The Adcom GDA 600 modification thread

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  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    just for orientation,,are they correct?
    I'm guessing yes-- now I have to work on seperating them a tad--thanks again,,as always Fred. Note; they are not soldered yet--not bad for a one eyed old man eh?
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited June 2010
    just for orientation,,are they correct?

    Yes.Are they labled 72017 and 72019?


    Will bending the pins on one forward and the other backwards give you enough clearance?
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    yep-(on the placement-correct regs in the appropriate slots)- I'm gonna play with bending the pins like you stated(tomorrow)

    BTW,, since my opamps are soldered--how/where should I make the measurements?
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited June 2010
    You'll be able to get a positive voltage reading on one side of diode CR100,and a negative voltage on one side of diode CR108. Actually you'll get a reading on both sides of the diodes but the lower number will be the one you'll need to know so you can adjust it if need be.
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    Okay,,I have to ask--when making the measurements,, I place the negative probe on the chasis ground and the positive on the points that you mentioned above and adjust to +/- 15 volts,,then I should be able to connect the power supply to the main board and go?
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited June 2010
    I place the negative probe on the chasis ground and the positive on the points that you mentioned above and adjust to +/- 15 volts,,then I should be able to connect the power supply to the main board and go?
    Yes thats it Goerge.While the voltages could also be checked directly at the output pin's of the reg's I thought it safer to measure at the diodes.The close pin spacing makes it a potential problem.The probe could accidentally slip and short across two pins and damage the reg.
  • davide256davide256 Posts: 50
    edited June 2010
    I was unsuccessful at getting my voltages down to +15/-15, If I trust my Radio Shack MM they are like 18.5/ -19.5 at pins 4 &8 with the lowest voltage adjustment I could get out of my regs. U100 didn't seem to do much in trying to adjust, U104 raised/lowered both. I may double check at the ribbon cable outputs tonite (I have some leads appropriate for this) to see what is coming out of the board matches the pin voltages. DAC is working fine but I'd like to get voltage in spec/balanced to be sure all is within design parameters. Sounds continues clean in base, starting to hear some background details that were previously masked, biggest change is what I would call white noise reduction, clarity at mid and lower volumes.
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    FTGV wrote: »
    Yes thats it Goerge.While the voltages could also be checked directly at the output pin's of the reg's I thought it safer to measure at the diodes.The close pin spacing makes it a potential problem.The probe could accidentally slip and short across two pins and damage the reg.

    Fred,, should I get a 15 volt reading at the diodes?I'm unsure which side of the diode to take the measurement and adjust.Heck,,I don't seem to get my rat shack on the proper ac voltage setting.
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited June 2010
    Fred,, should I get a 15 volt reading at the diodes?I'm unsure which side of the diode to take the measurement and adjust.Heck,,I don't seem to get my rat shack on the proper ac voltage setting.
    Yes you can get the readings at the diodes.On diode CR100 test the end of doesn't have the silver stripe.On diode CR108 test the end that has the silver stripe. Also be sure to set your rat shack meter to DC volts not AC:)
  • FTGVFTGV Posts: 3,644
    edited June 2010
    davide256 wrote: »
    they are like 18.5/ -19.5 at pins 4 &8 with the lowest voltage adjustment I could get out of my regs.
    The maximum supply voltage for the OPA627 is stated to be + - 18volts,so if your meter is correct you are exceeding the safe limit of the opamp.Also adjusting one reg should have no affect on the other.:confused:
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    FTGV wrote: »
    Yes you can get the readings at the diodes.On diode CR100 test the end of doesn't have the silver stripe.On diode CR108 test the end that has the silver stripe. Also be sure to set your rat shack meter to DC volts not AC:)

