Phono Preamp Power Supply Question

[suryabeep]

Hi everyone,

I want to build a phono preamp, specifically this one  - http://sound.whsites.net/project06.htm - but I don't want to use transformers and rectifiers. Will a max1044 +-18V circuit provide enough current for this preamp?
And a related question - how does one figure out the current consumption of a circuit without actually building it first? (I am a noob at circuit analysis)

My apologies if I shouldn't be posting phono stuff in this stompbox forum

[vigilante397]

Will a max1044 +-18V circuit provide enough current for this preamp?

Probably.

And a related question - how does one figure out the current consumption of a circuit without actually building it first?

I usually read the datasheet and find the maximum current draw, which would give a worst-case scenario, and plan around that. I said probably before because under no load (best-case scenario) NE5532 current draw is listed as 8-16mA, and under short circuit (worst-case scenario) current draw is typically 38mA. The MAX1044 can give a maximum output of around 20mA, which is between your best-case and worst-case scenario.

It's not as important in hobby stuff, but for my day job when I'm designing a power supply my boss tells me to plan for double the worst case scenario. So the NE5532 worst case is typically 38mA, but the WORST-WORST-CASE would be 60mA, so if I design for less than 120mA I'm told to go back to the drawing board and find a better solution.

It's difficult to know exactly the current draw of a circuit without building it and testing it, but SPICE simulation toolslike LTSpice can be useful in giving a good estimate.

Hope this helps

[PRR]

> how does one figure out the current consumption of a circuit

In this case... what is connected to the power supplies? ONLY the chips.

Now, the chips can run into class AB and suck more supply current for large outputs in low loads.

It's too cold tonight to teach that. I assure you that in this application, the "Max" supply spec for '5532 (twice) is adequate.

I assume you won't be driving shorts. If you drive DC into dead shorts (why??) the '5532 can make (and take) some more than 38mA per short from the one rail. If you drive audio into a short (could happen) then the 38mA flows only half the time so the average is under 20mA.

My experience with canned opamps and older SPICE models is that they do NOT correctly model supply current. The more commonly used netlist makes output current appear magically from global zero, NOT via the supply pins which are modeled as current sources (loads).

[PRR]

There are other fine RIAA MM preamp which use one '5532, cutting your demand in half.

I lived a long time with a '741 opamp on two 9V batteries. Battery life was not a problem, and zero line-hum in the power. Suggest you plan to start that way. You may find it fine.