headphone distribution, how many headphones can the amp handle

[klaukholm]

I may have to push my headphone distribution rig to the breaking point in a few weeks.

I have 2 furman HA6 AB that have 20 watts on each channel for a total of 2x20w stereo channels.
Each channel will feed Whirlwind SAT1 boxes going into 32ohms headphones.

Can I connect 40 headphones to each amp?

Normally I would have atleast 4 furmans, but as fate has it..

Will this work or do I need to search for another solution?

Can anyone predict what will happen as I reach the limit?
The amps have overload protection.

[Testing123]

Trying to visualize your setup - how many SAT1 boxes? One per 20W output?

[klaukholm]

10 sat boxes (4 outputs each) feed a total of 40 pairs of headphones.
The SAT1 has an xlr in and an xlr through that feeds the nex box.

SAT1 CP Communications - Whirlwind SAT-1 Headphone Amplifier / Distribution Satellite Box

Power amp FurmanSound.com - Pro A/V Product - HA-6AB

I also have a few Furman HR2 boxes

FurmanSound.com - Pro A/V Product - HR-2

[klaukholm]

From Furmans own site:

quote:
"The HA-6A connects to the first HR-2 box; another mic cable connects the first HR-2 to the second HR-2; a third mic cable connects the second HR-2 to the third HR-2; and so on. If low impedance headphones are used, up to twelve HR-2's may be chained together. If medium or high impedance headphones are used, 25 or more Remote Stations may be chained"

If 32 ohms is a medium impedance I am ok, but I am inclined to think they fall into what furman categorizes as low impedance in which case 24 headsets is the best I can do it seems.

[-Noodles-]

Seems like you've got it solved?

[klaukholm]

Typo on my part sorry!

The amps automatically bridge to mono if you do not use the left input.
There is only one xlr out which would have to feed 40 cans.
as I edited above, it is unclear to me if I cap out at 24 or if I can make it all the way to 40

another quote where furman more or less contradicts themselves:

"However, twelve HR-2 is the
recommended maximum."

[Testing123]

Might be better off to wire both headphone amp inputs in parallel so that it won't go into bridge mode, so you can spread the load out a little.

By the way, your 32 ohm headphones will be 16 ohms in mono, no?

Do you have access to all the equipment? Might be wise to do a dry run and see what happens.

[Jim vanBergen]

With that many headphones, you are way above the limit.

I suggest you find a small-wattage amplifier and create additional subsystems.
An HA-6 is only a 40W amplifier, so anything small will do nicely, you just have to make it a mono feed to the cans or be very careful with your wiring from the amplifier into your adaptor.

I have subrented Mytek and Aviom systems for really large setups, in addition to the Furman and Rane headphone amps I have. Is subrental an option? Do you have that many pairs of cans laying around?

[klaukholm]

Originally Posted by Testing123

Might be better off to wire both headphone amp inputs in parallel so that it won't go into bridge mode, so you can spread the load out a little.

By the way, your 32 ohm headphones will be 16 ohms in mono, no?

Do you have access to all the equipment? Might be wise to do a dry run and see what happens.

I wil do a dry run, but as things turn out I will not be able to do that until a few days before the session.
As a backup I can drive across country to borrow more amps, but that is a last resort.


I will try to track down two more amps, as I see there is a place in belgium that has Furman SP-20AB/E listed.
If they have them in stock I should be OK.

[klaukholm]

Jim, crazy question but will my Krell KAV150 (150w)
fry this system if I used it?

If I have time I will go in and disconnect the wires to one earpiece on all the headphones.
that way I should get twice as many whatever number that is.

[Jim vanBergen]

No, a 150W system won't fry your phones. But make sure you have a gain stage pre-amplifier, and personally I measure the voltage coming out of the amplifier before I plug it into a set of cans...and I use old AKG KM240s first!

If you measure, you don't want to send 50V going to a set of cans. I'd send the amp -10dB VU and turn the amplifier trim almost all the way down, measure the voltage (try to get less than 4v at first... one volt if you can dial it that low! And then slowly raise the amplifier attenuator, then the gain stage if you have to.

I have used Crown D75s, DC300s (150W/side) and even larger amps for setups like this. Wire the rig carefully, and you won't need to disconnect one side of the cans.

JvB

[klaukholm]

Thanks Jim,
your answer is truly helpful.
I wish I had people like you around here, but alas.

I will bite the bullet and use the old distro sytem one last time while I get my ducks in a row with the new setup. This session came up a bit to sudden (7 working days for a full movie score)

I just realized that by turning the left/right balance on the SAT units all the way to one side should reduce the load without having to mod the new cans (80 of Harveys cans)
Our old rig was 96 modified akgk240

Sometime week 2 I will test the limits of the system by adding one headset at a time. I figure it will be interesting for other people to know what the furmans can handle and what happens when the limit is reached.

[klaukholm]

So I hooked up 41 headsets to a single furman and ran them for a while. It seems to present no problem.

The question is if this is a "either works or not" situation or if prolonged stress on the amp could cause it to crap out mid session?

[Remoteness]

We have quite a few of the SAT1s and I like using Crown DC75s for that task.
We've made dual (L&R) Banana plug to XLR adaptors to run to the first SAT1.
There's enough power to blow your brain apart.

[klaukholm]

How many sats have you had on one chain?

[Remoteness]

At least two or three SAT1s with five or six headphones.
We had no problems. I believe we could have added more with no issues.
I've used larger power amps as well, but the DC75s have worked just fine our situations.

I've setup a few DC75s and branched the SAT1s off of them when I needed to feed headphone mixes that were further away from each other like different locations and such.

[Mr P]

I mix a theatre show where all FOH audio is delivered by headphones.

According to the sound designer's specification we can run a maximum of 28 pairs of headphones (7 boxes) on an amp rated to drive two ohms.

The distro boxes are made by ProCo and have 100 Ohm volume pots and 52 (or 54)ohm build out resistors. The headphones are 32ohm Sennheiser units.

As long as the amplifiers supplied are True Earth Negative and can drive low impedance loads, it works fine. It is very common for us to be supplied PA power amplifiers such as CA6s and 4801s.

Running high powered amplifiers is not normally a problem, but I always check the voltage gain of the unit, and pad down the inputs appropriately.

And so we get to do this again next week in the spiritual home of the Remote forum, NYC. I am secretly trying to smuggle just a bit of the Australian summer in my suitcase. Contraband Sunshine.

Cheers,

Phillip