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Isoclean Fuse

Recently, I purchased an Isoclean fuse for my ARC VT100 MkII. The value of the fuse for the amp from ARC, is 6.25A / slo-blo type.

When ordering the Isoclean fuse the sales person informed me that Isolclean doesn't have the exact value of 6.25, so I should go up to the next fuse value of 7A (they either had a 6A or 7A).

When I installed the new fuse, what I noticed (and I don't know if this has anything to do with the new fuse) is that the bias of the amp dropped severly (from right at 130mV, down to around 88mV). After installing the new fuse I rebiased the amp but I couldn't get the amp back to 130mV. The best I could get was around 127mV, and this was with the trim pot turned up all the way. (Please note that all biasing was done after letting the amp warm up, with no music playing, for a minimum of 30 minuetes).

Just to check, I removed the Isoclean fuse and inserted the original fuse. Now, the amp showed a bias of 145mV, which I was able to lower back to the proper 130mV setting.

My questions are:

1) Is it OK to substitute a fuse value of 7A for one that is supposed to be 6.25A?
2) Would putting the 7A fuse in the amp cause the amp's bias problem?
3) Are there any other problems that may occur by installing the wrong value fuse?

Any remarks / recommendations that you can make will be appreciated.
louisl
aaudio_imports's avatar
aaudio_imports
42 posts
 
To Louisl, you should ask ARC if the fuse value directly affects the bias. I have not heard of this before, but I am not familiar with the ARC circuit. If you want to return the fuse I would be happy to refund your money. You may also want to ask ARC if you can use a 6.0A to replace your 6.25A.

To Genesis168, The 6.3A fuse is only made in the 5x20mm size. The ARC amp as well as most all US made electronics use the larger 6x31.8mm size.
porziob
316 posts
 
Sometimes one should leave well enough alone. Isoclean fuses are not the answer to all future improvements, if any at all.
wc65mustang
524 posts
 
Here's my advice. Don't spend $25 for a fuse.
zargon's avatar
zargon
453 posts
 
A couple of comments. First, the only way I know of that a fuze can effect the bias is if it has a high enough resistance to cut the voltage from the power supply. It seems unlikely that a fuze would reduce the bias by over 25%. Something else is going on here.

Second, the MK II has 2 trim pots that need to be adjusted to set the bias, and it is an iterative process. Did you adjust both? Here is a link to an excellent treatise on how to bias this amp.
http://mycollins.net/audio/artube1.html
Since you are familiar with biasing, you probably know this already, but I put it here in case others may need it.

Third, I agree that you should not use a fuze of higher value than the manufacturer recommends, even though it is only marginally higher and would probably still protect the amp. The risk is just not worth it.
aaudio_imports's avatar
aaudio_imports
42 posts
 
I encourage everyone to read the reviews and comments written below by the press.

http://www.positive-feedback.com/Issue22/isoclean.htm
http://www.6moons.com/audioreviews/isoclean3/fuses.html
http://www.6moons.com/industryfeatures/isoclean/isoclean.html
http://www.soundstageav.com/audiovideonews.html
http://www.ultraaudio.com/equipment/isoclean_superfocus_80a3_pt3030g_ii.htm
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