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Post by sometrolls2 on Jul 10, 2006 23:36:38 GMT
The simplest design of a mains to switch, to fuse, to transformer to X-cans. The transformer tests okay, just under 14V when not loaded, but the 250mA time delay fuses keep going, sometimes they work for a couple of weeks other time not at all. Is a higher rated fuse okay or would this risk damage to x-cans?
Could the X-cans be responsible for the apparent issue and not the transformer?
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Post by PinkFloyd on Jul 11, 2006 9:14:54 GMT
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Post by sometrolls2 on Jul 11, 2006 12:37:59 GMT
30Va, there seemed to be a shortage of toroidals, so got an encapsulated 30Va from Rapid; it immediately killed the buzz that can be heard when the volume is turned right up with no signal, so seems a decent specimen.
The option of 315mA - 500mA is reassuring
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Post by PinkFloyd on Jul 11, 2006 13:39:38 GMT
As I say, T250mA works fine for me but if it breaks after a while then you can try going to T500mA. You need a value that is large enough to not suffer from "nuisance tripping", yet not so large that it doesn't fail during a genuine fault. Try between T300mA up to T500mA and see how you get on (I'd try T315mA for starters)
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Stormy
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Post by Stormy on Jul 11, 2006 14:17:42 GMT
Mine has been fine with a T250mA as well, and it's been running for more than three months (not sure how often I've switched it on in that time) with a 60VA toroid.
It is surprising that it blows on yours but, like Mike says, all you can really do is try a heftier fuse.
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xerxes
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Post by xerxes on Jul 11, 2006 14:45:03 GMT
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Post by sometrolls2 on Jul 11, 2006 17:42:35 GMT
It was the standard one 88-3358, although that and the premium audio grade are currently the same. Its completely quiet via headphones, and no hum is coming fom the PSU box.
I don't know how consistent Rapid are as the item pictured is branded differently, I guess that they work to some standards and deal with it if a batch is poor.
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rickcr42
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Post by rickcr42 on Jul 11, 2006 21:28:05 GMT
time to add my $0.02 a fuse is a safety valve meant to protect the equipment if something should go wonky so the last thng you ever want to do is increase fuse size or you are looking for trouble. Properly sized fuses popping mean one of two things 1-you inadvertanly used a fast blow fuse in a slow blow position 2-you have a short somewhere or other problem causing the surge that is popping fuses. go to a bigger fuse and you may find the fuses stop "popping" but the gear fries due to it no longer being protected Rickmongo out.....................................
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Post by PinkFloyd on Jul 11, 2006 21:53:17 GMT
Rick, the T250mA was my original recommendation for the DIY PSU and was running pretty close to the bone so it is possible that it's a bit on the keen side in this guy's setup. He says it goes every few weeks so it could just be it needs upped to T315mA or even a better quality (more accurate) T250mA. Mike. PS: the item in question is here: www.rock-grotto.co.uk/x-psu.htm
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rickcr42
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Post by rickcr42 on Jul 11, 2006 22:04:51 GMT
still Mike,a fuse that sometimes works/sometimes not on one unit yet is fine with an identical unit syas something is screwy somewhere.
Not having enough trafos current would make the trafos run hot as hell as it strained to provide current out of its range to do so but anything less than a power surge or short would not pop a fuse that was otherwise working fine not that I have any clue WHY this one is.
Caution is best so if the fuse increased in size (current allowed to pass) monitor the other parts for rapid heating which would preceed the inevitable flame out if there is a problem somewhere else
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Post by PinkFloyd on Jul 11, 2006 22:15:08 GMT
Original poster........ has this "fuse blowing" scenario just developed or has it been doing this from day one? What kind of volco levels are you listening at when it blows? Have you had a look under the bonnet of the X-CAN, in particular the area around the transistors? Are there scorch marks on the PCB around the transistors? Have you checked the valves? Replaced the valves with another set to see if the fault replicates itself?
Worth having a scout around under the bonnet.
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Post by sometrolls2 on Jul 11, 2006 23:05:10 GMT
Fuse would go when turning on before use. Time delay fuses have been used
Just moved to Russian valves, but made PSU then did tube swap within a week and have off loaded the original tubes already, so I can't identify the tubes as faulty as they sound good. It is getting hotter since the change, but most people find this and no burning yet.
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rickcr42
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Post by rickcr42 on Jul 12, 2006 13:20:17 GMT
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Post by sometrolls2 on Jul 12, 2006 20:30:30 GMT
The X-Cans syas 500mA, but thats post tranfromer and the fuse is pre transformer, so I was after an answer based on people extraordinary knowledge of the workings of the X-Cans
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rickcr42
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Post by rickcr42 on Jul 12, 2006 21:38:42 GMT
maybe I'm misunderstanding (or need to look at mikes page ) because that baffled me ALL current draw after the actual mains inlet drawn by the entire circuit is effected by the total current draw of every part so the mains fuse should be selected that will allow fpr the peak expected current draw if a fast blow or the total of all idling curren draws if a slow blow. is this particular fuse somehow in an offshoot circuit that has nothing to do with actual amplifier operation taking that requirement off ?? If not pre-or post trafos is all the same and in fact the fuse could be anywhere before the circuit and protect everything after that point. A trick used in some power amps is to use a main overall fuse then fuse the DC power feeds individually to each channel of amplification which means a lower value fuse for each channel protecting IT from harm independant of anything else so more often than not a fast blow with the main fuse,larger enough to handle totoal amp current draw protecting the entire amp from a dead short so a slow blow (which reacts FAST in the case of dead shorts ) this takes the turn on surge headroom requirement off the power supply fuses so they can be closer to ideal (not needing the extra headroom) while BIG UGLY on the trafos primary side can be a ballpark figure fuse
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Post by PinkFloyd on Jul 12, 2006 22:00:56 GMT
This is just a slow blow before the primary of the transformer Rick. 30vA transformer so really a T160mA should be fine according to Antrim transformers. Has the original poster tried the transformer "not" connected to the amp? does the fuse blow when not connected ampside? Mr. Wallwart and Mr. X-PSU doesn't have a user replaceable fuse, I just went with T-250mA before the primary for added "safety" here's the spec sheet for the transformer (30vA one) www.nuvotem.com/en/products/pdf/0030P1_0209.pdf
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Post by sometrolls2 on Jul 13, 2006 22:43:23 GMT
I think it has blown when connected, but there again I haven't turned it on and off a lot of times when unconnected. Its now got a 500mA and has been fine for a few days, after blowing 2 the day before the change.
