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Audio Research Classic 60 (ARC 60) - Valve Power Amp

Discussion in 'Audio Processors & Power Amps' started by gabreu, Sep 23, 2009.

  1. gabreu

    gabreu Member

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    Hi forum members,

    Although I am a recently registered member, I've been a regular reader of these forums for quite some time and know there are very knowledgable people around.

    I'm having an issue with an Audio Research Classic 60 power amp that has almost been driving me to insanity... :)

    I bought it second hand and it played fine for about 1 month.
    After that, I made a speaker upgrade to a pair of Monitor Audio GS60.
    The ARC played fine for about 1 week and then one day when turning it on the fuse (4A) blew. I've replace it several times but it just kept blowing right when I turned it on.

    From that day on I have sent the amp for repair more than once (on an authorized AR dealer), and this is what keeps happening:
    1. The amp comes from repair and plays fine for about 2 or 3 days
    2. After 2/3 days it goes back to doing the same (fuse blows when turning on)

    I would like to ask the following questions, if anyone is nice enough to answer:

    a) What can be the cause (theoretically) of the fuse blowing?

    It isn't a power spike, cause I have my outlet protected. Besides, no other equipment has ever shown any sign of these kind of problems.
    Could it be something in my setup that is messing up the Valves Bias and causing them to draw too much power?

    b) Have you ever experienced/heard anything similar? Any potential explanation for this?

    My setup is as follows:
    - Monitor Audio GS60 Speakers
    - Audio Research Classic 60 Power AMP
    - Arcam C-31 Pre-Amp
    - Arcam CD-33 CD Player
    - Michell Orbe Turntable


    Any help / advice / ideas are most appreciated!


    Thanks a lot in advance and regards to you all!

    Goncalo
  2. alexs2

    alexs2 Active Member

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    Hi...welcome to the forums.

    The only thing that's changed in your system is the speakers.

    Since then,you've had repeated problems with the fuse blowing.

    I assume this is the mains fuse,from what you've described,but in any case,the problem must lie with the change in speakers......

    1.is the impedance much lower than your previous speakers?

    2.If so,does your amp have separate taps for 4 and 8 ohm speakers,and are you using the correct ones?

    3.Have you discussed the speaker and amp matching with your dealer?
  3. gabreu

    gabreu Member

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    Hi Alex!

    That's right, it's the mains fuse I'm talking about.

    Regarding your questions:

    1. My previous speakers were a pair of Focal JM Lab Cobalt 816S, with an impedance of 8 Ohm. My current speakers (Monitor Audio GS60) have a lower impedance (6 Ohm).

    2. The amp has separate taps for 4, 8 and 16 Ohms. I'm using the 8 Ohm tap to connect the GS60s (6 Ohm).

    3. My dealer is fully aware of my setup, and he's also been scratching his head after so much we've already tried... :(


    By this time, it starts to seem like some kind of voodoo... so I was hoping you people around here could give me a hand with your knowledge.

    Many thanks for your reply!

    Take care!
  4. lbstyling

    lbstyling Member

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    when you say repair- what exactly has been repaired? are they just replacing the fuse?-when you say 'main' fuse- do you mean the one in the mains plug-or a house supply fuse/rcd?

    if it was the internal amp fuse i would almost certainly say-no load-ie you have a few strands from the + terminal touching the - one (at either the amp or speaker end)-ive done that one before- damn that kimber 8pr cable!!! all the conductors look alike :mad: honestly who uses black and dark brown for live and nutral!!!!:thumbsdow

    have you got any other speakers you can attach to the amp to try and see if taking that variable away gets you anywhere?

    what kind of volume are you playing at?-does it go when you have a larger demand in the music -ie dynamic peak?

    how old is the amp?
  5. lbstyling

    lbstyling Member

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    +i would use the 4 ohm taps for a 6ohm load dude :thumbsup:

    when a manufacturer claims the ohm rating of a speaker -its a constanly variable figure-so they average it. you may find that at lower frequencys it goes well well below this.
  6. Ianfromnotts

    Ianfromnotts Active Member

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    If the amp has been checked out that would suggest either a speaker fault or a wiring problem. I would try the following

    1. check all the speaker cables to make sure that there are no loose strands
    2. try the 4 ohm tap in case the speaker impedance is dipping way below 6 ohms at some points
    3= try the amps with some different speakers
    3= try the speakers with a different amp

    That should give enough feedback to diagnose the problem area

    If you are using long lengths of fancy cable that might be upsetting some thing maybe?
  7. gabreu

    gabreu Member

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    The first time this happened a valve was damaged, so they replaced a pair and re-adjusted the bias, etc...
    The second time some electronic components were replaced (don't know more details...)
    The third time the technician told me he couldn't find anything wrong with the amp.

    The fuse I'm talking about is the one in the amp (4A) that is placed right after the mains entrance (according to the schematics)

    I doubt this is the case as my cables have forks at both ends and the amp has some plastic pieces protecting the contacts/screws from each other.

