Adcom GFA 555

hertz9753
hertz9753 Posts: 310
edited July 2012 in Electronics
I bought one on Ebay for $262 shipped on Sunday and it got here yesterday. It is modded with AR RCA female cables for the input. It sounds great. :smile:

001.jpg
AVR-Onkyo TX-NR808
Front amp-Adcom GFA 555>Polk Audio LSi9's(Vr3 Castle Mods)
Center amp-Adcom GFA 5400>Polk Audio LSi9 bi-wired(Vr3 Castle Mod)
Surrounds-Polk Audio F/X500's<Onkyo TX-NR808
Sub-Velodyne SPL-1000R
Post edited by hertz9753 on
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Comments

  • PreCd
    PreCd Posts: 786
    edited June 2012
    Congratulations on purchasing an affordable amp that sounds pretty decent. I have had one myself for almost a year now and really like it. Again they are a great bang for the buck. If it were mine I would have a VMM handy and check DC offset at the speaker out leads. Let the amp warm up some and with the preamp connected check across each channel on the DC mV scale to see what it reads.

    Enjoy it! Great getting new gear.
    SDA2BTL
    Marantz CD5004
    Adcom GFA-545
    Bottlehead Quickie Tube Preamp
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  • cnh
    cnh Posts: 13,284
    edited June 2012
    $262 shipped! That's an excellent price for that! And a work horse of an amp. I have one that I use when I need to amp up the power which isn't that often. But it's good to know I have it when I need it!

    Have fun. That amp can compete with anything in its class and maybe some above. Adcoms are, in some ways, underrated amps. I remember attending one of the mini-Polk fests and watching two Adcom 565 mono-blocks pretty much outperform amps that cost three to six times their price on "certain" speakers. In other words, the Adcoms, which were the cheaper amps by comparison had, in fact, more "synergy" with a greater variety of speakers than the Bigger Badder Higher End Boys which seemed far more speaker "dependent". Pretty much took most of us by surprise at the gathering!

    Enjoy!

    cnh
    Currently orbiting Bowie's Blackstar.!

    Polk Lsi-7s, Def Tech 8" sub, HK 3490, HK HD 990 (CDP/DAC), AKG Q701s
    [sig. changed on a monthly basis as I rotate in and out of my stash]
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  • Polkie2009
    Polkie2009 Posts: 3,834
    edited June 2012
    Sounds like you got a really sick deal on that sweet little Adcom 555 bro! Always nice to get some new gear for the system:)!
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  • leftwinger57
    leftwinger57 Posts: 2,917
    edited June 2012
    That's a very good price for a solid tank of an amp.Mine was $300 even shipped and have not had any issues what so ever.
    2chl- Adcom GFA- 555-Onkyo P-3150v pre/amp- JVC-QL-A200 tt- Denon 1940 ci cdp- Adcom GFS-6 -Modded '87 SDA 2Bs - Dynamat Ext.- BH-5- X-Overs VR-3, RDO-194 tweeters, Larry's Rings, Speakon/Neutrik I/C- Cherry stain tops Advent Maestros,Ohm model E

    H/T- Toshiba au40" flat- Yamaha RX- V665 avr- YSD-11 Dock- I-Pod- Klipsch #400HD Speaker set-

    Bdrm- Nikko 6065 receiver- JBL -G-200s--Pioneer 305 headphones--Sony CE375-5 disc
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  • lanchile
    lanchile Posts: 560
    edited June 2012
    Congratulations!!!That is a nice unit! make sure to check bias and dc offset. I would also replace all those electrolytic caps for a healthier and longer life of your amp!
    Make it simple...Make it better!
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  • hertz9753
    hertz9753 Posts: 310
    edited June 2012
    Thank's for all the nice comments and info guys! :smile:

    1.jpg
    1.jpg 144.4K
    AVR-Onkyo TX-NR808
    Front amp-Adcom GFA 555>Polk Audio LSi9's(Vr3 Castle Mods)
    Center amp-Adcom GFA 5400>Polk Audio LSi9 bi-wired(Vr3 Castle Mod)
    Surrounds-Polk Audio F/X500's<Onkyo TX-NR808
    Sub-Velodyne SPL-1000R
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  • SRTer
    SRTer Posts: 372
    edited June 2012
    PreCd wrote: »
    Congratulations on purchasing an affordable amp that sounds pretty decent. I have had one myself for almost a year now and really like it. Again they are a great bang for the buck. If it were mine I would have a VMM handy and check DC offset at the speaker out leads. Let the amp warm up some and with the preamp connected check across each channel on the DC mV scale to see what it reads.

    Enjoy it! Great getting new gear.

