Common Ground Amps

riglehart

I have an NAD2200, which I was told on this forum isn't common ground. So, I built an AI-1. The NAD is solid, but I'd like to go back to the plain cable. You loose something with the transformer.

From what I can tell, wheather an amp is common ground or not is never published. Does anyone know if the other NAD amps 2600, 2700, 2400, c270, etc.. are common ground? I'm worried it might be a design feature of NAD in all their amps.

Are 99.9% of the amps out there common ground? Or is non-common ground fairly common. (no pun intended)

amulford

A large majority are common ground. I even have a "dual mono" that is common ground. Usually I check with the manufacturer if I have any doubts.

Onething to think about is brigdeabilty. Normally if you can bridge it, it's common ground.

FWIW, I know the NAD 2700 is, I have one.

Emlyn

Most two channel amps are common ground. From what I've seen, those that are not common ground often have a statement on the back of the amp or in the user manual saying something like "This is a balanced amplifier, do not connect to ground" which is usually there to alert people to potential problems with speaker switching devices rather than SDA's. This doesn't apply to all amplifiers though, so the first thing to do as said above is to check with the manufacturer's customer service line, and once you get an amp (even despite being told it is common ground) check the speaker terminals for continuity yourself with a meter to be sure it's working as designed. It's simple to do and potentially saves blowing something up.

hearingimpared

If you bridge two NAD 2200 mono they are not common ground. A single NAD 2200 in stereo mode, the grounds to the speakers are common. Take a VOM and measure (with the power off, unplugged would be better, with the speakers disconnected) from the ground of the right channel post to the left ground of the left channel post, you will find the reading is zero ohms.

univera

Why not buy my 2200 PE and bi-amp your Polks...

hearingimpared

I could be wrong here. I used 2200 on SRSs in the late 80s. I don't remember having any problems with them used as a single amp in stereo mode. I ran into problems when I used two bridged mono, one for the left and one for the right channels.

I read through NADs literature on the 2200 and don't see anything about non-common ground on a single stereo amp.

Here is the pdf of the 2200 manual.

The only thing I see about a difference in signal is the section entitled, "Inverted Channel for Powerful Bass." I think the best thing to do is to call NAD and check with them.

If I am wrong I apologize for the misinformation.

dudeinaroom

amulford wrote:

A large majority are common ground. I even have a "dual mono" that is common ground. Usually I check with the manufacturer if I have any doubts.

Onething to think about is brigdeabilty. Normally if you can bridge it, it's common ground.

FWIW, I know the NAD 2700 is, I have one.

Thats not always true. If it has a bridge switch it is most likely common ground. If it is the style(like a car amp) where you hook the the speaker up to the left pos and the right neg (or vice versa) the it more than likely is not. In this style of amp the left pos would be the hot, and the right neg would be hot also, but inverted.

amulford

Which is why I say to check with the people who made it if you have any question...

dudeinaroom

amulford wrote:

Which is why I say to check with the people who made it if you have any question...

exactly

dbnh

I have a 2200PE; the amp is common ground.

hearingimpared

I was pretty sure the 2200 and 2200 PE were both common ground when in stereo mode.

riglehart

If it is a common ground. That is awsome, because I can go back to the plain sda cable.

I have a question into the NAD support site on this. I'll post what they reply.

riglehart

NAD email support isn't answering after 5 days. My audio repair guy didn't have the service manual handy when I called him to ask, but says he "thinks" it isn't a common ground. He
confirmed that checking for continuity with an ohmmeter on the black speaker terminals would indicate common ground.

The ohmmeter test shows them to be common. Is that fallible?

What's the worst that could happen if I hook my 2.3TL up to this (or any) amp and it is not common ground?

PolkWannabie

riglehart wrote:

What's the worst that could happen if I hook my 2.3TL up to this (or any) amp and it is not common ground?

You don't want to go there ...

hearingimpared

riglehart wrote:

NAD email support isn't answering after 5 days. My audio repair guy didn't have the service manual handy when I called him to ask, but says he "thinks" it isn't a common ground. He
confirmed that checking for continuity with an ohmmeter on the black speaker terminals would indicate common ground.

The ohmmeter test shows them to be common. Is that fallible?

What's the worst that could happen if I hook my 2.3TL up to this (or any) amp and it is not common ground?

That test is sure fire. If you get zero ohms across the two speaker ground posts you have common ground. . . infallible!

univera

For what its worth, I used an NAD 7600 receiver to power my SDA's with no problem. It uses the 2200A amp section. Not sure how much difference there is in the "A" vs. non "A," but I would think they are made in similar fashion.

