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From: Dave Plowman (News) on 6 Feb 2010 05:34
In article <hkjdfb$qsf$1(a)news.eternal-september.org>,
N_Cook <diverse(a)tcp.co.uk> 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 dave(a)davenoise.co.uk London SW
To e-mail, change noise into sound.
From: who where on 6 Feb 2010 09:32
On Sat, 6 Feb 2010 08:28:56 -0000, "N_Cook" <diverse(a)tcp.co.uk> 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.
From: N_Cook on 6 Feb 2010 10:05
who where <noone(a)home.net> wrote in message
news:c6vqm55l574hri3b0hpermhg9049l1sqpb(a)4ax.com...
> On Sat, 6 Feb 2010 08:28:56 -0000, "N_Cook" <diverse(a)tcp.co.uk> 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


From: N_Cook on 11 Feb 2010 07:49
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 .




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