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.

In article ,
N_Cook wrote:
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.

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 London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote in message
...
In article ,
N_Cook wrote:
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.

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 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 wrote in message
...
Dave Plowman (News) wrote in message
...
In article ,
N_Cook wrote:
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.

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 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



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

In article ,
N_Cook wrote:
Dave Plowman (News) wrote in message
...
In article ,
N_Cook wrote:
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.

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.

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.

Yes - I know what it does. But you suggested this DC offset could be
caused by the type of music? I was merely querying this.

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

I have a kit DC offset protection unit from Vellerman sitting across the
also home built amps in the workshop. That triggers at +/- 3 volts. Many
older amp designs had preset DC offset, and this you set to zero, with a
tolerance of only a few millivolts.

I dunno how many watts of DC a say 100 watt speaker could handle for long.
I'd guess at it being quite small. Most books say when checking the
polarity of a speaker with DC to only use a 1.5v battery.

--
*A bartender is just a pharmacist with a limited inventory *

Dave Plowman London SW
To e-mail, change noise into sound.

In article ,
N_Cook wrote:
"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

I've never seen any amp (not seen every one, though) that allows an offset
anywhere near that as its spec. Usually only a few millivolts. DC just
isn't required for any audio signal, so would just heat up the speaker
coil unnecessarily.

--
*What boots up must come down *

Dave Plowman London SW
To e-mail, change noise into sound.

On Sat, 6 Feb 2010 08:28:56 -0000, "N_Cook" wrote:

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.

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.

who where wrote in message
...
On Sat, 6 Feb 2010 08:28:56 -0000, "N_Cook" wrote:

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.

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

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 .