Doubling PS problem

[fum]

yup, sittin with a 2 watt at present. dialed it in with a 1/2 watt, which was pretty dang hot.

I tried to up the toroid to the 12V toroid I have, cuz it's rated a 1.5 amps rather than 385 mA with the 9V.

I need to figure what 4 of these pres are gonna draw, I assume it's more than 385.

What the best way to figgur it? I was think to hook one up, with an open, and set my DVM to amps, and put complete the circuit with it?

Regards

ju

[ssltech]

yes, in a simple, single-secondary system that's correct... do it at the AC side of the bridge. However your meter will only give a true power reading if it's a true RMS meter, otherwise it'll be close but some error might be anticipated. The transformer won't be feeding a true, continuous current load, because it'll be "topping-up" the smoothing caps in bursts. That means the current draw will be bursty, rather than a smooth sine waveform. For a true RMS power calculation, your meter will have to calculate the true RMS current, which averaging meters don't really indicate. -They usually set them for minimum error with a true sine... in this case your current draw will not be a sine, so if you have an averaging meter, you should allow yourself a safe margin of error...

Fluke 87, etc all say TRUE RMS on the front, and they can be trusted. Fluke 73 doesn't say anything on the front about RMS and so I'd be inclined to give a 10% safety margin, just in case...

Keith

[fum]

I'm using a Fluke 111, which says it's a true RMS meter ( also does tasty things like freq, diode check, capacitance, continuity, etc.) Just have to keep your eyes on the 9V battery, cuz it makes your head do funny things when the battery is low ( I just checked that and it was right, dammit! ) [img]graemlins/.gif[/img]

I managed to get things correct with the larger torroid. So I'm feelin good about that =).

I would say 90% of my problems are the stupid human tricks I'm performing ( mis wire, or grabbing what you think are two resistors of the same value that aren't, etc. )

Anywho, thanks so much for your help, I got the Jensen pre's in today, so I can start workin on rackin them. They come with a gain adjust, 3 LED meter, and a -40db pad, and I'm gonna add phase, and phantom on the panel. Oh, and output transformers.

Regards

ju