deepak Posted May 21, 2007 Report Share Posted May 21, 2007 Do you know if it's an integrated or a poweramp? I really dislike having a preamp in the signal path right now. Quote Link to comment Share on other sites More sharing options...
cotdt Posted May 21, 2007 Report Share Posted May 21, 2007 Do you know if it's an integrated or a poweramp? I really dislike having a preamp in the signal path right now. just add a volume pot and it's an integrated amp. Quote Link to comment Share on other sites More sharing options...
Guest sacd lover Posted May 22, 2007 Report Share Posted May 22, 2007 My first move would be to dump the 12AX7 tube, and then choose from either a 6SL7, 6SN7, ECC40, or 5687 depending on how much gain is needed. Next would be to put the gain stage first and then the cathode-follower, or dump the cathode-follower altogether. I still don't know what that 330k resistor does so we'll leave it for now, but removing it might be an option. All those 10k grid-stopper resistors can likely be dumped as well, with a good wiring layout you don't need them. Then you can play with fun stuff like LED biasing on the tubes and an ultrapath capacitor between the B+ end of the transformer and the cathode of the EL84. I got my cotdt modded Doge 6210 today. I must say cotdt did a great job getting this circuit to sound good. I had a scare from the shipping pushing a resitor lead into a power cap and causing some serious hum and distortion in the right channel .... and several "oh no not again" thoughts. But I found the problem and the amp works fine. I must say the amp is dead quiet using a low gain 5814a with the circuit changes he made. I hear a swooshing sound everytime I change the volume, no doubt that weird input design. I have never heard anything like this before and I find it mildly annoying. I bet if cotdt moves the cathode follower behind the input tube, where it should be, the amp will be even quieter and more dynamic. Before when I had the perfectly working amp I could barely get a normal listening level at 3:30 with a 4-5 volt source and now I am running the volume at 10:30- 11:00 am with a 2 volt source. The sound has nice warmth, body, very good dynamics and a nice clarity without any hint of solid stateness. I had some static type discharge sound if I did anything that makes vibrations around the amp. I messed with damping the chassis using hockey pucks which helped. I am still not completely sure of the cause but it appears to be the output tubes. I put some tube dampers on the output tubes awhile ago and this toned the problem down noticeably. I am using a low gain 5814a instead of a 12ax7 and this is probably contributing to the low noise. I am going to put some dampers on the 5814's later on too. All in all I am very pleased with the amp. But if cotdt had not come to my aid I would have likely had a $400 boat anchor. So thanks once again Phil. Quote Link to comment Share on other sites More sharing options...
aerius Posted May 22, 2007 Author Report Share Posted May 22, 2007 I hear a swooshing sound everytime I change the volume, no doubt that weird input design. I have never heard anything like this before and I find it mildly annoying. Looking at the schematic again, I think I've figured out why. There's a current path from the cathode of the input tube, through the resistors, and to the pot and the grid of the tube. That's almost certainly the cause of the swooshing sound. Quote Link to comment Share on other sites More sharing options...
cotdt Posted May 22, 2007 Report Share Posted May 22, 2007 glad it works, earl! i'm going to try changing the Doge circuit on my amp, but i think eventually i'll sell my Doge to build myself a Push-Pull EL84 (Red Light District by SY) with a better transformer and LED biasing. Quote Link to comment Share on other sites More sharing options...
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