Page 3 of 4 FirstFirst 1234 LastLast
Results 31 to 45 of 48

Thread: Blown Adcom 555 II

  1. #31
    Senior Member Krunchy's Avatar
    Join Date
    Mar 2007
    Location
    New York
    Posts
    1,224
    I've been following this thread for a bit as it caught my eye right from the start. When I had the 4345's set up last in June (they are still not set up at this point, home renovations continue here ) I was using two adcoms 5802's to drive them and it sounded fine, really clean. I have no problems with them and although they have more juice than I will ever need (not my main reason for purchasing them, I rarely got them past the half way point) I would have to agree wholeheartedly that the quality of the juice is more important than the quantity.

    As a point of interest, I also have another amp that I really like set up with my 4313B's, and that is a Vincent SV-236. This is an Integrated Tube Amp/& solid state, the firts 10w are class A and the remaining 90 are ss.
    I do not know what people think of them and frankly do not care as I am very fond of the quality of sound that comes out of my little speakers, the system sounds incredible.....nice and warm, crisp & clean an interesting concept altogether.

    That said, maybe it would be interesting if we had another thread where people listed some of their favorite ams/systems :dont-know. For a while now I've been intruigued by the Mark Levinson stuff as well as the Aleph Pass units. I for one would be quite interested to hear what peoples personal experiences are with some of these components.

    Lots of candy out there! that in itself could be a problem.
    Just Play Music.

  2. #32
    Senior Member
    Join Date
    May 2008
    Location
    Westchester NY
    Posts
    1,120
    Krunche:

    ...good idea to have a thread on different amps, I suppose.


    Anyway, I've owned dozens of amps both tube and SS over the years. When I was looking for a large amp for a current system speaker build, I stated here that, in the past, I have placed a fair amount of reliance on the published THD stats and that I considered these to be indicative of how conservative a manufacturor rates their amps.

    Surprisingly, I learned that most here consider the THD rating of limited use since, according to many here, humans cannot distinguish between amps that have .1% or less THD.

    Anyway, based on that advice, in part, I bought a couple of new big Crown SS amps that l enjoy much.

  3. #33
    Senior Member Krunchy's Avatar
    Join Date
    Mar 2007
    Location
    New York
    Posts
    1,224
    Quote Originally Posted by robertbartsch View Post
    I bought a couple of new big Crown SS amps that l enjoy much.
    Hello Robert!
    To a large extent thats really what it comes down to is'nt it? As long as you are happy with your set up you are on the right track.
    Everything seems to be evolving all the time anyway, have fun now listening to your Crowns my friend & enjoy!
    Just Play Music.

  4. #34
    Senior Member jcrobso's Avatar
    Join Date
    Oct 2008
    Location
    Chicago
    Posts
    1,099

    Bob Carver did some experements years ago on this subject.

    Quote Originally Posted by robertbartsch View Post
    Krunche:

    ...good idea to have a thread on different amps, I suppose.


    Anyway, I've owned dozens of amps both tube and SS over the years. When I was looking for a large amp for a current system speaker build, I stated here that, in the past, I have placed a fair amount of reliance on the published THD stats and that I considered these to be indicative of how conservative a manufacturor rates their amps.

    Surprisingly, I learned that most here consider the THD rating of limited use since, according to many here, humans cannot distinguish between amps that have .1% or less THD.

    Anyway, based on that advice, in part, I bought a couple of new big Crown SS amps that l enjoy much.
    Bob also found out that once the amp distortion gets below .1% that it gets increasingly harder to hear.

