lunchbox/rack differences?

[ARM]

I'm in the market for a lunchbox or rack, but which one has the best specs and design?

-API
-BAE
-Purple
-OSA
-Atlas Pro
-A-Designs
-Avedis
-JLM (?)
ect......??

I know there are some power limitations when your running class A stuff.

Compatibility with Germ500 and Purple modules is apparently a problem too.

Any thoughts?

[LunchBoxHero]

I'm in the market for a lunchbox or rack, but which one has the best specs and design?

I know there are some power limitations when your running class A stuff.

Compatibility with Germ500 and Purple modules is apparently a problem too.

Any thoughts?

Hi ARM, thanks for asking this great question that so many have asked and I am not the most qualified to answer. So instead I am going to thicken the plot with a related question that hopefully one of our tech gurus can weigh in on... you are essentially asking about the quality of the power that each rack supplies.

I am wondering if there might be a way to build a "super lunchbox" - one that has no issues no matter which modules you load it with?

In technical terms what is the determining (and limiting) factor in how many modules and of what type a lunchbox support? If all the devices are meant to deliver +/- 16v dc to power the modules, is there an advantage to supplying this voltage at different specs so that the power supply does not get loaded down?

In the meantime, lunchboxhero is presently surveying manufactures and have asked them to specify the maximum power supply capacity, in Amps, at which proper noise and cross-talk performance specifications are maintained. (e.g. 3A @ +/-16VDC).

That should help us get to the bottom of which supplies would be best for your needs. As that info comes in it will be published in the database (http://lunchboxhero.com/500seriesdb.html).

[Eisen Audio]

In technical terms what is the determining (and limiting) factor in how many modules and of what type a lunchbox support? If all the devices are meant to deliver +/- 16v dc to power the modules, is there an advantage to supplying this voltage at different specs so that the power supply does not get loaded down?
Yes, the supply voltages are always fixed at + and - 16VDC. Granted, the limiting factor is current. The module draws (uses, requires) a certain amount, and the power supply can only supply (offer, deliver) a finite amount before its performance is compromised or it fails altogether.

Why is there this limitation? Because a proper power supply must supply clean (free of noise), and heavily regulated DC voltages. To do this requires active regulator circuitry - transistors, resistors, ICs. To regulate and pass large currents generates a lot of heat, and these devices can only have so much mass and dissipate so much heat given the amount of space, budget, heatsinking, available parts, and so on.

What conditions expose power supply limitations? Renegade modules - those which draw far too much current, or that draw the vast majority of current from only one supply (usually +16VDC, when converted to +24VDC) instead of drawing equally from the + and - 16VDC supplies.

How can we as end users know how to avoid power supply limitations? Suffice testing and measuring ourselves, only by knowing the facts... if manufacturers are bold enough to list them accurately and honestly.


In the meantime, lunchboxhero is presently surveying manufactures and have asked them to specify the maximum power supply capacity, in Amps, at which proper noise and cross-talk performance specifications are maintained. (e.g. 3A @ +/-16VDC).
Yes, I suggested wording the specification as such, because I believe that some manufacturers have been providing misleading ratings - "cheating" if you will. Specifically, if a power supply is simply rated as 3A @ +/-16VDC, without any stated conditions, then 3A could be the absolute theoretical max, or the point just before complete failure of the supply's regulators. However, in practice, one might find that (because of the limitations described above) the supply performance begins to suffer (higher noise floor, more cross-talk, wavering/sagging voltage, etc.) quite a bit sooner than this 3V max. Granted, it would be more fair to end-users to rate the supply capacity based on max current draw while maintaining proper specs. For example, 2.2A @ +/-16VDC.

[pan60]

at this point the best build i have seen is the Brent Averill.
as far as the power supplies go i am not the best qualified to answer ( i think Eisen Audio or some of the other tech's ), would offer better info their.
when you buy a unit, get the info as to power, and make a note, that is if you are to be concerned.
the new API is 3A +/- 16VDC so that is 1.5A per rail +/- @16VDC ( as i understand it ), so say you have some of the more power hungry units out their you should still be fine.
i think 150mA seems to be about it for the hungrier unit, and that is 75mA per rail +/- @ 16VDC so six of these would only be 900mA total or 450mA per rail @ +/- 16VDC
so with that average unit i would not be worried about.
please correct me if i am wrong here Jens