Newby: Issues with SDA-II's

[LaLaLand]

Hello Everybody,
Quick intro: I've never owned a home stereo (for a car: yes) and always wanted one. Didn't want to get into it until I had the money to buy something nice. My friend has owned SDA-1C's since new, and I've always drooled over them. I spent quite a bit of time trying to find the same, and never had the luck. So I just picked up a pair of SDA-II's in 'narual oak' with original cable, manual and boxes (they're beautiful! and sound great). I came home, hooked them up to my CD player (via NAD AV receiver T474 using pre-amp out to an NAD C272 amp, with 150W/C). When I bought the speakers all the drivers seemed operational. When I blasted the speakers at maybe 75 Watts on the first day, two SL2000 tweeters went out - the main tweeter off one speaker and it's brother in the other speaker (via SDA cable). Checked resistance and there is no reading in either tweeter. I'm no genius but figure I blew them...lol....but I'm smart enough to go and join this site immediately, so I can pick your brains, fix the speakers and turn them into a show-piece.
QUESTION:
What did I do wrong? It's all mechanical and electrical, so, unless the tweeters erode over time, this should not have been an issue.
Could the power interruptor (or whatever you call it) be bad, and should I just replace it with a fuse?
...I hope this site works....I could really use the help.....Thanks

[kawizx9r]

When I blasted the speakers at maybe 75 Watts on the first day, two SL2000 tweeters went out

^^^
Underpowered and turned up too high.

Welcome to the forum!

Time to upgrade to RD0-194's?

[LaLaLand]

Thanks for the 'welcome party'! :)
I'm confused. A 150 watt per channel amp is too small for these speakers? (My friend with the SDA-1C's run them with a Carver M1.0t - 200 W/c).
..and you mean that running my amp at 75W is too high? The amp is spec'd at a continuous (not RMS) 150W/c into 8 ohms (IHF of 340W at 4 ohms) at a THD of 0.02%. Man, I would have figured that's plenty power for this speaker.

What's the difference between the SL2000, RDO-194 and RDO-198 tweeters?

...and I have so many more questions that I'll have to spread them over the next weeks/months/years to keep you all entertained... :)

[kawizx9r]

I meant the volume was too high, not the 'wattage/current' your amp is putting out.

Drive a speaker to concert levels without the current to push them properly and you'll blow out a speaker, starting with your tweeters.

The RD0-194 are the current production silk dome replacements for SL2K's. The 198's replace the SL3K's.

I've never liked the SL2K's, too bright for my tastes. Heard 198's on 2.3TL's and loved it.

[rromeo923]

I swapped out my sl2000's for the RDO 194's on my 1C's and love the result! This seems to be pretty standard procedure here, as you will find when you read other threads.

[intangible]

The polyswitches should have tripped before the tweeters went out, shouldn't they? I would make sure all is right with the crossovers before putting another pair of tweeters in.

[Outfitter03]

The polyswitches should have tripped before the tweeters went out, shouldn't they? I would make sure all is right with the crossovers before putting another pair of tweeters in.

The poly switches are old too. I have seen posts in here for replacements, I believe from parts express. You can search for this.

When you drive speakers hard, I believe it is not just the current that causes the tweeters to blow, but the input wave form. When you overdrive an amp, the excursions gets clipped so instead of a sine wave you are sending a modified square wave through the speaker drivers. The tweeters are the most sensitive to failure from this.

[intangible]

That's true, but to drive that amp into clipping you would have to have the volume up to painful levels. They are blown though, so...

If it were me, I would take the hour to make sure everything checks out before I stuck $200 worth of new tweeters into the system that just blew two.

[LaLaLand]

Great information from all you guys. Really appreciate the responses! I guess I'll be looking for the polyswitches and check the pricing for the RDO 194's (the SL2000's are pretty cheap, so I kind'a like that).

Now, 'kawizx9r' mentioned that he thinks that the SL2000's are on the bright side - how do the RDO-194's compare?

