SDA SRS doubts

JPeixe

Hello Club Polk !

I'm new with Polk Audio, i'm used to work with active studio monitors, but last month my grandfather decided to give me his home cinema speakers, so now my studio is "heavier". I went to his home and picked up the speakers and amplifier, placed all the wires as he had, tonight i decided to search for both amplifier and speakers manuals to investigate a bit.
I have a pair of original SDA-SRS in perfect condition, they have exactly my age (25 years), and with the speakers came a DBX BX-3MK2 and DBX CX-3MK2 amplifiers. I noticed that my grandpa was only using one output for each side, and had used some kind of chant/cable connecting the low input to the high input on each speaker, explaining in a simple way, on each speaker he had a cable connecting red with red and other black with black, and the cable that comes from the amplifier only conecting to the low input of the speaker.

So my doubts are:
Is this a good amplifier for the speakers?
Are the cables connected right, or should i use 4 channels, 2 for each speaker?

Thank you in advance...

F1nut

The cable connectiing the top and bottom binding posts is called a jumper, leave them in place. You can connect the speaker cable to the top or bottom posts as long as the jumpers are in place.

Do you have the SDA cable that connects the left and right speakers? It is black with blade/blade terminals at both ends.

I'm not clear, are you using one amp or two?

Those are pro amps and not known for quality sound.

Mr. Bubbles

welcome to the forum. i don't know anything about those amps but the speakers are awesome.

JPeixe

yes F1nut, i have the black cable that connects the left to the right speaker, and its properly connected.

Schurkey

I'm going to have to do some internet searching, but I'm thinking the DBX amps are multi-channel and designed to be easily bridged.

You CANNOT USE THE AMPLIFIERS IN THE BRIDGED MODE or you will let the smoke out of them--or the speakers.

I'll post again when I've done some research...



[Edit] http://www.dbxpro.com/system/documents/485/original/bx3-mkII_Owners%20Manual.pdf?1323991493
The BX3 is a four-channel amp designed to be used in 4- 3- or 2-channel modes by bridging pairs of channels. Four individual channels at 125 watts/channel, two channels at 125, plus one bridged channel at 400 watts/channel, or two 400 watt bridged channels.

The CX3 is a preamp, no problems there.
http://www.dbxpro.com/system/documents/483/original/cx3-mkII_Manual.pdf?1323991419

SDA speakers require a common-ground amplifier, and a bridged amp cannot be common-ground. The BX3 may be common-ground when the user does not have the channels bridged. Apparently Grandpa used it without problem. The last two generations of SDA speakers were re-designed so that an isolation transformer could be installed in the SDA interconnect cable, to allow use with non-common-ground amplifiers including bridged amps. I'm reasonably certain that the ORIGINAL SDA-SRS is not compatible with that isolation transformer (sold by Polk as p/n AI-1)

Schurkey

You have four amplifier channels, you might as well use them all. Apparently, Grandpa didn't. (Which begs the question "How did Grandpa have the amp/speakers set up?")

If I were going to use that amp with those speakers, I'd REMOVE the short jumper wires between the high- and low-frequency binding posts. Use the four individual channels of the BX3 amplifier (NOT BRIDGED TO TWO-CHANNEL) feeding identical left-channel signal to left front and left rear, and identical right-channel signal to right front and right rear. The right front would connect to right low frequency on the speaker, right rear would connect to right high frequency on the speakers...and similar connection for left side. That gets you 125 watts to the mid/bass, and 125 watts to the tweeters on each side, while not bridging the amp.

VERIFY COMMON GROUND before you start!!!
Set the impedance switch to the 2--6 ohm position.

JPeixe

Well, im not experienced with these, so i dont even know what a common ground amp is.

Could please explain me what is the Bridged Mode? i didnt understood what that is but i dont want to ruin my amp or speakers.

