Simple EQ for Neve 1290

[ruffrecords]

HI Ian,

DC bias?

That was in reply to your post about measurements on the LM358

Cheers

Ian

 

[ruffrecords]

HI Ian,

I am using the 1073_1084 User Guide as found here

http://www.thehistoryofrecording.com/Manuals/Neve/1073_1084_User_Manual_Issue_5_1.pdf

That does not contain any schematics. You should be using this one:

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

So let's trace this step by step. What is the signal level at Pin P of the BA283?

Cheers

Ian

 

[Spencerleehorton]

Yes that is the schematic that I’m using.
Just out for xmas dinner will send P level once I’m back.

 

[ruffrecords]

Yes that is the schematic that I’m using.
Just out for xmas dinner will send P level once I’m back.

Have a great time. It is my granddaughter's 15th birthday today. We are going bowling first and then for a Thai meal. The it is back home to watch the final of Strictly Come Dancing.

Talk to you tomorrow!!

Cheers

ian

 

[Spencerleehorton]

Hi Ian,

signal level @ P on 283 = 2.96 vpp

 

[ruffrecords]

Hi Ian,

signal level @ P on 283 = 2.96 vpp

OK, this will be our reference. This same signal should also appear on the B205 pin F. Can you verify that?

Now with the HF and LF controls flat of off you should see exactly the same level at pin H on the B205. Can you verify that?

Cheers

Ian

 

[Spencerleehorton]

yes  2.96vpp on F of b205
on H of B205 = 352mvpp with C and E of B284 connected, without C and E connected = 978mvpp

i have detached gnd connection (39k/12k) and removed output connection on H and now with testing i get

H = 2.95vpp
F = 3.00vpp

so much better, so this pcb seems to be working but without anything else connected to it!!!!

with output connected (L into 283) H = 1.28Vpp

 

[ruffrecords]

OK, we are making some progress. As it is now (working) can you check if the bass and treble boost/cut actually works.

Cheers

Ian

 

[Spencerleehorton]

Yes there does seem to be movement with all pots, if i move frequency down to about 250hz the LF pot works, although CCW rather than CW and the HF works CCW if i then up the frequency to about 3khz.
when i select the frequency with the lorlin, pos 1 off, pos 2 to pos 5 the waveform gets smaller?

Is it meant to do this?

also to get anything to work i had to reattach gnd lead to 39k/12k resistor and now output is down to 2.48vpp

no inverter amp connected at this point and only scope on output of b205

 

[Spencerleehorton]

I will draw out how I’ve connected the pots as I can see a few ways that they can interpreted.
Hopefully my mistakes are just in how I’ve wired them up!!

 

[ruffrecords]

Yes there does seem to be movement with all pots, if i move frequency down to about 250hz the LF pot works, although CCW rather than CW and the HF works CCW if i then up the frequency to about 3khz.
when i select the frequency with the lorlin, pos 1 off, pos 2 to pos 5 the waveform gets smaller?

Is it meant to do this?

also to get anything to work i had to reattach gnd lead to 39k/12k resistor and now output is down to 2.48vpp

no inverter amp connected at this point and only scope on output of b205

OK, this looks about right.

Cheers

Ian

 

[Spencerleehorton]

So to use the lm358 opamp correctly I would have to input signal in both the inverted and non inverted inputs?
The b205 has H as output and M, would I use these the put the output of lm358 to input B of b211?

I was only using inverted input before.

 

[alexc]

I'm just looking for some drawings a good GroupDIY member posted years ago  ...  a couple of redrawn neve-e filter sections that were 'decomposed' showing the operation - in a very useful way.

Not too much regarding 'inductors' per se ..  but useful on the 'others'.  They certainly helped me understand the 'classic'  filter operations better.

You can let me know if it just is obscuring the o.p, and I'll take down.

 

[alexc]

OK - found a few ...  now this relates to 1081 filter sections, so again it may of no use..  but anyways ..

 

[alexc]

and this one ..

 

[alexc]

..  one more


There were more but that's what I have so far ....  also the corresponding  'curves'  from a 'sim',  I suppose  - or could be just  hand drawn diagram ..

I could put there up in there's any interest ..  I have about 8 of them from the same fine GroupDIY contributor  circa 2009 I think.

....

As always, there are lessons  that one take on board from the broader subject .. like this.

At e.e school, some 40years ago ...  they always would make you 'draw up' these kinds of equivalent circuits representing the situation at the various 'end points' of freq or resistance  ..  and with more 'canonical' forms  [lol - I said 'canonical']

 

[Spencerleehorton]

well ive tested each pcb on its own without its output connected back to 283 (L) and no inverter amp connected and get same voltage on input as output and eq does function.

so now i think its time to move onto getting the LM358 working with both the b205 and the b211.
once im confident that it works fine, i will revisit the inverter amps on the 284 pcb.

then i need to look at why when the output is put to L on 283 that it loads down and im dropping signal?

 

[ruffrecords]

I am puzzled as to why you have suddenly started testing without the inverter amps. The EQ will not function correctly without them. If you only get the same signal at output  as at the input of each EQ without  the inverter amps then there is definitely something wrong with them.

Cheers

Ian

 

[Spencerleehorton]

Ah ok, well at least we know they are wrong, how should I proceed in testing do you think?

I do still need to know how to hook up the lm358 correctly.

Also here is a drawing of the lorlin on my b205

 

[alexc]

Not sure really - but what I do when I need to 're-baseline'    ..  is  to 'remove from circuit'  the complex parts  ..  get some baseline going again on the 'platform'      ..  [  the input part  and the output part]  ..  good  if thats all good.

Then take a 'filter' assembly, and  focus on just that one ..  could be 'out of your platform'  ..  like a 'test' rig for example.

Could be any of the several  flter sections  ...  then, later  integrate that into your 'platform'  [prefereably with some measurements ..  maybe in dB]

And go from there.