Maker Pro
Maker Pro

A Stretch

SparkyCal

Mar 11, 2020
849
Joined
Mar 11, 2020
Messages
849
Bertus:

Thank-you . That was reassuring. Because I already had an assortment kit of electrolytic capacitors, I replaced the film one with the electrolytic one, when I read Audioguru's post. I will probably leave it as is, as it is already soldered and your comments suggest that it will likely not do any damage on a low power circuit. I have bookmarked your links and plan to read them, as i am VERY interested is such circuits. Being a musician, it is a good nexus between my interests and it will encourage me to learn more on the electronics front. Thank-you

Today, I will be building the power side of the circuit. I have built the rest. This time, I have mounted the input and output=jacks ina. project box, as I found the wires were dangling all over the place the last time I did this circuit.
 

bertus

Moderator
Nov 8, 2019
3,304
Joined
Nov 8, 2019
Messages
3,304
Hello,

I copied the text from you PM:

Presently, i am struggling through my third iteration of building this circuit. I am breadboarding it.

The good news is that I have ti working so that there is no noise. Meaning, my connections seem to be correct now. the problem however, is that the guitar signal makes it through the circuit and comes out the other side, but when i connect to a guitar amplifier, the circuit does not produce any distortion. the whole purpose of the circuit is to produce overdrive distortion.

I have a feeling it is because of the op amp I am using, and whether I have connected it properly.
ccording to its datasheet, the pin mappings are as follows:

Pin 1 Offset null 1
Pin 2. Inverting Input
Pin 3 Non inverting input
Pin 4. Vcc -
Pin 5 Offset Null 2
Pin 6 Output
Pin 7 Vcc+
Pin 8 NC

I have not connected the following pins: 1, 5. 8
Could this be the problem? Is there a pin that I should have connected but did not?

There is no need to connect the pins 1, 5, and 8.
The pins 1 and 5 are for offset compensation, when the opamp is used for precision measurements.

Bertus
 

SparkyCal

Mar 11, 2020
849
Joined
Mar 11, 2020
Messages
849
Thank-you. Sorry but I did not realize that we were in PM mode.
 

bertus

Moderator
Nov 8, 2019
3,304
Joined
Nov 8, 2019
Messages
3,304
Hello,

I have added the pin numbers and power connections on the opamp in the schematic:

sparcal_Overdrive pedal with tone-control comment pin numbers tl081.png

Bertus
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
When you turn up the "gain" pot then there will be LOTS of overdrive distortion caused by the diodes.
 

SparkyCal

Mar 11, 2020
849
Joined
Mar 11, 2020
Messages
849
Hi folks:

I am officially giving up on this circuit, but I don't consider it a failure.

I am convinced of one of the following:

Either:

1. The circuit itself is flawed- many people have commented on a capacitor being shown with reverse polarity- maybe that's it?

2. I may have burnt out a component along the way and that's what's causing it.

However, this si not a failure because along the way, i have learned a lot.

I am in the process of finding another circuit. I have the following op amps, so I am hoping I can find a particular circuit I can build to achieve overdrive, using one of the following op amps. And because I know being specific is important, I will try to describe these op amps with specificity:

I have the tl081cp. on it's face, it has the label: 3BA081M. TL081CP

The other one I have is the 4558D |JRC| 0058T. (I have tons of these ones as I bought them in bulk on Amazon)

Thanks for everyone for the links, resources, advice and time. It was not wasted. I know a lot more about this know, then when a started.
 

bertus

Moderator
Nov 8, 2019
3,304
Joined
Nov 8, 2019
Messages
3,304
Hello,

The NJM4558 is a dual bipolair opamp.
It connects like the TL082:

NJM4558_pinout.png

I have also attached the complete datasheet.

Bertus
 

Attachments

  • NJM4558_E.pdf
    121 KB · Views: 0

bertus

Moderator
Nov 8, 2019
3,304
Joined
Nov 8, 2019
Messages
3,304
Hello,

Did you already take the circuit apart?
Perhaps the capacitor C28 has a to small value and only high frequency signals are amplified.
Raise the value of C28 to 10 μF and see what happens.

Bertus
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
The circuit is a common one with a good design. With the diodes it causes overdrive distortion. With the polarity of C3 backwards it causes more distortion.
Amazon is not a reliable electronic parts distributor so maybe their parts are fake or defective.
EDIT: I disagree with its tone control that overloads the opamp when the tone control connects the 22nF capacitor C29 to the output of C3.
 
Last edited:

SparkyCal

Mar 11, 2020
849
Joined
Mar 11, 2020
Messages
849
Sorry but I have killed the circuit and took it apart. Before doing so, I switched out the op amp, I reversed the polarity of the capacitor that was on backwards, but not. etc. I have found a new circuit that i would like to start fresh with. Should I create a new thread for the new project?
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
Most overdrive circuits are the same, but if your new circuit is different then please begin a new thread for it.
 

SparkyCal

Mar 11, 2020
849
Joined
Mar 11, 2020
Messages
849
On my new thread, Martin suggested to stick with this circuit, as it is easier than the new one I picked, Upon reconsideration, I agree. So I am going to abandon the new thread- i will see if i can make a not there if i can't delete it, and move back here.
 

SparkyCal

Mar 11, 2020
849
Joined
Mar 11, 2020
Messages
849
There has to be something wrong with this circuit. I built it again- exactly according to Bertus' schematic and it still did not work. No sound at all coming out and rather, buzz.

I am miffed by this. I wonder if i have the right capacitors. I went out and bought the film capacitors but, for example, for the C23 470nF capacitor, the one I bought has the following on its face 474K 250H

Is the capacitor value correct?

I don't know why else this circuit will not work. Very frustrating.
 

bertus

Moderator
Nov 8, 2019
3,304
Joined
Nov 8, 2019
Messages
3,304
Hello,

What happens when you remove the tone control?

sparcal_Overdrive pedal with tone-control comment pin numbers tl081 no tone control.png
As Audioguru said, the tonecontrol can short the output.

Bertus
 

Audioguru

Sep 24, 2016
3,656
Joined
Sep 24, 2016
Messages
3,656
What do you have connected to the output of this overdrive preamp? it cannot drive a speaker, it is supposed to be connected to an audio power amplifier's input and its ground.

If you are using a 220nF film capacitor for C28 then it will be marked 224.

If you have a voltmeter then when the battery is 9VDC the pin 6 output of the opamp should be half at 4.5VDC. The TL081 opamp might not work if the battery voltage drops below 7VDC.
 

SparkyCal

Mar 11, 2020
849
Joined
Mar 11, 2020
Messages
849
Bertus and Audioguru. Your comments are giving me hope. I was getting disheartened building the circuit over and over with the same result. Your observations are the type of testing and analysis that is required to solve this. I will report back once I have a chance. Deal with a problem with my air conditioner this morning. And it is over 30 degrees C here
 

Alec_t

Jul 7, 2015
3,587
Joined
Jul 7, 2015
Messages
3,587
If that circuit gives just hum and no guitar sound, I suspect the fault lies with something simple, like a missing ground connection. Do you have battery negative, guitar plug ground and pre-amplifier input ground all connected together?
 

SparkyCal

Mar 11, 2020
849
Joined
Mar 11, 2020
Messages
849
To answer some quick questions. Yes, the out is being plugged into a Fender Hotrod Deluxe amplifier. I am not sure that all those grounds are connected together but wherever it says Ground, I run a wire from that connection to the negative rail.
 
Top