Neumann W492 equalizer DIY project (PCB docs added)

[JMan]

For the gain control on each band, you’d just need to calculate the resistor values for the correct taper (I forget if these are linear pots, but I think so, which simplifies things a bit). It should be similarly easy with the frequency controls, but you’d have to look at the schematic to be sure.

The unit does +/-15 dB, so 1dB steps is out. With a 12-position switch, you could probably work it out to do something like 2.5 dB steps, or 1.25ish on a 24-position switch. Alternatively, I think you could adjust the internal trim pots to set the overall gain range a bit lower (this is on memory, though, so you’ll definitely need to double check that this is doable). By balancing these two elements, you should be able to work out how to set your desired compromise of gain range and step size.

 

[TimG]

Mine is mostly built, with thanks to Dario.
I’m interested in the upgrade as my faceplate from Frontpanels.de has cutouts for it!

I didn’t see it in the thread? Sorry if I missed it.

 

[Kevin]

you will find the addon in the schematic there are extra capacitors

 

[TimG]

This stuff?!? More than a Xicon resistor.
8 more switches it is!

 

[TimG]

So do I pull R8 and wire this switch circuit from its pads?

 

[dario84]

So do I pull R8 and wire this switch circuit from its pads?
View attachment 113897

Yes thats exaclty what you do. Solder the resistors to the switches as shown and connect with wires to the pads of the board.

 

[TimG]

Thanks!
That shouldn’t be difficult or expensive.
Glad I got the front panel with all the options now!

(Welcome back from tour! Looked insane!)

 

[TimG]

Ok while waiting for my switches, I’m noticing if anyone is building these for this Frontpanels.de plate with “x2”, you will want to mount S2 and S3 from the bottom of the PCB, and similarly, R15 and R30 pads of the boost switches should get wired from the top.
They alternate top and bottom.

Anyone suggest a simple bypass circuit to use?

 

[TwentyTrees]

Anyone suggest a simple bypass circuit to use?

Volker (silent:arts) has a handy little relay bypass PCB called the HWBP36 (I think), his White Market listing has the details.

 

[thelivingroom]

Volker (silent:arts) has a handy little relay bypass PCB called the HWBP36 (I think), his White Market listing has the details.

You beat me to it haha. I now have a stock of several of his handy little boards like that, but back when I built my W492 I just used some perfboard, 4 relays, 4 flyback diodes, and some jumper wires.

 

[DarkSky]

I've recently finished racking a pair of the W492 modules in 2RU format with a customised switching harness. Some 'phone pics of the completed build attached for anyone who's interested.

FWIW, the front panel indicator lights are tri-color LEDs that show red when the channel is in bypass, yellow (red+green) when the channel is engaged but the band is off, and purple (red+blue) when the channel is engaged and the band is on. The switching relays and lamps are running off a separate internal power circuit (12V) that's supplied by the toroid at the rear right and has its own rectifier. The regular supply (-15, 0, +15, regulated) is next to it on the steel plate at the lower rear, with a mu-metal shield separating it from the i/o section.

I chose to go for 2RU in order to have a less crowded front panel (especially wth the addition of power switch and status LEDs). The front and rear panel I laser engraved onsite. The switches (and relays) plus the lower (freq) pots are wired off board. Otherwise the build is fairly standard.

 

[fragletrollet]

Looking good!

 

[Whoops]

View attachment 118845

Congratulations, that’s a work of Art

 

[estocastico7]

Hello,i want to make a w492 from creative clowns,but i dont know how to put bypass switch in channel one and two,is dificult to add?????it is possible to add led to this bypass switch???
I made a lot of guitar effects,and i suppose that is similar to true bypass in effects???
Thanks a lot,great project!

 

[JMan]

It sounds like you want to add a pretty straightforward true bypass to the entire channel (not to each frequency band like can be done with this project). There are various ways to do this. My preference would be to lay out a simple relay bypass on perf board, then use a DPDT switch to send your DC voltage from the power supply to the relay from one pole and to your LED from the other (just make sure you've calculated your current limiting resistor appropriately).

