Synergistic Red Fuse ...

Also, of course, a mains fuse would not be rated at 32 volts.

P.S: Unless perhaps a previous owner replaced the original fuse with a 32 volt automotive fuse, which might also explain why the fuse that was in there was a fast blow, rather than a slow blow which is what I’m pretty certain an MDA-10 is.

And if a previous owner had indeed replaced an MDA-10 250 volt slow blow fuse with a 32 volt automotive fast blow fuse, I would certainly not find it surprising that changing to a more properly rated fuse would make a transformative difference. And perhaps changing from the SR fast blow you went with to a slow blow would reduce the sonic downsides that you indicated resulted from the change.  As well as minimizing the risk that this expensive fuse will blow prematurely.

Best regards,
-- Al

Yes, Al, it's the Sunfire 300. On the back the Mains fuse says...
Line AC 12VAC, 50/60 Hz. The manual says 10 amp fast blow fuse.
It's quite possible the previous owner or a repair shop installed a 32 volt fuse.

I no longer use the Current Output since I bought Gallo floorstanders which only have one pair of inputs. (The Current fuse is a 5 amp Slow-blo MDL/Q). You have a great memory, as I did previously use a double-run to the speaker's upper and lower drivers.

I now use the Voltage Out since this is the standard output. As you know, the Current Output is for electrostats and tweeters. Due to the higher output resistance, there is less "body" or "slam" to the sound when used as a main output.

My impression is that the Gallo tweeters may be too revealing when using this fuse. It's the same result as when I tried the SR Black PC.
(I have even checked for correct speaker phase and polarity).

lowrider57:

What an interesting amp design from a real audio personality in Bob Carver. I will leave all the engineering to Al. This circuit is way more complicated than my thankfully simple SET amp circuits. 

Being you have an older amp , Al gives  very good advice in cleaning the fuse holders, power cord inlet, speaker ouputs and interconnect inputs. A good "spring cleaning" can be sonically very rewarding.

It sounds like the SR Black line of products are improving detail to a point that is not ideal for your system. That is my emotional response to my son's new 4K TV compared to my Panasonic Plasma TV. Too much detail that for me is distracting. He  loves the added detail.

The Isoclean fuse in my experience has a warmer, less detailed sound than the SR Black. Perhaps this or fuse or other fuses  that have gold in them would give you warmth but with less grain than the stock fuse.   

You may want to try one of the fuses offered by Music Direct. They are a fine company that has always honored their return policy.

Before ordering fuses from VH Audio or Parts Connexion be sure they accept fuses returns.

Audio Magic fuses are not normally returnable for a cash refund. At best one may be allowed store credit towards a future purchase.

When buying any product make sure to understand exactly what the terms of return are. 

Audio system enhancement and audio listening should be a rewarding and fun endeavor. I plan on having a very fun and rewarding session latter today.

David Pritchard

Lowrider & David, thanks for the additional comments. Lowrider, yes, in the rear panel photos of the amp that I’ve looked at via Google Images it says "120VAC 50/60 Hz" immediately under the fuseholder, as you indicated. But further down and a bit to the right, just under where the power cord emerges from the panel, the photos I’ve looked at say something like "for continued fire protection use original fuse type and rating only of MDA-10."

Here is a datasheet for the MDA series of fuses. Note in its title and in the first line under "description" the words "time delay," which would certainly seem to correspond to slow blow. Also, Digikey’s listing of that fuse, shown here, states "response time: slow." And the "nominal melting" spec of 1491.3 amps squared-seconds for the MDA-10 is well into the "slow" category, for a 10 amp fuse.

So if that same wording appears on the rear of your amp I would have a good deal of concern that an expensive fuse described as fast blow might not last too long in that amp, regardless of what the manual says.

Regarding Bob Carver, he certainly was (and still is) quite an innovative designer. For a goodly number of years starting around 1982 I used his model M400t amplifier, a 200 watt/channel amp in the form of a cube measuring just a bit more than 7 inches on a side(!). It was designed to emulate the "transfer function" of the very highly regarded Mark Levinson ML-2, a pure class A design rated at 25 watts or so into 8 ohms but capable of providing enormous amounts of current into low impedances. Although Mr. Carver pretty much admitted in a TAS interview a few years ago that as might be expected the design succeeded in emulating the ML-2 just to a loose approximation at best, it provided me with very satisfactory results for quite a few years, until I eventually transitioned to tubes. And it seemed every bit as powerful as its rating would suggest, at least when used in conjunction with the easy to drive speakers I was using at the time.

Prior to that time, though, I very briefly owned a predecessor model, designated as the M400a if I recall correctly, which was not designed to emulate anything and provided sonics that were quite disappointing. But the M400t was a "night and day" improvement on that earlier effort, and he presumably carried the benefits of those experiences forward into his Sunfire years.

Best regards,
-- Al

Al we share a common link in owning Carver products. In medical school, I "upgraded" to a used Bob Carver Phase Linear 700 amp. Well it certainly did make my Klipsch Cornwalls play LOUD ! I am not sure about all of his design skills, but he was one of the best self promoters out there. It would be interesting to tally how many companies he has started and then folded.

I think the ringing in my ears finally subsided when I bought my first
SET amp (Art Audio PX-25) in 2008! It took me a long time to overcome the audio dealers party line of the 1970's - bigger amps give bigger sound, no matter what the efficiency or type of speaker is used.

Thank goodness for the internet where approaches to a satisfying musical system can be discussed from multiple points of view.

Since this amp under discussion is a Carver product,
 is there a fuse made that has a built in fire extinguisher? 

A few of the Phase Linear 700 amplifiers could have used a fuse with that feature !

David Pritchard