Strapped Grounds & STANDARD Interconnect Discussion

inspiredsports

These are the days when I regret that 30+ years ago I resisted my ME/EE Father's urgings to become and EE. Instead, I chose the Marketing/Management/Finance route. That path has been rewarding and has funded my audio hobby, but I just don't have the textbook understanding, so please bear with me.

I have sifted through about 8 hours of information / misinformation and have formed opinions 1)2)3) if I am properly understanding the quote below from DarqueKnight's 10-11-2008 7:30 PM post published at . . .

http://www.polkaudio.com/forums/showthread.php?t=73304&highlight=strapped+ground

where he writes . . . "Prior to the Dreadnought, I was running my JC 1 monoblocks in a strapped configuration with the negative terminals of each amp tied together with a 9 AWG cable. The SDA interconnect was also a custom 9 AWG cable."

(I'm GUESSING the negative speaker grounds in DarqueKnight's amps were connected to each amplifier's chassis, in other words, NOT FLOATING GROUNDS which I understand can cause problems.)

On my NAD amps, I zeroed my Volt/Ohm Meter, set it to Ohms X 1,000, and read 0 (zero) on the meter touching any combination of negative speaker post to chassis possible. To double check, touching positive terminals did not cause the meter to move at all.


Sooooooo . . . here's what I believe:

1) I should also be able to strap the negative terminals of my NAD 2600's with a high quality heavy gauge wire and run ANY SDA speaker I wish using a STANDARD Interconnect Cable.

2) In layman's terms, I believe strapping my speaker grounds together has in effect turned my 2 amps into a "common ground" system.

3) I believe that I DO NOT NEED to build a custom or aquire an original AI-1 Amplifier Interconnect.

Can as many group members as possible PLEASE weigh in here and tell me if I am wrong ???



#################

P.S. I clearly understand using an AI-1 should improve sound, but I am not there yet and that is for another post. I just want to bridge my NAD's (sounds painful :-) and use my standard interconnect for now.

inspiredsports

I uncovered one more "hint" that may be relevent to my situation when I re-read DarqueKnight's first post at http://www.polkaudio.com/forums/show...trapped+ground

I believe he was strapping "monoblock" amps and then he goes on to say other high power amps he is contemplating are " . . . bridged designs that cannot have the negative terminals of each channel strapped together."

I do not believe my NAD amps are "monoblocks" as I have to physically unscrew a detent and change a small "bridging" switch on the back from "(OFF: STEREO)" to "(ON: BRIDGED MONO)", but I don't know for sure if the negative terminals can be strapped together or not.

I already contacted NAD's Internet help desk yesterday evening to learn for certain if I am able to strap the ground terminals together and am awaiting their answer.

george daniel

All that I can add,, and it's not what you want to hear,, but my brother went from a carver TFM 45 and the standard p/b interconnect on his 2.3tl's to the dreadnaught with monoblocs and there was a PROFOUND difference. So if strapping the neg binding posts/grounds together do not pan out,I would encourage you to follow DK's dreadnaught instructions,, I don't think that you will be disappointed. Good luck in your quest.

DarqueKnight

inspiredsports wrote: »

(I'm GUESSING the negative speaker grounds in DarqueKnight's amps were connected to each amplifier's chassis, in other words, NOT FLOATING GROUNDS which I understand can cause problems.)

The negative speaker terminals of my JC 1's are connected to the chassis.

inspiredsports wrote: »

I uncovered one more "hint" that may be relevent to my situation when I re-read DarqueKnight's first post at http://www.polkaudio.com/forums/show...trapped+ground

I believe he was strapping "monoblock" amps and then he goes on to say other high power amps he is contemplating are " . . . bridged designs that cannot have the negative terminals of each channel strapped together."

I do not believe my NAD amps are "monoblocks" as I have to physically unscrew a detent and change a small "bridging" switch on the back from "(OFF: STEREO)" to "(ON: BRIDGED MONO)", but I don't know for sure if the negative terminals can be strapped together or not.

When you switch your NAD amps from stereo mode to bridged mono mode, you are effectively converting them to monoblock amplifiers. All "monoblock" means is that one amplifier only handles one audio channel.

All monoblock amps are not bridged designs. Non-bridged monoblocks usually can be strapped if the negative terminal is at ground potential. Bridging is a method of connecting two complete amplifiers together for higher output. Typically, in a bridged amplifier, one of the two amplifer sections handles the negative portion of the signal waveform and the other amplifier handles the positive section. Therefore, in a bridged amplifier neither speaker terminal is at ground potential.

When your NAD amps are in stereo mode, their left and right channels each process a complete signal waveform and each channel has a signal path and a ground path.

