My First Fuzz...

[HighDeaf1080p]

No, no...its at the end.

I just stuck it in place of the passive volume pot that was the LAST thing before output on my original schematic.

I went from this:




to this:

[crochambeau]

Ah, then it might just boil down to emulating whatever load your previous final stage was working into.

[HighDeaf1080p]

You can see in those schematics posted above, I literally just took the "magnify" pot and turned it into the clean boost.

But, when I built it like the schematic above, it does not pass signal. I had to add back in another 100n "input" capacitor for the clean boost section after C5. Which is really weird. I'm going to test to ensure it wasn't something wrong with the breadboard or some oxidation issues tonight, but I removed and re-inserted both 100n capacitors several times, and unless both were there, I didn't get any sound. I was very tired though so it could have been anything wrong...fresh eyes will probably help me sort that out.

I'm very very close, though. I now have all the volume I wanted and more. I just need to verify with fresh ears that I'm not getting a change in tone or getting more break-up/distortion than I had before, and then I'll be ready to add it to the boxed up pedal.

I ended up with a 62k and a 75k resistor in series for R9 in order to get appropriate 5.5v voltage to the BS170. (I didn't have any resistors around 150k on hand)

Seems like 120K would be the ideal value for R9.

Its funny...I have a working pedal that sounds spectacular...and tonight it will get the final knobs put on (when my tiny .7mm allen wrench arrives in the mail). The only minor complaint I have is that to get full benefit of the pedal, I have to turn the amp up and down. This last little bit of knit-picky polishing is to relieve that one gripe, and its turning out to be just as involved as the whole rest of the pedal's circuit was. Haha.

But I have a feeling knowing how to boost a circuit without altering its sound will be a very important skill to have, so I need to take this step by step and really figure it out.

EF

[crochambeau]

Ah, I'm unfamiliar with the BS170 and that circuit implementation so I'm unable to weigh in on it beyond pointing out that the original implementation has the 2N5088 working into a 100K load whereas the later version has it stubbed into the FET/zener.

Ultimately though, trust your ears before digging into the circuit.

[HighDeaf1080p]

That's the original I'm working with...I removed C1 and C2 when I stuck it on my schematic...

[crochambeau]

Cool, I just haven't built one so I have no experience with which to punctuate my thoughts on it.

[HighDeaf1080p]

This page:

http://www.muzique.com/schem/mosfet.htm

Suggests that it has 10M input impedence:

"The Mosfet Booster has a 10M input impedance that will not load down any guitar that is plugged into it, and the moderately low output Z is capable of driving almost any circuit that follows. In addition, with the gain cranked up, any amp input can be over-driven for a smooth distortion sound."

I have a feeling the additional break-up I am hearing is caused by the MUCH higher volume I'm driving into the amp. Once I move up to my big tube amp from this small solid state amp I'm testing it on, I may LIKE the additional grit, but I don't want to lose out on any of the cleaner tones I was getting.

[crochambeau]

But that 10M is to "not load down a guitar". You already had an active stage that was loaded with 100K resulting in a sound you enjoyed, the guitar is out of the equation by several stages at this point, so don't hinge your thinking on the stand alone implementation of that booster.

I find, more often than not, that I *want* loading on stages. Not overloading (and I have 600 ohm inputs on my main mixer, so I do observe overloaded conditions on a regular basis), but the infinite impedance crowd is denying themselves a low of musical reactance. Remember, you're not feeding a guitar right now, you're feeding a 2N5088. Make it work a little for its rent.

(edit, sorry, I'm trying not to push your design at all, so instead of reading my previous statement as instruction, just keep it penned in the "food for thought" category).

[HighDeaf1080p]

Yea, I agree with what you're saying for sure. I've been considering adding back in a resistor to ground after C5 and seeing where that got me. It's a frustrating situation to be in having exactly what I want and only wanting it louder. I have to add a bunch of junk, but keep that junk from having any effect other than volume.

This is a DC fed circuit, so impedance and resistance are the same thing, right? So the original 100k Magnify pot was varying the load to give me different levels of output...but with this boost stage, I have to pick a static load? Thankfully, I can remove and stick the entire boost circuit back in as needed for testing, since I did it on its own separate breadboard (sometimes I actually think ahead).

"Since the mosfet is an enhancement mode device, the biasing required is not quite as simple as that used for jfet circuits. Resistors R1 and R2 form a voltage divider that establishes the reference voltage (Vr) that is connected to the gate of the mosfet through R3. The value of R3 essentially establishes the input impedance of the circuit, which is 10M as shown here."

[crochambeau]

How do I measure what load the boost stage is inflicting on the 5088, in comparison to the 100k pot?

You could measure current through P5 and watch the collector voltage to determine of that transistor is working as hard.

In my mind, an easier method would be to temporarily short C5 and measure DC resistance from the collector of the 2N5088 to ground. That is your load, as filtered through C5 (which introduces a variable in terms of bandwidth, but let's not complicate things...). Executing a similar test with the BS170 circuit will illustrate that the load on the 2N5088 is lifted by the very high input impedance of the FET and the zener (which is in a position I have never used personally, so once again I'm going to point out that I don't have any knowledge of what's going on there).

To further complicate things, in the original version you also have whatever input stage of the following device electrically adding to the load that the 2N5088 sees as it is in parallel with the output pot (between common and wiper), but this is a very, very minor element in comparison to the changes you've implemented.

tl;dr: slapping a 100K resistance to ground with DC blocking (a cap) between the two actives there would be my initial thoughts on exploratory surgery.

Furthermore, if the DC potential between the collector of the 2N5088 and the gate of the BS170 is similar I'd bypass C5 to see what happens (putting C5 in series with the aforementioned 100K load).

[HighDeaf1080p]

Haha...lot of things to try here. Thank you for those suggestions and I'll see what changing that impedance resistor on the gain stage does as well. I'll try to keep my head on straight and work through this systematically. Its amazing to me how this turns into tipping dominoes when something changes. When I was starting to change the potentiometers in the original circuit to better hit their sweet spot ranges, the new pot values were changing the amount of distortion and gain on the transistors, so it was like trying to hit a moving target. I went back to my original pot values for most of them and left it because I was losing a lot of my cooler sounds.

[crochambeau]

Everything affects everything, hahaha.

[HighDeaf1080p]

Ok...version 1 (without the clean boost stage) is complete. Behold:

[Chankgeez]

[crochambeau]

Does that flicker LED inject any noise?