Adcom GFP-750 Back in the System

2

Comments

  • Posts: 3,649
    edited April 2012
    If it worked in passive mode then it's possible his source had a non standard wiring config. on it's XLR ouput connector?.
  • Posts: 25,229
    edited April 2012
    FTGV wrote: »
    Actually their purpose appears merely short the inverted half of the input to ground avoiding the potential for extraneous noise pick up,sound should'nt change.

    Change how? If you don't short the input you get almost no sound out of the single ended cd input when used, not because of extraneous noise. Same with my Aleph 30.

    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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • Posts: 3,649
    edited April 2012
    heiney9 wrote: »
    Change how?
    Your words"won't sound right".According to the schematic the non inverted half (single ended)of the circuit should still be active with out the jumpers,shorting the other half to ground will keep it from acting like an antenna for RF noise pick up..
  • Posts: 2,588
    edited April 2012
    FTGV wrote: »
    Your words"won't sound right".According to the schematic the non inverted half (single ended)of the circuit should still be active with out the jumpers,shorting the other half to ground will keep it from acting like an antenna for RF noise pick up..

    I just took the pins out of the bal inputs and the sound has not changed as far as I can tell. I'm running a CDP into the RCA inputs.
    Thanks for chiming in FTGV. I'll make sure to ask him about that.
  • Posts: 25,229
    edited April 2012
    All I can state is my experience with said piece of gear with the jumpers removed when using the single ended cd input. I guess I have to ask, have you owned one and tried to play music through the single ended input with out the jumpers in place? They need to be there in order to get any sort of satisfactory sound from the unit. I don't know how much more plain I can state it.

    All I can do is refer whomever to page 3 of the owners manual

    http://www.adcom-usa.com/userguides/gfp-750-ug.pdf
    "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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • Posts: 25,229
    edited April 2012
    I just took the pins out of the bal inputs and the sound has not changed as far as I can tell. I'm running a CDP into the RCA inputs.
    Thanks for chiming in FTGV. I'll make sure to ask him about that.

    That's not been my experience, but I'll give it another whirl this week. It was probably a couple years ago I was using the the GDA 700 dac which is balanced so I was messing around with those inputs and jumpers. I'll concede I may have the results confused with the Aleph 30 and running it without the jumpers when I first got it, memory can be decieving at times.
    "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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • Posts: 25,229
    edited April 2012
    The third connection are the balanced inputs, which occur through standard XLR connectors.
    The balanced input impedance is 52 Kohms. Input pin 1 of the XLR connector is input
    ground, pin 2 is the positive input, and pin 3 is the negative input. As shipped, there is a
    shorting jumper between pins 1 and 3, which is the configuration for single-ended input.
    This shorting jumper should be used when operating the amplifier with the RCA input,
    otherwise you will not get the proper gain figure for the amplifier.
    If you operate the amplifier
    with balanced inputs, you will remove this jumper, and we advise you to save it carefully for
    future use.


    This from the Aleph 30 owners manual may be what my memory was telling me was the issue with the Adcom, so perhaps I was in error.

    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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • Posts: 2,588
    edited April 2012
    heiney9 wrote: »
    That's not been my experience, but I'll give it another whirl this week. It was probably a couple years ago I was using the the GDA 700 dac which is balanced so I was messing around with those inputs and jumpers. I'll concede I may have the results confused with the Aleph 30 and running it without the jumpers when I first got it, memory can be decieving at times.

    I didn't do any extensive listening so it may have changed but my first impression is it sounds the same.
  • Posts: 3,649
    edited April 2012
    I just took the pins out of the bal inputs and the sound has not changed as far as I can tell. I'm running a CDP into the RCA inputs.
    Thanks for chiming in FTGV. I'll make sure to ask him about that.
    Your welcome, thanks for the confirmation.
  • Posts: 3,649
    edited April 2012
    heiney9 wrote: »
    All I can state is my experience with said piece of gear with the jumpers removed when using the single ended cd input. I guess I have to ask, have you owned one and tried to play music through the single ended input with out the jumpers in place?
    No and I did'nt Google it either.:wink:
  • Posts: 25,229
    edited April 2012
    Oh, I'm sure I remembered it wrong :redface:. That's the way it goes.

    I wasn't asking the question to be snide, I was wondering if you had actually tried it because I was starting to have my doubts about what I was remembering at that point.

