Another Neve 1272 summing mixer.

"Start wearing purple, wearing purple...."

https://postimage.org/

Its almost funny how much the backplane halted building, but i couldn't see going any further until i knew these were definitely gonna work.
A few notes and reasons that solidified my using a backplane.
For one on the Forth Monkey channel boards and fitted the way i have it which made the most sense; power is on the top. I couldn't figure a more elegant way of covering the open wires even though theyd all be molex connections. Something about voltages running across the top just made me nervous. If i or someone else werent paying attention and opened up the hood with the power on.... The back plane fixed this dilemma.
Second is wiring and crosstalk.
Third it looks cleaner and will also be easier to troubleshoot.
Fourth is now i have very identifiable  buses that i can access easily and slickly at any point.
Im just waiting on a bunch of burr brown 2604s and Omron relays.
I have also redrawn TeeKay's modified ba226 amp that he sent me the schematic of. And that should take care of a few of the sends. The master section is coming along.

Please correct me where I am wrong.

Okay if I wanted to add a stereo channel....

I believe that stereo channels in mixers are akin to two mono channels just one is a left input and outputs to the left bus  and the other is a right input that outputs to the right bus.
I will then need to use a dual gang 5k log pot with each side using a gang for the stereo fader.  Currently each channel uses a single gang 5k log pot for the fader.
For the pan pot each channel uses a dual gang 50k linear pot so for a stereo channel I would need to use a 4 gang linear pot at 25k?  Or do I use a 4 gang 50k? 
And for the aux should I keep that at 22k-25k but just make it a dual gang?
I have a left and right aux bus even though the mixer has only one aux so my stereo channel aux output would go to their respective aux bus.
I imagine the 47k bus resistors can stay the same?

Thank you in advance and I hope all of you are safe, healthy, and well.  It's getting there I am still awaiting some relays and little stuff but I can see it.  And its still a lot of wiring.  I finished the modified ba226 that TeeKay sent me and am having a friend take a look to see if i screwed up anything.  It's bit bigger than the 2520 but I made it follow the same pin out so that when I make the receptacle boards it will be easier to implement.

Did I say thanks?
Good, cause I meant it.

Rocinante said:

Please correct me where I am wrong.

Okay if I wanted to add a stereo channel....

I believe that stereo channels in mixers are akin to two mono channels just one is a left input and outputs to the left bus  and the other is a right input that outputs to the right bus.

Click to expand...

Correct.

I will then need to use a dual gang 5k log pot with each side using a gang for the stereo fader.  Currently each channel uses a single gang 5k log pot for the fader.

Click to expand...

Correct.

For the pan pot each channel uses a dual gang 50k linear pot so for a stereo channel I would need to use a 4 gang linear pot at 25k?  Or do I use a 4 gang 50k? 

Click to expand...

It is a stereo channel. Why do you need a pan pot? Do you really want a balance pot?

And for the aux should I keep that at 22k-25k but just make it a dual gang?

Click to expand...

Dual gang would be sensible.

I have a left and right aux bus even though the mixer has only one aux so my stereo channel aux output would go to their respective aux bus.

Click to expand...

Don't quite understand this. How many AUX buses do you have?

I imagine the 47k bus resistors can stay the same?

Click to expand...

Correct.

Cheers

Ian

Thanks Ian.
No i dont want a balance pot (so that clears that up for me).
I put an extra unnecessary bus on the boards because i could i guess.
And thank you again.

I was warned. "It's an undertaking" they said.
I also made a few misjudgments.
Case size for one.
I thought that since i was gonna have an external psu depth wouldn't be crucial. Im not so sure now. Its getting harder to wire the master section and i feel like im limiting myself. And thats dumb.
That said its not a total wash as i can convert the one im using into a 8 space 500 rack which i planned on building sooner or later anyway.
I will have to rewire (make another 20 molex terminals) and redrill another 30 holes which sucks. I might just get it working then get back to case stuff.
I've been busy in the studio and at work and with my band but i do find time.
I'm on a small week and a half tour with my band saiudrom but right before i left i took a few pics.

imgur
https://postimage.org/

Another lesson.

The ez-ln72's were designed for the grayhill adjustable 71 series 12 position switches. 
What are some thoughts on using a single rotary gain switch (e.g. a grayhill 2 deck 2 pole adjustable 12 position) as opposed to seperate left and right gain switches?  So in other words one switch to control the Left and Right master out or two switches.
I already have the 1 pole grayhills but I feel like a single switch might be better. Thoughts?

