This Week on the Breadboard: The Golden F**k

[Chuck D. Bones]

I tried 2N5457 for Q1 & Q2. I had to raise the drain resistor by about 50% in both cases. The gain was more than 2x the gain with J201. Which is good if you want the extra gain and have low output pickups. Or if you have high output pickups and aren't interested in playing clean. 250mVp-p on the input was enough to drive both channels into distortion, mostly 2nd harmonic. Id was 245μA for Q1 and 86μA for Q2.

I tried a pair of 2N5457s & a pair of 2N5246s for Q3 & Q4. They both had about 1dB less gain than the J201s I had in there. Even though the 2N5457 & 2N5246 have higher transconductance than J201, they have a lower output impedance. In mu amps, output impedance matters.

I tried 2N5457 & 2N5246 in the output stage. With 2N5457, I had to reduce R14 to 330Ω to get the biasing right. The gain was 17dB higher than with the J201. This is good if we want more gain. With the 2N5246, I had to increase R14 to 2.2K to get the biasing right and ended up with 2dB less gain than the J201. Unless we want to add a bypass across R14 to bring the gain back up, the 2N5246 is not a good choice.

As Tomasz has demonstrated, we can use a variety of JFETs and get interesting results.

I'm leaving the MMFB201s in the board I already have assembled. When I build another one, I'll probably experiment with alternate FETs.

 

[fig]

The gain was more than 2x the gain with J201. Which is good if you want the extra gain and have low output pickups. Or if you have high output pickups and aren't interested in playing clean. 250mVp-p on the input was enough to drive both channels into distortion, mostly 2nd harmonic. Id was 245μA for Q1 and 86μA for Q2.

Quoted for emphasis [I really like that you explained this] - The number of variables that effect the sound between the plectrum and speaker are many, which in turn offer countless opportunities to get nearer or farther from the tone you're craving.
Plugging a guitar into a pedal is the easiest way to know if it sounds good or not, but knowing why gives you more control over it.

 

[Chuck D. Bones]

If you really wanna make the GF sound good, put a Treble Booster in front of it. I plugged in the Celestial Boost Deluxe and there's a whole new set of tones available. I put the NORMAL & TREBLE knobs on the GF around noon. With the BASS around 9:00 and TREBLE around 11:00, Black Sabbath tones are present. Adjust GAIN & VOLUME on the CBD to taste.

 

[micmac]

Thanks for the tips regarding Vp and Idss! I finished one of these bad boys yesterday (with stock values) and it's easily one of my favorite distortion pedals. Like Temol I like it more gainy, so 1987 mode it is for me, but the other two sound great as well. And I love how the pedal cleans up.

Edit: Treble Booster up front it is for me, too. A Dragons Breath, my favorite pusher.

 

[cooder]

Here's my iteration, I went with the recommendations in post #4 and installed 3k9 in R11 and C15 to 1nF C16 to 15nF. Still might change the later R16 to 10nF for some more brightness as I find myself having the 'normal' channel dialed a bit low and the bright higher.
Did the measuring of Idss on Q3 and 4 as the doctor prescribed thanks to the fab jfet tester from the ol' yard.
Great pedal, dig it.

 

[Chuck D. Bones]

Once I got the JFETs sorted on mine, I went back to R11 = 1K.

Last time I played thru mine, I set NORMAL at 10:00 and TREBLE at noon. Since my GF is bundled with a Cab Sim, I didn't bother with changing C15 & C16.

 

[jjjimi84]

Here's my iteration, I went with the recommendations in post #4 and installed 3k9 in R11 and C15 to 1nF C16 to 15nF. Still might change the later R16 to 10nF for some more brightness as I find myself having the 'normal' channel dialed a bit low and the bright higher.
Did the measuring of Idss on Q3 and 4 as the doctor prescribed thanks to the fab jfet tester from the ol' yard.
Great pedal, dig it.

It is so pretty......

 

[The Gator]

I know it's been a minute but I'm getting ready to build a batch of these.
I tried something completely different. I noticed the tone is actually scooped when turned below noon and mostly mid forward topped out. So I added a 10k in series with the pot and changed c16 to 47nf and it seems to emphasize this a little more.
I am using a j201 at Q5 with a Vp of approx. 1V.

 

[Chuck D. Bones]

Make sure Q3 has a higher Idss than Q4 or it will sound like .

Blending the NORMAL & TREBLE channels can create a mid scoop or a treble scoop depending on the ratio of the two knobs. I set the TREBLE knob around noon and then bring NORMAL up to around 9:00 or 10:00 to add a little bottom-end.

Increasing C16 moves the treble-cut freq down. Adding a 10K resistor in series with the TONE pot makes it a little brighter across the TONE knob's range.

 

[The Gator]

Thank you for the reply! This is a great discussion you started. I definitely took your advice on Q3 and Q4 when I built mine.
I like the sound I'm getting with both Les Paul and strat with this tone modification.
Before I felt the low end of the tone knob not very useful.
I too like a bit more treble gain than normal gain.