Auxilery input into comms - but only to one headset...

[James Remo]

Hi all,

First I'll start with the concept. I wish to be able to put an aux. input into my comms headset, mix it with the comms traffic but so that only I can hear it. It needs to be passive, discrete and preferably integrated into the belt pack. The aux input will either be a PFL cue from a sound desk or a 3.5mm headphone input from my ipod or laptop, so some form of isolating transformer would be a good idea to avoid putting hum (or in a lot of cases worsen the already existing hum) on the comms system. The signal from any stereo input needs to be summed to mono as I hate wearing double muff headsets. This is to use with a party line system that is Clearcom/tecpro/asl/metro/stonewood compatible (as most of my clients use)

 

So, firstly I went looking for a system that had this feature already built into it's belt packs. Clearcom's encore system has an aux headset connector, which I am lead to believe is an output only. Dead end.

 

Secondly I found a product from interspace called the CiO which rang almost every bell, but the price (£275 + vat list!!!) and the fact that this is an extra box (which requires a separate power supply) kind of ruled this option out. I've got a load of the interspace PC-Di boxes, and they are fantastic, but the CiO sadly did not quite fit the bill.

 

So to look down the home brew route. Unfortunately my electronics knowledge is sadly lacking, so I thought about bastardising an existing unit. I looked at the canford tecpro units, wishing they had an extra input channel. Lightening struck the old grey matter, and with a flash of inspiration I reasoned that if I got a dual channel unit, the audio from the second ring could be my extra input. Not so I hear you cry! On the Tecpro BP 113 units the audio from ch 1 is routed to the left side of a double muff headset, and ch.2 to the right. So a dual channel design and no mixer element involved. But there is also the BP115 I cry back! The monaural version! I seam to recall using a metro audio unit that was dual channel, but fed both signals into a single sided headset. Could it have been a DC2 I was using?

 

Could I achieve the mono sum of a headphone level signal by using the mono summing circuit from the rane notes? If so then a small circuit with a few resistors and a isolating transformer could do the trick, but the output of a laptop, ipod or headphone out on a desk is effectively a very small power amp, and I know better than to try to combine the outputs of a power amp together, damage could ensue.

 

Rather than alter the beltpack in any way I could make adaptor cables that have a 3 pin XLR for input to ring 1, then a 3.5mm minijack to input into ring 2. If the power supply is shared for both rings then I might have to isolate them in the comms box, to avoid sending 24v dc to the audio input on ring 2, but that is a bit beyond my means.

 

 

So to re-cap (just in case I've lost you all...)

1) Do any other possible solutions exist?

2) Would my <monaural dual channel belt pack as a mixer> idea work?

3) Is the metro/stonewood DC2 like the techpro BP 113 or the monaural BP115? (Might as well admit I'm bidding on a DC2 for £9.99 on ebay at the mo, worth a punt to see if it might work) The Stonewood website is greatly lacking in detail...

4) Can you safely mono sum a headphone signal via the method described for mic / line signals in the rane notes?

 

Thanks in advance,

James

[Shez]

The aux input will either be a PFL cue from a sound desk or a 3.5mm headphone input from my ipod or laptop

I may be thinking too far outside of the box here, but if each output you want to feed in to the system comes from a headphone socket, why not just use a an earbud type headphone? It won't block out the sound from your comms headset too much, it's very cheap and easy and avoids any electrical connections between systems.

[cedd]

I may be thinking too far outside of the box here, but if each output you want to feed in to the system comes from a headphone socket, why not just use a an earbud type headphone? It won't block out the sound from your comms headset too much, it's very cheap and easy and avoids any electrical connections between systems.

I was thinking of something similair, although it involved placing an in-ear headphone driver inside the earshell of the comms headset.

 

Otherwise, I think you're wise to make your mix post-beltpack, in line with the headset. You could make an adaptor to lift power from the comms system line (XLR male to female short lead, with a pair of wires connected to the DC supply pins to "break out" the DC supply) and then use a summing amplifier and headphone amp to mix your two signals together.

[peternewman]

Its very easy to extract the comms audio from the party line to a mixer input and then use said mixer to combine an audio input (PFL etc) to give a mixed listen in a pair of headphones plugged into the mixer, so logically you could build on this, so you use the mixer output to drive the headphones and then leave the mic as is.

 

To make it fit your needs, things like taking DC power from the comms system as Cedd mentioned. The one issue will be you might need to add in some mix minus/cleanfeed circuitry, as the party line will have you at normal volume, so the sidetone control wouldn't work for that.

 

Basically it is possible using existing kit, so with a bit of know-how it could be modified to work within your requirements (running off the circuit etc), however the more novel and simpler option of using an additional speaker in the headset may well be an easier and simpler route to go down.

[TAG1960]

I regularly use the CiO box, and whilst it is expensive, it works perfectly, and is always connected to the pfl circuit of any desk I’m operating.

I can monitor any desk channel whilst still receiving cues.

[Ynot]

The quality will essentially be about as good as the desk feed.

 

One way of doing just what the OP wants is to use a 2-channel master Tecpro PSU or similar.

Use channel 1 for everyone, but ch 2 just for the noise desk.

There's an aux feed into the PSU, which you can feed from the desk, and an input level control as well.

 

I can't remember whether the input feed will go to BOTH channels if the noise guy is switched to both channel working (I think not, but am not sure) but as an option you can switch between the channels if needs be.

[boatman]

Have you looked at the AD903 2-wire to 4-wire adaptor? It will allow you to interface the sound desk to the comms system. Just make sure you don't enable the comms on to the main output and you'll be fine.

