| loud pop early K200A-1 [message #19736] |
Sun, 15 December 2013 00:00  |
kustomhead
Messages: 121
Registered: April 2012
Location: Redding, Ca
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Senior Member |
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When plugging a guitar cord into the both hi and low inputs on the left channel there's a loud distorted pop/noise as it first makes contact with the jack. Also when I click on my boost pedal it makes a loud pop. The right channel works fine. Could it have to do with the 200U Memcor or GE .0047 50 volt cap that bridges the hi and low inputs? Anybody have this phenom? It's a very early A model 4-150-1 with serial# 18383.
[Updated on: Sun, 15 December 2013 00:19] Report message to a moderator |
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| Re: loud pop early K200A-1 [message #19740 is a reply to message #19736] |
Sun, 15 December 2013 08:09  |
stevem
Messages: 4775
Registered: June 2004
Location: NY
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Senior Member |
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Hi.
Your problem with both are more than likly contack issues, as even each input jack has a switch section in it.
These and all the selector swicthes sould get cleaned and lubed, the problem is the jack switches have to be cleaned with the help of some thin uncoated / painted plain cardboard.
If you look at the jack as you load a 1/4" cable end in it you will see the main tip prong start to bend, as this is happening you will see another flat metal section move also.
This is the switch section.
if you pray this section open you will also see two little contack points ( like automotive ing points of old) these two points need to get cleaned.
To do I load up/ saturate a long section of cardboard that is also thin enought to slid into that section of the switch and then pull it back and forth.
This will clean off both point sections at the same time.
To clean all the selector switches pack some torn off sections of paper towel around each switch to catch any excess and spray each swicth with only the amount you need to quit the noise.
While you are in there you might as well clean and lube all the pots in the amp.
Radio shack sells a cleaner / lube and some of the better stocked music stores now have the Detoxit brand of fader cleaner and lube.
Only a small amount of times have I had to resort to replacing a bad input jack, and those times have been when some else has already bent its switch section up.
[Updated on: Sun, 15 December 2013 08:22] Report message to a moderator |
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| Re: loud pop early K200A-1 [message #19743 is a reply to message #19736] |
Mon, 16 December 2013 06:32 |
stevem
Messages: 4775
Registered: June 2004
Location: NY
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Senior Member |
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Thats good, I guess your half way there.
No they all need to be of the switching type to keep things quite do to where the volume control is placed in the preamp circuit.
Mojotone parts sells the correct replacement Switchcraft jack, Switchcraft part number J12A for under 3 bucks.
If you have more than one amp of any kind, it pays to have some of these on hand!
Did your swicthes clean up and work out also?
[Updated on: Mon, 16 December 2013 06:39] Report message to a moderator |
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| Re: loud pop early K200A-1 [message #19747 is a reply to message #19736] |
Mon, 16 December 2013 16:28 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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I'm not sure which jack you have, but the standard Kustom jack used in most all of the amps after the Frankies is a Switchcraft #13E. See if that is the same as yours.
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| Re: loud pop early K200A-1 [message #19751 is a reply to message #19736] |
Tue, 17 December 2013 13:17 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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There are a few things that could cause the problem that you are describing. The input jack grounding and switching is one, another would be a bad (leaky) input cap on the preamp board.
If it gets leaky, the 10uF cap can let a small amount of dc voltage to pass through it. When you plug something into the jacks, this small dc voltage can discharge to ground and cause a pop or noise.
Try this test. Plug a guitar cord into the low input jack. Take a voltmeter and check for dc voltage from tip to ground. You may see a small initial voltage that will disappear when you take the reading, but what you are looking for is a constant dc voltage. Compare the right channel input with the left channel input.
This will only work on the low inputs as the high pass cap for the high input will block any dc voltage from the preamp.
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| Re: loud pop early K200A-1 [message #19776 is a reply to message #19736] |
Fri, 20 December 2013 06:39 |
stevem
Messages: 4775
Registered: June 2004
Location: NY
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Senior Member |
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DC voltage on a pot will make for scratchyness on a other wise good pot, you need to replace that cap that Bill posted about, and I would also do the one on the other channel while you are in there.
Thats the good news.
The bad news is that all of those other electroytic caps ( caps with a band at one end) in the amp are on the way out also to one degree or another, so be prepaired for other problems / maylays to turn up.
The best thing you can do in regards to all the other caps that have not fully gone DC leaky, including the two big main can type filters is to leave the amp on for a day, just idling.
[Updated on: Fri, 20 December 2013 06:42] Report message to a moderator |
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| Re: loud pop early K200A-1 [message #19778 is a reply to message #19736] |
Fri, 20 December 2013 13:13 |
chicagobill
Messages: 2006
Registered: April 2003
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Senior Member |
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You won't be able to see a leaky cap, at least not the kind I was talking about. It doesn't leak something physical, it leaks voltage between the two leads. A capacitor is supposed to block any dc voltage from one leg to the other while letting ac voltage pass through. If the dielectric breaks down the two legs can become connected in a way that they no longer block dc voltages and can eventually short out completely. If this happens to a large filter cap, it will short out the main dc voltage to ground and blow the fuse. It may also take out a diode or two before the fuse shuts things down.
In the preamp that you are working on, a 10uF electrolytic capacitor is the first thing that the signal passes through to get to the first amplification stage. There are about 8-9 dc volts that are used to operate the transistors and this input cap blocks those dc voltages from getting to the inputs where the dc voltages would be shorted to ground at the jacks.
Your test reading of 5.4 volts dc shows that the input cap is letting that about half of that dc voltage pass through it and to the input jacks. This dc voltage is causing the pop and distortion noises and is causing the volume pot of your guitar to make scratchy noises.
I would not use this channel until you get the problem fixed, as putting dc on the guitar volume pot is not a good thing to do. It can cause faster wear on the carbon trace of the pot.
If you plan to repair this yourself, you will need to remove the pc board from the front panel and solder in a new cap. As Steve suggested, if one cap has gone bad the others are probably on their way to cap heaven as well. I personally do not recommend total recaps, as they often cause more problem than they are worth. I would suggest that you replace all of the same 10uF caps on the one preamp board as long as you have it out. Looking at the schematic it looks like there are 4 of them.
You could just go ahead and replace all of the electrolytics on the board as long as it is out of the amp.
Good luck with the repairs.
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| Re: loud pop early K200A-1 [message #20614 is a reply to message #20613] |
Wed, 14 May 2014 14:56 |
kustomhead
Messages: 121
Registered: April 2012
Location: Redding, Ca
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Senior Member |
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I ended up selling it and now just have my K200B-4 head and a K50-2 1X12 combo. Both function perfectly, for now anyway! I don't think they were made that way because on the A-1 heads both channels are the same unlike the B heads where the left channel is "Bright" and the right is "Normal. It's just weird!
[Updated on: Wed, 14 May 2014 15:04] Report message to a moderator |
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| Re: loud pop early K200A-1 [message #20617 is a reply to message #19736] |
Thu, 15 May 2014 07:25 |
stevem
Messages: 4775
Registered: June 2004
Location: NY
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Senior Member |
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Greenfields, its likely that your 200A has a leaky cap off of the input jack to the first gain stage / transistor on that channel.
If you have a voltmeter and hook it up to the end of a short guitar cable do you read any small DC voltage?
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