SDA-1A with NAD

timmy9150

I just bought a pair of SDA-1A's and am driving them with a NAD 7155 receiver and a NAD 2155 amp that are bridged thru a Cerwin Vega non powered sub then to the speakers. I hooked them up last night assuming my NAD's were a common ground with the interconnect cable. they worked and sounded great but after doing more research this morning I find I might have been wrong. I noticed all the drivers weren't working (though they were free and not locked up) and the left speaked seemed to be driving a little harder even with the cable hooked up. I didn't check the tweeters and am now afraid to turn it on. I would like to remove the sub and just run the Polks but dont know if the sub was saving my system from the common ground problem. The NAD's are still set on 8 ohms and I would like the switch it to 4 ohms before I turn it back on. Any advice would be greatly appreciated. Thank you

quadzilla

Unless your amps are marked as being non-common ground, it's unlikely that they are. This is pretty much limited to dual monoblock designs, which yours are not.

You can test the drivers by turning off the amp(s), unhooking the cable from the amp, and touching the positive end to the positive end of a 1.5 V battery, and the negative cable to the negative side of the battery. All the drivers should move out. If a driver moves in, the wiring is reversed on that driver. If a driver doesn't move, it's likely frozen, the voice coil has shorted, or it's disconnected somehow.

So, welcome to club polk. The SDAs are great speakers, and there's lots of threads on restoring and upgrading them in the vintage speakers and DIY sections.

timmy9150

Thanks I was worried that since I was bridging my amps and not using the negitive speaker outputs it might cause a problem.

On3s&Z3r0s

I had similar questions about a similar setup using the same components actually, and I'm pretty sure that when you bridge them you are effectively turning them into monoblocks and you wouldn't have a common ground. I'd be surprised if the passive sub was somehow adding the ground back.

Let me see if I understand how you've got them set up... you have the receiver's switch set to bridged and you've left the left channel on it jumpered. Then, you've run the right channel pre-out on the receiver to the left channel input on the amp and it is also set to bridged? So basically you're using each one as a separate mono amp. I'm not familiar with CV's passive subs... I didn't know they made those for the home market. Anyway, I was cautioned to not use bridged NAD's that way with SDA's and definitely not with the regular stock interconnect cable. If you want to be safe while troubleshooting them, I'd unbridge the receiver and hook the speakers up normally to it, leaving out the sub.

RuSsMaN

SDA cable in place?

quadzilla

timmy9150 wrote: »

Thanks I was worried that since I was bridging my amps and not using the negitive speaker outputs it might cause a problem.

As others said, if you bridge the amps, they will no longer be common ground. You will need to find (good luck) or make an A1-I cable. It uses a transformer to isolate the speakers from each other so you can use bridged amps. There's instructions in the vintage speaker section, or just look here: http://www.polkaudio.com/forums/attachment.php?attachmentid=26698&d=1186346846

And yes, you may have damaged something if you had the SDA IC plugged in. Might be the amps, or it might be the speakers. If you weren't using the SDA IC, then you're ok there, but you won't get the SDA effect, which is what makes those speaker so worthwhile.

And crap, sorry. I missed the part about you bridging your amps.

timmy9150

OK now that I know that much. When I first set them up (with the IC cable)they played fine but when I walked away from the receiver to listen to them the left quit and came back on before I could turn around to turn it off. After that we were noticing the left channel seemed a little strong and all the drivers weren't working like people said they wouldn't without the IC cable but mine was still pluged in. If you think I should tonight I can try unpluging the cable and see what I get. I would like to do some trouble shooting to make sure I don't break anything else or so I find what is already broken. I'm in love with the sound the way it is and I can't imagine it gets better.

PS this is a great website

quadzilla

It's hard to say.... That might have been the amp resetting. First, take either the receiver or amp out of bridge mode, and use only that to test with. Next, do the battery test I described earlier. That will let you know if all drivers are still working and in phase. If that passes, then you can plug the speakers back in to either the amp or the receiver with the SDA IC unplugged and whichever one you use in stereo mode. See if the sound seems balanced between the two. If you get that far, plug in the SDA IC and see if the sound stage expands. If it does, then you dodged that one, and congrats on your SDAs.

If any of the drivers aren't working, you can check the for sale, as someone may have some, and you can call polk customer service. They have drivers for a lot of the older speakers still available. If the problem ends up being only with the SDA cable plugged in, you'll need someone to take a look at the xovers and figure out what burned out, or you can just rebuild them and that should take care of it. It doesn't sound like either amp is damaged, but you'll need to check both of those as well if it passes all of the above tests. Make sure it's in stereo, then plug in the speakers and bring the volume up slowly, making sure the sound is balanced.

pitdogg2

well the CV sub is 8ohm and you're running a pair of 4ohm speakers into it.
anybody else see a problem here ?

cascading crossovers comes to mind

ditch the sub

On3s&Z3r0s

I agree with all of Quadzilla's troubleshooting steps. Again, I'd use just the unbridged receiver by itself with the speakers as it will simplify things. One note as far as testing first with and then without the interconnect, obviously it's best not to mess with the IC cable while the amp is on and especially not when it's sending a signal, just like any normal speaker connection.

And once you've got everything hooked up, including the IC, you can do one last test with the balance knob on the receiver. First, hit the Mono button on the receiver so it is sending the same signal to both speakers. Then swing the balance all the way to the left. You should still hear sound from the right speaker, but it will be softer because only the dimensional drivers will be operating. Then go the other way, turning the balance to the right and listening to the left dimensional drivers. It accomplishes the same thing as listening for overall balance with the SDA IC plugged in, but doing it this way it's easier for me to hear exactly what I'm getting out of each dimensional driver. (When I had issues with my SDA 2's I'd get my ear right up next to those suckers to make sure I was getting sound out of all the dimensionals.)

