Hum on G2 audio

[ghylwood]

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Chiu, Andrew sent me a new board and I fitted it to my system. the hum was still there!

I then tried the first G2 board on the bench with only a power supply and telephone and there was No hum.

I then removed the transformer from my enclosure and tried that on the bench - NO hum

I then removed the second new G2 board and tried that on the bench and there was NO hum

Then I connected the back up battery (by this time it had been in use for 2 hours and was partially discharged) As soon as I connected it the HUM RETURNED.

I removed this and connected a 12 volt 5 watt lamp (400ma) load to the output of comfort and the HUM RETURNS   

Then I connected the G1 board on the bench and loaded that - There was NO HUM

It is clear that under test conditions on the bench, with nothing connected but phone, transformer and a load that there is hum on the audio of the telephone. ( This also been on door stations and keypads when in the enclosure.)

I have returned the latest G2 board together with my transformer from my G1 enclosure to Andrew, for him to replicate the hum in his workshop.

My comfort G2 is now running on a regulated DC bench supply and there is no hum on the board at all.

It seems the regulation on the G2 boards are not immune to mains hum and further smoothing is required.

I had a thought in the night!  - that the hum could have been induced via the mains from the many CBus dinners I have installed. However, when I turned them all off this morning and reconnected AC to the G2 board, the hum was just the same. The fact is the G1 board was and still is hum free and the G2 is not.

 

Kind regards  Graham Kemp     

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[slychiu]

Thats very puzzling because the G1 and G2 power supplies are essentially the same design except for the battery charging circuit. When you connect a battery that is essential a very huge capacitor and provides very good filtering We need to see if we can duplicate the hum at all. Did you say that with battery alone and no mains, there is hum?
Are there other potential noise sources besides the dimmers? Could you turn off all othr power one by one in the house?
I would like to know if Andrew finds the same problem
regardes

[ghylwood]

[font=\"Times New Roman\"]There is no hum at all when comfort is working by battery alone, OR powered by a smooth DC source.[/font]

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[font=\"Times New Roman\"]I have just powered everything off in the building and run comfort via a long extension from my office, with everything in there turned off. – The hum is just the same.[/font]

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[font=\"Times New Roman\"]It does cause some strange effects to the board as well; if someone presses door phone Comfort dials my mobile and because of the hum, Comfort can’t hear the DTMF tones from my mobile it keeps ringing the number back every minute. Then the only thing that will stop this sequence is a system re-set. I had 40 calls to my phone the other day, even though Comfort is set to just 1 re-dial attempt.[/font]

[font=\"Times New Roman\"]When the hum is removed, Comfort works as expected. [/font]

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[font=\"Times New Roman\"]I’m just hoping Andrew replicates this hum, because I have tried everything to eliminate it![/font]

[font=\"Times New Roman\"]Regards  Graham[/font]

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[ident]

I think you said that if powered by a battery but connected to a telephone line, the hum returns?
Let me know what Andrew finds, we are keen to get to the bottom of this

[ghylwood]

[font=\"Times New Roman\"]Chiu,[/font]

[font=\"Times New Roman\"]Finally we have got to the bottom of this hum on audio and it has now been resolved![/font]

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[font=\"Times New Roman\"]When I returned the G2 board, together with my transformer t Andrew, he immediately suspected the transformer, as it was not one they normally supply. It was the one fitted as standard when I bought the Comfort 1 panel in 2003 and worked fie with G1.[/font]

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[font=\"Times New Roman\"]However it only produces 13.5 volts AC. When I fitted the later transformer, supplied by Andrew, it worked perfectly with no hum whatsoever.[/font]

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[font=\"Times New Roman\"]A lesson to be learnt from me spending literally hours on this job would be to make people aware when upgrading from G1 to G2 that they check the transformer voltage is 15.5 Volts ac. The voltage regulation on G2 obviously needs more headroom to operate than that on G1.[/font]

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[font=\"Times New Roman\"]Many thanks for all your help and that of Andrew’s in resolving this issue.[/font]

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[font=\"Times New Roman\"]Regards  Graham [/font]

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