Small update, next step I feel is a call to either O2 support or BT. But not sure who is the first port of call?

I swapped the crappy "master socket" for an NTE5a type. No huge difference, but the line is generally louder and clearer when no microfilter is involved. My broadband speed also seems to have picked up. May be coincidence, but before and after saw a jump of around 500 kbps or more download speed. Nice side benefit.

What it has shown though is this fault is NOT purely DECT related as I had thought. I can now hear a significant difference on the trust old BT Duet 200 phone, previously I couldn't notice anything with the naked ear (not a phrase I thought I'd ever use!).

Once again this testing was carried out at the master socket with the ADSL off, routers, computers, all wireless devices off, nothing else plugged in.

I didn't invest in a voltmeter yet, but when installing the new master socket I tried the two feeds from the drop wire both ways around (blue and white are active, and I switched those two over and tested for any audible difference).

So, tried swapping EVERYTHING in the house, from the master socket inwards. No ADSL microfilter, telephone line clear as a bell. ADSL microfilter, noisy line, and unusably quiet dialtone/voice.

So, any suggestions on where to go from here?

Since your problem involves broadband hardware, your best approach is via O2. If Openreach send out a phone guy in response to a voice fault callout, he will probably run a mile when he sees that it involves broadband hardware. I would suspect a line card fault, but as someone who has had BTO guys on and off my premises over a 5-month period, I wish you luck

Hi

came very late to this while searching for my own problem....( buzzing on receive of BT synergy DECT AM phone, regardless if theres a DSL filter or not )

Anyway, this sounds like a sidetone problem to me. The hiss is coming from the mic circuits of the DECT phone. Normally this should not be heard, as it goes upstream only. The sidetone circuit in the phone ( all phones have one ) attempts to identify what on the line is from its own mic circuit, and subtract this from whats on the line ( ie to end up with just the speech from the remote end ).

To do this it relies on the impedance of the line being what it expects. It sounds like the DSL filter is presenting a different impedance, in the 0 - 4KHz region, , and so the sidetone cancellation in the phone isn't working properly.

This is a compatiblity issue really, but you could try changing the impedance a bit to see if this helps. eg try adding a 22nF cap across the line at the phone connect point ( ie after the filter ) - min 250V - , or adding a resistor in series eg 100R ).

hope this helps

D139 ( ex PBX design engineer )

Right then.

After too, too long, we have a working phone line. After backing off every time the £130 callout fee threat came over the phone, I finally bit the bullet and a BT engineer called early in the week.

They tested the line, noisy and quiet by default, much worse with ADSL microfilter.

Checked at the cabinet down the road, still a bad line.

Checked at the exchange and apparently better. But not great.

They changed some stuff, did some work at the frame, very little (if any) change in quality.

They replaced our ADSL equipment at the exchange for all new stuff (apparently). Still the same issue.

Had ONE clear call where our call was "intercepted". BT doing a lot of head scratching.

Today back the exchange they changed out something more significant, apparently very rare, might have been the card, not sure.

Then did something again with the ADSL gear.

And we have a very good quality phone line. Superb.

ADSL seems a little slower than before, so not sure if O2 can tweak a setting or two on that, but the phone works great.

Post deleted by billford