    About a year ago people started complaining about the sound in one of the production studios here at the radio station. The studio has JBL 4412A speakers. I listened to the sound in the studio and something had changed!
    There was a fuzziness to the sound, a low level distortion. The people said the speakers were bad, I doubted that it was the speakers. After checking out some things I figured out it was the old Crown DC300, I swapped it out with a different amp, sound was clean again.
    I took the DC300 to the shop and hooked it up, put 8 ohm resistors on and put a 1khz sine wave in, hooked up a scope. What I saw on the scope just blew my mind! On the left channel the positive half of the sine wave was clipped about half way up, but the negative part of the sine wave was OK.
    On the right channel the negative part of the sine was was clipped and the positive part was OK. This is very high amplitude distortion, but it didn't sound terrible, just kinda fuzzy. From what I saw on the scope I though it should have sounded much worse than it did!
    For years I have know that speaker distortion is usually much higher than amp distortion. The reason that we love JBL is because of their low distortion. This experience has reinforced my conclusion that the quality of the speakers is far more important than the amp. I don't get hung up on amps. I use good amps but I don't go crazy over them, JBL speakers,YES!
    I not putting down any one for their like or dislike of any brand of amp. John

  5. #35
    Senior Member
    Join Date
    May 2008
    Location
    Westchester NY
    Posts
    1,120
    well that is good to know that speakers are more important than amps.

    Anyway, for many years, I wanted a Macintosh amp but the high price always scared me away.

    I am pleasantly surprised that a few high power low cost DJ amps I have acquired perform well in a home setting. Consequently, I will likely never own a Mac.

  6. #36
    Senior Member
    Join Date
    Apr 2003
    Location
    Australia
    Posts
    7,942
    Quote Originally Posted by robertbartsch View Post
    BMWCCA:
    Well that is a good question.

    I am not forcing these amps to high levels of power. The Adcom is a 20 year old piece of electronics that I purchased from Fleebay. After a few months it just crapped out and now pushes DC into the speakers.

    The repair shop now claims the power supply needs to be replaced.

    The two identicle Crown amps is somewhat misterious. Both amps are refurbished units sold by the factory with full 3 year warranties. One amp runs ice cold. The other is very sensative to heat and needs a cooling fan to keep it from shutting down from thermal heat.
    http://www.adcom.com/data/manuals/gfa555IImanual.pdf

    Hi Robert,

    The manual has alot of coverage on fault conditions but it does hint that the amp is sensitive to load conditions as it is an ultra wide bandwidth design. I would take that as not always stable into capacitive loads. (have a look at the wiring).

    Also I am not sure why the power supply would need replacing if the protection circuits (thermal) where working or if the fuses blew (per the manual). My suggestion would be to call up Adcom if you have not already and go from there.

  7. #37
    Senior Member
    Join Date
    May 2008
    Location
    Westchester NY
    Posts
    1,120
    OK thanks.

    Apparently, it is not the power supply but the output boards.

    I assume this means some or all of the output transistors are fried. The shop originally quoated me $240 and I said that was more than the value of the amp. They reduced the repair to $170 and we agreed to proceed.

    I have not had good luck with old electronics so I'm reluctant to spend good money after bad. In the future, I plan to avoid old electronics since I can't repair stuff like this myself.

    The amp did work OK when I got it from Fleebay so I can't blame the seller, I suppose.

  8. #38
    Member TonyM's Avatar
    Join Date
    Jan 2009
    Location
    Northern Ca
    Posts
    34
    I'm curious if you ever asked Adcom for a quote. The outputs are usually matched devices and I know for the MOSFET amps some of them are no longer manufactured. I had to order a set through Adcom years ago. The 555 outputs might still be around though but I suspect they need to be matched.

  9. #39
    Senior Member
    Join Date
    May 2008
    Location
    Westchester NY
    Posts
    1,120
    Tony:

    Na.... I did not ask Adcom for the price of the output boards.


    I don't beleive I will be using this repair shop in the future, however. It is diffucult to find an honest shop anymore - everyone is a rip-off artist.

  10. #40
    Senior Member LE15-Thumper's Avatar
    Join Date
    Feb 2004
    Location
    Winnipeg, Canada
    Posts
    602
    Quote Originally Posted by TonyM View Post
    I'm curious if you ever asked Adcom for a quote. The outputs are usually matched devices and I know for the MOSFET amps some of them are no longer manufactured. I had to order a set through Adcom years ago. The 555 outputs might still be around though but I suspect they need to be matched.
    The outputs in the 555 do not need to be matched as they use emitter compensation resistors to help load share. As I said in my earlier post, I would be very surprised if the OP stage is bad. 90% of problems on those was on the input boards, usually drivers and resistors that would open but show no sign of failing.