Rocinante said:

The ez-ln72's were designed for the grayhill adjustable 71 series 12 position switches. 
What are some thoughts on using a single rotary gain switch (e.g. a grayhill 2 deck 2 pole adjustable 12 position) as opposed to seperate left and right gain switches?  So in other words one switch to control the Left and Right master out or two switches.
I already have the 1 pole grayhills but I feel like a single switch might be better. Thoughts?

Click to expand...

Should be OK. I can find no schematic for this design but assuming it is based on the 1073 line input section then the switch is just a stepped series resistor so it should be OK to place a pair together on one switch.

Cheers

Ian

Progress Report:
Well there was a lot of wiring that needed to be done and id say its about 75% done.  I am waiting for a few more parts but not many and I can actually say it is getting there.  I did have a few doubts regarding the ea-10468 in reverse and how I should implement grounding but I think ill see if how I have it wired works first before typing my concerns.    I succumbed to 'feature creep' with regard to the master section for awhile but came through the other side with a bunch of decent ideas after realizing that this doesn't need to have every option imaginable on it.  In just the master section anyways.  Hell not even on board in the same case.  So I will build an accompanying monitor controller/master section in a 1u sized case that can act as an extension of this as well as its own thing.  It'll match the 2u vu meter 'bridge' that I planned to add from nearly the beginning.  I also began learning and playing around with some of the basic logic circuits as well as scratched the surface with a teensy and an arduino which I admit am still having a difficult time with but I can see their potential uses being nearly endless.
Life, work, music, and family have also been demanding my attention but I will begin seeing where I screwed up here within the next few days and hopefully fix them.  Its been a project though.  To be honest this was probably (definitely) a bit over my head and (speaking of biting) I probably bit off more than I could chew but its been damn interesting and I can actually see an end in sight and most importantly I like doing it. The research. The wiring.  The desoldering.  The oops and the eurekas.
"Let us trudge down the murky road towards happy destiny"
Pic of the top
http://postimage.org/ 
and an awful pic of the front. 
http://postimage.org/

I've read most of the posts on this thread with great interest and as - it seems to me - always, Ian is very helpful. I definitely sympathize with a lot of the sentiments in your most recent post. I am doing something similar (it has stalled for a little while), and so many times during the "design phase" (or what it is that I do that passes for design), I would think to myself that this is beyond me, and put the project aside (this has been going on for at least a couple of years). Then I would come back to it, nut out a problem, and move a little bit forward.

Without doubt, my console project is certainly more than I can chew. However, I did eventually get to a point where I thought I had something (a basic design) that might be worth trying, so I started construction. I went modular, so if worst comes to worst I'll end up with a rack of pre-eqs.

I am hoping my luck (which I am sure is a large part of the success of the previous pieces of gear I have built) holds out. I originally thought I would build a transistor-based, passive mixing, 16x8x2 with 16 pre-eqs, pan, channel inserts, 4 x aux send/returns and master section. This collapsed to a 16x2 with 8 pre-eqs and 8 line eqs (mainly for cost reasons as the complexity is practically no different). What will actually be completed in the short term (to test) will be a 4x2 with 4 pre-eqs, pans, 4 x sends and 4 x returns, main LR out and monitoring.  I have the same sorts of distractions that you do, but I agree, it is really interesting and I also like doing it. Best of luck with finishing it off.

I am not sure where the "like" button went Squeaky but if it still existed I'd hit it.
I thank you for the encouragement and of course wish you the best of luck as well on your mixer.
After finishing many of the projects on this forum it seems only natural that one 'graduates' to building some sort of mixer.  There is a certain strangely comforting humility one gains when posting their blatant and unapologetic ignorance for all the world to see (or in our case some very intelligent designers, engineers, and hobbyists) that can either be terribly discouraging when looking in hindsight or another creative drive as one sees how far they have come. 
When I was building the Helios (using Ian's EQ filters) I got to communicate with some really interesting people from all facets of the pro-audio industry.  To this day I still have people contact me after reading that thread.
This mixer has been no different.  While researching or sourcing parts and ideas I have been lead down many a great conversation with a good deal of them regarding Neve mixing consoles and have learned more than I truly will ever know what to do with (well other than build a mixer of course).
  I had been warned about adding too many features and had thought "yeah, yeah, yeah," and really I should have paid some mind to what was being said.  That said, when all is done and hopefully working correctly I think I will have  something that I will honestly be proud of and is truly a useful professional tool and hopefully looks the part as well.
Where  ever I could get creative was a big driving factor.  I fumbled around a lot but I suppose it's the little design ideas that add up and make it something I built and not just another clone (no offense to clone makers)  I did imitate others ideas but I also stared endlessly at various problems until the solution arose from within me e.g. adding the insert push button switch below the mute switch on one of those ganged interlocking banks so that the layout was somewhat professional looking, and also figuring out how to implement that for a stereo channel.  I am sure its been done before but I also know i figured it out myself.
Ian has been the greatest guide I could have ever asked for.  Period.  I owe him.  A lot.  I am an appreciative person but really I can't even imagine how frustrating I must have been for him and salute his seemingly endless patience.  Once again thank you sir.
And thanks again to you to Squeaky.  Your timing was impeccable and your reply was definitely just what I needed.
It's 2 am here.  I have a few more app 992's to stuff and then.....
zzzzz....
cheers
Dylan

