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RF-83 Impedence


MudPuppy176

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I just bought a pair of RF-83s. I fried a channel in my Yamaha M-2 amp in about 2 minutes at less than indicated rated wattage (240). I sez hmmm, in 27 years I've only blown speakers with this amp. Like a dummy, I hook up an M-4 (120 watts) and fry it as well. Hmmm, two amps with cooked TO3s. Not easy nor cheap to replace. The 83s are advertised as 8 ohm speakers, but it seems the only plausible cause for these failures is less than an 8 ohm load on my amps. I drove my old 8 ohm speakers regularly with the amps' overload lights on fairly solid with no amp problems (sacrificing some sound quality for more sound quantity), but did need to replace some drivers from time to time. I read on another forum that a resistance measurement will yield about 75% of the impedence of a speaker. Anyone know if this is true and/or fairly accurate? Has anyone else had problems with RF-83s like I have?

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The nominal impedance of any speaker is a bit misleading. Measuring the DC resistance isn't going to tell you anything - it's not uncommon for "8" and "4" ohm drivers to measure exactly the same.

That said, I believe the lowest impedance dip on the RF-83 is around 3 ohms. They're listed as 8ohms compatible because the average impedance over every frequency is much higher. This behavior and nominal rating style is not uncommon.

How loud were you listening? and to what kind of music? Did the same channel blow on both amps?

I wonder if you don't have a short in the speaker wire - either in the middle or a loose frayed end near the terminals of the amp/speaker. I would probably recommend swapping the mains to see if the other channel of the amp blows up, but that's probably a bit insane at this point [;)]

The RF-83's will handle 1000W peaks (holy crap), so it's not unlikely for your amp to blow up before the speakers do. If you like it loud, then I might suggest investing in a nice pro amp - perhaps something like the Crown K2 - no fan, insane power, and one of the smoothest sounding amps ever made.

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I should add I swapped back to my old speakers for a few days between blowing the amps. The M-4 was fine until I hooked up the RF-83s. I closely inspected the wire (about 10 feet long) and see no frays or nicks. It was the right channel in both instances, so I also suspected a wire problem. Mayhaps new wire would be a "sound" investment before my shiny new McIntosh MC-252 arrives next week. In any event, the Mac should prove a formidable ally to the RF-83s.

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While things are outta commission, you might try inspecting the inside of your cabinet just to make sure there are no loose wires inside. It's a rare occurence, but I've seen it happen twice on the forum where the driver leads wiggle off during shipping...only one of those times did it trigger the protection circuitry on the receiver (the other time the driver just didn't play).

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PWK in the Dope from Hope papers stated that the range within with impedance was most important was from 250-500Hz as this was where the majority of the power was being transfered (this was probably based on measures of symphonic natural instruments so may not apply with "modern" music with more down low). But the point is that the impedence match is most important where the power resides. Although the big Heritage impedences varied with frequency, they where close to 8 ohms in the 250-500Hx range where it mattered - so he stated that they should be treated as 8 ohm speakers.

Now, if what you where listening to was a CD with some real low "modern" style music sound the real impedance may have been somewhat lower enough to knock down the amp.

What were you listening to (were you testing the spakers' limits?) and how loud? 240W sounds a little much...

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The problem is being caused by a loose connection in the speaker, and it's shorting out -- in other words, I agree with Dr. Who and you should get in there and take a look. Next, considering your listening habits and that your amps have no protection circuitry -- you should fuse your speaker lines.

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Firstly, thanks to you all for your help/suggestions/advice, its very much appreciated! Now for the replies: They're brand new RF-83's. There are no stray wires as I generously tinned both ends of the wire. 240 watts is not a bit much for speakers rated for 250-1000 watts apiece. I listen to mostly rock, some "harder" than others and like it loud and clear. I think America's Greatest Hits was being played during the smoking of the amp. Not the hardest of rock by any means, but "testing" the speakers at about 200/channel. The OL lights are calibrated at 420/channel (2% distortion) @8 ohms and were NOT even blinking. My old speakers could handle the OLs on fairly solidly for hours, with no amp nor speaker damage. As for protection circuitry, the relay actuates to protect the speakers if DC is detected at the speaker terminals (as in blown outputs?). Not really amp protection, but rather speaker protection. My dealer has an RA number and they are being sent back to Klipsch as replacements are on their way. This sadly does little to replace two very respectable vintage Yamaha amps. That's another bridge, I suppose. If my brandy new McIntosh MC252 gets smoked, Klipsch can expect a personal visit from a VERY unhappy camper. Your further thoughts and/or comments are welcome.d

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Here's the latest: The speakers were replaced today with a new pair. I have since bought a McIntosh MC-252 amp (250/channel). I didn't hook up the other pair to it, but the new pair today. Listening at 25 watts(yes twenty five) per channel causes the amp to overheat and shut down connected to the 8 ohm outputs. I find it hard to believe I got two defective pairs of speakers. The techs are naturally off at McIntosh and Klipsch today so I can't ask them what's up. Any thoughts?

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I had the 83's hooked to a HK 635(75 watts per)chno issues at really loud levels.You have a wiring issue of some type,I would not hook those interconnects or speaker cables to my to my set again until I tried somethig different.

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Obviously there is a problem here.... Is there any chance that the amps may be picking up and amplifying UHF? What else is connected to these.... Cd player? Sat Box? Cable Tv? home theater receiver???

Try and find / borrow a cd player with output level controls and connect it directly to the input on the amp. Drive the speakers, using the output level control on the CD player, let us know what happens.

Strange things can happen, and I agree that having 2 pairs of "problematic" speakers is very unlikely. JWCullison on the forum has run his Mcintosh with a 2 ohm stereo load ( 2 K-33 on each channel ) with no problems.

I have dumped the full output of my QSC PLX II ( 550 w/ch, 20 - 20khz ) into my RF3II's, with nary a problem. ( lost one tweeter, found out that the treble was boosted + 4 db in the Marantz AVR, and I set it flat, dunno what happened there, maybe conflicting remote signals ) So I really can't complain, the tweeter died of abuse.

Hopefully this problem will be fixed soon. Can you give us more info on the setup?

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Let me recap:

Old amp and speakers: no problems for 25+ years.

Change to RF83s, amp fries a channel in minutes.

Change amps and go back to old speakers, no problems.

Hook up RF83s, amp fries a channel in about an hour.

Closely inspect speaker wires, look fine.

Buy new McIntosh amp, hook up to old speakers (with new speaker wires), no problems.

Replacement RF83s arrive, hook up to new Mac. Mac overheats at 25 watts indicated (RF83s hooked up to 8 ohm binding posts).

Hook up the RF83s to the 4 ohm binding posts, voila, works fine. Loud, nice to say the least.

Simple conclusion: these are NOT 8 ohm speakers, I have two cooked amps and a new Mac that say so.

Interconnects, speaker wires, etc are not to blame. The only variable was the RF83s.

Could two pairs be assembled incorrectly? I suppose its possible, but highly unlikely. They are just not 8 ohm speakers.

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