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Is my Carver M-1.5T a Common Ground Amplifier???

Sluggo

Sluggo

Super Member
I recently aquired a pair of Polk Audio SDA-1A's
And they specify the power source must be
Common ground!The speakers use a inter-connect
cable to join them,Which I do not have attached,yet!
Talks with Tentoze(thanks much)It shouldnt matter
about the common ground until thier interconnected.
I have the goods to make a cable & paused to ask!
I know mainly polk is speaking of not to hook up Mono
Block amps or not to bridge amps to them,
I want to hook them up to my Carver M-1.5T Amp
and C-1 preamp and just want to make sure of this,
before procedding.I dont have the O.M. but a spec sheet that does not specify it:scratch2:
Sluggo
 
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Could you simply use a meter to check for continuity between neg R and neg L. If there is continuity they must be common ground? Yes? No?

You could also open the amp and inspect the backside of the speaker terminals. If the grounds are linked together you have a common ground amp.
 
Yes it is. I bet you're referring to running a pair of Polk SDA's arent you? But yes...you are good to go.

I have a pair of M-1.0t's and they are common ground when running stereo. But, having 2 of them, I'll be building the interconnect so I can run them mono to each SDA.

Nice amp...
 
Sounds great!

Went ahead and hooked it up,right on.I like it!
The rating on the SDA's say 10 to 500,so I wanted to
feed them a couple hundred watts and listen.
Off to make interconnects,thanks guys!
Mark
 
Stop!!!!!!!!! It is not safe to connect you amp to this!!!! You may blow-up your amp!!!!

All Carver amps use a Hot ground for one channel! You may short-out one channel on your amp and release the smoke if you connnect both of your negative terminals to this thing! :yikes:
 
goldear said:
Stop!!!!!!!!! It is not safe to connect you amp to this!!!! You may blow-up your amp!!!!

All Carver amps use a Hot ground for one channel!!! You may short-your amp and release the smoke if you connnect the negative of one channel to this thing!!!
Click to expand...

Hmmm...ran my SRS's for years with my TFM-45 with no problems. :scratch2:
 
Simple.


Take one speaker and connect the positive to one positive channel output.

Then take the negative and connect it to the opposite channel's ground.

If it works, meaning, you can rotate the balance to the opposite side and the sound goes away. they are common.


Man I'm good. :D
 
SDA SRS 1.2 said:
Hmmm...ran my SRS's for years with my TFM-45 with no problems. :scratch2:
Click to expand...
Ok. I'm not familair with the SRS's configuration. So this may or may not present a problem here. The thing that raised the gigantic warning flags for me was that his manual said that it required a "common ground" from the amp, and this usually this means that your grounds will be strapped-together by such a piece of equipment. :yes:

The issue is that virtually all Carvers amps use a hot ground on one channel's output. I know for a fact that the M1.5t does this, but I'm not familiar with the TFM-45s design.

This was one of Bob Carvers's tricks for reducing the size of his power supply. He inverted the phase in one channel, and then swapped the hot with the ground on the output. This way the Bass waveform, which is almost always in-phase between the two channels, was simultenouely pulling from opposite supply rails for the two channels, thus making his power supply more efficient. This was one of his big tricks to his so-called "Magnetic Field" power supply.

So on most (maybe even all) carvers the Red terminal on the right channel is actually grounded. And the Black termial on the right channel is hot. This means that if you connect your outputs to something that has a common ground between the two channels, you will short-out the right-channel of the amp! :yikes:

Connecting to most speakers does not present a problem, because they dont strap your grounds together. But if your speakers somehow connect the grounds together, then you will short your output stage, plain and simple. If these speakers do not actually connect the grounds together, then this must have something to do with the "stereo-wide" feature that is built into these speakers, and perhaps they will not blow up, but instead simply will not operate quite right. Unfortunately not knowing how these are wired, I cannot say for certain if this will release the smoke or not. But I do know that caution is in order here, as the Carver's use an unconventional grounding arrangement. :nono:
 
Im gon'a wait on hooking up the interconnects for now,until I sherlock it completely!
Without the interconnects in place,I beleive its like running
a regular set of speakers.Two tweeters though, do not produce sound until it is hooked up.
So until then,I am not getting the full flavour bouqet
 
Read my post. It's easy to figure out weather your common ground or you truly have have independent balanced outputs.
 
kc8mob said:
Read my post. It's easy to figure out weather your common ground or you truly have have independent balanced outputs.
Click to expand...
The carver amp is absolutely NOT balanced. It just inverts the phase to the right channel, and re-labels the Hot and ground for that channel so that your Red is grounded, and your Black is connected to your output transistors. I can 100% guarantee you that this is true on the M1.5t. :yes:

I'm not certain if your trick will reveal anything meaningful here at all, since the carver is not balanced. :no: I just checked my old dusty spare M1.0t, and it clearly shows the right channel output as being grounded. So if you connect a speaker between the Right channel's "hot" output and the left channels ground, you will get no sound at any position of the balance control. And if you connect between the left channel's ground, and the right channels hot, you should get sound at all positions of the balance control, but the minimum should occur at the center position.

