| 100 clamps down or cuts out [message #1595] |
Tue, 11 June 2002 22:31  |
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help! I have a 100 head that, if you turn all the way up for the cool distortion effect, it will "clamp down" or cut out. What's causing this? Can anyone tell me exactly what needs to be changed, using the schematics?
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| Re: 100 clamps down or cuts out [message #1596 is a reply to message #1595] |
Wed, 12 June 2002 06:44  |
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This could be a hard one unless you have test equipment.It could be a bad connection on a board, a worn speaker output jack.A bad volume control,and it could be a thermal problem with a component breakind down under high signal drive or temperature. Does it happen as soon as the amp is on.
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| Re: 100 clamps down or cuts out [message #1599 is a reply to message #1596] |
Wed, 12 June 2002 21:13 |
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It so far seems to happen within the first 10 minutes or so of use. It will do it in either channel too. Would a good place to start be to change the speaker output jack in the head? And, should I also change the speaker cab's jack? Could it be a speaker problem?
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| Re: 100 clamps down or cuts out [message #1600 is a reply to message #1599] |
Thu, 13 June 2002 08:03 |
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To check the jacks or you spk cord, turn the amp up with no input, listen at the spk for the white noise while you rock the cable around in both jacks and listen for it to cut out. I could describe to you how to test for thermal and intermitant problems in the amp but first let me know what level of a tech you might be, so I do not wast my time and yours if you have to take it to a repair shop anyway.
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| Re: 100 clamps down or cuts out [message #1624 is a reply to message #1600] |
Tue, 18 June 2002 14:01 |
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Well, I've tried what you said to do. Nothing is wrong with the head speaker output jack or the cabinet input jack. I thought maybe I should check it with a different guitar, so I did. Same problem. Bought a new guitar cord, same problem. It clamps down, or limits the volume (acts like a limiter) when the 100-1 volumes are up FULL BLAST. If you turn them down, one idicator position, or using a clockface as a guide--the 3:00 position, it does not do it, as far as I can tell. I did notice something that may or may not be an indicator of a problem: with the volume up all the way, and the guitar's volume pots turned off, I hear a crackling sound and sometimes some slight radio interference. Is this to be expected or normal? Could I have a speaker problem? I can solder and have minimal electronics know-how. I can handle inspecting for bad solders, etc. What should I try next? Thanks Steve!
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| Re: 100 clamps down or cuts out [message #1631 is a reply to message #1629] |
Tue, 18 June 2002 23:16 |
KustomBlues
Messages: 494
Registered: June 2001
Location: Michigan
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Senior Member |
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Huh? "Supersonic oscillation problem???" I've heard of oscillation, but supersonic??? What causes that? This sounds like an interesting problem. As a new lover of the 100 heads, I'm anxious to see what all our techies feel is the problem here with this guys head. Has anybody else had the problem that this guy has? I just seem to get the 70 year old asthmatic kind of problems with them.... :-)
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| Re: 100 clamps down or cuts out [message #1645 is a reply to message #1631] |
Thu, 20 June 2002 16:13 |
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The same thing that causes all oscillation - excessive positive feedback. Some you can hear as a squeal or tone. Motorboating is subsonic oscillation, because it oscillates at less than 20hz. Supersonic oscillation is above the high frequency range of hearing, or above the speakers ability to reproduce.
When it does happen, all of the power of the amp appears to be sucked out of it. What is really happening is the amp is reproducing (at full volume) the supersonic frequency that no one is hearing. The positive feedback producing it is usually much stronger and/or masks the "normal" signal.
It can happen with sloppy component placement. It can also happen when a conductive dust or mist somehow settles on the circuit boards. Lack of shielding, or an improper ground like a bad solder joint can also cause it.
I would look for something in the first stage of the amp since the effect seems volume control affected. Kustom amps use a small value capacitor to help reduce RF pickup. It could have opened or could have been improperly soldered.
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| Re: 100 clamps down or cuts out [message #1649 is a reply to message #1648] |
Fri, 21 June 2002 07:45 |
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after what you have described about the backind down the vol control, It really sounds like a bad volume control. some times you can spray out a dirty contol and they will not be scrachty, but they will still be intermittant.Or you still may have a thermal/conection problem.Take the amp out of the cab, warn it up somewhat with a hair dryer(dont over do it) get some freeze spray from radio shack, and go over all the boards and components to see if the problem goes away.Also with the amp warmed up tap on the boards with the plasic end of a screwdriver to try to pin down if its a bad solder connection.PS you do not have to freeze spray the power trans for the thermal test.
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