    I did Adcom warranty from 1988 to 2003
    LE15-Thumper
    "Give me JBL, or give me death"

  11. #41
    Senior Member
    Join Date
    May 2008
    Location
    Westchester NY
    Posts
    1,120
    Thx ....unfortunately, I really can't trust the repair shop. I took a new Crown to them and asked them if they could install a variable control to slow the fans. They called back and told me the fan bearings neaded replacing at $170.

  12. #42
    Junior Member zhid's Avatar
    Join Date
    Mar 2009
    Location
    cccp/usa
    Posts
    6
    the man who designed the adcom amps has desiged others as well.



    you may find something easy to build, from his designs,

    in this forum, utilizing parts from the amp you now have

    http://www.diyaudio.com/forums/forum....php?forumid=8

  13. #43
    Senior Member
    Join Date
    May 2008
    Location
    Westchester NY
    Posts
    1,120
    ..the repair shop told me it was the power supply board that went bad.

    The original quote was $240 but they reduced this to $170 after I told them the market value of a Adcom 550 was around $300 or so.

    Anyway, they did not replace the power supply board with a factory fresh board but mearly replaced the bad electronic components.

    All-in-all, I think it was a bad idea for me to buy old electronics - it just never works out for me.

  14. #44
    Senior Member Uncle Paul's Avatar
    Join Date
    Feb 2005
    Location
    Oregon City, Oregon, USA
    Posts
    388
    Quote Originally Posted by zhid View Post
    the man who designed the adcom amps has desiged others as well.



    you may find something easy to build, from his designs,

    in this forum, utilizing parts from the amp you now have

    http://www.diyaudio.com/forums/forum....php?forumid=8
    Thanks for that bit if info. I had no idea that Nelson Pass designed the Adcom amps.
    "Zobel is as zobel does"

  15. #45
    Moderator hjames's Avatar
    Join Date
    Nov 2005
    Location
    NoVA - DC 'burbs
    Posts
    8,547
    Quote Originally Posted by Uncle Paul View Post
    Thanks for that bit if info. I had no idea that Nelson Pass designed the Adcom amps.
    Not all of them, no ...
    According to Nelson Pass at his DIY Audio site

    http://www.diyaudio.com/forums/showt...p?postid=51801

    Quote Originally Posted by Nelson Pass
    I designed the 555. I believe the Mk II added a couple
    of what were considered improvements, and it seemed
    to me that it included triple darlington outputs instead
    of 2 follower. I might have the schematic around, but
    all told it was a simple bipolar design with a current
    sourced input diff pair followed by a common-emitter
    gain device that was also current sourced. This drove
    the followers.

    It was typical of all the 5XXX amps that I did the first one
    and then they improved it until it had too many parts,
    and then I would design the next in the series

    Americo Borza sent me an old 555 in the hopes that I
    would update it, and it still sits here, a perfect candidate
    since so many of them were built.

    Personally, I would score a few of these and run them till
    they die and then update them. If you wait long enough,
    an update will be issued.
    2ch: WiiM Pro; Topping E30 II DAC; Oppo, Acurus RL-11, Acurus A200, JBL Dynamics Project - Offline: L212-TwinStack, VonSchweikert VR-4
    7: TIVO, Oppo BDP103D, B&K, 2pr UREI 809A, TF600, JBL B460

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Adcom 555 II
    By robertbartsch in forum Consumer Amps
    Replies: 31
    Last Post: 03-23-2010, 12:42 PM
  2. Adcom GFA 2535
    By Fred Sanford in forum General Audio Discussion
    Replies: 14
    Last Post: 12-14-2009, 08:01 AM
  3. tweeter control 5's blown need fixing/replacing
    By jonrice in forum Lansing Product DIY Forum
    Replies: 0
    Last Post: 10-18-2006, 06:28 AM
  4. ADCOM GFA 555 II
    By Guido in forum General Audio Discussion
    Replies: 19
    Last Post: 10-06-2005, 03:42 AM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •