Painful Reality Posted July 30, 2003 Share Posted July 30, 2003 For those interested to build one or just see what it looks like here is the schematic. You'll notice that it is deceptively simple. Pretty much unfashionable too these days. It's nothing new under the sun, the circuit being a simple SRPP. Having tried both a cathode follower and a SRPP circuit for this linestage, I prefered the later. The aim of this linestage was to achieve good performances with a simple circuit without any esoterics (output transformers, CSS, etc.). Is it the ultimate preamp? Me think not... Is it a really good preamp, one that's easy to build and one that won't cost you a fortune (providing you don't go crazy with the parts)? Me think so... My advice only advice, keep the dual chokes and the tube rectification in the PSU. It add to the cost but gives you a much more relaxed presentation. If cost is that much an issue, replace by SS rectification and swap the chokes for dropping resistor (you're on your own in this case). In the eventuality you are interested in this preamp but a soldering iron is a weapon between your littl'hands, ask Erik Madaville politely. Don't be afraid to get him busy. I had to work hard enough to convince him so he will continue the build the Horus instead of me. I feel this little 2A3 amplifier deserves to survive my laziness. (Edition) For some obscur reasons the attached file just disapeared into the digital ether. Go figure!!! Quote Link to comment Share on other sites More sharing options...
Painful Reality Posted July 30, 2003 Author Share Posted July 30, 2003 BTW, You'll notice that there is no volume pot on the schematic. Put either one (100K value) after the line selector switch or after the preamp itself (in this case I'd go for a 10K value). Quote Link to comment Share on other sites More sharing options...
sunnysal Posted July 30, 2003 Share Posted July 30, 2003 problems soldering? call me "the terminator" I only hope my bad sodlering doesn't mean extra work for you in the near future! I owuld love to tackle a DIY preamp BUT I worry that I do not have the skills...some day perhaps. tony Quote Link to comment Share on other sites More sharing options...
Painful Reality Posted July 30, 2003 Author Share Posted July 30, 2003 Having found the upload function, and not feeling like working on my PhD, I'll use it. Here is a little SET amp using a WE417A or a 5842 cap coupled to a VT52. This is a nice simple design. Totally different from the Horus soundwise. This amp is not as versatile but if you are exclusively into Jazz trio and chamber music stuff, it might be the ticket. The TFA-2004 OPT might be replaced by a EXO-035 or EXO-036 from MagneQuest. Main drawback of this amp, the VT52 ain't build by anyone since the late 40's I think. You still find them easily though. One solution would be to replace the VT52 by a 6A3 (much cheaper and somewhat common). It's a direct replacement. Be warned, working with a WE417A might be a b**ch due to the extreme bandwitdh of this tube. Credit for this amp goes entirely to Gordon Rankin from Wavelength Audio. Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted July 30, 2003 Share Posted July 30, 2003 Jeff, thanks for all the goodies. I think our friend Eric (not Erik) will be interested at attempting the Pantheon as well. BTW, did I miss the Pantheon spec above? This forum has a nasty habit of occasionally dropping attachments. Maybe you could upload and post one more time? Thanks! Quote Link to comment Share on other sites More sharing options...
Painful Reality Posted July 30, 2003 Author Share Posted July 30, 2003 You missed it Chris... Geez I guess this the "Mission Impossible" forum where the attachement self destruct after being read. Here it is again. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 30, 2003 Share Posted July 30, 2003 I have a German background, Chris. Eri(k), as Jeff had spelled it, is actually correct. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 30, 2003 Share Posted July 30, 2003 Ah! You are talking about the rocket scientist Eric, no??? My mistake and apology, Chris... Eric -- I mean, Erik Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted July 30, 2003 Share Posted July 30, 2003 Ja, das ist recht. Es ist der "ear-splitten-louden-boomer" Eric Quote Link to comment Share on other sites More sharing options...
Painful Reality Posted July 30, 2003 Author Share Posted July 30, 2003 Last one... for the PWK fans here. Here is a nice 2A3 PP amp that should be a good match with K-Horns (according to Sunnysal of course, me I would personally use nothing but a Krell coz' I am an audiophile!). This is a really simple circuit that is somewhat inspired by the Sun Audio 300B PP amp. Since I am a sucker for punishement, I have to post it with Lynn Olson and Gary Dahl around. For those who don't know, these two guys have designed what must be THE absolute 2A3 PP, the Petite Amity. Compared to the Petite Amity the circuit I am presenting here must be a mere toy. But a really nice toy indeed. If your looking for the ultimate check the Petite Amity at: http://www.nutshellhifi.com/IT-Triode-Amp.gif If you are looking at your first DIY amp instead. Download the attached file. C+ value is missing on the schematics. It should be around 180-190V Jeff L Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 30, 2003 Share Posted July 30, 2003 Jeff, Why don't your schematics look like the Amity Craig Quote Link to comment Share on other sites More sharing options...
Painful Reality Posted July 30, 2003 Author Share Posted July 30, 2003 ---------------- On 7/30/2003 5:34:36 PM NOSValves wrote: Jeff, Why don't your schematics look like the Amity Craig ---------------- Instead of drawing, I'm building... Quote Link to comment Share on other sites More sharing options...
mike stehr Posted July 30, 2003 Share Posted July 30, 2003 Thanks Jeff. I have them downloaded. Pardon my ignorance, I've never seen power run from the center tap of the rectifier filament/heater winding. I'm used to seeing it come off the Cathode of the rectifier itself. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 30, 2003 Share Posted July 30, 2003 Jeff, Quote Link to comment Share on other sites More sharing options...
Dflip Posted July 30, 2003 Share Posted July 30, 2003 For the Amity here is some additional information from the website. This is a very particular amp, it only likes certain types of preamps. He also designed the Aurora which has several versions, all of which required higher levels of skills for soldering, reading drawings and lack of stupidity or skill. http://www.nutshellhifi.com/triode1.html Although the Amity is a beautifully simple design, it makes severe demands on the preamp. The preamp has to drive the combined capacitance of the interconnect cable, the input transformer, and the Miller C of the input tubes. This can easily add up to 200 to 600pF of capacitance, depending on how long your cables are and if you choose to use a 1:2 step-up in the input transformer (which quadruples the Miller capacitance of the input tubes). In all honesty, this is just too tough a load for most tube preamps, with 12AX7 cathode-follower preamps falling down the worst. (1mA cannot drive 600pF!) Preamps with 12AU7 cathode-followers aren't much better, sounding very "tubey," rolled-off, and old-fashioned. The same preamps can sound great driving a conventional power amp, so it's clearly an interface problem. (Passive preamps cannot be used with the Amity since the input transformer must be driven with less than 600 ohms source impedance. A passive preamp using a 10K pot presents 2.5K source impedance to the power amp in the -6dB position, which will cause a significant decrease in transformer bandwidth. No harm to the Amity will result, just degraded sound quality.) Quote Link to comment Share on other sites More sharing options...
Painful Reality Posted July 30, 2003 Author Share Posted July 30, 2003 ---------------- On 7/30/2003 7:29:37 PM mike stehr wrote: Thanks Jeff. I have them downloaded. Pardon my ignorance, I've never seen power run from the center tap of the rectifier filament/heater winding. I'm used to seeing it come off the Cathode of the rectifier itself. ---------------- An "old dog" teach me this trick whenever you have a rectifier filament winding with a center tap. Taking your voltage rail from the CT should make the wear on the rectifier plate equal. Old wive's tale or reality... no idea. DFlip, Thanks for putting this link as a reminder than in this case, ultimate comes with a price... a new preamp for 90% of the people! Quote Link to comment Share on other sites More sharing options...
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