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Discussion Starter · #1 ·
Hello...I recently purchased a clean pair of SDA-2's. My intention was to Bi-amp them with twin Rotel 980BX's run in mono mode. Basically like the Rotel amp manual shows how to do. The SDA speakers also have thier original interconnect cable.


Looking at the back of the SDA's it states "do not use with bridged output amplifiers".


I am unsure of the exact terminology being referenced here and am unfamiliar with much other direct 2 channel connects. I did some searching but found nothing relating to this topic. Thank you for any added insight or help.
 

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A stereo amp run in "mono mode" is a bridged amplifier. You will toast the amplifiers if you use them.


IAC, bi-amping speakers using the passive crossover networks built into the speaker is an utter waste of time and money.
 

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I don't believe SDA 2s are bi-ampable...should only be one set of binding posts. Some models of SRS2s are. However, no SDA likes a non-common ground amp. Mono blocks and some non-common ground amps, depending on the manufacturer can have their negative grounds strapped together and work. You've got to check. Hooking up a non-common ground amp to SDAs can damage both the amp and speakers if the umbilical is connected.
 

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Discussion Starter · #4 ·
Welll. I don't feel so sharp. After reading what "Bi-amping" really means it is not what I was intending to do. As Ron sated there is only one set of binding posts.


I was going to attempt to use a standalone Rotel 980BX amp for each SDA-2 speaker. The amps would be in "mono" mode. According to the Rotel amp literature this would basically have an amp powering the left channel and an amp powering the right channel.


Thanks for any input.
 

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Discussion Starter · #5 ·
After further searching it seems that attempting to power the SDA's with two seperate amps/chassis would be considered "ungrounded" and thus not possible...I think.


I had read that a dual mono amp would be considered "grounded" as it shares a chassis.


I was really hoping to use the two Rotel 980's I have with these speakers for a decent 2 channel system. Seems I may have to reconsider my amp budget/decision.


I am all ears if anyone wants to correct my understanding or lack there-of. TIA
 

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Quote:
Originally Posted by mlo97 /forum/post/18226800


I was going to attempt to use a standalone Rotel 980BX amp for each SDA-2 speaker.
That you can do!
Quote:
The amps would be in "mono" mode. According to the Rotel amp literature this would basically have an amp powering the left channel and an amp powering the right channel.

That will work fine. Just don't connect two amplifiers to the SAME speaker.
 

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Discussion Starter · #7 ·
Looking through the Rotel literature, I found nothing referencing the 980BX as being either gounded or ungrounded. Let alone when switching into "mono" mode.


I did not receive any user manual or info guide with Polk SDA-2's though they were in thier original packaging. I would love to get a copy of the original supplied info should anyone be willing to share it. I have been watching a couple auction sites.


The original owner made a comment that these speakers are power hungry and when fed good power perform very nice. I am not trying to rock the house just enjoy clean moderate listening levels...or as clean as this older stuff is capeable of.


Thanks for everyone time!
 

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If the Rotel is 2 monos in the same chassis, then you should contact them and ask if the negative grounds can be strapped together making it a common ground amp. Some similar designs can be and work just fine. I know that some models of Adcom can...some can't. You might also take this question over to the Polk Vintage forum. You'll probably be told the same thing, but there might be someone who's using that amp that will chime in.
 

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They have passive radiators (12" bass drivers) so they really aren't that hard to drive. I'm driving my SDA 2B's with a carver tfm-45 with 375 wpc and rarely turn the dial past 9 o'clock.
 

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Discussion Starter · #10 ·
Just testing things out today with a single Rotel 980BX which is near 120 wpc I could tell the linearity of the volume knob on Rotel 940AX tuner was not as crisp as I am used too. Casual listening had me at 10-11 o'clock. Very warm sounding speakers under these conditions, almost too warm. Maybe I need to think about adding a decent preamp instead of using my integrated pre/tuner.
 

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Quote:
Originally Posted by cornhulio /forum/post/18230095


They have passive radiators (12" bass drivers) so they really aren't that hard to drive. I'm driving my SDA 2B's with a carver tfm-45 with 375 wpc and rarely turn the dial past 9 o'clock.

Actually, those speakers are amplifier destroyers. They're fairly sensitive, but they're a tough, low impedance load. They used to fry old Carver M-400s. I sold those at retail decades ago, and if you threw away the damn cable connecting the two, they sounded pretty good. You can use the Stereo Dimensional Array mode if you have a two channel system, but not in a multichannel system. You can't mix active and passive surround modes without making a mess. I seem to remember they wouldn't work with the cord with amps that were "common ground." That may be why they aren't recommended for bridged amps, but the low impedance is also a reason. A bridged amp running a 4 ohm speaker sees a 2 ohm load. We used to light up Yamaha receivers with these speakers; we'd literally have small mushroom clouds and sparks explode off the output ICs. Ah, good times...
 

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With the cord, a common ground amp is required or sparks will fly since the cord carries a signal from the left speaker to the right speaker and vice versa. The big boys are 4 ohm, the smaller SDAs are 6 ohm and all the SDAs are rated highly (90-92 db) efficient.

http://www.polksda.com
 

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Quote:
Originally Posted by Paul Scarpelli /forum/post/18231577


Actually, those speakers are amplifier destroyers. They're fairly sensitive, but they're a tough, low impedance load. They used to fry old Carver M-400s. I sold those at retail decades ago, and if you threw away the damn cable connecting the two, they sounded pretty good. You can use the Stereo Dimensional Array mode if you have a two channel system, but not in a multichannel system. You can't mix active and passive surround modes without making a mess. I seem to remember they wouldn't work with the cord with amps that were "common ground." That may be why they aren't recommended for bridged amps, but the low impedance is also a reason. A bridged amp running a 4 ohm speaker sees a 2 ohm load. We used to light up Yamaha receivers with these speakers; we'd literally have small mushroom clouds and sparks explode off the output ICs. Ah, good times...

The early Carver M400 cubes weren't common ground and would go poof and you're right about AVRs not having enough current to run them...generally. As Carl said, the big boys are a heck of a load, but the mediums, 1Cs, 2s and CRS all do better with a high current amp, but don't usually fry stuff...at least not mine. I've run them on an AVR (not recommended) an 80w 2 channel (ok), on various 200w, 2 channel amps (excellent) and also on a TFM 45 which has plenty.
 

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a friend of mine just gave me a pair of vintage polk audio SDA 2a that were just sitting in her attic for a long time. i used them as fronts for my newly purchased yamaha RX-A1000.


i dont know pretty well about grounds but as i read all of your comments here i'm afraid i might burn my precious yammie reciever.


please help me what to do. maybe ill just give them to somebody else and save up for a pair of klipsch floor standing speakers or BIC acoustech PL89s.


i need help fast. thanks.
 

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i need to change my klipsch quintets satellites too.
 

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Polk sda 2's require a amp that can produce around 150 to 200 wpc to really come alive !! they will work on common ground amps! (most amps are common ground) i have NAD C272 running mine, and the interconnect cable( the cable connecting the 2 speakers together ) triggers the stereo array only ! with out it one tweeter and one 6 inch speaker on each right and left speaker will not work !!!

the polk sda's are concidered to be the best mass produced speaker ever built !! if you take the time to learn about them and get the right equipment to run them you will be amazed how they sound .

and the tweeters in those speakers are things of beauty absoutly magical !!!!

avoid bridge mode and use the interconnect cable ,, you wont believe your ears


Another thing these speakers like their backs close to the wall move your speakers around and listen to all possible positions you can put them in and keep them in ste spot that sounds the best !!!
 
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