The Adcom GDA 600 modification thread

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Comments

  • heiney9heiney9 Posts: 24,107
    edited May 2010
    It has to be a ground issue, check and recheck. If all else fails maybe check for a cracked PCB.........it's a long shot but it is sort of fragile since it has to support both transformers. Also if you have a magnifier check you solder joints to make sure there isn't a slight "bridge" across the terminals, some of those smaller caps have almost no space between them.

    Good luck

    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!
  • davide256davide256 Posts: 50
    edited May 2010
    The gain after power supply capacitor changes was with the old OP amps in. With the old listening level at about 10 oclock on the volume knob I found i had to lower it to about 8:30. Its entirely possible that this wasn't a gain so much as the old supply caps were damping loud transients... definitely had a sense of greater dynamics but no hum. Hum is in both channels after step 2, very audible at about 11 oclock on the volume setting. Will check washers, these were between screw heads and PCB. For the power caps, I have these soldered to 4 & 8 on the backside of the PCB OP amp holder, 18awg wire soldered to cap ground leads , the wires twisted and attached to chassis ground screw. Will check capacitors for bridging. Really curious to see how this turns out as before I saw the thread I was contemplating buying a DLink III DAC... had a good experience with the Musical Concepts Hafler mod so wanted to give this a shot. My soldering skill isn't the greatest but on the audio board the bad OP Amp forced me to look at every solder with NTF. Will recheck the power supply board and post any learnings.

    Modified AR Turntable with Grado Platinum
    Adcom GDA600 DAC (in transition)
    Linnn Genki CD Player
    Conrad Johnson PV-10 preamp
    Signature Mod Hafler DH-200 amp
    Magnepan 1B original owner (waiting for my 1.7 ship to come in)
  • FTGVFTGV Posts: 3,644
    edited May 2010
    davide256 wrote: »
    For the power caps, I have these soldered to 4 & 8 on the backside of the PCB OP amp holder, 18awg wire soldered to cap ground leads , the wires twisted and attached to chassis ground screw.
    I would solder the leads of these decoupling caps that should go to ground,directly to a ground trace/ground plane on the PC board instead of how you have it.Also be sure that the ones on the negative rail are installled with reversed polarity.
    Will recheck the power supply board
    Yes double check that the leads of all caps are soldered.
  • davide256davide256 Posts: 50
    edited May 2010
    still continuing to work this.
    1) recieved new OP Amp, it played wonderfully for 3 seconds then died so it appears to be a fluke that I have 1 channel working... I had swapped it with the working OP amp
    2) tried redoing the caps between pin 4& 8, then removed them, no real difference although bass may be better without.. hard to judge
    3) problem appears to create a feedback loop between preamp and DAC as moving preamp volume knob creates static transient that occurs with no other input source.
    4) same problem exists with optical and analog inputs, hum only exists with signal input

    I have some Cardas solder on order, used Radio shack brand to start with, will desolder and solder all with new solder.

