Deadringer II power problems...

[luks999]

hi

i powered my deadringer II up, and the 10R resistor blew...
too bad i used a 1/4W instead of 1/2W

whats the purpose of the Q7 and the R32 (10R) ?
they arent there in the original schematics. can i omit them and connect 9V directly to the 220uF cap?

thanks a lot

[madbean]

They are reverse polarity protection and for noise reduction. However, it is safe enough to bypass them if you want. You could put a 1N5817 or 1N001 in place of the 10R resistor and jumper through Q7 if you want. Or, if you have Q7 installed already just jumper through the resistor.

[luks999]

thanks a lot brian!

i jumpered R32 (10R) and now it works perfectly!
i also forgot the CLRs and both leds fried, but no big harm done.

wouldnt a 1n4001 in reverse between 9V and Ground do also polarity protection?

whats the purpose of 10R then? the bs250 seem to be fine without r32

anyway, cant wait to box it up 

[madbean]

The 10R combines with the small amount of series resistance on the BS250 to form a low pass filter on the power supply (with the decoupling caps). You can use higher values for the resistor which will handle the current better in terms of heat dissipation. At the same time, higher values will reduce the voltage supply to the effect. So, I picked the 1/2W to solve both problems: keep it noise free as possible and keep it as close to 9v (or 18v) as possible. But, it seems some people to have a problem with getting 1/2W resistors so I don't think I will continue doing that on any further projects. Probably not the BS250 either since some international customers had trouble getting those, too.

Anyway, if you have left the BS250 in that is all you need for reverse polarity protection. It does the job and then some, and has the least amount of voltage drop, too. If you jumpered it out, then yeah; a 1N4001 form 9v to ground would be fine.

[luks999]

Thanks a lot brian for the info
i left the 10R out and it works fine if i have some noise issue from the power supply, i will order a 1/2W resistor
the burnt 10R worked as jumper, but i now soldered a real jumper in, so that it looks nicer