    OK they both test at 15 volts,,that using an analog meter,,set on dc and measuring between the diodes,,can I assume that I can hook up the analog board now.U-108 reads + 15 volts and so does thee other when measuring across the diodes.
    JC approves....he told me so. (F-1 nut)
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    Okay-- bad fuse in the DMM,, I'm reading 13.72 volts at the diodes,,and the same negative voltage--hold on--ok--- got the measurements after adjusting the regs,, 14.99 positive-- 14.99 neg--I'm gonna fire it up in a few--heres a pic before I button it up.I have learned alot so far in this rebuild,,anyone with one of these should certainly give it a whirl--Fred did mention,,do NOT let the heatsinks touch,,and one from me---be sure that you can remove/replace the fuse onboard if you need to--ie,, careful with that regulator install,as it's next to the fuse.
    JC approves....he told me so. (F-1 nut)
  • heiney9heiney9 Posts: 24,108
    edited June 2010
    Very nice George, keep us updated on what you're hearing. I haven't received mine yet.

    H9
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    It's been playing for a few minutes--I'll keep ya'll updated.
    JC approves....he told me so. (F-1 nut)
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    Keb Mo done got my foot to tappin"very early,,but the detail and the "micro dynamics" seem to be much improved,and there ain't too much bass.The music/performer seems a tad more realistic,,it's just got that familar "analog" tone to it,,kinda like vinyl,,no kiddin' now,, for a digital recording,,it's very analogy sounding..I'm liking it very well,,oh yeah,,very easy to listen to.
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited June 2010
    Most excellent George.
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    For you old school guys like me,, if you have it,,put on Joan Baez "Diamonds and Rust",,or Joni Mitchell "Ladies of the Catnon", you know which tracks I'm talking about if you are say,, over 50,,I'll tell you what,,it literally brought tears to my eyes,,or eye,lol,,on SDA's,the adcom just really puts them right in the room scary good,,so good it oughtta' be illegal,,and in some states probabally is--come on--lemme' hear it from you guys that have done the mods--especially the burson regs..whaddya' think---me?? Goosebumps.:)
    JC approves....he told me so. (F-1 nut)
  • heiney9heiney9 Posts: 24,108
    edited June 2010
    George, trying to get a long listening session in right now. Having some tube issues with the Sylvania black plates currently and am switching to some Valvo 6201 gold pin in my pre. I'm really loving the mods (haven't done the regs yet) and the longer the dac is on the better it sounds.

    I'll get back to you later today, but WOW, is this Adcom sounding sooooooooooo good!
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
  • FTGVFTGV Posts: 3,644
    edited June 2010
    Goosebumps.:)
    Other than not having the capability to play hi rez data I would expect the modded 600 to be the equal of or surpass a number of newer gen DAC's in sheer SQ.
  • davide256davide256 Posts: 50
    edited June 2010
    hmm, not as easy as I thought to check the cable pin voltages, only get reading on the one pin of 5v, all others zero. Checked C120 before the rectifiers bridge, that was 7v either side of C120. Also measured -19 at the base of CR108, so voltage is same as at
    IC socket. If anyone has suggestions how to isolate, love to hear... either the transformer is putting out a higher voltage then it should or something in the circuit from diode bridge to reg is boosting voltage. Noting at this time that some of the edginess has returned to female voices, still rich and full but with sibilance edge.
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    pics of the ps might help--I just do what Fred says and it all seems to work out,,did you do anything extra or outside of the original plan? Not trying to insult,just trying to help.
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited June 2010
    davide256 wrote: »
    Checked C120 before the rectifiers bridge, that was 7v either side of C120. Also measured -19 at the base of CR108, so voltage is same as at
    The voltages at C120 will be pre rectified AC.Measuring both sides of CR100 and CR108 should give you two different readings.One side will be the preregulated DC voltage and the other will be the regulated DC voltage.(The pre regulated voltage will be higher).If you have installed them as George has I don't know other than a faulty DMM why you are getting readings of + -19 volt and would have expected the opamps to run very hot if not fail outright.
  • davide256davide256 Posts: 50
    edited June 2010
    Hi george, no differences between your reg PIC's and my board. I believe my voltages were at 19 before the PS reg change. However a previous pic bright blue cap at C120 got me pondering.
    So ok, I think I may have found another mfg. board error. The capacitors on my board don't have values, only mfg part numbers. C121 is supposed to be 0.047 uf and c120 is supposed to be 220 pf... but they have the same part number on them. C320 is supposed to be 220pf, it is a different number on the part. C310 is supposed to be 0.047 uf, part matches the numbers on C120/C121 so it appears I have 0.047uf at C120