    Also noted that on the power supply board near the off/on button one of the factory components marked on the board as a resistor instead has a capacitor. Will post picture later, curious if everone elses board has the same change.
  • FTGVFTGV Posts: 3,644
    edited May 2010
    davide256 wrote: »
    3) problem appears to create a feedback loop between preamp and DAC as moving preamp volume knob creates static transient that occurs with no other input source.
    Excessive DC offset can do this,if you have a multimeter check for DC voltage at the outputs of each channel.You should have less than 10 milivolts.Also check pin 4 and 8 of both opamps to see if your getting the + and - 15 volts DC.
    4) same problem exists with optical and analog inputs, hum only exists with signal input
    Interesting,that sounds like a ground loop but the 600 has a pulse transformer on the coaxial digital inputs so a ground loop shouldn't occur.Optical is inherently immune to ground loops so this is a mystery.
    Will post picture later, curious if everone elses board has the same change.
    What is the actual part designation on the board?Hopefully Goerge will chime in on this one as I don't have a unit to examine.
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    What can I do to help guys? Am I right in understanding that it's destroying the op-amps?
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited May 2010
    What can I do to help guys?
    He was wondering about the resistor marked as a cap on the PS board.
    Am I right in understanding thats it's destroying the opamps?
    It might be George,thats why I suggest he check the voltage pins on the opamp socket to confirm they are correct.I would remove the opamps and not reinstall them until you are certain they are.
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    davide256 wrote: »
    still continuing to work this.
    1) recieved new OP Amp, it played wonderfully for 3 seconds then died so it appears to be a fluke that I have 1 channel working... I had swapped it with the working OP amp
    2) tried redoing the caps between pin 4& 8, then removed them, no real difference although bass may be better without.. hard to judge
    3) problem appears to create a feedback loop between preamp and DAC as moving preamp volume knob creates static transient that occurs with no other input source.
    4) same problem exists with optical and analog inputs, hum only exists with signal input

    I have some Cardas solder on order, used Radio shack brand to start with, will desolder and solder all with new solder.

    Also noted that on the power supply board near the off/on button one of the factory components marked on the board as a resistor instead has a capacitor. Will post picture later, curious if everone elses board has the same change.

    A picture would help greatly--keep us posted.
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited May 2010
    I see Parts Connexion has the Burson series 1 voltage reg's on sale.For those wanting to squeeze a bit more out their GDA600,IMO these discrete regulators feeding the OPA627's should take it to the next level.Burson 72017 and 72019 are the suitable replacements for U100 and U104 on the PS board.

    http://www.partsconnexion.com/regulator_burson.html
    http://www.partsconnexion.com/t/Index/burson_reg.php
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    so the 72017 pops in U 100 and the 72019 pops in U 104?

    Thats is? Hmmmm,
    JC approves....he told me so. (F-1 nut)
  • heiney9heiney9 Posts: 24,107
    edited May 2010
    FTGV wrote: »
    I see Parts Connexion has the Burson series 1 voltage reg's on sale.For those wanting to squeeze a bit more out their GDA600,IMO these discrete regulators feeding the OPA627's should take it to the next level.Burson 72017 and 72019 are the suitable replacements for U100 and U104 on the PS board.

    http://www.partsconnexion.com/regulator_burson.html
    http://www.partsconnexion.com/t/Index/burson_reg.php

    Interesting............If you try it first George I'll give it a shot. Can't imagine it getting better :)
    "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 May 2010
    heiney9 wrote: »
    Interesting............If you try it first George I'll give it a shot. Can't imagine it getting better :)

    If Fred will give me a "paint by the numbers" I'll order them today.:)
    JC approves....he told me so. (F-1 nut)
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    OK-- I think that i understand this-- I'm gonna order them and I'll report back here,,,one thing,,for Mr. Fred-- do I remove the reservour" cap that I added to the op amps?
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited May 2010
    so the 72017 pops in U 100 and the 72019p pops in U 104?
    Yep
    Thats it? Hmmmm,
    Not quite,you'll need to remove a few parts,and having a DMM so that you can do basic voltage checks would be recommended.
    ,one thing,,for Fred-- do I remove the reservour" cap that I added to the op amps?
    They can stay,but you will need to remove R110 and R112.Also remove R111,R113,C122,C123 and install a wire jumper in their place.
    If Fred will give me a "paint by the numbers" I'll order them today.:)
    Sure be glad to help if your going to give it try.
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    OK -- onward we go to Phase II --stay tuned;)
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited May 2010
    OK -- onward we go to Phase II
    Wait til you get to phase 4,thats when it really begins to shine.;):D
  • heiney9heiney9 Posts: 24,107
    edited May 2010
    OK -- onward we go to Phase II --stay tuned;)

    Awaiting Phase II and the directions :).

