a "new" overdriver/fuzzular unit thingamobob

[pinkjimiphoton]

ok, i built another fuzz, tried bc109's but they are just way too hot. bc108's tho, offer a pleasing tone, as do ac176 ge's. tested it with low gain transistors, you can get useable tone with anywhere from 30-120 hfe. i like the classic fuzzface-ish ratio, 87hfe q1 and 105hfe q2. this is verified, built it tonite, it has the potential to be TOO distorted. it's pretty sick, you can overload q2 if you want and make it fade in and out. not that you'd wanna do that. overdrive your amp, add fuzz, or both. have fun!

it's another 10,000 monkeys kinda thing, i'm sure it's been done before. if so, please let me know!!

got a prominent 2nd harmonic, cleans up nice from the guitar, seems to respect your guitar's tone when changing pickups.
nice sustain, too, not too gated. crank the overdrive control over about half, and it starts to get fuzzy. pegged, it can be REAL fuzzy.

criticisms also welcomed. just having fun. peace!

[Keppy]

There's a jumper under VR2, correct?

[Gus]

Where is the schematic?

IMO you need a schematic to discuss how things work.  I could trace the vero and make a schematic.

If you do a web search for BC108 you get a to18 device so what is the pinout of the transistors in the vero  (I can figure it out) you show T092 based devices

What collector voltages and collector currents are you looking for?

I used Lt spice to sim it. Two gain stages in series diode clipping at the end.  With C to B bias resistors and running the stage at higher Ic than most effects the sim shows about 2.5ma current draw this will change with the setting of the trims.

With a circuit like this.  The "design" is more about the collector voltage.  C at 1/2 1/3 2/3 etc of the power supply voltage this sets how the stage starts to distort and if it is set more toward saturation or cutoff.

Have you done a temperature test yet?

[pinkjimiphoton]

There's a jumper under VR2, correct?

yes, keppy, there is. i probably should have written that on the bottom.

[Gus]

 The one in this thread is a little different because of the lower value collector resistor in the first stage and loading caused by the volume controls(ratio of output resistance to loading resistance)

Some similar circuits in a way.
http://www.diystompboxes.com/smfforum/index.php?topic=92997.0
http://www.diystompboxes.com/analogalchemy/sch/vulcan.html

The power supply and collector voltages and final total collector resistor values would help for a good sim of what is going on.

[pinkjimiphoton]

Where is the schematic?

don't have one, just kinda cobbling stuff together from other things i'd messed with in the past. i never worked with bc108/9's before, and originally figured i'd try and work up something with the 109's, but they were way too hot. so i tried the bc108's, and they all work, tho the magic seems to be with these gain ranges posted and the trimmers about half.

IMO you need a schematic to discuss how things work.  I could trace the vero and make a schematic.

i'd be honored if you did, i can hand-draw it, but i can't figure out how to do it with any legibility with any of the cad programs i've played with. it's a relatively simple circuit, i think... got a piece of this, a piece of that.. a little fuzzface, a little heathkit fuzz booster (the attack or overdrive control)... nothing in stone, just playing with stuff at hand. the caps were just chosen as "close enough" from years of messing with things. i've found certain ratios for ins and outs of stages seem to work well, often 1:10 or more likely 1:100 i guess.

If you do a web search for BC108 you get a to18 device so what is the pinout of the transistors in the vero  (I can figure it out) you show T092 based devices

it's just whatever comes stock on diy layout creator gus, if there's a way to change 'em, i don't really know it. it's real buggy on my computer, make more than one mistake gotta start from scratch.
fwiw, in this layout, from bottom to top on both transistors, ebc.

What collector voltages and collector currents are you looking for?

i was figuring the usual half b+ supply, somewhere around 4-5 volts. remember, i'm a hack bro.. i just mix and match stuff until i like the way it sounds. sockets are my friend!!!!

I used Lt spice to sim it. Two gain stages in series diode clipping at the end.  With C to B bias resistors and running the stage at higher Ic than most effects the sim shows about 2.5ma current draw this will change with the setting of the trims.

yah, tonally it seems to change a bit too when adjusting the trims. trim one has the most effect on tone, trim two on overall volume. if trim one is pegged, it becomes almost an octave up, where you can clobber q2 into cutoff and get a very mean gated fuzz. originally i started off with a 6.8k fixed resistor on c of q1, and a 4.7k on c of q2, but it didn't work out so well. it fuzzed immediately on power up, which i liked, but it was TOO fuzzy, if that's possible.

