I think I just smoked my Amp

Ummm… yeah… what the title says…

Just received a new pair of speakers, Thiel MCS1. I got them hooked up, powered up my pre and my amp, started playing a test track (a progressive house song), I immediately noticed a slight crackle in the right channel, and as soon as the song got to the part where the bass beat dropped, the amp went into protect mode. It stayed in protect for about five seconds, then the “operate” light came back on, but the audio did not return. I powered the amp down, tried powering back up, but the protect light immediately returned, but it was extremely dim. Now, the power switch does nothing; nothing lights up. I smelled the vents in the top, and nothing smelled burnt or out of the ordinary.

My uneducated guess is that the lower impedance (4ohm nominal, 3ohm minimum), strained an aging cap which then gave up the ghost, but really I have no idea. My previous speakers were a much easier load (10ohm) and the amp handled them just fine.


I really don’t know what to do now, but I’m bloody devastated.

My system: 


ARC D400


Auralic Aries


That's coincidental! Second thread today about a D400 that want bad. I hope that it's an inexpensive fix.

The D400 is a fairly old unit and given its high-current design, I’d be willing to bet that it’s the transistors that got exhausted vs a capacitor going bad. If transistors start to fail they will leak current one way or another and drive the amp into protection mode. Only way to know for sure is to send it to a tech, preferable Audio Research directly. I live one town south of their factory and they are incredible to deal with on service.

@rfnoise I don't think a filter cap failed. I think a fuse blew, which is why the amp faded out as you continued to try and power it up. The caps stored energy, which was drained off by trying to restart the amp.

Open it up and see if there are any obvious fuses. Hopefully the blown fuse is easy to spot. Replace with the same type and rating!

Check for fuses....that happened to me with my Ayre....sent it back to Ayre (expensive)....just replaced a fuse and sent it back.

Have you tried letting it cool down for 10 minutes (unplug it) or so before trying to power it up?
It would have no issue running into 4 ohm speaker loads.

If the fuse is blown, don’t replace it with an expensive "audiophile" fuse as the fuse might blow again as soon as you turn the amp on.

If the fuse does blow again, obviously the amp needs to go in for service.

And if the amp doesn’t turn on, then it still needs to go in for service.

If replacing the fuse works, then you’re one lucky guy.


The schematic shows two fuses. Most likely, one is at the power cord, the second is probably a rail fuse- which is located inside the amp.

I am with Ralph on this,  one or both fuses may have blown. Just try replacing them. (Of course, you can look at them and see if they are blown, too).

If a capacitor blew, you would see a darkened spot on the board or a distorted piece. 

I unintentionally shorted my McCormack amp once, and Pat and Steve guided me through the diagnosis. Yup, I blew out the rail fuse/s.

When my Ayre amp suddenly died, Ariel asked me to look inside- When I showed him the blackened spot in the amp, he said ship it back to repair the capacitor.

Have you checked you speaker connections/interconnects? Anything that might have grounded the signal?


if you blew a fuse -- or anything else that quickly either you have a coincidence, ro, i suspect, you shorted something liek a speaker wire, and that short likely is still there.  Check carefully.  In fact begin withe the speakers disconnected. if you hapen to own a VOM, with everything off, and ideally, but not reqyired, with the wires disconnected form the amp (its off, right?  and has been for a long time, right?) measure the resistance across the speaker terminals.

i lso dont think the discussion on 2 fuses above sounds right. You almost certainly have one line fuse on the 117 VAC (house power).  Other fuses woudl either be rails (+ and - power supplies) or speakers. Both are in pairs.  So i can see 3, btu not 2.  If there are really two , i suspect both are power/lie one for supervisory o similar power and very small.

If I remember, you recently purchased that unit used from a nearby dealer. Phone them for advisement.

Thanks to everyone who took the time to respond. The status of my D400 remains unchanged. Visual inspection didn’t reveal any possibility of shorted speaker cables.

