Double Tube Screamer

[Ctrl4Smilerz]

So, I've decided to dip my toes in DipTrace, in hopes to design a two in one tube screamer circuit. I started by replicating the circuit based on the Little Green Scream Machine circuit. I would like the circuit to have two of the clipping sections in series, which can be independently activated, but I have a few questions.

In the Little Green Scream Machine schematic the only switch is in the power section, are the two sections of the 3PDT unused, or does that just not show on the schematic? Since the switch is in the power section, would I need to replicate it for both clipping sections or is there a way I can reuse it for both? And finally can I keep just one output buffer that would go after the second clipping section? Thanks in advance for helping me.

 

[Robert]

There is no actual switch in the Little Green Scream Machine, what you're seeing is a single pad labeled "SW" that is grounded by the 3PDT to light the LED.

The 3PDT footswitch is not drawn on the schematic for the PCB.

If you are planning to incorporate the 3PDT footswitch into your PCB, then yes, you would use those unused portions for signal bypass switching.


As for your circuit... So you're wanting to duplicate the clipping stages only? What controls do you want to end up with?

 

[Ctrl4Smilerz]

There is no actual switch in the Little Green Scream Machine, what you're seeing is a single pad labeled "SW" that is grounded by the 3PDT to light the LED.

The 3PDT footswitch is not drawn on the schematic for the PCB.

If you are planning to incorporate the 3PDT footswitch into your PCB, then yes, you would use those unused portions for signal bypass switching.


As for your circuit... So you're wanting to duplicate the clipping stages only? What controls do you want to end up with?

That makes sense of the switch, thanks.

I would like to make it fit into a 125B enclosure so, the less I need to duplicate the better; I was thinking of just duplicating the clipping stages. Do you think that is enough to mimic the sound of two tube screens in series? Ideally the controls would be Tone, Drive, and Volume for both channels, so a total of 6 pots.

 

[cdwillis]

The tube screamer sound is the combination of the chopped off bass in the clipping section (720hz high pass filter), the clipping section mixing with the clean signal, that signal getting a 720hz low pass filter, then a tone control that can add back high end above 3khz. If you only have the clipping section it's not really going to sound like a tube screamer.

 

[Ctrl4Smilerz]

The tube screamer sound is the combination of the chopped off bass in the clipping section (720hz high pass filter), the clipping section mixing with the clean signal, that signal getting a 720hz low pass filter, then a tone control that can add back high end above 3khz. If you only have the clipping section it's not really going to sound like a tube screamer.

That makes a lot of of sense, I'll have to duplicate the tone section as well.

 

[Ctrl4Smilerz]

That makes a lot of of sense, I'll have to duplicate the tone section as well.

So I duplicate from IC1.1 to the Volume Pot, which should cover the signature sound, and reuse the input buffer, output buffer and power sections. Where I struggle is, if I'm reusing the input and output buffers, how can I design switching to use the buffers if either channel is activated and bypass them when neither channel is activated?

 

[Robert]

Just duplicate the entire circuit, it'll be easier.

Take a look at the Paragon Mini schematic.


Doesn't @jimilee have a dual TS PCB?

 

[jimilee]

Just duplicate the entire circuit, it'll be easier.

Take a look at the Paragon Mini schematic.


Doesn't @jimilee have a dual TS PCB?

Yessir.

 

[Feral Feline]

Jimilee's "TWOBSCREAMER" — great name.

 

[jimilee]

Jimilee's "TWOBSCREAMER" — great name.

I called it the king of scream.

 

[cdwillis]

It might be easier to fit two of the Lovepedal Eternity circuits in. They're clone of the Son of Screamer which is just a screamer with the buffers removed.

 

[Ctrl4Smilerz]

Just duplicate the entire circuit, it'll be easier.

Take a look at the Paragon Mini schematic.


Doesn't @jimilee have a dual TS PCB?

That makes a lot of sense, I probably should have started there, thanks.

It might be easier to fit two of the Lovepedal Eternity circuits in. They're clone of the Son of Screamer which is just a screamer with the buffers removed.

Yes, easier for sure, but a big part of this project is for me to learn DipTrace.

 

[jimilee]

That makes a lot of sense, I probably should have started there, thanks.

Yes, easier for sure, but a big part of this project is for me to learn DipTrace.

You’re on the right track. Laying out and modifying circuits helped me learn eagle and learn more about circuits. The more you learn this stuff, the easier it is to troubleshoot, also.

 

[Grubb]

I also learned how to tweak/hack pedal circuits by doing exactly what you're doing. Keep forging ahead.

One of my recent projects was to make a switchable Tubescreamer minus the in/out buffers (otherwise known as a Son of Screamer) but with the option to change the eq tuning before and after the clipping stage to Lovepedal Eternity values, which is essentially a retuned SOS in the first place. Messing around with filters on existing circuits is exactly where most pedal designs come from.

I found that researching common mods to pedals and then "baking them in", sometimes as switchable options, helped me learn how to creatively tweak circuits fairly quickly. Good luck with your project!