Stero problem from soundcard (Resolved)

[joddle]

I have a number of Dell 755s and 780s and all have the same sound issue. Each PC uses the onboard "soundmax" setup

 

I run a small language school and up until recently have used the front sockets on these machines without problems for input and output to stereo headsets each fitted with a mic for students to use.

 

However the pupils keep running their chairs over the headphone cables or knocking the plugs with their knees and we have lost several headsets so I decided to use the rear sockets instead so the cables are routed over the desktops and the plugs kept well away from the students. However when I do this the headphones then revert to mono and become quite noisy. If I connect the same sockets to traditional speakers the output then comes again in stereo!!! There is nothing wrong with the sockets or the headphones so why is this happening - ie only getting mono from the rear sockets. with headpnes but stereo with speakers!! Also I notice when using the rear sockets, the recordings from the mic are quite noisy.

 

As a temp fix I have used some cheap USB converters in the rear USB ports and although they work pretty well without undue noise and with

headphones they give stereo sound, I would rather have the sockets working properly - any ideas please??

[Plastic Nev]

That is extremely strange, though I can only surmise this is maybe due to impedance of the headphones. Headphones are usually of a higher impedance value than speakers, hence why front sockets are usually marked with a headphone symbol and rear sockets with a speaker symbol.

How or why that is making the signal only mono though is beyond me and could possibly only diagnose if I was there with some of my audio test gear as it is certainly nothing I have come across before.

I assume you have looked at all the sound settings in the computer?

The USB adapters actually may be the only way round it.

 

Nev.

[joddle]

I had thought it could be due to impedance issues - I don't actually connect the low imp speakers to the rear but amplified speakers so the load impedence is pretty high - probably many times that of the headphones. I have looked at the device settings, it seem only the mic setting can be altered - however if I use a set of headpbines with a 4 connection jack inserad of the normal 3 I get the stereo back!

[Plastic Nev]

Hi,

I have since had a look at the specifications for the Dell 755, it would seem that the rear output sockets are actually high impedance 190K ohm line out only, and not really suitable for headphones. The headphone sockets are only at the front and are 5 ohm.

 

Have a look at the spec and scroll down to page 29 here :-

 

https://www.dell.com/downloads/global/products/optix/en/opti_755_techspecs.pdf

 

Much earlier there is the motherboard layout showing the sockets for the back panel as well.

 

Considering it is like that for the 755, I assume the 780 is similar.

 

To be quite honest, I would look towards fully USB headphone mic units, as the way forward or go back to the front low impedance headphone ports. Low impedance headphones are unlikely to perform well on those high impedance line out ports at the rear.

I must admit it is the first time I have seen a lack of low impedance speaker ports at the rear.

 

Nev.

[joddle]

Many thanks Nev - I think you are right and the way to go is use USB headphones - they are not so expensive and plent good enough for what we are doing.

[Plastic Nev]

Indeed, there are plenty of the USB headsets for sale, mainly aimed at Skype users, however the one I have for that purpose has a quite good microphone producing very good sound quality and was quite cheap to buy, made by Plantronics.

 

Nev.

[joddle]

Thanks Nev - It think you are right and I should use USB headphones - they are cheap anyway and plenty good enough for what we are doing. I like the Plantronics sets anyway Thanks again.

[Plastic Nev]

OK Joddle, if there is nothing else shall I mark this as resolved?

[joddle]

Yes - and thanks again