I spent most of the day driving to retrieve my CODA amplifier from storage; maybe I should store my things closer to where I actually live 😐

I’m going to figure out how to open the case, and run down those fuses.

@bigkidz I appreciate the offer, but am located in Oregon, and trying to avoid shipping this amp if at all possible (no original packing materials). Coincidentally, my speakers were shipped from NJ.





New, the D400’s came with two extra 8amp slo blow fuses.  Maybe there was a reason for that.

Hopefully that’s all it is.

Crackling sound, DC protection engaged, plus blown fuse is very likely a shorted output transistor. Replacing a fuse is not going to help in that situation. Also, to make matters worse, those Sanken output transistors are no longer manufactured. A substitute may work or it could cause stability or distortion issues. SS amps are  finicky.

Well I managed to locate two fuses

the first, in the obvious place next to the power cable was one of these:

Due to the opaque nature of the cylinder, I can’t see whether the filament is intact or not.

The second fuse was on the main board. It was in a really awkward spot, but I managed to get it prised loose with a long wooden skewer. It’s one of these:

It looks to be intact, but I’ve had fuses on my bike that looked good, but actually needed replaced.


I’m going to go ahead and order both, and cross my fingers.

If it was the fuses, I’m curious to know what would cause that. Could there be something wrong with the new speakers that could cause that? Or just bad luck?



I’m guessing those are the metal devices lining the sides of the case against the heat sink. If it is a failed transistor, I’m guessing that’s game over for my amp?

Well, nothing amiss with these speakers. My CODA amp is driving them fine. Too bad it’s such a lousy match for my pre.

Fuses can fail randomly from thermal/mechanical stress, but also, alternatively, from component failure.

If the amp has failed transistors, it's not necessarily the end, depending on whether replacement transistors are available.

However, on an older amp, you're probably looking at a full refurb including the power supply caps at least.

Ultimately, the cost benefit ratio may be negative depending on how much you like the amp and how much work needs to be done.

Great amp worthwhile investment for refurbishment.Once done you are good for many years to come. Make sure the tech you choose is familiar with ARC SS products. If possible get it into the factory after forum trouble shooting advice.

All the best.

NEVER accept what you See visually with a fuse. Measure the Impedence. If this was a fuse, I'd be surprised, it would have had to be a VERY 'Slow Blow' variety.


I have a tech in Philly who has serviced my two ARC D240’s MKII’s and is a skilled tech. Let me know if you want an introduction.

Measure a fuse for continuity. it either has it{working} or it doesn't{not working}

Not sure about checking a fuse for Impedance.


Thanks for the offer; it’s awesome that you’ve got a tech that could work on your d240. If I need to my amp serviced, I’m hoping to be able to get that done locally. Not only would shipping an amp of this size be extremely expensive, but I don’t have the original packaging materials and wouldn’t even know where to begin in terms of trying to pack something like this for shipping.

Well this is interesting… in the schematic, it calls for a Bussman MDQ-8 fuse, but what I found in the amp was an MDA-8. Is this a problem? 

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You sir, are a gentleman and a scholar! You totally nailed it, replacing the fuse got it back up and running. Feeling a little sheepish that I didn’t figure that one out on my own.

I replaced the fuse with an mdq-8, as indicated by the schematic. Still curious about the mda-8 fuse I pulled out of the unit, wondering if that being the wrong fuse had anything to do with the failure.

Thanks to everyone that replied here; sorry for panicking and going off half-cocked when it was just a fuse.

I replaced the fuse with an mdq-8, as indicated by the schematic. Still curious about the mda-8 fuse I pulled out of the unit, wondering if that being the wrong fuse had anything to do with the failure.

@rfnoise Of course it did- it was the failure 😁

Fuses can fail over time. Since it worked after replacing the fuse, its no worries. The MDQ-8 has a slightly slower timing to when it blows out.