Hello Everyone! Effects pedal project...I need help!! I have a 555 timer in astable generating a continuous 0 to 9V square wave to drive a 4017 decade counter. The 4017 resets on Q4 so I have 4 outputs of approximately 9V. What I want to do is use each of those to 'turn on' some type of circuit that will change the phase of a guitar signal, so that I will end up with 4 different phases of the input signal in a continuous sequence at the outputs. My question is, what type of phase shift circuit should I use and how do I pass the guitar signal ONLY through the circuit being powered by the 4017 output that is high.

I'm using LtSpice for simulation and have found one possible solution to my problem...I used a lm741 op amp in an all-pass filter circuit with a virtual ground so that the input signal wasn't above and BELOW 0V, causing the opamp to not work correctly, but even then, the only way I can get my desired output is to connect the positive side of the guitar signal to the filter input and connect the negative to the virtual ground, which I assume is just not an option in real life when I build my pedal. I have read something about AC-coupling to be able to connect input and output to real groud, while using the virtual ground in the op amp stage...

If you can't tell, I'm a total newb to circuit design, (I did take an electronics course at ATI about 7 years ago) so I'm sorry if I've said anything that didn't make sense, and please let me know if this project is just doomed to fail...I'm just trying to come up with a somewhat original effects pedal if possible. I would also be happy if instead of a phase shift effect, I could get an octave tone or some synth-type sound that changes with each 4017 output. Any help would be greatly appreciated. Thanks!

...I can attach an image of my ltspice schematic if it would help

 

You're using a 741 opamp in LTSpice?

That's sort of like going to an exotic automobile dealership where every car is free (yes, even the Jaguars, BMW's, Rolls-Royces, Aston Martins, Ferrari's Lambos - you name it, they have it) and insisting on driving away in a '62 Ford Galaxy with bald tires and a missing fender they had hidden in the back lot.

Anyway, posting a graphic image of your schematic is pretty much a minimum requirement around here.

Adding your LTSpice .asc schematic file is a plus, for many of us have LTSpice installed.

Use the "Go Advanced" and "Manage Attachments" buttons.

 

Thanks for the reply SgtWookie. Yes, I figured the 741 was a poor choice, it was just the most common op amp I knew of, but I just read a little about the LT1115, I think maybe that's a better choice...?

Anyhow, I still just don't know if I can connect the input signal to the virtual ground, I assume that is just not safe or realistic to think that it wouldn't cause problems in a real-life circuit, right? I also am not sure I'm simulating a guitar signal input in a proper way...I have been using .wav file for the guitar signal, but I replaced it with a sine wave to post it on here. I only have one of the all-pass circuits going right now because I don't know how I should connect the input signal to all 4 filters, or how I should tie the outputs. Again, help with any (or all) of these issues would be awesome!

So here's my .asc file:

 

My question is, what type of phase shift circuit should I use and how do I pass the guitar signal ONLY through the circuit being powered by the 4017 output that is high.

You could use a 4066, it's a quad analog switch. Remember, to actually hear the effect of a phase shift on audio, you will have to mix the phase shifted audio back in with the original audio, which will create a "notch" in the frequency spectrum. Sounds like you're trying to make a phaser where the frequency of the "notches" in the spectrum changes in discrete jumps, instead of sweeping up and down? Sounds like it could be cool. Instead of having multiple phase shift sections that the audio is switched between, why not use one phase shift section and have the output of the counter switch different control voltages to a voltage controlled resistor to control the phase shift?

 

I agree with Bitrex.

Right now, you're using the 4017 output to selectively power circuits. This is not a good idea from several standpoints. For one, you'll get lots of loud "pops" in the output when powering one opamp down, and the next one up. For another, opamps need bypass caps across their Vcc/GND terminals; and the 4017 has meager source/sink capabilities.

I don't have much time today. I replaced your 741 opamp with a TL07x model. This covers the TL071, TL072, and TL074 models. These opamps have been around for many years and are dated, but are very popular for audio. They are very low noise, and have far better bandwidth and far lower distortion than the 741.

I've attached TL07x.zip, which contains:
TL07x.sub - place in ...(switchercad)\lib\sub
TL07x.sym - place in ...(switchercad)\lib\sym\opamps

I've "tidied up" your schematic a bit:

You had left the 4017 clocken\ input pin floating; CMOS inputs must always have a current path to either Vdd/V+ or GND/Vss.
You had outputs tied to ground. Don't do that. Leave unused outputs floating.

I've used the "Label Net" feature to eliminate some wiring; it makes the circuit easier to understand. Note that the output is labeled "Out" - it shows up that way in the simulation.

To the .tran statement, I've added startup and uic. This starts all external voltages at 0v, and skips the initial operating point. That will help to run the simulation more quickly.

I've moved things around a bit so that the schematic is wider than it is tall. Makes it easier to see things when you're running the simulation and you have two horizontal windows.

 

Wow, thanks! You guys are awesome, I knew there had to be a better way to go about this. I will redo this with bitrex's idea and now that I know about the "label net" function, I can definitely clean up my schematics a bit!

Thanks again to both of you, and I will get crackin' on the 4066 version tonight.

 

Something that you'll find super awesome is that you can feed the simulation a SHORT .wav file, and it can write an output .wav file so you can actually hear close to what the real output will sound like.

 

Yes I have been using a .wav file input and saving the output for that purpose, very nice funcion of ltSpice! I've been trying to read about the 4066 mentioned earlier and am not quite sure how y'all are suggesting that I use it...I haven't found many good example circuits for it, just pinouts and specs. Are you guys saying I should use it INSTEAD of the 4017 or in addition to it? I would understand how to use the 4017 outputs to 'flip' the switches of the 4066, but I was thinking y'all meant the 4066 could somehow flip the switches in sequence, or 'count' like the 4017...

 

Use the 4066 in addition to the 4017.
The 4066 is just a quad analog switch.
The 4017 is used to select which switch is closed.

 

I can't seem to find an ltSpice model for the 4066 anywhere. The only one I found was only a single switch, not a quad...? Could you point me in the right direction as to where to find the .sub and .asy files? or possibly upload them here if you have them?

 

That's OK; use the single switch version, and put four of them in your schematic.

There is a CD4066 model on the Yahoo LTSpice User Group:
http://tech.groups.yahoo.com/group/LTspice/files/ Lib/CD4066/
You will have to be a member of the group to access the files.
It is a single channel of a 4066. In some respects, this is a good thing.