SDASRS Carver Mono Amp Problem?

rduval

I have a pair of SDASRS and a Carver M1.5t that I've been using for years. I wanted a bit more kick so I bought a pair of Carver m1.0ts figuring I'd bridge them to Mono and run them that way.

Problem is that they worked fine until I plugged in the Polk interconnect cable (for the imaging) then I got a terrible squeal like feedback and one of the amps went up in smoke!

Anybody know why? Is anyone else running this setup succesfully? Was it just a bad amp? I'm getting it fixed but I'm afraid to try again!

I can't see why this wouldn't work! Carver (Sunfire) said the amp is common ground in both stereo and bridged mono modes so there shouldn't be any difference.

Thanks

Rick

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RuSsMaN

A SINGLE amp may be common ground, but using two SEPARATE amps is *not*. How could they be common ground in different chassis?

Did the amp actually 'smoke'? If it didn't, hopefully the resistors in the output stage simply opened and stuck open, that can be fixed.

Cheers,
Russ

rduval

Beats me..I was just going by what the techs at Carver/Sunfire told me.

All I know is that without the crossover cord plugged in they worked fine, as soon as I plugged it in...POOF...smell of fried electronics and a howl.

Don't know what to do now....hoping somebody here can advise me if there's a way to make this setup work and or if there's another early model carve amp that can be bridged that will work.

Rick

F1nut

What Russ said!

In the bridged mode the amps (any make) are mono blocks and therefore do not share a common ground, PERIOD!

You will either have to find a AI-1 interconnect cable (very hard to find), make one or try this, some folks have reported that they have linked the negative terminals together to make them have a common ground. If you try linking them make sure that the wire you use is the same gauge as the speaker wire.

hoosier21

The SDA speakers are just like any old pair of speakers when the interconnect cable is not connected, that is why you had no problem with the Carver's in mono without the interconnect connected.

I have always been told, the older SDA's with the blade blade interconnect WILL NOT work with any mono type amp (or any non-common ground). And that the AI-1 type interconnect will not work with these B-B type interconnect speakers. The AI-1 is a Pin-Blade type interconnect, even if you took an AI-1 interconnect and changed the end connectors to blade-blade it would not work. I believe that Polk changed the crossover design AND created the AI-1 interconnect on later models to allow mono and or non-common grounded amps to be used with the SDA speakers. The AI-1 interconnect has an isolation transformer that allows the audio signal to pass, but “isolates” the two amplifiers from each other.

In simple terms, when you plug the interconnect cable into the speakers for the "SDA effect", you are actually connecting the neg. of each the amp (and speakers) together, the "SDA effect" is communicated through this connection. If you have amplifiers that are not at the same (common) ground point (and this means more than just being plugged into the same outlet that has a ground wire that both amps share), and/or you don’t have the isolation AI-1 in place, the two amplifiers neg. terminals are tied together though the interconnect and any difference in potential (non-common ground means they are not the same, different) of the two amplifiers is seen as current, amplifiers don’t like incoming current, and poof you burn your amp.

Last thing, be VERY careful about connecting the neg. of the amplifiers together with speaker cable, I would ask Carver and Polk about this first, and make sure whoever you talk to knows what in the heck they are talking about. I have heard of this being done on some amps (can't remember the model or MFG., but just be careful.

If I made any errors, you EE’s speak up.

Tour2ma

To hopefully clarify what was said above...

The M-1.0t's are common ground amps. Each amp individually, whether in stereo or mono service is common ground in and of itself.

However, two 1.0's running mono have nothing in common, ground or otherwise. This is why the problem occurrred when you plugged in the SDA IC. It's certainly the most violent reaction I've read. I don't understand why the 1.0's simply did not jump into protection mode...

I agree with hoosier, talk to Carver about whether an common ground can be established between two 1.0's running mono. Also ask why both amps did not save themselves.

Talk to Polk CS about the interconnect question. I have not heard what hoosier has heard concerning the blade-blade model SRS's, so I am curious.