Please correct me if i'm wrong ,

after check the various docs posted ,
on the 80 series consoles , the signal go to the first module like 1073 pre+eq by the input transformer and preamp card
and go out by the ba283 amp card and output transformer
than :
go to the input of the auxes-bus assign module that have another line in transformer and preamp card for unbalancing the signal
and here the signal can be assigned to one of the busses ,  send to external recorder by the dedicated "record" output ,
regulated to L-R by the Panpot potentiometer (it have dedicatet Doa ? )
regulated by auxes pots for send it to the dedicated aux outputs ( that i do not found output amp card and transformer )
regulated by the volume channel fader control than assigned to the L-R Summ "rail" with another amp out card and another transformer ,
than:
from the L-R summ "rail" finally to the L-R Master box that have another input transformer and preamp card stage ,
insert selector ,  Master fader , and than amp out card with output transformer,

total  from input to Master out :
3 preamp transformers - 3 preamp card -3 output amp cards - 3 output transformers
(inserts excluded , like 2254 ,LA2A,Pultecs, etc..)

right ?

and:
also aux send masters out and returns have dedicatet input and output transformers with preamp and amp cards ?

that i do not found is the auxes amp card and transformer out from each channel module ,
are they summed in different way ?
and about the  Panpot  Doa or circuit ?

thanks in advance
S.

Honestly Geoff Tanner has this subject  for all to read in his papers (and on his website) and is very open to discuss the specifics.  I haven't bought the papers yet but plan on it  as they essentially describe  Neve consoles  in specific detail.  It really seems like Neve had a spare no expense venture  and it's no wonder they are as expensive as they are.  The damn things are just filled with transformers.  That said the aux bus routing was dependent on the console but for all intents and purposes itwas just variations of the 3415 or later 1272 cards (with a 1246 in between?).  The b110 is essentially  the input of a b183/283 while the b112 is essentially the output section.  The 3415 was also used in the aux and made up of two  b338 and b340 but it seems that it was dependent on what model and what function for how they were implemented. I am NO Neve expert. Far from it actually.  So yes it seems they all had an input transformer and all used output transformers.
How the aux section is actually implemented is a mystery to me though but from what i gather one could use 1272s for the sends and returns and that would be 'correct' (i was gonna use b338s but it became too expensive for me so i decided in using jlm regurtitators for my send and returns. I will also use the regurgitators for my monitor outs.
Id really like to see how they used the audio ground and at what points they tapped it. I know they used a 'bus bar' but i dont know where they exactly tapped into it. I'm currently stuck on this right now. I had built a vero board 'utility' board but im currently redesigning it as it is not working correctly. I know its my grounding as im fairly certain i have the xfmrs and zobel network wired correctly. I will post a pic of the board soon along with a diagram.

SIXTYNINER said:

Please correct me if i'm wrong ,

after check the various docs posted ,
on the 80 series consoles , the signal go to the first module like 1073 pre+eq by the input transformer and preamp card
and go out by the ba283 amp card and output transformer
than :

Click to expand...

Correct

go to the input of the auxes-bus assign module that have another line in transformer and preamp card for unbalancing the signal
and here the signal can be assigned to one of the busses ,  send to external recorder by the dedicated "record" output ,
regulated to L-R by the Panpot potentiometer (it have dedicatet Doa ? )
regulated by auxes pots for send it to the dedicated aux outputs ( that i do not found output amp card and transformer )
regulated by the volume channel fader control than assigned to the L-R Summ "rail" with another amp out card and another transformer ,
than:

Click to expand...

