The old common ground issue....

Bacchus

hello all,

I am a newbie on this form. I recently decided to replace a system I sold which included polk 10b monitors and a sansui au-g99x amp that I sold after I got married some years ago. Now that I am divorced I want to put together another killer system using classic polks.

I was fortunate and found some good deals online and got a set of polk sda 2a ($140) in great shape and also a set of CRS ($250) also in minty condition. Both sets are blade/blade interconnects.

I also purchased a sansui B-2101 amp and pre-amp with 200w rms to supply something close to a reasonable amount of power to these great speakers.

So as you might have guessed the issue has now come to my attention of the common ground..... I have been informed that this amp is not a common ground amp so now I have alot of nice gear that will not work together as expected.

my questions are:

can anyone confirm that the sansui B2120 is not a common ground amp?

If the amp is a non common ground amp can I use these speakers without attaching the interconnect cable safely or is this just a no go with no hope of making it work.

I was told that a polk "isolation transformer" will solve my problem but that polk no longer offers them... does anyone have one for sale or know where I can get this??? also wondering if I would need one or two, one for each set.

thank in advance for any information provided

Bacchus

F1nut

You can test the amp yourself with a VOM. You want to check the resistance between the negative binding posts.

If the amp is a non common ground amp can I use these speakers without attaching the interconnect cable safely or is this just a no go with no hope of making it work.

You can do that, but you're basically losing half of each speaker and not getting the benefit of the SDA technology.

I was told that a polk "isolation transformer" will solve my problem but that polk no longer offers them... does anyone have one for sale or know where I can get this??? also wondering if I would need one or two, one for each set.

You cannot use the AI-1 isolation transformer with blade/blade SDA's.

agfrost

I'm not the last word, but looking at this post here and this documentation here, it appears that it is not. Can you check at the amps outputs?

FTGV

agfrost wrote: »

... this documentation here, it appears that it is not.

Agreed.

zingo

Strap the outputs before he takes the time to resell it?

Bacchus

agfrost - thanks for providing the links, especially the article. I read it and cried a bit....lol

now the choice has to be made......aaaaaarrrgh.

I bought SDA because I wanted to enjoy the SDA effect so simply pulling the interconnect cable can get me by for a bit but ultimately something is going to need to be replaced, which royaly sucks for me but hey... thats how it goes when you try to exceed the ordinary.

next question then becomes -- For those of you who are running SDA speakers in your systems what are you using to provide the power?

was at Fry's electronics the other day and nothing they had really looked up to it in my opinion, just your generic big box store run of the mill decidedly average recievers etc....I picked a nice powerfull classic reciever (b2101) but unfortunately I screwed that one up good by not doing my research well enough first.. a bit of help selecting a new amp set up to target would be greatly appreciated. Looking for 200w rms min.

F1nut

zingo wrote: »

Strap the outputs before he takes the time to resell it?

Only do that if the manufacturer says it's ok otherwise it could be bad juju.

F1nut

a bit of help selecting a new amp set up to target would be greatly appreciated. Looking for 200w rms min.

Take a look at Audiogon, plenty of choices there.

leftwinger57

Bacchus ,you asked and now the answer.I run an Adcom gfa 555 rack mount face amp @200wpc.That runs into an Onkyo P-301 pre/amp>various sources that are both shared and 1 is not, like my Denon tt.All other sources that eminate from my Yamaha RX-V665 go from audio out to tuner in on the Onkyo pre.So I get I-net radio ,F.M.,CDP, t.v.sound,VGA cable to the big tv to watch concerts and the dock and I-pod.I also run multiple sets of speakers through a Niles 6 zn selector for variety. I really can do an A-B-C-D test between all my sets.I have 0 problems w/ the Adcom SDA 2b combo and already have done both some cosmetic and physical mods.

TennMan

I have an Adcom GFA-555 amp & Adcom GTP-450 preamp. I had an Adcom GFA-545II (100 wpc) that also powers the 2B/CRS speakers well.

FTGV

zingo wrote: »

Strap the outputs before he takes the time to resell it?

Not with this one.It has a balanced ouput stage so negative terminal is not tied to ground.

