June 1, 201610 yr OMG that looks better than any comercial amp, regardless of price. You sir have a gift, also, I'm sure it sounds terrific.
June 2, 201610 yr Thanks everyone. Just two more plates to mill and the chassis are done, then off to have them finished The pot will come shortly. I'm going to use an encoder and Kevin's digital attenuator boards.
June 3, 201610 yr Beautiful build, Kerry! After building something so complex, you should relax...by building something simple.
June 6, 201610 yr I don't know if it matters to you...but I think I'd want a amp top plate where I can easily access all the trim pots and test points if I were to build another one I also just noticed now, but is there a reason you put the front end tubes in the front? does it simplify the attenuator wiring?
June 6, 201610 yr I may put in holes to adjust the output offset, though its not really needed given the T2's servo. The batteries, likewise do not need to be adjusted once set. The small input tubes were moved to the front for aesthetic reasons. Since the attenuator needs to sit in the middle of the board (given the size reduction), it doesn't add any distance to the trace runs.
June 6, 201610 yr ah, I brought it up because when I switched output tubes the offset and balance changed pretty significantly. I ended up adjusting the batteries to 738/742 in order to fix this.
June 6, 201610 yr 6 minutes ago, nopants said: ah, I brought it up because when I switched output tubes the offset and balance changed pretty significantly. I ended up adjusting the batteries to 738/742 in order to fix this. that is strange. What tubes did you use? I have swapped multiple quads of old and new EL34s with no perceptible change in balance and offset. My experience has been like Kerry's, you set it and forget it. The only time I have seen differences is with the 6dj8s if both halves of a tube were significantly out of balance.
June 6, 201610 yr I switched between some matched rfts and xf2s, not really sure why it happened. I can try switching the 6dj8s and see if that changes anything. I figured two volts on the batteries wasn't a huge deal in any case.
June 7, 201610 yr I've added an adjustment across the 510R resistor to set the output voltage. This works off the second to last stage, so the tubes really shouldn't change things, though if things vary too much, I suppose it could.
June 7, 201610 yr Is there any chance someone has A) a chassis laying around for the lil knight boards (the thick blue ones) or B) designs for a chassis? I'm coming down the home stretch with this (if everything works right the first time, a big IF) and casing/heatsinks is the only thing I still need to scrounge up.
June 8, 201610 yr Do not know if Georgp still has any, though recall there was a group buy some while ago. If you're running your/any Sato-Denki order I would like in! *remembered those were for standard amp-boardsets*
June 8, 201610 yr The one I had made was for the standard amp boardsets. To fit the shrunk amp board you would need a new toplate and brackets. The psu board is practically the same.
June 16, 201610 yr Well i finished my T2 build and it fired up first time and much to my delight with no smoke or flying parts. Have yet to put music thru but there appears to be no noise thru the amp with open inputs. With less than 100mv between + and - and 8v between outputs and ground i think i am a happy bunny. I am about to install V1 of Kevins Attenuator and was wondering about feeding this from a single 12v supply. I was considering taking the spare pin on the power sockets and picking up 12v from the power supply to feed the att. I will use the nano board to supply 5v and 3.3v. Is thisa good or bad idea?. Any other better suggestions.? Want to get this installed asap so i can listen to it. A long build but very satisfied.
June 16, 201610 yr Congrats on the build! I think you should be good using the 12v supply. Just make sure there is enough current available. I don't recall the requirements but can takes look at some point. I feed the attenuator board off of the 3.3v out from an Uno board. Again, just double check current between the Uno and Nano. The only other thought is whether it might generate some noise into the amp when changing the volume. Good luck and keep us posted on your progress
June 16, 201610 yr Thanks Kerry, Noise was my concern to. So my back up plan was to install a small toroid transformer in the p/s and feed a separate 12v to the Att so as to keep it completely isolated from the Amp. Only time will tell, will keep you posted. Curious as to why the spec for the Filaments of the 6922 was specd at 1.4 a when total was about .7a. My ones are running at 7v which i dont like and i will have to add a resistor. With this winding loaded to 1.4a the voltage is correct. Edited June 16, 201610 yr by iwik
July 17, 20169 yr So here's some renders of the amp and PS. I've got to mill out the amp plate now Edited July 17, 20169 yr by Kerry
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