Just an extra note on the bridging in general... the SDA 1A's are a low impedance speaker to begin with and when you bridge the receiver/amp you are cutting the impedance in half. (The NAD manual discusses this too, and I have a downloaded 7155 manual I could email you if you don't have one already.) In a nutshell, the manual says two things about that... first, if you use bridged mode, you are supposed to set the impedance switch to 4ohms no matter what speakers you're driving, and second, they advise against using bridging with speakers less than 8ohms (even though they give specs for 8/4 ohms in bridged mode). This is why I was advised not to do bridge even if you have the custom interconnect with a transformer that Quadzilla described.

If you really want to use that sub, you might consider using RCA y-splitters on the receiver's pre-outs. One side of the Y to the receiver's main in and one side to the amp's inputs. Then use just the amp to drive the sub and the receiver to drive the speakers (nothing bridged). Just an idea... I'm sure others will chime in if they think I'm baked here.

timmy9150

Thanks for all the answers. What a fast education I'm getting. I want to lose the sub anyway as I feel the speakers will give me everything I want. But I would still like to bridge the amps if I can (love the power). So tonight I will unbridge and do the trouble shooting in 4 ohm mode with just the reciever to see where I stand. Right now the non working drivers are the same on both speakers so I assume it has to do with the IC cable circuit.

quadzilla

I used to think watts were really important too. But since I started paying attention, I realized that most of the time, my amp is only outputting about 3 watts, with a very occasional jump to 30 watts on peaks. My next set of amps will only be outputting 45 wpc, and I think that's going to be plenty. But then, I don't turn it up to ear-splitting levels either. So really, I think your receiver at 55 wpc is likely to drive those fine.

timmy9150

Well looks like I don't have to worry about bridging for a while. You were right, I blew the amp out of my receiver. running it now as a pre amp because the amp seems OK. Ran it without the IC cable first then powered down and pluged it in. Sounds great so far (can't turn it up much, the wife is watching TV). Are the upper outside drivers and outside tweeters connected for the IC cable as they seem weeker than the rest on both speakers. Thanks again for all your help. Time to go put flowers on my receiver.

Tony M

Sorry to hear about that. You have a good attitude I can tell and will move on and chaulk it to learning about these special speakers.

Welcome to this site. Use that search box and you'll find alot on your perticular set.

timmy9150

With a great site like this one I have to have a little good attitude, such great help I really can't express my gratitude. Still a little bummed about my receiver but it was my own fualt. Some times I just charge ahead and shouldn't

quadzilla

timmy9150 wrote: »

With a great site like this one I have to have a little good attitude, such great help I really can't express my gratitude. Still a little bummed about my receiver but it was my own fualt. Some times I just charge ahead and shouldn't

My condolences on the receiver. It can likely be fixed fairly easily though. There's a guy in McKinney TX that specialises in vintage gear repair. I can get you his contact info. There are plenty of others around too. Just post in the electronics section.

And yes, those drivers are the dimensional drivers, and they run at a lower volume than the others. If you search under the recent and vintage models for yours, you'll find the manual with an explanation of SDA and how to set up the speakers for the best sound. They aren't set up like you would other speakers, so do please read it.

timmy9150

I saw on another post about the set up and will look up the manuals. If I could get the contact information that would be great. I might not fix it right away though as like you said I really didn't use all that power anyway. Just boosts my ego. I'm sure no one else on here has one as big as mine. Ego that is.

Tony M

timmy9150 wrote: »

With a great site like this one I have to have a little good attitude, such great help I really can't express my gratitude. Still a little bummed about my receiver but it was my own fualt. Some times I just charge ahead and shouldn't

Me to, me to...:redface:

quadzilla

timmy9150 wrote: »

I saw on another post about the set up and will look up the manuals. If I could get the contact information that would be great. I might not fix it right away though as like you said I really didn't use all that power anyway. Just boosts my ego. I'm sure no one else on here has one as big as mine. Ego that is.

No, many are much bigger. I'll look the guy up and pm you the contact info.

Also, if it helps, I've destroyed my share of stuff too. But I see it as an opportunity to learn how to fix whatever I destroy.

On3s&Z3r0s

One thing you might try before you ship it off to the repair shop is popping the cover off and looking for blown fuses. I had another NAD amp open just this weekend and was suprised at how many fuses they had in there. I haven't had the 7155 open in a while so can't remember what it's got for fuses, but it's worth a shot.

timmy9150

Good Idea thanks

timmy9150

No luck on the fuses, they are all good but nothing looked or smelled burnt. I know that doesn't really mean anything but I can remain hopeful can't I? After much thought since I like tinkering with and learning new things I will probibly fix the receiver and build the A1-I cable to bridge with. After playing with the system I agree with Quadzilla that 55wpc is lots more than I need. It's just the thought of figuring it all out and making it all work that keeps me coming back for more. Quadzilla, you said something about a guy in TX that could look at it and you would PM me. Where do I look for it? In the persomal Messages on this site or somewhere else? Thanks again for everyones help. This has been an adventure both on my wallet and in my mind.

timmy9150

Also continuing my education when bridgeing the NADs you set them for 4 ohms even with 8 ohm speakers what does that do for 4 ohm speakers?