Another common ground question

heiney9

Another common ground amplifier question. What exactly is the concern with running a non-common ground amp with a pair of SDA’s? Is to protect the amplifer or the speakers? I certainly don’t want to damage the speakers in any way, but would a particularly stout amplifier which could absorb having its outputs shorted for short periods of time be alright running a pair of SDA’s?

My impression of the common ground issue is the destruction it can do to the amplifier not necessarily the speakers. Maybe Raife could comment here as I know he is running (or was) a Pass Labs “X” amplifier with his SDA’s. I’m looking seriously at getting a Pass Labs X150 and am trying to determine if 1) It’s common ground (sent an email to Nelson which I’m sure he’ll answer shortly) 2) If it’s not common ground and the neg terminals cannot be tied together can I run this amplifier w/o damaging my SDA’s. I can consult Nelson Pass further about what affect it may have to amplifier itself, but I’m more concerned with the affect it has on the SDA’s.

I know Madmax (he’s mad you know) runs his SDA’s with the Carver Silver 9T mono’s in a non-common ground configuration. The short and skinny question is; if the amplifier is robust enough can it be used in a non-common ground configuration w/o damaging the SDA’s? Or is the damage going to happen to both?

H9

engtaz

Great question. Thanks for posting it.

george daniel

Good question,, FWIW, I've been running a pair of 1C's,with Odyssey mono's,,pin blade interconnect,no transformer,no strapping of negative posts,,,for about 4 months,,no issues,, sounds great,,I did inquire, before attempting this, and was told that there should be no issues (Klaus).So far,, so good.

fredv

For blade/blade SDA's. The ground post of the speaker are connected via one of the blades; therefore, the 2 monblocks will be equivalent to have 2 -ve speaker posts connected. This implies both the amp and speaker can be damaged.

For pin/blade SDA's, the blade is a dummy and not connected. When connected the SDA's to the monoblock, there is no direct or indirect connection between the 2 amps ground. Therefore, it won't damage to the speakers and the amps; however, the dimension array are not used.

heiney9

The amp in question is not a mono bloc. I don't follow your 2nd statement. The dimensional array should still output sound.

fredv

Sorry for not being clear. I used monoblocks because they are kind of similar to non-common ground stereo amp, barring 2 blocks are indirectly connected their ground via the elelctricity ground :-)

The pin-blade cable are only connected at the pins of 2 ends. That means the blades are not physically connected via the SDA cable as the blade-blade version. If I remember correctly, the "female socket" of the blade of the speaker is connected to the speaker's -ve binding post. Since the 2 blade ends are not connected at the cable, the 2 -ve binding posts of the speakers are not connected due to (1) non-common ground on the amp side, (2) SDA cable has no connection via 2 blade ends.

In order to send the SDA signal from one side to the peer speaker, there must be a complete loop, PIN1 -> SDA cable's pin connection -> PIN2 + the ground connection via the speaker's -ve binding posts which doesn't exist for the above reasons. Since the loop is not complete, and there is nothing to drive the SDA dimensional array because the dimensional speaker's -ve pins is not connected to the other side by any means.

fredv

Apparently, my memory isn't that great :-) My say was based on Rich's original post here http://www.polkaudio.com/forums/showpost.php?p=426799&postcount=18
Good reading on pin/blade cable. Sorry for the slioght twisted info.

heiney9

OK, so I was hoping more knowledgeable people would chime in here. Appreciate the comments so far but I'm still not any closer to finding the answer to my question.

FredV: So assuming my 1C's are pin/blade (not sure because the terminal has been modfied for a single bannana plug) then if I choose to the go the route of a non-common ground config my dimensional drivers will still output the correct sound? I believe this is the same set-up George Daniel is using.

I saw Ken perusing this thread yesterday and I was hoping he'd chime in. I just really need to know the risk to the SDA's if run in a non-common ground config. The amplifier in question is certainly robust enough to handle just about any type of load.

H9

jakelm

I like bananas.....:D

fredv

Hi H9,

If you use non-common amp, not strapping the -ve speaker binding post, and the cable is pin/blade, then there will be no signal to the dimensional array side. This is definitely the case to my 2.3 and 1.2TL. The easiest way to spot that is to use the balance control if there is one to turn all the way to one side, or simply unplug the RCA of one channel. One channel will be absolutely silent.

I concede that monoblocks are not necessary non-common ground as the -ve speaker binding post can be tied to the chassis, and the chassis is tied to the earth pin of the IEC connector. In theory, the 2 monoblocks are indirectly connected at the wall outlet's earth ground, so not quite a complete non-common ground. George can help to check to measure the -ve binding posts to see there is any connectivity. Even there is none, I am sure the 1C's still sound good without the SDA wide sound stage.

heiney9

fredv wrote: »

Hi H9,

If you use non-common amp, not strapping the -ve speaker binding post, and the cable is pin/blade, then there will be no signal to the dimensional array side. This is definitely the case to my 2.3 and 1.2TL. The easiest way to spot that is to use the balance control if there is one to turn all the way to one side, or simply unplug the RCA of one channel. One channel will be absolutely silent.

