Audiolab 8000A amp , 1984

N

N_Cook

Guest
Anyone familiar with the protection/ op relay cct?
Would seem to monitor the junction of 2 resistors fed from each channel
output.
Pink, Rch, 47K
Purple, Lch, 56K
Why unequal? all inside looks original
Monitors for any sustained DC, clipping or excessive ac or all 3?

The pair of 1M resistors off the outputs are feedback into the amps via IC1
 
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:hjci7t$noa$1@news.eternal-september.org...
Anyone familiar with the protection/ op relay cct?
Would seem to monitor the junction of 2 resistors fed from each channel
output.
Pink, Rch, 47K
Purple, Lch, 56K
Why unequal? all inside looks original
Monitors for any sustained DC, clipping or excessive ac or all 3?

The pair of 1M resistors off the outputs are feedback into the amps via
IC1
Click to expand...
Can't say this necessarily applies, but Yamaha uses different value sensing
resistors so that in the unlikely event of opposite DC offsets at both amp
channels' outputs, the protection circuit won't be "fooled".
If you had +50 volts at one amp output, and -50 volts at the other, the
protection circuit would not trigger, and you'd have two blown speakers.
Maybe this logic applies here.

Mark Z.
 
Mark Zacharias <mark_zacharias@sbclobal.net> wrote in message
news:00b9284a$0$16939$c3e8da3@news.astraweb.com...
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:hjci7t$noa$1@news.eternal-september.org...
Anyone familiar with the protection/ op relay cct?
Would seem to monitor the junction of 2 resistors fed from each channel
output.
Pink, Rch, 47K
Purple, Lch, 56K
Why unequal? all inside looks original
Monitors for any sustained DC, clipping or excessive ac or all 3?

The pair of 1M resistors off the outputs are feedback into the amps via
IC1






Can't say this necessarily applies, but Yamaha uses different value
sensing
resistors so that in the unlikely event of opposite DC offsets at both amp
channels' outputs, the protection circuit won't be "fooled".
If you had +50 volts at one amp output, and -50 volts at the other, the
protection circuit would not trigger, and you'd have two blown speakers.
Maybe this logic applies here.

Mark Z.
Click to expand...
I'd not thought of that, it makes perfect logical sense now
 
Mark Zacharias <mark_zacharias@sbclobal.net> wrote in message
news:00b9284a$0$16939$c3e8da3@news.astraweb.com...
"N_Cook" <diverse@tcp.co.uk> wrote in message
news:hjci7t$noa$1@news.eternal-september.org...
Anyone familiar with the protection/ op relay cct?
Would seem to monitor the junction of 2 resistors fed from each channel
output.
Pink, Rch, 47K
Purple, Lch, 56K
Why unequal? all inside looks original
Monitors for any sustained DC, clipping or excessive ac or all 3?

The pair of 1M resistors off the outputs are feedback into the amps via
IC1






Can't say this necessarily applies, but Yamaha uses different value
sensing
resistors so that in the unlikely event of opposite DC offsets at both amp
channels' outputs, the protection circuit won't be "fooled".
If you had +50 volts at one amp output, and -50 volts at the other, the
protection circuit would not trigger, and you'd have two blown speakers.
Maybe this logic applies here.

Mark Z.
Click to expand...
With this amp +/-44V so 4Vdc maximum available in that worse case, 3.1V if
following impedance is 100K and still 1.1V if 10K impedance


--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm
 
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