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Ampeg b4r question

Discussion in 'Amps and Cabs [BG]' started by toonman, Mar 22, 2014.

  1. I bought a used Ampeg b4r a few weeks ago and I love this amp, but, the other day I noticed several things didn't work properly. the first problem I noticed was the texture switch, it made no change in tone what so ever. So I took the amp apart and looked at the schematic closely and noticed that the 1M OHM resister for the texture circuit was missing. It looked as if there never was a resistor soldered in. :meh: I thought this was strange so I soldered in the correct value resister and the texture button worked. :bassist: Could Ampeg have missed and left it out?

    The other problem I'm having it the 15db pad has no attenuation at all. I haven't had a chance to really troubleshoot this problem But I did inspect the circuit board and all components are there and of the correct value. any ideas why the 15db jack doesn't attenuate the signal?
  2. beans-on-toast

    beans-on-toast Supporting Member

    Aug 7, 2008
    There are 2 1M resistors but it appears that both should be in the texture circuit. Maybe it was missed. At times there are components on the schematic that aren't installed, in those cases they say Do not place or install. Other times, there are revisions and parts change or are deleted. If the circuit functions after installing the resistor, it is safe to say that it should be there.

    Concerning the input pad. I would check that the proper components are in place. It would be best to test the resistance of the pad resistor in case it is mislabeled. It could also be the level of the input signal might not allow you to hear a difference . This is where a scope or a good voltmeter and a signal generator comes in handy. With a consistent input signal you can measure the level before and after the pad and see what it is doing.