    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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • Posts: 878
    edited April 2012
    heiney9 wrote: »
    chandler9a, you could have waited a few weeks and I'm sure audiocr381ve would have his up forsale. :razz:

    H9

    No joke, I was actually going to hold off and wait for his :cheesygrin:

    I can't wait to hear this piece, it will be by far the nicest addition to the system.
  • Posts: 2,588
    edited April 2012
    chandler9a wrote: »
    No joke, I was actually going to hold off and wait for his :cheesygrin:

    I can't wait to hear this piece, it will be by far the nicest addition to the system.

    Hey! Don't join in with his ball-bust! :cheesygrin:
  • Posts: 3,649
    edited April 2012
    chandler9a wrote: »
    No joke, I was actually going to hold off and wait for his :cheesygrin:
    Wait until after he upgrades the caps in the signal path thus releasing all the Mosfet goodness.:wink:
  • Posts: 2,588
    edited April 2012
    FTGV wrote: »
    Wait until after he upgrades the caps in the signal path thus releasing all the Mosfet goodness.:wink:

    Hold up now, what do I need to upgrade? Upgrading caps is only going to effect the active mode though, right?
  • Posts: 878
    edited April 2012
    no ball busting, maybe just a little... Seriously, I am looking forward to how this pre sounds. I'm going to try it on my Fathers 1.2TL as well, should be interesting.
  • Posts: 3,649
    edited April 2012
    Upgrading caps is only going to effect the active mode though, right?
    Correct the input and ouput coupling caps only come into play in active mode.The DIY tweaker types with OCD using it in active mode might find it sonically benificial to replace certain generic quality caps with somthing better.
  • Posts: 2,588
    edited April 2012
    FTGV wrote: »
    Correct the input and ouput coupling caps only come into play in active mode.The DIY tweaker types with OCD using it in active mode might find it sonically benificial to replace certain generic quality caps with somthing better.

    Me wants to try it. Where do I go to find more info?
  • Posts: 2,588
    edited April 2012
    chandler9a wrote: »
    no ball busting, maybe just a little... Seriously, I am looking forward to how this pre sounds. I'm going to try it on my Fathers 1.2TL as well, should be interesting.

    I'm guessing you'll be quite shocked at the difference it makes.
  • Posts: 3,649
    edited April 2012
    Me wants to try it. Where do I go to find more info?
    Well it's only for those comfortable with soldering and desoldering PC boards and some minor electronic assembly/disassembly ,heres a primer.
    http://www.head-fi.org/t/392211/adcom-gfp-750-diy-mod-finally-finished-warning-not-dial-up-friendly-loads-of-pics
    http://www.diyaudio.com/forums/pass-labs/37960-replacing-adcom-gfp750-caps-2.html
  • Posts: 2,588
    edited April 2012
    FTGV wrote: »
    Well it's only for those comfortable with soldering and desoldering PC boards and some minor electronic assembly/disassembly ,heres a primer.http://www.diyaudio.com/forums/pass-labs/37960-replacing-adcom-gfp750-caps-2.html

    I'm really comfortable with it after 4 crossovers in 2 pairs of SDA's. Thanks for the link!
  • Posts: 3,649
    edited April 2012
    There seems to be a lot of these floating around CP so I'm surprised few if any having been modded.Personally I would restrict the mod to changing caps in four sections of each channel as in the 2x10uf and 2x 100uf.Somthing like Sanyo OsCon's would be well suited.
  • Posts: 2,588
    edited April 2012
    FTGV wrote: »
    There seems to be a lot of these floating around CP so I'm surprised few if any having been modded.Personally I would restrict the mod to changing caps in four sections of each channel as in the 2x10uf and 2x 100uf.Somthing like Sanyo OsCon's would be well suited.

    If you tell me the exact parts to order, I will do it. I have no clue where the locations for the parts are on the board but I'll find em' and get those worthless cylinders out of there.
  • Posts: 25,229
    edited April 2012
    FTGV wrote: »
    There seems to be a lot of these floating around CP so I'm surprised few if any having been modded.Personally I would restrict the mod to changing caps in four sections of each channel as in the 2x10uf and 2x 100uf.Somthing like Sanyo OsCon's would be well suited.

    If you are willing to tutor as in paint by number, I'd give it a shot. I found the DIYAUDIO post too long and complicated and not specific enough. That pre cost me a lot of money and I don't feel like taking a huge chance on ruining it. But if you can break it down where the best place to upgrade some caps would be, I'd give it a whirl.

