Sunfire Signature... what is this?

Recently bought a Sunfire Signature amp, believing I was getting the 600x2 model. The front panel has "Sunfire" above the Joules meter, and "Load Invariant High Fidelity Stereo Power Amplifier" below. A Bob Carver signature is on the upper left of the panel. The rear panel has "Sunfire Signature" just above the serial number (which starts with 99), and a lot of the other normal printing. The two speaker fuses are labeled "5 Amp SLO-BLO MDL/Q", and the AC line fuse is labeled "10 AMP MDA-10 120 VAC", which makes me question if this is a Sig-600. Any thoughts?
How high does the meter peg out at? Should be either 380 joules or 480 joules.
The needle goes nearly to the 500... 450+ for sure, but I read that there was an adjustment pot for the meter on a board in the amp. I have a Sunfire Cinema Grand (405x5) that has 6-amp MDQ-6 fuses on each channel, which also leads me to suspect this amp is not 600w/channel.
If it says Signature on the back and has his signature on the front face as you say then it is surely a Sig 600. He did not make a Sig 300 etc....

If the binding posts have the red and black plastic covers, then it is a first generation. If the solid steel posts with an IEC, then the second version.

The 600 is very powerful and you should notice this immediately in your system.
I wasn't sure how much difference I would hear, going from one Sunfire at 800w/ch to another at 1200w/ch (4-ohm speakers).

The lack of difference was what made me start wondering.

All the manuals I can find on-line show 15-amp AC input fuse for both the 300 and 600 watt Sunfire 2-ch amps. Since this is a '99 model, maybe the 1st generation was different. And maybe I should send it to Rita's, for a tune-up.
Yes you are 100 percent right. Send it in and it will come back better then new. I could not believe the improvement. Also get an iec and use a better power cord.

Yours is the Sig 600 and I understand now that you already had lots of power before the 600.
The word "Signature" on the serial number sticker and the 480 Joule meter reading indicate pretty conclusively that you have the real 600 watt version. Also, it is likely your serial number is preceded by the designation "SS." This is yet another reliable indicator.
Carver has been profligate in post sale autographing. He'll sign pretty much anything he designed, so his signature on the front has come to mean very little.
Telling the difference between 400W and 600W is pretty close to impossible, all else being equal. This is only about a 1.5db difference, after all.
All of Carver's Sunfire "Load Invariant" designs use fundamentally the same circuit, with more or fewer output devices. They all sound practically identical, which is to say they all sound terrific.
Not sure why you'd expect to hear much if any real difference. Most listening is at lower W's and very few peaks ever approach using all that headroom. As noted, the differences in your pre- and post-purchase amps is really kinda minimal (maybe 1.5dB if you could A/B 'em) so unless components have deteriorated and/or you're crankin' 'em all the way you'll likely have to imagine any big change.
Looking at some rear panel photos that are available on the web, and at manuals that are available at the Sunfire website for what appear to be comparable later models, it appears that the 5A fuses (changed to 6A in later models) protect just the "current source" outputs, not the "voltage source" outputs.

My guess is that the 600W rating only applies to the voltage source outputs, and the CONTINUOUS output power capability of the current source outputs is far less (with the difference between the two outputs in terms of short-term (dynamic) power capability being much smaller). I suspect that the current source outputs are created by just putting the voltage source outputs through low value resistors having high power handling capability. The fuses are probably provided just to protect the resistors, with the voltage outputs being protected by circuitry.

So the 5A fuse rating, corresponding to 200W into 8 ohms, is probably understandable. The 10A main fuse does seem somewhat incongruous with the 600W/channel rating, as the 1200W AC input it would support (120V x 10A) would require that the amp be 100% efficient to output 2 x 600W continuously, which of course is not possible. Perhaps it's a design oversight, or perhaps the 600W continuous rating is a bit optimistic.