I concede that monoblocks are not necessary non-common ground as the -ve speaker binding post can be tied to the chassis, and the chassis is tied to the earth pin of the IEC connector. In theory, the 2 monoblocks are indirectly connected at the wall outlet's earth ground, so not quite a complete non-common ground. George can help to check to measure the -ve binding posts to see there is any connectivity. Even there is none, I am sure the 1C's still sound good without the SDA wide sound stage.

George ? Help me out here

heiney9

Here's what Nelson Pass had to say:

The X series have common ground, but neither output is at
ground - the outputs are balanced. This means that if you
bleed a small amount of current between the channel outputs
it will be OK, but I doubt that it will work as Polk intended.

Under no circumstances should the outputs of the amp be
directly connected together.

I suggest that you check with Polk. You have two channels
that know what ground is, but no output terminal is directly
connected to ground.

FWIW, anyone care to comment furthur?

H9

jakelm

Hmmm.... What he states at the begining is that it is common ground. But then what he describes after is that it isnt. If its not connected directly to ground, then its not common ground, right?

My Hafler has its speaker grounds connected directly together which is connected to the grounded PS caps. Thats common ground.


Do I sense a bit of confusion?

heiney9

Yes, I'm a bit confused. I did send the schematics for the 1C's and I sense he looked at how things were wired. But I'm still not 100% sure if this amp will work with the SDA's and get the intended output from the dim. drivers.

Suggest a follow up question???

jakelm

You really need to see the boards, or at least a schem shot of the amp. A picture of the inside, would be worth a thousand words.

heiney9

jakelm wrote: »

You really need to see the boards, or at least a schem shot of the amp. A picture of the inside, would be worth a thousand words.

Nelson is very free with giving info, schematics and things like that but he usually doesn't make a schematic available until after the amplifier is discontinued. Perhaps if I asked nice enough he'd send me a copy.

Jake here the link to the 14 page owners manual, anything in here that might give an idea.

fredv

The X150 OM doesn't have the schematic, so I can't say for sure. Since I happen to be building the Aleph30 and have the A30's schematic, I can use that for reference. According to the A30 schematic, the output -ve connection is grounded to the power supply's 0 volt which is the chassis ground. So, if both channels are in the same chasis, then they have common ground as both channels -ve output are connected to the chassis. Most of Nelson's design seems to have this similarity, e.g. F4. So, I wonder his answer meant something else. How about fire up a simple question to him such as, "If I use a DDM to check the 2 -ve binding posts of the X150, do I expect to see zero ohm?" That should provide the answer that you need if you are eyeing on the X150 which is excellent amp.

BTW, the requirements of common ground to to complete the circuitry of the dimensional array.

heiney9

fredv wrote: »

The X150 OM doesn't have the schematic, so I can't say for sure. Since I happen to be building the Aleph30 and have the A30's schematic, I can use that for reference. According to the A30 schematic, the output -ve connection is grounded to the power supply's 0 volt which is the chassis ground. So, if both channels are in the same chasis, then they have common ground as both channels -ve output are connected to the chassis. Most of Nelson's design seems to have this similarity, e.g. F4. So, I wonder his answer meant something else. How about fire up a simple question to him such as, "If I use a DDM to check the 2 -ve binding posts of the X150, do I expect to see zero ohm?" That should provide the answer that you need if you are eyeing on the X150 which is excellent amp.

Well an Aleph 30 or the rarer Aleph 60 is really what I have my eye and on as well as the newer Aleph J. I saw an X150 on e-bay in hopes of maybe getting it less than market which seems to be right around $1700-1850 used which is way over the budget of $1200 I set. So I probably won't be getting the X150 but I need to know if it will work before I even consider it now or in 6months.

The "X" series uses a balanced "super symmetry" design which I don't believe the Alephs use. The X150 can be run either single ended or balanced and balanced is the only way the "super symmetry" is effective. When run single ended jumpers are used to simulate a balanced circuit. That's about all I know. From what I understand the First Watt and Aleph series are different than the "X" series because of the super symmetry concept.

Are you saying that the Aleph 30, 60 and J are common ground? If so I'll wait for one of those to come up FS because frankly I'm a little discouraged with all the conflicting info I'm getting about blade/blade, pin/blade, common ground, etc :eek: . This is way too much money to be guessing if its gong to work out satisfactorily with the 1C's. I'll sleep on it and give Ken a call tomorrow and see if he can shed anymore light on the subject.

Thanks for the help so far.

H9

heiney9

Better yet, want to build an extra Aleph 30 and sell it to me? . That would make me very happy!!

heiney9

fredv wrote: »

The X150 OM doesn't have the schematic, so I can't say for sure.

