Simple EQ for Neve 1290

[Spencerleehorton]

would you say this would get me close to 1H inductance?

http://www.ebay.co.uk/itm/10x-RM8-Pot-Core-Ferrite-Bobbin-Philips-Epcos-Coils-/361200418349?hash=item541938fe2d:g:gIQAAOSwWKtUyQKT

if i used 0.1mm wire?

I hope i could make both 100mH and 1H from these?

also as you've said i dont need to use transformer, would i still be implementing this within where the 5k pot is within the Neve or somewhere else?

regards

Spence.

 

[Spencerleehorton]

Here we go!

It is announced as Al630, so you need 1260 turns for 1H. Cross-section is about 28mm², which indicates a maximum square-section of wire of 0.022 mm² resulting in a diameter of 0.14mm.
Mean Length Turn is 42mm. Closest gauge is 0.125mm (AWG36), resulting in a DC resistance of about 75 ohms.
You would need only 400 turns for the 100mH, for a DCR of about 25 ohms.
Beware that adjusting the final value needs to be done in-circuit, checking the actual circuit's response. Most inexpensive LC-meters give very inaccurate values. If you need super-accuracy, you should wind a few percent more turns than the calculation and adjust for teh final value. Also beware that properly setting the two halves of the core is important; there could be as much as 5% variation between an not-too-well seated core and one that's properly set. You have to rub them against each other.

 

[Spencerleehorton]

I suppose the next question is current, what current does the 553 need?
Also I'm wanting to put a VU meter driver in circuit and I I can see it gives out 12v as it has a 7812 regulator so will it be good to feed it 15v from the 24v on the Neve 1290?
If I'm right, I need a 9v drop and if say the 553 needs 200mA I would need a 47ohm resistor.
And am I right in thinking the 2520 works best on 16v?
If so I would need a 39ohm resistor to bring the 24v to 16v?

Again this is all assuming the 553 needs 200mA.

Please put me right if I've got this wrong!!!!

 

[Spencerleehorton]

I’m the final stages of getting this going!! I know it’s been ages but been busy with other stuff!!
I have 9 X Neve 1290 mic pre’s now and have put in the 5k output pots on all.
In a stereo 2U I’ve got the 1290 and the 553 eq.
Will be testing today and put up some photos once finished.

 

[Spencerleehorton]

Finished the final connections and tested with generator and scope, looks good on scope will now test with mics.

 

[Spencerleehorton]

well to my ears, the API-553 eq is very subtle, still some more testing with fresh ear tomorrow as ears tired after long rehearsal!!
think i might be better set trying to do the proper Neve EQ, will look into doing some pcbs and winding some inductors.

 

[Spencerleehorton]

I have looked into building the 1073 EQ with the B205, B211 and B182 pcbs, will probably order the inductors from Carnhill, just wanted to ask if i need 2 x Carnhill VTB9043 per channel as it looks like on the 1073 schematic that there is a C and D?
so is there 2 x B182 pcb? with a Carnhill VTB9043 on each or just one B182?

 

[alexc]

That api 553 circuit is very nice when it's done well. 

In my case, with a 1ru 'dual mono' version with relay-bypass added, I found that  inductor  shielding is very 'nice to have'  [ie. critically important]. 

After I had tamed the inductor hum,  I found this eq to    'do the job'    nearly    'most of the time'. 
The bass is quite responsive and works great either way - boost or cut;  the high band is quite 'airy' and mostly I use it to cut high freqs 

...  I do think one needs to check the 'break frequencies'  and so on, to suit one's own taste and  what with whatever 'inductor' variation you might have over the original. 

The mid freq  was quite  tricky to keep 'away' from the low and hi bands,  once one starts messing with different inductors  etc.

So,  some patience is required in 'scaling'  of some of the R and C values  to  suit one's part choices  (pot law is important here I think)  ..  somewhat 'by ear' as well as by 'calc' and by  'measurement'  [ the 3 Rs of audio eng]

And finally, I think good quality potentiometers and switches is a good idea ....  I like 'alps' pots  in general, both single deck and dual deck ....  you can get 'stereo' with such (and 2x compact 553 style eqs)  with a good chance of success [imho -  which not always a given for stereo eqs].

I ended making two of these    'dual channel api-ish  553 eq' boxes and funnily enough, I use them all the time  with my own  'neve-e style 1272' build        ...    as well as my  'gyraf 1176 style' build   

That makes it  2x  channels of  'preamp-eq-lim'    otherwise known as 'channel strips' ,    for quite modest cost .. 

Certainly the 553eq is a great example of it's kind  - easy to use 'in the moment'  eqs  [very important in a stereo mix-down context  ...  each hand, grab a knob, both sides and turn together  till sound is good-er]


Anyway - fab - carry on!