    What numbers should one look for? I have not checked my Adcom GFA-555 mkii.
    Fronts: Polk RTi A9
    Center: Polk CSI A6
    Rears: Polk RTi A7
    Receiver: Pioneer Elite SC-35 (140 watts x 7)
    Amplifier: Adcom GFA-555 Mk.II (200 watt @ 8 ohms)
    Sub: Polk DSW PRO 500 (10 inch, 200 Watt)
    TV: Samsung 59 inch 3D Plasma 600 Hz PN59D7000
    Sources: Samsung BD-D6700 3D Blu-ray Player, DirecTV, PS3, iPhone 4 and IPod Classic with Apple Lossless Tracks
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  • PreCd
    PreCd Posts: 786
    edited June 2012
    SRTer wrote: »
    What numbers should one look for? I have not checked my Adcom GFA-555 mkii.

    If you can get 40 mV and under you are good. Around 50mV and you should be contacting a service department. Mine reads 10mV on both channels which says the amp has very closely matched transistors. However I replaced all the filter caps and small electrolytics on the power supply board.

    Keep in mind this is for my GFA-555 MKI and I do not know if you are looking for the same numbers on your MKII.
    SDA2BTL
    Marantz CD5004
    Adcom GFA-545
    Bottlehead Quickie Tube Preamp
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  • lanchile
    lanchile Posts: 560
    edited June 2012
    SRTer wrote: »
    What numbers should one look for? I have not checked my Adcom GFA-555 mkii.
    I am not sure but I think your amp does not have variable resistor to adjust dc offset, but if it has, it should be set to as close to "0" volt as possible. and for bias voltage, I would set it to 20millivolts to start, I would check heat sink to see if they get too hot at idle. some people set them at lower voltages and some will set them at higher. there is not an "exactly" number for bias but you can set them around those numbers. a good example is with Acurus DIA100 the bias is set to around 3millivolt that is WAY TOO LOW!!! I had one and I left them at 15millivolts and made a huge improvement in sound and I always kept and eye on the heat sinks to make sure it was not too hot, after increasing bias it run just warm at all time, before increasing bias it was as cold as ice and sounded harsh.
    Make it simple...Make it better!
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  • Monster Jam
    Monster Jam Posts: 919
    edited June 2012
    $300-$350 is about the going price of the 555 on eBay. $262 is a great get!
    Do you hear that buzzing noise? :confused:
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  • PreCd
    PreCd Posts: 786
    edited June 2012
    If you are going to set bias do it right:

    http://www.audiolabga.com/pdf/GFA555II%20Adcom.pdf
    SDA2BTL
    Marantz CD5004
    Adcom GFA-545
    Bottlehead Quickie Tube Preamp
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  • lanchile
    lanchile Posts: 560
    edited June 2012
    PreCd wrote: »
    If you are going to set bias do it right:

    http://www.audiolabga.com/pdf/GFA555II%20Adcom.pdf

    10millivolt? I find it low!!! I would set it at least 20millivolt.
    Make it simple...Make it better!
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  • SRTer
    SRTer Posts: 372
    edited June 2012
    Where should I start measuring?
    Fronts: Polk RTi A9
    Center: Polk CSI A6
    Rears: Polk RTi A7
    Receiver: Pioneer Elite SC-35 (140 watts x 7)
    Amplifier: Adcom GFA-555 Mk.II (200 watt @ 8 ohms)
    Sub: Polk DSW PRO 500 (10 inch, 200 Watt)
    TV: Samsung 59 inch 3D Plasma 600 Hz PN59D7000
    Sources: Samsung BD-D6700 3D Blu-ray Player, DirecTV, PS3, iPhone 4 and IPod Classic with Apple Lossless Tracks
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  • lanchile
    lanchile Posts: 560
    edited June 2012
    SRTer wrote: »
    Where should I start measuring?
    Do you see those big resistors on the back of the ouput transistors? well measure the voltage across resistors and that will be the voltage for bias and there is a variable resistor (blue plastic round screw head) and adjust them. I do not know your knowledge in electronics but you should be careful since there is LIVE VOLTAGES INSIDE...that can kill you.:eek:
    Make it simple...Make it better!
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  • leftwinger57
    leftwinger57 Posts: 2,917
    edited July 2012
    PreCd wrote: »
    If you can get 40 mV and under you are good. Around 50mV and you should be contacting a service department. Mine reads 10mV on both channels which says the amp has very closely matched transistors. However I replaced all the filter caps and small electrolytics on the power supply board.

    Keep in mind this is for my GFA-555 MKI and I do not know if you are looking for the same numbers on your MKII.

