Erik Mandaville Posted July 26, 2003 Share Posted July 26, 2003 Good Morning! We are having some technical problems with our computer, so I want to get this contribution placed before it shuts down again... I completed my own version of Jeff Lessard's Horus amplifier yesterday afternoon. Building them was an absolute joy; however, a dull chassis punch for the 2A3 socket presented a real challange. As mentioned before, the amplifiers are built on chassis from IAG (International Audio Group). I have used silver-clad OFC copper wire insulated with Teflon, as well as a shielded input cable consisting of an all silver conductor plus silver shield. The majority of capacitors in the PSU are Solens, with Jensen oil capacitors coupling both sections of the 5687 in the input stage. The amplifier is essentially the same as Jeff's published schematic; however, I elected to incorporate what we are calling the "Western Electric Detour Connection" on the output. This is the same as the so-called "Ultrapath Connection" -- I just prefer to give credit where due in this instance. It was used many years before the "Ultrapath." I really wanted to use a cobalt output transformer, but that was simply too expensive. I am very satisfied with the permalloy OPTs, though! Also included is some transient/spike protection in the form of MOVs across the power transformer primaries. Once the wiring was done and during the initial smoke test, I discovered that I had no B+ voltage. Worried I may have an open secondary on the PT, I began to troubleshoot the problem. All voltages on the secondary windings were good, so I sat and stared at the rectifier tube wondering what was going on -- it worked fine in the Moondogs. Then it suddenly hit me that the connections on the socket didn't look to be in quite the right place. I looked very closely at the tiny numbering on the cast ceramic octal sockets, and found that the numbering was wrong! I subsequently rewired the socket, and all voltages were dead-on. The only deviation from the schematic were the heater voltages on the 5687 -- which are a little high. Jeff and I have discussed this, and think that the reason is likely due to differences in line voltage -- we are running a bit hotter here in the U.S. I will be installing a simple dropping resistor plus capacitor next week to bring this back down to a more appropriate level. Any Horus owners here might want to look at this, since it is good to keep the heater supply within a fairly close tolerance of specs for the tube. Things are not bad as is, and the tube works fine. The amplifiers worked perfectly from the first flip of the switch. As a former Moondog owner/user, I can report that the difference between the two circuits is not subtle. The Horus has transient response capability that is nothing short of stunning. It has a very quick, open, and articulate sound, which in all honesty makes the Moondogs sound dull, compressed, and closed in. I listened late into the evening to a great variety of music, and can say without hesitation that the Horus is the finest single-ended amplifier I have heard. Please lets not get into the tiresome discussion about whether so few watts can really provide the kind of power needed for accurate music reproduction. This is simply my interest, and SETs fit my taste and listening habits. ...and I have to stop writing at this point so my (computer wizard) wife can try to figure what caused this recent computer problem. I have more to say about my Horus adventure, as well as some things about its future! Incredible amplifier! A very big thanks and respect to and for its designer! I have pictures forthcoming to share with you all. This will take just a little time since a picture CD needs to be made from my roll of film. Either that, or I'll just buy a cheap digital camera and learn how to do this myself! I am so very happy with these new amps! Quote Link to comment Share on other sites More sharing options...
Deang Posted July 26, 2003 Share Posted July 26, 2003 That's great Erik, I just don't know what you're going to do with all that power. What happened with the "dull punch"? I always thought the holes were drilled out? Are you still running the Lowther driver with your Scalas? If so, do you know what the actual nominal impedance of the setup is? What load did you end up presenting to the Horus'? You mentioned being a "former" Moondog owner -- where did the Doggies go? Were you able to make the comparisons before they moved out? Weren't you running the same setup as Leo? It's surprising that there would be that much difference. I've had Jeff's schematic for these bookmarked for some time. I bring them up every now and then, and almost have myself convinced I can build a set. It's not hard to imagine the great sound there would be using a pair of these with Heresies for late night kicking back sessions. Isn't Jeff a joy to converse with? Open, honest, and of all things -- humble. Quote Link to comment Share on other sites More sharing options...