When your NAD amps are in mono mode, the two stereo channels are connected together and one of the amp's channels is used to process the negative portion of the signal and the other channel is used to process the positive portion of the signal. The whole signal is then combined at the amp's output terminals and there is no ground path at the output terminals.

Systems

The fact that your NAD has the the stereo/bridge switch indicates it is common ground unit.You could join the negatives as long as the switch is in the stereo mode only.

As a further confirmation, measure the resistance between the 2 negative terminals.It should measure between 0-100ohms.

inspiredsports

I'm positive the NAD is common-ground in STEREO mode.

It's in the BRIDGED mode that the original owner's manual states the speaker wires "must be floating with respect to circuit ground".

GV#27 wrote: »

. . . As a further confirmation, measure the resistance between the 2 negative terminals. It should measure between 0-100ohms.

First, I'm doing all tests with the 110v cord unplugged and every off and cold.

The resistance is effectively ZERO . . .
--- Between left negative and right negative terminal
--- Between left negative and chassis
--- Between right negative and chassis

The results are the same whether the bridging switch is set to bridged mono or set to stereo.

######

I know I'm sounding thick, but I still am unclear as to what happens if I strap the negatives if the amp is set to bridged mode.

Does where DarqueKnight says "there is no ground path at the output terminals" mean that I absolutely CANNOT STRAP THE GROUNDS unless I want to use my amp as a fireworks display on the 4th of July, or does it mean that strapping CREATES the path to ground. I need one of you who knows to tell me that in plain English.

inspiredsports

george daniel wrote: »

All that I can add,, and it's not what you want to hear,, but my brother went from a carver TFM 45 and the standard p/b interconnect on his 2.3tl's to the dreadnaught with monoblocs and there was a PROFOUND difference. So if strapping the neg binding posts/grounds together do not pan out,I would encourage you to follow DK's dreadnaught instructions,, I don't think that you will be disappointed. Good luck in your quest.

Thanks George, but that seems to open up another whole can of worms that I was intending to reserve for another post. My SDA-2B's work with the AI-1 by SERIAL NUMBER, but are BLADE/BLADE, and that somehow requires a special adapter to ground.

Post #5 at http://www.polkaudio.com/forums/showthread.php?t=75554 speaks to this, but the author was unable to recall the exact work-around that Polk specified in the past.

Originally posted by strider: With some help I was able to get my blade/blade 2B's to work with the AI-1. There's a post around here somewhere with my serial numbers in it, I'll try to dig it up if I get the chance.

Come to think of it, what I did was documented to a degree on the forum; possibly in a couple different posts. IIRC I needed to connect the neg binding post to the small blade socket inside the cabinet to complete the circuit.

I was unable to locate those posts. With the supposed need to ground EVEN when using the AI-1, it worries me that I'm right back here at the STRAPPING ISSUE and I wanted to develop a firm understanding of that first.

DarqueKnight

OK, let's try again.

inspiredsports wrote: »

I'm positive the NAD is common-ground in STEREO mode.

It's in the BRIDGED mode that the original owner's manual states the speaker wires "must be floating with respect to circuit ground".

That's right. In bridged mode, two of the output terminals will each be providing 1/2 of the signal. Therefore, neither can be tied to ground, or a short circuit will result.

In stereo mode, a complete amplifier section is provided for the signal and ground portions of the left and right audio channels.

In bridged mode, the left and right channel amplifiers are combined to handle a single audio channel. Now, one amplifier section handles the positive portion of the audio signal and the other amplifier section handles the negative portion. This doubling of amplifier sections provides increased output power per channel.

inspiredsports wrote: »

I know I'm sounding thick, but I still am unclear as to what happens if I strap the negatives if the amp is set to bridged mode.

You ABSOLUTELY CANNOT strap bridged amplifiers. You usually can strap mono amplifiers that are non-bridged designs if their negative output terminals are tied to ground.

You ABSOLUTELY CANNOT create a common ground configuration with NAD 2600's in bridged mode.

In most brigeable stereo amplifiers, such as your NAD 2600, only the positive terminals of each channel are used in bridged mode. The negative terminals are electrically disconnected from the signal path. Treat them as if they do not exist in bridged mode.

In stereo mode, the negative terminals of each channel of the NAD 2600 are tied to ground. In bridged mode, the negative terminals of each channel are electrically disconnected from the signal path and the positive terminals of both channels carries 1/2 of the audio signal.

If you want to use bridged 2600's with your SDA 2B's, here are your options:

1. Disconnect the SDA cable.

2. Use an AI-1 interface. You will either have to find or make a pin/blade to blade/blade adapter or change the blade/blade sockets on the 2B's to pin/blade sockets. I don't know if those sockets are still made. Ken Swauger in Polk customer service can tell you if they still have any or he can tell you who the vendor was and you can contact them.

