Hello DIY,
My active speakers/ monitors ( Event Opal) , 2 way, with AB amps, started doing something interesting recently.
When powering off, the woofer, on one side/ channel only, moves in then out. Sometimes accompanied by a slight thump.
The other side/ channel, doesn't move much if at all, and is quiet.
This is a new characteristic
What could be going on?
🤔
My active speakers/ monitors ( Event Opal) , 2 way, with AB amps, started doing something interesting recently.
When powering off, the woofer, on one side/ channel only, moves in then out. Sometimes accompanied by a slight thump.
The other side/ channel, doesn't move much if at all, and is quiet.
This is a new characteristic
What could be going on?
🤔
That happens to me too. Let me know if you find out what it is, as I could use a little more sleep.
mr. pass is the only one who could get away with such a reply, and make me laugh at the same time
well done 👍
bravo 🙂
well done 👍
bravo 🙂
Its a power-off transient - as the voltage rails drop at some point a power amplifier feedback loop will stop working and this can lead to currents being output to the speakers with no input. The severity of this probably depends most on the mismatch in rail filter capacitors or quiescent current draw on thos rails - either will cause one rail to drop faster than the other which exacerbates the situation.
There's also the possibility that the preamp powers down faster and it outputs an offset voltage, which is then amplified by the power amp until that in turn becomes dead.
And both things can happen together of course...
Often amps have protection circuit which disconnects the speakers at power off (and at power on for a small delay), and its possible for such a circuit to fail over time, allowing the behaviours above to start manifesting themselves. However its more common for a protection circuit to failsafe and disconnect the speakers all the time.
To investigate this, if you feel competent to do so, you would monitor various voltages during shutdown - the voltage rails for amp and preamp, and the preamp output and of course the speaker output.
There's also the possibility that the preamp powers down faster and it outputs an offset voltage, which is then amplified by the power amp until that in turn becomes dead.
And both things can happen together of course...
Often amps have protection circuit which disconnects the speakers at power off (and at power on for a small delay), and its possible for such a circuit to fail over time, allowing the behaviours above to start manifesting themselves. However its more common for a protection circuit to failsafe and disconnect the speakers all the time.
To investigate this, if you feel competent to do so, you would monitor various voltages during shutdown - the voltage rails for amp and preamp, and the preamp output and of course the speaker output.
so i took some measurements....
operating dc (offset)= 0.3v
during power on / power off: peak 1.6v to just over 2 v, slightly different on vs off
main power supply caps look okay visually
they are chemicon/ nippon, "brown", kmq 1000uF, 50v, 105c
operating dc (offset)= 0.3v
during power on / power off: peak 1.6v to just over 2 v, slightly different on vs off
main power supply caps look okay visually
they are chemicon/ nippon, "brown", kmq 1000uF, 50v, 105c
Capacitor aging. They don’t all age at the same rate. Keeping an amplifier turn-on/off transient free is a matter of carefully managing several time constants - so that the various parts of the amp come up at just the right rate. Get one of the time constants wrong and you get a transient. The time constants required to be transient free may go against best practices for other reasons (like clean clipping at low frequency) so they are not always followed. If an amp develops a transient over time, yiu probably just lost some capacitance somewhere or added some leakage current, upsetting the former balance. Putting in new caps may or may not have the same leakage characteristic as the originals, so it’s no absolute guarantee that recapping will fix it. But it might. Or make it worse than it was. There is no rule of thumb that can even be used to determine the cap values, you would just have to analyze it and look at the power-up characteristic.
hi, thanks for the reply and feedback
all electrolytic the caps were replaced in 2019, brown chemicon for main filter in ps, and panasonic elsewhere (low voltage).
all output devices were replaced as well ( all were very carefully matched )
rectifiers were also replaced
after the 2019 refurb, and careful adjustment of bias, and other calibrations ( as per service procedures) the units ( event opal monitors)
performed and sounded great 👍🙂
a few months ago, i started to get a strange, intermittent, noise-crackling/ burping sound- from one monitor. it was seen on the scope and traced to a daughter card (off the main amp board). then a few weeks ago, the other monitor had the exact same issue (once, hasnt returned ..yet )
the the monitor with the serious noise issue showed something new- the woofer moving in and out upon power on and power off
but the monitors, both of them, when in operation, seem to sound fine
dont know if these issues are all related.. guess they could be
but after so much work during the refurb, this has become very annoying
the opals are great, very well regarded monitors, so this is truly frustrating and disappointing
its as if the opals have caught covid... 🤐
* ive attached some schematics and service repair info for reference
🙄
thx
sw
all electrolytic the caps were replaced in 2019, brown chemicon for main filter in ps, and panasonic elsewhere (low voltage).
all output devices were replaced as well ( all were very carefully matched )
rectifiers were also replaced
after the 2019 refurb, and careful adjustment of bias, and other calibrations ( as per service procedures) the units ( event opal monitors)
performed and sounded great 👍🙂
a few months ago, i started to get a strange, intermittent, noise-crackling/ burping sound- from one monitor. it was seen on the scope and traced to a daughter card (off the main amp board). then a few weeks ago, the other monitor had the exact same issue (once, hasnt returned ..yet )
the the monitor with the serious noise issue showed something new- the woofer moving in and out upon power on and power off
but the monitors, both of them, when in operation, seem to sound fine
dont know if these issues are all related.. guess they could be
but after so much work during the refurb, this has become very annoying
the opals are great, very well regarded monitors, so this is truly frustrating and disappointing
its as if the opals have caught covid... 🤐
* ive attached some schematics and service repair info for reference
🙄
thx
sw
For sure, this means something is failing. Of course, what? Not old enough that the PS caps should have started to dry, but only testing will tell you for sure. You seem to be a DC amp, so be sure the fault is not upstream. Unplug the source and verify the issue remains.
could an issue on the daughter board, that contains part of the input stage (see schematics from previous post) cause this dc offset issue?
and...
the monitors have built in protection, including a circuit that is supposed to protect against dc offset.. any relevance to the issues at hand?
and...
the monitors have built in protection, including a circuit that is supposed to protect against dc offset.. any relevance to the issues at hand?
DC protection will have a time constant so you can always get a very low frequency pulse through. So does a DC servo.
perhaps amp goes into some oscillation on power down, instability, and produces very low frequency, which moves the cone in and out
its not dc on the output, if cone goes in and out
its not dc on the output, if cone goes in and out
Never seen a low freq oscillation. Usually RF and "poof" Seeing the cone move is very low frequency, as in difference in speeds of the rails collapsing, servo going out of lock etc.
He needs to get a scope on it. All else is conjecture.
He needs to get a scope on it. All else is conjecture.
from an earlier post of mine:
so i took some measurements....
operating dc (offset)= 0.3v
during power on / power off: peak 1.6v to just over 2 v, slightly different on vs off
so i took some measurements....
operating dc (offset)= 0.3v
during power on / power off: peak 1.6v to just over 2 v, slightly different on vs off