Simple EQ for Neve 1290

[ruffrecords]

As regarding the inductors I would like to discuss the fact that my inductors DCR is much lower than the winding sheets I have got from CJ,
My DCR for instance on the 10H is 151R and on the original wound ones it should be 700R.
As my one was wound on 6000AL with 1300 winds and the original was on 800 AL with 3500.

Would one have a better peak etc?

If I was to add resistance would it help or is mine better?

It is unlikely to make much difference. The Q of the circuit depends on the characteristic impedance of the circuit. The is made up of the inductor resistance and other resistors in the circuit. Good design practice is to make the inductor resistance only a small proportion of the characteristic impedance so its effect is usually very small.

Cheers

Ian

 

[Spencerleehorton]

So I take it from what you have put that my inductors are better as their inductance is the same but DCR is much lower?

 

[ruffrecords]

So I take it from what you have put that my inductors are better as their inductance is the same but DCR is much lower?

Depends what you mean by better. Your inductors have a lower DCR but we have no idea what other parameters are such as the BH curve of the core material. All real components are non-ideal so it is a designers job to ensure his circuit takes this into account.

The DCR of an inductor determines the maximum Q of the circuit but in audio the actual value of Q we need is a lot lower than this However, the DCR does also affect the accuracy of the cut/boost achieved so in that sense a lower DCR can be better..

Cheers

Ian

 

[Spencerleehorton]

So could it be that mine are not so good as the DCR is too low?

Is that why I’m not seeing much boost or cut when I probe on the pot out puts?

The originals after all have AL800 on both, I think they are on P22 and P30 and mine are P18 N30 - AL6000 (10H) and P18 N48- AL2800 (2H).
Can I add the difference in resistance and see if it improves? Or is it just the core material and AL which will change the curve?

I’m only testing with sine wave so maybe putting square wave or audio in I will see more difference in gain?

 

[Spencerleehorton]

My other area of discussion would be to use polyester, polypropylene or polystyrene caps, what would be best and why?

 

[Spencerleehorton]

From what I’ve read so far polyester caps are unsuitable for HF, and polypropylene are better and best is polystyrene caps.
Polyester are the least accurate and not used in precise circuits, where polystyrene are much better.
I’ve changed my caps from polyester in my wah wah over to  polystyrene and got much better results, so I will do the same with this  eq once I’ve got it working

 

[Spencerleehorton]

Right i'm back off hols and have used the LM358 chip to substitute the inverter amps incase they do not work.
23v going into LM358 and GND connected, used pin 2 as input from H on B205 and used pin 1 as output connected to M on B205.
The signal going in is 1.05v on F, the signal on Pin 1 of LM358 is 554mv and on Pin 2 is 689mv.
but the signal on H the output is 396mv!!?

If i just run the B205 and the B182 pcb i get 2.3v when eq is In on output and when in bypass it is 5.18v on output!!! quite a difference.
Tracing the signal on the B182 i get 396mv on input and 326mv on output.

So it seems that still the B205 has a big output problem? everything seems correct but output is really low?

How should i proceed? anyone got any voltages or ideas please?

 

[Spencerleehorton]

well with no one who seems to understand this circuit fully i don't know how to proceed, i'm being forced into shelving this project as the LM358 when i try to put a signal into it and see it on its output, i see very little?
I appreciate these are inverter amps but i thought these would amplify the signal?
without the inverter amps i get exactly the same output, which is down at 3.40v rather than  5.35v, i'm loosing 2v somewhere?

Also when twiddling the MF control from the centre to fully CW i get boost and from centre to CCW i get boost?

 

[Spencerleehorton]

The only thing that is a major difference is that Im not using a separate inductor for 200mH, I'm using the 200mH winding which i have put on the same inductor which I'm using for the 450mH, 1H and 2H winding.
I cant see that this would be an issue but could be wrong? and thoughts on this?

Should i be able to put a signal into the LM358 and get a signal out of it? I know this sounds dumb but when i do put a signal into it i dont get a signal out of it!!!

 

[ruffrecords]

So could it be that mine are not so good as the DCR is too low?

Is that why I’m not seeing much boost or cut when I probe on the pot out puts?

The originals after all have AL800 on both, I think they are on P22 and P30 and mine are P18 N30 - AL6000 (10H) and P18 N48- AL2800 (2H).
Can I add the difference in resistance and see if it improves? Or is it just the core material and AL which will change the curve?

I’m only testing with sine wave so maybe putting square wave or audio in I will see more difference in gain?

