Amp protection cct problem or problem owner?

[N_Cook]

Audiolab 8000A trips out on a bass note using the amp at about 60 percent
volume.

Trigger voltage tested at somewhere between 3.5V and 4.5V DC + or - wrt
ground either channel, is that the expected sort of 8R speaker protection
level?
A function of the inductance of the speakers, generating back emf or
something ?
I asked the owner if he played weird stuff and he made no comment.

 

[N_Cook]

Can any reproduction equipment produce DC unless faulty? Can't see why it
would need to, since it's not an audio signal. I'd also be surprised if a
faulty electronic instrument producing DC would get through the recording
chain too.

--
*If they arrest the Energizer Bunny, would they charge it with battery? *

Dave Plowman [email protected] London SW
To e-mail, change noise into sound.

A bit of clarification perhaps.
Not a matter of trying to hear DC sound. The DC monitoring is to protect
speakers from being damaged should there be a fault in the pa then the
output line instread of being nominal DC 0V it should jump to 40V or more DC
rail voltage.

Is 4V trigger level too low for some sorts of music and or speaker
inductance effects. ?There is some integration/standoff time , maybe
shortens with higher detected voltage. At 4.5V it is about 1/2 second before
relay clicks over, but 4V corresponds to only 2Watt of DC power

 

[N_Cook]

A bit of clarification perhaps.
Not a matter of trying to hear DC sound. The DC monitoring is to protect
speakers from being damaged should there be a fault in the pa then the
output line instread of being nominal DC 0V it should jump to 40V or more DC
rail voltage.

Is 4V trigger level too low for some sorts of music and or speaker
inductance effects. ?There is some integration/standoff time , maybe
shortens with higher detected voltage. At 4.5V it is about 1/2 second before
relay clicks over, but 4V corresponds to only 2Watt of DC power

http://sound.westhost.com/project33.htm
mentions

"The detector circuit shown in Figure 1 (1) is simple and works well, and as
shown will not trigger with a 30V RMS signal at 5Hz, but operates in 60ms
with 30V DC applied, and in 50mS with a 45V DC supply. This should be
sufficient for most applications, and allows the use of a non-polarised
electrolytic capacitor in the filter. "


well above 3.5 to 4.5 V dc fault trigger levels

 

[N_Cook]

Can't answer that question, but I make an observation. A pair of
Mission 700 speakers kept tripping an Akai audio amp at modest power
levels - maybe 30% - even though the vendor asserted their
suitability. Eventually Mission conceded that the problem was the
speakers - a far_from_eight_ohm impedance at particular (low)
frequencies.

And NOT on weird stuff.

I vaguely recalled some speakers caused false dropouts of some amps.

This Audiolab, unfortunately, has the track side of the protection cct
mainly covered by ironwork supporting the transformer. But as far as I can
trace out, it has 3 Tr like that Trace cct alluded to before, but 2 100uF
standardelectrolytics downstream of the trs , one for either polarity after
the diverting diodes. I'm wondering what to put in there to keep the DC
protection but reduce the efect of 10Hz or so high level ac tripping

 

[N_Cook]

Returned to this one again. The 2x 100uF are back to back for
"non-polarised", will try and monitor before replacing. Not possible to
monitor the join without making a long thin soldering tip and working blind.
Will still have to make a Frenchman ;-) ,soldering tip to desolder them .