ac/dc voltage separation

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Big Sammy

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Hi....I'm new to the forum, and excited to be here!! I am trying to wire a flashing led to the volume pot. on a guitar, so that the louder the guitar is played, the faster the led will flash. The problem is that this circuit sends a signal to the amp. Is it possible to separate the voltage coming from the pickup (I assume AC), from the voltage coming from my circuit board (9v. DC)? I've read that a capacitor can be used to filter ac out, but I'm not sure if it would read a flashing voltage from my circuit board as AC, as it is flashing....
Thanks for any help you can give me!!!
Big Sammy
 
I am trying to wire a flashing led to the volume pot. on a guitar
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You can't drive a LED directly from the guitar volume pot. Post a schematic of your circuit and perhaps we can help.
 
Hi...I'm not trying to fire the led off of the volume pot. I am using the volume pot as a variable resistor to vary the flash rate. But it is the same volume pot the pickup is wired to, and my 9v. flasher/led circuit is putting a voltage out the volume pot to the amp. I want two different circuits running through the same volume pot. But I only want the pickup signal to get to the amp., so is there any way to separate the two signals AFTER the volume pot so only the pickup signal gets out to the amp? I was originally thinking a capacitor, as it can be used to separate AC and DC, to DC and allow AC to pass, but I don't think the pickup signal is AC...it would be a magnetic signal. I don't have a schematic, as I am flying by the seat of my pants. I can scrap this idea if it won't work, I just liked the idea of the louder the guitar was turned up, the faster the led would flash....
Thanks....
 
Hi Big Sammy,

I suggest to replace the pot by a dual pot (stereo) and use one of them to increase the flash rate of your LED circuit.

That way you won't have to worry about interference and separating AC and DC. The LED flasher, if built with a timer IC won't have pure DC on the pot.

Here is a LED flasher. Slow is about 1Hz, fast approximately 10Hz.

Boncuk
 
You can pick off the signal, from the volume control pot, with a cap that the feeds a simple transistor (or op amp) isolation circuit (called a "unity gain follower")

What that does is isolate the signal being passed to the flasher circuit, without fundamentally changing the signal in your amplifier, which you can then pass to the LED trigger circuit.

Very basic electronic construction.

I can provide a schematic, if you like.
 
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I am using the volume pot as a variable resistor to vary the flash rate
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I thought you were trying to vary the flash rate according to the guitar signal level rather than the pot setting?
 

it doesnt work that way, it will only change its flashing speed if you have a variable oscillator driving it
in your way turning the volume pot up and down may only make the LED a bit brighter or fainter

Dave
 
What flash rate are you planning? Below about 4Hz won't be very noticeable. From 6Hz to 9Hz is a danger zone where flashes can trigger epileptic fits in susceptible observers. Above about 15Hz will appear as a more or less continuous light with an annoying flicker.
 
I've built a simple flashing circuit using a 555 timer IC, along with a 470 and 1 K resistors, a 1uF 16V radial capacitor, and a 9 V battery. The original circuit called for a second resistory (220K), but that is the one that I am using the volume pot to replace. The volume pot in the guitar is a 250K pot, and I am quite happy with the variey of flash rates I get with it. The Led's are running some fiber optics which will show up on the front of the guitar. I will also wire a switch to the circuit so it doesn't drain the battery when not in use. My problem is the volume pot also has the pickup signal running to it, and my circuit puts out a signal as well to the amp, which is the one I want to seperate after the pot, so only the pickup signal goes to the amp.
Possible? cowboy Bob, i would love to see the plan you have, to see if it would work....
 
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It seems your circuit needs a mod to separate the audio using a capacitor. But you need to post a schematic of your circuit, showing where you connect the pickup, so that we can see what mod is needed.
 
Hey Cowboybob... I would love a schmatic if you have one...I'll check it out and see if it will work for what I'm going for.....I've tried to add a schematic for what I have, but can't figure out the attachment.....
 
That is not a schematic, that is a mess of wires and components where anyone can guess what is connected to what.
Other than that, you can´t use the same pot for volume and flash rate. You would end up with horrible noises in your guitar sound.
The double pot idea seems like the easiest way to achieve what you want.
You want this circuit to let you know of your guitar´s volume right?
 
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Big Sammy said:
Hey Cowboybob... I would love a schmatic if you have one.
Click to expand...

OK.

I'm not quite through with the simulations yet, but essentially I'm using a 555 timer set up as a voltage controlled oscillator (whose output would feed the LEDs), being driven by a unity gain op amp getting it's signal from the output of the volume control on your amp.

I used a similar circuit (without the oscillator), connected to the volume control of a '46 Seeburg jukebox, to control its incandescent lights so they'd flash in intensity and rhythm with the music being played. Made that old jukebox come alive.

The unity gain amp circuit, correctly designed, totally isolates your guitar amp circuitry from the LED controlling circuit. It can hang off (be connected to) your guitar amp volume control without affecting the tone (or anything else) of your amp.

Give me a day or two to design the schematic.
 
Other than that, you can´t use the same pot for volume and flash rate
Click to expand...
Yes you can. I've designed a circuit to do that but was waiting to see what the OP has come up with so far. Yer tiz.
 
I don´t think that loading a guitar pickup with 10K will do much good to the sound, volume pots are 500K usually and it has its reasons. Maybe if you had some buffer before the volume pot.
 
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You're right about the 10k (I'm no musician so I just guessed at a pot value). The circuit in post #16 was drawn before the OP said what the pot resistance was. Here's a revised circuit for the specified 250k pot. I haven't included a transistor stage for driving the LEDs. The audio output needs to feed into a preamp with an input impedance of at least 100k to avoid loading the pot signal too much (the circuit effectively halves the impedance seen by the pickup, so would benefit from a buffer amp stage following the pot). The flash rate upper limit is 5Hz on safety grounds and should not be increased if epilepsy sufferers are likely to view the flashing LEDs.
 
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