R/E/P Community

Please login or register.

Login with username, password and session length
Advanced search  

Pages: [1]   Go Down

Author Topic: Neve monitor section as line mixer  (Read 4077 times)

jrsgodfrey

  • Newbie
  • *
  • Offline Offline
  • Posts: 11
Neve monitor section as line mixer
« on: May 11, 2004, 11:36:59 AM »

I've seen several of these for sale over the years -- some 8 ch versions, one 16 ch version on ebay now -- and was in a studio recently that used one as a line mixer for DAW returns.

What, besides the actual unit, is needed to turn one of these into a functional mixer? They are passive, are they not -- so would one need something for makeup gain?

Thanks

erikj

  • Newbie
  • *
  • Offline Offline
  • Posts: 9
Re: Neve monitor section as line mixer
« Reply #1 on: May 11, 2004, 04:39:17 PM »

jrsgodfrey wrote on Tue, 11 May 2004 08:36



What, besides the actual unit, is needed to turn one of these into a functional mixer? They are passive, are they not -- so would one need something for makeup gain?

Thanks


Depends on what your def. of a functional mixer is.

The one I saw was an absolute mess underneath the panel.  I bought a pretty sweet one a while back, had 16 channels, sends, a patchbay, pans, etc.  When I turned it over, the wiring was damaged and disgusting--no boards, point to point with flying components, cold solder, broken solder, rotted shields, etc.  There was a bus bar attached via wires, which had bumped into some of the fixed wiring in shipping, so a few locations were just smashed.  

If you have enough line amps for the amount of outputs you want, the service manual for the console it was ripped out of, a good source for the pots that will need replacing, and a box of different types of transformers, it would probably work as a DAW summer with a send or two, but not much else.  More knowledgable Neve people can give you what model numbers might be cool.
Logged

John Klett

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 475
Re: Neve monitor section as line mixer
« Reply #2 on: May 11, 2004, 05:10:33 PM »

These are passive.  Actually a strategically placed class A buffer in each input would be a good thing but you don't NEED it.

Assuming you don't get a pile of junk...  They do make nice line mixers if you set them up right.  These are often 8 or 16 input mixers on panels using a single bus extrusion.  There are little pins that stick out with white (most of the time) single wires going to switches.  The pins are actually legs off the free ends of  the "drop-on" resistors.  You would come off the red pins that are the buss itself and take that to a make up gain amplifier.  Ideally you want a 1272 on each buss for makeup gain.  

There are a number of variations on what you do about terminating the buss if it's short.  
Ideally the buss impedance should be somewhere between 200 and 300 ohms so you may need to put a loading resistor on buss to pull the impedance down.

So... here you go...

The drop-on resistors in the buss extrusion would probably be 7K5 or 15K.
Let's say the drop-on resistors are 15K
Let's say you want 24 inputs.  Passive loss summing busses have to have the drop-on resistors terminated all the time - to zero volts or to a relatively low impedance source...
So the buss impedance without loading is 15K divided by 24 (24 equal resistors in parallel) or 625 ohms.
If you throw a 1200 ohm transformer primary across that...
To find the equivalent impedance you invert the values and then add them - then invert the result.
For example take 625 ohms and 1200 ohms in parallel.
Inverted... 1/625 +1/1200 = ~ 3/1200
Inverted again... this is 1200/3 = 400 ohms
the general formula...
1/Rtotal = 1/R1 + 1/R2 + ... + 1/Rn
The answer is always a lower value than the smallest resistor
You could throw another 400 ohms of resistance across that and get the impedance down to 200 ohms

...OR

Maybe we wire the transformer primary to 300 ohms (10468 transformer)...
For two resistors (only) you can do (R1 x R2) divided by (R1 + R2)
For the 625 ohms and 300 ohms.
R1 x R2 = 180000
R1 + R2 = 900
180000 / 900 = 200

now...  figure the internal "zero" of a console is -4dBu (-8dB below operating level of +4)
a -4dBu signal is attenuated because the buss is a voltage divider and adder.
20 Log X
X = (buss impedance) divided by (drop-on resistor + buss impedance)
that works out to -37dB
start at -4dBu (top of drop-on) and drops by -37dB to reach -41dBu
that's why it's called passive loss
then you need 45dB gain to get to +4dBu

old - useful and may be correct - can't remember

http://www.technicalaudio.com/zoop/passiveloss.jpg
Logged
John Klett / Tech Mecca
http://www.technicalaudio.com

jrsgodfrey

  • Newbie
  • *
  • Offline Offline
  • Posts: 11
Re: Neve monitor section as line mixer
« Reply #3 on: May 13, 2004, 11:08:38 AM »

Thanks for the comprehensive answer. Over my head, as I am not a tech, so let me try to summarize.

