The Adcom GDA 600 modification thread

11213141517

Comments

  • SCompRacerSCompRacer Posts: 6,572
    edited August 2012
    All hail Jay! All hail Jay! Thanks for the kind words but you did great! I've read about them Hakko's, but using it makes me want one to replace my spring operated solder sucker. One handed, trigger control action. Love the tone of the pump changing when you have a clean, cleared out hole in the PCB.

    Some of them solder joints reminded me of working with the RoHS lead free solder. The stuff just didn't want to flow completely out of the hole in the PCB. We ended up adding more solder and having another go with the Hakko 808.

    thumbnail.aspx?q=4846364465496199&id=216db7721a2557f93749edfb2ec5d31b

    I didn't hear it before but it was a great sounding modded DAC in the retro rig downstairs and in the main rig upstairs!
    Make yourself necessary to someone. Ralph Waldo Emerson

    Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ & Pro 11+ * Signature Series Sonore Music Server w/Deux PS* Twisted Pear Buffalo III Dual Mono ESS Sabre32 DAC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *

  • sda2mikesda2mike Posts: 3,135
    edited August 2012
    well, as i posted, it's back:cheesygrin: i had some lengthy sessions friday and saturday..it's a huge improvement! like going from a redbook cd to a well-done re-master! it is not sutble! i was pushing some serious current into my 2btl's and i think my ears were the weak link;) the bass now has incredible slam and depth!that's on all recordings...not just when it feels like showing up, like before;) the drum sounds are great! snares sound like snares....you can almost se the wires in the snare drum...pianoes sound better than ever...and the SDA???? holy schnikeys! active alive and all over!! this is a must do upgrade! thanks to george daniel for this thread and for doing the surgery! i couldn't have done it! the parts he sent back are TINY:)

    mike
  • heiney9heiney9 Posts: 23,459
    edited August 2012
    Pretty serious upgrade, eh. It's been so long since I did mine that obviously it still sounds fabulous but I forget what the stock unit sounded like by now. It would be nice to compare the stock unit again.

    All I know is I grin from ear to ear with my rig. Finally have things dialed in where I like them as far as cables, tubes and gear, etc.

    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!
  • sda2mikesda2mike Posts: 3,135
    edited August 2012
    with the stock unit, i thought i'd reached the pinnacle of what my system could do...it was depressing when i took it out of service to send to george...veiled, digital and lifeless..now, there's things jumping all around the room!
  • heiney9heiney9 Posts: 23,459
    edited August 2012
    The Adcom dac's were very, very good for their day especially the BB PCM-63 chipset. Add a modern, better Op-amp and better caps in the signal path and beef up the PS section with new caps and Viola', you have a superb sounding updated DAC that sounds excellent, for a fraction of the cost of something comparable, new.

    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!
  • FTGVFTGV Posts: 3,530
    edited August 2012
    Great job Rich and Jay.
  • george danielgeorge daniel Posts: 11,809
    edited August 2012
    sda2mike wrote: »
    well, as i posted, it's back:cheesygrin: i had some lengthy sessions friday and saturday..it's a huge improvement! like going from a redbook cd to a well-done re-master! it is not sutble! i was pushing some serious current into my 2btl's and i think my ears were the weak link;) the bass now has incredible slam and depth!that's on all recordings...not just when it feels like showing up, like before;) the drum sounds are great! snares sound like snares....you can almost se the wires in the snare drum...pianoes sound better than ever...and the SDA???? holy schnikeys! active alive and all over!! this is a must do upgrade! thanks to george daniel for this thread and for doing the surgery! i couldn't have done it! the parts he sent back are TINY:)

    mike

    Took me long enough Eh Mike?-- I'm glad that you are happy with it.
    JC approves....he told me so. (F-1 nut)
  • sda2mikesda2mike Posts: 3,135
    edited August 2012
    well worth it George! Thank you!
  • heiney9heiney9 Posts: 23,459
    edited March 2013
    Dangerboy (AL) just bought a GDA 600 so I bumped this for him.

    Still interested in Jay's and Mike's thoughts now that you've had some serious time with it.

    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!
  • sda2mikesda2mike Posts: 3,135
    edited March 2013
    H9, it's still a must-do upgrade...it hasn't 'worn on me', the effect of the upgrade, that is...see post #484, that sums it all up..thanks

    mike
  • agfrostagfrost Posts: 1,978
    edited March 2013
    I'm still exceptionally happy I both a) got the DAC (thanks, Dave!) and b) did the George/Fred modding (thanks, Rich!). When I first got it, I could toggle between my CD player's analog outs and the Adcom via my preamp's remote, and the sound via the modded DAC was clearly better--quieter background, more spacious & airy soundstage, and more... Now that I've upgraded my preamp to the Manley Shrimp, I've lost my ability to toggle back and forth, but I'm still offering the Adcom pride of place in my rack. Super happy with my current sound.

