Chris Robinson Posted January 17, 2003 Share Posted January 17, 2003 Leo, nice write-up ... I'm REALLY looking forward to hearing them. In fact, I've never heard RF-7's, and that would be a real treat for me. So if you've got the time, just let me know and I'll swing by on the way home some evening. Of course, you are very welcome to come on out to the boonies ("it's not the end of the world, but you can see it from here ...") with whatever you'd like to bring, and we'll do it up. I would love to hear your Moondogs with the Klipschorns; that would provide me with the last possible upgrade path from the Wrights (which I love). I don't think the Pantheon will be up here until mid/end-February at the earliest, so you have plenty of time to run those 'dogs into a fine groove. PS: Craig, it's not the signature version; just a "plain old" -3. It actually has a very nice, small footprint and besides for sounding great, it looks great sitting between the two Wrights Quote Link to comment Share on other sites More sharing options...
Audio Flynn Posted January 17, 2003 Share Posted January 17, 2003 LEOK, The ability to perceive amp "voicing" or character and matching to speakers is more surprising to me than expected. The RF-5 demo I heard 2 weeks ago with Aragon and Rotel high power SS was the worst sounding Klipsch I ever remember hearing. The experience does encouage me to pursue different low power amps new and old to experience with the Chorus IIs. "Builder" has that old HK SS he likes; I will keep an eye open at yard sales in the spring for that one. I wish I had my old Marantz 2225 to try. I really like the P6D PWM. Hard for me to pass on assessing new technology. Non-fatigueing and neutral are the 2 terms that come to mind first. Initial review later in the weekend. The SET is great to read about but finances will most likely keep me looking for the best deal on an Eico or Scott for most of this year. Mobile, It is great information to read that you post. I save many of your posts for my son and I to reference years from now. With Daughter and wife both needing tuition support currently it will be quite sometime before I can explore the active tube preamp endeavor. Thanks to all for the great information! Rick Quote Link to comment Share on other sites More sharing options...
leok Posted January 17, 2003 Author Share Posted January 17, 2003 Audio, Glad the P6D is working out. It gives you an opportunity to really enjoy those Chorus-IIs while you decide if you want to do something else. leok Quote Link to comment Share on other sites More sharing options...
Deang Posted January 17, 2003 Share Posted January 17, 2003 Yes, SET is wonderful, and I love my Apollos - however, I love the sound of the Scott as well, and if it was the only thing I could have -- I would be perfectly content. Yes, they sound that good. Keep looking. Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted January 17, 2003 Share Posted January 17, 2003 Thanks for the comments, Rick. Good stuff is getting cheaper and cheaper... and it's easier to sell gear now than ever in history. Leo, glad you like your Moondogs. Some nice comments about them. As much as you like them now, they will actually only get better. I think the low end of the watt scale is where the magic is with SET amps. Tried to convince Dean on this, but he'll find out someday. The vintage amps definitely have a magic that is hard to beat. But a good SET amp is more open and in the air...the sound actually leaves the gear and speakers, and starts to actually exist on its own, apart from anything. This strange separation is almost exclusive to the low watt, zero feedback, single ended triode domain. To put it in succinct fashion, there is nothing like the sound of SET. But Dean is right in taht some of these vintage amps, judged on their own, can make one forget the quest for something around the corner. At least for a while, anyway. kh Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 18, 2003 Share Posted January 18, 2003 That's great about your new amps, Leo! I really love mine, although I use a 5Y3 rectifier in 'em. I agree with KH on his take on the Sovteks -- you should really get some of those, and they just can't be beat for the