Allen & Heath Mixwizard WZ16:2DX

[Bobbsy]

I guess it comes down to how you use a monitor desk.

 

In my experience, you want the maximum number of independent outputs so I've always used the main outs as one feed and set each Aux up as pre fade so they could be additional monitor mixes fully independent of the faders. If they were post fade, any changes made on the faders would affect all the other monitor mixes as well.

 

...but there's no one "right" way of working. At least A&H caters for both options (even if you need to open up the board to change the jumpers).

[Gnome]

Hi Boatman

 

OOI where did you get the Service Manual, do A+H make them available?

[boatman]

Yes, you're right David. They plan to use this desk purely as a monitor desk (probably on-stage). They already have a 24 channel Soundcraft Spirit LX7 for the main PA. The 6 Aux outputs of the WZ16 make it an ideal monitor desk for the size of gigs they run. As I understand it, they plan to use the 16 direct outputs on the WZ16 to feed the LX7.

 

I have noticed that the direct outputs on the WZ16 are "Impedance Balanced" rather than true balanced and wondered if a rack of balancing transformers would be a good idea. Any thoughts on that?

[Lamplighter]

I have noticed that the direct outputs on the WZ16 are "Impedance Balanced" rather than true balanced and wondered if a rack of balancing transformers would be a good idea. Any thoughts on that?

I find that the impedance balanced outputs generally work well, you only need transformers if galvanic isolation is required.

Brian

[boatman]

Hi Boatman

 

OOI where did you get the Service Manual, do A+H make them available?

 

It's actually a service manual for the WZ20, but the modules are the same. It came as a pdf file from the new owners of the desk and I suppose they must have got it from A&H.

[MarkPAman]

As I understand it, they plan to use the 16 direct outputs on the WZ16 to feed the LX7.

 

The WZ16 will make an excellent small monitor desk, but I'd really advise them to get (you to make!) a splitter box so that the two desks can run completely independently of each other. This gives several advantages:

 

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• Most importantly, gain adjustment on the Wiz will not effect FOH.
  
• Only the channels needed for monitors need be patched in and can be re-patched for support acts. I often find at the end of main band soundcheck that HH, Toms, & OHs are not used, so I can then (take a note of the gain) and reuse these for the support band's vocals etc which means the main bands important channels do not get touched.
  
• System can be run without the Wiz for simple events & the Wiz could be used for something else.
  
• Would be easier to use a different desk for monitors if needed.
   
  

 

As for the Aux sends, if only using the 6 outputs, then have them all post fade. Means there's a slider to grab when a mic gets pointed into a speaker. Then, if a 7th output is wanted, use the main right out & the pan becomes the level control for this, though the gain curve may not match the other six. I tend to use the right out to set up my own mix, via the control room out so I get PFL when selected.

[boatman]

Thanks Mark. Sounds like good advice, I'll pass it on.

[boatman]

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The WZ16 will make an excellent small monitor desk, but I'd really advise them to get (you to make!) a splitter box so that the two desks can run completely independently of each other. This gives several advantages:

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If I build a passive splitter; how does it affect the use of phantom power? If the FOH desk is supplying phantom power to mics on stage, will it be a problem at the monitor desk if there is no galvanic isolation? Alternatively, should the phantom power come from the monitor desk and will that cause a problem at the FOH desk?

 

I did work with sound very briefly, but it was over 40 years ago at Television Centre, hence all the questions!

[Simon Lewis]

Sending phantom from two desks can cause problems, but it depends on whether the desk(s) can withstand this. I've done it accidentally many times, but haven't had anything go pop. Usually, it is easier to send phantom from the monitor desk.

With regards to current flowing in the screen of the cable connecting the two desks, issues can arise if the equipment suffers from pin one problems. One trick often used with passive splitters is to use individual or global earth lift switches. Of course, if deployed, this stops phantom working from the desk connected via the earth lift.

 

Transformer splits are often feted as the ultimate answer, but although they can offer excellent galvanic isolation, much depends upon their construction (Faraday shields etc.). Furthermore, the microphone will still "see" the impedance of each desk input, and there will be additional capacitance.

 

Transformer splits - done properly with good quality Lundhal or Jensen transformers will not be cheap. Passive splits seem to work quite well with modern desks where Pin 1 has been sorted out and EMC problems have beed addressed. However, there are still loading issues to be considered.

 

I should add that there is some very good reading material on this subject from Jensen Transformers, Rane and the AES amongst others.

 

 

Simon

[dbuckley]

I have noticed that the direct outputs on the WZ16 are "Impedance Balanced" rather than true balanced and wondered if a rack of balancing transformers would be a good idea. Any thoughts on that?

Impedence balanced is "true balanced". What impedance balanced doesn't have is differential drive.

 

If memory serves there are A&H instructions on changing the output of a GL from imedence balanced to differential, so maybe the same instructions apply to a WixWiz.

 

Whether you'll get any benefit from going differential, or indeed adding transformers depends on your setup, but for most folks, the answer is that impedence balanced is entirely satisfactory. Unless the transofmers are high quality an can take line level without saturating, then transformers will probably degrade the signal.

[Simon Lewis]

Changing the impedance balanced outputs to differential outputs involved the addition of an Analogue Devices chip. I've done this on a GL2200, but not bothered with any other A&H desk. For all the situations I've encountered, the impedance balanced outputs are fine. Since this is being used as a monitor desk, the amps can't be too far away?!

[boatman]

Thanks to all for the useful advice.

 

We are going to make up a 16-way multi-core with XLR plugs at one end and a socket/plug pair at the other. The plug at the latter end will be on a short tail with pin 1 left unconnected. That will allow us to tee off the mic to the monitor desk and take the phantom power from the LX7. It seems like the optimum solution.

[jamesperrett]

 

If I build a passive splitter; how does it affect the use of phantom power? If the FOH desk is supplying phantom power to mics on stage, will it be a problem at the monitor desk if there is no galvanic isolation?

 

If the monitor desk can supply phantom power then it should also be able to withstand phantom power on the inputs as the audio input circuitry doesn't differentiate between its own phantom power or other people's.

 

I must admit, I've disconnected pin 1 on one set of outputs on my recording splitter though - just to be safe. Thinking about it... if everything shares a common power ground then disconnecting pin 1 may not actually make much difference.

 

James.

[boatman]

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If the monitor desk can supply phantom power then it should also be able to withstand phantom power on the inputs as the audio input circuitry doesn't differentiate between its own phantom power or other people's.

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The schematic shows that the +48VDC line for phantom power does not float when PP is switched off, but is connected to ground. That would put a 6.8k resistor from each leg to ground on every mic input, making a resistive divider. If I'm not mistaken, the resulting phantom power at the mics would then only be 24V rather than 48V.

 

Interestingly, the electrolytic caps on the mic amp inputs are marked on the schematic as 47/25. I assume that's 47uF and 25VDC, but I suspect they should probably be 100VDC. I got a plentiful supply of 100VDC caps so can replace any that look a bit iffy.

[boatman]

Ok, so the desk arrived in the workshop this afternoon. I have tried to make some DC measurements but found the power rails change randomly from the standard +15/-15V to +6V/-24V and back again. This makes diagnosing the input channel fault rather difficult.

 

The pdf manual has a specific omission for the power supply with a blank block in the schematic containing the words "Power supply not shown in public version". This makes me wonder if this random supply switching is deliberate or a fault. If it's a deliberate design, it does seem a bit odd as it would considerably reduce the headroom when the supply was at +6V & -24V.

 

I have submitted a ticket to A & H but have only received an automated reply so far.

 

Does anyone have any experience with servicing this desk that they would be willing to share?