Hi All.
Hoping for some help.
I have a pair of Rotel RL 870 Speakers.
When I first set them up for a listen, there was no sound out of one of the enclosures.
The only way in was via the woofer hole on the baffle.
As well as the fixing screws the woofer appeared glued on. I couldn't budge it so this project sat around for 6 months.
I recently re focused and was able to budge the woofer from the baffle with a piece of timber and a mallet.
I carefully tapped the woofer around its circumference, and without damage was able to break the grip of the glue.
I tested both the woofer and tweeter with the battery (1.5v) method on the terminals.
Both drivers are alive and moved outward when +ve terminal aligned with +ve battery.
A careful look at the crossover and solder points hasn't revealed any obvious broken joints in the wiring.
Any thoughts for further tests?
Also the thick internal cabling is marked "SUPRA".
Should I replace this with the CAT5 solid core wiring while I'm at it?
Also the capacitor might need to be replaced?
Hoping for some help.
I have a pair of Rotel RL 870 Speakers.
When I first set them up for a listen, there was no sound out of one of the enclosures.
The only way in was via the woofer hole on the baffle.
As well as the fixing screws the woofer appeared glued on. I couldn't budge it so this project sat around for 6 months.
I recently re focused and was able to budge the woofer from the baffle with a piece of timber and a mallet.
I carefully tapped the woofer around its circumference, and without damage was able to break the grip of the glue.
I tested both the woofer and tweeter with the battery (1.5v) method on the terminals.
Both drivers are alive and moved outward when +ve terminal aligned with +ve battery.
A careful look at the crossover and solder points hasn't revealed any obvious broken joints in the wiring.
Any thoughts for further tests?
Also the thick internal cabling is marked "SUPRA".
Should I replace this with the CAT5 solid core wiring while I'm at it?
Also the capacitor might need to be replaced?
Attachments
Have you measured the resistance from the outside? Short the terminals temporarily then measure and it should respond to the woofer resistance plus the inductor resistance.
Have you confirmed the amplifier is OK?
Have you confirmed the amplifier is OK?
Thanks Allen.
I reversed the speaker leads to eliminate amp issue.
What do I short, the woofer terminals or the speaker enclosure terminals?
I reversed the speaker leads to eliminate amp issue.
What do I short, the woofer terminals or the speaker enclosure terminals?
And then am I measuring the woofer terminals, after shorting the enclosure terminals?
Do I set the meter to ohms?
Is that slightly higher than the woofer resistance?
Try using the 1.5V on the enclosure terminals.
Try using the 1.5V on the enclosure terminals.
That doesn't really look like a professionally produced crossover but more like an experimental proto type. Maybe it's just not wired correctly. You could open up the working unit for comparison.
Sorry Allen.
I'm all over the place today.
Revised feedback.
Good speaker:
1.5v test on woofer terminals = healthy pop and movement.
7.2Ω from enclosure terminals.
Speaker with inoperative Woofer:
1.5v test on woofer terminals = small pop and little movement.
1.2Ω from enclosure terminals.
The woofer reads 0.6Ω on its own.
Both woofers have identical feel when tapping the cones.
Also there is no rubbing sound coming from the voice coil area.
The cone wires coming from the terminals and disappearing into the cone appear intact.
This is without wires connected?
Seems damaged, then.
Short your meter probes and see if it reads zero, otherwise adjust reading.
Seems damaged, then.
Short your meter probes and see if it reads zero, otherwise adjust reading.
That appears to be a shorted voice coil. It doesn't necessarily have to rub to be no good. I wouldn't try to use it as is.
Would removing the dust cap and cleaning the voice coil gap make any difference?
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I'm inclined to think no, but at this point unless you can find an obvious external cause then I'd suggest you don't have much to lose.
It's a shame.
These are well proportioned late 70's speakers with genuine walnut veneer and well proportioned bookshelf cabinets with quality drivers (scanspeak tweeters).
The crossovers may appear prototypes, but apart from the iron core inductors, sand cast resistors, & electrolytic caps, the layout has plenty of room to work and allows for anchoring of the leads.
I'd say original woofers will be either expensive or difficult to find.
Maybe my only alternative is to replace them with modern woofers of similar size and output??
We have rebuild services here, time is 24 hours to some months, it depends on shop.
Few dollars, about a third of the speaker price.
They cut the cones off the frames, not salvaged.
Few dollars, about a third of the speaker price.
They cut the cones off the frames, not salvaged.
I can't find any information on these speakers, Cliff, other than they were made for Rotel in Denmark in the 1970s and sport a 20mm Scanspeak D2008 tweeter and an 8" treated paper cone bass mid sourced from an unknown UK manufacturer.
I suspect the RL 870 enclosure is sealed like that of the 'Made in England' RL 850 attached, in which case it may be posssible to find a suitable replacement 8" driver that will at least get you up and running.
I suspect the RL 870 enclosure is sealed like that of the 'Made in England' RL 850 attached, in which case it may be posssible to find a suitable replacement 8" driver that will at least get you up and running.
