passive headphone splitter with volume control per headphone

[pucho812]

Trying to figure out the best way to impliment a passive headphone splitter with volume control.


Me knows that I can run into the splitter and between the input and each individual headphone output jacks. There would be one resistor on the hot and one on the cold. That will give me the splitting I need. But Wondering how to impliment passive attenuation for each headphone. Is sit possibe to stick just a 10K lin stereo pot after the resistors and before each out :?

(basic schematic without the volume control)

 

[ruffrecords]

I built one exactly like this about 20 years ago. Only difference was it only had 4 phones outputs. I still have it and it still gets used. The only difference is I think I used 68 ohm resistors.

Never used individual volume controls but a 10K stereo pot may not work. You need to think about the impedance of the phones. Let's say they are common all garden 32 ohm types. With a 10K pot, all the control will happen near the fully up postiton of the pot. At the centre position there will be over 40dB of attenuation. If you have 400ohm DT100s though you would be nearer the 20dB of a regular audio taper at the half way postion. Only gets worse if you mix and match phones of different impedances.

Ian

 

[amorris]

our boxes have the attenuator affecting the input before the split.

the kids here burn the pots by running too hot a level (d-75 or greater) to the pot (2watt rated?) then turn it way down, soaking that voltage through the pot to ground. I tell them everytime, and they still do it.

 

[Svart]

I bought a rolls active headphone amp off of ebay for 30$, couldn't be happier.

 

[NewYorkDave]

Not trying to piss on your parade, Pucho, but multi-output headphone amps with source select, level, pan and tone controls are so cheap nowadays it'd be less trouble to just buy a couple of those and run line-level feeds out to the studio.

Trying to do a passive split with variable level on each output is a pain in the ass, for the reasons the others have mentioned.

 

[pucho812]

[quote author="NewYorkDave"]Not trying to piss on your parade, Pucho, but multi-output headphone amps with source select, level, pan and tone controls are so cheap nowadays it'd be less trouble to just buy a couple of those and run line-level feeds out to the studio.

Trying to do a passive split with variable level on each output is a pain in the ass, for the reasons the others have mentioned.[/quote]

Piss all you want dave just not on me. I said the same thing but the head tech around hear feels it can be built for cheaper. I disagree when for about 30-40 bucks you can get a furman or other such unit. He had me looking into it.

My buddies studio is using some bringer headphone boxes. Totally worth the money one of the few products they make that is.

 

[sodderboy]

The best passive box out there is the Simon Systems CB-4 for ONLY $375. But it is built like a tank. Number 2 is the Redco "Little Red Cue Box". The Simon uses 5W Mallory pots, the Red uses 1 W Sfer pots. They blow a lot, even with the newer design revisions. Any DIY implementation of these designs will be expensive.
One place uses ProCo boxes that all have blown 2W pots. They are mono pots. I have looked to make them better and these are the prices I have encountered with quantities less than 50:
Mallory mono 12.5W pots, $30. Stereo, $45.
CTS mono 5W, $4. Stereo, $12, back-ordered or lead-timed everywhere.
So once you get a design that will be robust, you are spending way more than the newer products mentioned earlier.

And something that I learned recently is that all the industry standard cans like 240 and T20 are now supplied with impedances less than 60 ohms standard. "Lower impedance for higher volume!" Is the buzz phrase on AKG's website. You have to special order 600 ohm cans, which are the correct impedance for our favorite Jurassic cue distribution systems. The new lo Z cans have been blowing cue boxes all over the place. The new self-contained headphone systems can drive 8 ohms no problems with no burned pots.
Mike
PS: I can dig-up the circuits for the aforementioned boxes, plus the Power Station circuit if you have the budget and the boss refuses to accept and embrace change.

 

[magicchord]

Do you think something like this might work:
(edit) Needs to be driven by speaker outputs of a small power amp.

In this design, the headphone sees between 75 and 150 ohms unless you turn the pot all the way down in which case it sees zero. I'm thinking this will make the distro box more tolerant of different values of headphone impedance. Also, shunting the wiper of the pot fakes it into a sort of pseudo-audio taper. Not precise, but good enough for this.

 

[bobkatz]

[quote author="pucho812"]Trying to figure out the best way to impliment a passive headphone splitter with volume control.


[/quote]

The real key here is to have a bunch of medium wattage 2K ohm stereo audio pots. With that I don't think you need any buildout resistors, or worst case, say 100 ohms per channel/pot, and you usually just builld a box with pots and the TRS jacks.

