Need help with very old Sunn model 8 PA cabinets

[jazzmonkey]

I hope I have this posted in the right place.

These are not mine, our band has been borrowing these from a friend for rehearsal space and I hadn't looked at them until the other day. When I did, this is what I saw. This is how they've been hooked up since we've been using them, and they've sounded OK, but we are using a POS powered mixer so there is no other reference point.

Now in full range wouldn't you just connect to the upper terminal pair as indicated by the switch diagram? What is the point of the short patch cable? No one knew, including the owner of the cabs. He's the type who buys gear when he sees a good deal, and naturally these came with no manual.

Thanks in advance for any insight.

 

[Mr. Foxen]

Looks like a bad plan. What is the word on the switch covered by the patch cable?

 

[jazzmonkey]

Up switches to passive. Down switches to biamp. It was in passive mode so hopefully the horn was protected by the crossover.

 

[billfitzmaurice]

Now in full range wouldn't you just connect to the upper terminal pair as indicated by the switch diagram?

If as it appears those are for full range input using an internal passive crossover you'd only use one of them, the second would be a parallel output.

 

[jazzmonkey]

Thanks Bill. Is there any purpose for the patch cable then? Funny thing is that we were getting sound from the cab in passive mode when hooked up this way, although I don't think the horn was producing any sound.

 

[bobcruz]

I can't see clearly but the picture looks like the switch is set for bi-amping; a full range signal is coming into the low-frequency driver from the powered mixer using a speaker cable; and an instrument cable is carrying the full range signal from the parallel low input to the horn, thus bypassing the crossover. The horn should have been destroyed by this unless you were lucky and the instrument cable has a break in it (is it tied in a knot?) and isn't passing signal.

 

[billfitzmaurice]

I can't see clearly but the picture looks like the switch is set for bi-amping; a full range signal is coming into the low-frequency driver from the powered mixer using a speaker cable; and an instrument cable is carrying the full range signal from the parallel low input to the horn, thus bypassing the crossover. The horn should have been destroyed by this unless you were lucky and the instrument cable has a break in it (is it tied in a knot?) and isn't passing signal.

If the crossover is toast they may have jury rigged it like that to get it to work, and even in the bi-amp mode there should still be a cap in line with the tweeters for turn-on transient protection. But that cap alone is not adequate, sooner or later the tweeters would be toast as well.