Erik Mandaville Posted July 14, 2004 Share Posted July 14, 2004 I've recently had the pleasure of performing general maintenance and repair work on Edster's very fine pair of JFL 2A3 Horus monoblock amplifiers. In addition to this work, Edster also had shipped to me from Transcendent Sound, a Grounded Grid preamplifier with stepped attenuator upgrade. These two projects have taken up the last few days, and I thought it might be of interest to some to see and read a little bit about what has been going on. There has been a veritable camel's back worth of information and discussion on this forum concerning Jack Eliano's 'Ultrapath' connection, and I will leave the majority of the history and description of the circuit out of this thread. For those interested in learning more about it, I can provide a link to a more comprehensive source of information. The following is a list of the primary things I did to Jeff Lessard's amplifiers: 1)Ultrapath connection using a total of 57uf from the OPT primary to cathode 2)Removal of the bypass capacitor from the 2A3 cathode resistor 3)Installation of a 100uf Black Gate capacitor across the input cathode resistor (which is a more common practice than leaving it out). The technical explanation behind my reasons for this will also not be included here. It comes down to a personal preference issue, however some of the benefits of the practice include an increase in gain and greater bandwidth -- some say at the cost of a slight increase in distortion. 4)Drilling the chassis to accept heavy-duty binding posts. 5)1 tube socket pin retaining clip broke away from the 2A3 socket in each amp, and new sockets are now on order -- along with a pair of 5687s for myself (more on that below!) 6)Reversal of the orientation of the 2A3 socket to put the filament connections toward the power supply end of the amp. 7)Add dropping resistor on 5687 heater supply to lower it from 7.28 volts. First and foremost I would like to say that it was a pleasure to be able to work on these amplifiers. Having built my own version of the design last year, I am very familiar with the circuit, and Jeff did an exceptional job with these. The straightforward and neat layout of the wiring made working on them very intuitive. The size of the chassis is perfect for the parts within, and I wish when I built mine that I could have afforded the same quality I ended up with, but slightly larger in size. Cost is what prevented that, however. Lastly, with one amp completely Ultrapathed, it was tested in the system with one of my own amplifiers in the other channel. The new Horus is incredibly hum-free for a directly heated amplifier, and I noticed it was also about twice as loud at the same volume as my own amplifiers (which, seemingly like many DRDs, need a little extra preamp gain to bring them to life). But! There was something truly special about Ed's Horus. It had a realness or palpability in terms of how it played music that was different from both my own former Horus and the current DRD parafeed amplifiers. I had actually forgotten that Ed had OPTed for the cobalt parafeed transformers, and I emailed him about that. He answered in the affirmative -- and with one of these: The preamp being used at the time was the Grounded Grid I had finished the day before, and the GG/Cobalt Horus combination was something really special. So, it seems I had not heard the Horus in it's best voice. I have preferred my own DRD parafeed combination to the Horus I had made, but the cobalt version of the amplifier(which I could not afford)is something to which I have decided to return. I have a dedicated drawer in my parts bin with the Horus input/driver sockets, as well as the cathode bias resistors and all parts needed. I plan to start saving for the cobalt OPTs (they are not cheap), and want to rebuild the Horus amplifier with cobalt on the outputs. I already have the Ultrapath connection in my amps, so don't need to worry about that. So: DRD 2A3 Parafeed/Ultrapath v.s. JFL (Cobalt)2A3 Horus/Ultrapath -- and the winner is...............I honestly believe it to be the Horus. I think the Ultrapath is an outstanding modification to this amplifier, and the cathode bypass on the front end is something that can easily be reversed by Ed if he so chooses -- CLIP! A couple of very poor quality pictures (sorry!)follow. edit: Is there any way to correct the spelling in a subject heading!? I forgot an 'n' in Transcendent! Erik Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 14, 2004 Author Share Posted July 14, 2004 Well, I hope I reduced this correctly. This is the interior after the Ultrapath was installed. The Ultrapath cap is the big Solen with the red zip ties. edit: Well, may attempt to flip the orientation of the pic from horizontal to vertical failed.... Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 14, 2004 Author Share Posted July 14, 2004 Here's a fuzzy picture of the new GG with the extra pair of inputs (total now 4) as seen on the back of the chassis. Quote Link to comment Share on other sites More sharing options...
Speedball Posted July 14, 2004 Share Posted July 14, 2004 Look's like a clean job to me! ...... ...... Pat Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 14, 2004 Author Share Posted July 14, 2004 If you are considering a stepped attenuator kit, this one is really well done and reasonably priced. The resistors were installed with tweezers since they are extremely small, and you need a good iron with a very fine tip for detailed PCB work. This control works very well. Quote Link to comment Share on other sites More sharing options...