Nearly. Signal flow in a routing module goes input transformer->> pre fader driver amp -->fader->>post fader driver amp-->direct out amp-->output transformer.
AUX sends are connected to either the pre or post fader driver as appropriate. Pan pot is connected to post fader driver. Bus assigns (LR etc) are connected to pan output. Summing buses are all unbalanced.

from the L-R summ "rail" finally to the L-R Master box that have another input transformer and preamp card stage ,
insert selector ,  Master fader , and than amp out card with output transformer,

Click to expand...

Inserts are usually post fader

total  from input to Master out :
3 preamp transformers - 3 preamp card -3 output amp cards - 3 output transformers
(inserts excluded , like 2254 ,LA2A,Pultecs, etc..)

right ?

Click to expand...

Probably just two output transformers, one in the 1073 and one in the final bus output.

and:
also aux send masters out and returns have dedicated input and output transformers with preamp and amp cards ?


that i do not found is the auxes amp card and transformer out from each channel module ,
are they summed in different way ?
and about the  Panpot  Doa or circuit ?

thanks in advance
S.

Click to expand...

AUX buses are summed exactly the same as the other buses mainly using a 1272 module.

Cheers

ian

Hello Ian,
thanks for post!
then no output transformer in the : "Busses-auxes-panpot" module ? (aka switching module , if i'm right)
"Doa driver" output card ?
all the aux sends , busses assign and the L-R master are summed to the proper "rail" in unbalanced mode?

about panpot it is controlled with some driver or only pot ?

also read somewhere that the mic input transformer can be used as line input with a "mod" like a "pad" ,
any info about ?

thanks
S.

ruffrecords said:

CorrectNearly. Signal flow in a routing module goes input transformer->> pre fader driver amp -->fader->>post fader driver amp-->direct out amp-->output transformer.
AUX sends are connected to either the pre or post fader driver as appropriate. Pan pot is connected to post fader driver. Bus assigns (LR etc) are connected to pan output. Summing buses are all unbalanced.Inserts are usually post faderProbably just two output transformers, one in the 1073 and one in the final bus output.
AUX buses are summed exactly the same as the other buses mainly using a 1272 module.

Cheers

ian

Click to expand...

SIXTYNINER said:

Hello Ian,
thanks for post!
then no output transformer in the : "Busses-auxes-panpot" module ? (aka switching module , if i'm right)

Click to expand...

The 8000 series covers a lot of consoles many of which were customised. In many cases there was one group per track so 16 and 24 groups were common. Direct outputs were not common until the later in-line series of consoles appeared. So some 8000 series consoles undoubtedly had a direct out built into the routing module, complete with output transformer but a lot did not.

"Doa driver" output card ?

Click to expand...

Originally the class A 2N3055 output stage unbalanced output was used to drive buses. Later it was replaced by the BA440 DOA.

all the aux sends , busses assign and the L-R master are summed to the proper "rail" in unbalanced mode?

Click to expand...

Yes.

about panpot it is controlled with some driver or only pot ?

Click to expand...

There usually was a single driver for all the buses and pan pot. The output of the pan pot went direct to the buses. Here is a link to the 1885 routing module which has two AUXes and four groups:

https://drive.google.com/file/d/0B_n67A1hN3qtWDJKNFNWd2ZfNmc/view?usp=sharing

also read somewhere that the mic input transformer can be used as line input with a "mod" like a "pad" ,
any info about ?

thanks
S.

Click to expand...

Most of the classic input modules had a separate line input transformer, the 31267, arranged as a 10K:600 step down and fed into the later stages of the preamp. I am not sure, but I think there was a modification for units with no separate line input to add one by including a pad in front of the mic pre input transformer. This certainly possible and many other manufacturers used this technique.  I do it on my own tube mic pre designs. The only problem with it is that it does not has as good a noise performance as using a separate line input transformer. You would typically used a balanced attenuator consisting of two 4K7 resistors and a 150 ohm resistor which provides a 10K balanced input and attenuates the line level signal by about 36dB. A nominal +4dBu input is dropped to -32dBu so the mic pre gain needs to be set to 32dB to restore the level.

Cheers

Ian

Why are not the red and white connected to anything on the 10468?

Cheers

Ian

Tie red to brown and white to black?

Rocinante said:

Tie red to brown and white to black?

Click to expand...

NO! that would short the transformer primaries according the the diagram you posted. Do you want the primaries in series or parallel?

Cheers

Ian

"Primary halfs are connected in series"

Is what i found.

Hense my confusion and how i came (wrongly) to the conclusion i did.