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  1. #1
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    Need help with Cambridge Audio 550A

    Greetings,

    I am new to the forum and would appreciate some input from fellow music lovers.

    A few years back, my CD player took a dump and I decided it was time to step up a bit in quality. My receiver was over 30 years old (Realistic STA-64) and was a bit noisy. On power up you can hear what sounds like a 60hz transformer hum and as the volume is turned up there is plenty of background hiss. The volume pot was getting scratchy as well. Time to move on.

    I did a bit of research and settled on a matched set of Cambridge Audio 640A amp and 640C cd player. I unboxed and carefully installed the equipment. Pop in a CD, hit play. I was completely disappointed in the sound. The sound stage was all messed up. Detail was lacking. And, what happened to the bass? After a bit of pondering, I tried reversing one of the speaker wires. BINGO!!!. Wow! What sound! What detail! Iíve never been a fan of CD based music. It just seemed sterile and lacking detail (yet oh so quiet). Iíd never really heard any CD music on decent gear and just assumed there was just too little sampling being done for CDís to have any real fidelity. I was now officially blown away.

    I was still bothered about spending so much on an amplifier (I know itís relative) and having a polarity issue like this. What about resale if I tried to sell it later? I talked to the folks at Audio Advisor and they sent me a new 640A. Same problem. Reverse polarity on one speaker output to get good sound. They tested my return unit and said nothing was wrong with it. I had over a decade of experience as a computer network engineer and was pretty handy with cables in general. I tested everything on my end. The only fix was reversing the polarity of one speaker. I sent the replacement amp back and just plugged my trusty STA-64 to the 640C (topped off with Paradigm Atom speakers). Despite the hum and hiss, it still sounded light years better than any previous stereo system I have owned.

    In retrospect, I should have just kept the 640A, reversed the cable and be done with it. I did a google search at the time and found two references with links regarding a reverse polarity issue with the 640A. Both links were dead. Now, even the google references to this issue are gone.

    Fast forward to the present dayÖ

    Audio Advisor upgraded their components to the 650 series. I patiently waited for the 650A to go on sale, but no joy. They finally put the lower wattage 550A on sale, so I pulled the trigger. I read a couple of reviews and it looks to be a fine replacement. After arrival, I carefully cabled up and hit the power button. I fired up Spockís Beard ďDay for NightĒ (being a Prog lover) Alas, disappointment. The whole thing just sounds mediocre and messed up. The treble and bass are both weak, with lack of detail. The whole sound stage sounds jumbled and compressed. The specs on this should crush my STA-64, but it just sounds so lousy. I tested all the cables and verified polarity of all connections. Nothing. On a hunch, I tried reversing polarity of one speaker. Still sounds like crap. I tried switching right and left channels from CD to amp. Crap. I just donít get it .

    I put the STA-64 back in line and it sounds great (ignoring the hum and hiss). I canít believe that 3 different amps from Cambridge would all have similar sound problems, but I have quadruple checked my cables and nothing seems wrong on my end. The bad variable is always the Cambridge amp. If my STA-64 ever dies (35 years and counting), Iím toast. I have approval from Audio Advisor to return the 550A, but I would really prefer to solve this problem and keep the amp. I would appreciate any sincere input provided from the group.

    Thank you in advance. TR

  2. #2
    Super Moderator Site Moderator JohnMichael's Avatar
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    I owned a Cambridge 640A and had no problem with polarity. You mention the amps but not what speakers you are using and I am also interested in your speaker cables.

    I had a friend who replaced some blown drivers and did not pay attention to polarity when he reinstalled them. He could not understand why he did not have the bass he had before or the imaging.

    If the amp sounds fine with one speaker reversed and no other troubles I say live with it and enjoy. Int. amps at those prices will not have much resale. I am truly surprised you have had 3 samples with the same problem. I am sure CA would repair it for you and bring it to original design.
    JohnMichael
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  3. #3
    Forum Regular blackraven's Avatar
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    It sounds like the CA gear is not a good match for your Atoms which do not put out much bass. I would consider a Marantz amp with a nice warmer sound. I use to own the CA 840c and 740c CDP's and they are very detailed with tight bass but not warm by any means.
    Pass Labs X250 amp, BAT Vk-51se Preamp,
    Thorens TD-145 TT, Bellari phono preamp, Nagaoka MP-200 Cartridge
    Magnepan QR1.6 speakers
    Luxman DA-06 DAC
    Van Alstine Ultra Plus Hybrid Tube DAC
    Dual Martin Logan Original Dynamo Subs
    Parasound A21 amp
    Vintage Luxman T-110 tuner
    Magnepan MMG's, Grant Fidelity DAC-11, Class D CDA254 amp
    Monitor Audio S1 speakers, PSB B6 speakers
    Vintage Technic's Integrated amp
    Music Hall 25.2 CDP
    Adcom GFR 700 AVR
    Cables- Cardas, Silnote, BJC
    Velodyne CHT 8 sub

  4. #4
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    Update

    Thanks for the replies.

    I thought I'd give it one more stab before boxing it up and sending it back.

    Normally I'm very methodical when troubleshooting problems like this. I change only one varible at a time. Changing more than one thing at a time can give misleading results. But, I was frustrated and in a hurry,

    I thought I'd give the "B" speakers setting a try. I recabled the speakers and checked the speaker cable type for reference (hand made by Audio Advisor. No model #).

    It was then I took a look at the interconnect cable between the amp and CD. What on earth was it? I have no clue. I ran out the the garage and grabbed some left over interconnect cable from my home theater setup. Probably Monster cable or similar from Fry's.

    I fired things back up. Hey, that made a noticable difference. Bass improved. Detail improved. Not quite the sound I was looking for, but definitely sounding more like a decent quality stereo system.

    Not sure now if it is the B speaker setup or the interconnect cable, but the improvement was dramatic. I need to isolate the problem further and see if I can get the sound I want.

    TR

  5. #5
    Forum Regular blackraven's Avatar
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    You should consider a Marantz or NAD amp. Both have a warmer sound and would pair well with the Cambridge CD player. If you could swing the dough the NAD C-356BEE should do a great job and be very dynamic. It has lots of dynamic headroom and 2.6dB at 8ohms and 4.4 at 4ohms.

    If you want a 2ch receiver in the $400 range, then look at the Harmon Kardon 3490. The HK receivers have a warmer sound more like vintage 1970's receivers. It may not give the same amount of detail and resolution as an NAD integrated though.

    The HK 3490 has preamp out in case you ant to get a separate power amp and use the HK as a preamp. It also has Phono input.
    Last edited by blackraven; 09-29-2011 at 02:19 PM.
    Pass Labs X250 amp, BAT Vk-51se Preamp,
    Thorens TD-145 TT, Bellari phono preamp, Nagaoka MP-200 Cartridge
    Magnepan QR1.6 speakers
    Luxman DA-06 DAC
    Van Alstine Ultra Plus Hybrid Tube DAC
    Dual Martin Logan Original Dynamo Subs
    Parasound A21 amp
    Vintage Luxman T-110 tuner
    Magnepan MMG's, Grant Fidelity DAC-11, Class D CDA254 amp
    Monitor Audio S1 speakers, PSB B6 speakers
    Vintage Technic's Integrated amp
    Music Hall 25.2 CDP
    Adcom GFR 700 AVR
    Cables- Cardas, Silnote, BJC
    Velodyne CHT 8 sub

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