| K100-2 Reverb [message #380] |
Sat, 24 February 2001 15:20  |
BC
Messages: 583
Registered: March 2000
Location: Kentucky
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Senior Member |
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Help! My reverb is on...and it wont turn off!
I have run into this problem a couple of times on the 100-2 heads. Without a footswitch it will not completely turn off. Not a big problem .....but it is just not "RIGHT" Anyone solve this problem before?? Also there is not a good variation in the amount of reverb on the control. It starts on "about right" and goes to "Grand Canyon" BC
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| Re: K100-2 Reverb [message #381 is a reply to message #380] |
Sun, 25 February 2001 13:46  |
GaryH
Messages: 19
Registered: January 2001
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Junior Member |
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In looking at the schematics I have for the K100-2, there are some differences that I see between this and the reverb circuit used in the 200 series (PC303) that would affect how much reverb is heard as the knob is turned up.
Interesting thing that's different about the Kustom reverb is that when the reverb is on, the knob varies between just the dry signal (sort of) at the CCW end, and just the reverb return (no dry signal) at the CW end of rotation. This differs from almost all other amps, which always have the dry signal present all the time and mix the reverb into it, and accounts for the "Grand Canyon" effect. Major reverb happenin' here!
Because of the design of the reverb mix circuit, there isn't complete isolation of the signals at each end, so a little reverb may leak through even with the control fully CCW, and a bit of the dry signal probably gets through on the CW side as well.
It looks like on the 200 series they used a control with a built-in switch to shut the reverb off when the control is turned all the way down, even in the absence of a footswitch. There are also some resistor changes on PC303 that would appear to help this problem as well, and would be easy and cheap to implement on your K100-2.
The one that will have the most effect is resistor R170, a 15K ohm resistor. This is the resistor that controls how much actual reverb sound there is at the maximum rotation of the reverb control. The larger the value of this resistor is, the lower the reverb volume will be at maximum. This has been changed to a 22k ohm resistor in the 200 series; using this value or higher on your 100-2 will mean that the volume of reverb you hear with the control turned off will be reduced as well. You could wire in a larger value trimmer potentiometer in place of the resistor (say a 50k-100k ohm or so) and use that to set the maximum reverb amount (with the front panel control all the way up) that you want. There should be more than enough reverb to allow for quite a bit of adjustment. This will also give you a much smoother transition between the dry and reverb amounts.
There are also four other resistors that were changed which make up part of the mixing circuit. These are resistors R173, R174, R175, and R176, all 15K ohm resistors. They were all changed to 33K ohm resistors, and this change will provide even more isolation of the reverb signal when the control is turned all the way down. These can be 1/4 or 1/2 watt resistors, and should be readily available at Radio Shack.
I don't have one of these boards, so I can't tell you the exact locations of these resistors; you'll find them near the transistors mentioned above, and will have to trace the circuit a bit to be sure you've got the right ones. The color code bands for a 15K ohm resistor are: Brown, Green, Orange, and probably Silver (the tolerance marker for 10% tolerance).
Another interesting thing I see looking at the schematics is that the K100-2 has both the bright switch and the bright boost circuits of the K200 series built-in and permanently enabled...I'll bet that guy has some serious treble!
Hope this helps BC; feel free to email me with any questions. gh
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| Re: K100-2 Reverb [message #382 is a reply to message #381] |
Sun, 25 February 2001 18:50 |
BC
Messages: 583
Registered: March 2000
Location: Kentucky
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Senior Member |
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Thanks Gary! I suspect some component has failed ......probably one of the resistors you mentioned.....as I have also owned K1002s that worked properly! I am certain I am not the only one to have run into this so your help will benefit others as well! Thanks again! Now I need to plan a shop day to fix a bunch of little problems! Brad
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