Neumann W492 equalizer DIY project (PCB docs added)

[Lasselakken]

Just wanted to share a few pictures of my finished project. I managed to squeeze two channels into 1U. Omeg pots are from Rapid Online (UK) and I used some green/red LEDs to show if filters are in or out. The front is made with letraset and all drilling is hand held, so absolutely nothing lines up, but I kind of like it that way.
I drilled three 3mm holes in each pcb which enabled me to mount them on adhesive plastic stands.

https://www.dropbox.com/sc/31hak3r6m673pwi/AADsQao3RyE0nvIyI-ixrmWOa#/

 

[Gustav]

Finished two channels today (managed to fit them in a 2RU box).

I dont understand how switching the resistor in and out works as bypass for the individual bands. I can't figure out what the significance of that single resistor is, no matter how long I stare at it. If someone could/would explain, I would be very grateful, and quite possibly grow a little smarter.

Gustav

 

[Lasselakken]

The Danes are on a roll 
I have a couple of Lundal LL 1540 input transformers lying around. Would it make sense to use them as input transformers instead of first half of the first NE5532?

 

[Lasselakken]

And here's part of the LL1540 data sheet...

 

[audiox]

I dont understand how switching the resistor in and out works as bypass for the individual bands. I can't figure out what the significance of that single resistor is, no matter how long I stare at it. If someone could/would explain, I would be very grateful, and quite possibly grow a little smarter.

The resistor is there just to avoid switching noise (to keep the switch poles in the same DC potential). When the switch is open, the 330k forms a voltage divider with the low value resistors connected to the non-inverting op-amp input and attenuates the audio signal almost 50dB. Which is enough to give a "flat" response.

 

[audiox]

I have a couple of Lundal LL 1540 input transformers lying around. Would it make sense to use them as input transformers instead of first half of the first NE5532?

Makes more sense to use WITH the op-amp U1A which provides low source impedance for the following circuitry.

 

[Gustav]

I dont understand how switching the resistor in and out works as bypass for the individual bands. I can't figure out what the significance of that single resistor is, no matter how long I stare at it. If someone could/would explain, I would be very grateful, and quite possibly grow a little smarter.

The resistor is there just to avoid switching noise (to keep the switch poles in the same DC potential). When the switch is open, the 330k forms a voltage divider with the low value resistors connected to the non-inverting op-amp input and attenuates the audio signal almost 50dB. Which is enough to give a "flat" response.

Thanks!

Gustav

 

[Rocinante]

So I am getting real close to hooking up the 2 x 15v 50va Triad toroidal through the 1518 psu via PCB Grinder and testing these guys but as I was rereading the thread (for the umpteenth time)  I realized my xfmr's current seems much higher than many others.  I guess my math was way off.  I got this from Digikey:

http://www.digikey.com/product-search/en?WT.z_header=search_go&lang=en&site=us&keywords=237-1333-ND&x=0&y=0&formaction=on

Specs say this toroidal current is 3.34 amps of current.
A little look-see from one of you fine gents (or ladies) would be just the bees-knees.  I really don't feel like blowing this up but I feel like that might be too high of a current.  Thanks.

 

[pvision]

So long as the current rating is high enough the rating doesn't matter.  The trafo just delivers what is required

The current draw of the equaliser is tiny - see my earlier post for details.  You could use a much smaller transformer

Your transformer will give about ± 21 volts DC after the regulators

Nick Froome

 

[Gustav]

Your transformer will give about ± 21 volts DC after the regulators

Its probably a typo, but the the transformer will give you about 21 volts after rectification, the regulators will regulate that back down to their nominal values (15V for the  7915/7815), which is all by the book.

Just to avoid a "But I only need 15V!" scare...

Gustav

 

[Rocinante]

Nick, Udo; thank you.
I picked up the "nicer" 7915's after reading enough posts about them failing so hopefully they'll be alright. I probably should have gone the 337 route since that's what I did with the 1176 I'm finishing as well as the ml12 PSU I just finished.
Thanks again for replying so fast. I'm just two 5.1k r short (which USPS should have here today) from finishing since i misplaced them somewhere which is pretty silly and frustrating. Not a ton of a variety of knobs for the omeg pots either. 4mm is a peculiar size apparently.  The hunt continues.

 

[pvision]

Yes sorry, typo.  I meant rectifiers

Nick Froome

 

[Gustav]

4mm is a peculiar size apparently.  The hunt continues.

http://www.musikding.de/Adaptor-4mm-6mm

Gustav

 

[Rocinante]

Thank you Gustav.  Not so coincidentally I just found that after following a post on here regarding the same thing.  Those will do perfectly thank you.

 

[Greg S.]

DOES someone have the Matchcode for the 2 Missing Pots? (Digikey e.g.)
For us Europeans, it makes no sense to by in US. It's too expensive Brian

I know that a whole bunch of you are waiting for me to get the BI 10K lin pots back in stock.  It is still going to be quite a while.  I thought I'd point out though that Digi-Key has the exact same part in stock.  Their part number is 987-1665-ND.  You could buy six of those and two of the 2x10K pots from me and that would give you a complete kit.  A little more money, but no waiting.

Brian

 

[Gustav]

Thank you Gustav.  Not so coincidentally I just found that after following a post on here regarding the same thing.  Those will do perfectly thank you.

I have to admit, that I have found the plastic types to be better, but I can't seem to find them anymore

Gustav

 

[Gustav]

DOES someone have the Matchcode for the 2 Missing Pots? (Digikey e.g.)
For us Europeans, it makes no sense to by in US. It's too expensive Brian

I know that a whole bunch of you are waiting for me to get the BI 10K lin pots back in stock.  It is still going to be quite a while.  I thought I'd point out though that Digi-Key has the exact same part in stock.  Their part number is 987-1665-ND.  You could buy six of those and two of the 2x10K pots from me and that would give you a complete kit.  A little more money, but no waiting.

Brian

http://www.banzaimusic.com/Alpha-16mm-stereo-10k-lin.html

Not conductive plastic, I know...

Gustav

 

[kante1603]

Hi Gustav,

excuse me chiming in,but since this circuit is dc coupled it is absolutely necessary to use conductive plastic pots (see reply #3 on the first page).

Best,

Udo.

 

[Greg S.]

thx G 

 

[kante1603]

If you're looking for the Omegs here's a link you can check (for german/european buyers):

http://www.alphastat.de/products/omeg/omeg.html

Send an inquiry to Mr. Kirchhoff,he is very helpfull and has managed to get some "exotic" pots for me a while back.

Best,

Udo.