So, to make a 4 buss mixer, I would need 4x 1272, 4x transformers, some various resistors, power supply for the 1272s, and somebody with the knowhow to put it all together. That it? (What about the auxes, would I need amps for them?)

Sorry if I've oversimplified.

You think it's worth it from a cost angle?  Can I figure $500 for the monitor section (there are 8 ch. ones listed for this out there) $500 for each 1272 and another $500 for parts: $3000?  + Labor???

Anybody out there actually done this/had this done?

Thanks.

John Klett

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 475
Re: Neve monitor section as line mixer
« Reply #4 on: May 15, 2004, 03:58:27 PM »

The 1272's have the input transformer already - you just need complete modules.

Neve monitor panels can be 8, 16 or 24 input and as long as they have the same value drop on resistors you can connect them together to make on large mixer.  The limit for a mixer with 15K drop-on resistors is 50 inputs and for 7K5 resistors it's 25 inputs.  This is because the buss impedance would become too low and the make up gain required to bring the level back up would become too high...  signal to noise will become a problem... etc.

You can MAKE as passive loss mixer from parts though you have to shield the busses.  This in one reason the older Neve consoles had such good noise specs.  They had the busses in fully enclosed metal boxes (fin-like extrusions with lids).  You can buy heat sink extrusion and approximate this yourself.

We rebuild Neve frames in the shop so we've done this more or less.  You are just recreating a Neve monitor/remixer.

From a cost point of view... well - you can buy a brand new passive loss summing line mixer with sixteen inputs mixing to eight busses for maybe $6000 or so depending on how it's configured.

If you assume $500 each for two eight input monitor panels plus eight 1272's for $500 each you are up to $5000 in parts.  Figure $1000 for your time and, optimistically, you are dead even on money.  Your says Neve so you can always sell off the parts and recover most of what you have into it.
Logged
John Klett / Tech Mecca
http://www.technicalaudio.com

Geoff_T

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 406
Re: Neve monitor section as line mixer
« Reply #5 on: May 30, 2004, 05:30:08 PM »

john klett wrote on Sat, 15 May 2004 20:58

The 1272's have the input transformer already - you just need complete modules.

Neve monitor panels can be 8, 16 or 24 input and as long as they have the same value drop on resistors you can connect them together to make on large mixer.


Hi

The 8014 panel was 8 track with a rev return at the far right

8016/26/36 panels were 16 track, also with a rev return but more aux sends.

8028/38/48 panels were 8 track but had B338 amps buffering the output of the stepped fader. The 8028/38 were stereo panning but the 8048's were quad panning.

8028 and 38 used three of these panels for 24 track, though the 8048 could take four for 32 track.

Most of the panels will need a lot of repair/restoration to make them useable and they break easily when out of the console... especially the tufnol posts supporting the bus bar extrusion. Be prepared to remove every wire from the bus bar to allow it to be removed in order to gain access to the front panel components.

The 71 pin female painton connectors were pretty horrid even back at Neve and the wire clips fight the weight of the loom and connector hanging off them, almost ensuring bad connections.

I haven't looked at sources for the mating connectors... Plessey/Painton dumped that division years ago and McMurdo took over the products for a while. I don't think they make the sockets now.

Far wiser to replace with a modern Elco or similar connector.

I would be very leery about buying any of these panels considering the cost of fixing them, and obtaining the parts (inc. patchbay)and line amps (3402/3405/1272)to make them useable

Logged
Geoff Tanner
http://www.auroraaudio.net/main.shtml
http://www.grandmasterrecorders.com
    http://www.amazon.com/gp/reader/0595093329/ref=sib_dp_pt/104 -6861899-0350336#reader-link

NB Please do not pm me if you want a fast response... please email me.

John Klett

  • Sr. Member
  • ****
  • Offline Offline
  • Posts: 475
Re: Neve monitor section as line mixer
« Reply #6 on: May 31, 2004, 12:02:19 AM »

yeah - it's often a salvage operation...  you get the extrusion and the buss strips, panels and knobs etc...  The 8 input panels are often in better shape simply because they are small and don't flex as much...  I think I said somewhere that one could build a passive loss mixer from scratch...  but the Neve buss extrusion is a pretty neat thing.
Logged
John Klett / Tech Mecca
http://www.technicalaudio.com
Pages: [1]   Go Up
 

Site Hosted By Ashdown Technologies, Inc.

Page created in 0.033 seconds with 18 queries.