This Week on the Breadboard: The Yankee ScrewDriver Deluxe Turbo

[Chuck D. Bones]

I've been fooling around with the Skreddy Screw Drive Deluxe for a while now and I think I'm finally finished.

I knew I had to replace the MOSFET 1st stage because MOSFETs are noisy. I had gone with a JFET 1st stage on the Diamond Peak mod and it worked well. The 1st stage gain control is tuned to be a MIDBOOST, similar to the Diamond Peak and Hybrid Fuzz Driver. If you want it to be full-spectrum boost control, then make C2 bigger for more bass and maybe reduce C3 for more treble. It's 100uF in the original Screw Driver and Lunar Module pedals.

The major breakthrough was making the 3rd stage a mu-amp. I got the idea from the Sabro Lighthouse, which is a mod of the Toneczar Openhaus. The mu-amp does a couple of good things: it boosts the gain over 20dB and it helps stabilize the Ge transistor's collector voltage. The gain of the mu-amp depends strongly on the JFET used. The two JFETs that produced the most gain, by far, were the 2SK193 and J201. If you use a J201, it needs to have an IDss >1mA. I wanted to be able to get the original Screw Driver gain range, so I added a TURBO switch that allows me to turn the mu-amp's 20dB gain boost on and off with a toggle switch. I know what you're thinking: "Can't that TURBO switch be a stomp switch?" Yes it can! Mu-amps have a high output impedance, so I added a BJT buffer (Q5). Q5 can be any high-gain Si NPN. I tried several different trannys for Q3: a few AC127s, a Tesla 104NU71 (thanks, Joe!) an MP38A and a 2N1308. Surprisingly, they sounded very similar. The Tesla produced the highest gain, so I went with that one. NB: the 104NU71 did not have the highest Hfe. Hfe does not govern the gain in a mu-amp, Hoe does. No, that is not a rude joke. Hoe is the output conductance of a transistor. Lower is better. The Bias Trim is there to compensate for the Vp variation in Q4. Once it's set, you'll never need to change it.

I also improved the TREBLE (called BRILLIANCE on the Screw Driver) control so it has more range and doesn't change the volume when the knob is turned.

Q2 can be any low noise Si transistor. Q1 can be any N-channel JFET with Vp around 3V or so. Not all J112s will have the right Vp, but I had no problem finding one that did. Bought 'em from Tayda a while back on a hunch.

With TURBO off and MIDBOOST and FUZZ turned down, it will play clean. Crank everything and turn on the TURBO and it has sustain for days with no noise or squealing, even on a breadboard. Max gain is around 100dB according to LTSpice. The most I could measure was in the 70's, but that is a limitation of my test equipment.

L-R: VOLUME - TREBLE - BASS - TURBO - FUZZ - MIDBOOST
Q1 on the far right, Q5 on the far left.

 

[jubal81]

Can't resist. Gonna have to make a layout for this one.

 

[steviejr92]

Oh this is going to be good I can tell!

That turbo switch is going to be fun with no hiss either? Yes please!

 

[KR Sound]

This looks really cool, man.

 

[cooder]

Count me in....

 

[Sturdag Lagernathy]

Looks very cool, how different soundwise is it from the Screwdriver?
Where does "yankee" come from?

 

[Barry]

A Boneyard Screwdriver! I'll have a double!

 

[Chuck D. Bones]

Looks very cool, how different soundwise is it from the Screwdriver?

Similar, but not identical. I have not spent enough time A/B'ing them.
It's a Screw Driver at heart and it does what a Screw Driver does: it takes a Fuzz Face, adds gain & tone controls and makes it fit anywhere in the pedal chain.

Where does "yankee" come from?

I'm glad you asked that. Back in the late 19th century, The North Brothers Mfg Co in Philadelphia began manufacturing & selling a ratcheting spiral screwdriver under the Yankee brand name. It can be operated like a standard screwdriver, or if the handle is pumped in & out it becomes an "automatic" screwdriver.

Here's Robert DeNiro using one in the movie Brazil.

And a more detailed video here.

 

[KR Sound]

I haven’t seen Brazil forever. Didn’t even remember that DiNero was in it.

 

[szukalski]

The Yankee screwdriver was fascinating for me as a youngster. Thanks for the schematic and the memory!

 

[jubal81]

Been trying to learn EasyEDA this week and I'm really liking it. This might be goodbye forever for Eagle.

 

[iamjackslackof]

Been trying to learn EasyEDA this week and I'm really liking it. This might be goodbye forever for Eagle.

Any chance you'd want to share the Gerbers? I immediately decided to lay this out in eagle when I saw it, and yours looks far better than I could manage.

 

[jubal81]

Any chance you'd want to share the Gerbers? I immediately decided to lay this out in eagle when I saw it, and yours looks far better than I could manage.

Since it's Chuck's design, I'm gonna defer to him for how he wants to handle PCBs and files.
I think I'm pretty much done, though. Even got most of the 3D models looking pretty close. The connections match with the basic PedalPCB 125B layouts, so all the foot switch boards on the shop here will work with it. Only difference is I have connections at the top for the audio jacks which connect directly to the outside pads at the bottom for easy wiring.

 

[iamjackslackof]

Looks great. Love that it matches PPCB 3PDT breakout boards, I always do that on mine. Same with the I/O jack connections at the top, makes for very neat wiring.

 

[Chuck D. Bones]

Still fiddling a few component values. Looking for a wee bit more brightness.

 

[music6000]

Something Like This:

 

[Chuck D. Bones]

Swap the BASS & TREBLE and we're good to go. Makes for a cleaner board layout that way.

 

[Chuck D. Bones]

Update. I spent some time, maybe too much time, dialing-in the tone. I reduced C3 & C7 to gain a little brightness. Lowered Q1's output impedance by reducing R4 and and adding R18. Increased R9 to get better adjustment range from the Bias Trim. But the big change was the TREBLE control. I tried a bunch of different things and finally settled on a BMP-style control. Note that VR4 is 10x smaller than on most BMP circuits. Makes the R's & C's more interactive and reduces the losses. The freq response is flat at around 1:00. Gets pretty dark below 9:00 and pretty bright above 3:00. With TURBO off, MIDBOOST & FUZZ at zero, it plays clean, even with Humbuckers. I'm calling it done.

 

[MattG]

This looks awesome Chuck! I have a few things to wrap up, then this is definitely moving to the top of my project queue!

 

[Alan W]

Wow! I hadn’t thought about Yankee in a long time! For a few years in the early 70s I had a Yankee hanging off my toolbelt, getting more use than almost anything else, building and striking stage sets. Imagine life before cordless drills, and the number of screws involved in scenery. Hinges, toggles, all over the place. They came in several sizes, but the one that got the most use was about 18 (?) inches long when collapsed and got ~10 inches longer. This was great ergonomically, since much scenery is too big to work with other than being on the floor, so that length meant you could bend down over something and let your upper body weight do some of the work. I may still have a toolbox sized one somewhere… Stanley bought the Yankee company, and it became their name for their top tier hand tools.

Oh, and I wanna build one too.