-- Al
Hmm.. ok, the reason I bought the 600 is that I had a 200x5 (C-1000), and although I didn't hear anything "wrong" with it, when I got the Cinema Grand 400x5 hooked up, there was a definite improvement (I know, different technology). So, I went with the "if more is better, still more is more better" philosophy.

It does make sense that there would be a point of diminishing returns. The 10-amp input, as Almarg notes, seems under-rated for 2x600w channels, and my speakers are 4-ohm (magnepan), so *could* pull 1200 watts each, which the amp wouldn't be able to supply for very long.

I hardly ever crank up the volume *really* high, but I again, at moderate levels, I hear an improvement between the
300w/ch C-1000 and 800w/ch Cinema Grand (into 4-ohms). I don't detect an improvement between the 800w and 1200w Sunfires, and maybe that's not to be expected, at moderate volume levels.

The "SS" mentioned by Rpfef appears at the end of the serial number, another clue that this is a Sunfire Signature.

I think I will send the amp to Rita's, and if I still hear no difference when I get it back, I'll figure out what to do, then. I'll have over $2k in it by then, and probably can't recover all of that, but I could then re-sell it with a clear conscience.

Thanks for the input. Great forum.
Your new amp is very powerful and is of a different design then most SS amps. It does indeed drive difficult loads with its rated power into 8 and all the way down to 2 ohms.

It drove my large and very difficult to drive Soundlab M1 speakers with absolute ease. It always ran cool also. To my ears it greatly surpassed the stock 300 watt stereo amp in my system.

Bill at Carver's authorized repair facility will do what is needed and go thru the entire amp with extraordinary care to every detail. My Sig 600 came back with an entire new right channel board, power supply caps and the voltage rails adjusted for maximum performance. He also replaced many caps with higher rated ones based on learnings over time.

I put an iec on mine and used a good quality aftermarket cord. All of these things really improved the sound to my ears on my SL speakers. I think it will be a keeper for you. I think it shares the same sized transformer for two channels as the transformer in that multi-channel home theatre Sig amp.
Doesn't the Sunfire amps have a feature for solid state sound or tube sound. I looked it up and it said, For those who prefer the crispness of solid state amplifiers, there is a voltage source output, and for tube sound, there is a current source output. You put it on which ever one sounds best for you.
Which one do people like the best?
Twilo, the manuals suggest that the current source is possibly better for planar and/or ribbon speakers, the voltage source for conventional cone-type drivers. For the magnepans, I prefer the current source. Some classical pieces will bring tears to your eyes, the sound is so poignant.

You can also bi-wire, if your speakers allow for it.

I think "best" would definitely depend on the speakers you're driving, and the material you're playing.
Grannyring, Bill at Carver's repair (formerly Rita's) did work on my Cinema Grand... the service isn't cheap, but it's worth every penny. That amp got damaged by lightning, Bill brought it back to life. Soon, he'll be getting a look at this sig-six.
I own a Sunfire 300 and use both speaker outputs; VOLTAGE (traditional SS sound) to the woofers and CURRENT output to the tweeters. The current output is a more natural sound, for example, horns sound more realistic, less bright....but that's my taste.
The 600 Signature has a massive power supply and when u get it back from Bob Carver you will definitely love it.

PS... download the manual, it's very well written.
I've had mine (SS 600x2 and CG 405x5) since about '02 (and '06) and they're both KEEPER's . Incredible performance, never loses its "cool". I have had to replace the meter lamps once or twice. If they ever sound less than 100% it's time to seek out his techs and get it rebuilt. They're the last amps I hope to own.
Thanks! for sharing -Ricktpt.

Agreed, even that 1st Sunfire power amp circa 1995/96 is still a killer. Has not been anything like it (now or since). Other owners feel free to chime in here...
Keep me posted & Happy Listening.
I love my 600x2 and have been looking for another for a long time. Problem is lots of other folks want them also.
my Sunfire 300x2 (1994) drives my Carver Amazing Loudspeakers....

A Marriage made in Audio Heaven
Random: For those that need an original spec bulb replacement for the Sunfire amplifiers you can get them on ebay from with instructions