dubai2000 Posted July 26, 2003 Share Posted July 26, 2003 Congrats - having built those amps you must be proud indeed. In a sense I am glad I can't listen to them as I might find my Wrights insufficient - no, seriously: I think SET amps can be really magical, they simply seem to provide a different kind of flavour. After all, who wants vanilla pudding every day, some chocolate is nice as well (LOL). Happy listening. Wolfram Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted July 26, 2003 Share Posted July 26, 2003 Erik, Good morning, indeed! Congrats on your Horus project going so well. And thanks for the detail on the post. Looking forward to the pics, too, when you have a chance to come up for air. One thing I'd be interested to hear about: What in the way of testing equipment does it take to check out your work on a project such as this? I'm doing some reading on basic electronics, tubes, and soldering and just may get bold enough to order a Paramour kit to start out with a reasonable beginner's project. Regards, Dee Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 26, 2003 Author Share Posted July 26, 2003 Dean: my using the phrase "...former owner" was a poor choice of words,I guess. I still own the Moondogs, and they will be perfect for our 'second' system. I was just so pleasantly surprised by the difference between the two amplifiers. I told Leo about the then called 'Ultrapath connection'I picked up from the article Jack Eliano did for VTV -- which is now the amplifier sold by Welborne Labs. This has to do with a change of position (and type) of the cathode bypass capacitor on the 2A3. Leo tried it and liked it, but took his amplifiers a big leap further by using the MagneQuest plate choke and shunt feed (AKA parallel feed)OPT. I'm fairly sure Leo also got the cobalt OPT. I would really have liked to get those, but my investment in the project was already substantial for us. Jeff's original schematic does not use the 'Western Electric Detour Connection' (we seem to prefer this term to 'Ultrapath' since it gives credit to the people who first used it over 50 years), but it works so incredibly well in this application. As is, the large cathode resistor on my Horus amplifiers (which I may still call 'Icarus'!!!)is unbypassed. I will try it both ways, but the sound right now is profoundly good. (Dang! some poor guy in the Tour de France just crashed on rain-slick roads. We have the live coverage on TV right now...) Was it you, Dubai, who asked me about the Lowther/La Scala combination? I had been using the 15ohm PM2A Lowther driver in parallel with the 16 ohm La Scala woofer -- with no other drivers in the La Scala connected. The combination was really pretty good. I'm using the speakers on their own with the Horus, so I can get a better feel for how each behaves with the amps. The impedance match is not ideal, but it's easier on an amp when coupled to higher impedance than the other way around. I have the Medallion II rear-loaded horn cabinets on the inside of the La Scalas, and have worked with them in terms of position to where they both present a nice image. More than the image issue, the horns couple very well with the room, which is one of the differences I noticed when I first started using them in 1998. I had built several two way designs using great dynamic drivers (Peerless, Vifa, Audax, SEAS, etc.) and while they all could sound good, they sounded small and compressed compared to horns. For me, high efficiency seems to have an absolute correlation with detail and transient response, and it is just a kind of presentation I prefer. The Lowthers have an oustandingly good midrange, but tend to roll-off just a bit at the frequency extremes. And this last point is what shocked me about the Horus amplifiers. They are amazingly fast and articulate for a single-ended amp; indeed not unlike a good solid state design in certain respects -- but absolutelly do not have a grain of grit or ragged edge of what I have heard in some SS designs. Again, such incredibly high efficiency speakers has much to do, I think, with casting such characteristics in an even stronger light. I am also not using any of my preamps, and have the Horus coupled to my ($42 CD/DVD player -- has a good DAC, though!)by way of a two foot interconnect. I have found I simply don't need the extra gain of a preamp, since the Horus can achieve full output with 2 volts in. Modern source equipment can easily supply what I need in that respect. I am planning on building a passive volume/switch control unit based on the use of Sowter transformers. These posses a high input impedance, with an exremely low -- virtually open circuit -- output impedance. That's the problem with most passive designs that use conventional potentiometers. with a 50K pot, one might have more than 25K ohms on the output; and high output impedances have serious problems driving the capacitance of long cables.... Man! I'm just blabbing on and on hear, huh?! Yesterday afternoon was better than Christmas as a child. Not just because something I built was working well, but because it sounded so fantastically refined, and had this lucid, polished glass like quality that I had been trying to achieve with all the surgery I have done on my poor Moondogs. Lastly, I took one picture of the system, and when I stooped down to take a close-up of both amps side-by-side, I ran out of film So I'll get another roll and take some pictures of my dogs, too! You there Edster? Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 26, 2003 Author Share Posted July 26, 2003 Dee: The only test equipment I have is a good multi-meter. Some people have oscillascopes, signal generators, etc. So I have no way of measuring things like THD; and I have to say I'm glad about that!!! Such equipment can also be used to greatly help in troubleshooting problems. I don't know how many bugs I've chased down with just a multi-meter, though! One check faulty diodes, open or shorted transformer windings, and so forth. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 26, 2003 Share Posted July 26, 2003 Okay Eric I'm going to let the Cat out of the bag here. I purchased Jeff's last set of Horus Chassis and plan to build a set myself and was waiting to see how your corner cutting on the transformers worked out. While this is all fresh in your memory I'm going to call in the favor you owe me . Could you make me a complete parts list with part numbers and where you purchased them for these amps. I seriously don't think these amps will be my cup of tea but I figured on the 2A3 SET choices these would be the best amps a guy could try and selling them would be a breeze if I decided to do so. Craig Quote Link to comment Share on other sites More sharing options...
AnalOg Posted July 26, 2003 Share Posted July 26, 2003 Erik, Great stuff, I could almost hear your system with the details you've given. Oh by the way, GET A FRICKEN DIGITAL CAMERA! ----------------------------------------------------------------- I'm doing some reading on basic electronics, tubes, and soldering and just may get bold enough to order a Paramour kit to start out with a reasonable beginner's project. ----------------------------------------------------------------- Dee, Just upgrade the Paramours with better iron and choke, don't forget the cap. If that experience suits you, build the Foreplay with all the modds, it's a sweet little line stage coupled with the Paramours. Tom Quote Link to comment Share on other sites More sharing options...
AnalOg Posted July 26, 2003 Share Posted July 26, 2003 Craig has gone over to the DARK SIDE! Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted July 26, 2003 Share Posted July 26, 2003 ---------------- On 7/26/2003 9:02:38 AM rf3iicrazy wrote: Dee, Just upgrade the Paramours with better iron and choke, don't forget the cap. If that experience suits you, build the Foreplay with all the modds, it's a sweet little line stage coupled with the Paramours. Tom ---------------- Tom, Yep, have already ordered the iron and cap upgrade from Bottlehead. Being a tech newbie AND weinie, Craig is going to back me up if I decide to punt. Dee Quote Link to comment Share on other sites More sharing options...
dubai2000 Posted July 26, 2003 Share Posted July 26, 2003 And he'll reappear enlightened Wolfram Quote Link to comment Share on other sites More sharing options...
AnalOg Posted July 26, 2003 Share Posted July 26, 2003 Dee, The Paramours were my first attempt at any soldering & building of a electrical component. If I can do it, anyone can. Just practice your soldering first on a bread board with hook up wire & cheap resistors, you can get this all at Radio Shack. Remember: Before you touch anything under the hood, make sure the caps are discharged. It gives you a hell of a sensation, I KNOW! Piece of cake!! Tom Quote Link to comment Share on other sites More sharing options...
rtaylor Posted July 26, 2003 Share Posted July 26, 2003 Craig,you have gone to the dark side! bad! Randy Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 26, 2003 Share Posted July 26, 2003 Craig has gone over to the DARK SIDE! No he has not I think you know me better than that !! I just feel that being in the business so to speak I owe it to my customers to have a handle on what all different types of amplifiers sound and what they can and can't do. I've never had a top quality set of 2A3 SET amps here to listen to on my own system and after a few members here have turned down free repairs on there SET amps I have realized there is only one way I will ever get to hear them on my own system is to build them. Like I said I can always sell them ! Craig Quote Link to comment Share on other sites More sharing options...
rtaylor Posted July 26, 2003 Share Posted July 26, 2003 Eric, where is Paramoor sp? located? Quote Link to comment Share on other sites More sharing options...
