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DIYstompboxes.com  |  DIY Stompboxes  |  Building your own stompbox  |  (funkless) Guyatone Cross Over Box 0 Members and 1 Guest are viewing this topic. « previous next »
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Author Topic: (funkless) Guyatone Cross Over Box  (Read 726 times)
Posts: 6

(funkless) Guyatone Cross Over Box
« on: March 01, 2012, 03:14:29 PM »

First post - Hello! I was wondering if anyone out there can shed some light on this problem please. I've got what seems to be an early Guyatone Crossover Box which is working, sort of. The problem is that it only seems to be working at certain frequencies and the filter cuts off very quickly and sharp. Just so you get an idea the filter woks on my 2,4,5 and 6th strings but not on the 1st or 3rd! I might also add that this is with both the Drive (sensitivity) and the decay knobs turned almost all the way up. BTW I do realise that by having the decay knob turned up all the way that would make the filter cut off faster and when I turn it down it does slow the decay down, but not by too much. It's almost as though the pedal is not sensitive enough or the frequencies are not reaching high enough to trigger the effect.  I've searched for a schematic (obviously) and all I came up with was the one for the Vox 1904. My pedal is a little different (earlier?) than what the schematic shows and I've highlighted the differences in the attached revised schematic. Apart from not having a DC jack or a switchable LED, most noticeable to me was the sensitivity controls differed greatly (esp. the 500k pot being 50k!) I've also attached a labelled picture of the inside of the pedal as well as the component side of the board with the traces ghosted over to make it easier to follow. Yes, I did change that 2.2meg resistor but only to replace the 2.2meg that was there before. IC and Transistor are the same as on the schematic and all the resistors have been tested. Curiously, The polarised 16v cap (labelled BP) and the other 16v cap are the other way around in my pedal to what the schematic labels (circled on the schem).
So my eyes are particularly drawn to the Drive (sensitivity) section being the problem. I wonder if the differences in resistance and capacitance were a later revision to correct the exact problem I'm having.  However, I thought I would post this and see if any better brains could see something I missed Smiley If anyone needs more info msg me. Any help would be awesome,

Posts: 5417

Ian M. - England

Re: (funkless) Guyatone Cross Over Box
« Reply #1 on: March 02, 2012, 12:07:41 PM »

I don't think the differences in the schematic will be causing the problem. The first thing I would do is try replacing the capacitor marked BP on the schematic, if that was bad it could cause the symptoms you've described.

Nice first post by the way, the info you've given really helps people who might try to help you Smiley
Posts: 6

Re: (funkless) Guyatone Cross Over Box
« Reply #2 on: March 06, 2012, 03:52:20 PM »

Cheers for that, I was hoping I'd given enough info. I went ahead and ordered both of the electrolytics and the other components that differ from what's in my Crossover box.  Shipping was the same, what the hell!  I'll change that non-polarized cap first (had to dig for that one Grin) like you suggested and hopefully that works. I'll mess about with it a bit once it's working properly and try the 500k pot and different cap. I'm curious to see how the sensitivity might change. Thanks for the advice, I'll let you know what happens when the components arrive!
Posts: 6

Re: (funkless) Guyatone Cross Over Box
« Reply #3 on: March 12, 2012, 03:29:53 PM »

Result! I changed those two electrolytics and it got the pedal working again. At least now the pedal was filtering evenly across all the strings. I swapped out the 50k pot and the .056 cap for the schematics original values and then hey, it really sprung to life! Thanks for the help Ian, much appreciated Smiley The box is no longer funkless!
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