3dzapper Posted July 14, 2004 Share Posted July 14, 2004 Erik, What is the source for the 55uF capacitor? Do you use the recommended PIO? Here is a poor klutz' with big hands stepped attenuator: Alps Blue Rick Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 14, 2004 Author Share Posted July 14, 2004 Hi, Mark..and thanks. I don't know that there is a benefit. I was commissioned by a friend to put the preamp and attenuator together, and I thought I would post a pic of the control for those who might be interested. Like seemingly everything we discuss, there are opinions on either side of the fence concerning the use of a variable log control (inexpensive or more so) or fixed, high quality resistors that approximate a log taper in individual steps. If someone were to use a single volume control without balance or level controls (which is what I did on Wolfram's GG -- his does have level controls for each channel), I would think that using close tolerance resistors between each section (right and left)of the conrol would perform better in terms of tracking. I have almost never used anything better than Alpha pots that cost a few dollars. The attenuator kit is a nice one, though, and some might prefer it to carbon comp potentiometer without detents. In theory, I guess, a quality metal film resistor might be a superior resistive element compared to a carbon strip. Should resale of the preamp ever become a consideration in the future (not that any of us ever change our equipment!) a stepped attenuator might add to the value of the component. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 14, 2004 Author Share Posted July 14, 2004 Cardas binding post upgrade Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 14, 2004 Author Share Posted July 14, 2004 That attenuator looks really nice, Rick! The 57 uf is a paralleled combination of two 630volt Solen capacitors -- 1 at 10uf, the other large one at 47uf. The original oil cap, which is sold as an upgrade with the Welborne DRDs is what I think you are talking about. I honestly could not hear the difference between the two, and I already had the 47uf caps on hand. The extra 10uf capacitor came from the hum cancelling circuit in the original Horus design. The Ultrapath offers isolation from PSU issues, and the amps are very quiet without it. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 14, 2004 Author Share Posted July 14, 2004 Not so far, but I am not testing in ideal circumstances. The preamp as whole sounds very good, but whether the attenuator has anything to do with that would really require switching between it and a carbon comp, listening at the same level to the same music, etc. -- and soliciting as many opinions as possible -- to set up a more controlled experiment, in other words. It's a good quality switching device, though. I kind of like the concept of the signal going through one individual resistor at a time, but liking a concept has nothing to do with it's efficacy in terms of performance. Quote Link to comment Share on other sites More sharing options...
edster00 Posted July 14, 2004 Share Posted July 14, 2004 I am looking forward to getting the Horus back so I can hear the difference in the circuit (I hope I can hear the difference). I am also looking forward to hearng the GG preamp since I have read so many great comments about it. I thank Erik for all the work he has done on my behalf! Quote Link to comment Share on other sites More sharing options...
jt1stcav Posted July 14, 2004 Share Posted July 14, 2004 Erik, yer da man! Quote Link to comment Share on other sites More sharing options...
ssh Posted July 15, 2004 Share Posted July 15, 2004 Interesting post, Erik. I'd like to hear Jeff's comments. The design of my 2A3 monoblocks is a little different from the Horus, but they do have the cobalt transformers, and I'd say, "Save away". I didn't think they were currently available, but Jeff may have been brand-specific when he told me that. Once again, you've posted an informative, thought-provoking thread, with make-me-drool pics of your work. Nice job. SSH Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 15, 2004 Author Share Posted July 15, 2004 Thanks for the kind words. ssh: The Ultrapath modification is one that Jeff heard and saw in LeoK's converted Moondog amps. Leo tried this small circuit change after I had posted the results of my own experiment, also using my Moondogs as the platform. It's one that JFL liked, and I built it into my own Horus amps from the beginning. The change is not necessarily one that will make an amplifier sound like a totally different component, but one that provides both power supply isolation and very likely a little more detail. So, I hope Edster is not expecting a jaw-dropping experience, but I sure liked what I heard after I had finished the first channel! The Welborne Labs website has quite a bit of information on Eliano's Ultrapath, and is a circuit brought back to life from the time of my parent's childhood! It works very well, I think. I felt comfortable making these changes in Jeff's Horus, knowing that he also seemed to prefer the Ultrapath after hearing LeoK's amps. Otherwise, this pair of Horus is largely intact. The only other thing I did was add an easily-clipped-out (if desired) Black Gate bypass capacitor on the input stage cathode resistor. Some take that out as a subjectively more 'pure' route, but I think there are some worthwhile benefits, including lower the output impedance to the following stage, an increase in overall gain, and likely improved bandwidth of audio frequencies. It's not at all critical to the circuit. Like my Horus built on the same schematic, the 5687 (input and driver) had almost a full volt over spec. on it's heater supply, and that's something that can shorten tube life and reduce performance if it goes on for a long period of time. I put in a dropping resistor I had on hand to bring it much closer to 6.3 volts. Just a little preventative maintenance. Hi, Jim! Erik Quote Link to comment Share on other sites More sharing options...
ssh Posted July 15, 2004 Share Posted July 15, 2004 My experience has been that otherwise small (or, based on other's doubts that there is an audible difference, negligable) additions to the stream can make a significant difference for one who has spent time listening to a high quality amp before the additions were made. My bet is, that Edster gets a little excited with the improvement... once he survives the anxiety of waiting to get to hear it. SSH Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 15, 2004 Author Share Posted July 15, 2004 I sure hope so! I sincerely appreciate the trust he (and others!)have shown in allowing me to work on their much valued, often quite costly components. The really beautiful chassis that came with the amps are now getting a few hand-rubbed coats of tung oil, and look absolutely stunning! I appreciate your comments and support Ssh! Erik Quote Link to comment Share on other sites More sharing options...
Daddy Dee Posted July 15, 2004 Share Posted July 15, 2004 Erik, Last year when I got the Wright's you mentioned some possible mods. Was ultrapath what you were thinking? I've been wondering about that very thing. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted July 15, 2004 Author Share Posted July 15, 2004 Hi, Dee! Indeed it was! The Wright 2A3s have gotten great reviews from those who use and support low power SET amps, but my feeling is that they probably don't have the this so-called Ultrapath connection. More likely, a more common cathode resistor of approx. 750-1K ohms, and 100uf or so electrolytic bypass capacitor of that resistor. If you could send me a picture of the inside of the amps, I could draw a schematic from that (with only roughly derived values for caps and resistors, though). Quote Link to comment Share on other sites More sharing options...
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