Need help designing a resistor sequencer.

[elframbo]

Hey, thanks again for the info and sorry for the delayed reply.

I don't have many different capacitor values so I put a matching capacitor in parrell with the
original 0.1U capacitor. I also changed the value of R1 leading from pin 7 of the 555 timer to
a 470k resistor.

From the 4066 chip I only used two resistors instead of three in my first test. R1 was 10k
I omitted R2, and for R3 I used the 470k resistor. Vr1 is 100k and I am in the ball park on
speed.

Upon testing this in the pedal with a guitar playing I found that it didn't seem to make a
difference as far as the distortion and cleaner sound. But, I noticed a constant pulse sound.
Even when I wasn't making sound with the guitar I heard a constant loud pulse that was very
noticable during play. The pulse was probably 8 per second as best I can tell.

I later found I made an error and R3 from the 4066 was not connected to pin 8. I corrected this
and added a 100k resistor in the R2 spot. Another test and the pulse is still there, but now
I am hearing the distortion changes that I am trying to achieve.

How can I eliminate the pulse? Is there something I need to change in the resistor sequencer,
or is the positioning of the R10 in the pedal schematic too close to an opamp?

A second question... could this sequencer be used as a diode sequencer? In the pedal schematic
D4 and D5 are clipping diodes and I have mosfets there for now. But, most put an LED there to
replace one or both of them. Could I use this to switch say an LED, mosfet, and diode in and
out of D4 or D5 in the same way I am switching out the pedals R10? Just a curiosoity to
see what can be done with the pedal and this timer circuit.

Thanks!

 

[(*steve*)]

There may be multiple causes for the noise.

The first is that digital noise from your circuit is bring picked up inside the pedal.

The second is that changing this resistor is changing some voltage level in the circuit (which is most likely because it's in a feedback loop from memory) and this is causing the changes of level to be seen as a signal. Essentially you're injecting noise.

(and there will be others)

If your circuit is ramping up the resistance then letting it suddenly fail, the sudden fall may create an audible thump or click.

An alternative is to ramp both up and down, but an even better solution is to have an actual ramp rather than a series of steps. This way the ramp speed will dominate over the steps, and presumably be at a speed which introduces noise at an inaudible frequency (and also presumably) which is below the low frequency response of your system.

I suggest you look at "vactrol"s. They are essentially a LED and an LDR in a light tight enclosure. If you power the LED from a ramped current source, the resistance of the LDR will vary in a ramped manner.

Because of the isolation, you won't need to have any electrical connection with the power supply of the pedal, and that can eliminate (or at least reduce) problems with digital noise.

As to using the 4066's to switch other things, sure. As long as the voltage I'd within the limits and the additional resistance doesn't upset the circuit, you should be fine.

One additional thing I've not pointed out is that running low level signals along long wires is also a recipe for noise. The vactrol solution I provided above would allow the signal to remain close to the board with the low impedance (and thus noise insensitive) LED current connections running between the circuits.

 

[elframbo]

Thanks, that is a lot more in line with what I was wanting to begin with and sounds like a great solution. I had looked at photo resistors before because D5 is part of the clipping circuit. When it clips the wave the LED lights up, so I wondered what a photo resistor would do.

I looked at the vactrol's as you suggested and it really does look like the answer, but it's a bit expensive for what I'm doing with this project. Can I acheive this effect by placing a red led in the clipping circuit say at D5 and a photo resistor at R10? I would need to make a housing for the LED and resistor to seal in the light. But, in effect would this be the same?

Thanks again for all the help, I'm learning a lot from this process and I appreciate all the information you have given me. Any other ideas of circuits I can learn from /use for beginer projects?

 

[(*steve*)]

Most people make their own vactrols by sticking together a CdS cell and a LED. A couple of layers of shrinkwrap does wonders

Some people go to the additional effort of 3D printing little enclosures for them.