price. I'm curious what you did to the ground lead on the filament supply to the 6SN7s...would you share that with us? On the preamp issue: I went the passive route for awhile, but it simply doesn't have the jump and sparkle that a good active gain stage has. For me, music was present, but just seemed rather deflated to me. Here's what you can do, though: If you want to compare the difference between active and passive preamping, they are really, really, easy to make from scratch (yeah, I know....here I go again, right?). Everything you need for one is at your friendly Radio Shack! Cheap plastic chassis RCA jacks two 10k log-taper volume controls a couple of plastic knobs All a passive preamp is, of course, is a potentiometer between your source and your amplifiers. CD players will put out about 2 volts, which is more than enough for the Moondogs. For best results, though, you've got to have the preamp within say a few feet (or closer!) of your amplifiers. Otherwise cable capacitance becomes and issue, and you'll lose some high frequency reproduction. This is also why 10K pots are better than 50k or 100k -- the higher output impedance of the 50k or 100k volume control can have trouble with longer cable runs. The downside of a 10k control, is that it's lower input impedance requires turning the volume control up a bit higher to get adequate volume. I actually removed the 100k resistor on the grid of the first 6SN7 on the Moondogs, and installed a 100K volume control in it's place -- which is just a passive preamp installed on the amplifier, itself. I found this very helpful with active gain, since many tube preamps can have pretty high gain. In otherwords, it's possible to impose too much gain on the amp input, and cause buzz, distortion, and other yuk stuff. I suggest you also check out the Ultrapath line stage at Welborne Labs. It's about $300 cheaper than another one in question, here, and has a gain of under 6dB, which is really ideal for the Moondogs. also consider these: I have a copy of the original Ultrapath schematic by Jack Eliano, and it is quite easy to buid, but does not use a battery supply. If you're interested, I also have a 5Y3 rectified, dual 6SN7 preamp schematic by Eric Barbour -- whose knowledge of tube audio and hollow state technology is extensive, to say the least! He designed a truly fantastic linestage, which is based on a single sub-mini tube -- I have lately been comparing this single tube/SS hybrid to my AES preamp (AE-1), and this tiny little tube can nearly keep up with 4 6SN7s! Bottlehead Foreplay: A truly great kit, which uses a direct-coupled cathode-follower topology. It's an OUTSTANDING value at under $200. I built a tube rectified version of this thing, which is really great! Grounded-Grid Preamp: Offered by Transcendent Sound, designed by Bruce Rozenblit, who is a very talented and experienced designer. I think the kit version of this, complete with a high quality chassis, is around $400. I built an SRPP preamp by Rozenblit some years ago; and although a good performer that taught me lots in the building process, just doesn't have the 'drive' and presence of a low output imped. cathode follower. The Grounded Grid has gotten some really good reviews. ...I had a thought last night about modifying the cathode bypass on the Moondogs to an Ultrapath output. Have to have a look at the schematic to see if this might be possible. Anyway, do consider a quick, homebrew passive line stage. They can be made in a 'snap,' and you just don't need to spend $300 to see what it sounds like compared to active gain. If you like it, get a couple of good Noble or Bournes pots, some decent RCA jacks, and you'd have a passive as good or better than what's available at exponentially higher prices. The passive I built had the interconnects connected directly to the volume controls, thus doing away with yet another point of possible oxidation, poor ground, etc. Let me know if I can help! Erik Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted January 18, 2003 Share Posted January 18, 2003 Erik, I do believe he HAS a passive line stage. IT IS all he is using. It is a Creek OBH-12 with an ALPS pot. kh Quote Link to comment Share on other sites More sharing options...
