Pungent Bzzz - Speaker distortion sim (schem inside)

PenPen · January 15, 2006, 08:26:56 PM

I'd like to start this with a story. Back when I was 16 in a little punk band, our bass player had just got a new Hartke amp. It had a problem, though, it would cut out at random times, and out of frustration he kicked it. He put his foot through the grill cloth and put a nice dent and hole in the speaker. I plugged my guitar into it to see how it sounded, and it spit out this farty sputtering, but then broke down into a quieter clean as the note decayed. I thought it sounded cool, but it was his amp, so he replaced the speaker and things went on.

When I first built Doug Deeper's GarageFuzzz, I was amused at the sputtery sound it made, and it occillated a lot, so I marked it off as a fun noise box, and moved on. Then I got to thinking about it. The sputter sound it made reminded me of that broken speaker from years ago. But a real speaker doesn't just cut out fully, at lower signal levels it will still put out some sound. So, I began changing the design until I was satisfied with the result. I removed portions, changed the bias of the gain stage, and added a few things. I am very happy with the results, it sounds like a really bad amp being pushed into a broken speaker.

First, I wanted to kill the occillation and ground noise it created. Since the occillation seemed to be sensitive to ground noise, I tried isolating the collector. By adding a 10 ohm resistor to the collector of N1, that seems to be eliminated now. I could not get occillation at any level. If anyone tries building this and gets occillation at its current value, try upping R5 to 100 ohm, and please report if that helped.

Next, I added C3, which allows higher frequencies of any level bypass the negisistor. This provides the notes to decay into quieter clean. Any high level signals that can push N1 into turning on are amplified by it, I still don't fully understand how these things work, but a signal generator poked around was amplified at the base of it. So, big signals are futher amplified into that sputtery sound, and lower ones are filtered and passed as they are. VR1 provides a sensitivity control. I like to call it the "Damage" control, since when its turned up the signal goes straight to N1, thus turning it on easier. Roll it back some and it only breaks if you hit the strings hard, other wise it passes a high frequency signal. Since the occillations are gone now, a traditional volume control was added. In the original GarageFuzzz, Doug noted the sensitivity to ground noise, and hence a normal volume couldn't be used. It works fine now. Diodes do not make sense at any part that I tested, they really didn't change the sound at all, and I wanted a clean breakup anyway.

Q1 can be pretty much any NPN small signal transistor. I tested low hFE transistors, 2N3904, BC107, and an MPS2222A from Radio Shack. These all worked fine for me.

N1 MUST be a real 2N2222A. The ones from Radio Shark do NOT work. I ordered a bunch from Futurlec. I'm not sure if the 2N2222A's SmallBear carries will do the job. These seem to be the only transistors that operate as a negisistor, and are suitable.

Comments, anyone?

hank reynolds 3rd · January 16, 2006, 07:23:19 AM

Hi PenPen
The big cheese/great cheddar has a setting that splutters and breaks up as the note decays, and i was wondering if this is similar to the sound your pungent buzz makes..
looks like a simple, cool sounding build

Cheers
Sam

PenPen · January 16, 2006, 10:27:55 AM

Thanks for the response. I haven't ever built the Great Cheddar so I'm not sure if it sounds similar to that setting. The only way I can describe it is speaker distortion. I've played through some really bad cheap amps and this nails that sound. I'm going to be working this week on getting some samples recorded, I'll update once I am able to post them. I don't currently have a setup to easily record samples and get them on the internet. Plus I don't have anywhere to host them yet. As soon as I am able I'll put some up.

Yes, the circuit is very small and simple. The only issue I've seen others have trouble with on the GarageFuzzz is the difficulty finding the right part for N1. I know its bad design to rely on a particular part for a design, however the fact is most transistors simply won't operate when hooked up as N1 is, and I've not found anything that can replicate the sound properties that it has. I can assure you, though, if you order the 2N2222A from Futurlec it will work just fine.

MartyMart · January 16, 2006, 10:28:10 AM

Hmm, can't quite get this to work ...
Using a real metal can 2N2222, I can get huge gnarly output, only when
shorting the 2N2222's base/emitter connections, right at the 10uf cap
output ....
Perhaps it is the "wrong" 2n2222 ( has no "a" tag )
I'll persue it some more ..

MM.

PenPen · January 16, 2006, 10:47:20 AM

Quote from: MartyMart on January 16, 2006, 10:28:10 AM
Hmm, can't quite get this to work ...
Using a real metal can 2N2222, I can get huge gnarly output, only when
shorting the 2N2222's base/emitter connections, right at the 10uf cap
output ....
Perhaps it is the "wrong" 2n2222 ( has no "a" tag )
I'll persue it some more ..

MM.

Hmmm. What is the voltage on the emitter? It should be around 6.2V. If this is on a breadboard, I also had some troubles from the inconsistant connections and capacitance of the board. To test, I'd set VR1 with a fixed resistor, or just a straight wire, and omit everything after the 10uF.

Since you said you got output after shorting the E/B, I wonder if perhaps your 2222 has a higher 'turn on' point than mine, and by biasing it slightly it comes on easier. I had thought they all had the same point in which they kicked into tunnel mode, but this could be a wrong assumption. Maybe try a higher gain Q1, or rebiasing it for more output at that stage?

