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EBOW LED help!

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dataplex

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hi

i have finally built a number of working ebows using this schematic ::

**broken link removed**

what i really want to do now is to add an amber LED to each ebow, which brightness is controlled by the level of the input. meaning that the louder the string is vibrating, the brighter the LED will be.

i understand i would probably connect the led somehow to the same output as the driver coil, but how?

any help would be greatly appreciated!
thank you

-dataplex

p.s here is a video of all the ebows ive made at work : https://vimeo.com/32643008
p.s 2 happy new year!
 
The LM386 does not produce enough voltage (and current) to drive an LED. You will need an additional amp for that. And what is an ebow anyway? E
 
The LM386 does not produce enough voltage (and current) to drive an LED. You will need an additional amp for that.
No.
An LM386 is a power amp, not a weak opamp. With a 9V supply it has a peak output of 3V in an 8 ohm speaker which is 375mA. It can drive at least 18 ordinary red LEDs.
 
I think something like this is what canadaelk is talking about. It will light the led at a lower volume than just putting it across the output of the 386.
I watched your video but it's still not clear how it works.
 

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I think something like this is what canadaelk is talking about. It will light the led at a lower volume than just putting it across the output of the 386.
My circuit is very sensitive. Your circuit with the transistor is 3V/0.7V= 4.3 times more sensitive so the LED might be triggered by noise in the LM386.
 
hey guys, thanks for all the help so far.

i am a novice, and to make sure i understand ronv's circuit correctly - i put together this modded ebow schematic. does this make sense? i really can't afford to burn up any more LM386!

https://i.imgur.com/wVVuF.gif

am i safe to hook it up?

thanks again guys, your help is greatly appreciated!
 
ok i went on and put it together anyway.

it works, but in reverse. when there is no input at all, the led is very bright. when the input coil is active, the led goes dim. any ideas on how to reverse it?

any help would be great... thanks guys!
 
ok i went on and put it together anyway.

it works, but in reverse. when there is no input at all, the led is very bright. when the input coil is active, the led goes dim. any ideas on how to reverse it?

any help would be great... thanks guys!
 
ok i went on and put it together anyway.

it works, but in reverse. when there is no input at all, the led is very bright. when the input coil is active, the led goes dim. any ideas on how to reverse it?
Your schematic shows a transistor with no emitter arrow and no part number. So we don't know how it is connected. Since it works backwards then the transistor must be a PNP type instead of an NPN type.
Or maybe the output coupling capacitor has its polarity connected backwards so it conducts DC.
 
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sorry for not including that information audioguru. i am using a 2n2222 transistor, emitter to ground like in the schematic ronv posted above.

i will look into the polarity you mentioned early tomorrow morning.

when i figure that out, i have one further question;
i get exactly the same effect if i connect the led directly from the 220uF capacitor (with a 600ohm resistor inbetween). is there a reason why using the transistor method is better?
connecting it directly seems simpler...

again, thank you all for your help!
 
sorry for not including that information audioguru. i am using a 2n2222 transistor, emitter to ground like in the schematic ronv posted above.

i will look into the polarity you mentioned early tomorrow morning.

when i figure that out, i have one further question;
i get exactly the same effect if i connect the led directly from the 220uF capacitor (with a 600ohm resistor inbetween). is there a reason why using the transistor method is better?
connecting it directly seems simpler...

again, thank you all for your help!
 
A very high level from the amplifier will light an LED.
A low level from the amplifier will turn on the transistor that lights the LED.

I don't know why they show a polarized capacitor as two boxes with one box full (the negative wire to the speaker) and the other box empty (the positive wire from the power amp) with no polarity marking. We usually use a polarized capacitor symbol with a "+" at its positive wire.
 
Could it be that you hooked it up to the wrong side of the 220 Ufd. capacitor? At that point the voltage is about +4 volts with the sine wave imposed on that level. That might give your symptom.
If the volume is always high enough to light the LED by putting it at the output that's cool.
 
it seems to be a signal level problem.

i hooked it up with a weaker pick-up coil (8ohms instead of 300ohms) and the LED worked perfectly, going from nothing to bright when a string is plucked underneath the pickup.
the 300 ohm coil however seems to keep the LED bright when nothing is happening BUT makes the LED go dim when it's receiving a signal!

very strange... any thoughts on why this would happen? can a signal that is too great make a LED go dim?

thanks for all the help guys, im almost there!

(p.s the capacitors polarity is fine, the schematic has the blank bar on one side = negative side ;))
 
If the cable from the pickup coil is not a shielded audio cable then it will pickup mains hum and radio interference which will be an input to the LM386 amplifier which will light the LED all the time. Then if the pickup or amplifier is too sensitive then the amplifier will clip badly when receiving a guitar signal which might dim the LED. the transistor increases the sensitivity of the amplifier.
The sensitivity of the amplifier can be reduced by connecting a resistor in series with the capacitor that is between pin 1 and pin 8.
 
Make sure the input wires and the output wires are well separated. It sounds like it is oscillating at a very high frequency.
 
hmm... why would a distorted signal make the led more dim than a hot signal? i would love to understand that...!

unfortunately, i cannot change the current ebow circuit - as it works perfectly for my other needs.

to get the led working better, could i possibly use a white or amber LED (they require higher voltage to run) and/or use more resistance in between the amp and LED? maybe 1kohm?

thanks again guys!
 
The circuit works backwards so something is wrong.
With no signal then the LED should be off but yours is on. When the amplifier is clipping then the LED should be at max brightness. When the input signal is much higher than normal then the amplifier is severely over-driven but it is not designed for it so the operating point might shift and dim the LED.
 
Feedback

Here are a series of simulations that show what I think is going on:
I have inserted a small amount of capacitance between the output and the input. This could be present if your output and input wires are close together. Also added some capacitance across the input cable that I think might simulate your twisted pair in the picture.
The first picture is with 300 ohm source resistance and an input that won't light the led. Notice it takes a bit for it to break into oscillation, but when it does it continues - so bright LED.
Second picture is with a higher signal input. Notice how it is on and off. Dimmer LED.
Third picture is with 8 ohm input. No oscillation because of the low input impedance. So now the LED lights only when the signal is present.
The trick here is to find out the feedback path. I would move wires around until the LED goes out with no signal present.
 

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The E-bow circuit has an input pickup coil and an output driving coil. If the coils are too close together then there will be positive feedback.
 
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