MLF Drive -- I *didn't* build this, but I watched it being built

[midwayfair]

My friend Mike Friedman -- who commissioned the Van Gogh mini pedal duo and the mini Engineer's Thumb -- asked for a soldering lesson. Instead of just having him sit around soldering a mesh of wire, I thought this would be more fun.



Rullywowr gave me a little Fo-SHO boost board a while ago, and it was lying on the bench, so I decided we'd build something on that rather than go straight for perfboard. I figured the circuit's biasing and caps were appropriate for several types of transistors, which would add a bit of fun once it was built. I didn't have the schematic in front of me, but I figured it couldn't be too tough to wing it (I did eventually print one out for the schematic reading lesson and realized that I should have used 10M for the base resistors instead of 2M2).

Mike did all the soldering, and considering it was his first time handling a soldering iron, he did a great job -- there weren't any cold joints, bad connections, or anything.

Along the way, I gave him a crash course in understanding the parts of a simple booster, and understanding biasing (and why the pot makes scratchy noises) and did my best to introduce him to the idea of impedance and how it affects things.

Once it was soldered up, we tried different transistors, starting with the MOSFET. Since he asked some questions about germanium transistors, we also tried a germanium transistor (gain 70), then progressively gainier silicon transistors (2222A, 3565, and MPSA13). He settled on the germanium because it was a little warmer, but we taped the other transistors inside the case so he could swap them out.

The we went through the boxing process, using one of Josh's optotron boards. I should have just had him solder the chip directly to the board, since it was sticking up so much, but the lid did fit in the end (just barely).

Finally, I did the letter on the case, since Mike was less confident of his ability to do that part even though it was just his initials.

The base color is Oz Green from Pedal Parts Plus, which is just an awesome finish.

In the end, Mike was really happy with what he ended up with, and I had a good time teaching him. And this is certainly far more robust a box than my first!

[jimilee]

Thus endeth the lesson! Great job both of you. What a fascinating way to both reach someone and introduce them to the hobby. That's about as coll as giving guitar lesson I imagine.

[lincolnic]

Very, very cool of you to give this lesson. One of my best friends just asked me for soldering iron advice today, so I'm hoping to be able to do the same soon!

[Rockhorst]

I didn't know you could just stick a germanium transistor in place of the BS170, I just assumed those would bias differently. But it seems to fit the rule of thumb: JFETs bias like tubes, MOSFETS bias like bipolars. Interesting.

[stevie1556]

That is a great way to give a soldering lesson!

Is the clip at the top of the enclosure for the extra transistors?

I absolutely love the colour of the enclosure! Looks beautiful.

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[gtr2]

Cool!

Josh

[midwayfair]

I didn't know you could just stick a germanium transistor in place of the BS170, I just assumed those would bias differently. But it seems to fit the rule of thumb: JFETs bias like tubes, MOSFETS bias like bipolars. Interesting.

MOSFETs require both positive and negative bias on the gate (or a reference bias voltage), which makes their biasing appropriate, for the most part, for any type of transistor (FETs still work if you put positive bias on the gate, and in fact it can be beneficial sometimes, but in this case there's only one place that the pot would make sound), and they require the input cap. So if we'd built a FET booster instead, it wouldn't have been able to accept other types of transistors.

If I wanted to make a project or test board that could accept all three types of transistors and still have a full boost, it would be an AMZ MOSFET booster with trimpots for the drain and source resistors. The gain pot on Jack Orman's booster is just so much better than the SHO's, but the SHO has fewer parts and is less complicated.

Is the clip at the top of the enclosure for the extra transistors?

It's two pieces of double sided tape -- the other three transistors we tried out are stuck between them.

[neve1272]

i wish i could have an impedance lesson 

[Jabulani Jonny]

Along the way, I gave him a crash course in understanding the parts of a simple booster, and understanding biasing (and why the pot makes scratchy noises) and did my best to introduce him to the idea of impedance and how it affects things.

I'd pay good money to have a Patton crash course on these topics. Good money. I can pay in quality beverages as well.


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[pickdropper]

That's really cool, Jon.  I hope he enjoyed it.

[raulduke]

Well that must be about the most fun 'learn to solder' lesson you could have (as a guitarist).

Really cool!