If somebody could scan and post a diagram of how those SRSs are supposed to be connected, then I could tell you for sure if this will present a problem, or not.
 
The NAD 2200PE employs the same or similar phase inverting technique in the right channel. I've posted a pic from the brochure. You can see that the Positive of the right channel is tied to Ground at the speaker terminals.

Paul
 

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SLUGGO said:
Heres a pic of the back of one of the SDA-1A's,
(Notice the small interconnect plug-in underneath
binding posts)
http://imagehost.vendio.com/bin/vie...llow_track_link=1&track=02376692eb-cbc4b&sp=1
Click to expand...
Thanks for the picture. It definitely warns only to use with common ground amps, which tells me that that this interconnect cable might be strapping your grounds together. :nono: I don't know this for a fact, but lacking more any definitive info here, I would not even consider connecting it so long as you are running your carver amp. :no:
 
Im going to call over to Lynwood tomorrow and
talk to someone at Carver/Sunfire and get their skinny
And Ive written back to Helen at Polk Audio to
see if they have a list of Flagged amps for these speakers.I am listening to some Peter Gabriel right
Now with them hooked up to the Carver.
Its the interconnects being hooked up that might cause a problem with this Amp.
I am Glad I asked this Question and appreciate
your responses,I'll post what I find out tomorrow!
In the Meantime,I hook them up to some Nad gear
that make them sing!
Mark.
 
I talked to Rita (at Sunfire...also Carver Repair) about running my single M-1.0t amps to a pair of SDA's and it was no problem at all. She has already rebuilt one of them and I have a second M-1.0t there now for being redone. The rebuilt amps will also be able to handle a 4 to 6 ohm speaker better than the original amp did 20 years ago. I told her my intentions were to run an amp bridged to each Polk SDA speaker with the building of the AI-1 interconnect for using non-common ground amps or bridging amps.

I'll call her again tomorrow (Monday) to verify but I'm thinking that the M-1.5t may be a little different internally than the 1.0t. But I do know that a single M-1.0t running stereo with the interconnect cable (or without) works fine.
 
:scratch2:
avguytx said:
I talked to Rita (at Sunfire...also Carver Repair) about running my single M-1.0t amps to a pair of SDA's and it was no problem at all. She has already rebuilt one of them and I have a second M-1.0t there now for being redone. The rebuilt amps will also be able to handle a 4 to 6 ohm speaker better than the original amp did 20 years ago. I told her my intentions were to run an amp bridged to each Polk SDA speaker with the building of the AI-1 interconnect for using non-common ground amps or bridging amps.

I'll call her again tomorrow (Monday) to verify but I'm thinking that the M-1.5t may be a little different internally than the 1.0t. But I do know that a single M-1.0t running stereo with the interconnect cable (or without) works fine.
Click to expand...
If this is true, then perhaps you are OK afterall. :scratch2: The M 1.0t, and the M1.5t both have the same inverted outputs arrangement to the right channel. :yes: But I still can't help but wonder why this big warning is on the back of speakers then. :scratch2:
 
The SDA's were such a find,Im sooo looking forward
to listening with the interconnects.
The C-1 preamp is Sonic Holography and I think
should add to the SDA effect.
The NAD is an integrated 3140 that I just hooked up
at conservative 40 watts is plenty for the speakers.
Im really Interested in the results you'll get them
after the Crossver work and be able to mono amp them.
whats your preamp avguytx???
Mark.
 
I'm with you SLUGGO. On my side of the coin, I have the power but don't have the speakers yet! lol. With an M-1.0t on each one, I don't think I'll be hurting for power. I know the amp says it does "100 watts into an 8-ohm load" but that's also one of those BS ratings at 1kHz I'm sure. In the real world, I would imagine it's still a solid 550 to 600 mono full bandwidth at a reasonable THD. They typically rate the amp bridged at 8-ohm and I called Rita and one of the Sunfire techs I know and they both said with the "new" outputs on the amp, it should be fine at 6-ohm.

I have the C-1 preamp as well but I don't use the Sonic Holograpy much since I'm not at the correct distance from them most of the time. Now when I am, I do like using it. With a pair of SDA's and the cable connected, I wouldn't use the S.H. It would be doing electrically what the speakers are doing with the crossover.

Now to get the friggin' speakers...lol.
 
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