common ground amp

[ohskigod]

i have a pair of sda 2b that i would like to find a better used amp upgrade than the one i have now. i know it has to be common ground (still dont know what that means really) to work well with the sda, but while i am hunting for an amp, is there a way to easily tell if it is common ground or not? do certain brands run common ground, while other brands do not. i have to assume that the integra adm 2.1 amp i am using now is common ground, because it sounds pretty good. but while i have been searching for a used, perhaps vintage amp with some more power, i know if i accidently buy one that is not a common ground, i'll be screwed.

any advise from those with more experience?

[PolkWannabie]

If you are looking at something that you are not sure about you can always check with the manufacturer or in a lot of cases you can check here.

[hoosier21]

most amps are common ground, so it is not as hard as it sounds, it is harder to find one that is NOT common ground. Ask here on the forum and somebody can help out I am sure.

If you have the SDA 2B's, you can build a homemade AI-1 interconnect and then you can buy any amp you want with no worries.

Good luck.

[racer4551]

The easiest way to tell if the amp is common ground is to take an ohm meter that is set to continuity and take one lead of the ohm meter and touch the neg terminal on the left output of the amp and take the other lead and touch the right negative terminal output of the amp and if it shows continuity you have a common ground amp,if nothing happens then you have a non-common ground amp.Basically the amp is considered a common ground if they share a ground for all the negative outputs on the amp.Hope this answers your question.

[ohskigod]

anyone know of parasound amps are common ground?

[cfrizz]

What I do know is the Parasounds come with 3 pin plugs. If you have 3 pin sockets it will work!!!:D

[Emlyn]

Originally posted by ohskigod
anyone know of parasound amps are common ground?

Parasound Halo JC1 monoblocks? Definitely not common ground, but if one can afford the $6000 to buy a new pair, getting an in-line transformer should be no problem.
Used Parasound HCA3500? Dual mono design with two power cords--not common ground.

All other current Parasound designs? Yes, they're all common ground, but verify with Parasound customer service or a dealer if uncomfortable, especially with twin blade SDA speakers (which the 2B speakers are/were).

[kelley]

http://clubpolk.polkaudio.com/forum/...+common+ground
Here's a starting point for you. Call Polk and the amp manufacturer to double check before you fire it up (hopefully you will see no fire)! If you do go this route, make sure you use heavy gauge speaker cable for your jumper, no lamp cord. A run of the heavier Monster Cable should do.

[hoosier21]

Originally posted by Emlyn
especially with twin blade SDA speakers (which the 2B speakers are/were).

the pair of 2B's I had had a pin blade interconnect.

[Emlyn]

Originally posted by hoosier21
the pair of 2B's I had had a pin blade interconnect.

The pair of 2Bs I have now (Studio version) have the twin blade interconnect. My best guess is they were made in late 1988 or early 1989 from the date stamps on the drivers.

Kind of confusing to keep track of these things. ;)

[hamzahsh]

My ADCOM GFA-7605 came with 3 pin IEC detachable power cord.

;)

[hoosier21]

Originally posted by Emlyn
Kind of confusing to keep track of these things. ;)

As far as SDA models, that is an understatement.


cfritz "If you have 3 pin sockets it will work!!!" please explain????

[cfrizz]

The regular 2 vertical pins with the round one that goes underneath. (ie 3 pins) It might not be the correct terminology, but whadaya want I'm not an electrical engineer!:D I'm sure there is one on this board, get the right term from them!;)

[ohskigod]

anyway i can get some feedback as to how to build the interconnect i need to not have to worry about common ground. i'm assuming it will involve speaker wire, but where do i get the connectors to attach to the wire (and of course, which connectors are they)?
again, thanx in advance for the help.

[ohskigod]

someone mentioned above that just had to build the cable and that is it, but dont i need to do something to the speaker to get the new connector to fit?, i'm referring to the A1-1 cable mentioned by hoosier

[hoosier21]

cfrizz, I am not taking you to the mat on this, but the AC power cord's plug, has little to do with the common ground or non-common ground issue we are talking about:)

ohskigod, tell us, is your interconnect the blade blade or pin blade? If it is blade blade, you are stuck with common ground amps only, no modification or fabrication of the AI-1.

