Results 1 to 5 of 5

Thread: Randall RG100es Frequency Oscillation Problem Howling Noise Troubleshoot Help

  1. #1
    Junior Member
    Join Date
    Mar 2017
    Posts
    2

    Randall RG100es Frequency Oscillation Problem Howling Noise Troubleshoot Help

    Hello all,

    I have a vintage Randall RG100es that has some issues. The main problem is that the amp will start to produce a loud frequency oscillation on both channels when you start to turn up the volume past 1:00. It happens sooner on the red channel. The frequency will actually sweep up in pitch as you turn up the volume knob. It is not a guitar feedback issue obviously. This will happen with nothing plugged into the input.

    I would guess that this is a problem in the circuit somewhere after the volume knob, but I don't have a ton of evidence to back that up. Have already cleaned it out and DeOxit-ed the pots and jacks. I am an audio engineer with good knowledge of circuits and repair. Can anyone point me in a direction on this specific issue?

    Will new output transformers get rid of some of the ridiculous hiss this amp emits?


    Thank you all!

  2. #2
    Supporting Member The Dude's Avatar
    Join Date
    May 2010
    Location
    Sioux Falls, SD
    Posts
    3,904
    “Yeah, well, you know, that’s just, like, your opinion, man.”

  3. #3
    Old Timer
    Join Date
    Jun 2007
    Posts
    4,874
    Welcome to the place.

    Which controls do this, the gain controls or the master volumes? The amp is oscillating at higher volume settings because of too much gain, bad lead dress, who knows why. You will need to start by trying to find out what section of the circuitry is causing the problem and they fixing it.

    As for the hiss, try plugging a guitar into the FX return jack. Now turn the guitar's volume control all the way down. How loud is the hiss? The hiss that you hear now is being generated in the power amp circuit. Now remove the plug from the return jack and compare the level of the hiss. Any increase in hiss is caused by the preamp circuit.

  4. #4
    Junior Member
    Join Date
    Mar 2017
    Posts
    2
    Quote Originally Posted by 52 Bill View Post
    Welcome to the place.

    Which controls do this, the gain controls or the master volumes? The amp is oscillating at higher volume settings because of too much gain, bad lead dress, who knows why. You will need to start by trying to find out what section of the circuitry is causing the problem and they fixing it.

    As for the hiss, try plugging a guitar into the FX return jack. Now turn the guitar's volume control all the way down. How loud is the hiss? The hiss that you hear now is being generated in the power amp circuit. Now remove the plug from the return jack and compare the level of the hiss. Any increase in hiss is caused by the preamp circuit.
    Thank you, Bill!

    The master volumes are the ones which do this. Although I believe they will begin to oscillate sooner if the gain is higher.

    I will do that trick with the FX loop when I get my hands on the amp again. It's in storage. Also, I meant transistors not transformers.

  5. #5
    Junior Member
    Join Date
    Mar 2017
    Posts
    4
    Have the same issue on my RG100ES XP. One of the Ceramic Capacitors on the Circuit board near the reverb connectors is microphonic I bet. I changed mine because it thumped when tapped with a tweaker tool. (yellow 472Z 1KV (.0047uf 1KV) schematic says ".005uf") The replacements I tried also thumped. Bummer right? Well I guess that part of the circuit is for the reverb and meant to amplify the signal from the tank. I am not an expert but I think that is causing the feedback.

    Let us know if you make any progress with figuring it out.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Randall RG100ES overdrive problem
    By tonepumpamps in forum Music Electronics
    Replies: 6
    Last Post: 03-17-2017, 02:46 PM
  2. '72 Bassman High Frequency Oscillation
    By StonesFan in forum Maintenance, Troubleshooting & Repair
    Replies: 5
    Last Post: 07-12-2014, 01:50 AM
  3. Carvin X-60E problem - Loud distortion howling noise
    By janupa in forum Maintenance, Troubleshooting & Repair
    Replies: 1
    Last Post: 09-10-2013, 05:46 PM
  4. Randall Rg100es - Red chanel barley works
    By Prybar in forum Maintenance, Troubleshooting & Repair
    Replies: 3
    Last Post: 02-03-2011, 02:38 PM
  5. randall rg100es
    By porky in forum Schematic Requests
    Replies: 3
    Last Post: 06-15-2009, 05:24 PM

Tags for this Thread

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •