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Adding an LED to a Tone Bender clone?

 
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power chord hack



Joined: 31 Dec 2005
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PostPosted: Mon Aug 02, 2010 10:49 pm    Post subject: Adding an LED to a Tone Bender clone? Reply with quote

I have an early version of a Bone Bender & I want to add an LED power indicator.
I know how to do it (i.e. how to wire it) but I don't know enough about the circuit & the germaniums (with their pos ground) to know if it'll mess w/ the tone or fry the transistors.

All it involves is adding the LED between an unused lug on the 3PDT and ground. So by doing this I THINK all that'll happen to the Bender circuit is it'll get a drain of a few mA from the LED.

What I'm worried about is:
1) I've heard the germaniums are way sensitive little buggers & by altering the current I'll make it sound like crap.
2) I'll create some funky ground loop & zap the germaniums.

This is essentially what I'm doing:
http://www.beavisaudio.com/techpages/StompboxWiring/
The pedal is already wired thus w/ the bypass so I's just be adding that LED.

So... ?
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sonicblue



Joined: 15 Mar 2007
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PostPosted: Tue Aug 03, 2010 2:22 pm    Post subject: Reply with quote

You can do it. I think the LEDs are generally left out of the PNP/germanium designs because they are primarily powered on batteries and no LED = longer life.

The LED (+ current limiting resistor) will be between +9V and the switch/-9V, not in the signal path, so no tonal issues per se (unless you are really paranoid about the current draw).

I think you only need to worry about blowing the germaniums if you were to plug in the wrong polarity power supply. (Rocking out in the Arizona desert with 120+ degree weather might do it too -- not sure! Laughing ) A good design should also have a failsafe diode in there to protect the transistors from reverse polarity.

Ground loops, not to worry, that's a different issue.
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power chord hack



Joined: 31 Dec 2005
Posts: 8445
Location: LOSING IT in a windowless grey cube

PostPosted: Tue Aug 03, 2010 10:08 pm    Post subject: Reply with quote

Cool.
Thanks

OK - another question...
Do you think one of these would work w/ the PNP?



I assume it should work since it should have the same polarity as a 9V...

EDIT: duh, just realized I can test the polarity with my meter. Rolling Eyes
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sonicblue



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PostPosted: Tue Aug 03, 2010 11:14 pm    Post subject: Reply with quote

You'll have to reverse the leads, otherwise :::boom:::! Laughing
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Structo



Joined: 21 Nov 2004
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PostPosted: Wed Aug 04, 2010 8:34 am    Post subject: Reply with quote

As I recall Analogman Mike telling me when I was talking to him about his Sunface Germanium fuzz pedal, he doesn't put a led on those for that reason. The extra current draw affects the tone so he doesn't install one.

You can try it to see what it does on your circuit, you may or may not like it.
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