And, I did try a 2200 with an NAD pre for a short term listen. Wasn't for a long time, but nothing happened to my speakers.

ESavinon

I've used my nad 2200 pe in stereo mode with all my sdas speakers without a problem.

rocketman

As long as there is no reading on the volt meter between thr two ground posts there is nothing to worry about.

autoconsortium

I went through this issue when I bought Lexicon 501 monoblock amplifiers. Everyone told me there were definitely not common ground. After a call to Bryston (they made this amp for lexicon, it is just a Bryston 7B with a different logo on it) they also told me they weren't common ground 'as far as they knew'. I paid mucho bucks for these and wasn't ready to just dump them on ebay in favor of common ground setup (I have Polk SDA SRS speakers). I strapped the grounds and they have been working fine for over a year with tons of use. Apparently they are common ground...or I'm just frying them over time...who knows. Sounds damn good though.

c0redumpt

I'm going through this issue as we speak, as I have located a nice Krell KSA-100 amp for sale. I'm just thinking whethere this amp (a) has enough juice for my 1.2 TL's and (b) whether it indeed is a common ground amp.

Anyone here have any opinions?

danger boy

yeah.. email the manufacturer and they'll know 100% for sure if the amp you are looking to power you SDA's is common ground or not. I did.. and found out my Adcom is common ground.

Polk65

I just read this thread and to add a little more confusion...

A NAD 2200 showed up for cheap on craigslist last year. I downloaded the online manual and after reading the sections "inverted channels" and "commutating power supply" I used the NAD webpage form mail to ask if this model is a common ground amp suitable for vintage Polk Audio SDA speakers with the interconnect cable. Three days later the reply was NO it is not a common ground amp. I followed up with another question asking which other models of this time period are not common ground and never received a reply. You don't want to see the fireworks that a non-common ground amp can cause with these.

fredv

Since you have the 2.3TL, worst comes to the worst, you don't get the SDA effect. There should be no damage to either the speakers or the amp even though the amp is not common ground. The pin-blade cable doesn't strap the grounds of the speaker posts, not like the blade-blade.

riglehart

Here's the verdict from NAD "support center". Email reply was...

2200 = common ground
2600 = common ground (I assume 2700 is, too, since I can't find any difference other than the THX logo)
270 = common ground
272 = common ground

These are the only ones I asked about.

hearingimpared

riglehart wrote:

Here's the verdict from NAD "support center". Email reply was...

2200 = common ground
2600 = common ground (I assume 2700 is, too, since I can't find any difference other than the THX logo)
270 = common ground
272 = common ground

Bugs Bunny first base

Bugs Bunny second base

Bugs Bunny third base

Bugs Bunny short-stop

Bugs Bunny right field

Bugs Bunny center field

Bugs Bunny left field

Bugs Bunny pitcher

Bugs Bunny catcher

QUOTE Bugs Bunny vs. The Gashouse Gorillas

lawdogg

Bumping from the grave - I have a 2200 Power Envelope that I REALLY want to use with my 3.1TLs.

• The 2200 Power Envelope manual, on p.5, warns against connecting common ground equipment but only when the channels are bridged.
• The 2200 Power Envelope service manual, page 2, says in big capital font, "CAUTION: DO NOT CONNECT THE OUTPUT OF THIS AMPLIFIER TO ANY HEADPHONE ADAPTER, SPEAKER SWITCH, OR OTHER DEVICE THAT USES A COMMON GROUND FOR LEFT AND RIGHT CHANNELS."

Soooo. Not sure.

lawdogg

P.S. I just looked at the circuit diagram on the NAD 2200PE. Definitely not common ground. Shucks.

Schurkey

What ohm reading do you get when testing left black speaker post to right black speaker post?

I don't know of a better test than a simple ohmmeter connected across the black posts. Less than one ohm resistance, you're set. Of course, this will require the amp to be in stereo mode, bridged/balanced amps are not SDA-compatible without an isolation transformer.

I have heard of manufacturers who don't friggin' know whether their product is common-ground or not, and give bad advice to SDA owners. Adcom, for example has told at least two folks on this forum that a certain product is common-ground when it was not.

lawdogg

Thanks for the bump in the right direction - wouldn't you know, there's continuity between grounds. So the 2200 Power Envelope IS common ground after all.

Schurkey

lawdogg wrote: »

there's continuity between grounds. So the 2200 Power Envelope IS common ground after all.

Measuring "continuity" is NOT ENOUGH.

You need to read the actual resistance in ohms. 20 ohms resistance may still register as "continuity" but will not sound correct on an SDA speaker system.

Less than ONE ohm should be sufficient.

lawdogg

Yep it measures ~0ohms across the R/L negative speaker terminals.