MiniFuzz

[Gargaman]

While I'm breadboarding I would like to discuss a famous simple project here in Brasil, it's called MiniFuzz, from a guy named Bertolla.
First, I got a nice/honest sound, lots of volume,  but a substantial noise too. I have build one of these already (I can't remember if there's was such noise on breadboard), into the box, the noise is ok. Now, on the breadboard again, I noticed that when I touch the diode, the noise decreases considerably. Is that a clue?
I'm using a wallwart for power supply as I do for others projects. I also know that a circuit on breadboard could behave different than into a box.
I got a lot of questions on this one, but first I woul like to focus on this clue.
Thank you very much, sirs.

The schematic:


R1 - 1M
R2 - 10k
C1 - 474 (0.47uF)
C2 - 224 (0.22uF)
D1 - 1N4148
Q1 - BC517 Darlington
P1 - A100k

[nocentelli]

Most DIY pedal makers would recognise that circuit as the "Bazz fuss", designed by Hemmo P and modified by Tim Escobedo, homewrecker and other diy stompbox internet pioneers over the last 15+ years. I think the original Hemmo circuit used a normal npn bjt transistor, and he later updated the circuit to use a darlington with a smaller collector resistor: This is what your minifuzz most closely resembles. However, the darlington bazz fuss usually uses the MPSA13 transistor, whereas the BC517 in your schematic has a quoted hfe of many times that of the MPSA13. I can't say whether that higher hfe would translate to higher gain and therefore greater noise, but if you have it on the breadboard you could try swapping the BC517 for an MPSA13 if you have one, or cobble together two standard npn transistors into a darlington arrangement to see if the transistor itself is causing the extra noise. I have built several bazz fusses before now, and don't remember them being excessively noisy.

[smallbearelec]

I'm using a wallwart for power supply as I do for others projects.

Do you get the same noise when you power with a battery? Is the wall wart filtered and regulated or just a normal consumer device?

[Gargaman]

Yes, good catch, Leo! It's pretty much the same, a Bass Fuzz has 10uF caps and 2N5088.
I tried swapping the BC517 to a 2N5088. I really liked the sound, but when I hit a note, it decays (like gatting??) in less then a second.
So, with only one 2N5088, it doesn't sustain the note, it dies.
Should I mess around with a normal npn bjt transistor and differents (lower than 10k) values for the collector resistor?
How should be the Darlington arrangement with two standard npn bjt?
I don't have MPSA13.
Smallbear, my wallwart is a 1 Spot style. I've used with no (not too much) problems with other projects on breadboard; even with the boxed one, the wallwart works good (acceptable noise). I'll try to get fresh battery, but they are quite expensive here. Or maybe I should just go on and pray for silence when boxed, but I don't think it's smart
Thanks!
Best regards.

[Cozybuilder]

How should be the Darlington arrangement with two standard npn bjt?
I don't have MPSA13.

[Gargaman]

 
It's pretty much the Darlington symbol...

[smallbearelec]

I walked a guy through this build because I had never done it and wanted to know what it sounded like. Here's the thread:

http://www.diystompboxes.com/smfforum/index.php?topic=112626.0

Please read through that...I think you would like my Ursa Minor, or one of the other Electra variants, much better. Also note: If you add a 3-terminal regulator and filter cap to your wall wart, you will lower the noise level greatly.

[Gargaman]

Tks, SmallBear!
I'll read calmly this post latter.
What is a 3-terminal regulator?
By filter cap you mean that big capacitor (47uF/100uF) from + to - ? This never helped on my breadboard.
Maybe I'm a little neurotic about noise, I always thought that a perfect build would be completely silent (when not rocking!)
Anyway, I'm gonna mess up a little bit things here.
I also found here http://www.home-wrecker.com/bazz.html about different diodes changing the sound.
Best regards

[nocentelli]

Should I mess around with a normal npn bjt transistor and differents (lower than 10k) values for the collector resistor?

If you swap the darlington for a single npn, you need to increase the collector resistor to 100k or so to get the gain up to delay the gating.

[Gargaman]

Yes, Leo, I realized I got your first post wrong!
So, if I will use a single npn, maybe I should try a bigger (100k) resistor.

If you swap the darlington for a single npn, you need to increase the collector resistor to 100k or so to get the gain up to delay the gating.

Will be too much asking how this work technically?
I arranged two 2N5088 (hfe 300 and 400 aprox.) as a Darlington and it dit worked! I feel the sound a little bit thinner and the noise persists.
I think I should move on with the initial schematic and see what happens inside the box.
What about voltages I should get if I intend to use one npn and a bigger resistor?
Smallbear, I prefer Electra sounds instead, but I'm building for a guy who liked the minifuzz sound.
Thanks for helping!
Best regards

[Gargaman]

I decided to build one with the initial schematic (Darlington and 10k)
and other one with a 2N5088 and a bigger resistor.
For this last one, I tried a 47k.
Got the same fuzz sound and a bigger sustain! Still gates after some seconds, with some harshing sounds, but it's ok.
I tried a 560k and the sound became less fuzzier and more like distortion.
Is there a sweet spot on here? I'm fooling around 120k. Math and theory will help me a lot here, wouldn't?
Anyway, with a single npn the noise is absolute minimal!
Is there any way to get rid of the harsh sound when the notes are decaying?

[smallbearelec]

What is a 3-terminal regulator?
By filter cap you mean that big capacitor (47uF/100uF) from + to - ?

