[rums]

Hi Super-Knowledgeable Head-Fi'ers,
 
Kind of a different question and I'm a bit over my head here.  We have an older Mitel phone system at our office that has a music on hold input jack.  Unfortunately, every audio source we've tried (radio, iPhone, laptop, etc.) sounds like absolute garbage -- we have to crank up the volume on the device and on the phone side it's just a quiet, distorted mess.
 
I did some digging around and found these specs for the phone system (see the attached image)
 

 
 
Based on the specs above, would something like an inexpensive Fiio E10 / E07K / E09K (not sure which one...or perhaps something else?) amp with the iPhone (and a line-out if necessary?) do the trick to get some half-decent (for a phone), non-distorted sound?
 
Any feedback or suggestions would be great.  Thanks!

 

[mikeaj]

I'm not really understanding what an amp would do here other than change the level into the phone system, which is already possible and what you were doing if you were using a laptop, iPhone, etc.

Distortion seems likely if the input level is too high. The spec there lists an input level of -6 dBm (dB referenced to 1 mW). That's 0.25 mW. Input impedance is 600 ohms, so we're talking about 0.388 V rms into the device to transfer 0.25 mW. If you maxed out an iPhone, it would exceed that a little bit on peaks on material reaching close to 0 dBFS (full loudness), causing clipping distortion.

As for low volume output, what are you listening out of? A phone? Low compared to what? Output level depends on everything that's going on internally and whatever you're using to play it back. Internally it's a normal telephone system? Normal ~3 kHz bandwidth? Can't expect too much there.

Have you thought about making a recording of the sound you hear and analyzing that? Run some test tones through and see what happens?

 

[rums]

Hi,
 
Thanks for the reply.  I'm not expecting any type of high-fidelity at all, as it is just a normal phone system and this is the stuff people listen to while on hold.  "Low" meaning barely audible through the phone headset compared to the clear, loud sound of voice when a call is picked up.  Best I can describe it is as very clipped, distorted audio that's barely audible, and that's with (or as a result of) the source iPhone being cranked all the way up.  Any volume less than 90% makes it so quiet that you can't hear it through the handset unless you're in a quiet room.
 
My (basic) understanding is that the amplification out of a headphone jack in a laptop / iPhone / etc. just isn't powerful enough to meet the specs required by the input jack, which is why we are getting the barely audible distorted audio.  The thought was that by incorporating a headphone amp we could drive the required inputs without all of the clipping, but unfortunately I don't understand the input requirements of the phone system specs well enough to guess if it'll work or if I'm way off track.
 
Thanks again.

 

[mikeaj]

The specs of the input jack are not that unusual. Should be similar to most line inputs out there except maybe the max input level it can take is pretty low at that -6 dBm.

It should be a much easier load than most headphones, and next to every source (and especially anything that can handle headphones) should be able to deal with it just fine. Really doesn't seem like having a slightly worse amplifier is the source of any of these problems. I mean... you realize we're talking levels under 1 mW? If an iPhone or laptop weren't powerful enough for that, I wouldn't know what to say.


It's something else, or that's the way it's supposed to be, or the electronics are faulty. Maybe somebody else has a better idea. I'm certainly not familiar with this systems and might need to research these things a bit more to get ideas.