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Ampeg SVT pro fan runs continously, seems loud

Discussion in 'Amps and Cabs [BG]' started by OldSchool50, Mar 1, 2016.

  1. OldSchool50

    OldSchool50 OldSchool50 Supporting Member

    Mar 15, 2013
    I recently picked up Ampeg SVT5 pro in great shape with very low hours (It had been in storage for several years.) Sounded great and quiet at first but after less than 10 hours of use the fan came on a few minutes after turning on and it doesn't go off. It's seems on the loud side, not crazy loud but definitely noticeable when things are quite. One pre-amp tube so I doubt it runs that hot.
    Should this fan run all the time? It wouldn't be so noticable if it cycled off after cooling but it doesn't. Any thoughts what the problem might be? I did have some trouble figuring the bridge mono vs stereo and didn't use the right cable initially. Could that have messed something up?
    Probably needs professional check but thought I'd throw it out there.Also posted on Ampeg club.

    THanks for any help
  2. OldSchool50

    OldSchool50 OldSchool50 Supporting Member

    Mar 15, 2013
    Follow up on the fan in my ampeg set 5 pro. Does anyone know if the thermal sensor is built into the fan or is there an external control on the nearby board?
  3. pfschim

    pfschim Just a Skeleton with a Jazz bass

    Apr 26, 2006
    SF Bay Area
    I don't have the answers to your 5Pro fan/sensor questions, but I will add that the fan on my 6Pro gets very loud indeed.
    of course, at 1100w, the fan noise is hardly a factor unless I try to use the amp in a recording situation .. which I don't.

    Very noisy multi stage fan in these amps, and the screws that hold the chassis together are so tightened down that my mere mortal tools will not budge them.
    So, the case remains closed, and the fan remains noisy.

    good luck fixing your 5Pro fan noise problem
  4. OldSchool50

    OldSchool50 OldSchool50 Supporting Member

    Mar 15, 2013
    Thank for the input. I'm starting to think it's just normal and I didn't notice it before. My main questions now is whether it should run continuously, which mine does after a minute or two even if I"m not playing. Even thought the fan is tight, I think some of the noise is vibration. Think I"m going to live with it for a while and see how it goes.
  5. BasturdBlaster


    Feb 19, 2012
    Crandon WI
    It seems my 4pro's fan comes on right away and I also have a B2Re which it's fan also comes on right away and that one is actually noisy.

    On a side note, I work in an environmental lab that has tons of equipment with each instrument having at least 6 or more fans. These fans range from 12vDC, 24vDC, 120vAC, large, small, etc. These fans are on for sometimes years at a time. I replace them quite often. It can be astonishing how loud a "bad" fan can get, sometimes they squeal and whistle so bad, sounds like an airplane. Anyway, if you really are convinced that its too much for ya, it can be relatively easy to replace them. First thing I would do is try to see the model number on the fan and just google it, there are many many suppliers for these seemingly common fans and they aren't at all expensive.
  6. OldSchool50

    OldSchool50 OldSchool50 Supporting Member

    Mar 15, 2013
    Thanks for this. It confirms what I'm thinking, that it's OK for the fan to run continuously and that the much of the noise Im hearing is actually vibration, either a loose fan or even the lid. I"m going to try a few more things before heading for service.
  7. dagrev

    dagrev Supporting Member

    Jun 21, 2006
    The constant and abnormally loud fan is true of the 3PRO as well (not that it matters but has 5 tubes). It's certainly noticeable when nothing is going on. When I started using the V-4BH (all tube no fan) I noticed how nice no fan noise was.
  8. OldSchool50

    OldSchool50 OldSchool50 Supporting Member

    Mar 15, 2013
    Good news to report. The noise I was hearing was vibration, apparently from the lid of the amp. I took off the lid (12 short screws, 2 longer), checked the fan and mounting. Mounting screws were tight, housing intact and the fan itself did not seem unusually loud, even with the lid off. WHen I put the lid on the vibration was loud enough to be annoying.
    I got some of that thin foam insulation for windows and doors, cut pieces to create a foam gasket around the inside of the lid, cut around the screw holes. Screwed lid back in back in place and the vibration is gone, just a low fan hum but much improved.

    Thanks to those who offered idea. This one was an easy fix. I hope
  9. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    I'm late to the party but here is some information concerning the SVT5 Pro's fan. There is a temperature sensor on the power transistor main board. It is a small device. It connects back to a fan control circuit.

    If there's a problem, the first step is to check the related connectors. Ensure that there isn't dust on the sensor and surrounding area. A buildup of dust can make the sensor think that it is hotter than it is and it doesn't cool properly. Check the voltages where indicated on the schematic.

    There are the related circuits. The board silk screening will identify the components.

    Fan control:

    SVT5Pro fan control.JPG

    Sensor LM-35:

    SVT5Pro sensor.JPG
    Last edited: Mar 8, 2016
  10. OldSchool50

    OldSchool50 OldSchool50 Supporting Member

    Mar 15, 2013
    Thanks Beans on Toast

    I think my vibration problem is solved but if the fan is multi-speed or supposed to turn off when cooled then I may try to clean the sensor. Several people have told me the fans in their SVTs (other models) run continuously and sometime noisily so I had assumed that was the case with mine, but I will definitely look at the sensor and see if that changes anything.
  11. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    Good that you figured out the vibration problem.

    For a gigging amp, it's still worth checking out the inside for dust at least once a year as part of a regular maintenance program.

    The fan has a DC motor, like a variable speed drill. As the DC voltage changes the fan speed will change. At the highest temperature, full speed, the voltage going to the fan is -4.6VDC. The voltage from the sensor will vary with temperature. You can test it to see if it is working at hot and cold and should see a difference.

    In addition to checking that the sensor is dust free, check the fan blades. If the fan is dirty, it can be noisier. Some amps remain relatively clean, others can really get full of gunk. If it needs to be cleaned, do not shoot compressed air into the amp. Use a vacuum or carefully wipe. Also check that the fasteners on the fan are tight.

    There are potentially lethal voltages inside the amp, even when the power is off and unplugged. If the electrolytic caps have not been discharged, be very careful.
    Last edited: Mar 9, 2016

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