    I promised some months ago I'd add a shot of my power supply board once I got the Nichicon FGs soldered in, so I'll take the opportunity to do so now...

    8d75efd3-d9e0-440d-9d5e-d87508e2cb4d_zps277e1eec.jpg
    Jay
    SDA 2BTL * Musical Fidelity A5cr amp * Marantz DV-9500 * Modded Adcom GDA-600 DAC
    Micro Seiki DQ-50 * A hodgepodge of cabling * Belkin PF60
    Preamp rotation: Krell KSL (Thanks Rich!) * Manley Shrimp * PS Audio 5.0
  • SCompRacerSCompRacer Posts: 6,572
    edited March 2013
    agfrost wrote: »
    I promised some months ago I'd add a shot of my power supply board once I got the Nichicon FGs soldered in, so I'll take the opportunity to do so now...

    8d75efd3-d9e0-440d-9d5e-d87508e2cb4d_zps277e1eec.jpg

    Kewl! Good job Jay! It looks and sounds great!
    Make yourself necessary to someone. Ralph Waldo Emerson

    Salk SoundScape 8's * Audio Research Reference 3 * Bottlehead Eros Phono * Park's Audio Budgie SUT * Krell KSA-250 * Harmonic Technology Pro 9+ & Pro 11+ * Signature Series Sonore Music Server w/Deux PS* Twisted Pear Buffalo III Dual Mono ESS Sabre32 DAC * Heavy Plinth Lenco L75 Idler Drive * AA MG-1 Linear Air Bearing Arm * AT33PTG/II & Denon 103R * Richard Gray 600S * NHT B-12d subs * GIK Acoustic Treatments * Sennheiser HD650 *

  • george danielgeorge daniel Posts: 11,809
    edited March 2013
    congrats!
    JC approves....he told me so. (F-1 nut)
  • kindkind Posts: 3
    edited July 2014
    Hi guys!
    Sorry for wakening this thread up :-)
    Life goes on and I've just got my GDA-600. Actually I like it's sound, but I'm mad about mods.

    I've ordered OPA627 and going to order caps for replacement.

    Read all 17 pages carefully. Everything is clear except .1 bypass film caps.
    May be there is name for it? I can't get which one to order.

    Appreciate for your help.
  • FTGVFTGV Posts: 3,530
    edited July 2014
    They are Panasonic V series stacked films. Digi Key part# http://www.digikey.ca/product-detail/en/ECQ-V1H104JL/P4525-ND/13790

    When/if installing try to keep lead lengths as short as poissible.
  • kindkind Posts: 3
    edited July 2014
    Thanks!

    I've unsoldered original OpAmps.
    Installed Dip8 socket and have tried 2 OpAmps: LM4562 and AD8599.

    LM4562 sounds too sharp and flat, but very dynamic. Didn't like it actually.
    AD8599 is very good, but it sounds just like original Adcom 7AA OpAmp (which I like a lot BTW).

    I also biased OpAmps into class A.
    Just soldered 3,3 kOhm resistor to 1 and 4 leg of socket, and another 3.3 kOhm resistor to 7 and 4 leg.
    Seems like it made OpAmps sound more tight.
  • soundfreak1soundfreak1 Posts: 2,709
    edited July 2014
    Gl with the mod, did my 700 and have been thrilled with the results, my tech did a 600 also for a friend and is was fantastic. Big diff. Enjoy
    Main Rig:
    Krell KAV 250a biamped to mid/highs
    Parasound HCA1500A biamped to lows
    Nakamichi EC100 Active xover
    MIT exp 1 ic's
    Perreaux SA33 class A preamp
    AQ kingcobra ic's
    YAMMY cdp
    Lehmann audio black cube SE phono pre, Audioquest phono wire (ITA1/1)
    Denon DP-1200 TT. AToc9ML MC cart.
    Monster HTS 3600 power conditioner
    ADS L1590/2 Biamped
    MIT exps2 speaker cable
  • FTGVFTGV Posts: 3,530
    edited July 2014
    kind wrote: »
    I also biased OpAmps into class A.
    Just soldered 3,3 kOhm resistor to 1 and 4 leg of socket, and another 3.3 kOhm resistor to 7 and 4 leg.
    Seems like it made OpAmps sound more tight.
    There is already provision for a resistor or optionally a fet for biasing the stock op-amp into class A.I don't have a schem handy so not sure of the value.3.3 k seems low and may be pulling excessive current through the opamp's output stage.

