Amp protection cct problem or problem owner?

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.

Reply to
N_Cook
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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.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Reply to
Dave Plowman (News)

percent

protection

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

Reply to
N_Cook

wrt

it

a

recording

*

DC

before

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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

Reply to
N_Cook

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.

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.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Dave Plowman (News)

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.

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    Dave Plowman        dave@davenoise.co.uk           London SW
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Dave Plowman (News)

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.

Reply to
who where

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

Reply to
N_Cook

Check speakers/wiring/crossover.

Reply to
Meat Plow

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 .

Reply to
N_Cook

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