DIY (cheap!) IEM personal monitoring system

[cedd]

Hi all

I have a few jobs coming up where I need to deploy a pretty basic personal monitor mixing system. This will specifically be used in orchestra pits alongside click tracks. Most of the musicians won't be familiar with Aviom/Roland/Behringer/whatever fancy personal monitor mixers, and indeed they are probably way more complicated than we need. I need each musician to be able to mix probably 3 inputs - a general foldback mix (that I'd produce on the desk), a click/shout mic channel, and a "more me" channel.

I need to provide this to probably 15 musicians.

There's nothing out there that particularly fits the bill, and the budget for the entire project is probably no more than £500.

I'm not adverse to electronic design work though, so I've got a bit of a plan. Input and criticisms welcomed!

I build a system based on cat5 cable. 4 pairs gives me 3 balanced lines and DC per cable. Centrally I have a rack with 12V power supply and a patchbay in it. This would have some inexpensive rack mount preamps in it (Behringer) and some passive splitters too. The idea being that it's possible to patch signals up each of the 3 cat5 pairs to each musician, and the rack would have utilities like being able to split and amplify mics going to front of house for the "more me"channels. It'd also house a small mixer for the click and shout mic.

 

Each musician would then have a compact mixer, mixing the 3 channels and providing a headphone output. I might also allow for a local line input. There'd simply be level and pan for each signal. I might also include some sort of signal present led's.

PCB design and manufacture is straightforward, as is 3d printed enclosure manufacture.

 

So the question is, can you see it working? Any obvious gotchas or hints?

 

I'd toyed with a central rack of headphone amps and then simple local attenuators for each musician, but the ability to mix a few channels is attractive. More work in the design process though. I'd equally toyed with going unbalanced with more available sources, which is easier to build and design, and cable lengths should be relatively short - 10m absolute maximum

 

Anyone done similar?

[J Pearce]

I wouldn’t be trying to do this in the way you describe. Without doing PCB manufacture you’re going to end up with a rats nest of cabling, splitters, mixers and general mess that will be a nightmare to troubleshoot and the sort of thing liable to hum and noise. I think you’ll also struggle to do this in budget, unless you already have a lot of it in stock.

 

If Aviom/ME1 or even behringer powerplay are outside of the budget I’d probably go for an X32 (or X32 rack with expander output box), some of the little battery powered headphone amps that take an XLR feed, an access point, and the behringer personal monitoring app. Most musicians will be able to install this, you might want some cheap/old tablets/phones for any who struggle with this.

[Stuart91]

I agree with Jon.

 

A few years back I helped a church implement personal mixers in a similar fashion - Soundcraft Notepads, which were only being used for the "more me" function. It worked, but even that very simple implementation involved a load of cabling and quite a bit of troubleshooting. I don't think I'd have liked to do that in the context of a busy theatrical fit-up. The church have since moved onto the A&H ME1 system.

 

I've imposed the X32 system on quite a few bands and they seem to take to it quite well. With appropriate cabling and headphone amps you'll probably be north of £1k but it might be a worthwhile investment rather than spending £500+ on parts for a bespoke solution that's of no use to anybody but you.

[TomHoward]

I'd think I'd start with the approach of using cheap headphone amps, or a central headphone amp rack and extend the headphones if the distances are shortish, Behringer X32 rack with outputs, and make little Arduino / ESP32 boxes with 3 encoders hard coded to the bus sends on that musician's mix and send the data over ethernet. But you'd need quite a lot of outputs from the rack and maybe a stage box. Might work if you already have an X32 rack to hand.

[cedd]

I've got an XR18 to hand, so I can do 6 mixes on smartphones/tablets using Q Mix. One of my options was to stick a few central headphone amps in the rack with it. I could potentially make up some little attenuator boxes that also had a pan control to select between the click channel and the foldback mix, which I send up a stereo 1/4" jack cable.

It doesn't allow for a "more me" channel though - the pit have to work with 6 groups of mixes. I could maybe think about doing that locally at the attenuator box, but then I need a line/mic - headphone amplifier, and that then essentially becomes what I've just described above!

Having another digital device isn't hugely attractive - I'm already going to be going A-D and back again through my own desk (Roland M480) so another A-D and back is going to see the latencies stacking up. A wholly analogue system is my preferred choice. Roland's REAC protocol is great but it doesn't allow me to easily get to those digital signals and send them to any other device apart from an M-48, which I can't afford!

 

I'm not adverse to PCB design - that's kind of what I had in mind. I'll do some head scratching first though about if I can make it work with central headphone amps and the XR18 (or the Roland itself, though there's no dedicated monitor app, so I'd have to trust somebody with the ipad that had everything on it, which I'd rather not do!

[Brian]

I'd buy the cheapest line mixers I could find, like the Behringer MX400 at sub-£20 each. Mod the output stage with a couple of transistors to drive phones, add an RJ45 socket to take in three of the line feeds plus power. That's the muso end of things done, plus they have a fourth local line level.

 

If you really need stereo then a PULSE MLX402 at £22 will do the job.

[cedd]

I'd buy the cheapest line mixers I could find, like the Behringer MX400 at sub-£20 each.

Funnily enough I'd just been looking at an MX400 and MA400 combo. If I stuck them both alongside each other then I've got 4 line inputs, a mic input with thru, and a headphone out. £36 per unit. I'd maybe even go as far as to put their innards in a custom enclosure. If I went local power supply then I could get 4 line inputs down the cat5, or do 3 as planned and then pish the 12V up the final pair (which gives local line in for keys etc.).