    >>>Can anyone confirm what would be the effect of having a much larger capacitance at C120 than the design? Its definitely a greater decay time for bridge diode voltage, will that equal greater rectified voltage? I checked rat shack, NA, so will have to order on line if its the problem for my voltage.
  • FTGVFTGV Posts: 3,644
    edited June 2010
    davide256 wrote: »
    I believe my voltages were at 19 before the PS reg change.
    That wouldn't be possible if the values of R110,R111,R112,R113 were correct.Do the 5 volt reg's measure correctly?
    Can anyone confirm what would be the effect of having a much larger capacitance at C120 than the design? Its definitely a greater decay time for bridge diode voltage, will that equal greater rectified voltage?
    Those caps are for noise suppression across the transformer secondaries they will not change the voltage.
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    You guys are loosing me--yours is a GDA 600 (stock?)I can post a pic of mine and label the components/values if you would like.
    JC approves....he told me so. (F-1 nut)
  • heiney9heiney9 Posts: 24,108
    edited June 2010
    You guys are loosing me--yours is a GDA 600 (stock?)I can post a pic of mine and label the components/values if you would like.

    I'm completely lost too George. I may pull the Op=amps now and get some voltage readings at the appropriate pins before I start the regulator mod. I do know the op-amps get fairly warm, but until now never thought to measure the voltage to see if it was in spec.

    Fred, so I simply pull both Op amps from their sockets and measue at pin 1 & 4 as you described in an earlier post and the voltage should read +15 vdc or -15 vdc?
    "Appreciation of audio is a completely subjective human experience. Measurements can provide a measure of insight, but are no substitute for human judgment. Why are we looking to reduce a subjective experience to objective criteria anyway? The subtleties of music and audio reproduction are for those who appreciate it. Differentiation by numbers is for those who do not".--Nelson Pass

    Pass Aleph 30 | EE Avant Pre | EE Mini Max Plus DAC | MIT Shotgun S3 | MIT Z P/C's | updated SDA 1C| SQ Box Touch/Welbourne Labs P/S- Tubes add soul!
  • FTGVFTGV Posts: 3,644
    edited June 2010
    You guys are loosing me--yours is a GDA 600 (stock?)I can post a pic of mine and label the components/values if you would like.
    He has done all the mod's including the Burson regs,but says he was/is getting +-19 volts with both new and old regs.There also seems to be a part value discrepancy with a couple of snubber caps,which could have just been a change in production due to not having the other value in stock?
  • george danielgeorge daniel Posts: 11,989
    edited June 2010
    FTGV wrote: »
    He has done all the mod's including the Burson regs,but says he was/is getting +-19 volts with both new and old regs.

    Oh :o
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited June 2010
    Oh :o
    Yeah it's a head scratcher,the voltages on the stock reg's would have to be correct as long as the right resistors were installed.


    Is yours still singing?
  • davide256davide256 Posts: 50
    edited June 2010
    Mine is still singing but the sibilance is definitely an undesireable change. I am wondering at this point if the adjustment screw on U100 is broken since turning it either way has little effect.
    Would it be a reasonable trouble shooting step to remove the reg at u100 and see if i can then adjust to a -15 voltage? Also checked intersection of CR107, CR105, -7v to ground, would have thought it should be 0. Also note that when I first started adjusting the voltage was -24
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