Neumann W492 equalizer DIY project (PCB docs added)

[lars on]

@TwentyTrees

What voltage or db did you had when you adjusted the trimmers ?

 

[TwentyTrees]

What voltage or db did you had when you adjusted the trimmers ?

I don't recall, and I'm not sure it really matters what the absolute level is - just that what you're measuring on the other side is 15dB louder at the required frequency. If I remember right, I swept the band in question at 15dB using REW to establish the exact frequency being boosted; zeroed the band gain, and used the tone generator function in Reaper at somewhere around 0dBu (0.775V); then used Voxengo SPAN to measure the increase with the band gain turned all the way up; then trimmed that to +15dB. Much easier (for me) than going by voltages and trying to convert to dB.

 

[andow]

Hmm, that's really interesting - it's definitely a pronounced change on my build, max low mid / high mid bandwidth increased to 0.45 Q (just under 3 octaves) and minimum decreased to 3.6 Q (1/3 octave). Original Q was around 0.7 or so (more or less 2 octaves).

I spent some time testing various values of RB1-3 and slugging the pot all kinds of ways, measuring the results in REW, and I ultimately preferred how a linear pot worked here. That said, this is a bus / mastering EQ for me so I do tend to use it more with wider Q settings. Having reviewed my notes, if I was looking to get a narrower bandwidth / higher Q I'd start by increasing RB2 in relation to RB1 and seeing what happened there. Let us know what you find!

My bad, I had one wire connected to the wrong side of the resistor....  :-[

Your values actually work pretty well! Except that I added 820R for RB1 (in your drawing) as I don't need the extra wide setting at it gives me a little more evenly spaced control.

I'm using potentiometers throughout with a gain of 10dB, and since they are all linear the stereo matching is pretty good actually!

I'll post some pictures when it's finished....

 

[andow]

I've had a chance to re-check the Q range this morning - here's the full range at +15dB 460Hz in the low mid band (ignore the slight wibbliness at top and bottom of the frequency spectrum, that's a problem with the calibration file I'm using in REW - the W492 is flat as a pancake otherwise):

Yes, you're right that the range is a bit cramped at the far end of the rotation, and that would explain why the pot normally ends up in the 6-11 range for me.  ;D  The way I have things wired, inverse log would work better than log to spread things out a bit, but that entirely depends on how you hook things up and label your panel. Of course, tracking between two log pots (inverse or otherwise) is going to be worse than between two linear pots, so stereo work would be less precise - rotaries would have been my preferred choice, but I just couldn't make room in a 2U build!

Here is the Q range of mine. (Sorry for the bad pic)
A log pot would be nice but linear is totally fine and better for stereo matching, like you said.

I notice you have the same boost over 10kHz as I do. I guess that's just part of the circuit...

 

[lars on]

Ok, I'll make some tests with REW.

 

[lars on]

Hi,

Here are the test curves of my dual mono EQ.
Are the shelfs ok ?

LOW
https://www.dropbox.com/s/7kzbzklo48yuo8t/0_Low%20%2B15_400Hz.jpg?dl=0
LOW MID
https://www.dropbox.com/s/ql03frl41inkswz/1_LowMid%20%2B15_1Khz.jpg?dl=0
HIGH MID
https://www.dropbox.com/s/pjdst1yua9ygkr8/2_HighMid%20%2B15_1Khz.jpg?dl=0
HIGH
https://www.dropbox.com/s/0fvc8k2xnu5fasz/3_High%20%2B15_3Khz.jpg?dl=0

 

[TwentyTrees]

Here are the test curves of my dual mono EQ.
Are the shelfs ok ?

Probably - do they boost and cut in equal amounts, and are they flat when centred? If so, you're golden.

 

[lars on]

Yes very flat !

 

[andow]

Here is my version of the W492, called the W492Q  ;D

 

[andow]

A peek inside...

 

[TwentyTrees]

Here is my version of the W492, called the W492Q  ;D

Wow! Seriously impressive build, very tidy and well laid out. Congrats on a great piece of work!

 

[TwentyTrees]

Yes very flat !

Sounds like all is good then! Great news.

 

[Whoops]

Here is my version of the W492, called the W492Q  ;D

Beautiful Build. Great wiring and care. Congratulations

I just stopped making parametric EQs because there's nothing that I can build that beats this one nowadays:

 

[Gold]

Apologies if this question has been asked and answered. What components in the shelving sections control the bandwidth or slope of the shelf?  In other words what do I change if I want the rise or fall to be sharper or more gentle?

 

[dvbutanero]

Here's a little test on my just finished build of the W492.
I've used pcbs from pcbgrinder, and used Omeg pots (Had to tweek a little bit to fit the boards).
This is my first audio build so be gentle.
I've yet to silk screen the frontplate.
https://www.youtube.com/watch?v=oKLWss_uJBk


I will upload the audio test later.
It has a very high gain and I get distortion when pused (Thinking its coming from my converters). ¿Has anyone though of adding a trim pot?.

 

[mistasanshou]

Here's a little test on my just finished build of the W492.
I've used pcbs from pcbgrinder, and used Omeg pots (Had to tweek a little bit to fit the boards).
This is my first audio build so be gentle.
I've yet to silk screen the frontplate.
https://www.youtube.com/watch?v=oKLWss_uJBk


I will upload the audio test later.
It has a very high gain and I get distortion when pused (Thinking its coming from my converters). ¿Has anyone though of adding a trim pot?.

how much did it come up to?

 

[winner]

I've had a chance to re-check the Q range this morning - here's the full range at +15dB 460Hz in the low mid band (ignore the slight wibbliness at top and bottom of the frequency spectrum, that's a problem with the calibration file I'm using in REW - the W492 is flat as a pancake otherwise):

Yes, you're right that the range is a bit cramped at the far end of the rotation, and that would explain why the pot normally ends up in the 6-11 range for me.  ;D  The way I have things wired, inverse log would work better than log to spread things out a bit, but that entirely depends on how you hook things up and label your panel. Of course, tracking between two log pots (inverse or otherwise) is going to be worse than between two linear pots, so stereo work would be less precise - rotaries would have been my preferred choice, but I just couldn't make room in a 2U build!

Excuse me, forgive me for a lot of questions, I am indeed a novice, haha, I redrawn the icon with variable bandwidth according to your prompt, I would like to ask you to check if it works, thank you

 

[TwentyTrees]

Excuse me, forgive me for a lot of questions, I am indeed a novice, haha, I redrawn the icon with variable bandwidth according to your prompt, I would like to ask you to check if it works, thank you

Yep, looks right to me. Thanks for redrawing, that should make it easier for future builders.

 

[kroeger1991]

I am building four of the W492s right now.  Im am using the OPA1656 as opamp. Anyone used them before?
Michael

 

[TwentyTrees]

I haven't, but would be interested to hear your thoughts once you have them in circuit. They're SMD parts as I understand it, so I'm assuming you're using a SOIC to PDIP adapter? The fact that Fig.1 in the datasheet is a Baxandall tone circuit should be an encouraging sign for EQ use though, I'd think.

One thing to watch in a lot of faster, ultra low distortion modern op amps is local decoupling of the power rails - if you're using the Audiox boards, they're laid out for NE5532s and the OPA1656 may (or may not) need a different arrangement. It'll be worth reading through the OPA datasheet a time or five to make sure you know whether you need to sneak any additional caps in there somewhere to stave off potential oscillation and instability. You might need an oscilloscope to tell how well it is behaving once in.

As ever, other, wiser heads than mine may be able to offer better advice!

I am building four of the W492s right now.  Im am using the OPA1656 as opamp. Anyone used them before?
Michael