    George at first I was a little disappointed in this mod because it was really analytical and hyper detailed. But, I have to say after about 200 hours break-in this thing is phenomenal. Same detail but it's soooooooo smooth.

    Detail in spades, great extension and the decay and air around instruments is superb. Vocals are just unbelievable. I also find that the DAC needs about 30 minutes of warm up for it to sound good.

    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 May 2010
    FTGV wrote: »
    Wait til you get to phase 4,thats when it really begins to shine.;):D

    Hey,, I gotta' survive the second phase first,lol and H9 nailed it--ohhh,, so smooth,,yessir,detailed too,,ya'll hear what the man said?;)
    JC approves....he told me so. (F-1 nut)
  • Poee7RPoee7R Posts: 902
    edited May 2010
    Damn, damn, damn, you guys are killing me here.

    George, Fred, Ben or anyone feeling like doing this to mine for a couple bucks? :D


    Dave
    Once again we meet at last.
  • davide256davide256 Posts: 50
    edited May 2010
    Ok pictures attached and some more data

    R113 on the power supply board has a capacitor instead of a resistor
    Pins 4 and 8 measure -21/+21 V vs the -15/+15 mentioned above
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    Poee7R wrote: »
    Damn, damn, damn, you guys are killing me here.

    George, Fred, Ben or anyone feeling like doing this to mine for a couple bucks? :D


    Dave

    I'll do it if you are not in a hurry,,I do this for fun/hobby,so it won't be a quickie.:)
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited May 2010
    davide256 wrote: »
    R113 on the power supply board has a capacitor instead of a resistor
    R113 should be a 3k32 resistor.How did that cap get in there?
    Pins 4 and 8 measure -21/+21 V vs the -15/+15 mentioned above
    Maximum supply voltage for the OPA627 is rated at + -18 volts so thats why they are failing.That cap in the regulator circuit is likely part of the issue for the negative voltage but doesn't explain why the positive reg (LM317) is putting out 21 volts also.
  • heiney9heiney9 Posts: 24,107
    edited May 2010
    davide256 wrote: »
    Ok pictures attached and some more data

    R113 on the power supply board has a capacitor instead of a resistor
    Pins 4 and 8 measure -21/+21 V vs the -15/+15 mentioned above

    If you look at the pics I posted as Fred states there should be a resistor at R113. Wow!
    "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 May 2010
    You da man Fred.;)
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited May 2010
    Poee7R wrote: »
    Damn, damn, damn, you guys are killing me here.

    George, Fred, Ben or anyone feeling like doing this to mine for a couple bucks? :D


    Dave
    I would gladly do it for you Dave but looks like George has you covered.Also shipping might be a pain.
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    FTGV wrote: »
    I would gladly do it for you Dave but looks like George has you covered.Also shipping might be a pain.

    Fred--I'll definately defer to you,,as your expertise far surpasses mine--take him up on it Dave:)
    JC approves....he told me so. (F-1 nut)
  • FTGVFTGV Posts: 3,644
    edited May 2010
    Fred--I'll definately defer to you,,as your expertise far surpasses mine--take him up on it Dave:)
    You are plenty capable sir,and I would be concerned that shipping up here would be expensive and a hassle with customs etc.
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    Whatever you guys decide is fine with me,I'll be happy to help folks with any upgrades. Let me know :)
    JC approves....he told me so. (F-1 nut)
  • Poee7RPoee7R Posts: 902
    edited May 2010
    Im happy to be helped, haha.

    Whichever of you fine gentlemen, I would be grateful. Due to logistics, George you would probably be best option, Pm inc.

    Thank you Fred for the offer, as always, you rock.


    Dave
    Once again we meet at last.
  • george danielgeorge daniel Posts: 11,989
    edited May 2010
    Guys just remember,when attempting this mod,, "never get out of the boat";)

    Edit; stay close to the original plan,is what the above statement means.
    JC approves....he told me so. (F-1 nut)
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