Suitable toroid/PSU for this application?

[audiovisceral]

I would like to hook up four of these stereo DAC modules to one power supply:
DAC module picture

Each module requires ~15V (+/-) and ~6V (+). You can buy the units with an optional toroid that hooks directly to the PCB:
Toroid hooked to module
Toroid wiring diagram

Can I just use one of these included toroids to power all four boards?

If not, are there any beginner-level toroid/PSU solutions that would work instead?

Thanks.

 

[sahib]

Schematic says 13-0-13 and 0-8V. Although 15-0-15 would not do any harm, 0-6V might be too low as the regulators normally have a voltage drop out of about 1.5V. However, if exactly what is specified in the equipment manual then they must have used a low drop-out regulator, in which case it will be fine.

Answer to your question.

You mean you would like to hook them up to a single transformer. If each module comes with its own toroidal transformer then I am sure the transformer current rating is sufficient for only one unit. Also by judging the size from the picture that is how it looks. In which case single transformer will not supply four boards.

Simply, find out the current requirement of each board from the user manual, multiply that by four. This is your bear minimum current requirement from the transformer. However, in addition you should increase that by about 25% for a healthier operation.  

 

[audiovisceral]

Schematic says 13-0-13 and 0-8V. Although 15-0-15 would not do any harm, 0-6V might be too low as the regulators normally have a voltage drop out of about 1.5V. However, if exactly what is specified in the equipment manual then they must have used a low drop-out regulator, in which case it will be fine.

Answer to your question.

You mean you would like to hook them up to a single transformer. If each module comes with its own toroidal transformer then I am sure the transformer current rating is sufficient for only one unit. Also by judging the size from the picture that is how it looks. In which case single transformer will not supply four boards.

Simply, find out the current requirement of each board from the user manual, multiply that by four. This is your bear minimum current requirement from the transformer. However, in addition you should increase that by about 25% for a healthier operation.  

Thanks. The PCB schematic actually says 15v and 6v, but ya, they supply a 13v and 8v toroid.

So I guess I need a '36v center tap dual secondary' transformer like one of these:
http://www.hammondmfg.com/266.htm

Is there any risk from having too much current? eg. If you only need 0.5A and you had a 2A transformer?

Also, this is probably really dumb, but if your toroid is already giving you the approx. voltage and current you need, why do you usually need a separate PSU part for the PCB? Why can't the power transformer just feed the actual circuit directly?

Thanks again.

 

[sahib]

Increasing the voltage rating means you will be dissipating unneccesary power.

Apart from the economics, generally the risk of having a transformer with a much greater current rating than what is required is, that if the rectifiers have much smaller current rating then in the case of a high surge during  charging the reservoir capacitors at start-up, all this current will be dumped onto the rectifiers and may damage them.  This obviously depends on the size of the reservoir capacitors too. Equally if the power supply is not short circuit protected and there is a short on the output, all this current will again be dumped onto the power supply. These are the points you have to consider. But in the case of a ratio of 0.5A to 2A not very much to worry about. If you really want to be safe, then you can either use appropriately chosen fuse on the AC input of the rectifier, or place a current limiting resistor between the output of the rectifier and reservoir capacitors.

I am not very sure on your last question though. You can not power a circuit with AC straight from the transformer. If you did not mean this then the reason each card uses its own on-board PSU is that probably because the  PSU can only feed one circuit at a time. You can of course use a much larger stand-alone power supply to feed more than one card but there can be a concern of cross talk and it would be up to the designer to make that decision.