    Nope, not at the moment... :(

    When the amp is playing fine (first few days after coming from repair) I can play at low or high volumes, everything is fine.
    Then, after 2 or 3 days when I try to turn it on again (after being off since the previous day), the fuse just blows... I don't even get to play any music!

    From then on, the cycle is this:
    1. Turn switch on
    2. Fuse blows immediately
    3. Change fuse
    4. Go to step 1. :(

    I believe it's nearly 20 years old.


    I must also add the following, could be important:

    1. Already tried the same speakers AND cables with a different amp - every time the ARC goes to repair I use a substitute transistor amp (Advanced Acoustic MAA-406). Never had any kind of problem whatsoever!

    2. Already tried turning the ARC on with nothing connected (no speakers and no interconnects), and the behavior is the same (fuse keeps blowing)

    Thanks you all for the replies you've been posting, please any ideas or comments are mostly appreciated!

    All the best!
  8. alexs2

    alexs2 Active Member

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    As above,I would use the 4 ohm tap for these speakers,as a nominal 6 ohm rating often means dips to lower values.

    As an example,my B&W 805s are nominally 8 ohm speakers,but dip to below 3 ohms in the bass regions.

    Valve amps are usually stable with capacitive and reactive loads,which should rule out cable problems,but as I've said originally,the only thing you've changed is your speakers,and the interaction of new speakers and amp has to be the problem.

    Try the 4 ohm tap and let us know how you get on.
  9. lbstyling

    lbstyling Member

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    this is strange!!
    hard so say whats up here-but, i would suggest sending to a serious engineer (i can suggest one if you like-though i guarentee nothing, and not cheap!)

    if this was ss i would have said the transistors have been shorted- but its not and the draw thats shorting the internal supply fuse pops with no load- does this happen without the source connected AND no load?

    im drawn to say its the amp circuit itself not any power supply-unless theres a warm up circuit there thats gone.
    power supply problems tend to be kind of obvious-your engineer would have picked this up.

    again- i think this is a specialist problem- its not conforming to the usual suspects so requires serious investigation.

    sorry i cant help more man.:thumbsdow
  10. gabreu

    gabreu Member

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    Hi there, thank you all for the answers/ideas you've been providing!

    @lbstyling: yes, the same happens without anything connected (no pre and no load), just the amp connected to the power outlet.

    @alexs2: I will try out your suggestion, once I get the amp back (it's out for repair... again! :(
    I'll let you know afterwards how it went.

    Any more ideas or things to try out?

    Regards to all!
  11. Ianfromnotts

    Ianfromnotts Active Member

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    I had a problem with my TL12s with the mains fuses and the internal fuses blowing at power up. In my case it was easy to track down as I had just put NOS rectifiers in - Phillips Miniwatt

    Replacing the phillips with NOS branded Mullards cured the problem - might be worthwhile swapping rectifier tubes if you have some spares lying around
  12. motile rod 2

    motile rod 2 Member

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    I have a very similar set up to yours, MA gs10's paired with an Audio research vs55. While I haven't experienced the same problem, for about the first 3 months I was using the 8 ohm taps and it sounded fine. Then I thought I'd try the 4 ohm taps, and the sound completely changed, so much smoother and so much more dynamic. Now it feels like the volume just goes on forever without sounding harsh, and it sounds like a different and much more expensive amp. So I would highly recommend using the 4 ohm taps!

    I'd also interested to hear your thoughts on the sound of your set up, as I'm almost certainly going to be getting gs60's in a couple of months.
  13. gabreu

    gabreu Member

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    Hello again,

    To my despair, I've tried using the GS60s with the 4 Ohm tap on the amp and the result is the same (use immediately blows).
    The amp has just returned from service and they find nothing wrong with it, works perfectly well on their lab.

    So, to my disappointment I've finally decided to give up on this amp.
    I was buying it second hand and am returning it to its previous owner (he accepts it back).

    I am now considering buying an Audio Research VS60, but am a bit concerned whether this amp will have enough power to drive my speakers (it's a bit less powerful than the Classic 60).
    I've started a thread to discuss if the VS60 will be a good match for the GS60s here:
    http://www.avforums.com/forums/audi...2-audio-research-vs60-monitor-audio-gs60.html


    @motile rod 2:

    The GS60s are excellent speakers.
    Recently I had the opportunity to try a Pass Labs X250.5 power amp on my system and all I can say is I had an "eargasm". :)
    This power truly revealed all the GS60s potential... Superb dynamics and definition, excellent sound stage placement, basses with a weight and control I didn't know my GS60s were capable of until then!
    Too bad this power is off my budget limits, otherwise I'd look no further.

    To sum up, if you like your GS10s I'm sure you won't be disappointed with the 60s.


    Many thanks & respect to all you fellows that took the trouble of answering my questions and provide some help!

    Regards to you all,

    Gonçalo Abreu

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