Hello, I'm trying to learn some electronics. I've been tinkering with effect pedals for a while, and now I'm trying to create a little crazy idea that i had.

What I want is to make a pedal that gradually adjusts the gain of an opamp over time, then expands/compresses the output to retain the same volume level. The idea is to have clean signal fade into an overdrive/distorted signal over time.

So what I thought I'd do was to have an LED start to fade in when it "sees" a signal, which in turn is catched by an LDR that works as a variable resistor controlling the gain of the opamp. Now here is where I'm getting stumped, I can't seem to get the LED to work. The circuit I tried to use as a base was this one:

but it doesn't work. Are there any modifications I need to do to get this to work with the guitar input signal instead of the microphone signal?


DocZ

 

I do not see any diagram mate

 

We will not see the diagram until it is approved by a moderator because the OP is a nOOb here.

 

why is that ?

 

Hello,

Please upload the image localy.

Attachments and Images
How do I attach a file to a post?

To attach a file to your post, you need to be using the main 'New Post' or 'New Thread' page and not 'Quick Reply'. To use the main 'New Post' page, click the 'Post Reply' button in the relevant thread.

On this page, below the message box, you will find a button labelled 'Manage Attachments'. Clicking this button will open a new window for uploading attachments. You can upload an attachment either from your computer or from another URL by using the appropriate box on this page. Alternatively you can click the Attachment Icon to open this page.

To upload a file from your computer, click the 'Browse' button and locate the file. To upload a file from another URL, enter the full URL for the file in the second box on this page. Once you have completed one of the boxes, click 'Upload'.

Once the upload is completed the file name will appear below the input boxes in this window. You can then close the window to return to the new post screen.

What files types can I use? How large can attachments be?

In the attachment window you will find a list of the allowed file types and their maximum sizes. Files that are larger than these sizes will be rejected. There may also be an overall quota limit to the number of attachments you can post to the board.

How do I add an image to a post?

If you have uploaded an image as an attachment, you can click the arrow next to the 'Attachment Icon' and select it from the list. This will be inserted into your post and can be located where you want it displayed.

To include an image that is not uploaded as an attachment and is located on another website, you can do so by copying the full URL to the image, (not the page on which the image is located), and either pressing the 'Insert Image' icon or by typing [img] before the URL and [/img] after it, ensuring that you do not have any spaces before or after the URL of the image. You can insert pictures from your albums (?) in this way too.

Bertus

 

So a light controlled "volume normalizer"? So the output from the lightest pluck to a full chord hit hard come out of the box at the same volume level?

 

Sorry about the posting/image error. I just did what I'm used to, and didn't actually bother to look up the correct procedure on this forum - for that I am sorry.

Yes the idea is to have a clean signal turn distorted over time, but not increase in perceived volume. But that is the general idea, first I need to find a good way of having the LED / LDR thing respond to the audio input.

I need the LED to start fading in once it sees a signal, and either switch off, or fade out when the signal is below a certain level.

I did some experiments with my pedals, using a splitter->SG1->Fuzz, then feeding the other clean signal to the same amp. I got some interesting effects. Now I'm trying to tweak it, and put it into a box.

DocZ

 

I'm curious, what is the reason for the level of the illumination on LDR decide control for distortion level?

 

No other reason than I thought it would be a simple method of controlling either the volume or gain over time. My plan was to control the fading of the LED with some sort of timer circuit. And then have some sort of signal-aware switch to start the LED fade.

Using that either as a gain resistor or signal attenuator. If I would go for the latter, I would need some sort of compressor/expander circuit on the other side to control the perceived volume.

I am sure there probably are better and easier ways of achieving this, but I am very new to electronics, so I'm happy for any input I can get

DocZ
Docz

 

A distorted signal has up to double the power of a clean signal when they both have the same amplitude. Half the power of a very distorted signal is in the added harmonics.

Your extremely simple circuit will not work because the transistor is not biased properly. If you manage to adjust the pot so that the transistor is half turned on then when it cools or if the supply voltage drops a little then the transistor will turn off and the opposite when it is heated.
If you manage to get the transistor half turned on then the LED is a shunt rectifier so the sound signal at the collector is always severely distorted.
The signal quickly turns the transistor on a little then turns it off a little so the LED will appear to be always lighted.

 

Yes, that is exactly what is happening, the LED is just lit. so I guess it's back to the drawing board, and doing some extensive reading / googling to find a suitable circuit.

DocZ

 

1) You need to convert the AC audio signal from the guitar into a DC voltage with its amplitude depending on the amplitude of the signal. A fairly complicated active rectifier circuit will do it because the ICs that were used in 1968 are not made anymore.

2) You need a voltage-controlled amplifier (or attenuator) which is very complicated because the ICs that were used in 1968 are not made anymore.

3) You need an overdrive circuit which is simple but they all sound different so you must find an old one that sounds good to you.

4) You need a timer circuit to slowly increase the overdrive and brighten the LED.

5) You need an LED driver circuit which is simple.

It seems to be much too complicated for somebody who is learning about electronics.

 

Thank you for your reply.

The way I see it is I need some kind of signal aware switch, that starts the LED fade in. I thought I could use some of the "Voice activated LED" circuits I found on the web for this - but swapping out the microphone signal with a clean guitar signal straight from the guitar doesn't seem to work. My guess was that I needed some kine of impedance matching - but now you say I need a complicated active rectifier circuit. I don't want the brightness or fade time of the LED to be relative to the level of the signal comming in, I just want it to check if there is a signal present. If there is a signal - start LED fade in, if not - switch LED off (or fade it out)

Second I need any kind of overdrive circuit that will allow me to use the LDR as a gain resistor - my plan was to use a very simple circuit, maybe based off a Ruby from Runoffgroove. This is the easy part - I've built a number of these, and my plan was to use the LDR instead of the gain pot.

Third I may need to add a compression circuit - but that is not crucial.

I don't get why 1968 get's into the equation - did this kind of pedal exist back then? I thought it was just one of my crazy ideas

DocZ

 

Maybe I can just skip the whole LED thing and use a timer circuit as the gain resistor?

I'll read up on the LED timer circuit.

DocZ

 

A timer has an output that is simply on or off. You want the amount of distortion and LED brightness to increase slowly when activated by a signal. So instead of a timer you want a circuit that slowly ramps its voltage which can drive the LED that can shine on an LDR if you want. The LDR can increase the gain of an opamp to produce clipping distortion.

A circuit that slowly ramps its voltage is called an integrator. It can be an opamp with a capacitor used for negative feedback that slowly charges. It can be activated by a peak detector circuit plus a flip-flop.