Will
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Post by Will on Dec 28, 2010 7:58:19 GMT
At some point, I'm going to have to build myself a Valve headphone amp, because I've never listened to one. The thing that seems to crank the cost up is using a transformer to "match/drive" the headphones, so I've been looking to find a design that does not use a transformer output, and also has a decent voltage to run the tubes. I came across this design gilmore2.chem.northwestern.edu/projects/showfile.php?file=ciuff_prj.htm and was wondering if anybody had built it. or had any opinions ? The amp has 280V kicking about, but I'm comfortable with these voltages The last valve amp I heard was one that my Dad built, years back, and the last valves I handled were in RF tx'er's, with much higher voltages.
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Post by Deleted on Dec 28, 2010 9:28:18 GMT
It's not very suited for low-Ohmic cans. It can only put out 40mW in 32 Ohm and with high amounts of distortion at that. the class-A output current of 50mA is simply too low for driving low-Ohmic cans. Only 300 Ohm and higher is recommended for these designs. It's actually an indeed/bravo/miri .... with the output FET changed to some tubes and a higher voltage.
I suggest you look for a design with overall feedback and a differential input stage in an OTL design.
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Post by victoriaguy on Dec 28, 2010 16:12:26 GMT
The output transformer for most valve headphone amps needn't be very expensive, and is a small proportion of your total cost in parts and labour anyway. Disclaimer: I've built quite a few valve projects, but the three headphone amp projects are still in my parts bins, waiting for January.... The HeadWize archive is a great resource. As well, check out: Pete Millett Mapletree Audio Hagerman Castantet
for some more ideas.
Cheers John
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Post by bizzie on Dec 28, 2010 20:25:55 GMT
Not full kits as they don't come with transformer and case and need a certain amount of valve knowledge but Broskie does some good amp kits and are based on his aikido topology, I have built the low voltage (24v) linestage HP amp using 6Gm8 valves but these are very rare now and getting expensive but sounds very good and not at all noisy. glass-ware.stores.yahoo.net/listheam.html
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Post by tubesurf on Dec 29, 2010 8:35:20 GMT
How about the Bottlehead Crack? No output transformer - many good reviews. Designed for higher impedence headphones though. I'm in the middle of a build right now - very easy with excellent manual.
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XTRProf
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Post by XTRProf on Dec 29, 2010 23:53:39 GMT
Hi Will, I'm really not in favour of an OTL amp, although I like the idea very much, after hearing how my friend blew up a FR speaker. "Transformered" (ha, ha, Transformer the movie ) tube amp don't have that problem. But I'm in favour of a tube HA as tube amp do sound more like REAL LIVE music after some good matching. Your AKG should sound very good with tube amps because of it's characteristics. However, being 62 ohmer, it is definitely not suitable for an OTL amp. If I'm to build one I will go for a "transformered" tube amp. Nah, forget it until I get the SC Class HA working first. Must resist or it will be another thing lying a round ............
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pjc68
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Post by pjc68 on Dec 30, 2010 0:41:00 GMT
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Will
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Post by Will on Jan 1, 2011 11:46:02 GMT
Hi Guys,
Thanks for all the replies, I really appreciate it, especially the links to bottlehead and glass-ware.
OK then, if I accept having iron on the output, can anyone suggest a design suitable for K701's? I'd still like a high voltage design.
The kits look excellent, but would prefer to build from a circuit. The reason is that I'm in the dark when it comes to valves, and by having a circuit to look at, and having to find possible alternatives when it comes to building it, I'll learn a whole lot more than just plonking the supplied parts in the right place. Shame that SEX kit doesn't have a circuit diagram at large, as it looks ideal
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Post by Deleted on Jan 1, 2011 12:52:04 GMT
Not full kits as they don't come with transformer and case and need a certain amount of valve knowledge but Broskie does some good amp kits and are based on his aikido topology, I have built the low voltage (24v) linestage HP amp using 6Gm8 valves but these are very rare now and getting expensive but sounds very good and not at all noisy. glass-ware.stores.yahoo.net/listheam.htmlHi Bizzie Good call the aikido is a good sounding amp . I've built the linestage (superb) and the high voltage HA. i could never get the HA quiet enough but i think that it was due to my Hard wiring. I'd love to have another go with the pucka circuit boards as the sound showed great promise. i have a little dot which sounds pants compared to the Aikido. will i think you have a pair of HD650 which should be fine with tubes. ;D Will I may have some 6BM8 (RCA cleartops) if you want to try this out. take care
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Post by cyteen on Jan 1, 2011 14:01:48 GMT
A little while ago deano showed his bijou here. rockgrotto.proboards.com/index.cgi?board=m&action=print&thread=4731 Its an OTL design but with variable negative feed back to increase the range of headphones it can drive. Its a mega thread at headfi so its well tested has schematics and pcbs available if you get lazy or impatient and some have had good results with k701s. There's even a OCL version hidden in the thread somewhere.
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Post by Deleted on Jan 1, 2011 14:21:27 GMT
Hi cyteen interesting Circuit from my point of view I'd have a few reservations re the use of feedback and the P.P design. if it where me I'd be looking for SE and no FB to get the best from Valves.it's just my opinion and as i have not had a listen to the HA can't comment on the sound. it.s a really nice regulated PSU though but again I'd go the whole hog and reg up the filaments also. Will the Hammond traffos are good for the cash and I've used plenty of them. let me know what design you end up with as i may have a spare for you. if you must go with the 701's I'd go TX coupled OP it's so much more elegant than just beefing up the FB. i may be wrong and am definitely biased towards SE and Iron. just an opinion
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Post by cyteen on Jan 1, 2011 14:40:38 GMT
The feedback is there for flexibility, the k701 @ 62-64ohm can be run with a degree of feed back now and later if Will were to feed his addiction and get higher Z phones the feedback can be reduced to zero.
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Will
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Post by Will on Jan 7, 2011 10:43:47 GMT
After some good advice, I've pretty much settled on building up a WD-HD3S. The only stumbling block is the OP traffo, but that can be sorted I reckon. This'll be a project for later this year, but It'll be nice to have some glowing tubes. Funnily enough, Mike had one of these amps, and seemed to quite like it WAD-HD3
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Post by bizzie on Feb 7, 2011 11:36:15 GMT
I have a pcb for a wad hd3 that I'll not use due to being happy with the amps I already have if you want it PM me and we'll come to a deal.
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rowuk
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Post by rowuk on Feb 8, 2011 21:41:45 GMT
If you are going to use a transformer, then you could also use a MOSFET output stage..............(no more distortion than the tubes, no saturation of the output stage...........) The Bravo can be DIYourselfed!
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Post by Garage1217 on May 30, 2011 23:34:25 GMT
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