With a circuit like this.  The "design" is more about the collector voltage.  C at 1/2 1/3 2/3 etc of the power supply voltage this sets how the stage starts to distort and if it is set more toward saturation or cutoff.

Have you done a temperature test yet?

you nailed it. about half power supply seems to be the most versatile...for a change, you don't have to crank the overdrive pot to get useable distortion. i originally tried 10k for gain and 100k for output, but it was just too much.
i settled on 2k pot for the distortion, tho 1k is probably fine. thinking the e resistors should get replaced with maybe 100-500r trimmers, too to dial it in a little more. this is the first actual revision. the original layout probably wouldn't have worked, if i post it you'll see why... but i don't want anyone to try and build it and be dissapointed. the caps were huge...10u i think for all of 'em, but then i realized it would be way too unstable so went with smaller values i had used before.

this thing SINGS with ge ac176's in it. very tubey sounding. but i didn't wanna have to deal with the hassles of the germanium, and the bc's aren't too "shrieky" in the highs while still cleaning up nice.

no temp test, what do you mean? should i hold a lighter to it?

[pinkjimiphoton]

The one in this thread is a little different because of the lower value collector resistor in the first stage and loading caused by the volume controls(ratio of output resistance to loading resistance)

Some similar circuits in a way.
http://www.diystompboxes.com/smfforum/index.php?topic=92997.0
http://www.diystompboxes.com/analogalchemy/sch/vulcan.html

The power supply and collector voltages and final total collector resistor values would help for a good sim of what is going on.

thanks bro.
i will post the voltages when i get a chance a little later, got my kid here today and we've got some stuff we have to do first. today, i hope to walk him thru making his first fuzz on vero.

[Johan]

Where is the schematic?

IMO you need a schematic to discuss how things work.  

+1.
J

[Gus]

A sim screenshot.  I used parts from the stock LT spice download.  You can adjust the bias with the C to B resistors as well

The part numbers are not the same as on the vero.  To the left of R11 is a guitar cable sim.  R7 and R8 are the trims(I don't like trims)  the voltage drop across R13 can give you the current draw, current = voltage difference(9VDC-8.6VDC) / 100ohms, 4ma how long will a battery last?

[pinkjimiphoton]

thanks for doing the schematic and sim, gus.

other than the transistor values and the diode clipper, looks to me like what i built up.

i know you don't like the trimmers. at about half way up on both, that would be about (next closest value) r1 and r7 should be probably about 560r, and r3 and r8 about 2.7k i would imagine. at those values, it will work
if the gain of the transistors isn't too high. i don't like 5089's or 2222's cuz they ALWAYS are way too "hot" for every fuzz circuit i've tried them in, and i tried both of those in this. this definitely preferred lower gain..high gain was too fuzzy, and would make q2 cut off...if you turned the overdrive knob up. with the lower gain ones, half way up is a fair overdrive, full blast is over the top for my uses. it WANTS to be an octave fuzz i think, betting if i matched the two halves of the clipper it would do it, tho maybe having the asym clipping there is what's giving that effect via the half wave rectification? i am beginning to understand some things i guess.
i think i'm gonna re-do this so that vr1 has the third leg tied to ground  (or a small value resistor) rather than being tied to the wiper as it is now. i just checked the voltages, and that ends up way too high, i didn't check til now, and definitely want to get the voltage to c of q1 lower i think...right now it's more clean preamp and less fuzz there, which is probably why it sustains well and wallops q2 so hard?

anyways, i took voltage readings... the battery alone is a little dead, cheap carbon comp kinda dollar tree variant, reading 8.06v with no load.
b+ when connected, read after the 100r current limiting resistor is 7.82v.

here's the trannys as set by ear (like i said, i wanna play with q1 some still, this was mostly just a proof of concept experiment at random fuzz design)

q1
c  7.47
b  .72
e  .04

q2
c  5.18 (at this setting, unity gain is half way up, at 4.5v, unity gain is about volume full)
b  .66
e  0.0 (as expected, being directly grounded)

any chance you could please re-sim with the voltages i posted and see what it does?

