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Opamp current draw
Opamp current draw
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Old 20th July 2003, 05:14 PM   #1
5th element is offline 5th element  United Kingdom
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Default Opamp current draw

Ive completed my new active xover which includes four opa627 and four opa2134. Everything worked fine upon powerup and test appart from a low level thudding (very soft, not a hard piercing thud) thru the bass (opa2134's). This was solved by placing 0.047uf caps from the ground to power supply lines. Anyway running off 7.2 volt lines the total thing draws 58.2 mA (BB state that under +-15v the idle is 5mA and +-14v the idle is 4mA) when not asked to do anything appart from idle. Now BB states that the idle current for opa627 is 7.5 mA and opa2134 is 5mA.
This makes a total of 4 opa627's (30mA) and eight 2134's (two ops in 1 case) at (40mA) for a total of 70mA.

Now the 58.2 mA i measured was only on one rail so I assume the ops are drawing a total of 116.4mA. This seems a little off the 70mA BB said they should draw especially if this should drop with voltage. I only say this because I assumed the low level thudding is oscillation but only opamp bound. I experienced a similar thing in my poweramp when it oscillated. Now when the power amp oscillated much more power was consumed. I also got the poweramp to oscillate silently.

I was thinking that maybe I just got rid of the noisy oscillation in the opamps yet they are still drawing much more power then they need to be. The one thing that to me doesnt make any sense is that when the whole hifi is powered up they draw the aforementioned 58.2 mA. But when music is played too loudly for ears comfort they dont draw anymore maybe 0.2-3 more mA but thats nothing to the 58.2.

I used to run the active xover from a battery supply of 12 Nicads giving the +- 7.2 volts. These are rated at something like 550mA hours at rated voltage. In the old xover I used 6 TL07x's. The batteries lasted a good week before recharge (xover not powered up overnight tho) Now I get about 5-6 hours. Which makes sense from the near 60 mA they draw. I think this is a little rediculous going from a week to a few hours.

Do I have a problem.

Thanks in advance Matt
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Old 20th July 2003, 08:23 PM   #2
millwood is offline millwood  United States
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Default Re: Opamp current draw

Originally posted by 5th element
Now the 58.2 mA i measured was only on one rail so I assume the ops are drawing a total of 116.4mA.

idling current is spec'd from positive to negative rail so the idling current in your case is precisely 58.2ma.

No, you don' t have a problem.
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Old 21st July 2003, 12:11 AM   #3
SY is offline SY  United States
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Opamp current draw
Apart from millword's on-the-mark comments, 7 volts rails seem low to me. Is there a reason you're running them at that voltage?
"You tell me whar a man gits his corn pone, en I'll tell you what his 'pinions is."
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