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Problem with Aguilar DB750 fan

Discussion in 'Amps and Cabs [BG]' started by mrbassman_de, Apr 28, 2004.

  1. mrbassman_de

    mrbassman_de Supporting Member

    Sep 14, 2003
    Recently I purchased an Aguilar DB750. Great sounding amp with lots of power and punch ! Unfortunately - the two cooling fans create an audible high frequency tone (not only the air noise). It's absolutely unacceptable in silent environments.

    Anybody out there with the same problem ?
    How can I fix it - Any advise would be helpful ! :help:

    Please don't bother me with: "Throw it away and buy x or y" ...
  2. Lockout


    Dec 24, 2002
    I'm interested in what others have to say about this also... I have the exact same problem with my DB728, even on the low fan speed setting. :(

    I've even been thinking about buying a small fanless power amp to use at home for practicing because the noise level of those fans is driving me insane.
  3. todd 4ta

    todd 4ta

    Apr 3, 2003
    If the fan is a standard size, you may be able to find a replacement from a computer cooling web site. There are many options out there, and lots of models with various speeds and noise levels. (they usually list the rpm, CFM and dba for each fan)

    Here is an example of one site with a lot of fans: Eagletech

    I have a Soundtech PS802 power amp that has two 40mm x 40mm x 20mm fans which were a little noisy. I bought two mag lev ball bearing fans which should be here tomorrow. They should be less noisy and have more output.
  4. Lockout


    Dec 24, 2002
    Aren't computer fans designed to work with different voltages than the fans in amplifiers? Computer fans are usually rated for 12v, but the fans in my DB 728 are rated for 115v... I don't know very much about electronics, but doesn't that make quite a bit of difference? Could someone explain a bit on this?
  5. doc540


    Jul 28, 2003
    Beaumont, Texas
    Daum! I wish I could find them again, but years ago I snagged a small, but heavy duty little fan in a chrome cage which blew quietly like a hurrican. I hung it on the back of a modded, tweed '59 Bassman, and it kept everything nice'n cool. About the size of a orange and ran on 110.
  6. todd 4ta

    todd 4ta

    Apr 3, 2003
    You would definitely want to match the new fan with your current specs. The two fans in my Soundtech just happen to be 12v, so the PC fans worked for me. Some of the electronic supply places have fans with a wider range of specs.

    Here is the place I got my fans: Buy Extras

    They have fans for 12v, 5v, 115v, but I'm not an electronics expert so you would want to verify that you were getting the right fan for your amp. I was just pointing out a source for some quieter fans.

  7. sheepdip


    Apr 14, 2004
    You can solder a resistor across the hot lead and the fan connection thus lowering the voltage to the fan thus lowering the operating speed.

    You can also get a larger bladed fan and operate it at a lower speed with increased air flow. If it will fit.
  8. Lockout


    Dec 24, 2002
    That'd probably work, but it would decrease airflow... I don't think I'm willing to risk that with my DB728. :(

    Do you think that placing rubber grommets between the fans and the side of the amp's casing might cut down on the noise somewhat? Or probably not noticeably?
  9. mgmadian


    Feb 4, 2002
    Austin, TX
    I'd love to hear how this turns out, as I've considered doing this as well. Please let us know how it goes... power amps often sound great at volume, but the fan noise invariably bugs me when recording or practicing at lower levels.
  10. mrbassman_de

    mrbassman_de Supporting Member

    Sep 14, 2003
    I've dismounted the original fan and there are all informations on its label:
    Model: MINEBEA NMB 3110PS-12W-B30
    Voltage: 115 V AC (!!)
    85 mA
    2600 rpm
    28 dbA noise
    28 m³/hr air movement
    size 80*80

    So: The problem for me is to get two silent 115V fans (the Papst fans are driven by 12, 24 or 230V)

    Any advise for me ?
  11. Fred Labbidie

    Fred Labbidie Guest

    Apr 22, 2004

    You complained the DB 750 fan noise was unacceptable in a "silent environment". You are now looking for a "silent fan". I hope you know that this is going to be a tough quest.
  12. fast slapper

    fast slapper

    Dec 11, 2001
    Fresno, CA
    Maybe you can rig an external switch to turn off the fans under quiet use. I'm sure the amp won't scorch at low volumes.
  13. Lockout


    Dec 24, 2002
    I just tried this yesterday, and I thought I'd report on my results, just in case anyone was wondering. :)

    What I did was I cut a piece of somewhat thick rubber into 8 pieces and drilled a hole into each one. Then I slid them onto the fan screws between the fan and the amp casing, in hopes of isolating the fans' vibrations and possibly lowering the amount of noise they make.