    The OPA1602 also looks like an interesting option.It's an SMD part so an adapter would be required.
  • kindkind Posts: 3
    edited July 2014
    I don't have a schem handy so not sure of the value.3.3 k seems low and may be pulling excessive current through the opamp's output stage.
    Neither do I. :-)
    OpAmps are warm but not hot. So current seems to be ok.
    15V / 3300 Ohm = 0,0045A.
    Diyers experiment with lower and higher values.
    The OPA1602 also looks like an interesting option.It's an SMD part so an adapter would be required.
    I'll keep that in mind, thanks.
    AD8599 is SMD as well. I soldered it to extra dip8 socket. In fact I don't have skills in that, so that was funny :-)
  • Sev1Sev1 Posts: 2
    Hi all, I know this is a super old thread, but I'm currently modding my GDA 600. I had a question regarding the output stage. Every inverting Op-Amp Diagram I have seen shows a resistor prior to the - Input on the Op-Amp. In the GDA 600 schematic, I don't see a resistor in line between the PCM63 output and the Op-Amp Input. I do see 2 resistors, but they appear to be tied to the +/- power supplies.

    Also, if the output stage is an inverting Op-Amp followed by a non-inverting buffer, does that mean the output of the DAC is inverted?

    Thanks!
  • FTGVFTGV Posts: 3,530
    edited July 2016
    Since the PCM63 dac chip has a current output the opamp directly following it is configured as an I-V (current-voltage)convertor or transimpedance amp,not as a standard inverting opamp.While the inverted opamp connection does invert phase other phase shifts in the circuit result in the actual output phase being non inverted.
  • lightman1lightman1 Posts: 8,608
    What???? :/
  • Sev1Sev1 Posts: 2
    Thanks FGTV! Regarding the 2 resistors after the PCM63. Area they in the signal path?
  • george danielgeorge daniel Posts: 11,809
    Wow,,,it's been 7 years,,, mine is still purring like a kitten,,time flies,,many thanks to Fred for his comments and advice!
    JC approves....he told me so. (F-1 nut)
  • heiney9heiney9 Posts: 23,459
    This was a fun project. About a year ago I moved mine on to someone here. I currently am running a slightly modded Eastern Electric DAC Plus w/discrete DEXA op-amps and I have to say as good as the Adcom was, the EE is a LOT better. But then it should be.

    Getting ready to swap the tube output caps from what looks like Mulitcaps w/EE script to Clarity Cap ESA's and I am replacing (3) I/C voltage regs with DEXA discrete voltage regs. Should improve it even more.

    Doing the Adcom mod has given me the confidence to do this mod. The Op-amps were plug-n-play since they were socketed.... :D
    "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!
  • agfrostagfrost Posts: 1,978
    Still running mine; still happy with it. Thanks George, I believe some of the caps I installed were extras you passed along from your original purchase.
    Jay
    SDA 2BTL * Musical Fidelity A5cr amp * Marantz DV-9500 * Modded Adcom GDA-600 DAC
    Micro Seiki DQ-50 * A hodgepodge of cabling * Belkin PF60
    Preamp rotation: Krell KSL (Thanks Rich!) * Manley Shrimp * PS Audio 5.0
  • keckkeck Posts: 20
    Good day to all,
    I am new to the forum. I have just purchase the Adcom GDA600, still waiting for it to arrive. Did some search and found out this thread discussion on the its mod. I am very interested to unlock its potential :) .
    I have already ordered all the components needed for the PS and Analog section mod. It actually cost nearly twice than the $ i pay for the GDA600 :# . as mention previously by annihilatorg. So glad that this thread is still active and thank you so much for all the members contribution to make it happen ;)
    Am so excited for the big project, but will not start in this few weeks cos i would like to hook up to listen the original DAC potential first.

    My current setup:
    1) Azur 651C
    2) MSB link dac
    3) B & K Reference 5 S2
    4) Adcom GFA535II
    5) Polk Audio SDA 2B
    6) Infinity Kappa Series 6.2 (sometimes only)
    7) Klipsch RF25 (sometimes only)
    8) Azur 350A (sometimes only)
  • keckkeck Posts: 20
    Hi all, i have received my GDA600 a week ago. Hook it up and it sounds really good.
    Today i just open up and realized that the a lot of the caps seems like not the original. Is it being modded by someone else previously or is there any other version that anyone known of?
    The red caps are all Rubycon Black Gate , The caps at power section is Nichikon Muse
    kj04djluydtw.jpg
    dcz3azv9u6em.jpg
    dtsnhdziqgol.jpg
    spa9garpwhpj.jpg
    xf8mxre27ex1.jpg
  • heiney9heiney9 Posts: 23,459
    Looks like some caps were replaced, but it's not a full mod as the op-amps and the caps in the signal path of the op-amps look stock. That's the part of the mod that really gives most performance boost. It's also the more expensive part of the mod
    "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: 3,530
    edited March 23
    And hey they installed a $50 "audiophile" fuse. That alone should improve it an order of magnitude. ;)
    At some point you might want to install a pair of quality 8 pin DIP sockets and try rolling some different opamps. There are several dual opamps that are worth trying and are relatively inexpensive.Some of the better opamps in standard DIP packages are getting harder to find as they are being discontinued in favour of SMD devices.The latter would require a special SMD to DIP adaptor.
Sign In or Register to comment.

Howdy, Stranger!

It looks like you're new here. If you want to get involved, click one of these buttons!