 

At the rack end I can foresee a panel of RJ45 outs (I don't plan on using ethercon for this, so a standard 16 way patch panel should work) and then a cheap behringer 1/4" jack patchbay or 2 to patch the various inputs to the monitor mixers.

The big question is how to do the splitting/buffering. The MX400's are unbalanced inputs which I think I'd get away with at line level in this environment. I'd need to unbalance and then split up to 16 times. I think we're probably beyond the limits of of a passive split here, and this might need to be where a custom pcb came in.

 

 

[sunray]

It seems to me you are proposing mixing standards (RJ45 & Jack).

If you are having a jack patch field and you go for something like the MX400 with jack inputs then I'll ask; why not use 4 way jack leads right through? Unless of course you are thinking of removing the jacks from the mixer and replacing with a single RJ45.

Also bear in mind most mixers of this ilk are basic unbalanced inputs (as you state) the cable can possibly be 4 core with an overall screen... don't knock it till you try it, I worked with a guy for years before I found his foldback was just that on a XLR5, I'd always assumed it was HiFi grade 4way screened cable.

 

It also seems you are more than capable of doing a bit of electronics work, have you thought about adding a headphone amp inside the MX400 to avoid multiple boxes?

 

 

Not so long ago I did some work on an AV system with ceiling speakers, I was astounded to find they had been installed by the IT department and were only PC speakers, the type with a stereo amp in one and a lead to the other speaker. The original 3.5mm jack had been removed and joined using choc bloc to the single screened cable running the ceiling void, a similar arrangement for the mains too. There were certainly more than 16 hanging on the one signal lead. It sounded fine and I was surprised what was being used.

 

 

Or local Hospital Radio distribution consists of 4 channels of audio around the hospital on CAT2 cable and an isolating transformer to each TOA amp at the wards. The same system in another hospital uses Maplin stereo GLI transformers for a single service and I started using the second (spare) channel or OB's from the wards feeding a radiomic straight into the transformer, meaning the radiomic was loaded with loads of transformers.

 

[ninjadingle]

If you wanted an off the shelf product it looks like the Art MyMonitorII would be perfect, but out the budget. Maybe get a secondhand one and reverse engineer it?

[cedd]

Thank you everyone for your thoughts.

 

I think I've settled on buying a set of these and modifying them to be externally powered. I have a carbon copy (named brand) version already and there's loads of space inside, so I can blank one of the xlr inputs and replace the other with an ethercon. They have a regulator that'll accept up to 30 odd volts, so I could very safely feed them with 12 or 24V to counter voltage drop. Balanced inputs so less worries about unbalanced runs. I'd still have an extra pair to each unit so I'm even considering building in a simple cue light to each one too!

Then in the rack I just need a few of these to split my mixes, plus some ethercon sockets and a power supply. Voila, monitoring setup!

My plan would be to split the pit in to 2 or 3 groups and put each group on an aux that could be controlled from an iPad in the pit. Then there's at least a degree of control. I'd make up a few break-in cables so that one or 2 of the amp units could be fed with their own custom mix via 2 xlr's, so I retain the flexibility to do something special for the one off musician who needs something different.

 

Parts currently on the slow boat from China.

[TomHoward]

They look exactly like named brand, even down to the stupid centre negative power supply socket which means we have to have separate PSUs for named brand ones compared to all other generically 12V powered kit.

[cedd]

It was all going really well until I realised somebody had an attempt at making a fraudulent purchase on my AliExpress account back in September. Didn't manage to buy anything, but they did succeed in changing my default address to one in Columbia.

Stupid me didn't notice and has just ordered the scammer a lovely bunch of IEM amps which are currently on their way to him, with no way of cancelling the order.

 

Ho hum

 

Thankfully I only bought 2 to play with for the time being. Plus a load of cheap in ear headphones.

[sunray]

They look exactly like named brand, even down to the stupid centre negative power supply socket which means we have to have separate PSUs for named brand ones compared to all other generically 12V powered kit.

Actually centre negative is the correct use, more acuratley the way the inventors designed them and the way they were all used at the beginning, until some stupid person/company decided to go the other way and somehow it became popular.

It's by no means uncommon to find products with centre negative, my latest router and a CCTV camera (which really is a PITA as the rest in the system is centre +ve) for example.

 

[richardash1981]

Actually centre negative is the correct use, more acuratley the way the inventors designed them and the way they were all used at the beginning

I had always assumed this dated from Germanium transistor designs, which were mostly PNP transistors and so designed as "positive earth" circuits with a single negative supply rail (so the case was connected to the +ve PSU terminal, and you wanted the outside of the plug to be also).

The other way round makes more sense if you are designing with (incoming) PSU negative connected to case, as is more often the case these days, because it's harder to short the PSU if the plug touches on it's way through the case.

 

[sunray]

Actually centre negative is the correct use, more acuratley the way the inventors designed them and the way they were all used at the beginning

I had always assumed this dated from Germanium transistor designs, which were mostly PNP transistors and so designed as "positive earth" circuits with a single negative supply rail (so the case was connected to the +ve PSU terminal, and you wanted the outside of the plug to be also).

The other way round makes more sense if you are designing with (incoming) PSU negative connected to case, as is more often the case these days, because it's harder to short the PSU if the plug touches on it's way through the case.

 

In the early days we used to call them 'Sony plugs' and since forever I have been under the (possibly incorrect) impression they invented them. I recall an article in a magazine, possibly PEor PW, explaining why they are centre negative and why the standard should remain...

Oh well, that's progress.