    It did lower the noise level slightly, but not very much. One thing it helped with, though, is with isolating the vibrations. Most of the tubes in my DB 728 are pretty badly microphonic, and the small vibrations that the fans made were causing a low frequency rumble of sorts through my speakers whenever the amp was being used. Putting the rubber between the fans and the case helped eliminate that sound, so I'm glad I tried it at least. ;)

    I'm still going to get it retubed, though, and I'm still going to try to find some quieter fans.. but as Fred said, it's not going to be easy to find quiet replacements. :(
  14. How quiet are you playing? My DB728 fans aren't bad at all. The noise is the fault of the tubes, (Svet 6550's are HORRIBLE about microphonics) not the fans.
  15. Lockout


    Dec 24, 2002
    Pretty quiet... I don't play very loud when I'm practicing at home. When I'm playing with a band I can't hear them at all, but at home they're pretty loud. I usually don't leave it racked at home, so that probably contributes to the problem too.

    Would it be possible that the fans are starting to wear out? My DB728 isn't exactly new (I bought it used so I'm not exactly sure how old it is, but it's #164) and I noticed when I took out the fans that even if I spin the fan blade around slowly with my finger, it makes some noise when it spins. Most other fans that I have dealt with (mainly computer case fans) barely make any hint of noise when I do that.

    Do you think it could be possible? If so I could probably just buy a new pair of the same fans..

    PBG, were you talking about the noise coming out of my speakers, or do the tubes actually make noise inside the amp? I'm just a little unsure of what you meant... the sound I'm hearing is coming from inside the amp.

    Oh by the way PBG, I think I might make a trip up to Electric City Music to get my amp retubed/biased and checked over (just to make sure it's still in good working condition)... After reading about what people have said about them, they seem like a better place to take it than any of the stores down here. Only problem is that it's a 90 minute drive. :(
  16. Sounds like there's something wrong with the fans. The bearings may be going. Sometimes, dust gets in there and literally grinds them out. My fans are dead quiet. You can get replacements at any large electronics supply house like Digikey or Mouser. Just look for 110-120 volt models. They oughta run around 20 bucks apiece.

    Yeah, speaker noise can come from fans vibrating microphonic tubes. The tubes shouldn't do that. It's a common symptom of Svetlana/SED tubes, which are what Aguilar uses. If you're going to replace them, JJ Electronics KT88's, Sovtek KT88's, or EH 6550's or KT88's are all great replacement choices. Microphonic power tubes will roar softly, sort of sounding like the ocean in a seashell. Rebiasing won't fix them; it's a problem with the way they're made. It's funny that Aguilar makes such stellar amps, but uses tubes that don't hold up.

    Any old TV/electronics repairman SHOULD be able to service the amp. Authorized service centers are often bound by manufacturer restrictions on parts, even if the amp is out of warranty. Aguilar ONLY recommends you use "their" tubes in the amps, and "their" power tubes are just VERY expensive Svet/SED's. MOST music stores are far from qualified to service amps, but if you've heard good things about a place, it may be the exception.
  17. Lockout


    Dec 24, 2002
    That's exactly what mine sound like. Putting those pieces of rubber around the screws between the fan and the 728's back panel did help some though, it made that sound much less noticeable.

    Yep, I'm going to be getting a set of JJ KT88's from www.eurotubes.com soon. :)

    Yeah, sorry if I wasn't clear about that, I meant I was getting new tubes put in and biased, not getting the old tubes. :)