[Asterisk-Users] Poor sounds on Adtran 750

[Rich Adamson]

> I changed from a tdm100B card over to an Adtran 750 as I added more PSTN 
> lines last week. I have a Sangoma A104u card and 12 channels FXO 
> connected to PSTN lines. I am experiencing very poor audio quality with 
> hum on the lines and poor volume. When I connected the Adtrans I 
> upgraded the firmware to the latest and reset the config to the factory 
> default. I also upgraded Asterisk to 1.2.
> I am at a loss to explain why the quality has become so poor, has anyone 
> any advice?

I'm not useing a 750, but just suggesting a possibility...

Check to ensure the fxo lines have proper termination/impenance settings.
600 ohm in the US, etc.

There was someone trying to use another channel bank some time ago
in the Colorado area (I forgot the exact make/model), and the fxo
card specs were actually listed as 15,000 ohms (no 600/900 ohm at all).
He had the same 'hum' issue, and that was certainly understandable.