As I said  before, the Q of the circuit depends on the characteristic resistance of which the DCR of the inductors is usually only a small component. So unless the EQ is a very unusual design this should not materially alter the response or the gain.

Cheers

Ian

 

[ruffrecords]

Can you post the actual schematic of the LM358 and B205 you are testing.

Cheers

Ian

 

[Spencerleehorton]

I was using LM358P but supplied it with 23v then looked at spec sheet and it said supply with up to 16v! !
So more than probable that I’ve blown that one!!!

I’ve just isolated the b211 within what I’m calling the eq loop!!
And no matter where I put the inverter amp (C and E or K and M) it doesn’t make the signal louder?
This is on my channel A which I thought maybe the inverter amps may work!!

I have put a signal through them and I do get a signal from the output, sending signal into M and then probe on K I get a signal but the signal it half volume, if I probe on the generator it is 3v per div, once I probe on the output of inverter amp its only 1v per div?
If I connect the other way round I don’t get signal to output?

 

[ruffrecords]

I was using LM358P but supplied it with 23v then looked at spec sheet and it said supply with up to 16v! !
So more than probable that I’ve blown that one!!!

I’ve just isolated the b211 within what I’m calling the eq loop!!
And no matter where I put the inverter amp (C and E or K and M) it doesn’t make the signal louder?
This is on my channel A which I thought maybe the inverter amps may work!!

I have put a signal through them and I do get a signal from the output, sending signal into M and then probe on K I get a signal but the signal it half volume, if I probe on the generator it is 3v per div, once I probe on the output of inverter amp its only 1v per div?
If I connect the other way round I don’t get signal to output?

The inverting amps act just like op amps. It does not make sense to try to measure their gain in isolation. The basic way each EQ section works is illustrated in the documentation. In  general there is a 6K8 resistor in series with the input and another one from the output to the input to act as feedback. With controls centred this is a unity gain inverter so there is 0dB gain. The frequency selective components alter the effective values of the two 6K8 resistors to produce boot or cut.

Cheers

Ian

 

[Spencerleehorton]

I am testing each Pcb with the pots set to off position so I would assume I would get same level with eq in or out?

Could you confirm that with the inverter amps in it should amplify the signal?

As I can only get the signal to be lower when inverter amps are used?

What should the inverter amps actually be doing?

 

[alexc]

You could try 'prototyping' a 'filter' section  outside of your  main 'diy platform'.

Reduce the variables and focus on the 'building block'  ie.  a swinging filter stage with an active

Get the' flat' filtering action working right first  ..

  ...  then look at the 'travel' on each of the controls  -  filter stage gain of course, and then the frequency 'selective' thing.

When you get that going, then think about the integration into the wider context  ..  which in this case is all 'series'.

Otherwise, re-group and tackle again.

 

[Spencerleehorton]

Well the HPF works fine, the b205 is down at least 2v in output along with b211 which is down as well.

My question I don’t feel has been answered, does the inverter amp amplify the signal as when I run each board on its own (b205 b211) the output is down.
When I attach a inverter amp its level goes down even more!!

Does the inverter amp add make up gain to b205 to bring it up 2v?

 

[ruffrecords]

As I said earlier, the EQ with controls flat (of set to off) should have unity gain.

Cheers

Ian

 

[Spencerleehorton]

i take it that when you mean unity gain it should be the same level when in bypass as when the eq is on but each pot is set to off?

quick test this morning shows this:

using LM358, supping with 18v from 2 x 9v batteries

putting in sinewave at about 0.775vac

getting 1.5vpp on input pin 2 (LM358) and getting 974vpp on output pin 1 (LM358)

in bypass on output im getting 9.01vpp and EQ on (only put in B211 pcb) 6.47vpp

if i swap round pin 1 and pin 2 on LM358 i get the same output but the pins swap in voltage

output is still down when EQ is in?

 

[ruffrecords]

On an LM358:

Pin 1 is the output
Pin 2 is the inverting input
Pin 3 is the non-inverting input

If you have this set up correctly for use with a single supply then you should have arranged a dc bias at half the supply voltage on pin 3. There is no point measuring at pin 2 because this is a virtual earth if the circuit is working properly. The 'input' to the circuit is not pin 2 but the other end of the resistor feeding it. Again, can you please post the schematic of what you are testing.

Cheers

Ian

 

[Spencerleehorton]

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

I have 283 and 284 pcbs i am then putting in each individual pcb to test (b205, b211 and b182)

DC bias?

Also i haven't put in the 10k resistors to gnd or the 180pf or 470pf caps?