Serious echo issues with A400 connected to Charter phone interface

We are working on switching our phone system over to FreePBX. We were planning to keep using our Charter phone lines for a while and deal with a SIP trunk transition later, so we bought a Sangoma A400 to connect to the box that Charter provides that gives us RJ11 “analog” lines. I know they’re not truly analog copper connections like a real PSTN provider would give you.

Now, I have experience with FreePBX but not the analog side of things like DAHDI. I was assuming this configuration would work no problem. It does WORK, as in calls can be made and received, but there is a terrible echo. Oslec doesn’t help much at all, and we didn’t get the version of the card with HW EC.

I’ve read about the troubleshooting steps for echo over DAHDI channels, such as adjusting the tx and rx gains. They all seem to reference calling a local milliwatt test line, which I don’t think is applicable in this setup. (Is it??) So I’ve just been doing some experimenting with gain values. The echo is reduced to a reasonable level if I turn the tx gain down to around -20. This makes it too quiet though. It’s so quiet that even DTMF tones don’t always register.

What is the correct way to adjust the gain values in this kind of situation?

Apparently fxotune doesn’t work with Sangoma cards. Is there another similar tool meant for Sangoma?

Is there anything at all I can do to make this work out? Any other settings to look at? Like I said, I’m not familiar with the analog/DAHDI side of FreePBX/Asterisk and maybe there’s something I’m missing.

it may be best to open a support ticket at

Looks like it’ll require me to purchase support credits. I’ll probably just accelerate migrating to SIP trunking rather than doing paid support since this was just going to be a temporary way to connect lines anyway.

Before I go to far into that, does anybody else have any tips or have I exhausted my options for non-paid support?

We will want some local FXS extensions down the road anyway for fax machines, so at least buying the A400 wasn’t a total waste.

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