I just built an EZ1290 board from Martin on this forum. I used a 16V 10VA doorbell transformer for my 24VDC power supply (built from 4 diodes an LM317 and 2 caps) and it seems to work great. I haven't done loads of testing but it seems to be very quiet. I definitely didn't notice any 60 or 120 cycle hum.
The transformer was free (came in the kit with a new doorbell and the old one still worked) but can be found very cheap on ebay and also locally (hardware stores). It was labelled 16VAC but actually put out around 21 VAC when I measured it. Rectified I was getting around 30VDC. I ran this through a regulator and set it at 23VDC to be careful in the beginning. The transformer seems to have enough power to do the trick. I ran it wide open with a 1kHz bias signal into a scope and measured DC voltage and wasn't getting any voltage sag. Also the transformer never even got warm to the touch nor did the regulator. Seems to be a good setup. Of course more critical testing and listing for hum will be in order, but I can tell from quick listening and recording tests that it's very quiet. Possibly one more option for those here on a budget (or with a door bell xfmr laying around)
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EDIT: I should add that I had this all loose (not mounted) so I could move components around on my bench to listen for noise. With the power supply near the PCB it's still very quiet. Why not mount the Power Supply inside the chassis?
The transformer was free (came in the kit with a new doorbell and the old one still worked) but can be found very cheap on ebay and also locally (hardware stores). It was labelled 16VAC but actually put out around 21 VAC when I measured it. Rectified I was getting around 30VDC. I ran this through a regulator and set it at 23VDC to be careful in the beginning. The transformer seems to have enough power to do the trick. I ran it wide open with a 1kHz bias signal into a scope and measured DC voltage and wasn't getting any voltage sag. Also the transformer never even got warm to the touch nor did the regulator. Seems to be a good setup. Of course more critical testing and listing for hum will be in order, but I can tell from quick listening and recording tests that it's very quiet. Possibly one more option for those here on a budget (or with a door bell xfmr laying around)
. EDIT: I should add that I had this all loose (not mounted) so I could move components around on my bench to listen for noise. With the power supply near the PCB it's still very quiet. Why not mount the Power Supply inside the chassis?
