Simple EQ for Neve 1290

[Spencerleehorton]

The question now to ask is about the signal path.

My plan is to just try the hpf in and out of circuit as I can’t get all pcbs to work.

The signal comes into 284 Pcb into U and out of P then into output 5k pot then off to 283 input L then to output txf.

I see each Pcb basically has its own gain stage but are they connected in series?

I say this because if the signal comes out of P of the first gain stage on 284 where does the signal then get to for instance the ba205 pcb?

Is it as per my drawing or does the signal route a different way?

 

[Spencerleehorton]

Is this the signal path?

 

[Spencerleehorton]

Just realised that picture is wrong gain stage 1 is on 283 pcb

 

[Spencerleehorton]

http://www.thedonclassics.com/nv73eq-diy_schematic.html

In these schematics I don’t understand why it says from P of NV73 mic pre And then on same feed it says to P of NV73?

Can anyone explain this?

 

[alexc]

The second diagram is closer ...

The 1073 signal flow is like on the 'block diagram'.  Of course, things get a little more complex with the 'wiring diagram'.

You can use a plain old 'signal tracing' thing as there aren't any high voltages or high amplitude signals going on.

I would ensure that the 'front end' is basically  sorted first  ..  ie you can get both parts passing clean signal.

ie  the BA184 part, and the BA283AM part. 

Then I would check that the output section is working ..the BA283AV with the T03 class A driver and transformer.

Get the basics of the EQN. S7 switching so it at least 'bypasses' the EQ filter sections.

Then focus on the filter sections each in turn which are series connected 

ie.  the first filter (1 of 4)  BA205_1  and the second filter (2 of 4)  BA205_2 are both handled by the one 'make up gain' part BA284_1

and the third filter (3 of 4) BA211 has it's own 'make up gain' part BA284  ..  and the fourth filter (4 of 4) BA182 has no 'makeup gain part.


You can debug each  of the sections  'removing them'  from the chain and checking individually and so on until you get the basic signal flow correct.

Sorry if I'm covering old ground here ...  this stuff is usually easier to 'do' than to 'talk about'.

The other thing you can do is take a snapshot of the 'wiring diagram' and 'seperate out' the blocks so you can simplify the view of the tangle of wires  

I use a pic editor to  'slide and dice' the diagram and rework it, with highlights of connection lines as I understand / trace  the thing of interest.

 

[alexc]

In your N73 diagram, the P thing just looks like a redundant notation - the P lines are the same.

And the Neve block diagram has a few errors in part names too.

 

[Spencerleehorton]

Right I’ve got the first b205 going, seems the gain stage c to E on 284 has a problem so I used K and M stage, will look at C and E gain stage and see what is happening!!

 

[Spencerleehorton]

Also I’ve compared DCR on inductors and my inductors have fairly close inductance but DCR is much lower!
What effect will this have?

For instance my 10H windings DCR is 151.8R and the T1530 10H winding is 702R,  will I need to put a resistor in 510R to make up the difference?

 

[ruffrecords]

Have you got this?

https://www.technicalaudio.com/neve/neve_pdf/1073-fullpak.pdf

It should be your blueprint for the 1073.

Cheers

Ian

 

[Spencerleehorton]

Yes ian has loads of mistakes!!

 

[krabbencutter]

Have you got this?

https://www.technicalaudio.com/neve/neve_pdf/1073-fullpak.pdf

It should be your blueprint for the 1073.

Cheers

Ian

https://www.technicalaudio.com/pdf/Neve/Neve_1073_1084_User_Manual_Issue5.pdf

This is the "more correct" one 

 

[Spencerleehorton]

I think the most useful question at the moment so I can move forward is what is the signal input and output for the b205 Pcb?

 

[ruffrecords]

I think the most useful question at the moment so I can move forward is what is the signal input and output for the b205 Pcb?

It sits around one of the inverting amplifiers in the BA284. One of these has its input on C and its output on E. The other has its input on K an its output on M.

The mic pre output is from pin P of the BA284. This feeds the bypass switch and also pin F of the B205 so that will be the input. Its output is from pin H which also has a connection to the inverting amp (EC) in the BA283. The output  pin H then feeds the BA211 pin P (its input) and this has the other inverting amp (KM) in the BA284 wrapped around it. The presence output is from the BA211 Pin C which via  1K2 resistor feeds the BA182 HPF board. The output of this is the wiper of S4b which then goes to the other side of the bypass switch. With the controls flat of off you should be able to see the same signal level at all these points. Divide and conquer.

Cheers

Ian

 

[Spencerleehorton]

Thanks Ian that was really helpful apart from you put "The mic pre output is from pin P of the BA284" which i think you meant P from BA283, as P on BA284 i think is for higher gain settings?

I can now see everything is working but big difference in volume when engaged, eq on is about 4 times lower than when in bypass!?

on B205 where should M go? I've got it back into H at the moment?

 

[Spencerleehorton]

this is how i have it connected now:

output P from BA283 goes into F on B205
C on BA284 is going to M
E is going to H on B205

H fron B205 (output) to B on B211
C from B211 to M on BA284
K on BA284 to B on B211

C on B211 (output) to Com1 on pot (with 1.2k)
Com 2 on pot to L on BA283

is this correct as its working but level is ridiculously low!!!

 

[Spencerleehorton]

Also you have said pin P on 211 is input, I think you meant B?

 

[Spencerleehorton]

This is how I understand it to be,

Is this correct?

The inverting amps seem to be a problem

 

[Spencerleehorton]

when ever i connect the amp C and E on BA284 to B205 it lowers the signal?

 

[Spencerleehorton]

Small success so far, have just put in b182 Pcb and get good signal through with eq on and off, so problems with the other two pcbs

 

[Spencerleehorton]

same small success with the B211 pcb, seems to work fine after one wire was wrong.
Seems all my problems lie with the 205 pcb will remove from circuit and go over all connections.
as it is when ever i attach inverter amp (C and E on 284) the signal is halved?