Guest joewhite903 Posted September 21, 2007 Share Posted September 21, 2007 Hi , im looking for plans to build my own 1Watt Stereo valve amp for my SENNHEISER HD 25 SP headphones, ive done a few searches on google but not had much luck, I can source all parts myself no problem, But I cant find any Plans for such a small amp. I know there are people out there that have done it before. Hope some body can help. Thanks Joe Link to comment Share on other sites More sharing options...
Pete Alcock Posted September 21, 2007 Share Posted September 21, 2007 Hi Joe, It beats me why you'd want a valve amp to take out with you to drive headphones, but hey. Given that you only need a watt or so, a true class A design could be realised. A good friend of mine has built these kits from a valve amp specialist called AUDIONOTE. There are circuits published on this page. The thing is, they're not exactly compact and certainly not robust. Might be a starting point for you though. Good luck. Pete. Link to comment Share on other sites More sharing options...
Jivemaster Posted September 21, 2007 Share Posted September 21, 2007 1 watt isn't small for a valve amp! Most of the Dansette style record players had a single valve amplifier giving 3 watts -a Triode - output pentode if I remember rightly. Valves are not robust and they need transformers (HT and o/p) so they get heavy and twice so for stereo. For mobile use valve amps need to dry thoroughly from any risk of condensation or there is a HT tracking risk. some amps had a "standby" setting which was heater supply on HT supply off for warming up an amp that had spent a day in a van then gone into a warm room and become moist with condensation. The big amps thought nothing of 1000v HT rails. Link to comment Share on other sites More sharing options...
themadhippy Posted September 21, 2007 Share Posted September 21, 2007 they need transformersno they dont,there are numerous designs that dont use an output transformer,as for the ht,the transformer aint that big,especially for a low power amp. Link to comment Share on other sites More sharing options...
Dmills Posted September 21, 2007 Share Posted September 21, 2007 Headphone driving glass fet amp?Some sort of simple cathode follower? HT rail from a stack of PP9 batteries in series (Should last for ages), heater from a wall wart, or as an alternative, use a 12V AC wall wart, feed the heaters directly, and a small 12 or 15V transformer wired up backwards to generate the HT.It is not exactly difficult (Especially for what you actually need which is more like a few tens of mW), but I have to ask WHY? Regards, Dan. Link to comment Share on other sites More sharing options...
Jivemaster Posted September 21, 2007 Share Posted September 21, 2007 ..... heater from a wall wart, or as an alternative, use a 12V AC wall wart, feed the heaters directly, and a small 12 or 15V transformer wired up backwards to generate the HT.................but I have to ask WHY? Regards, Dan. Great cunning plan! Like the AC wall wart idea. I've seen Valve pre-amps in DI box size cases woth a little window to show and cool the tube! I'd use an ECC8x (because I have a dozen or so spare! ) and as a double triode with 12.6v heater they would work for stereo! 1K and parallel 10uF in the cathode to neg rail, 10K as the anode load, 1Meg as the grid bias resistor and 0.1uF as a input cap 10uF as o/p cap and try it Link to comment Share on other sites More sharing options...
Guest joewhite903 Posted September 21, 2007 Share Posted September 21, 2007 sorry for the confusion folks, im wanting the amp for home use, I love listning to my music from the record player/Cd player, through my headphones but a modern day amp just dosent give as lovley a sound, so I want to make a small valve amp just for them, ta Joe Link to comment Share on other sites More sharing options...
Dmills Posted September 21, 2007 Share Posted September 21, 2007 Just remember that that output cap has a couple of hundred volts across it, so make sure it is rated appropriately. Also, it may be worth putting a couple of back to back zenners (and 100 ohm resistors) across the output socket so that that cap discharging (if the cans are plugged in after HT is up) doesn't cause quite as much of a click. Jivemaster, you scheme would seem to suffer from rather a high output impedance for headphones? How about running it as a cathode follower (self biased as in your setup).After all with a line level source, we are not really looking for voltage gain for this application. Finally, as the HT is isolated from the filament with this scheme, you can minimise hum by biasing the filaments relative to the cathode with a couple of zenners (I cannot remember for sure, but think that it was putting the filament at -40V or so relative to the cathode was what I saw recommended). Danm, I will have to dig my copy of Langford Smith out and have a play. Totally off topic at this point, but it is a fun toy project. Link to comment Share on other sites More sharing options...
KevinE Posted September 21, 2007 Share Posted September 21, 2007 You might end up forsaking any quality benefits by building such a thing! 1W through your HD25's is pretty much at DJ levels anyhow! I'd just stick to a decent solid state pre-amp. Link to comment Share on other sites More sharing options...
Guest joewhite903 Posted September 22, 2007 Share Posted September 22, 2007 You might end up forsaking any quality benefits by building such a thing! 1W through your HD25's is pretty much at DJ levels anyhow! I'd just stick to a decent solid state pre-amp. Hi there im not a DJ I Got these headphones cause I really like the sound Quality on them and id rather build a valve amp for them , but I dont have any plans for such a small amp, the only plans I have are for a 60watt Stereo unit, Which is obviously too big and I dont know enough bout valves to modify the design, and I really dont think im the only person out there that has tried this before, so im hoping somebody has some designs for such an amp, TA Joe Link to comment Share on other sites More sharing options...
KevinE Posted September 22, 2007 Share Posted September 22, 2007 What I mean is that 1W is the sort of amp you'd need to drive the HD25 at DJ levels..which is very loud, usually. For personal listening in your armchair a few milliwatts will be fine. Link to comment Share on other sites More sharing options...
Guest joewhite903 Posted September 22, 2007 Share Posted September 22, 2007 im significantly deaf, so normall levels arent fine for me (runs in the family) , I normally run my heaphones straight from my pc to and the levels just arent quite loud enough Link to comment Share on other sites More sharing options...
KevinE Posted September 22, 2007 Share Posted September 22, 2007 I see! Best to mention things like that in the topic from the start!! :) Link to comment Share on other sites More sharing options...
Guest joewhite903 Posted September 22, 2007 Share Posted September 22, 2007 I see! Best to mention things like that in the topic from the start!! :)SORRY Link to comment Share on other sites More sharing options...
themadhippy Posted September 22, 2007 Share Posted September 22, 2007 if your feeling adventurous how about this Link to comment Share on other sites More sharing options...
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