Neumann W492 equalizer DIY project (PCB docs added)

Makes sense.  When I ordered the transformers a few months ago I wasn't thinking about the voltage post-rectifier, just about the rated voltage

I'll look for some different regulators to see if I can still use these trafos

Thanks!

pvision said:

The mains incoming earth is not earthed to the chassis yet either

Nick Froome

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Just as a side note:This is the SAFETY GROUND!Please never ever run your unit without having it connected.It will save your life one day!

Udo.

kante1603 said:

pvision said:

The mains incoming earth is not earthed to the chassis yet either

Nick Froome

Click to expand...

Just as a side note:This is the SAFETY GROUND!Please never ever run your unit without having it connected.It will save your life one day!

Udo.

Click to expand...

Point taken!

Next question…

The first channel worked first time.  The second is being more intractable.  It doesn't pass audio.  Using a test lead connected to an amp I've tracked the signal as far as the second gain pot where everything is OK.  The third gain pot just gives a low hum and no signal

The schematic suggests the boost / cut pots (P1, 3, 5 & 7) are wired in series. P1 and P3 are, and P5 and P7 are, but there appears to be no continuity on the board between P3 and P5 and it's round there that I lose the signal

The pots in my version are OMEGs and are wired off-board

The schematic I have is dated 23.6.2008 - have there been revisions since then?

Nick Froome

Hello Nick,

I have seen broken green Omegs sometimes.A quick check is to measure its' resistance on the outer pins which should show you roughly the max. resistance as well as the wiper is working.Best done when out of circuit,just lift the wiper and one of the outer wires.
Otherwise why not compare to the healthy eq and trace it (feed the same signal to both eqs at the same time).Might be a faulty part/op amp too.

Best,

Udo.

A few notes that may be of use to first-timers like me and to W492 builders in general

* there is no provision for mounting the board so if you're using off-board pots you'll have to make up a mount
* off-board pots double the build time & quadruple the hassle of the project
* if you're wiring off-board it's easy to get the pots reversed, generating yet more hassle & rewiring
* OMEG pots don't fit the board as supplied - the pins are too thick
* the pot mounting holes are through-plated so if you drill them out to mount pots you are likely to lose links between the top & bottom of the board
* C8 and C20 are left unstuffed (let me check those two part numbers)
* NE5532 chips pull about 15 mA max each, there are 8 per board so the current draw is only about 60 mA average, 120 mA max / board, across two voltage rails so the demand on the PSU is miniscule
* of the 8 pots, only #4 and #6 require twin gang pots
* Dan DDT's front panels make life easy and the back panels for mounting the pots & switches are a really good idea
* the unit is balanced in & out
* there is no provision made on the PCB for gain trim or for transformers
* there is no provision made on the PCB for a per-channel bypass switch
* the plated-through holes & small diameter holes make desoldering incredibly difficult - take lots of care before stuffing

When fault-finding you should have signal on each end of every boost/cut pot.  I think you'll find all faults are the result of operator error - it's a very easy board to stuff & build, pots notwithstanding. 

Dan's panels ideally need knobs of about 10 mm diameter - 14.5 mm knobs cramp the lettering slightly.  The OMEG pots have a 6 mm shafts and most knobs for 6 mm shafts are 14.5 mm or larger

Overall it's a very good-sounding EQ, particularly at the low end.  I haven't trimmed it yet, or run any sweeps, but it's warm at the bottom end and, for me, the boost is a little bit narrow at the mid & high end.  I'll report back after some calibration

This might be a good eq to build with switched boost & cut and possibly switched frequencies

Thanks to Audiox, Gustav & Dan for the ideas & parts & to Udo & others on the forum for help along the way

The link below has some interesting reading for those wishing to change the Q of the equaliser
http://sound.westhost.com/articles/state-variable.htm


Nick Froome

Just read Ben Lindell's very useful blog post on using Fuzzmeasure for sweeps. These are the results for the second MF band of channel 1 of my newly-completed W492 EQ

These sweeps are with the band bypassed then + & - 5, 10 & 15 dB at an indicated 2K

The "out of band" effects are considerable. All the bands seem to affect the low end as well as the selected boost / cut frequency. Are other people seeing this?



Nick Froome

A quick snap of my first project. I just need a little Neumann badge for the front panel...



Nick Froome

Hey guys idk if you are still sourcing for correct pots. I was, and then i found these
http://www.elektronicaonderdelen.nl/passive-components/rotary-potentiometers/conductive-plastic-omeg.html

I ordered pots for 4 channels in total, cost was 75 euros with shipping. Lets see if these guys work out properly, atleast they were alot cheaper than the other pots ive seen around here.

Im not sure about the roster in those pots but if they dont fit my pcd i just wire them.

OK, new sweeps after a bit of rethinking my test setup. I knew something was up, just wasn't sure what. I think I had the output feeding the input. My new sweeps look more sensible

Interestingly channel 2 drops about a dB when mid 1 is switched in - you can see it in the graphs. The rest of the sweeps are as smooth (with 1/3rd Octave smoothing) and they were done at 44.1 kHz. As I'm using the Fireface I'll try some at a higher sample rate

Channel 1


Nick Froome

Channel 2

Hey so im finishing up my taw and mouser orders and noticed most people used bourns more affordable 200r and 10k trim pots, so they fit fine?

Rocinante said:

Hey so im finishing up my taw and mouser orders and noticed most people used bourns more affordable 200r and 10k trim pots, so they fit fine?

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You can always bend the legs.

I would use a resistor and adjust as needed, if I wanted to save a little.

Gustav

Does someone know, where to get the Pots from?
10KLIN PA11QXF???
Mouser?
THX

Greg S. said:

Does someone know, where to get the Pots from?
10KLIN PA11QXF???
Mouser?
THX

Click to expand...

Here we go:

http://tbaudiogear.com/?product=neumann-w492-eq-diy-pot-package

thx

IThanks Gustav. I went for the 3/8 and 1/4 figuring at worst I would have to bend one. As far as pots goes almost half this thread is about finding the right (and affordable) pots. Tb is out of stock.  Laura at Taw might have some ill let you all know she is supposed to get back to me today. I'll ask how many sets she has left.

So I just got off the phone with Laura from TAW and I couldn't agree more with everyone regarding how awesome she is.  Very nice person.  As far as whether or not TAW carries the Omeg pots needed for this the answer is; Yes they have the Omeg pots for this as well as the Wima caps.  As a matter of fact she is thinking she might even put together a little kit for this. 

Cheers

Rocinante said:

So I just got off the phone with Laura from TAW and I couldn't agree more with the sentiment that everyone else who has dealt with her regarding how awesome she is.  And the answer is; Yes they have the Omeg pots for this as well as the wima caps.  As a matter of fact she is thinking she might even put together a little kit for this. 

Cheers

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fine Mate