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Vox TB


 
6/5/1999 6:36 PM
John C.
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Vox TB
This one is killing me.  
 
I'm sorry but I have to ask for help again.  
Vox Tone Bender.  
Anybody has the schematic on hand?  
Positive to ground.  
(in the schem, I'm afraid that the signal  
was incorrectly connected to ground of the imput jack,  
and the "9vplus" to the tip of the jack )  
 
The pedal works, as long as it is the only one connected to my power supply.  
If I have any other pedal connected to the power supply, then I must  
get some kind of short circuit (don't know if that is the correct  
term in english for putting together a plus and a minus line)  
and any of the pedals work at all.  
 
I know it must be something quite simple and obvious...  
but I can't find the clue!  
 
JohnC
 
6/5/1999 7:05 PM
zachary vex
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you actually figured out the whole problem yourself, except for the audio cable.  
 
a few fuzzes use positive ground. naturally, when you connect a negative ground pedal to the same power supply as a positive ground pedal, the ground connection between the two pedals made by the audio cable causes the positive terminal of the power supply to "short-circuit" directly to the negative terminal!  
the fix for this annoying problem? use a different power supply for your positive ground pedals. most of the time, this means all but one of your pedals will be supplied by one master p.s., and one of them (in this case your vox tone bender) will get it's power from another supply, maybe a spare wall wart you have sitting around.  
 
some modern power supplies have individual taps for each output, each one "floating", so you can use one p.s. for any combination of pedals with negative or positive ground.  
 
zachary vex
 
6/5/1999 7:50 PM
John C.
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>some modern power supplies have individual taps for each output, each one  
"floating", so you can use one p.s. for any combination of pedals with  
negative or positive ground.  
 
Oh, I see. Thanks a lot! Really!  
It's a pitty I just finished a nice new hum-free power supply.  
Is there something I could do to convert it in  
one that works ok with both kinds of effects?  
 
I'm afraid the answer is going to be: no :)  
 
JohnC
 
6/5/1999 8:25 PM
zachary vex
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if there is another equal set of windings on the transformer of that power supply, you are in luck... if they are completely separate, perfect. if those windings share a terminal with the ones you are using, and the power supply uses a bridge-type rectifier, then the common lead will have to be the ground connection. just build another d.c. rectifier and filter/regulator circuit using the extra windings to power it.  
 
or, if you are already using the only correct-voltage windings on your transformer, you'll have to build another one just for your positive ground supply, or like i said before, use a spare wall-wart for the tone bender.  
 
theoretically, you could use a modified bipolar supply (say a +/- 15 V computer or opamp supply with a new set of regulators) with the ground the same on all your boxes and the positive lead used for most effects and the negative one used to feed the negative supply lead on your tone bender. keep in mind that sometimes the reguators introduce noise (a sort of hiss) into high-gain audio circuits like fuzzes.  
 
you might be better off using a battery in that one effect for the cleanest and simplest results. after all, that's what it was designed for. you could even build a little external switch in a box that would lift the battery-to-ground connection at the "ring" of the input jack so as to save the battery without disconnecting the cord or modifying the actual vintage pedal.  
 
zachary vex
 
6/6/1999 9:24 AM
John C.
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>use a spare wall-wart for the tone bender  
 
As I only have one effect with this characteristic positive to ground, I think I'll include a small 300mv wall-wart I have arround, without it's case, inside the box I just made for the power supply, to feed the Tone Bender. I remember it was "clean" enough.  
 
>theoretically, you could use a modified bipolar supply (say a +/- 15 V  
computer  
 
Huau, that's a good idea! For this or another project...  
I have one, and I didn't think about it.  
They are even almost cheaper, bought new, than to build a power supply.  
 
Thank you!  
 
JohnC
 
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