I wasn;t sure if there was something useful in the OM, because he really explains in detail what the "X" series is all about. I thought perhaps some key words or phrases might jump out and give an idea. In reading thru it still doesn;t really give me a clue.

jakelm

If you only had the amp with you. We could find out real quick

heiney9

jakelm wrote: »

If you only had the amp with you. We could find out real quick

That is true, but I had a feeling that it wasn't going to be common ground to the chassis. So my original question has been answered by FredV and now I know the ground is what completes the circuit for the dimensional drivers.

I guess at this point I can either modify my I/C terminal back to stock and build an AI-1 cable or just settle on another "common ground" designed amplifier. Although if the Aleph series is common ground I'll wait (probably and eternity) for one to come up FS.

madmax

This is just too complicated to answer. What is common ground? Does that mean the grounds are hard wired together or just linger around zero potential difference with each other. What if the two amps lay at some voltage below neutral but both are the same potential? OK to use together when? DC or AC differences? Low voltage/high current differences or high voltage/low current differences? Do the ground voltages stay the same when driven? SDA's are a pain in the a$$...
madmax

heiney9

heiney9 wrote: »

OK, so I was hoping more knowledgeable people would chime in here. Appreciate the comments so far but I'm still not any closer to finding the answer to my question.

FredV: So assuming my 1C's are pin/blade (not sure because the terminal has been modfied for a single bannana plug) then if I choose to the go the route of a non-common ground config my dimensional drivers will still output the correct sound? I believe this is the same set-up George Daniel is using.

I saw Ken perusing this thread yesterday and I was hoping he'd chime in. I just really need to know the risk to the SDA's if run in a non-common ground config. The amplifier in question is certainly robust enough to handle just about any type of load.

H9

It was just pointed out by my bro that perhaps the first sentence in the above post was a bit "pissy". When I said "more knowledgeable people" I meant it as more than a few people, not as he took it to mean as a higher level of knowledge. He made me feel a little guilty about how that might read. Thanks to all who have posted so far.

H9

Systems

heiney9 wrote: »

The X series have common ground, but neither output is at
ground - the outputs are balanced.

You have two channels
that know what ground is, but no output terminal is directly
connected to ground.

FWIW, anyone care to comment furthur?

H9

What he is saying is that both channels are connected to the same or common ground point, but the output stage is a bridged(balanced) configuration .Therefore the negative speaker output terminal is not tied to ground.Does that help.

fredv

Hi H9,

PM or email me via the forum, I will send the Aleph 30 service manual just for the sake of have another pair of eyes on the circuit. My plan is to build both on same chassis which will effectively tie the 2 -ve speaker binding posts together. So, please yell at me if you think I read the schematic wrong. It will not be fun to burned all 12 matched FETS at once, and it will smell bad, too

FWIW, this is the sentence from the SDA instruction manual:

"Now you are ready to connect the amplifier to the speakers. But first, there is one word of caution. The SDA-SRS 1.2 and 2.3 must be used with common-ground amplifiers or amplifiers for which the negative (-) output terminals for the left and right channels can be wired together directly. If you wish to use non-common ground or floating ground ampliers, you MUST use the AI-1 Amplifier Interface available from your Polk dealer."

For horizontal bimap:
"THE LOW FREQUENCY AMPIFIER MUST BE COMMON GROUND UNLESS THE AI-1 ADAPTER CABLE IS USED."

I think the 1C can't bimaped; otherwise, you have a lot more options.

jakelm

If the -ve post are tied together (no matter where they are grounded), then the amp is common ground. Isn't that what "common" ground means? They share the same ground? They both have the same ground in common? Or do you have to have both of the -ve post ground directly to the chassis to be considered a common ground amp?

Systems

Generally when an amp is referred to as having common ground it means the negative speaker terminals and power supply ground are connected or common.
The Pass amp is different in that both its channels power supply grounds are connected(common) but because it basically using two bridged amps in one chassis.Therefore the two negative terminals are not at ground so cannot be connected together unless you want some excitement.ie sparks.

jakelm

GV#27 wrote: »

Generally when an amp is referred to as having common ground it means the negative speaker terminals and power supply ground are connected or common.
.

GV. I know you must be getting tired of explainig this. But can you explain my Hafler , if you have time? The 2 -ve speaker posts are soldered together and soldered on the wire bridge that connects the 2 PS caps ( the wire going from -ve cap screw, from cap 1, to +ve cap screw, on cap 2). The connection is not connected to the chassis, but is still considered common ground? Is that cap bridge ground?

fredv

You are qutie right. This is how I interpret as well. Common ground really means common -ve output terminals. There is virtually zero ohm between them. At the SDA's production days, many newer topology/design that we are seeing today simply didn't exist. Roy connected the -ve terminals of 2 bridged GFA-555 and caused some damages for this exact reason. In my Mcintosch manual, it actually says that when the amp is bridged, neither post is ground, the ground is floating!!

jakelm

But fred, my understanding is, when most amps are bridged , the common ground goes out the window and becomes an inverted phase ground (my new lingo)..IPG..lol.