Headphone distro boxes

[mylesgm]

I'm in need of headphone distribution boxes and am planning on making 8. Each box will feed two headphones and will have an xlr in and xlr out so that I can chain them. I've done this in the past by simply paralleling the output of the amp to multiple trs sockets and as most HP amps are rated to around 20-50ohms and most studio headphones are 600ohm this doesn't seem to be a problem as long as all the headphones are the same. But whenever I have to do large sessions (like the 22 piece string session coming up on monday) I have issues as I have to borrow headphones and I have mismatched sets and of course if parallel too many headphones the load drops too low and can damage the amp driving them. So I was thinking of a way to minimise these problems. I could set the headphones up in series so the more headphones the higher the impedance load but then I'd have to have an elaborate switching method inside the distro boxes or always have all the headphones plugged in. So what about putting a dummy load across the inputs to each distro box say around 16ohms/5 watt so that there is a minimum load on the amp at all times? Will this be an issue if I chain up multiple distro boxes? Will the volume available to the headphones be too low?

The headphone amp I'm using is a SM Pro Audio HP6 which has 6 separate stereo amps with a nominal output @ 32Ohm 600mw per channel according to the limited specs.

So any thoughts?

[Kurt]

Sm, be!@#$%^&, Phonic et al all make headphone amps so cheap these days you could just buy another one and save a lot of hassle. Still have 2:1 splitters but only ever need to run one per amp output.

[mylesgm]

I could but this way they will be more flexible, and hopefully will outlast both be!@#$%^& and SM Pro audio...

[rob]

"dummy load across the inputs "
do you mean put 16ohm in series in each distro box or in parallel? Cause it sounds like you mean in parallel. If so, this won't help matters at all.

What about putting passive volume pots in each box so the levels can be set to suit mismatched HP models ( and the listener's taste )
500R dual gang linear is perfect,but you'll have to hunt to find some.
Put say 100R in series with each pot's CW terminal. Then worse case load on the amp with 24 HPs is more than 4 ohms

[adamcal]

DEX has a product that I have been using for about 20 years and almost perfectly matches your request.

Its called a HD4S, XLR in and through to chain them, 4 headphone outs, a switch to select A, B, or A+B (ie stereo) and has large resistors inside specifically for connecting to a power amp. Its solid metal and about the size of a DI box.

You can (for example) hook up 2 boxes in series from one power amp, set one to A the other to B and you have 2 mono feeds, feeding 4 outs each.

Or set them all to A+B and now you have 1 stereo send feeding 8 stereo outs, adding boxes for 4 outs more at a time.

In my studio I have 3 poweramps (p2200's) each with 2 boxes. so I can make 6 mono sends (band tracking), or 3 stereo sends (smaller band) or feed them all one send and get 24 high powered headphone outs. or some other combination.

I dont think Daniel is actively pushing it but I bought some last year, and said he still has some.