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Just When I Thought it was Going to Be Easy

SparkyCal

Mar 11, 2020
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Question. As I can’t determine if this op amp is dual,or single, how important is it that the second op amp be buffered? And if it is important, I guess I can assume the pin mapping for a Tl082
 

VenomBallistics

Aug 30, 2018
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scrolling back and reviewing the pic you provided of said TL081, the Texas Instruments logo looks kinda suspicious.
so we are probably looking at a knock off clone part. At least its a functional part.
You can check by simply shifting your bread board connections to use amp 2 to see if it has one. for your detective work, the buffering isn't too important. The current victim need only live long enough to solve the puzzle ... then it can go up in a puff of magic chinesium smoke. The goal is to know if you even have a second op amp to buffer.
 
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Audioguru

Sep 24, 2016
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Amazon and ebay sellers probably get fakes and defective parts from the garbage bins of real manufacturers.

SparkyCal, All or some of your opamps are marked wrong. Then you cannot be certain of what specs they have or even know if they are electrically defective.

I order parts online from digikey.ca and if I order before 8:00PM then the shipment is delivered to me in Canada the next morning. Then they must have a warehouse near me in Canada. I never noticed the delivery charge because it was low.
 

Audioguru

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He doesn't need a buffer opamp. Some guitar pedal circuits use a dual 4558 opamp because it is an "improved" old 741 opamp (and is stereo). In Google, the same circuit as in this thread has a dual TL082 opamp with only one of the opamps used.
 

SparkyCal

Mar 11, 2020
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Ok. I will go with not buffering the second amp. I will first test to see if there is a second amp.
I take your point about not being able to determine specs on kick offs. I once bought 2 op amps in a package from sayall for $11. Sure, they were from a storefront vendor but at the rate of errors I was making at the start of these projects, I’d have been broke. So, for now, in the learning mode, these flawed ones will do, seeing that they work once the mystery is unraveled.
 

Audioguru

Sep 24, 2016
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Sayal was a liquidator. They have never been a real electronic parts distributor like Digikey or Newark.
Sayal bought unused genuine surplus electronic parts and items from companies then sold them cheaply.
Now that there is ebay and AliExpress who sell very cheap fake or defective parts, maybe Sayal buys then sells them now.

Amazon buys anything from anybody.
 

VenomBallistics

Aug 30, 2018
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You are starting to drill down to a rational strategy.
What you have is probably good enough for your current experimentation phase.
As you figure out what you really want to do, stock up on genuine parts to persue those goals.
In the pedal industry, you see the TL072 used extensively. It's very similar to a TL 082, enough so that they are drop in replacements for eachother for the most part.
Worth considering a large quantity buy at some point.
You might find a love affair for transistor based fuzz that negates any need for op amps. So ... Flog all the results you need out of what you have to help guide your part stock direction
 

Audioguru

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Fuzz is severe distortion for people with good hearing. For people whose hearing of high frequencies is destroyed by age or deafened by very loud rock "music" then the fuzz is muffled and is simply a different kind of tone.

The tone control in this distortion pedal circuit adjusts the amount of high frequency fuzz.
 

SparkyCal

Mar 11, 2020
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I was never a fan of fuzz even in my early years as a guitarist. I know guitarists like Hendrix made it cool, but it just isn’t for me. @AG. I take your point and thankfully the build enables me to curb the fuzz out or minimize it.

on the topic of the 10k tone control, what would be the effect if I used a 20k tone pot? I am running out of 10k
 

SparkyCal

Mar 11, 2020
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By the way VB, I did, at one point built a transistor based pedal which sounded fuzzy. The effect has its place, and it’s more a matter of personal preference. It may also be a requirement if one does LSD. Lol
 

SparkyCal

Mar 11, 2020
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You are starting to drill down to a rational strategy.
What you have is probably good enough for your current experimentation phase.
As you figure out what you really want to do, stock up on genuine parts to persue those goals.
In the pedal industry, you see the TL072 used extensively. It's very similar to a TL 082, enough so that they are drop in replacements for eachother for the most part.
Worth considering a large quantity buy at some point.
You might find a love affair for transistor based fuzz that negates any need for op amps. So ... Flog all the results you need out of what you have to help guide your part stock direction
I think your advice is sound. I left the board and this hobby a while back because I allowed myself to get frustrated with not having a formal electronics education and not understanding much of what I was doing. But I dialed that down and am trying to keep it a fun hobby.
 

Audioguru

Sep 24, 2016
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At maximum resistance, the 10k tone control cuts 727Hz a little (-3dB) and cuts higher frequencies more at -6dB per octave.
A 20k tone control will cut 364Hz -3dB and higher frequencies at -6dB per octave.
Good hearing can hear 20,000Hz.
 

Audioguru

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If you want the original tone control range with a 20k pot then change the 22nF capacitor at it to 10nF.
 

SparkyCal

Mar 11, 2020
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Thanks @AG as I have many more 20k and 10nfs , than I do the alternative
 

SparkyCal

Mar 11, 2020
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Is there any way of using two different op amps in this circuit?
 

VenomBallistics

Aug 30, 2018
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As I think of it ... More refined control over tone can be good.
A parametric EQ might be nice
 

Audioguru

Sep 24, 2016
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You need only a single opamp. I have used many TL071 single audio opamps for hifi circuits but the TL081 is the same. Your original circuit used the TL081.

You can make a unique sound. The TL071 and TL081 have a problem called Opamp Phase Inversion. If an input is driven within a few volts of the positive or negative (your circuit's ground) supply, then its output suddenly goes as high as it can. It sounds weird, try it. the gain must be low and you must play fairly loud or a preamp can be added to increase the input level from the guitar.
The waveform of a sinewave has the problem here:
 

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SparkyCal

Mar 11, 2020
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Thanks AG. Will put it on my list of things to try. I just finished building the circuit using the flawed op amp, and it works perfectly; including LED, DC barrel and stomp switch. Next, I will be putting it in a box.

I also just discovered the joys of working with solid wire, rather than stranded. It is saving me a ton of time.
 
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