When I get off work I'll mess with rebiasing the first stage, perhaps that is the problem everyone has had with this and the GarageFuzzz. I'll also try a few more of my 2N2222A's to see if others have problems. Thanks for building!

MartyMart · January 16, 2006, 11:13:06 AM

FIXED !!
...... or should I say "Broken ...... speaker" !

I had a couple of other 2N2222's around ( different make ) and this works great now.
I have them in both Q1 and Q2, when Q1 was a 3904, it was sounding a bit "polite" !
Now it does indeed sound like a "screwed up amp/speaker "

Q1 C 8.31v
Q2 E 7.24v

Thanks,

Marty.

PenPen · January 16, 2006, 11:37:50 AM

Quote from: MartyMart on January 16, 2006, 11:13:06 AM
FIXED !!
...... or should I say "Broken ...... speaker" !

I had a couple of other 2N2222's around ( different make ) and this works great now.
I have them in both Q1 and Q2, when Q1 was a 3904, it was sounding a bit "polite" !
Now it does indeed sound like a "screwed up amp/speaker "

Fantastic! Thanks for the report, Marty. I was a bit worried no one would attempt this given the troubles people had before with the GarageFuzz circuit, the crucial problem being N1. Guess the solution is to try several different parts until you find one that works well. The whole tunnel mode operation of that part makes this build very hit and miss with most people, and most give up before putting too much into it. Thanks again!

A 2N2222 for Q1 certainly does work well. When I first began breadboarding and tweaking the design, I also used one for Q1. Only after finishing the design did I test the other transistors in that spot, to make sure it was tolerant of different parts. Currently I have a BC107 there, simply because I got several from a transistor value pack and I wanted to use them up. I have the aforementioned bass player coming by this evening, he wants to hear this thing himself. Glad you could confirm that it does indeed sound like damaged speaker distortion like I thought it did. It sounded that way to me, but others can have a different idea of what that means.

Dragonfly · January 18, 2006, 06:34:11 PM

heres a quickie vero layout for it....i havent tested the layout yet, but looks to be correct. let me know if there are any mistakes...

i added pop filtering, reverse polarity protection, and power supply filtering to the original circuit as well....

andy

PenPen · January 18, 2006, 07:45:57 PM

Thanks for making a layout, Andy. I was meaning to make a perf layout graphic, but I haven't yet made a 'perf palette' in GIMP yet to make it, and I've been pretty busy with work and other projects this week. I'm searching my software for some app to record some sound clips of this thing, that and fixing my build of this (first time I've done board-mounted pots, and it didn't go as well as hoped) have been my priority this week. This makes one less thing I have to do, and as usual its a fantastic layout.

I had forgotten about the pop-resistor and power supply stuff, I normally don't associate that stuff with the circuit since its the same for every build. I put those in when I made my final perfed version and forgot to put those in the schem. Thanks for including them.

Dragonfly · January 18, 2006, 10:59:26 PM

Quote from: PenPen on January 18, 2006, 07:45:57 PM
Thanks for making a layout, Andy. I was meaning to make a perf layout graphic, but I haven't yet made a 'perf palette' in GIMP yet to make it, and I've been pretty busy with work and other projects this week. I'm searching my software for some app to record some sound clips of this thing, that and fixing my build of this (first time I've done board-mounted pots, and it didn't go as well as hoped) have been my priority this week. This makes one less thing I have to do, and as usual its a fantastic layout.

I had forgotten about the pop-resistor and power supply stuff, I normally don't associate that stuff with the circuit since its the same for every build. I put those in when I made my final perfed version and forgot to put those in the schem. Thanks for including them.

i figured i'd do a layout because it sounds like it might be a cool circuit...thus, i wanna build one soon

...thus, the layout

ive been trying to remember to include all the "extra's" in my layouts recently, simply because its easier to build it right in the first place than to try and fix a problem....my early layouts didnt have some of the extra's...

i'll post a build report when i (eventually, time permitting) get a chance to build it.

nice work,
andy

Ben N · January 19, 2006, 02:51:58 AM

Cool! A kind of Link Wray tribute fuzz, if you will! I'd love to hear some samples.

Ben

doug deeper · January 19, 2006, 02:09:53 PM

cool man!
the idea with the garage fuzzz was to kill the oscillation, but just barely. so it has that squishy buzz thing going on top.
i guess r4 (in your schematic) should be a 5k trimmer (in the actual garage fuzzz) and trying different 2n2222as is a good idea as well since they vary quite a but.

PenPen · January 19, 2006, 02:56:26 PM

Thanks for the kind words, Doug. I could not get the original GarageFuzz to quit oscillating no matter what R4 was set to. I tried values from 1k to 4k7, they all oscillated, and actually 1k sounded really bad, and not 'bad' in a good way. Oscillations didn't stop until I put that isolating resistor on the collector, that cleared it up right away. Thanks for the ground breaking work on negisistors as a distortion mechanism, they really are incredibly unique sounding and I had never heard of it before seeing your design.

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Pungent Bzzz - Speaker distortion sim (schem inside)