    I to have an original 555 and was curious about these measurements. Now I do not have a Fluke but I do have a Craftsman Multimter#82015. I used it mainly to check ohm resistance when installing alarms but this is a little different.I have a volt,dc scale,a volt ac scale,an Ohms scale ,and another labled A DC.The+ probe is in v ohm aM
    and the negative probe is in common.When I tried I got #s all over the place from 42.3 to 47.3 but then it flutuatates.Am I doing this right and are the reading so far correct. What I did was to take the lead that came from one side of the Adcom to a lead to the speaker selector took it off and then got the reading .A is this the right meter and did I do the right thing.. Also do you have to do both atthe same time.
    2chl- Adcom GFA- 555-Onkyo P-3150v pre/amp- JVC-QL-A200 tt- Denon 1940 ci cdp- Adcom GFS-6 -Modded '87 SDA 2Bs - Dynamat Ext.- BH-5- X-Overs VR-3, RDO-194 tweeters, Larry's Rings, Speakon/Neutrik I/C- Cherry stain tops Advent Maestros,Ohm model E

    H/T- Toshiba au40" flat- Yamaha RX- V665 avr- YSD-11 Dock- I-Pod- Klipsch #400HD Speaker set-

    Bdrm- Nikko 6065 receiver- JBL -G-200s--Pioneer 305 headphones--Sony CE375-5 disc
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  • PreCd
    PreCd Posts: 786
    edited July 2012
    First off be very careful. What you want to do is disconnect your speaker leads from your amp. Let it warm up some (5-10 minutes) and with your preamp connected place the red lead of your volt meter into the red speaker out of your amp and the black lead of your volt meter into the black speaker out of your amp. Either be on the mV setting on your meter or decipher the decimal points. Do this for the right and left channel. It should not fluctuate much but you may see a little.
    leftwinger57 wrote: »
    I to have an original 555 and was curious about these measurements. Now I do not have a Fluke but I do have a Craftsman Multimter#82015. I used it mainly to check ohm resistance when installing alarms but this is a little different.I have a volt,dc scale,a volt ac scale,an Ohms scale ,and another labled A DC.The+ probe is in v ohm aM
    and the negative probe is in common.When I tried I got #s all over the place from 42.3 to 47.3 but then it flutuatates.Am I doing this right and are the reading so far correct. What I did was to take the lead that came from one side of the Adcom to a lead to the speaker selector took it off and then got the reading .A is this the right meter and did I do the right thing.. Also do you have to do both atthe same time.
    SDA2BTL
    Marantz CD5004
    Adcom GFA-545
    Bottlehead Quickie Tube Preamp
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  • leftwinger57
    leftwinger57 Posts: 2,917
    edited July 2012
    My pre-amp was not on . Time for a new test and again would the lead from the Adcom going to the speaker selector serve the same purpose. It would be just that much easier to get to those wires on top if they infact do come from the Adcom left and right speaker jacks......
    2chl- Adcom GFA- 555-Onkyo P-3150v pre/amp- JVC-QL-A200 tt- Denon 1940 ci cdp- Adcom GFS-6 -Modded '87 SDA 2Bs - Dynamat Ext.- BH-5- X-Overs VR-3, RDO-194 tweeters, Larry's Rings, Speakon/Neutrik I/C- Cherry stain tops Advent Maestros,Ohm model E

    H/T- Toshiba au40" flat- Yamaha RX- V665 avr- YSD-11 Dock- I-Pod- Klipsch #400HD Speaker set-

    Bdrm- Nikko 6065 receiver- JBL -G-200s--Pioneer 305 headphones--Sony CE375-5 disc
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  • PreCd
    PreCd Posts: 786
    edited July 2012
    I am not familiar with the speaker selector switch. If it where me I would take all other equipment connected to the speaker out leads off and take the readings directly from the amp.
    leftwinger57 wrote: »
    My pre-amp was not on . Time for a new test and again would the lead from the Adcom going to the speaker selector serve the same purpose. It would be just that much easier to get to those wires on top if they infact do come from the Adcom left and right speaker jacks......
    SDA2BTL
    Marantz CD5004
    Adcom GFA-545
    Bottlehead Quickie Tube Preamp
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  • lanchile
    lanchile Posts: 560
    edited July 2012
    PreCd wrote: »
    I am not familiar with the speaker selector switch. If it where me I would take all other equipment connected to the speaker out leads off and take the readings directly from the amp.

    Why all this trouble? He should just take amp out and check all, but if I am not mistaken, this amp does not have trimmer to adjust dc offset. what I would check first would be the bias and then dc offset later, also I would replace all those old electrolytic caps. the amp has to be disconnected from any source just connected to the outlet power!
    Make it simple...Make it better!
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  • PreCd
    PreCd Posts: 786
    edited July 2012
    This is not good advice my friend. The bias being off is not dangerous to a set of nice speakers. DC offset is. So let him check his offset and then go about the business of setting his bias according to the instructions posted from Adcom IF he feels comfortable doing so. This amp needs to have the preamp connected to get a accurate reading when looking at DC Offset. Every amp is not the same.........
    lanchile wrote: »
    Why all this trouble? He should just take amp out and check all, but if I am not mistaken, this amp does not have trimmer to adjust dc offset. what I would check first would be the bias and then dc offset later, also I would replace all those old electrolytic caps. the amp has to be disconnected from any source just connected to the outlet power!
    SDA2BTL
    Marantz CD5004
    Adcom GFA-545
    Bottlehead Quickie Tube Preamp
    · Share on FacebookShare on Twitter