Face

I believe Poee7R summed it up.
http://www.polkaudio.com/forums/showpost.php?p=963707&postcount=10

Simple solution, just use one amp.

bsoko2

Face wrote: »

I believe Poee7R summed it up.
http://www.polkaudio.com/forums/showpost.php?p=963707&postcount=10

Simple solution, just use one amp.

Use an AI-1 interconnect cable and you can use whatever amps you want in any combo?

Bill

inspiredsports

THANKS to all for your patience and advice, and especially to DarqueKnight for taking a second stab at it!

The light bulb finally lit up and I've got it now. I can visualize what's going on with the circuitry, and won't bridge unless I obtain a properly adapted AI-1 or clone.

I know for a fact my NAD 7600 Receiver will easily drive these speakers because it's been doing so for 21 years. Bridging with the 2600 I just aquired is whim and I may let it pass, but right now the idea is intriguing and I have an almost irresistable urge to put all that power at my fingertips.

DarqueKnight

Why don't you disconnect the interconnect cable and listen to the amp in bridged and stereo modes? That will give you a good indication of any difference in sound quality between stereo and bridged modes.

inspiredsports

DarqueKnight wrote: »

Why don't you disconnect the interconnect cable and listen to the amp in bridged and stereo modes? That will give you a good indication of any difference in sound quality between stereo and bridged modes.

That's a great idea that I never thought of because I'm always geared toward experiencing the SDA effect.

I wonder if the impedance the speaker presents to the amp will change much without the Interconnect Cable in place. Naturally, I'm interested in how they perform with the halved impedance bridging yields, and to learn how that contributes to the behavior and sound quality of the amps.

Schurkey

inspiredsports wrote: »

That's a great idea that I never thought of because I'm always geared toward experiencing the SDA effect.

I bought my SDA-1Bs new in '86 or '87. About six or eight months ago, I finally "pulled the plug" and I'm enjoying my "new" speakers.

Minus the SDA effect, the speakers are now more clear (intelligible) and don't sound as "phase-y". Everything that was good about them before is still there except for the "beyond the speakers" imaging. If I could find something "wrong" with the speakers, maybe I'd fix the SDA circuit--but everything seems to check out OK. I think I just quit appreciating it.

Next Step: Move the 8008BB to the center channel, connect the Palladiums to the Polks...

inspiredsports

Schurkey wrote: »

. . . finally "pulled the plug" and I'm enjoying my "new" speakers. Minus the SDA effect, the speakers are now more clear (intelligible) and don't sound as "phase-y" . . .

Hmmmm . . . I wonder if you have a bad component or wiring problem because I personally can't imagine any SDA's sounding better without the SDA effect.

I'm just briefly disconnecting because I don't yet have the special AI-1 cable my type of amplifier requires for bridged mode use with SDA's. I want to audition my AMPLIFIER'S SOUND QUALITY when bridged, and not the speaker's sound quality with Interconnect disconnected.

Enjoy your SDA's, and I hope things work out to where you can use your IC cable again in the future to get great sound.

inspiredsports

DarqueKnight wrote: »

Why don't you disconnect the interconnect cable and listen to the amp in bridged and stereo modes? That will give you a good indication of any difference in sound quality between stereo and bridged modes.

Well, after conceding and deciding that bridging my NAD 7600 with its complementary 2600A may not be worth the trouble, you just had to make this suggestion, didn't you?

I removed the IC cable and listened to several varied and familiar recordings to get a baseline using JUST the 7600.

SIDE NOTE: I don't remember ever listening to these SDA-2B's without the IC cable, but was pleasantly surprised at how good they still sounded with the two 6.5 SDA drivers silent.

I then carefully bridged both units, using the 7600 to drive the left side and 2600A to drive the right.

I'm ruined for life !!!!!!!!!

The treble and midrange opened up a bit and sounded slightly clearer, but it was the bass that impressively both tightened up and seemed infinite, not that it really seemed strained before. But I gained a sense that I could just keep turning the dial up to the point of damaging my body before damaging the speakers.

I'm monitor with a decent quality Extech Sound Level Meter on a tripod at the apex of the sweet spot triangle, and had been listening at up to 80-85 db with the 7600 alone. I'm not sure how to qualiy this, but the bridged amps easily pushed 95db with a quality of sound that really did not seem any louder than the single amp at 80+ db. It was just an astounding, pleasing, enveloping sound.

NEW QUESTION: With new RDO198-1's and Sonicaps (just hit 48 hrs. burn in), is it OK to push them this hard? And I wonder just how much sound these relatively small SDA-2B's can make?