leok Posted January 18, 2003 Author Share Posted January 18, 2003 Erik, I am currently using the Creek OBH-12 passive. Interconnects from sources are .5M, with a 1M pair to the amps. I've copied your note as a reference if I do begin a line stage investigation. Right now I have plenty to keep me occupied like: Is your reference to the "cathode bypass" on the Moondogs, by any chance, C5? What do you think that cap does? Up until now I've left it out of the circuit because I want to better understand its impact. I'm about to insert it. I don't need the extra gain and I thought that if it has the usual electrolytic increase in ESR with frequency, then it will act as a mild bass boost. I hope it doesn't mess up those totally transparent highs. Well, I'll know in a few hours, or days if I have to let the cap settle down. I promised myself I'd listen to this amp Ron's way first. After all it's his design. If that wasn't what you were refering to, I'd still be interested in your thoughts on the C5 contribution. If you were refering to C4 .. well, what I really have to do is understand what "Ultrapath" is. I'll check Ron's descriptions. If things don't have to be grounded I normally let them float and attach them to signal or chassis ground via a big resistor, like 1M Ohm. I did this in three places on the Moondogs: 1) Main ckt Gnd to chassis (this minimizes ground currents betwen amp and source) 2) Speaker-side output transformer "Com" to chassis (this keeps common mode EM racket picked up by the speaker wires out of the main ckt (and audio) Gnd. 3) 6SN7 DC heater ckt to main ckt Gnd (this was the mistake, but I don't know why). I've left 1) and 2) in. I had thought the 5U4 was the appropriate replacement for the rectifier. I'll look up the 5Y3. Sovteks are on the list. By the way, now that I have the tubes from ETOLS, they look more like Tungsol in the picture: http://www.tubeworld.com/2a3.html They are branded "Champion" from France. Thanks, Leo Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted January 18, 2003 Share Posted January 18, 2003 Leo, so you dont have the Mullard GZ-37? Also, remember Erik's take on sound and what you find best can be different from his point of view. He is not a fan of oil caps as he feels they compromise the high end. These kinds of points are important in understanding someone's perspective. For example, although Erik and I both have Moondog 2A3 amps, they are vERY different from one another in the fine points. He goes for a totally different type of sound as well, evidenced by the Transient Grid Pre rec and the dislike of oils (I also have Audio Note Tantalums). Neither is wrong per say but something to be aware of. I personally find the oils offer a more natural reproduction of the high end, and have noticed that people that dislike oils, whether for measurement or listening, prefer a more highlighted high frequency range. AGain, it is just perspective and taste, as well as what one is used to. I believe Erik also employs Mylars as coupling caps. On another note, ole Ron didnt really design the Moondogs circuit exactly although he modified it from others. It's actually been around for a longer time in one form or another. It's a more traditional approach to SET design but one that is very hard to foul up. There are many, such as Thorsten Loesch, that prefer other designs (interestingly enough, he also has a distaste for oil caps). I strongly advise listening to the amps and letting them breakin before doing any big time mods. Also, finding the right tube combination is really important to getting them to sing. I believe Erik does not like hte GZ-37 in the rectifier spot either but I prefer this to the GZ-34/5AR4 although I was using the Sovtek. The GZ-37 has the most relaxed and sublime midrange. kh For those interested, here is another GREAT wiring job with battery bias and a number of other tweaks including caps and silver wiring. This is SPROCKET's amp he procured for a very reasonable price. Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted January 18, 2003 Share Posted January 18, 2003 So Kelly, what IYHO is the rectifier of choice for the Pantheon pre-amp? I hope you haven't already answered it somewhere else that I might have missed. Thanks. Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted January 18, 2003 Share Posted January 18, 2003 Mullard! Heh... Jean-Francois is throwing you an email. 5R4 will work and is cheap. Ditto with 5Y3. I love Mullard rectifiers but they are getting $$$ and they dont have all types. You can get the break for Mullards that arent identified on label. kh Quote Link to comment Share on other sites More sharing options...