[dbuckley]

The AD903 is exactly what the OP doesn't want, it puts external audio onto the comms line, but the OP wants external audio to his ears only.

 

To the OP - you've not found what you want because you dont know the right magic words to describe "auxilliary input" - it is called a programme (or program) input. Many intercom beltpacks have this feature, look at ClearCom for examples. Sadly, the UK most popular Production Intercom and TecPro systems dont, so either a hacking or a bodge box is called for.

[boatman]

The AD903 is exactly what the OP doesn't want, it puts external audio onto the comms line, but the OP wants external audio to his ears only.

.

.

 

Exactly, and that audio to the comms circuit would be the output from the mic on the sound desk. The external comms would come into the desk on an auxilliary input and be mixed with any other source as required. Hence the warning about not enabling the comms onto the main output bus. The OP would then use his normal desk headphones for everything.

[paulears]

All I do is use a pair of Beyer DTs with the lead split through a small breakout box to send the mic signal to the Tecpro pack 4 pin connector. The audio out that goes to the headphones normally, is diverted to an XLR wired pins 2 and 3 - no connection to the pin 1 earth allowing the comms circuit to be isolated from audio earth. On the mixer the channel used for comms in isn't routed anywhere, and hitting the pfl gives conventional comms. All the usual monitoring can be done as usual, just switching pfl in when it's needed. It also offers a useful extra function in that it is possible to route comms to PA or even monitors if you wish - I've used this a few times in rehearsal when the dsm can't get hold of the director because they're faffing about - he can ask for a PA and just talk on the cans to everyone. Damn handy system, and just takes a small amount of wiring

[themadhippy]

How about a high speed change over switch.Something like an AD7512 with control from a simple 555 oscillator circuit running at a suitable high frequency. To avoid extra power supplies maybe pick up the supply from the coms.

[James Remo]

Shez - The low tech solution is what I'm trying to move away from

Cedd - Will look into summing amps and headphone amps

TAG - Glad to hear it works for you! Just can't justify the price

Ynot - The aux input of all masterstations I've ever come across goes to both channels.

dbuckley - Program is a term I'm well aware of, but in order to clarify that it's only for my headset I chose not to use that term. Which clearcom belt packs have you seen with an aux in? As I said all my research has thrown up is an auxiliary headphone output on clearcom beltpacks. I'll happily be corrected and can easily pick one up from Canada when I'm there next month.

boatman/paulears - great idea if I'm behind a desk, I ought to have mentioned that I'm more often employed as system or radio tech, so won't always have a desk to route through. Having a fly lead to plug into the headphone out of a receiver (I mostly work with sure premier / uhf-r which have a headphone jack on the front panel) without having to switch headsets is part of the application for this idea. The other (fairly major) part is to inject ipod / laptop (dvd sound) into my comms headet for those yawn inducing corporate jobs.

themadhippy - Erm, yes. Sounds great! Bit beyond me, but sounds great!

 

If I win the stonewood DC2 I'll give my idea a go and see what happens. Does anyone have any advice on if you can safely mono sum a headphone signal via the method described for mic / line signals in the rane notes? That's my major concern. From having a sneak peak inside the interspace di box I can't tell if the mono process happens before the tx or after, was hoping to nick their circuit if pre- tx!

 

Thanks for all of your input so far, I'm going to knock up a system like paulears uses for the time being, and will let you know how my experiments go.

 

Any other input? (Pun fully intended)

[dbuckley]

dbuckley - Program is a term I'm well aware of, but in order to clarify that it's only for my headset I chose not to use that term. Which clearcom belt packs have you seen with an aux in? As I said all my research has thrown up is an auxiliary headphone output on clearcom beltpacks. I'll happily be corrected and can easily pick one up from Canada when I'm there next month.

 

You may not like or choose to use the correct terminology, but its what the intercom and IFB industry calls what you call an auxilliary input.

 

Products: ClearCom Encore 602 in the modern range. Many older ClearCom beltpacks with six pin XLR have been able to do programme in, though prior to the modern stuff it was a hardware mod. Now its a software "mod".

 

Yes, these packs also have a 2.5mm jack for an extra headset but thats nothing todowith programme in.

 

If you fancy something that sits on a desk rather than on your belt then most of the master stations allow individual programme in. I commonly use an older (cant remember the model number, the predecessor to the CS222) ClearCom two channel stage managers console that has programme in which can go to any combination of places, including just my ears. I also have a 1u 2 channel rack station with programme in.

 

Alternative options include the AB-100 announcers console, which can do what you want (and more besides) or if you want the best audio in the intercom universe then have a look at the Studio Technologies 230 announcer console.

 

Surprised Mac hasn't chimed in here, although I know the intercom stuff pretty well, he's about fifty times better than I am at this stuff!

[Pete McCrea]

Ynot - The aux input of all masterstations I've ever come across goes to both channels.

I'm 99% certain that the Stonewood Audio SA-CMS2 Base station has a switch to allow selection of the channel that the Aux input goes to. Spec Sheet here...

[mac.calder]

Another method (a tad messy if you want mobility) - the larger clearcom user stations (ie the 4 channel matrix systems) have a Program input - you then assign the program feed to a channel, then when you listen to that channel, it mixes in program audio. Overall balance is controlled by a knob on the front pannel. If mobility is really an issue, the propper 4 pin extension cables are not THAT expensive (just make sure you get the right stuff... scroller cable will induce a heck of a lot of noise).