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Post by alvinsawdust on Aug 31, 2010 20:21:50 GMT
Hello Chaps
Thanks for taking an interest in my poorly amp. As Mike said, i replaced the damaged resistor and ran the amp for a couple of hours,but unplugged it when i smelled something was amiss. I opened her back up and both resistor ends were just about to pop out.
I bought the amp about a year ago and unknown to me at the time, Darkvoice was having in house business problems and eventually led to a company split. As a consequence i don't think my amp was built with the love and attention it should have been.
Darkvoice don't build to the same standards as British, American or European gear and communication with the company was poor when my first amp turned up damaged. Even so, i really like the way amp drives my HD650s and and will do what it takes to get her back on her feet.
Once again many thanks for the input from everyone.
John
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Post by Deleted on Aug 31, 2010 20:25:33 GMT
nice one mike a man must have his amp after all and it's really good of you to sort the thing.which for me speaks volumes for this forum and people on it i bought my HD650 to use for late night listening not really expecting to much in the way of enjoyment but after your great work on the V2 headphones are now my preferred option. I've been busy lately with the addition of a neco v2 and the little hot er i mean dot and some HD25 1 II. I've also dug out a pair of AKG K100 from my college days which for me are good except the bass. i find that I've listening to music more now that ever safe in the knowledge that no ones being disturbed. thanks to all for a great place more power to your elbow mike
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Post by alvinsawdust on Aug 31, 2010 20:27:12 GMT
I've asked John to chip in to give a bit more "history" about the amp.... funnily enough, he changed the resistors (again) and the one in the opposite channel blew up this time so this is not limited to one side it seems. I didn't think it "was" a resistor thing, thought the problem may have been further down the line causing excess current to run through the resistor.... obviously not. Well, those 20 watt Chinese resistors must be better built than the Arcol equivalents..... I'll get a couple of 50 watters and send them over to John, see how they go. Thanks for all your input. Mike Thanks for the offer of the 50 watters but i have a branch of Radio Shack less than a mile from me.Will pop in over the next couple of days.
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Post by PinkFloyd on Aug 31, 2010 21:54:11 GMT
I've asked John to chip in to give a bit more "history" about the amp.... funnily enough, he changed the resistors (again) and the one in the opposite channel blew up this time so this is not limited to one side it seems. I didn't think it "was" a resistor thing, thought the problem may have been further down the line causing excess current to run through the resistor.... obviously not. Well, those 20 watt Chinese resistors must be better built than the Arcol equivalents..... I'll get a couple of 50 watters and send them over to John, see how they go. Thanks for all your input. Mike Thanks for the offer of the 50 watters but i have a branch of Radio Shack less than a mile from me.Will pop in over the next couple of days. Dennis, I am so sorry I didn't spend more time with this, I genuinely thought it was something further down the line causing the resistor to blow a gasket and just didn't have the time to investigate it further. It's not usually a simple case of replacing a "blown" component, most of the time a fault somewhere else is "causing" it to blow and finding the culprit can be / is very time consuming. If it's a simple case that the 20 watt resistors are underrated then a 50 watt alternative is the answer. Now, if the other Arcol 20 watter had blown (the one on the other channel) when the amp was with me then it would have suggested that, yes, it was a resistor problem.... it was only when you replaced them yourself and the resistor on the other side blew as well.... this does suggest we need to fit something a bit more beefy here I am really surprised, though, how the stock 20 watters lasted so long.... Arcol is a good resistor..... the stock resistors must be even better! There is no heat dissipation via the metalwork the way the resistors are mounted so you are PURELY relying on the resistors aluminium housing to dissipate the heat so the "20 watt" rating is, in fact, nothing like 20W.... "20W" assumes the resistor is mounted on a heat dissipating surface. 50 watt "should" do the trick but I'm still not happy with the hotspots in these DarkVoice amps.... I certainly wouldn't trust one running 24/7 in my home.... they could prove quite dangerous in certain situations...... Seems that's the MAJOR "hotspot" in your particular amp.... if you can get a 100 watter in there, then, even better... belt and braces and all that..... I don't like working on these DarkVoice amps, or should I say I don't like sending them back with "my" name on them as "fully operational".... should the shit hit the fan (ie: burn your house down) then I would be quoted somewhere along the line Fit as big a resistor as you can accomodate in the space, lose the attached LED assembly (you know when the amp is ON, the valves glow) and, touchwood, you'll be cooking on gas again.
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Post by Deleted on Aug 31, 2010 22:15:39 GMT
Hi Mike,
> by the way hows the HD amp with TX gain stage coming. a good place for transformer winding is AE Europe who i think are in Rotterdam. just down the road from you i think.
Yes, Rotterdam is very close by indeed, the closest bigger city. Funnily enough I will first try OEP transformers from the UK. Ordered them from Farnell. They look promising but to keep the distortion low for the lower frequencies at higher levels is the most difficult part. It is still only 'in my mind' as far as develloping goes and needs time to 'mature' there but the parts have been ordered and I am going to use the housing of an old experimental power amp I once build. Now I will need (to make) time to build it.
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Post by Deleted on Aug 31, 2010 23:21:59 GMT
hi Frans I've not heard farnells so can't say how the may sound but if they are not up to speed in the high frequency department you could use a nice small value tuning cap across the TX. I've used that as a work round with some iron to good effect but your TX's may be fine. keep us posted on that it's an interesting idea. do check out AE I've had some nice C Cores from them at a very fair price. Mike not to many people stick their necks out to help others like you have it's nice to see.
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Post by Deleted on Sept 1, 2010 5:14:06 GMT
Hi Shaun,
Indeed a compensation network at the secondary resistor + cap (and maybe even a primary one) will be badly needed for proper squarewave reproduction (and thus amplitude and phase/time alignment). 25-30 kHz -3dB should be possible without much problems. This network is not incorporated in the posted 'theoretical design' because it distracts from the basics. At low freq the transformer doesn't act like a coil anymore and becomes very low Ohmic/resistive and will be a troublesome thing. This means the input stage will likely have to be able to provide high currents just like the output stage.
When it is finished I will post pics and specs/graphs. People that know me will only hear me say that it is just as good as my other amps or not because I only describe what I hear in AB-x tests. I know it's a shame and should do subjective write-ups too, but feel such a description is kind of personal and may not reflect other peoples descriptions of the sound.
Sorry for the thread hi-jack, the rest will be in: Set The Controls For The Heart Of The Sun/Class A Single Ended, Variation on a Theme
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Post by alvinsawdust on Sept 4, 2010 8:31:24 GMT
Just a quick update guys.
Manage to make contact with one of the people who used to work at Darkvoice and he has advised me to replace the resistors with 2x 25w 1k ohm in parallel each side.Got some Vishay ones on order.
Should arrive monday,will keep you posted.
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Post by Deleted on Sept 6, 2010 15:56:10 GMT
hi sounds good Mr sawdust keep us posted take care
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Post by alvinsawdust on Sept 7, 2010 19:48:15 GMT
Fitted parts last night and had 2 hours of blissful listening before tiredness kicked me upstairs to bed. Amp still runs hot as a bastard but thats the nature of the beast.So far nothing smells out of place,fingers crossed thats how it's going to stay. Can't thank you all enough,especially Mike for giving me the confidence to repair it myself Regards John
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Post by Deleted on Sept 7, 2010 23:44:14 GMT
thats just great i hope all goes well with the DV from here on take care
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