leok Posted January 18, 2003 Author Share Posted January 18, 2003 Kelly, The Rectifier is a GZ-37, 1967 vintage, maybe it's Mullard. I can't tell. The box looks military. I inserted C5, and certainly don't like what it does after 10 minutes of burn-in. So, I'll give it a few days. The high end perfection is gone. It sounds like an amplifier. A very good one. Is that where the battery bias is applied in SPROCKET's amp (1st 6SN7 stage)? The reason I tried no-C5 1st is no burn-in is required to evaluate it. After a few days I'll disconnect C5 and see if there is an improvement. I think C5 is a big voicing factor and I want to understand it before I move on to things like $80 tubes. As far as oil caps .. I like that direction. leok Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted January 19, 2003 Share Posted January 19, 2003 Hey, Leo: Guess I missed where you mentioned your Creek passive! No wonder I was always having to go to remedial reading when I was in school! My brother has the same Creek unit, but uses it to balance the output level in a bi-amped system. Anyway, it sounds like you have a great set up. Kelly is providing really sound advice, Leo. As he has suggested, I think it a good idea to build the amp as originally designed, get very used to its sound, and then experiment one step at a time. That way, you'll have a much more educated idea about changes your making. Like Kelly, my Moondogs are now, years after I built, to where I'm comfortable with their performance. I'm surprised to that he remembers what capacitors I'm using, which are very inexpensive mylar caps. These are certainly 'brighter' sounding than the Hovlands, which are still good capacitors. Much of my reason for voicing the amps like this has honestly more to do with my increasing inability to clearly hear high frequency information. The AE-1 preamp I recently repaired had all oil capacitors in the signal path; and while I thought the preamp sounded very rich, it had a 'dark' quality. I have poly caps in those spots now, and it has been an improvement for me. The oil capacitors are of a very good quality, though. Ok, on to a couple of other things before this gets too long! C5 is an important part of the input stage, and I would include it as shown on the schematic. I know you said you don't need the extra gain that bypassing provides, but it also influences impedance characteristics of the tube -- which subsequently becomes important to the following stage. Increased distortion resulting from degeneration (inverse feedback)is another possibility that might result from not bypassing the cathode resistor. In other words, it's function has more to do with balancing things out than it does with the subjective perception of the amp's characteristic sound. Degeneration is sometimes used in output circuits to improve linearity and distortion, but in my opinion, this situation is different. I obviously need to go and study this stuff some more in greater detail, but I would leave that in for the time being. Or get in touch with Ron Welborne about it for hopefully better clarification. I think you will find his response probably shorter than this! High voltage rectifiers: I also don't listen at very loud levels, and also found that my vintage RCA 2A3s were being driven 75 volts beyond their maximum RCA manual rating. Ron W., simply shrugged when I asked about this, but I wanted my expensive (too expensive!) tubes to last as long as they could. So I lowered the plate voltage (taken between plate and cathode)to 250 VDC. Since the 6SN7s plate supplies branch off from the B+, I needed to balance those out to bring them back up to what's on the schematic. I'm now using Sovtek 2A3s, and bypassed R13 with another power resistor to bring the voltage up to about 275 on the 2A3. That is such a rugged tube, though, that it can take considerably higher voltages without damage. In short, the 5Y3 rectifier provides more than adequate DC for my needs. The Mullard GZ37 is such a fine tube, though! Maybe I'll just put those back into service! Man that shot Kelly supplied of the battery bias is nice! Ok, I'm just about done -- sorry this has gone on so long. Leo: if you like the sound of the amp minus the bypass cap., maybe experimenting with the kind of capacitor you use to couple the different stage (C7 and C8). I've got a nice .22mfd from the AE-1 preamp, that I want to try in the Moondog. Having a mix of oil and plastic capacitors might be nice, just as mixing tubes can sometimes result in cool things! Have a good Sunday, Erik Quote Link to comment Share on other sites More sharing options...
leok Posted January 19, 2003 Author Share Posted January 19, 2003 Erik, Thanks for the response. I left C5 in, with the units on all night, and this morning it sounded much better. I can understand how people might prefer this direction in voicing, but it just sounds like a loudness circuit to me an it turns violins into lasers. Maybe I'm just matching the Moondog voice to the RF-7, but for now C5 is back out. I left it positioned so I can easily re-attach it. The impedance seen by the 1st 6SN7 stage is lower than that seen by the second. There is no cap on the second stage cathode (and that one drives the 2A3). To me, C5 is directly in the signal path in that the output of that 6SN7 stage is proportional to the voltage between the input grid and cathode. Any frequency dependent ESR of C5 directly influences the gain at that frequency, Any nonlinearity in the ESR of C5 becomes part of the signal. What I've heard so far souns a lot like an electrolytic in the signal path. Still, the sound is terrific either way .. this is hair splitting. Leo Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted January 19, 2003 Share Posted January 19, 2003 Leo, you might find this mail from Jean-Francois interesting (he was lurking, the ole dog). Once again, please remember he is French Quebec, hence the strange syntax. "Leok seems to have some decent ears. He doesn't like the result when putting in C5 (the input tube cathode bypass cap) in the Moondog. It might be problem indeed. The best is probably to remove it. The sensitivity takes a dive though. But boy it's worthed to ditch it." I asked him to provide some more thoughts on it and should hear something. I might post it in here. kh Quote Link to comment Share on other sites More sharing options...
leok Posted January 19, 2003 Author Share Posted January 19, 2003 Kelly, Thanks so much for making that contact. It clears a lot of questions I thought I had begun to resolve. Thanks also to Jean-Francois for his lurking and voicing his opinion. Leo Quote Link to comment Share on other sites More sharing options...
Deang Posted January 19, 2003 Share Posted January 19, 2003 You guys have no idea how bady I wish to understand what you are talking about. Leo, someday, when you are settled in with the Moondogs -- I would like to shoot you a schematic of the Apollos. I would be very interested in any thoughts you might have regarding the design. Of course, I don't ever see me getting to the point where I would be willing to trade dynamics and power for any additional degree of anything else. However, it would be interesting to hear your thoughts. Kelly, I already know what you think. Yeah, yeah, I need more blooming bloom. Quote Link to comment Share on other sites More sharing options...
jazman Posted January 19, 2003 Share Posted January 19, 2003 Leo, Erik, Kelly, I've been following this thread with much interest for many obvious reasons. One of which is, I've not modified my Moondogs from the original build by the first owner. This is not a bad thing considering how well they were assembled, the components used, and how wonderful they sound. I have made one tube change as the result of one of my GZ37's going bad. I've been using 2 vintage Amperex 5AR4 rectifiers and really like them. I am planning to replace the GZ37 and will spend some time evaluating the GZ37 vs the Amperex 5AR4's. In the meantime I am getting a couple of Mullard 5AR4s soon to further determine which sounds best in that position. At present, I think the the 5AR4/GZ34 may have more low end blossom than the GZ37. I also recently decided it was time to use the Rogers 2A3 tubes and put the vintage RCA blackplates back in the boxes. I had only listened to the Rogers briefly after first aquiring them. I'm still trying to research who actually manufactured them for Rogers. Initially they sounded heavy and without the wonderful midrange of the RCAs. After almost two weeks, they have blossomed into a very wonderful sounding pair of tubes. The mid range has opened up, not quite to the point of the RCAs, but the low frequency is better than the Sovteks. This is really a very smooth sounding 2A3 tube, with very good balance. Maybe after having a better handle on tube flavors, some internal mods to the Moondogs may be in order. Klipsch out. Quote Link to comment Share on other sites More sharing options...
No Disc Posted January 19, 2003 Share Posted January 19, 2003 Jazman, Thanks for confirming my suspicions. I also thought the Sovteks were a bit lean on the bottom end. This is probably more of a issue with the Wright Monos than with the Moondogs, nevertheless, I am running my Vintage RCAs now. -tb Quote Link to comment Share on other sites More sharing options...
mobile homeless Posted January 19, 2003 Share Posted January 19, 2003 The 5AR4 probably does win in the bottom end to my ears over the GZ-37. Where the GZ-37 goes to the next level is the MIDRANGE. IT is here that I make the comparison between the Sovtek 2A3 and the CRC VT95 RCA Black Plates(the RCA having the BIG win on the midrange). I think it is a similar comparison in a way. The midrange of the Moondogs with the GZ-37 seems to have a more liquid, relaxed, and see-thru quality. The bass is VERY good with the Mullard GZ-37 but the 5AR4 might have a bit more definition and extension. To me, however, the midrange is just worth the difference. That said, I have not had Mullard 5AR4 yet in them. Perhaps I can convince ole Jean-Francois to send me a pair to audition. One thing is for sure, the Mullard GZ-37 wins HANDS DOWN in the looks department. It's a beautiful, graceful tube. In some ways, the tubes SOUND like they look! See this shot I made of the Moondog layout with GZ-37 Below is a pic of Sprocket's Moondog with the 5AR4 and RCA on top plate for shortest wire path kh Quote Link to comment Share on other sites More sharing options...
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