I wondered if it was a largely hamless cap issue, or was revealing a problem that the Walmart had hidden. When unplugged there is some kind of discharge into the 'phones, so maybe the X-cans power regulation end might be doing something in the other direction when starting? Additionally the Russian tubes will have somewhat different requirements to the Jans-Phillips
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Post by PinkFloyd on Jul 14, 2006 12:54:34 GMT
I think it has blown when connected, but there again I haven't turned it on and off a lot of times when unconnected. Its now got a 500mA and has been fine for a few days, after blowing 2 the day before the change. Excellent! You may want to try replacing the T500mA with a T315mA and see how you get on with that. The "whoosh" and discharge into the 'phones happens with them all, perfectly normal, just unplug your 'phones before switching off and when switching on wait about 30 seconds before plugging your 'phones in. Alternately, leave the amp switched on all the time. Mike.
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rickcr42
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Post by rickcr42 on Jul 14, 2006 15:55:22 GMT
pretty much all headphone amps have this problem,worse if there are output caps which lose DC bias when you turn off power causing a "pop" sound. Then there is the the fact that plugging or unplugging headphones causes a dead short on the output of the amp because of the way a TRS jack is configured. So turn it off or on and you get pops or other noises from the capacitors charging and disharging but keep it on and unplug the cans for whatever reason and you also get pops.Pops loud enough to do damage to the headphones if the volume control is way up.Kind of screwed no matter what you do -------------------------------------------------------------------------------- Maxim :www.maxim-ic.com/appnotes.cfm/appnote_number/3687-------------------------------------------------------------------------------- Headroom :"Turn Down Your Volume!
You wouldn't play around with speaker cables while your power amp is on because you know the leads might short together and blow up the amp! Well, a headphone amp is a miniature power amplifier, so when you plug and unplug headphones the contacts do short to ground momentarily, and you can blow up a headphone amp plugging in headphones. We could design in protection circuits, but we don't because they sound notoriously bad. So PLEASE, turn off, or at least turn fully down, your headphone amplifier before plugging in or unplugging your headphones.
Incidentally, there are other reasons to turn down the volume on your headphones, even while listening. Learn about avoiding tinnitus."----------------------------------------------------------------------------- Maxims solution is smart but adds the dreaded "more in the signal" path that no matter what the claim will be audible.Maybe for portable use a non issue considering what the source will be (you think the output stage of an iPod or portable CD player is a quality signal ? One as good as your home rig sources ? ) but not something I would be comfortable with in any high end headphone monitor system. Headroom's solution is fine for their amps because they are direct coupled but useless for any cap coupled amp and has no effect on the fact that TRS plugs short the TRS jack when inserted so does zero for the "hot" plugging in of cans so again not a full solution. What is a FINAL solution to the amp/cans interface and pop/tick dillemma ? 1- The Elaborate Solution where stupid humans need do nothing,the turn on delay muting relay with a rapid off response.Turn on the amp and it mutes the output for a preselected time period,turn off the amp and it instantly mutes the output.Taking this to a full output protection circuit for both the cans and the amp it can also have "fault" sensing that again will trigger the "instant off" whenever there is DC on the output of a short circuit condition. The crap about "audible consequences" is just that.these type of circuits have zero impact on sonics because they are not IN the circuit path but ALONG SIDE the circuit monitoring it so those audible consequences are all about adding cost to the design,adding circuit complexity (some knucklheads can't even get a relay right ) and finally adding to the overall size of the amp itself.Look ionside the average amp and you will usually find ZERO extra space for any additional circuitry so again about cost plus on shelf/in the pocket footprint 2- The QUICK and DIRTY Ricksville Solution,a simple $5 DPDT toggle switch on the front panel labelled "MUTE" that lifts the headphone connection from the amp output.Now this is too easy,too cheap and too sensical (rickisms ) to be a solution for most stupid humans because it means you gotta DO something ! You can't just look at the switch and yell "mute" at it but must take your tired ass over to the switch and flip it or it will not work.You also can't toggle it AFTER you hear the POP then blame the switch for not working but instead need to get into a routine where everytime you operate the power switch or swap cans the first act is the mute switch and all potential pops,clicks,whooshes,Country Western Music sneaking in will be eliminated without ANY effect on the amps sonic quality. But like I said,means humans need to actually THINK and then DO so maybe the costly space grabbing automatic solution is better after all
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