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Calling All "Vintage" Integrated/Receiver Owners
Oct 27, 2015 at 3:04 PM Post #15,227 of 19,143
sirmarc said:
I'm wondering what resistance the amp is seeing. I know these amps don't like under 4 ohms
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That's why I was wondering how the sub was set up.  Could be the sub has a common ground on the input and the 9100 is not built that way.  It could also be that the summing circuitry ( which joins left and right into mono for passage to the sub amp ) is faulty.
 
It could also be that whoever worked on the unit left a cold-solder joint that opens after a while.
 
Oct 27, 2015 at 3:32 PM Post #15,229 of 19,143

Just checked the schematic and all speakers are common ground - so scratch that.  I also thought this amp might have dual power supplies like the SA-8500II, but it doesn't.  I'm thinking it was hooked up incorrectly and is overheating.
 
Oct 27, 2015 at 3:39 PM Post #15,230 of 19,143
I thought the ka-9100 was a dual mono design, it should have 2 power supplies. I checked his post and he only had the sub hooked up to one channel. Why I wonder? And I also wonder if running A left and right and only one channel of B could be the culprit. I'm guessing you're also a tech jnorris lol
 
Oct 27, 2015 at 5:10 PM Post #15,234 of 19,143
Well, it could just be coincidence that the sub was hooked up only to the left channel, and that's the channel that is now having problems...but it does set off some alarms...

Make absolutely sure there aren't any stray strands of speaker wire touching each other, and run just the A speakers to the main speakers, no sub, and see what happens. If you still get shutdown on one channel after a while, I strongly recommend checking DC offset.
 
Oct 27, 2015 at 7:18 PM Post #15,236 of 19,143
sirmarc said:
Wouldn't the DC offset being too high in one channel be more dangerous to the speaker than the amp?
Click to expand...


Well, theoretically, yes. However, many amps have circuitry that shuts down the speaker outputs if the DC Offset gets too high, in order to protect the speakers from exactly the damage you're referring to. So I thought perhaps that might be happening.
 
Oct 27, 2015 at 7:52 PM Post #15,238 of 19,143
sirmarc said:
I thought the ka-9100 was a dual mono design, it should have 2 power supplies. I checked his post and he only had the sub hooked up to one channel. Why I wonder? And I also wonder if running A left and right and only one channel of B could be the culprit. I'm guessing you're also a tech jnorris lol
Click to expand...


One big power transformer and two large filter caps, whereas the SA-8500II has 2 and 4, respectively.  The sub should have been run from both channels, but since the input impedance of the sub amp is probably pretty high I doubt the difference in load would have made that much of a difference.  A stray wire is a very likely culprit.
 
The DC bias being off would have caused the DC offset circuitry to go into overdrive and may be what's cutting out the channel.  Most amps of that vintage touted "Output Capacitorless" circuitry which, without protective circuitry, would endanger the speakers should the bias shift.  It could also be a component failure - I mean the thing is almost 40 years old!
 
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