 

[DarkSky]

Hello,i want to make a w492 from creative clowns,but i dont know how to put bypass switch in channel one and two,is dificult to add?????it is possible to add led to this bypass switch???
I made a lot of guitar effects,and i suppose that is similar to true bypass in effects???
Thanks a lot,great project!

If you have room for a pair of 3PDT switch, you could assign two poles to a hard bypass per channel and the third pole to supply power to the LED.

Alternatively you could use a pair of SPST switches and a pair of DPDT relays, with the switch providing power (or not) to both the LED and Relay (per channel) and the relay applying the hard bypass.

In my implementation (as described pictured a few posts back) I had the bypass switch control four relays per channel to engage/bypass the individual bands, which allows LEDs to do double duty indicating the status of each band as well as the overall bypass status of the channel. However that involves a bit more effort than required to achieve what you've described.

 

[estocastico7]

If you have room for a pair of 3PDT switch, you could assign two poles to a hard bypass per channel and the third pole to supply power to the LED.

Alternatively you could use a pair of SPST switches and a pair of DPDT relays, with the switch providing power (or not) to both the LED and Relay (per channel) and the relay applying the hard bypass.

In my implementation (as described pictured a few posts back) I had the bypass switch control four relays per channel to engage/bypass the individual bands, which allows LEDs to do double duty indicating the status of each band as well as the overall bypass status of the channel. However that involves a bit more effort than required to achieve what you've described.

Yes i simple 3pdt work to me,i think it is the simplest way to make bypass per channel.The dificult to me is what i have to solder in this 3pdt,i dont know very well how do it,thanks!

 

[DarkSky]

Yes i simple 3pdt work to me,i think it is the simplest way to make bypass per channel.The dificult to me is what i have to solder in this 3pdt,i dont know very well how do it,thanks!

The simplest scheme would be to connect the hot and cold signal lines of the output for a channel (i.e. output XLR pins 2 and 3) to the centre (common) pins of each pole of one of the switches. Then connect the pins for one throw to the input for that channel and the pins for the other throw to the (pcb) output of the channel. The third pole will have positive voltage connected to the common pin and the current limiting resistor (for your LED) connected to the third pole throw adjacent to the pcb output connections.

The chief shortcoming of a setup like this is that the input load of the pcb remains connected when the unit is in bypass (presenting a lower impedance to the driving device than would otherwise be the case). For most cases that should not be a problem.

However if it's a concern, you could add some isolating resistors (300R - 500R should suffice) between the input XLRs and the pcb and also between the input XLRs and the 'bypass' throw of the switch. Other options would be to either move up to a switch with more poles or add relays to fully isolate the input as well as the output.

 

[estocastico7]

The simplest scheme would be to connect the hot and cold signal lines of the output for a channel (i.e. output XLR pins 2 and 3) to the centre (common) pins of each pole of one of the switches. Then connect the pins for one throw to the input for that channel and the pins for the other throw to the (pcb) output of the channel. The third pole will have positive voltage connected to the common pin and the current limiting resistor (for your LED) connected to the third pole throw adjacent to the pcb output connections.

The chief shortcoming of a setup like this is that the input load of the pcb remains connected when the unit is in bypass (presenting a lower impedance to the driving device than would otherwise be the case). For most cases that should not be a problem.

However if it's a concern, you could add some isolating resistors (300R - 500R should suffice) between the input XLRs and the pcb and also between the input XLRs and the 'bypass' throw of the switch. Other options would be to either move up to a switch with more poles or add relays to fully isolate the input as well as the output.

Thanks a lot,you are very hepfull!!!

 

[oran.outan]

Hi

I finally finish this build…
Great sounding, also very quiet and clean…
I like to A/B and just add a true bypass…
W492 PCB are from French GC audio, power supply from dear @volker , frontpanel from @Frank frontpanel.de

Enjoy*
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