Bacchus

Thanks for the input.

the adcom 555 and 555II meet my power requirements but from looking online it appears as though I can only hook up one pair of speakers to this amp....?

I have a set of SDA 2a and CRS and would like to be able to get both fired up will this be possible using the Adcom amp?

newbie308

Carver TFM-35 is another good amp that can be had on the used market for a reasonable price. I ran my SDA 1A's with the Adcom GFA555 II and then the Carver TFM-35 before settling on a EL34 tube integrated. I preferred the Carver over the Adcom, but then I like analog meters!

Bacchus

yes would like to run all four

The carver as well only has out put on the back panel for one set of speakers....??? I have a set of sda 2a and and set of crs that I would like to power how is this done with an amp like the adcom or the carver with only two channels to tap into on the back pannel???

Schurkey

Bacchus wrote: »

yes would like to run all four

The carver as well only has out put on the back panel for one set of speakers....??? I have a set of sda 2a and and set of crs that I would like to power how is this done with an amp like the adcom or the carver with only two channels to tap into on the back pannel???

If the amplifier can handle driving the very-low impedance load, just connect both right-channel speakers to the right channel output, and both left-channel speakers to the left channel output.

First Guess: Both the Adcom and the Carver have better-than-average current capacity for low-impedance loads...but what you're asking is beyond their design limits. You need two common-ground stereo amplifiers driven from the same preamp, or a multi-channel amplifier. Optional: some way to control gain of each pair of speakers independently of each other.

F1nut

yes would like to run all four

You would like to, but you're not going to. Both sets of those speakers are 4 ohm loads, running both sets together will drop the load to 2 ohms or less. Neither of those amps can handle that.

Bacchus

so you guys are saying that the SDA's are designed to be a single set of speakers in any given sound system...?

Bacchus

I wasn't really planning on Rocking out was planning on using them as front 2a's and rear crt for movies mostly.

sda tech.... stereo dimensional array.... eliminating cross interferance by way of sending out signals that cancel out signals originating from the right speaker heard by the left ear and vice versa...yes I have read up on these speakers, targeted them and purchased. I did not read anywhere where they were only to be used a solo singular pair that could not be used with additional set of speakers.

seems to me that the vast majority of STEREO amps have two channels and four speaker out puts on the rear. I am not interested in 5.1 7.1 or 9.1 home theater systems. I am looking for a two channel stereo system that utilizes four speakers preferably the sda 2a and crs sets I currently own. stereo is two channels left and right, not necessarily two speakers.

Bacchus

not looking for 4.x 5.x 7.x or 9.x just good ol skool two channel stereo system that provides lots of good clean power to two sets of sda speakers. 4.1 would seem to imply four independent and unique channels fR, FL, RR, RL. the system I am trying to put together is a two channel (L&R) system that allows for two sets of speakers (a,b & A+B) to be implemented.

Also, I am looking at the SDA instruction manual and it is showing both the SDA 2b and crs as rated at 6 ohms.. on polk site is says 4 ohms... what gives here??

Schurkey

Bacchus wrote: »

Also, I am looking at the SDA instruction manual and it is showing both the SDA 2b and crs as rated at 6 ohms.. on polk site is says 4 ohms... what gives here??

The 2B may be rated at 6 ohms, but you don't have 2Bs. Didn't you say you had 2As?

Different models...different impedances.

F1nut

I am trying to put together is a two channel (L&R) system that allows for two sets of speakers (a,b & A+B) to be implemented.

That's not a 2 channel system, period. What you are wanting to do will sound like dog poo.

tonyb

You need 4 channels of amplification, period. You can't run both pairs off of one 2 channel amp. Old school receivers with A and B speaker switching, most won't be able to handle the power required.

tonyb

Ooops, double post, my bad.

chandler9a

just go with two channel only (one left, one right), you won't be disappointed. Running all four is not an option with SDA's. You can use them for surrounds but its a waste of SDA technology IMO, and I've done it.

Ive got a GFA- 555 I would sell if you decide to go that rout. Just shoot me a PM

Bacchus

pm sent