#runoffgroove

This is another great RunOffGroove project. It’s a unique twist on the classic Ibanez Tube Screamer. The UBE Screamer replaces the op-amps and transistor stages in the Tube Screamer circuit with inverters from a 4049UBE hex inverter.

I built this from a PCB I designed. The board is project on OSH Park. Check out the build Docs below. I used a black powder coat enclosure from Tayda electronics a red anodized dress nut and red anodized aluminum knobs from Lovemyswitches. I used the desktop mill to engrave the labels and logo through the powder coat.

Build your own!

Check out the build page for links to PCB Boards parts list and wiring diagram.

Read the build post here for PCB and parts: http://www.super-freq.com/ube-screamer-pcb-v1-1/

What does it sound like?

Here is another 22/7 build. It’s a Big Muff variation. This unique circuit replaces the transistor stages of the classic Big Muff with CMOS inverters. It’s a unique flavor of Muff. CMOS inverters have their own unique flavor of distortion and have been used in many classic pedals like: Craig Anderton’s Tube Sound Fuzz, Way Huge Red Llama, Blackstone Appliances MOSFet Overdrive.

The 22/7 was created by the unstoppable genius over at RunOffGroove.com. They have a lot great stompbox designs and great information, be sure to check out their site.

Build your own

I designed the PCB and created a project over at OSH Park. Check out my build Docs to read more about the circuit and learn how to make your own! The PCB is designed with the the pots, switch and LED mounted to the board for ease of assembly.

Build post here for parts and PCB: http://www.super-freq.com/22-7-on-osh-park/

Build Process

For this build I used a powder coated enclosure and milled the labels and logo through the powder coating with a desktop mill. This process works for me and I can do everything myself at home with no chemicals and little set up and clean up. I want to give UV printing a try in the future, I’ve seen a lot great results! I’ll be writing a blog post about it in the future.

What’s it sound like?

Sounds a lot like a Big Muff but with its own character. The hex inverters have their own flavor but the strong clipping inherent in the Big Muff architecture dominates the sound giving it the characteristic Big Muff sound. I suspect you hear hex inverters as the last inverter is overdriven by the rest of the circuit. I’d say you get the classic Big Muff clipping sound but you don’t get the over saturated sound you can get with a Big Muff when the input is too hot or the sustain high.

The 22/7 has a switch that changes the range of tone control through three different ranges. This changes the range and sweep of the tone control to match other big muff models. There is a Classic option which is described as an average tone model of classic Big Muff models. A Flat option which creates a flat tone response removing the mid scoop of the classic mode, this is a well known mod. Last is the Scoop mode which creates a deeper mid scoop, I compare this to the sound of the original Way Huge Swollen Pickle.

I like the last mode on its own, but the flat mode sounds better with the band. writing this in 2021 I’m spending all of my time playing at home so all the modes sound great!

This has been my favorite Big Muff of late! It’s got a good sound and the tone control hits a very usable range.

Built and test this second version of the 22/7 by RunOffGroove.com. Sounds good. This is a great alternative for Big Muff fans. The OSHPark project is public and verified.

22/7 is a Big Muff built around CMOS inverters in place of the transistors used in the traditional BMP circuit. The CMOS inverters have a tube like sound when over driven.

Order PCB here: 22/7 PCBs on OSHPARK

Parts List

CapacitorsC1        100µC2                   33nC3            100nC4             220pC5               150pC6                150pC7             100nC8              100nC9                  3n3C10                6n8C11                 10nC12                10nC13               100nC14               150pC15     100nDiodesD1-4    1N914D5              1N5817D6           LEDICIC1       CD4049UBEResistorsR1      100KR2                 470R3       1MR4       1KR5      33KR6       1MR7        33KR8       1MR9        39KR10         27KR11                  1MR12      1MR13               330KR14           100KR15         RLEDSwitchRANGEON OFF ON PotsSUSTAIN A100K 16MM TONE    B100K 16MMVOLUME   A100K 16MM

Parts

Wiring

If you don’t want to build your own this one is for sale on Reverb.

This is the second version of the UBE Screamer board. This version fixes a mistake with the reverse polarity diode. I’m calling this ready for public consumption and will add it to the OSH Park projects pages soon.

The enclosure is grounded through the jacks. The bottom cover though doesn’t make an electrical connection to the main enclosure body due to the powder coat. I used a drill bit to remove the powder coat inside the count sink recess, this allows the screw to make contact with the back cover for full shielding.

Order PCBs at OSH Park

Partslist

CapacitorsC1      10nC2      2n2C3        470nC4       100nC5        1n5C6        150pC7         100nC8       100nC9        100nC10       100uDiodesD1        1n4148D2         1n4148D3         1n5817D4             LEDICIC1      CD4049UBEResistorsR1       1M 1MR2         470kR3          470kR4        100kR5          100kR6        10kR7        1mR8       10kR9        100kR10       100kR11       100kR12       220kR13      Rx  (see note)R14       330R15         RLEDPotsTONE   B500k 16MM      VOL      B100k 16MM    GAIN    B500k 16MM

UBE Screamer Parts list

Wiring

Build your own! Check out my OSH Park projects page. Or buy this one at my Reverb shop.

4049 and 4069 are widely used in DIY guitar pedals for high gain distortion. They have a high gain, need few external components and they have no railstick when clipping the signal. And they even clip the signal softly and slightly asymmetrically as mentioned in an earlier post. 

And there are also quite a few jfet boost or distortion pedals out there, however they have a huge disadvantage of needing manual biasing for every single transistor. And that is not only a pain for DIY'ers, its also impossible (or at least very expensive) in commercial guitar pedals. Have a look at RunOffGroove's otherwise excellent guitar pedals or their fetzer valve pre amp, for more info on biasing a jfet.

A single stage cmos inverter is essentially a single stage class a amplifier, with two matched, complimentary transistors. So placing a resistor from the output to the input like so: 

causes it to stabilise it self at exactly its optimal bias voltage. 

And with a resistor to ground from the input, the bias can be offset by what ever voltage you feel like, to achieve an asymmetrical distortion.

Notice that these waveforms are simulated, and the inverter stage in the simulation does not have exactly the same transfer function as a 4069, but close. I suggest you test different bias offsets to find out what will make the most even and amplitude independent distortion (desired for clean channels), if you want to use this idea.

And it can also be used for a high gain soft clipping with a higher input signal. (more than roughy a 15th of the supply voltage peak to peak).

However, I'm not quite sure if it will do well as an input stage for a guitar amp or pedal. Because if I place a resistor on the input to increase the input impedance, the gain drops, and that is because the gain is equal to Rfeedback/Rinput. So there is a risk that the stage may become extremely noisy since the feedback resistor (the one from the input to the output) will have to be very high resistance to have any useable gain. But here is how I imagine it could work, if noise turn out not to be a problem (will test this as soon as I get a chance):