Simple EQ for Neve 1290

[Spencerleehorton]

Well I’m 45 now!! Been fiddling and making stuff for about 5 years or so now, love attempting stuff then getting frazzled and having to ask a million questions to try and figure out what’s wrong!!
I’ve had a five year plan of getting 16 decent preamps and 16 compressors and a good interface and mics.
Using this gear is the best thing as couldn’t afford to buy any of it second hand, once these last few projects are done I’m gonna knuckle down and record and produce my mountain of songs!!
Over 200 but getting through them as have done 4 albums this year!!!

 

[alexc]

Even better ...

 

[Spencerleehorton]

Thought I would have problems!!
Need to redo wiring as have noticed the phase switch is after the output txf?
I had it before input txf, is there a reason which is better?

Also the bypass switch,  does it need that 2.7k and the 22uf?
The  P connection on the ba283 normally connects directly to L, or I’ve put in the 5k output pot between P and L.
Just wondered why more resistance is needed here and a cap? Stray DC? also the 39k to gnd?
I’ll try with and without, just thought this would effect the signal, or rather reduce it?

 

[Spencerleehorton]

well I've connected it up as per schematic and in bypass all works as it should but with the EQ in i get nothing?

Had a B- wire off the start of the inductor on the BA211 pcb which is doing the job of T1295 and T1530

still no sign of eq when engaged, apart from in bypass if i twiddle the frequency lorlins i can see the waveform change a tiny bit?
must have some wrong connections somewhere?

 

[Spencerleehorton]

I'm getting some movement in the HF and MF that i can see on scope, big level difference between bypass and on, when the EQ is on the level is quite low.
ould someone redraw the on/off eq switch just so i know I've got it right please?

 

[Spencerleehorton]

need a bit of help wiring the EQ bypass switch please, try to compare to AML version schematic as im not familiar with how the bypass switch is drawn on the 1073 full pack?

 

[Spencerleehorton]

Does the output pot 5k go in between P and L on BA283 then the output of HPF (15nf/12k) to U of BA283 then P of BA283 back to 6.8k/620R?

then the other outputs on MF the 2.7k/8.2k to U (input) of BA284 then back into 1.2k/10k pot leg?

I am still in the dark about how to put the EQ into bypass? could someone explain please?

 

[Spencerleehorton]

There must be someone here that knows how to build this!!???

 

[Spencerleehorton]

signal only comes through on pin 2 of output when B- (0v) is attached to pin 3 of input?

Sorry was confused here, looked at one schematic ez1290 and then looked at 1073 fullpack, one looks like B- (0v) is attached to pin 1 on input and other looks like it’s only connected to txf output!!
Also I was disconnected on gnd on my scope!! Doh

One channel preamp works great the other when I adjust output pot the waveform cuts off rather than go smaller so will have to trace signal and see why it’s going funky!!
wired output pot wrong!!

Eq not working yet!! Have done a mod to 211 Pcb and put in 220k after 2.7k and put in 450mh winding to 200nf, AML version uses 220nf here?
Also AML version has bypass buffer!?

 

[Spencerleehorton]

I’ve downloaded the don classics schematics and going to see if I can get it going today, the bypass switch is featured on there, a few things I don’t understand yet bu I’ll see if I can get the hpf going first!!

 

[alexc]

Hi Spencer - I sent you a PM with some info on how the switch is connected.

Here is an illustrative snap of my chineve 1073 schemo [attached a few posts back] which shows the EQ In/Out switch.

Note the 'eq substitute resistor' 2K7 which the S7 EQN. switch on the original implements the same.

Hope this helps .. 

..  you can 'correlate' the chineve schemo quite closely to the orig. There are some diffs of course, but it is similar in most of the important stuff.

 

[alexc]

Didn't know of a 'bypass' buffer in other related '73s  ...  how  does that go ?

 

[Spencerleehorton]

this doesn't really help me i'm afraid, is the 2.7k in there when the EQ is not engaged? or are you saying leave it out? looks to me like it switches in the 2.7k when in bypass then whatever those EQ conections are switches them in?

What are those EQ connections the outputs or inputs from?

Also does the BA294 feed the BA205 or does the BA283?

 

[Spencerleehorton]

i can see the eq working fractionally but not 18db of +/- also the signal is down massively when putting EQ in so something isnt right!!
its seems part of my wiring is correct as in the control pots for the EQ but where i have it into the amps isnt, just need clarity on where to put it all in

 

[Spencerleehorton]

right here is where i'm at with it:

After much farting around R7 on BA283 started to smoke so replaced and re adjusted TR3 (2N3055), 5k pot for some reason must have shorted or something? but its fixed now.

Ive now looked at all the inputs and outputs and trying to establish from the 1073 schematic how all the BA205, Ba211 and BA182 are wired together with their inputs and outputs, Along with BA283 and BA284 pcbs.

I think i'm right in saying that the signal path uses the BA283 U is input and P is output of first stage then input is L on second stage.
At higher gain levels it uses the first gain stage on BA284 input U and output P on this stage.

The Eq is now put into the other two gain stages:

Gain stage 2 on BA284 input is C and output is E

Gain stage 3 on Ba284 input is K and output is M

should i be putting a signal separately into each EQ pcb?

or are they all wired in together?

from what i can see on the Don audio schematics is should be BA205 input is F and output is H into BA211 input is B output is C into BA182 input is COM A output is COM B.

is this correct?>

 

[Spencerleehorton]

It seems I’m not getting an input into ba182 (K) so I’m not getting anything on M either?

getting good signal on ba284 C connection going to F on BA205 but signal on output of BA205 at H is much lower,
so BA211 input is really low and into gain stage from BA284 K and M there is no signal.

Someone must have a complete schematic that its possible to follow surely?!!!

 

[alexc]

The 2K7 is switched in when the 'eq is bypassed'  and 'switched out' when the eq is active

I send you some more info in email ..  cheers

 

[Spencerleehorton]

ok Alex, did you get my email?

seems its just me and you!!!

will post my inductor specs incase they are not what they should be!!

BA211 inductor

200mh is 185mh at 16.7R
450mh is 595mh at 29R
1H is 985mh at 36.3R
2H is 2.07H at 49R

BA182 inductor

1.3H is 1.36H at 47.4R
3H is 3.13H at 75R
7H is 7.57H at 123R
10H is 10.77H at 151.8R

 

[Spencerleehorton]

check here for the AML 1073 with the bypass buffer

http://www.audiomaintenance.com/downloads/ez1073addon_colourbook.pdf

 

[Spencerleehorton]

my problem seems to lie with the BA182 output, tbh i want to double check the feed to all these pcbs.
ba205 seems to have good output on F, BA211 and BA182 are off