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Thread: Hafler amp problems

  1. #31
    Figge
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    Originally posted by still4given
    Do any of you know how I can test those transistors while I'm waiting? It there a way to test them with a multimeter?

    well simply set the multimeter on diode test and try how the transistor leads it should show around 500 when leading, then swap cables and there should be nutn, oneway lead. try on all 3 legs, (transistor chassi = 1 leg) in diffrent combinations. if the multimeter beebs = transistor shorted, however i dont think theres any problem with it, the fuse should keep blowing if so.


    oh and when doing the test the transistor must be out of the circuit...
    Last edited by Figge; 10-07-2004 at 01:59 AM.

  2. #32
    Senior Member still4given's Avatar
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    Shucks, I don't think my multimeter has a diode test on it. Maybe time to upgrade.


    Blessings, Terry

  3. #33
    Alex Lancaster
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    Hey Terry: You are getting pretty enthused about electronics; If You´re going to buy a new multimeter, get one with a transistor checker and a frequency counter, You can spend a bunch of money, but try to get one on "special" from Radio Shack I´ve used them for years, maybe they even have one with a capacitor and inductor checker (which if You keep going, You will need),for about $100, next stop, an Oscilloscope, I guess.

  4. #34
    RIP 2011 Zilch's Avatar
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    Ummmm,

    Don't think I'd be probin' MosFETs with no multimeter. Nope....

    See HERE

    And HERE

    A Pass Laboratories pdf with more than you wanted to know....

    Last edited by Zilch; 10-07-2004 at 10:37 AM.

  5. #35
    RIP 2010 scott fitlin's Avatar
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    Terry

    Do yourself a favor, and find a good tech shop and have the amps repaired properly, or give Hafler a call, and send it to them for overhaul!

  6. #36
    Senior Member still4given's Avatar
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    Re: Terry

    Originally posted by scott fitlin
    Do yourself a favor, and find a good tech shop and have the amps repaired properly, or give Hafler a call, and send it to them for overhaul!
    Hi Scott,

    That's probably sound advice, however, I've been wanting to learn this stuff for a long time. I have almost no investment in these amps and to be honest, given the availability of parts, it really takes someone like myself, who is willing to hunt them down, to get one fixed. The tech I took the first one to, made a couple of calls and was told that the parts were NLA and that was as far as he was willing to go. I can buy these amps on ebay all day long for $150-$200. It would cost me more than that for a tech to source the parts and fix it and then I still wouldn't know any more than I do now. I really, really want to learn how to fix these things and this seems like a prime opportunity for me to do that. I can't help but think there are other folks here who are interested in this as well and may therefore be learning right along with me. I can't be sure of that, but it seems logical to me.


    Zilch,

    Thanks for the links. I have printed them out and will be reading up on this as I await the delivery of the caps I've ordered.

    Blessings, Terry

  7. #37
    Senior Member still4given's Avatar
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    Well the new caps arrived today. They seemed to do the trick. Both amps are playing now without any hum. They aren't quite as clear as I was hoping for. Not bad but they seem to distort at a lower gain that I thought they would. The biggest surprize was when I tried the caps in my Soundcraftsmen PCR-800. WOW! that amp really kicks. These caps are too tall to work in the PCR-800 so I have to get the right size but i am totally impressed with it right now. The bass authority is really nice.

    Anyway, any tips for tuning up these Haflers? Maybe set the bias? If so, how do I go about that?

    Since I have two, would I be better off strapping them and running one on each side?

    Thanks for all your help. It's really good to have them running again.

    Blessings, Terry

  8. #38
    RIP 2011 Zilch's Avatar
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    Originally posted by still4given
    Since I have two, would I be better off strapping them and running one on each side?
    You KNOW the drill: if they're designed for bridging, strap them and make an "empirical determination."

    If you want to dig deeper and "tune" them, you can't "wing" it like we did with the power supply filter caps. You need the schematics, owner's manual, and, preferably, the service manual. Read up and learn how they operate, and what adjustments (usually none) are available.

    Experienced techs recognize analogous circuitry and design approaches within and among various genres of amps. The basics are the same in just about all of them, though. Schematic in hand, and with a little more equipment than you have (oscilloscope, signal generator,) you can follow the signal path through the circuitry and diagnose problems, if any, or at least confirm the product is performing according to specifications.