    If you need a schematic, I can probably find one on-line somewhere.

    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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • Posts: 2,588
    edited April 2012
    heiney9 wrote: »
    If you are willing to tutor as in paint by number, I'd give it a shot. I found the DIYAUDIO post too long and complicated and not specific enough. That pre cost me a lot of money and I don't feel like taking a huge chance on ruining it. But if you can break it down where the best place to upgrade some caps would be, I'd give it a whirl.

    If you need a schematic, I can probably find one on-line somewhere.

    H9

    Totally agree. The DIYAUDIO thread was all over the place. I'd be in on this experiment too but would also need some guidance. I'd even be willing to make a little video of exactly how to do it for future modders (if it is indeed a worthwhile upgrade).
  • Posts: 1,215
    edited April 2012
    Hi Guys,
    I'm the one that bought Shane's 750. I had it
    connected to my TPA Buffalo III via balanced connections and to my Aleph 30 balanced also. The jumpers are inside to select the use of the cd input. It can be used with either type-balanced or se on cd input only. So I switched a set of jumpers inside the case to use the balanced inputs. At least thats what I recall. I had the manual but must have deleted it. My system works fine now using the same all balanced connections with my Forte preamp. The passive worked fine but the active mode was quieter. Thats using the cd input via balanced
    connections. Hope that clears things up.
    Main system: Lyngdorf TDAI 2170 w/ Pioneer 42" plazma-> Polk LSiM 703 w/Tivo, Marantz tuner, BRPTT: Nothingham Spacedeck-> Pioneer PL L1000 linear arm-> Soundsmith DL 103R-> SUT->Bottlehead ErosDigital: I3 PC w/ Jriver playing flac -> Sonore Ultrarendu -> Twisted Pair Audio ESS 9028 w/ Mercury IVY Vinyl rips: ESI Juli@24/192-> i3 PC server
  • Posts: 25,229
    edited April 2012
    It's supposed to be quieter, sometimes up to to 50% quieter. The passive stage has much less gain because it's passive not active. As far as opening the case to switch the jumpers, you are mistaken as the jumpers fit into 2 of the 3 holes on the balanced cd input.

    There is nothing wrong with the pre-amp in passive mode, that's exactly how it's supposed to work, passive has no gain therefore you need to turn it up a lot more to get the same output as the active circuitry.

    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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • Posts: 25,229
    edited April 2012
    Ooooops mis-read Bikerboy's post. If the active was quieter then there was an issue, most likely a connection issue.

    Shane, have you been able to use the balanced connections yet?

    Still baffled about having to open the unit to switch the balanced cd input. That is NOT how it works unless someone bastardized that one or some DIY procedure from another owner.

    Here is the owners manual

    http://www.adcom-usa.com/userguides/gfp-750-ug.pdf

    You can clearly see at the bottom of page 3 looking on the left the jumpers short the 1 and 3 positions in the input. Go to page 4 and look at 10,11,12.

    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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!
  • Posts: 786
    edited April 2012
    It is not out of the question that there was more than one layout for the 750. My GFA-555 went through 3 revisions that I know of with all having a different PCB layout and changes made to various components. My GFP-565 is the same so I would not doubt that there are different variations of the 750. That may explain the jumper inside the case.
    heiney9 wrote: »
    Ooooops mis-read Bikerboy's post. If the active was quieter then there was an issue, most likely a connection issue.

    Shane, have you been able to use the balanced connections yet?

    Still baffled about having to open the unit to switch the balanced cd input. That is NOT how it works unless someone bastardized that one or some DIY procedure from another owner.

    Here is the owners manual

    http://www.adcom-usa.com/userguides/gfp-750-ug.pdf

    You can clearly see at the bottom of page 3 looking on the left the jumpers short the 1 and 3 positions in the input. Go to page 4 and look at 10,11,12.

    H9
    SDA2BTL
    Marantz CD5004
    Adcom GFA-545
    Bottlehead Quickie Tube Preamp
  • Posts: 25,229
    edited April 2012
    But there wasn't, other than they changed the color of the boards when they moved final assembly out of the USA, which I'm still not convinced makes a difference in sound.
    "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 Labs XA25 | EE Avant Pre | EE Mini Max Supreme DAC | MIT Shotgun S1 | Pangea AC14SE MKII | Legend L600 | BlueSound Node 3 - Tubes add soul!

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