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Circuit problem...


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5/10/2000 12:17 AM
Charlie
Circuit problem...
Hello all,  
 
My son and I have put together JD's Bluesbreaker using R.G. Keen's layout. We are getting a whine from the amp when the pedal is turned on and increases with the volume. Ground problem maybe? We ran thru the trouble shooting hints but no luck finding the problem. Also we substitued a 25k pot for the 22k tone since we couldn't find one local to us. Any advice is most appriciated and thanks.
 
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5/10/2000 12:34 AM
aron

The whine sounds like you are getting oscillation from the the layout. Try moving the input and output leads apart from each other. You may have to shield the input and output wires.
 
5/10/2000 2:08 PM
Rob

Yeah, I was thinking alone these lines. Also keep the drive & level pots wires short and away from the other wires.  
 
I'm not exactly sure if it's a whine or a buzz. Does the unit work? If it's oscillating it may come and go depending on how you set the pots. Usually breaking into oscillation at some consistent point when you advance them.  
 
It might also sound 'fuzzy' but that's might be hard to tell if you don't know what to listen for.  
 
Regards  
Rob
 
5/12/2000 10:57 AM
jens

I have been watching this thread closely as I'm having a whine-problem with my fat gnat. Sound is coming through and doesnt sound too bad at low drive and tone settings.  
 
At Steve Daniels advice I shortened all wires. I cut away 130cm / 51 inches :-). Still got trouble though.  
 
I am now re-wiring. Does the kind of wire affect oscillation? one-core vs multicore. I'm now putting in 7 core, 0,08 cm / 0,03inch wire. Does it strike you as a good/ bad wire to use (too thin?).
 
5/12/2000 1:33 PM
Rob

For wiring, the thickness of the copper will have little effect but it's better to er on the thin side.  
 
In most cases it's best to keep the wires short and to twist wire that go to the same pot together. Shielded cable is better than twisting. It's usually not a good idea to have wires near each other that go to different parts of the circuit. For example I would definitely not be putting the wires for the Drive pot through the same multi-core as the Level pot. Similarly it's not a good idea to have the input an output signals too close, a possible place people would do this is the bypass switch. The best deal is to twist the input signals together with a ground, or better, use shielded cable. Now do the same to the output signals. Because of the high gain used in distortion units you should take the most care as humanly possible.  
 
If your circuit isn't in a metal box, for example during prototyping, you might try laying down a few sheets of paper on top of a metal panel and connecting the panel to the circuit's earth, then plonk the circuit down on the paper - watchout you don't tug the cord so the circuit ends up shorting on the metal though.  
 
Regards  
Rob
 
5/12/2000 3:05 PM
jens

Thanks for your advice.  
 
This is basicly why I am re-wiring the thing, to try getting a better separation of the in / out signal wires to see if that helps.  
 
What I meant by multicore was however several copper pieces that lead the "same signal". Not a telephone style cable with several separately insulated wires inside....  
 
jens
 
5/12/2000 8:29 PM
Rob

There is virtually no difference between solid core and multi-strand conductors, breakage due to flexing is the only issue here.  
 
Another tip, if your're using vero-board (ie. the board with all the holes and the copper strips in one direction) try running strips next to wiring that involves the high gain circuits and connect these to ground. Grounding any unused strips can also help keep interference down. "Surround with Ground" is a good moto to remember.  
 
Regards  
Rob
 

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