I also read a thread in here where someone mentioned upgrading the crossovers and replacing the polyswitch with a fuse. I like the fuse idea because they should work even when they are old :)

'intangible' mentioned "checking the crossovers" out. I really wouldn't know where to start and what to do - how do I check the polyswitches?....I chose the name 'LaLaLand' for a reason.... :)

[george daniel]

Trust us,, you are most likely "clipping" your amp-- remember,,the polyswitches are old,,they need to be replaced or "jumped",,I drove my SRS 2's with a Belles 350 power amp,,and the poly's would trip fairly easily,, after I rebuilt the crossovers,never had a problem again,,you are better off,and stand less chance of tripping the poly's with a higher powerr/current amp than with a receiver rated at 150 watts,, so,, you should either replace or remove them,,if you remove and jump em'' just be carefull cause you have no tweeter protection.I dive my 1C's with a 40 watt tube amp,, no polys,,no issues either.Good luck,,have fun and enjoy.

Welcome to Club Polk.

[LaLaLand]

OK, I get it: what I'm reading here is "Don't waste your time checking the polyswitches, just replace them". I'll put on my "Git'r'done" cap and start doing my research.

To 'george daniel': the NAD amp has a soft-clipping feature that should have given the speakers some protection, and, again, I didn't have the amp turned to max volume. I don't mean to sound like I am arguing the fact that my amp may be too small, I'm just trying to learn....
So, I'm thinking that running this 150W/c amp at 100W/c should have been a piece of cake for the speakers; I should have been in the 'safe' area of the amp, considering that it has IHF dynamic power of 340W at 4 ohms, and a clipping power of 180W...

Now I'm starting to get braincramps :) Thanks again for all the input to all of you. This forum is EXCELLENT!!!!!

[cnh]

Running a NAD C272 is a legitimate power amp rated 150 @ 8 ohms x 2 and a lot more than that into a 4 ohm load, so I would not worry that much about your power for now. As someone said above--old tweeters, OLD polys--fry things...it's age and it happens. I have SDA 2Bs with the original SL2000s (yes, they get 'bright')--I take care to not overdrive them and whenever I actually get to it...I WILL upgrade to the RDOs but I 'really' don't want to have to start messing with the 'internals' because I'm a 'wood/electrical/metal shop incompetent with a Ph.D. in another field!

You shop guys. My hat is off to you. But I don't have the time or patience to 'retool' myself and tinker with crossovers, resistors, caps, etc. I do enjoy reading about that and how manly it all is, though (even as he wonders how people can get so 'excited' about such things). If you can do that LaLaLand--my hat is off to you and you'll do fine here!

So my suggestion, take a look inside (if you're up to that) and call Polk up and order yourself some RDO-194s if you have SDA-2s or 2A.

And WELCOME TO CLUB POLK!

cnh

[Big Dawg]

One point to note - if you're pushing your volume past 12:00 you're driving your amp too hard. If you need to make you ears bleed, and 11:00 or 12:00 doesn't do it for you, you need more amp (or more sensitive ears).

Your NAD is a solid mid-fi piece. In general, separates will give you better sound quality, but that receiver should hold you until you are ready to upgrade (and you will be, eventually). I'd agree with others here, you need to replace your poly switches (not jumper them until you have upgraded your gear).

[Big Dawg]

BTW, Welcome to Club Polk!

[LaLaLand]

Thanks again for the welcomes and also for all the help. I understand the bigger picture much better now.
I think the amp is big enough - I don't really have to push it much further than 50% load. It's in a 16'x25' room with 20' ceilings, so I know that that's an issue also. Will be looking at overall room sound dampening soon.
The question now is how to combine the home theatre and stereo system. Right now I'm running the amp via a pre-amp output on the A/V receiver (NAD T747), but I also have a NAD C162 lying around that will be used for the basement stereo system in the future. Not sure if I can integrate that unit somehow and still use the Polk's as the front speakers of the home theatre system.....maybe I'll start another thread on that....
You all have a great night/weekend now!

[inspiredsports]

Welcome aboard!

I just wanted to let you know that I've had 4-ohm 1986 SDA SRS II's paired with both my (rebuilt) 150W NAD 7600 Receiver and NAD 1700 pre / (rebuilt) 150W 2600A power amp for years. I can push Dark Side of the Moon to over 110 db at 13' away in a 28X32X8' room (I don't do that without earplugs) without blowing anything up (even with soft clipping off).

As an aside, NAD receivers use essentially the same components as their corresponding separates so there is not a downside to using an NAD receiver, as there is with nearly every other brand receiver on the planet. The high current design they employ allows for huge amounts of headroom that can deliver perhaps triple the rated wattage (without clipping) for up to a half second if I recall correctly.

Your amp will even power SRS's without a problem.

[LaLaLand]

Thanks 'inspiredsports'. That's REALLY good to know!