Please post results of any Polk/ Carver conversations you have.

Good Luck...

rduval

I called Polk tech and spoke to a fellow named Kam (Maybe Ken, not sure). Really nice and seemed very knowledgeable.

He said that to run the Carvers (or any bridged amplifier) I would need the newer crossover (signified by the blade+pin cable as opposed to the blade+blade cable) and the interconnect cable with the isolation transformer built into it.

He also said that they haven't had the cables available for a couple of years but that he was pretty sure that there was someone on the forum who builds them on request.

Unfortunately, since I have the earlier blade+blade crossovers, the cable wouldn't help me anyway.

If I want to run Mono amps I will have to run true mono amps (not bridged) and they MUST be common-ground. He said this can be simply tested by taking a multimeter (on resistance/continuity of course) and verifying that the ground on the rca inputs and the ground on the speaker outputs are all connected directly to chassis ground.

He also said something about hooking the grounds together but I admit I sort of blew by that while considering other things he was saying. It related to the way the imaging crossover works and that to work properly they must have a common ground between the 2 speakers.

Anyway, on the amps he suggested a number of possible older mono amps such as Adcom 565, some Conrad Johnson, Crown, etc.

Looks like I'll have to go amp shopping again after I rebuild the carver 1.0's that I cooked.

Anybody else running Mono amps? I've tried a number of other steroe amps like Class

Tour2ma

Can't really comment on mono-blocks, but a more powerful 2 ch amp is also a possibility...

Since you're a Carver fan, check out his Sunfire Stereo amps. Used on ebay the Symphonic Reference goes in the $800 to $1000 range. His Signiture Stereo amps go in the $1200 neighborhood.

kelley

I'm one who has posted in the past about running mono amps with the negative posts jumpered. I currently use 4 Denon mono amps to biamp my 3.1tl's. I only have to jumper the 2 amps on the lower end. The highs have never given me a problem. I too have heard the almighty noise that comes out of the speakers when you don't use common ground. Mine was so bad though that now each time I rewire and turn on the amps I try to get my heart prepared in case it happens again. I've had it happen twice in a little over 10 years and both times were almost as loud as a gunshot going off in the room. No humming! No damage though. The first time it happened was the day I brought my speakers home from the store and didn't bother to read the manual. Once I got in there and read up I noticed the part about common ground. I too called Polk and was told they didn't have any of the special cables. I called Denon and asked what I needed to do to make my amps common ground. Their reply was to run a wire from the negative post on one of the amps to the other. I use the wire between the B speaker negative outputs on my amps which I don't even have turned on. I always ran Monster Cables sized wire for my jumper until last year when I was redoing everything and needed the Monster for something else. I decided to use some lamp cord and POW! That's when the second time happened. I went and bought another run of monster cable and built it up with banana terminators so it would be secure and I haven't had any problems. I have no idea why the slightly smaller wire didn't do the trick. I know it is probably a little more resistive but not that much. I don't take responsibility for your amps if you follow my example but I have been running this way for a long time. You need to call Carver on their tech line and ask them about making your amps common ground. I have the pin/blade srs connector, but as long as you can make your amps common ground I wouldn't think the connector is going to be a factor. If you go this route just make sure you have the jumper secured between the amps so in case you bump something or the wife is dusting or whatever you don't get a nasty surprise. Mitch

F1nut

Nice post Mitch.

"I have the pin/blade srs connector, but as long as you can make your amps common ground I wouldn't think the connector is going to be a factor."

As Hoosier stated, "the older SDA's with the blade blade interconnect WILL NOT work with any mono type amp (or any non-common ground)." This is because Polk also changed the crossover in the later models.