am i right in thinking most of the fuzz is coming from the clipper, and not from stage 1?

if i were to lower the voltage on q1 to about half supply, do you think the tone will improve?
would it become more of a fuzz, and less of an overdrive?

appreciate you guys taking the time to help me thru this.

i looked at the two circuits gus posted, i do see a bit of resemblance, in different ways, but it seems to be a little different from my circuit in both cases.
of course, i'm just taking a cookbook approach, i have a decent understanding of caps on tone, but am really just starting to learn about changing the gain of the circuit.
wondering if perhaps an emitter bypass cap on q1 would improve the tone a little bit by giving it a little more gain. it's function there is kinda like a cathode bypass in a tube circuit, isn't it?

thanks again, look forward to your replies!

[pinkjimiphoton]

oh, and sorry,,,

i don't know how to determine what battery life would be, but i'd assume if it's drawing 4ma, you could probably leave it plugged in for a week or so and it would still work.

remember...i'm the 10,000th monkey on the 10,000th typewriter on the last day of the 10,000th year.   

[LucifersTrip]

remember this one?


http://www.diystompboxes.com/smfforum/index.php?topic=99677.0

[pinkjimiphoton]

ave lucifer!


yah, i do...and yes, it does have some stuff in common with *my* circuit!!

i will re-read that thread, and see what info may stick to the abcess between my ears. thanks bro!! i have a feeling the coupla answers i seek are about to be answered.

no diy *god* needed... love it!!

[Gus]

Some thoughts about this type of circuit.

There are interactions in this type biasing the C to B resistor not only bias the transistor it also is a feedback element.

So what "feeds" the base becomes part of the gain/EQ.  the guitar or bass etc before the circuit and the first gain stage before the second gain stage

So the gain stage can be looked at like a inverting opamp with limited gain.  The collector signal is inverted with gain compared to the base.
 
A DC sim of this biasing

Note the relation of the hfe to the collector voltage with the change of the C to B  biasing resistor

This is one reason you need to select the transistor if you want to use a fixed value collector resistor.  You might want a fixed value collector resistor because it it can be part of the setting of the next stage gain setting depend on the design of the stage.  

You can also add a series resistor before the stage to reduce the gain like you see in some FF like circuits however this changes the interaction of the guitar cable with this type gain stage.

How you set the collector voltage also sets what "side" of the waveform get clipped first then you have the order this happens in to think about

Then you need to adjust the high pass filters with the selection of the coupling cap values.

If you place a volume control between stages you add series resistance as well as a voltage divider and a changing load on the stage before the volume control

IMO what looks like a simple circuit has a number of things to think about when designing a fuzz.

[pinkjimiphoton]

wow, thanks gus.

so what i really need to do i take it is look at the b-c resistor, and find a value that works best there to get the gain in the ballpark of what i'm looking for.

i had toyed with trying a bazzfuss kinda deal there with a diode, too, but i don't think it would work very well.

i like the range of distortion and tone it's got at this point, but i don't like saturating q2... what about maybe adding either a resistor from b to ground to make a voltage divider, or am i misunderstanding?

also, looking at joe's fuzz you posted yesterday, could i use the same trick i put in my toneblaster (and in joe's fuzz) and add a diode in series between stage one and two to limit the saturation of q2?

sorry for all the questions... trying to learn, NEVER gonna happen!!

[pinkjimiphoton]

ok, i played with this a little more after taking a little time off.
i did some experimenting, and changed it just slightly.

changed out vr1 (1k) and r2 (100r)  for a 50k trimmer and a 2.2k resistor. now it doesn't overload q2 the way it did, you can crank the overdrive knob on full blast and it's a very (imho) useable
fuzztone, that cleans up nice and linearly with the guitar volume. about half way up, you get a nice overdrive, kinda like an sd1 or ts_ without the nasal mid hump. the overdrive control all the way down is just a shade below unity (it doesn't turn off because of the small resistor to ground).

it is LOUD AS @#$%. you can have the overdrive pot all the way down and just slam it with the balls control. i like it with the overdrive knob up about 2/3rds of the way, and volume to taste.

