.

JR

Thanks for the addtional thoughtful replies Abbey Road and JohnRoberts.

Seems this will not be as easy as i was hoping for (like anything is....).
I would rather not have to add summing amps and more electronics in the new desk, then i think it will be easier to expand the desk with another bucket and just replace the summing busbars with longer ones.
Just thought it would be a good idea to have two separate units, ut maybe not..

Need to think this one over another a bit more...

If I had to do it, I would choose to add summing amps to the side-car, for a number of reasons:
a) better noise performance; with a single bus architecture, noise increases linearly with the number of channels, but with arborescent architecture, noise increases logarithmically
b) with "passive" summing, gain needs to be adjusted vs. number of channels, so interconnecting two bus implies readjusting gain or accepting uncalibrated operation
c) it allows the side-car to be used on its own, although with reduced facilities
Admittedly, none of these issues is a deal-breaker, but added together, they are a significant incentive.
However, the nail in the coffin for direct bus extension is
d)  longitudinal noise created by the voltage differential between units

I think the other guys have said it all, The unbalanced connection between the two consoles is what would worry me the most. You might get away with it but it is a lot of work to find out. I know you have seen the size of the 0V bus bar inside a Neve. Connecting two of those together via s significant length of cable worries me.

Cheers

Ian