I think Tour's suggestion of getting a stereo amp (common ground) is the best solution for Rick. Since he likes Carver, I would suggest the TFM-75, it's a real powerhouse.

kelley

I would think though that if your mono amps were common ground between the 2 amps wouldn't the speakers see them as a stereo amp? I don't understand why it would be any different. I'm not the expert by any means, though. Just giving my opinion.
I just went through the web and did a search and came up with this post on another site. I bet those results were impressive!
http://www.goodsound.com/askme/2003_04_21.htm

F1nut

Ah, you know I shouldn't post tech stuff at 3:30am. You are correct, hooking the negative terminals together should work with either type of interface cable.

rduval

I read the "Goodsound" post at the link you mentioned above and I think it would work as long as you bi-amped horizontally (ie one stereo amp for the highs and the other for the lows). If you did it vertically as the reviewer suggested you'd be in the same "non common ground" problem plus it would seem an awful waste of all that power just driving the highs.

Anyway, when I get the 1.0's back in the next week or so I'll take the plunge and try running a LARGE common ground wire as you suggest but I will be prepared to pull one set of speaker cables (on banana jacks) the instant anything sounds funny.

If that doesn't work I may look at the TFM-75 as suggested. Does anyone have any experience with the amp? Does it sound similar to the M1.5t's?

I saw one on Ebay last week and it was up to $799 us with 2 days to go!

How about the new sunfire big stereo amp (Ultimate II is it?) Any opinions on it?

Rick

Toronto, Canada.

kelley

I would check with Carver first. You shouldn't have to pull any wires quickly, just have your finger on one of the power switches for the amps and kill it. Although if it's already killed one of your amps before, your finger isn't going to be as fast as electricity and you're going to be smelling smoke. I don't want to see you tank a newly fixed amp! 1-360-862-1742 this is the number to the Carver Service Center according to their website. Call, call, call! I realize you have 2 amps sitting around and I would be doing exactly what you are in trying to employ them both. That said, if my speakers were not biampable I would go with these other guys suggestion to get one powerful amp. But I understand you wanting to use something that's already bought and paid for. Yes, you could biamp the other way which I've done in the past in regards to the post, but answer man set him up for a bad situation. That post is many months old so either he blew his **** up and didn't bother reposting, or got the right info somewhere else.

rduval

I know what you mean and I appreciate your advice.

I have called Carver and basically I got a shoulder shrug (over the phone of course).

The problem seems to be a feedback loop through the amps. It does start quiet and quickly (very quickly) increase. I'm reasonably confident that I will be able to get one set of banana jacks out quick enough to interrupt the looping.

I'll let you know how it turns out....

kelley

You wont be pulling any wires, all you have to do is turn off one amp if you sense something is going wrong.

DarqueKnight

This is a direct quote from an internal Polk
Audio memorandum:

"TO: All interested parties
FROM: Customer Service
RE: The Carver M 1.0t

According to Carver, all model M 1.0t amplifiers, after serial number 5000 will work with all Polk SDA's. Further, all units with serial numbers of 8 digits are also compatible.

These new designs now employ a chassis switch for inverted and non-inverted output.

Due to the new circuit design, all units prior cannot be retrofitted."

DarqueKnight

This is a direct quote from an internal Polk
Audio memorandum:

"TO: Sales
RE: ADCOM and CARVER mono amplifiers
FROM: Chris


ADCOM and CARVER mono amplifiers can be used with Polk SDA speakers, under the condition that output grounds of the amplifiers are strapped. In the case of the CARVER amps, strapping the grounds is sufficient.

In the case of the ADCOM amplifiers, the amplifiers must have output grounds strapped and an additional ground wire should be run from chassis to chassis. If noise is present after these two grounds are connected, a 3:2 adaptor should be used on the AC cord to eliminate the ground on the AC cord."

kelley

Interesting, thanks.

rduval

OK, I finally got my 2 carver 1.0's back and I tried them WITH a ground between the negatives...work like a charm..no problem.

It was a $500 lesson but what the hell, who said audio equipment was going to be cheap anyway...

Rick

Tour2ma

Thanks for posting this update...

kelley

Good to see it worked out for you. I was wondering how it would turn out.