I bought a bunch of them years ago from a manufacturer of headphone boxes, intending to build my own. Later on I had no need for them and gave them (maybe a dozen) to Fred Forssell. Generally these pots are special order :-(. Fred might still have them and be willing to sell them to you. Check with him.

 

[ruffrecords]

[quote author="magicchord"]Do you think something like this might work:[/quote]
Looks pretty good to me. Worth buidling as is just to see.

Ian

 

[Martin B. Kantola]

Just my 0,02 euro...

If you're planning on using them in the studio (as I did) you might end up frying those pots with your power-amp (as I did...).

Had a heavy metal band recording and there was a lot of smoke. Think there were 6 x 600 Ohm stereo pots, but 2W rating was simply not enough.

Should be fine for "normal" volumes, though...

Martin

 

[ruffrecords]

[quote author="Martin B. Kantola"]If you're planning on using them in the studio (as I did) you might end up frying those pots with your power-amp (as I did...).

Had a heavy metal band recording and there was a lot of smoke. Think there were 6 x 600 Ohm stereo pots, but 2W rating was simply not enough.[/quote]
According to my calculator that needs about 34 volts rms at the input of the phones box to get 2W into those 600 ohm pots which means the amp driving it would be capable of putting 150W into 8 ohms.

Ian

 

[SSLtech]

Martin,

Welcome! -(I'm Ashish's 'B-format friend' :wink:... we met earlier in the year.)

The problem with this type of passive headphone box (which I only usually encounter in the USA) is that people need to use them close to full output.

When people run a 100+Watts amp at close to full level, then expect a low-impedance potentiometer to 'take up the slack' while some people drop it to 100mW and others drop it to 500mW, there'll always be smoke. more so when some people use 8Ω phones and others use 400Ω.

People need to be engineers to stop it smoking, and most engineers even forget the power factors involved.

I HATE passive volume controls. In the studio I used to work at in the UK, there were NONE. you either took the cue feed at the level sent to you, or you mixed your own and used a local amplifier. (console cue coud be fed in on a stereo return if the client objected to mixing their own cue)

If you're going to use one of these and you don't want to replace the post ALL the time, you need to make sure that the person who wants it loudest has his controls set to 100%, then everyone else just trims it down a bit from there. That way, nobody's dissipating more than milliwatts.

We have about 30 or so of the passive headphone boxes from Redco or some similar maker. They have a lifetime warranty. -Thank god. there are never more than 25 working at any given time, the pots are ALWAYS burning up, and there are ALWAYS units being rotated through the 'infinite warranty' programme.

Keith

 

[Martin B. Kantola]

[quote author="ruffrecords"]
According to my calculator that needs about 34 volts rms at the input of the phones box to get 2W into those 600 ohm pots which means the amp driving it would be capable of putting 150W into 8 ohms.

Ian[/quote]

Yep, sounds about right... Stupid as it is, but one goes for a pretty big amp just to get enough voltage.

The headphones were probably 250 Ohms, and if we assume that the pots were turned almost to 100% I guess it would be pretty tough on those poor pots. Too late for me to do the math...

Martin

 

[Martin B. Kantola]

[quote author="SSLtech"]Martin,

Welcome! -(I'm Ashish's 'B-format friend' :wink:... we met earlier in the year.)[/quote]

Thanks Keith, of course I remember you! Did you listen to my B-format recordings yet?

I HATE passive volume controls. In the studio I used to work at in the UK, there were NONE. you either took the cue feed at the level sent to you, or you mixed your own and used a local amplifier. (console cue coud be fed in on a stereo return if the client objected to mixing their own cue)

After the smoke incident I decided to build some dedicated headphone amps (class-A, optical bias servo) and my clients have been very happy ever since. Designed them to be loud enough for even the heavy metal guys, but still within limits to save drivers.

Since monitoring affects performance directly, it's very important IMHO.

Martin

 

[SSLtech]

Oh yes! -And I'm most intrigued by the capsule sonic behavour... In fact I'm so fascinated that I'm already begun trying my own version.

I've started gathering parts and a plan, as well as metalwork, but I've not told anyone what I'm up to just yet... you of course already know!

Recently I recorded a 200 voice choir with a 50-piece orchestra in B-format... and I would REALLY like to have the option of an LD mic. -Time to learn more, I think.

But the best thing about classical gigs... no headphone mixes!!! :wink:

Keith

 

[BIASKING]

I've used these in all my studio's headphone volume controllers. Very high quality and work great.

https://theelectronicgoldmine.com/collections/standard-potentiometers/products/g26362a