api 512c power supply
« on: June 13, 2004, 04:15:43 AM »
I'm racking two api 512c modules and wondering if anybody has some experience here. I've found this schematic:

Questions I have:

1.  Will this supply two units?  (not one like it describes)

2.  Is the wall wart a good/bad idea over a toroidal?

3.  Is there a better design anyone's aware of floating around?


api 512c power supply
« Reply #1 on: June 13, 2004, 04:32:56 AM »
Well if the psu will supply 2 modules is connected to the fact if the transformer/wall wart is able to deliver enough current. The 7X18 series voltage regulators are able to deliver up to 1A current which should be enough for two modules although i don't know the power consumption of two 512C.

Normally a torodial transformer is the best choice when you mount the power transformer inside the case. But with a wall wart you normally have the transformer outside the case so there shouldn't be any problems with added noise from the power trafo. Personally i like to have everything inside the box as i don't want to have additional things laying around so i would go for a torodial but i guess this depends on your taste.
I don't see any big disadvantages of both solutions, maybe someone more experienced can help.



api 512c power supply
« Reply #2 on: June 13, 2004, 06:01:16 AM »
Thanks infernal. I have found a reference sheet on that regulator and you are right, it's 1a. The spec sheet here on the 512c's says the Power Consumption is ±12/18 Volts/DC, @40ma.  Is that straight math then?  ie, does that mean up to 24 channels would actually run on this 1a circuit, power transformer notwithstanding?

It would be nice if someone with actual api power supply experience could chime in.  I have tech who's willing to check my work and touch things up and his only comment was that he didn't think this diagram was as quiet a supply as he's seen.  Of course he didn't elaborate but did mention something about the quality of the regulators.

api 512c power supply
« Reply #3 on: June 13, 2004, 06:56:48 AM »
Well as i get it the power consumption adds up with the channels you are powering. So if your api modules need 40ma you should have plenty of power with those 7X18 regulators (of course you need a nice beefy power transformer to power those regulators).

I think there are better regulators out there than the 7XXX series but to be honest all of my projects have those regulators and i didn't have any problems.
As far as other designs i know of Peterc's power supply which can deliver +-18V and 48V and also SSLTech's psu. But both also use the 7X18 regulators.
Peterc's psu can be found here:

I don't have the source of SSLTech's psu but if you want it i can email you the pdf file for it. I just need your mail address.

If i were you i would buy a nice 30VA torodial transformer and use it with SSLTech's psu. Those 30VA i buy have 2x0.83A at 2x18V. With this for example i power my Sontec clone which is 1 amp board and 10 filter boards, with 14 melcor DOA's and one balancing board. And the regulators don't run very hot. But i always mount heatsinks on the regulators (if there is enough space) even if it's not necessary. I just like to have everything as cool as possible. I also always try to buy/make a more powerful psu than necessary. It's just nice to know to have more than enough power available and a bigger transformer isn't much more money wise.


Bo Hansen

api 512c power supply
« Reply #4 on: June 13, 2004, 03:57:51 PM »
Hi Bob,

Yes, this PSU is ok for two API card, the 78/79 regulators are ok fore one amp and up to 100 mA it is ok with out heat-sink, so it is only the size on the AC wall plug-in adaptor and the electrolytic capacitors before the regulators (and heat sink) that decide the current limit under one amp.
A wall adaptor or a small transformer on aprox. 300 to 500 mA and the 1000uF  shall be ok for two API 312 or 512 card.

On the phantom section you shall change the 1k resistor to to 470 ohm, and of course there must be two 6,8k phantom feed resistors even to the second card.

I met a man with a dollar, we exchanged dollars, I still had a dollar.
I met a man with an idea, we exchanged ideas, now we each had two ideas.


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