I have to confess. I'm really excited with my Sony CDP950 with 20years old TDA1541 DAC. Several tweaks & heavy modifications resulting upgrades in sound each and every time. I always set my mind towards the final tweak-a tubed CD player- since last year and starting to spare my money for collecting tubes, HV transformer and other component. And of course continuing learning how tubes works.
Last tweaks were the opamp change, the bypass operation here and the non-oversampling things.
At the end of last year I've heard that a Blind Test for CDP and/or DAC going to be held in January 2010, so it's time to put the effort. Top cover is cut for tube base plate and top loading system. Also 2 left over 8mm thick acrylic plates for beauty and tube protection were made with my own hand :).
Schematic is as always..from Mr. Lampizator himself, a SRPP with 2x 6N2P-EV, for this I thanks Pak Dino. I plan to use hybrid tube rectifier - AC heaters all the way and 6X4 tube-USA origin I got as a gift from Pak Ado. HV tranny, sockets and resistors were from Pak Alex. Thanks to these good people! I can keep the mods at low cost, in term of materials that is :).
Socket, components & wiring were planned, sketched & routed. Keeping with my Reuse-Reduce habit, wiring and, diodes and the capacitors are all used ones.
The simple plan is you tap the Iout signal from the TDA1541, route them to the 6N2P grids. There is a 60-100R from grid to ground which convert the current to voltage. Here is the I out wire, doesn't have to come out of PCB bottom this time :)
Piggy bagging the HV tranny..
Refinished top covers & tube base
Now the messy, tiring & fun parts...no..not that fun anyway..
I blew my cheap compo speakers-I think the tweeter just gave up-they got 75VDC for a second or so..sigh...stupid me. Also I've got 255VAC on my right hand fingers..boy..felt the jolt up to my arm pit..the hairs there felt smoother now :). How about the sound?...there is music..very low level..even I have cranked up the volume..lots and loud hum, check and recheck everything..no result, de solder & resolder the R's..also not helping. changed the AC heaters to DC with 7812 regulator..even worst..I gave up, just pull out the tubes- de solder the 220VAC from HV tranny and get ready for the next day Blind Test just with Non Oversampling tweak.
I have said the NOS tweak is a leapfrog compare to Bypass tweak. The blind test result confirmed this..at least the for Jury, session 3 got number 3 out of 5 players. This old CDP-loses to would be winner-CDP333esd nosed-reclocked-BGed and external tube buffered CD960..interestingly 4 out of 5 players using TDA1541 !. The non Jury said other way..last position for my old CDP..so..I have to make my CDP really sings or else...
In order to understand what is going on, I've made a simulation in orcad, yes there is 6N2P Spice model out there. Simulating the SRPP with Iout of 1kHz at 0.4mA (TDA1541 datasheet) shows nice high Vout :0... So what might happen? Searching the Lampizator site for (hidden) clue..no result--Mr Fikusz hiding something? nhaaa!... My tubed CDP very low Iout-Vout signal indicates that the Iout from DAC is being corrupted a great deal, like everything here in Indonesia :).
I can only point that the BB OPA2134 as the I corruptor !. Gothca...the opamp pair on temporary detention now. Turn on the CDP next the HV switch...yes..a big YES...Ingram Washington sings loud and clear!..almost no hint of hum..this AC heater tubes!..
Ingram Washington sings :"...What the difference a day make...." this day for me was 1 week after the blind test. The OPA2134 now permanently out of my CDP..too bad though as I can not directly comparing NOS-OPA2134 and SRPP. Or is it necessary?..No it is not necessary.
The difference is very clear right away. I will spare my comments for later :)..my wife just shortly said.."empuk"..means (maybe) "smooth" in English..that with up to now unbearable to hear CD from David Foster & Friends..
Wiring & sound testing this way :) with Gainclone amp and 2 samsung small speakers.
Bunch of resistors to try. And finally testing in my system..with a C out coupling rig for finding the right caps. I'm tired but fully satisfied. There are some minor tweaks must be done on the HV PSU, R values & types, Cout and last but not least the CD transport itself..maybe a Phillips CDpro2 transport Clone..:). Thanks for reading my DIY audio adventure.