    Hint: Your local repair guy (possibly even the one who told you wrong, here,) likely has a HUGE backlog of stuff he can't make the time to fix. Find the one who has racks full of stuff awaiting his attention. Volunteer to help him out on Saturdays, or whenever, so you can learn. You want "bench time," even if it's just changing line cords and replacing fuses to start. Once he's satisfed you're competent, he may "farm out" his overflow to you. Our local
    vintage audio recycler has been doing that for 30 years here now. If you like this stuff, and develop your skills, it can serve you well into your retirement....

  9. #39
    Senior Member still4given's Avatar
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    I have part of the manual and part of the schematics for this amp. Someone gave me step by step instructions how to set bias over at the DIYforum. I'm going to study that and see if it looks like something I want to tackle. It's more detailed than I expected.

    I'll try strapping the amps tonight and see how they sound.

    Thanks, Terry
    Last edited by still4given; 10-12-2004 at 01:26 PM.

  10. #40
    Senior Member Ian Mackenzie's Avatar
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    Terry,

    There have been previous Hafler mods in TAAS, write them for details.

    But you can't make a silk purse out of a sour's ear.

    They were always a bit harsh as I recall, but not bad for a 80 's mosfet amp. People would bypass the caps in the signal path hoping to re invent the amp. But it should a do nicely for bass.

    If you really want heaven, do a search on diyaudio.com for an Aleph 5 or 60, easy to build. Absolutely no comparison with the Halfer genre.

    Ian

  11. #41
    Administrator Mr. Widget's Avatar
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    Originally posted by Ian Mackenzie

    But it should a do nicely for bass.

    Years ago I had one of the DH200s. I did the Mod Squad thing to it and ended up using it as a bass amp. I was quite happy with it in that application.

    These days I have a Hafler P3000 and a pair of 9505s. They are not Aleph league, but are not slouches either.

    Widget

  12. #42
    Senior Member still4given's Avatar
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    Originally posted by Ian Mackenzie
    Terry,

    There have been previous Hafler mods in TAAS, write them for details.

    But you can't make a silk purse out of a sour's ear.

    They were always a bit harsh as I recall, but not bad for a 80 's mosfet amp. People would bypass the caps in the signal path hoping to re invent the amp. But it should a do nicely for bass.

    If you really want heaven, do a search on diyaudio.com for an Aleph 5 or 60, easy to build. Absolutely no comparison with the Halfer genre.

    Ian
    Hi Ian,

    Thanks for the advice. May I ask who TAAS is and how can I get a hold of them?

    I am noticing a bit of harshness. I thought it was because something is out of adjustment. Maybe it's just the sound of the Hafler. I will mess with it a bit again tonight. I only had a few minutes last night and tried strapping them. I got some weird kinda phasing issues. I didn't have time at all to play with any. I goint to try switching wires around and see if it goes away.

    Mr Widget,

    What is the "Mod squad" thing. Did it make much difference? If I can't get these to sound clearer in the high end, they may get relegated to driving subs of PA speakers.

    Blessings, Terry

  13. #43
    Administrator Mr. Widget's Avatar
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    Originally posted by still4given

    Mr Widget,

    What is the "Mod squad" thing. Did it make much difference? If I can't get these to sound clearer in the high end, they may get relegated to driving subs of PA speakers.
    The Mod Squad were (perhaps still are?) a group that sold modification kits and performed modifications on popular audio products. The kit I bought was primarily a bunch of bypass caps. There may have been a few other tricks, but I certainly can't remember now. As for improvement? Well I built my DH200 from a kit (David Hafler, the founder of Dynaco, was trying to do it again in the 70's with kit amps and preamps but eventually only sold built amps.) and I installed the Mod Squad kit during the initial assembly so I had no point of comparison. I only kept the amp for a couple of years.

    Widget

  14. #44
    Senior Señor boputnam's Avatar
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    Mod Squad

    "The grooviest gang of fuzz who ever wore a badge..."

    Sorry - someone had to do it, and I needed to beat Giskard to it!

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    "Indeed, not!!"

  15. #45
    Senior Member still4given's Avatar
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    Re: Mod Squad

    Originally posted by boputnam
    "The grooviest gang of fuzz who ever wore a badge..."

    Sorry - someone had to do it, and I needed to beat Giskard to it!


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