Tucson Annie
New Member
Hi Guys,
I'm playing around with a 386 chip, learning about what it does. I decided to follow a simple circuit layout in Forrest Mim's Timer, Op Amp & Optoelectronic Circuits and Projects book just to see the simple use of the chip. If anyone has the book, the circuit is on page 43 (I'd draw the circuit but I have yet to purchase any circuit sim software....off topic: has anyone ever heard of Circuit Shop by Cherrywood Systems? It looks easy and cheap **broken link removed**).
So, being a guitar player I decided to use my guitar as the signal source. I plugged it into a 10k pot the circuit design called for as a volume control and then the output was an 8 ohm speaker (after a 220uF cap). It worked, but the sound was weak....so, I figured it's because I believe passive guitar pickups have a high output impedance, so I put a 1 M ohm resistor on the input. I got nothing...no sound...so, I lowered the resistor value to 470 K and actually got a better sound than with just the 10k pot....so, I figure I am on the right track as far as input impedance goes.
The next step was to put a 10 uF cap between pins 1 and 8 at Forrest Mim's suggestion to crank up the gain....well, all I got was a bunch of nasty feedback noise....so I lowered that cap value to 1 uF and except for some crackles and pops, the gain was actually pretty good with just a little distortion of the guitar signal.
Then, I decided to get fancy and put this all in a box. Now, the noise is crazy bad and I'm guessing it is because the wires I used to put this all together in a little box are long (some over 6 inches) and they are picking up noise....my question after all of this is: Is that a reasonable assumption? My wiring is correct and even though I am not planning to use this as a practice amp, I'd like to know what's causing the noise....I figure today I will re-breadboard it with shorter wires and see if the problem goes away.
I'm rambling, lol...does this make sense? One last question: is there a way to check output impedance on a guitar pickup without opening up the guitar? I don't think it would be as easy as checking the resistance on the guitar cord ...I'm new to all this....I appreciate any input!
Annie
I'm playing around with a 386 chip, learning about what it does. I decided to follow a simple circuit layout in Forrest Mim's Timer, Op Amp & Optoelectronic Circuits and Projects book just to see the simple use of the chip. If anyone has the book, the circuit is on page 43 (I'd draw the circuit but I have yet to purchase any circuit sim software....off topic: has anyone ever heard of Circuit Shop by Cherrywood Systems? It looks easy and cheap **broken link removed**).
So, being a guitar player I decided to use my guitar as the signal source. I plugged it into a 10k pot the circuit design called for as a volume control and then the output was an 8 ohm speaker (after a 220uF cap). It worked, but the sound was weak....so, I figured it's because I believe passive guitar pickups have a high output impedance, so I put a 1 M ohm resistor on the input. I got nothing...no sound...so, I lowered the resistor value to 470 K and actually got a better sound than with just the 10k pot....so, I figure I am on the right track as far as input impedance goes.
The next step was to put a 10 uF cap between pins 1 and 8 at Forrest Mim's suggestion to crank up the gain....well, all I got was a bunch of nasty feedback noise....so I lowered that cap value to 1 uF and except for some crackles and pops, the gain was actually pretty good with just a little distortion of the guitar signal.
Then, I decided to get fancy and put this all in a box. Now, the noise is crazy bad and I'm guessing it is because the wires I used to put this all together in a little box are long (some over 6 inches) and they are picking up noise....my question after all of this is: Is that a reasonable assumption? My wiring is correct and even though I am not planning to use this as a practice amp, I'd like to know what's causing the noise....I figure today I will re-breadboard it with shorter wires and see if the problem goes away.
I'm rambling, lol...does this make sense? One last question: is there a way to check output impedance on a guitar pickup without opening up the guitar? I don't think it would be as easy as checking the resistance on the guitar cord ...I'm new to all this....I appreciate any input!
Annie