 

[Spencerleehorton]

thanks dude, but i think i'll put this 553 into another enclosure and work on the Neve EQ now, might be better paired with another couple of api-312 channels.
I need something more true to original Neve to my ears, so i'm working on the pcbs as we speak!!

 

[alexc]

I can understand the want for a neve styled eq, no  doubt!

I have my trusty old 'chineve tnc 81' units, all modded to my basic satisfaction, and the closest I personally have heard of the classic.

Now that's just simply a case of I've never used the real thing or even a good modern re-creation  of the hardware  ;D

I especially like the hpf and lpf filter switches ...  most of the time I have these going .. 

My 'chineve tnc 81' is a little busy on the front of the 1ru rack, so I have to have it up fairly close  to my  eyes - to see the dials ! - and really  get the most out of it - so it's my 'most used' lounge channel, right next to my computer etc.

Next role for the pair that I have, is going to be on the output of the 'neve-e style sum bus'  build I did a few years out  and that sits under my tv ..  for those  'tv jam'  occasions

 

[Spencerleehorton]

What inductors did you use for the b211 pcb?
I’ve read that the b211can use a custom wound vtb1952 which is the same as the T1295 but has the extra 200h winding.
I have some cores and bobbins here so could wind my own as per don classics and also copper shield them which I’m not fully sure how that’s done?
Any advice also on what the T1530/vtb9050 values are as well please.

 

[alexc]

Well, my 'Chineve TNC 81'  neve-e style commercial builds  did not use any 'name' parts  as stock ..  but as part of my 'taming the inductor hum', I replaced with some carnhill standard inductors for the 1081 type builds.

I can't remember the model identifiers anymore ..    but they were the ones rightly specified for modern re-creations of the 1081. I can look them up if needed. 

Thus I replaced the ridiculous stock sino inductors (tossed them into the ocean) with good quality moderns and was amazed at the difference even without shielding, but I had come so far I wasn't going to settle for the usual dross in the 'hum' region.

I did 'encase' those replacement Carnhill inductors in some oep 'mu-metal cans' and ended up with crudely but effectively shielded carnhill tapped inductors with 'flying leads' - I mounted them upside down, 'gooped' up the lot but good and simply soldered the leads into the footprints of the original 'nfg inductors'. 

I did a lot of measurements etc and verified the mod was correct of course.

The freqs did change a bit, cause the 'chineve' thing was only a good approximation to the real deal ..  but remained close enough to not worry much.  I would say my modified filter sections approximate fairly closely 'on paper'.

SO - all the 'orrible hum and noise and hash  disappeared  and the miraculously became useable and very, very quiet  [some other mods were done in the area of replacement of transistors], despite the  stock  'inglorious basterds' approach of the psu, which was typical sino crap.

Signal transformers remain stock and complete crap - BUT it is a testimony to the incredible and undoubted greatness of the original, that even 1000 semi skilled practitioners can't entirely  'fork it orp'.

 

[alexc]

Copper shield is fine and all, and certainly does improve in some kinds of e-m interference  but to my mind  ..

    'there is no substitute for iron'    It truly is 'the rock of ages'

 

[Spencerleehorton]

I’m going to end up buying the Carnhills but want to give a go winding some inductors first.
I have some mumetal which I can put them in as well.
Just need more specifics of what H or mh the windings are on the b211 to proceed.
On the schematic it doesn’t say but I’ve worked it out I think as the 160mh and the 1H windings then the other inductor is 200mh.
If this is the case I just need to build one with these 3 windings?

 

[alexc]

I can review my notes on the inductor section - I think I have the approx L values for the tapped inductors etc somewhere.

Inductance is a measurement that in audio requires some skill, one which I don't have sadly  :-X 

In my 'transposition' of inductors from 'who the f** knows what'  to  proper  'modern recreations', I did mostly rely on 'relative measures'  ...

ie.    measure and  test    as best you can the coil inter-connects, series resistances  and some 'indicative L measurements'  [if you have them]  of both the 'old' and 'new'  out-of-circuit to get the basic parameters of each

..  and then try to 'manually' correlate all that -  with some known info  ...  the originals  ...  and some specs from the  modern, be they 'chineve' or some other manufacturer, say Carnhill.

I'll take a review and see what the inductor L values are in my build. I think I have a 'data pack' of all that, I'll check.

 

[Spencerleehorton]

Thanks very much, all I wanted to verify was what windings it uses and what inductance each winding is

 

[Spencerleehorton]

Just need to verify that I need two inductors:
1 with 130mh, 700mh, 7000mh, 10,000mh
And one with 160mh, 1000mh and a 200mh winding you replace the other inductor?

Is this correct to complete this circuit or do I need any of the other winding found on the original inductors?

 

[Spencerleehorton]

Also DCR of windings would help!!

 

[CJ]

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[CJ]

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