Check out this article:
http://diy.smallbearelec.com/Projects/SmWart/SmWart.htm

The components through capacitor C1 are what is in a typical wall wart. To make it quieter and suitable for effects, you want to make a small box containing the 7809 and capacitor C2, LED if you want. The result is a really quiet sub for a battery. Preferably, your wall wart should be 12 volts to give the regulator enough headroom.

Is there any way to get rid of the harsh sound when the notes are decaying?

Gating is almost always an indication that the transistor is mis-biased. I did not encounter gating when I built the version in the thread, Do hear harshness in the distortion, and I think that's native to this design. If you want smoother clipping, IMO, get away from this circuit.

[Bobandy]

When I first built this I could not get good results until I added a simple (3 part count) jfet boost in front of it. I ended up running two bazz fuss back to back with an mpsa18 with germanium diode for the first and mpsa13 with silicon for the second. I just used trimpots for the resistors and I think I used 10uf or 22uf for all the caps but it sounded really good after that.  Also, I was picking up radio stations until I added a 10n cap to ground on the input which cleaned up the noise a bunch. This was the first successful circuit I built and was perfect for a beginner build.

[PRR]

> substantial noise

What is "noise"?

Hiss? Hum? Buzz? Ticks? Peruvian radio?

Different causes and cures for different "noises".

[Gargaman]

Hi, Paul, sorry for the the lack of accuracy.
It's the kind of normal noise with gain pedals, I think, it's between hum and buzz. I suck at describing noise.
Just like the Boss DS1 with high settings with no signal.
With the Darlington, it's there.
Maybe I will record some celphone video, should be easy to figure out.
When I crank the pot to max, some radio comes into to.
Not peruvian..

[Gargaman]

Here's the noise
https://www.youtube.com/watch?v=XD5GEFnaSHQ&feature=youtu.be
Sorry about the video quality.
The Darlington is on the breadboard with a 100k resistor.
I tried changind diodes. Try 1N60 and 1N270, they are much quieter, but it only works when guitar volume pot is at max.
When I roll down the guitar volume pot, it's a very ugly sound.
I'm using a cheap strat, with a humbucker at bridge.

PS.: this seems to be a really limited circuit. Someone could explain why there is so strange sound when rolling the guitar volume knob down? Is there a way to defeat it?

[PRR]

> between hum and buzz.

So it is Wall Power (50/60Hz) leaking into the pedal.

If you took your whole rig on batteries out in the fields, there would be no hum/buzz.

And no low-cost power and no paying audience.

When you come in from the field, near power wires, you have to enclose in a metal box, and you have to filter the power you get from the wall-outlet.

With a low-gain device it may not be bad; high-gain devices will boost-up the least wall-power sneakage.

Bear has given you general thoughts on DC filtering. However for this pedal, which uses very little power (a battery would last weeks and may be your best quick fix), an R-C filter with maybe 470 Ohms and 100uFd ought to make the DC clean enough for playing.

[Gargaman]

Thank you so much, Paul.
I'm gonna box this up and compare how it goes inside and outside. Also gonna check Bear stuff before by next building (maybe a peruvian radio receiver)
Since you mentionated, can you briefly explain how to calculate the amount of power this pedal use?
Best regards

[Hatredman]

What is a 3-terminal regulator?

It's this little guy:





http://pdf1.alldatasheet.com/datasheet-pdf/view/257559/WINGS/78L09.html

[PRR]

> how to calculate the amount of power this pedal use?


R2 - 10k

The only path from battery red to battery black is through R2.

R2 is 10K.

So even if everything else were a dead-short, it CAN'T suck more than 9V/10K or 0.9mA.

And the "everything else" can't be a dead short, because then it could not do anything useful.

In a traditional amplifier stage we "know" the Collector is probably about half of supply voltage (so it can swing either way). That would be 4.5V/10K or a half a mA.

This is a distorter, Collector sits quite low, so the signal gets "dented". We can compute it from diode drops: Collector is 1.5V to 1.8V above ground, leaving a little more than 7V across 10K.

However any of these values is so low that we can just fling a net over all of them and call it "a half to a whole mA" without any real thinking.

A 9V battery is about 400 mA-Hours. If the pedal is a half mA, it may run 400mAH/0.5mA or 800 Hours. 33 Days straight! 3 months at 4 hours every night. For 2 hours @ 2 nights a week, the battery will die of old age before it runs flat. Battery is no-hum/buzz and a very practical thing for extended testing, even for gigging.

If you take Leo's idea to make R2 100K, then current is 1/10 and battery life is a year NON-stop. I had a box like that, left it on for months at a time, never quit. Battery rot (acid leak) from old age is more likely than run-down.

Note that an LED itself will add 1mA to 20mA! 10 or 100 times more power than the audio circuit!

Sorry for the joke about Peruvian radio. I grew up next to one of the most powerful AM radio transmitters in the US. Taught me a lot about boxes and shields. I once did a quiet Christmas Concert in a church which had nearly no electricity (little hum/buzz), my system had low hiss, but a low-power radio station nearby was leaking Hungarian Dance Hour into my recording. Because of political friction and profit opportunity, there have been powerful AM transmitters just inside Mexico beaming into the US, which were easy to receive even when you did not want to. I have had trouble with police and taxi radios passing by.

You are in Brazil so you won't have Mexican Radio, or baseball, but there's radio transmitters everywhere. "Peru" was a random choice nearer to you.

It is good to know *which* type of "noise" you are fighting, to know what might help.