Ill try to take some photos of the back side of my amp with the cables connected as my grandpa had, im not an expert in this but in my way of thinking, i think it would be better to send 2 cables to each speakers instead of 1 cable and jumpers. but my doubt now is what outputs of the amp should i use without puting my amp in Bridged Mode. My grandpa also had another 2 technics sb-8 speakers connected to the amp, now they are not conected to the amp because they were not good.

please check this manual, and see the back side panel of the amp.
http://www.dbxpro.com/system/documents/485/original/bx3-mkII_Owners%20Manual.pdf?1323991493

atm i only have the SDA SRS connected to it with 1 cable to each speaker, they are connected to output A Front L and R. if i put another to cables to it, should i use output B Front L and R, or output A Rear L and R? (my grandpa had the technics speakers connected to output A Rear L and R)

also, in the back side panel, button nº1 (according to manual) is in 2CH BTL mode, and the "speaker impedance" button nº7 (according to manual) is on the left position, saying "A,B - 2-6Ω<->6-16Ω" (the other position is "A+B - 4-12Ω<->12-16Ω")

thank you for the help btw

Mr. Bubbles

I agree with Shurkey here. If using that exact equipment, I would connect as Shurkey suggested.

JPeixe

well, i was watching the manual, and according to the images my grandpa didnt had the speakers cables well connected to the amp.

in page 8 from the manual, i found the 2CH connection scheme it wasnt connected this way. in the image of page 8 i can see they connected the cables from the left speaker to both RED connectors of the LEFT A output (front and rear), and right speaker to both RED connector of the RIGHT A output (front and rear). my grandpa had it connected to RED and BLACK A output (front) and not only REDS (front and rear REDS / no BLACK). and had the second speaker system (wich i will not use) connected to the other RED and BLACK from A output (rear)

JPeixe

Mr. Bubbles wrote: »

I agree with Shurkey here. If using that exact equipment, I would connect as Shurkey suggested.

Yes but my doubt is this, where to connect my other 2 cables? and wich mode to select and impedance? in my amp i can see 8 outputs, 4 A and 4 B, 2A front & 2A rear / 2B front & 2B rear.

(edit) or should i connect exactly has the manual says on page 8, channel mode switch as my grandpa had (2CH BTL), and use all RED connectors?

i also didnt understood the impedance switch button, and has i dont have SDA SRS manuals i dont know if the speakers receives same impedance on both inputs.

JPeixe

well, i was reading the manual, and has more has i read, more doubts are coming. for what i understood my grandpa had this connections all messed up. frist of all he is using 2CH BTL wich is a bridged mode, and for what i understood i need a common ground amp. but for what i read on the manual page 8, in 2CH BTL we just use RED connectors, and my grandpa was using RED and BLACK.
my head is almost exploding, i will not connect my speakers again until i solve my doubts cuz i dont want to blow the speakers or the amp. i will wait for some of your replys hoping that i can solve this

. p.s. im also thinking about replacing the top cover from the amp by an acrylic cover with same size cuz it is beautifull on the inside, should i do it?

Schurkey

Connecting to all "red" output posts of the amplifier is how you use the BRIDGED mode. DON'T do that. Apparently, Grandpa was connecting to red and black terminals, so he was correctly NOT using the BRIDGED mode.

I'm guessing that the bridging switch was bumped accidentally, Grandpa did not use the amp with the switch set to 2CH-BTL. You want that switch set to 4 CH, all the way to the right as you look at the back panel.

The impedance switch should be set to 2--6 ohm position, NOT the 6--16 position.

As best as I comprehend how Grandpa has the amp wired, he was using two amplifier channels to power the SRS. (The other speakers he had connected may or may not have utilized the other two amplifier channels.) This is fine, but perhaps not optimum. Two of the amplifier channels were "doing nothing" to power the SRS. If you use all four amp channels as I described previously, you may get better results. The speakers won't play LOUDER, but they will have additional potential current supply, and these speakers may appreciate the potential extra current.

The DBX amps are lovely; I wouldn't install a plexiglass cover, though. If that's what you want...go for it. Be sure to replicate any vents in the plexy that exist in the OEM cover.

Schurkey

Look at the speaker wiring on Page 12. That would be more like what you're going to need. One difference is that you don't need the external x-over box, just a pair of Y-cables from the preamp- Left channel preamp output to left front and left rear input on the power amp, and the same for the right channel.

