leok Posted February 22, 2003 Share Posted February 22, 2003 In case anyone's interested in cleaning up the highs on a pp design, the "Ultrapath" concept that Erik suggested for the Moondogs (or any SET) also works on a pp amp. Generally there is an electrolytic cap on the cathodes of the output tubes. A low ESR (polyprop. or other exotic plastic) cap from that (or those) cathode cap(s) to the B+ input of the output transformer does the trick. For the output currents into the transformer it bypasses two electrolytics: output tube cathode cap(s) and B+ cap. I added a set (4 caps total) to my pp amps and the result is cleaner (smoother), more extended highs. Klipsch speakers are very responsive to a cleaner top end, so if you are so inclined, it's worth the effort. leok Quote Link to comment Share on other sites More sharing options...
Chris Robinson Posted February 22, 2003 Share Posted February 22, 2003 Leo, looking forward to hearing your Ultrapath-upgraded Moondogs with the Klipschorns, 6SN7 pre-amp, et al. tomorrow! Hopefully you'll do your usual capable review of what you hear! Quote Link to comment Share on other sites More sharing options...
Deang Posted February 22, 2003 Share Posted February 22, 2003 Shouldn't have posted this Leo, for now you know your mailbox will contain an endless trail of questions from yours truly. Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted February 22, 2003 Share Posted February 22, 2003 Leo: I've been meaning to write to you, but this works well, too. I've got the bypass cap in it's original (bypass) position, and figuring out where I can put the additional C4A (aka ultrapath cap). I'm finding a preference to 'improve' the cathode to ground connection, but certainly notice a change -- and one I don't care for as much as the ultrapth output. Also, I detected some higher pitched hum when very close to the speakers, and traced this to the absence of C5. I tacked in a new Radio Shack 100mfd electrolytic, and things have improved. Regardless of a now quieter background, that sparkling clarity I got when I first experimented with the ultrapath output is no longer there. Now that you have both large poly caps (cathode bypass and ultrapath output), do you still prefer the combination of both as opposed to only the ultrapath? I should have ordered a 50mfd Solen this past week, but was so busy I forgot to. Also! I found an interesting volume control modification for increasing high frequency response at low volume levels. Often a lower listening levels, there is a bit of roll-off of some detail, which can be brought back by bypassing the input and wiper of a volume control with a small capacitor -- say 47-100pfd (picofarad). This capacitor remains effectively out of the circuit until the volume is turned down, and then begins to act as a high-pass filter. With my less efficient hearing and tendancy to listen at only moderate levels, I want to try this. It was often used on guitar amps for the same purpose. Right now, I'm saving every penny I can for a computer-based audio server from Dave Mallett. We very much need a new CD player, and the MSB unit we've seen in another thread is something I'm going to try. Take care! erik Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted February 22, 2003 Share Posted February 22, 2003 Correction! That's MBS Audio Server. I've been up since 3:30 this morning! Quote Link to comment Share on other sites More sharing options...
leok Posted February 23, 2003 Author Share Posted February 23, 2003 mdeneen, Erik, Based on my observations and limited theory: I certainly find the addition of the bypass (Ultrapath) cap to be an improvement, and wouldn't go back. I am listening to several string quartet recordings now that used to sound thin and sharp. All 3 2A3 tube types I have now sound much more relaxed and natural. The hf is cleaner, and more extended .. not louder. Actually, in the Moondogs, the bypass cap is large enough to handle all output frequencies. In the pp amp, they handle only from high hundreds of Hz up. As is generally the case, reduced distortion makes the impacted frequency region less obvious, so the sound becomes fuller, not as influenced by hf distortion. Besides improving the output current loop by providing a lower impedance path between tubes and xfmr., the reduction in current through the existing output tube cathode-gnd cap(s) reduces esr and its impact on grid/cathode voltages. (my original problem w/ C5 in the Moondogs). Erik, I'm following the MSB story with interest. leok Quote Link to comment Share on other sites More sharing options...
Erik Mandaville Posted February 23, 2003 Share Posted February 23, 2003 Gotcha, Leo. I agree, I prefer the utrapath output...there was indeed a difference with C4 in its stock position. So I need to send out an order -- think you got yours from Madisound, right? No need to answer, here, I can go have a look there myself. Thanks! As for the MBS system, I just bought a book at Barnes and Noble, which is dedicated to using computer-based music playback. There are some basics I am aware of, but I have a great deal to learn. The flexibility such a system would afford is of interest, and there are very high quality sound cards now available. I just need to read-up on all of this. I think it could turn out to be a good investment -- certainly equal to or better than many stand-alone players in the same price range. Have a good Sunday, Erik Quote Link to comment Share on other sites More sharing options...
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