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Audioguru

Sep 24, 2016
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I looked through all your threads and posts looking tor the 3.3uF capacitor that I recommended from 220nF and found it in your different thread over 1 year ago. It is C28 to ground which is in series with the 1k R46 at pin 2. 3.3uF passes most audio frequencies.
When C28 is 220nF it cuts 727Hz and all lower frequencies like in the TS-808 screamer circuit and in a You Tube distorted guitar video.

The gain control affects how much distortion you have, maybe it is wired incorrectly.
Here are a couple of schematics:
 

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SparkyCal

Mar 11, 2020
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I am sure it is not the 3.3 capacitor, as it works fine when I insert it in the breadboard build. I think it is the wiring, that I plan to look at later. I will report in. I think I know how to build this circuit and have done so successfully many times now, due to the help I got here. One aspect of the circuit that I sometimes screw up, is the branch of the circuit that goes to the two soft clipping diodes, the capacitor, the 500k pot, then to the 1k resistor etc. How could I use my multimeter to troubleshoot that part?

p.s. I want to learn troubleshooting, as I think it will help me to learn better and internalize what I learned from the mistakes I make.....hopefully, so I stop repeating them
 

SparkyCal

Mar 11, 2020
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I looked through all your threads and posts looking tor the 3.3uF capacitor that I recommended from 220nF and found it in your different thread over 1 year ago. It is C28 to ground which is in series with the 1k R46 at pin 2. 3.3uF passes most audio frequencies.
When C28 is 220nF it cuts 727Hz and all lower frequencies like in the TS-808 screamer circuit and in a You Tube distorted guitar video.

The gain control affects how much distortion you have, maybe it is wired incorrectly.
Here are a couple of schematics:
I will use your recommendations on the next build. I may be running my iron too hot (it's at 450), because I think I am frying diodes. I swapped the diodes for red LEDs and the circuit worked and produced great sounding distortion.
 

Audioguru

Sep 24, 2016
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My temperature controlled Weller soldering iron is 53 years old and is always at 371 degrees C (700 degrees F.
I always use name-brand 63/37 tin/lead rosin-core solder.
One solder joint takes 1 second. I have never fried any electronic part.
I am glad to hear that you got it to work well.:)
 

SparkyCal

Mar 11, 2020
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@AG....

In my builds, I have used the original schematic for the voltage divider part of the circuit. I have also tried using your alternate version, whereby you are using 100K resistors and 10uF capacitors.

I have done so many builds that failed and that succeeded, that I have lost track of which was which. What I am wondering is whether your schematic for the voltage divider circuit is just another way of getting to the biased voltage we need. In other words, your schematic will achieve the desired voltage, just as well as the original...right?

The reason why I am asking, is that I am out of 47uF capacitors called for in the original schematic, and am planning to just use your schematic.
 

Audioguru

Sep 24, 2016
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Since the original circuit used a TL081 opamp that has Jfet inputs, its maximum input bias current is 200pA which is very close to zero current, then any value for the voltage divider resistors up to 200M ohms are fine.
The old 4558 dual opamp maximum input bias current is 0.5uA and the two inputs use 1uA then voltage divider resistors up to 100k are fine.
Then the 100k voltage divider resistors with 10uF capacitors are fine.
The original circuit was designed by someone who did not look at the datasheet specs.
 

SparkyCal

Mar 11, 2020
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You're probably right. A little surprising however as the gentleman who posted it, makes a living out of building pedals- Wampler
 

Audioguru

Sep 24, 2016
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A little surprising however as the gentleman who posted it, makes a living out of building pedals- Wampler
The voltage divider can use any equal resistor values when the opamp that he always uses has very low input bias current.
But Wampler did not see the problem with his input capacitor value being way too high that might cause input overload of the opamp input if the guitar is thumped.
 

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SparkyCal

Mar 11, 2020
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My temperature controlled Weller soldering iron is 53 years old and is always at 371 degrees C (700 degrees F.
I always use name-brand 63/37 tin/lead rosin-core solder.
One solder joint takes 1 second. I have never fried any electronic part.
I am glad to hear that you got it to work well.:)
I changed my temp to 371 and it works great. Thanks
 

SparkyCal

Mar 11, 2020
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Here is a pic sure of two completed pedals. They both work!!!!!!

Both are using the 4558D chip.

Both are housed in wooden boxes that I bought for $2.00 at the dollar store. They are great for prototyping.

I have a few steel boxes being delivered. My next goal is to learn how to connect a true by-pass. I beleive Harald posted a diagram, so I will circle back to that. Then I may tackle hooking up a stomp box switch (the 9 pin ones).

Thanks for all the help and patience. I think I finally got the hang of this particular build.
 

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SparkyCal

Mar 11, 2020
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What I find amazing about this cheap build, is the following.

With professional pedals (such as my Fultone OCD) which cost me over $200.00, you get great distortion, but not a lot of control over definition. You get control over degree of distortion, but not so much, definition.

With the cheap build we did, the definition is remarkable. I'll explain from a musical perspective:

Take the song Fly by Night by Rush. It starts with a D chord that gets augmented.

Now, with a regular distortion pedal, you can get that D sounding very distorted and good. But, the distortion comes with the price of erosion of clarity. In other words, it sounds good, it remains a D chord, but it sounds like a wall of sound.

With the cheap build we did, it sounds like a D chord, it sounds distorted, but I can dial in just the right amount that makes the chord's notes clear, while still hearing them distorted. I'm not sure if that makes sense to you. That's not easy to achieve. Love that feature of this new pedal. I wonder if it is due to AG's changes?
 

SparkyCal

Mar 11, 2020
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I did another build with my iron at 317. The diodes worked. Maybe I had been frying them previously.
 

Audioguru

Sep 24, 2016
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I listened to Fly by Night by Rush and the D chord at the beginning sounds fairly clean (low distortion).
You can adjust the amount of distortion with the gain control or with the intensity of your playing. Play intensely and you produce lots of distortion. Play softly and you produce low distortion. Then the musician can control it with his playing style.
 

Audioguru

Sep 24, 2016
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I watched a guy on You Tube showing how he plays the G "Chode on his guitah ", mate!
 

Audioguru

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Messy ling wires all over the place on a breadboard cause feedback.
I think the gain pot has the gain too high causing crosstalk between the opamp input wires and its output wires.
 

SparkyCal

Mar 11, 2020
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Messy ling wires all over the place on a breadboard cause feedback.
I think the gain pot has the gain too high causing crosstalk between the opamp input wires and its output wires.
Reduce the pot to what value?
 

Audioguru

Sep 24, 2016
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You reduce the resistance of the gain pot which reduces the gain by "turning its knob counter-clockwise".
The gain pot is a variable resistance from zero ohms to 500k ohms. When the pot resistance is zero then the opamp gain is 1 (the input level is the same as the output level). When the gain pot is 500k ohms then the opamp gain is a massive 501 times.

With fairly low resistance from the gain pot and a fairly low playing level then the diodes do not produce any distortion.
 
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