Headphone volume pot circuit

[jlascotty]

Hello, I'm new to the forum so apologies if I've posted this in the wrong place.

I need some advice on building a headphone volume circuit. I've had a go at it but I seem to be hitting a brick wall.

It will be used in radio/recording studios fixed to desks to allow presenters/vo artists to adjust the volume headphone level individually.

So it will go - Headphone amp - Pot - jack headphone port - headphones.

We use a Berhinger HA8000 Headphone amp - which has 100omhs output.

I've tried connecting various dual gang 47k log pots but as it is turned - the last 10% makes a very noticeable jump in volume.

Am I using the right pot? do I need to ad an extra resistor?

Thanks

 

[Mooly]

The way to do it is to put the pot before the amplifier input, not on the output. Just look at your numbers... a 47000 ohm pot feeding headphones which are relatively low impedance. To do it your way would need a pot of around 10 to 100 ohms... not practical and not available.

 

[jlascotty]

Would that mean I need an individual headphone amp on every station if they want to adjust their volume?

There HAS to be another way?

Thanks

 

[Davey]

The Behringer HA8000 already has an individual level pot for each output, does it not?

Dave.

 

[jlascotty]

It certainly does. Which under normal circumstances is fine. With it being a radio studio however presenters and guests would like the option of having a volume control in front of them. Unfortunately by hook or by crook this has to happen. Thanks

 

[Mooly]

So you want something like this. You could fit plug/sockets to suit. This will be a low resistance pot... but its not the ideal way of doing things though as I mentioned.

PSG03722 - PRO SIGNAL - HEADPHONE VOLUME CONTROL, IN LINE | CPC Products&MER=e-bb45-00001001

 

[00940]

Another question: are all the headphones used in the studio the same ? Or should the solution work for a wide range of headphones impedance ?

 

[jlascotty]

Mooly - that could work but I'd ideally like a professional looking volume control which I could fit to a desk.

00940 - We do use a wide range of headphones but the majority of them are DT250's 80omhs.

cheers

 

[Mooly]

Is price a consideration ?

WP8 - CLOUD - WALLPLATE CONTROL FOR 16-R | CPC


Click the "further information" link on this one. You would have to read the data sheets and see if it was suitable.
RH-8C - CLOUD - SELECTION VOLUME CONTROL FOR 16 | CPC

 

[Mooly]

Final thought. Would an "L Pad" attenuator work here ? Perhaps someone with more experience of these could advise,

Browse for Products | CPC

 

[jlascotty]

Again that would be perfect but I dont really have a budget - thats why I was looking to make the circuit - which now seems impossible.

I've been looking at Millenium HP 1 - Thomann UK and also RDL ST-SH2 STICK-ON MODULE Stereo headphone amplifier

but again any cheaper options would be greatly appreciated.

thanks

 

[Mooly]

They are headphone amplifiers that would normally take a line level signal as an input.

The volume control acts on that line signal rather than on the output, which is the normal way of doing things. Just like an ordinary domestic hifi amp, the volume control adjusts the signal fed to the power amplifier stage. You never normally fit a volume control after the power stage that drives the speaker/headphone. There are two reasons for that. One is efficiency, particularly with speakers where the excess voltage lost in the control has to be dissipated as heat. Secondly, speakers (and to a lesser extent headphones) like to see a low output impedance driving them. Adding a resistance alters the characteristics of the driver and the response becomes uneven because the "impedance" of the speaker (headphones) isn't constant with frequency.

With headphones the power and heat bit is negligible. The non linear response would be a problem for audiophiles... so how accurate and transparent has this volume control to be ?

 

[Mooly]

As you have had limited success with a 47k pot you might find a 1k type does the trick. You would have to try it and judge it subjectively but for the cost its worth a shot.

PC2G16ECO1KB - OMEG - POT, DUAL GANG, LOG, 1K | CPC From This Range

 

[Mooly]

Wired like this with the phones connected between the wiper and ground, not with the pot in series.

That's me done for today

 

[00940]

Another option might be to use a rotary switch with discrete resistors. A 2poles, 12positions would be an ok compromise for attenuation, work and price.