if you don't like trimmers (hi gus) , vr1 and r2 can be replaced with a fixed resistor... around 22k i tested it (as that was about what the 50k trimmer i tried was set to) and it was ok, but still a little bit touchy.
27-33k should be about perfect there i'd imagine.

next up, i played with the jumper from q2 e to ground. i tried a 1k trimmer, didn't like it. i put a switch in temporarily, and tried it with a jumper, a couple different fixed resistors and some diodes like in my toneblaster.  it was a little more aggressive with the direct connection as expected,  and the diode clipper there (made with 1n60 germaniums ) was noticeably softer. it had a nice compression to it. i also tried an led there, which worked and sounded pretty good!!  when all was said and done, my favorite was a single 1n60 with cathode to ground from q2 e. so i left it there. softened it up just a little bit, no more overloading the transistor the way it had before, nice sustain with a touch of the compression the toneblaster has, and the octave up sound came back a little bit more.. it's not an octave up, it's fairly subtle. but you can hear the second harmonic. i like it.

also tried the joe davidson trick from his vulcan fuzz with a diode before b of q2, but i didn't like it. turned it into a very smooth buzztone with almost zero sustain. some guys may like that, but it's not for me.

tried a couple small bypass caps for the bc resistors as suggested by lucifer, but it kinda killed the high end just a little too much. i may play with it a bit more, i have a feeling a much smaller cap than i tried...maybe 47p to 100p (i tried 1000p, 470 p and 220p cuz they were handy) will help, and will try that too.

appreciate the advice and help brothers!! thank you!!

so anyways, to make it a little easier if someone is crazy enough to wanna try this, here's some voltages. you'll notice they are RADICALLY different from the earlier version on q1.

first up, same batt, still slightly weak:
at battery:
7.87v

after current limiting resistor (rcl on the vero)

7.67

q1
c  2.75 (was 7.47!!!)
b  .87 (was .72)
e 0.0  (was .04)

q2
c   5.22 (was 5.18)
b   .87   (was.66)
e   0.20 (was 0.0)


so anyways, now it works, i like it quite a bit so far. i'll try to get an SPT going for it asap so you can hear it, and will update the vero in a couple minutes.

pink out.

peace.

[pinkjimiphoton]

here ya go, verified layout. this is just slightly different from the layout i built, the original board i had designed is what i built mine on, but this is indeed right.

if you build this, please let me know!!
peace out

[pinkjimiphoton]

this has been updated and modified a little...
will try to up a vero and schem for the updates as soon as i can, basically the updates are footswitchable overdrive/fuzz modes with a tricolor led.
the led changes from blue for overdrive to red for distortion, and i set it up so they're on when the effect is bypassed so you know what's what. this particular tricolor thing, i cut off the lead for the green, and have it fed with a 10k resistor after the current limiting resistor to the common anode (maybe i'm confusing anode and cathodes, sorry..the common lead) and another between the red led lead and it's connection to the switch. this grounds right to the ground rail, so one of these two led's is always on.

changed the second bc108 to one of them FET 2n2222 variants...changed it from fuzz to a real nice rich distortion with a lot of mids...or overdrive, or fuzz at the extreme settings still.

the second footswitch also activates a second 1n60 diode clipper between the output of the original diode clipper and the output cap.
when that's engaged, it also activates a small trimmer mounted on the footswitch itself so i can adjust between the two modes and get them roughly the same volume.

i tried a few different things, and this seemed to work best. on the second footswitch, all the middles are tied together, and go to ground. one side for the diode clipper, and the other side it's got the trimmer. i ran a second wire from the wiper of the volume control to the wiper of a 100k trimmer, and tied one leg right to the footswitch. now, when it's in "red/distortion" mode, it's the same volume as when in "blue/overdrive" mode... just mess with the trimmer until you get it unity gain, or a bit of a boost.
unity gain is about half way up, it's a booster above that. can get pretty loud.

here's a couple pics:







of course, stupid pedal trick to follow soon.

what i did

[pinkjimiphoton]

as promised

http://www.diystompboxes.com/smfforum/index.php?topic=101058.new#new

[pinkjimiphoton]

schematic :