AnalOg Posted July 26, 2003 Share Posted July 26, 2003 Trust me, I'm very familiar with Craigs listening habits and musical tastes. He'll have the Proud Poppa Syndrome, then he'll pass them on for lack of power. Tom Quote Link to comment Share on other sites More sharing options...
Deang Posted July 26, 2003 Share Posted July 26, 2003 Well Craig, I think you're making a good move. Especially since I know it's common for you to be slinging solder until 1 AM. No one here has cornered the market on the best sound at all volume levels, with all types of music. Personally, I can't think of a better way to go for late night listening, or for those times you just don't feel like "jamming". I know folks here have this perception of us sitting around with blood running out of our ears, but we both know we mostly enjoy playing up the power thing for fun. Not that it isn't important to us, but it's not like we listen to 90 to 110 db every time we turn the system on. I do think plenty of power is important, and more times than not I'm glad I have it -- but since I've lost the Cornwalls and Scott, I have nothing available to me past 10 PM. Even if I had a system after 10 PM -- it would be for 80db and below. I can't think of a better application for good SET than this. I think it will be your cup of tea. Good amps sound good, and I believe a pair of Horus' probably sound outstanding. I'm sure you'll have no trouble figuring out how and when to listen to them. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted July 26, 2003 Share Posted July 26, 2003 Owe and folks I'm going to have a nice new NOSValves product offered up and it will have some major balls !! like 60 clean watts this should debut in the fall sometime ! The details will be released when there available ! The transformer have already been custom specified and I'm waiting for the first set to arrive. Then I have to figure out what chassis to use and so on and so forth. Craig Quote Link to comment Share on other sites More sharing options...
AnalOg Posted July 26, 2003 Share Posted July 26, 2003 Now thats what I call a teaser ad. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 26, 2003 Author Share Posted July 26, 2003 Craig: That's neat about the chassis. The complete parts list for the Horus is on the MagneQuest website. I have the URL someplace, and can certainly get that to you -- I'll help however I can. The only corner I really took on the transformer issue has to do with the fact that the OPT I'm using is permalloy rather than cobalt. Jeff happened to have a pair of 8 ohm peramalloy on hand, and I bought those. Otherwise, the grid and plate loading chokes are the same. I bought the power transformers from AES, as well as the filter chokes, dual 100mfd filter capacitor, and all of the Solen capacitors. I baught all my resistors at a small, well-stocked store in Tucson, and got all the rest of the stuff from Mouser. To save money, the original plan was to make this a stereo amplifier, and I bought a Hammond chassis for that. After that was all punched and drilled, I decided to purchase chassis for monoblocks from a company called IAG here in TX. I had seen the website a couple of times, and Jeff (a good guy!) reminded me of what fantastic chassis they sell -- extremely high quality, with very thick aluminum and solid, machined aluminum feet. I have always thought the utilitarian sort of look had a certain charm, but after the investment I made, a really wanted to build a pair of really nice-looking monoblocks. So I ordered the extra power transformer, filter chokes, etc. to make two mono amplifiers. If you build these, there are a couple of things (small things) to note on the schematic (which I printed off the MagneQuest site), and I can mention those down the road. I had not planned on that output connection between the bottom of the OPT primary and cathode, which involves a monster of a capacitor -- the big 47mfd Solen. This required some really major and careful work in order to make enough room, since another 47mfd poly cap is also used as the input capacitor from the PSU to the 5687. I was still able to achieve a neat appearance, and was able to maintain reasonably good distance between the power supply and signal portions of the amp. I actually am using a total of 57mfd. on that output capacitor, since I added another 10mfd Solen I had from the original version of the schematic. This is the same connection I made on the OPT of my Moondogs, but it works even better in this case. Ok! I just finished a second roll of film, and will take that to have a picture CD made. It's true, I really need to get with the times! Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.