If you have the pin blade type of interconnect, look at the file I attached.


good reading
http://clubpolk.polkaudio.com/forum/...&highlight=AI1

http://clubpolk.polkaudio.com/forum/...highlight=AI-1

Julian Hirsch reviewed the SDA-1 in the Dec 82 issue of Stereo Review

"Removing the grille reveals an array of six drivers and a large,
12-inch, flat "cone" passive radiator for the bass drivers. There are
actually two separate speaker systems, sharing a common bass section,
within each SDA-1 cabinet. They are designated the "stereo" and the
"dimension" subsystems. Like previous Polk speakers we have tested,
the SDA-1 bass section uses two 6-inch cone drivers located about
midway up the front of the speaker board above the passive radiator.

"Above each bass driver is a driver of similar size that handles the
frequency range from 125 to 2,500 Hz, and above these are two newly
designed 1-inch dome tweeters with light plastic domes driven by
low-loss "litz wire" voic coils. The left and right midrange driver
and tweeter each make up a subsystem, the two being isolated from each
other acoustically and electrically.

"In operation, the two speaker cabinets, a mirror-image pair, are
placed (typically) about 6 to 8 feet apart and at exactly equal
distances from the rear wall. For best results, the listener should
be seated equidistant from the speakers, whch should form an angle of
about 45 degrees with the listener. In each cabinet the innermost
pair of drivers forms the "stereo" system and the outermost drivers
the "dimension" system.

"The left and right speakers are connected to the amplifier in the
usual manner. The amplifier MUST have a common ground between its
left and right output terminals. (Most amplifiers meet this
requirement; check your amplifier's instruction manual for warnings
about the use of external speaker switches or accessories that require
an output circuit with a common ground.) A special cable, supplied
with the SDA-1, interconnects the two speakers. In the left speaker,
the dimension section carries the L - R signal, while in the right
system it carries the R - L signal (the inverse of the L - R signal,
180 degrees out of phase with it).

"When the speakers are installed correctly, the output of the
"dimension" speaker section on each side is delayed by the period
needed for it to cancel the sound reaching the ear on that side from
the opposite channel's "stereo" section. The actual operation of the
Polk SDA system is somewhat more involved and depends to a
considerable degree on the Hass (precedence) effect, which causes the
earliest arrival of a sound to establish its apparent direction of
origin.

"Most of the specifications for the Polk SDA-1 speaker system, as
listed in its instuction manual, deal with its driver and crossover
characteristics. However, the manual does state that the midrange
drivers operate as fourth-order vented systems, with their small vent
openings located just above and between the drivers. The rated
impedance of the system is not given in the usual manner, but its d.c.
resistance is rated at 5 ohms. The recommended price of the Polk
SDA-1 is $850 each, but they are normally sold only in pairs at
$1,700."

To measure the frequency response, the speakers were driven
individually as ordinary speakers, with no connection between them.
The smoothed and averaged room response was within +/-2.5 dB from
about 150 to 12,000 Hz. There was a tweeter resonance at about 13,000
Hz, which created an output peak of about 5 dB at that frequency. The
overall in-room response was +/- 4.5 dB from 20 to 20,000 Hz.
Sensitivity is a high 95 dB SPL measured at 1 meter when driven by
2.83 volts of band-limited pink noise. The electrical impedance
measured on a single system was a minimum of 5 ohms in the vicinity of
100 Hz and varied between 5 and 12 ohms over the full audio range.
When operating as a normal system, the music may cause the amplifier
to "see" a load as low as 2.2 ohms, although Hirsch states that it is
unlikely to load any reasonably good amplifier or receiver unduly.

"Briefly, a properly installed pair of Polk SDA-1 speakers produces a
broad, precisely defined sound stage, not only between the speakers,
but extending appreciably beyond the speakers, but extending
appreciably beyond the laterally as well. The effect is very similar
to that achieved by all-electronic imaging systems [such as Carver's
Sonic Holography, or QSound-encoded material --Darryl], although the
exact position is not quite so critical with the Polk speakers.

"The sound of the Polk SDA-1 is beautifully balanced, with a total
lack of bass heaviness, in spite of its psychoacoustic manipulations
and the fact that it reaches an octave or so deeper into the low bass
than many speakers of similar size. Under some conditions we found
that it sounded a little bright or crisp, probably because of the
tweeter peak at 13,000 Hz, but this was usually evident only in a
direct A-B comparison with a speaker system lacking a peak at that
frequency."

[kelley]

My previous posted link goes to an individual that had the blade/ blade interconnect. Read it thouroughly, it has more to do with which amp you run than the interconnect termination between the SDA's.