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Old 23rd October 2003, 03:49 PM   #11
sounder is offline sounder  Canada
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Quote:
Originally posted by jean-paul
Only 2 diodes can be enough. I'd prefer a more elegant way though.

Changing/adapting the PSU will be cheaper than replacing a burnt subwoofer....

Jean-Paul

That last sentence caught my attention! My sub is decoupled w/ 4.7uF. If the op amp fails, could it still damage the sub? I haven't connected it yet, still testing it w/ an old speaker/amp. Seems to be working fine...so far. Wouldn't the op amp warm up if run at maximum, it's runs at room temp now?

David
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Old 23rd October 2003, 03:51 PM   #12
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Quote:
Originally posted by jean-paul
Only 2 diodes can be enough. I'd prefer a more elegant way though.

Changing/adapting the PSU will be cheaper than replacing a burnt subwoofer....

Are you suggesting 2 zenner diodes to limit voltage?
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Old 23rd October 2003, 03:54 PM   #13
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Op amps can fail even if run within the ratings. Some kind of
speaker protection is always useful.

Maybe Jean-Paul has a differing opinion, but I think the worst
that can happen if an op amp fails due to overvoltage is DC
out. A capacitor on the output should protect the speakers
in this case.
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Old 23rd October 2003, 04:04 PM   #14
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Quote:
Originally posted by Christer
Op amps can fail even if run within the ratings. Some kind of
speaker protection is always useful.

Maybe Jean-Paul has a differing opinion, but I think the worst
that can happen if an op amp fails due to overvoltage is DC
out. A capacitor on the output should protect the speakers
in this case.

Thanks again Christer

David
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Old 23rd October 2003, 04:11 PM   #15
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Quote:
Originally posted by Christer
Op amps can fail even if run within the ratings. Some kind of
speaker protection is always useful.

Maybe Jean-Paul has a differing opinion, but I think the worst
that can happen if an op amp fails due to overvoltage is DC
out. A capacitor on the output should protect the speakers
in this case.

Agreed, but I'd prefer a capacitorless coupling with the subwoofer and a circuit running below absolute max. to be sure it has a long usefull life. Besides that I think ( no, I am sure ) a 4.7 uF in series with the subwoofer is a tad too small

Please calculate the -3dB point and you'll see what I mean.
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Old 23rd October 2003, 04:17 PM   #16
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I assumed the 4.7uF cap was after the opamps but before the
power amp, otherwise it sounds way off from a reasonable
value.
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Old 23rd October 2003, 04:23 PM   #17
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If you want to be cautious why not try using some 3 terminal regulators, eg LM78 / 79 (or similar), to drop down to +/- 15V ?

The 5534/32's should be pretty bullet proof then ...

I would not use a zener in series with the supply lines (too noisy and poor regulation) or a zener shunt regulator - the 3 terminal regulator would be just as easy to do and will give better results.

BTW - is your +/- 22V supply regulated or just smoothed ?

My **guess** would be that +/-22V will be OK, providing ....

(1) the PSU doesn't go above +/-22V --EVER--.
(2) You don't try to get max output swing into a low impedance load (rated to do 32V swing from +/-18V).
(3) You don't try testing the claim to "indefinite" short circuit protection !!!!

Dave

Dave
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Old 23rd October 2003, 04:39 PM   #18
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Quote:
Originally posted by Christer
I assumed the 4.7uF cap was after the opamps but before the
power amp, otherwise it sounds way off from a reasonable
value.

I think I'll try either the lm7815 option or replace the transformer. It's only $5 canadian. (about 5c in real money )

Thanks again
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Old 23rd October 2003, 06:07 PM   #19
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Make that LM7818/7918. More headroom and far enough from the max. values. +/- 20 V would be nicer though.

My advice is to better phrase your questions as you see there is confusion. It is also better to reply at the questions members pose.

We still don't know if the PSU is regulated or not, what voltage the transformer is and if the 4.7 uF is in series with the subwoofer or between the active filter and the sub-amplifier.


You see ? A schematic might help as well in confusing items. A simple block diagram will do in this case.
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Old 23rd October 2003, 06:23 PM   #20
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Quote:
Originally posted by jean-paul
Make that LM7818/7918. More headroom and far enough from the max. values.

My advice is to better phrase your questions as you see there is confusion. It is also better to reply at the questions members pose.

We still don't know if the PSU is regulated or not, what voltage the transformer is and if the 4.7 uF is in series with the subwoofer or its amplifier.


You see ?

The PS in not regulated, the 4.7uF is in series w/ the subwoofer power amp. As for the replies, I have only a few minutes here and there during my day to scan the replies; other necessities
of life preval unfortunately. I'ts more a matter of unintended oversight than anything else.

All your interest and assistance is valuable to me.

David
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