PolkieMan

Welcome to the forum.:cheesygrin:

Grandpa must have liked you very much

Be sure and download the SDA Handbook, a large pdf file so give it a couple minutes.

http://vr3mods.com/uploads/SDA_Handbook_2011_Rev2.pdf

Yea plexy does not help dissipate heat, bad idea unless you mount an additional cooling fan or beef up the one installed.
2 channel BLT mode is what I would use.

JPeixe

i will buy the 2 extra cables. i would like to know what type of cables would you choose for it.

about the plexi, the fan is on the backside so that i wouldnt change, and if i put the top part on plexi i would need to make some holes or grids cuz the top casing got lots of holes.

ill put the 4CH mode, as described in page 11 from DBX manual. when i have all setup ill put here some photos, thanks for all the explanation

PolkieMan

Speaker wire? I use 12 gauge pure copper CL2 with banana plugs.
I also used that same wire to make an interconnect cable, it is quite durable.
I do have kimber cable but only because salesman threw it in with the speakers

http://www.monoprice.com/products/product.asp?c_id=104&cp_id=10401&cs_id=1040115&p_id=9436&seq=1&format=2

http://www.monoprice.com/products/product.asp?c_id=102&cp_id=10239&cs_id=1023901&p_id=2816&seq=1&format=2

Schurkey

JPeixe wrote: »

ill put the 4CH mode, as described in page 11 from DBX manual. when i have all setup ill put here some photos, thanks for all the explanation

Page 11 is for "Dual two-channel system". You want Page 12, minus the external crossover.

Schurkey wrote: »

Look at the speaker wiring on Page 12. That would be more like what you're going to need. One difference is that you don't need the external x-over box, just a pair of Y-cables from the preamp- Left channel preamp output to left front and left rear input on the power amp, and the same for the right channel.

PolkieMan wrote: »

2 channel BLT mode is what I would use.

You'd run the amp in balanced mode even though there's no AI-1 isolation transformer???!!!

Or are you making a joke about two BLT sandwiches?

PolkieMan

Schurkey I thought this amp was common ground?:redface:
Sorry I am wrong again:rolleyes:
Under no circumstances should you ever hook up these speakers
till you are sure it is common ground or have an AI-1 Transformer.


here a good thread on the subject
http://www.audiokarma.org/forums/showthread.php?t=340305

Schurkey

PolkieMan wrote: »

Schurkey I thought this amp was common ground?:redface:
Sorry I am wrong again:rolleyes:
Under no circumstances should you ever hook up these speakers
till you are sure it is common ground or have an AI-1 Transformer.


here a good thread on the subject
http://www.audiokarma.org/forums/showthread.php?t=340305

It MAY be (and apparently is) common-ground when NOT BRIDGED. Far as I know, it is not possible to have a common-ground bridged amplifier, since there is essentially no "ground" connection between speakers and amp. When connecting speakers to a field-bridgeable amp like this one, the speaker cables are connected across the + (red) posts on the amp, there isn't a connection made to the negative (black) posts. Amplifiers that are "factory-bridged" permanently, such as the Aragon Palladium or Iridium amps, may use a red and a black binding post, but the black post doesn't have any connection to the chassis ground.

PolkieMan

Thanks for setting me straight on that.
So as long as it's used like any normal amp, no bridging, it should be fine.

Schurkey wrote: »

It MAY be (and apparently is) common-ground when NOT BRIDGED. Far as I know, it is not possible to have a common-ground bridged amplifier, since there is essentially no "ground" connection between speakers and amp. When connecting speakers to a field-bridgeable amp like this one, the speaker cables are connected across the + (red) posts on the amp, there isn't a connection made to the negative (black) posts. Amplifiers that are "factory-bridged" permanently, such as the Aragon Palladium or Iridium amps, may use a red and a black binding post, but the black post doesn't have any connection to the chassis ground.

JPeixe

the speakers are working as charm im just sad i dont have a "big" space for them. i thought about selling once or twice but it seems that in europe, polk audio sda srs are rare and not that known....

JPeixe

do anyone know where could i sell my speakers in europe? or to US but i think the shipping costs would be super high...