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feed back with volume down? [message #7873] Mon, 13 November 2006 13:07 Go to next message
mommytime is currently offline  mommytime
Messages: 42
Registered: August 2006
Member
Good Day All,

OK, maybe my K200 B5 is burning up inside.

I now get a feed back ‘howl’ which builds slowly on its own, even with the volume turned down.

The sound is feedback like, but its not actual feedback. If I start playing while the amp is making this sound it will actually stop building the feed back sound until I stop playing, then it starts again.

If I simply turn the amp on it doesn’t make this sound, I have to strike a note or chord to get it started, but after it starts I can’t stop it unless I simply play over it. Playing over it DOES make the unwanted sound dissipate, it ALMOST stops completely

Any ideas what would cause this?

Thanks, have a good week.

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Re: feed back with volume down? [message #7874 is a reply to message #7873] Mon, 13 November 2006 13:35 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4730
Registered: June 2004
Location: NY
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No matter which channel you use it does this?

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Re: feed back with volume down? [message #7875 is a reply to message #7873] Mon, 13 November 2006 15:55 Go to previous messageGo to next message
mommytime is currently offline  mommytime
Messages: 42
Registered: August 2006
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Yep, all channels.

I have not experienced anything like it.

It appears to not happen until the amp is warmed up a little.

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Re: feed back with volume down? [message #7876 is a reply to message #7873] Mon, 13 November 2006 23:04 Go to previous messageGo to next message
rodak
Messages: 511
Registered: October 2001
Location: Georgia
Senior Member
Could it be the reverb tank freaking out?

www.combo-organ.com

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Re: feed back with volume down? [message #7877 is a reply to message #7873] Tue, 14 November 2006 07:02 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4730
Registered: June 2004
Location: NY
Senior Member
It could be many things, my first guess would be bad solder joint on one of the preamp boards, may be on a cap or one of the tantalum caps going bad making the amp go off ontp oscilations.
One of my 250s had a bad joint on one of the large orange drop type caps, I think it was on the top preamp board.

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Re: feed back with volume down? [message #7878 is a reply to message #7873] Tue, 14 November 2006 11:59 Go to previous messageGo to next message
mommytime is currently offline  mommytime
Messages: 42
Registered: August 2006
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I was thinking it may be the reverb tank, I have a similair issue on a silver tone, but it does'nt stop building the feedback on the silver tone.

I will pull it apart, disengage the reverb and see what happens.

Thanks for the ideas, I will let you know.

W

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Re: feed back with volume down? [message #7879 is a reply to message #7873] Tue, 14 November 2006 14:39 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4730
Registered: June 2004
Location: NY
Senior Member
If its thremaly realated, than it will not be anything to do with the reverb pan.When you get it out of the case use a blow dryer to warm up the 4 circuit boards in the amp one at a time, you can use some wax paper or pastic food rap to isolate the other boards from the heat, in this way you should beable to narrow it down to the problem board.

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Re: feed back with volume down? [message #7880 is a reply to message #7873] Tue, 14 November 2006 14:42 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4730
Registered: June 2004
Location: NY
Senior Member
Or the other way to do it would be to take the amp out of the case, unscrew the lid but leave it on, play the amp untill it acts up, and then with can of freeze spray from radio shack you can do the oppsite of what I discribed in the post before and you may even beable to narrow it down to the very componet or joint that is bad.

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Re: feed back with volume down? [message #7886 is a reply to message #7873] Fri, 17 November 2006 23:41 Go to previous messageGo to next message
Optyk is currently offline  Optyk
Messages: 125
Registered: August 2006
Location: Texas
Senior Member
Strange thing, but I had this exact same phenomena happening on myh k200-B5 head. It happened regardless of whether any or all four channels were turned on or turned off. It happened regardless of whether anything was plugged into the inputs. Changing volume or treble or bass or reverb settings on any/all channels seemed to make no difference in the squeel. Even with the reverb turned off on all channels, I got the squeel. For some reason, I figured it had something to do with the reverb, so last night, I took the unit out of the housing, unplugged the reverb tank from the main board, removed the screws and took the tank completely out. Running the amp without the reverb tank gave me no feedback, so I knew I had the culprit located, at least I knew whatever it was was inside the tank assembly.

So I took a razor knife and very carefully slipped the blade underneath the rubber/felt covering that seals the tank. When I got inside and could see, I discovered there was a piece of paper that ran the length of the inside of the tank. It looks like it was originally on the inside side of the rubber felt covering, but age had made it peel off so it was just a loose piece of paper resting on top of the springs inside. I debated on whether to try to reattach it to the covering, but finally decided to just leave the paper out completely. So using duct tape, I sealed the covering back to the tank, sealing it up again. I remounted it, plugged everything back in and fired it up. (I realize I may have to open the unit back up and use some sort of glue to reattach that covering and get rid of the duct tape, but this was a temporary fix so I could test to see if it made any difference.)

No feedback so far. I cranked it up loud with a guitar running into it. Cranked all 4 channels up simultaneously (not maxed out, of course) and still no feedback. If this actually fixes it, this is a real cheap fix. I'm going to give the amp a workout this weekend and see if I can get it squeeling again. I'll report back first of the week and let you know how it turns out.

Rod

PS, I don't know if this is actually true or not, but it seems to me like the reverb sounds much richer now than before. It might just be my imagination, but man, my Gretsch DuoJet sounds sweet running into that unit now.

There's only two kinds of music. . . . blues and zippity doo dah.

[Updated on: Fri, 17 November 2006 23:52]

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Re: feed back with volume down? [message #7888 is a reply to message #7886] Sat, 18 November 2006 10:34 Go to previous messageGo to next message
Optyk is currently offline  Optyk
Messages: 125
Registered: August 2006
Location: Texas
Senior Member
OK, I got up this morning and put the unit through its paces and unfortunately, it's still feeding back, so ignore my previous message. I'll post again if I can figure out what it is that's causing this.

Rod

There's only two kinds of music. . . . blues and zippity doo dah.

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Re: feed back with volume down? [message #7889 is a reply to message #7888] Sat, 18 November 2006 20:48 Go to previous messageGo to next message
mommytime is currently offline  mommytime
Messages: 42
Registered: August 2006
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I am lucky.

I was about to pull the head apart, screw drivier in hand, and my door bell rang.

It was my new '67telestar guitar...I had plug too it in, I did and there was NO feed back!

So try this, everytime you approach your amp, do so with your fingers crossed, its working for me.

IF it starts again I'll let everyone know, cuz its important!

Thanks for sharing, I hope luck is on your side too.

Mommytime

LSD-Putting the inert back in inertia.

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Re: feed back with volume down? [message #7892 is a reply to message #7873] Mon, 20 November 2006 06:49 Go to previous messageGo to next message
stevem is currently offline  stevem
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Registered: June 2004
Location: NY
Senior Member
Anything sitting on the springs inside the reverb tank will deaden the reverb to some degree, and infact on some of the original hammond reverb tanks there are adhesive foil lables that with age I have seen come loose and from the amp beening sat in different positions in transit eitheir got stuck in the springs or worse shorted across the pans output or input jack.

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Re: feed back with volume down? [message #8644 is a reply to message #7873] Wed, 30 May 2007 20:34 Go to previous messageGo to next message
mommytime is currently offline  mommytime
Messages: 42
Registered: August 2006
Member
well, its back.

I get the same hum, but this time I can make it stop when it has 2 cabs plugged into it instead of 1?

The other thing is, the amp sounds richer, more bottom when I only use one cab, now the hum is back I have to use 2.

Any ideas now?

The hum does not build when there are no speakers hooked up, plug in the speaker cable and it starts, unplug and plug back in and it starts again.

It does not increase in hum sound unless I am NOT playing, playing seems to stop it from building the hum noise????

Very strange indeed!

Mommytime.

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Re: feed back with volume down? [message #8646 is a reply to message #7873] Fri, 01 June 2007 06:42 Go to previous messageGo to next message
stevem is currently offline  stevem
Messages: 4730
Registered: June 2004
Location: NY
Senior Member
How would you hear a problem without speakers hooked up?
Your comment that the problem stops went 2 cabs are hooked up would lead me to say that the problem lies in the output stage driver board.For whatever reason the difference in inpeadance and inductance when running two cabs is stopping the oscilation problem.
Tapping around with a chop stick on the boards may help you to track down where it originates, as might grabbing componets with needle nose plyers raped in electricial tape.

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Re: feed back with volume down? [message #8647 is a reply to message #7873] Fri, 01 June 2007 15:03 Go to previous messageGo to next message
mommytime is currently offline  mommytime
Messages: 42
Registered: August 2006
Member
Correct, I can't hear the sound with out speakers plugged in, but I can tell that the sound/ocillation stops and restarts each time I plug and unplug the speakers, as opposed to it coninueing to build whether the speakers are plugged in or not.

I will tap around.

Thanks

LSD-Putting the inert back in inertia.

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Re: feed back with volume down? [message #8648 is a reply to message #7873] Mon, 04 June 2007 12:26 Go to previous messageGo to next message
The_Philth is currently offline  The_Philth
Messages: 9
Registered: May 2007
Location: Downey, California
Junior Member
I had the same problem happen with my K-250. Without any cables connected to the input, I had all the pots dimed and tapped everything with the handle of a small screwdriver to see if I could zero-in on the culprit. To my dismay, I found that I was the new owner of an amp that produced a hundred-plus watts of white noise and a high-pitched squeal.

So I just went ahead and took the amp apart and doused all the electronics with PUREtronics contact cleaner and that seemed to eliminate almost entirely the unwanted noises.

If you go this route, be sure to twist and turn each pot until the noise goes away. By the way, the noise was there even when the Volume was dropped all the way. However, after its bath-- the noise went bye-bye!

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Re: feed back with volume down? [message #8709 is a reply to message #8648] Thu, 28 June 2007 23:31 Go to previous message
RoyC is currently offline  RoyC
Messages: 97
Registered: April 2000
Location: East Central Illinois
Member
Here's something to try (if you haven't already)

Where the reverb tank plugs into the amp itself (RCA plugs?), pull those plugs out and clean them. You might get lucky.

Several years ago my K200-5 was making it's own noise, much like what you're describing, and after cleaning the plugs, it hasn't done it since.

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