Erik Mandaville Posted November 3, 2002 Share Posted November 3, 2002 This topic still needs time to develop, but a quick switch of the secondaries on the Moondog OPTs enabled a more proper match for the La Scalas, and we spent an afternoon and evening listening to a variety of music. I had been using the La Scalas with my little ASUSA K2003 for the past couple of weeks, and I have been very surprised by the performance of this much less expensive amplifier. I built both the ASUSA and Moondogs from kits, and the ASUSA parts count and quality are rather different from the sort of quality Ron W. supplies with all of his kits. The ASUSA is a very 'quick' sounding amplifier with excellent high frequency extension (in my opinion), and has right now become the preference to use with the La Scalas. The Moondogs were 'darker' sounding, and didn't seem to have the polished, crystalline voice of the ASUSA. I'm not sure I would describe the ASUSA as 'better,' just different in this application. There was one modification I did to the Moondogs that might be coming into play: In place of the 100K resistor (grid-to-ground)in the input stage, I've installed 100k linear pots to help provide some attenuation control to match some of the rather high gain outputs of the preamps I have built. The Moondogs only require a couple of volts to swing the amp into full output, and lots of preamps, especially if used within close proximity of the amplifiers can throw the amp into clipping with very little effort. I now have my amplifiers 25 feet from my preamp and sources, and use homemade shielded interconnects that measure about 14-16 pfd/foot in capacitance -- which is lower than many cables. I'm now needing to turn the volume control up on the Moondogs approximately half-way to get decent output, which as a result is considerably lowering the input impedence of the amplifier (thus making it more difficult for the preamp to drive). What I think I'll try (a trick I read about on the Welborne Labs forum)is installing a 10K 'buffing' resistor between the wiper and grid of the first 6SN7 (great pictures by the way, Kelly!), so that the amplifier might 'see' a higher impedence as the volume control is rotated. Either that, or I'll install a fixed T-pad in place of the potentiometer. My speaker cable (cross-connected cheap coax) is also twice is long as it needs to be, and there may in fact be some capacitance/loss issues related to that. I had made a much narrower version of the popular CAT 5 speaker cable ($.35/foot from Radio Shack) that sounded absolutely stunning with my Lowthers, and have given those to a friend who like them better than his mega-buck Jena-Labs cable. The CAT 5 cables are what might be described as 'clean' and 'bright' which is what I like -- it sounds the way music used to sound when I played drums in jazz and rock bands years ago. That's why I love horn-loaded designs! They come closer to anything I've heard at reproducing the characteristics of real instruments. The Lowthers just can't match the low-end reproduction of the La Scalas, but have a midrange ability that is astonishingly good -- so is that of the La Scalas, by the way! In short, I'm going to pull the bonnet on the Moondogs today, and work on the input impedence issue a bit. I think the Moondogs have enormous promise, and I know many of you use them with your Klipschs. I wish I could share this little ASUSA stereo amp., though...it is so surprisingly good. I'll post results for those who might be interested.... You all have a good Sunday! Erik Quote Link to comment Share on other sites More sharing options...
foldedhorn Posted November 3, 2002 Share Posted November 3, 2002 I was looking at the ASUSA to drive my La Scala's but ended up with Decware. Quote Link to comment Share on other sites More sharing options...
Colin Posted November 3, 2002 Share Posted November 3, 2002 great post, Erik, thanks! Quote Link to comment Share on other sites More sharing options...
Deang Posted November 3, 2002 Share Posted November 3, 2002 If you have paper/oil or copper/oil in the Moondogs, you might prefer the sound of the Auricaps, or REL Thetas in their place. Quote Link to comment Share on other sites More sharing options...
NOSValves Posted November 3, 2002 Share Posted November 3, 2002 Deang where some info a the Rel Thetas ? Who sells them ? Quote Link to comment Share on other sites More sharing options...
jazman Posted November 3, 2002 Share Posted November 3, 2002 Erik, I don't quite understand this. "The Moondogs only require a couple of volts to swing the amp into full output, and lots of preamps, especially if used within close proximity of the amplifiers can throw the amp into clipping with very little effort." It this caused by adding the volume attenuation to your Moondogs? My Moondogs are on a shelf directly under my Cary preamp, connected by 1 m Haycinths, phone pre on same shelf connected to Cary with .5 m Hyacinth IC. My Rega Planet and Scout TT one more shelf above using 1 m. and .5 meter IC's'. Why am I not having a problem with all my sources very close together and my Belles less than 7 ft away?. The gain on my Cary is zeroed at 6 oclock and I seldom get close to 9 o'clock for CD sources and can go to 9 o'clock for phono sources. I'm very curious. Klipsch out. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted November 4, 2002 Author Share Posted November 4, 2002 Jazman: What I am essentially saying is that, if your sources are say within a few feet of your amplifiers, many people can obtain quite satisfactory sound without using a preamplifier. The couple of volts on the output of a CD player can easily drive the Moondogs without the need of active preamplification. I used to use the Moondogs this way (but with a passive linestage I built for volume and switching control), and things worked out very well. With my amplifiers now more than 20 feet from my sources, I need the extra gain provided by an active line stage -- CD straight into the amplifiers doesn't work for a number of reason, long ICs being the main problem. Without the extra drive capability of an active preamp, one suffers miserably from poor high frequency response imposed by the capacitance of a long run of interconnect. This is even a problem with certain high output impedence preamplifier circuits -- the high output impedence can't drive the capacitance of the cable. My preamp uses a direct-coupled, cathode follower topology, which has a very low output impedence. Thus, long runs of cable are not such a problem. Your system seems to be just fine, don't worry about it! If you want to put a volume control on your amps, it's easy to do, but I would use a 5K-10K resistor between the wiper of the volume control and the grid of the input tube. Erik Quote Link to comment Share on other sites More sharing options...
jazman Posted November 4, 2002 Share Posted November 4, 2002 Eirk, Your situation is completely different than mine, so no need for me to do anything. I'm at the point where I think every component has melded to create a great sounding music system, and I hesitate to change anything other than consider a possible network swapp in the Belles. Not even a TT mat, because as a new turntable design, the platter material was one of the design parameters meant to have the vinyl mate with it. I'm through spending money for a while, I hope.......? Klipsch out. Quote Link to comment Share on other sites More sharing options...
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