Olson - Fuzz Master  [schematic]

Discussion regarding early stompbox technology: 1960-1975 Please keep discussion focused and contribute what info you have...
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Post by pinkjimiphoton »

man, i wish lucifer's trip was still around... dave! we miss ya! :icon_twisted:

anyways, for no particular reason this caught my eye the other day scrolling thru the diystompbox forum on farcebook:


https://i.postimg.cc/G4S3V9qq/olson-fuzz-master.png
olson-fuzz-master.png

so i figured, since i finally have a wee bit of downtime between jobs, i'd slap one together.
so i vero'd it up.... this IS verified, with a caveat or two we'll get to later...


https://i.postimg.cc/CdYZjBtq/Black-Knight-Fuzz-1.png
Black-Knight-Fuzz-1.png

i changed the input and output caps from 3.3n to 39n for no good reason on the vero layout... i left the output cap that size, but made the input cap 3.9n ultimately cuz above that it was just too damned wooly sounding. also made the c resistors for the actual fuzz part a little bigger, i split the 10k resistors off to a 4.7k and a b10k trimmer "just in case" so i had a bit of wiggle room to mess with. this proved fortuitous with some ge's.

i experimented with a bunch of npn's... si doesn't work well in this circuit. ended up with 3 ac128's, all over the place in hfe... one's about 40, one's about 60, and one's about 100. i say about cuz they're ge. if ya BREATHE too close to them, the gain changes of course.... i socketed them, and found little difference swapping them around tonally, but ended up with the usual low gain in q1 and worked up from there. i did look up the 2sc175's, and their gain is in the ballpark with what i used.. of course i made the circuit npn so it would play nice with other stomps.

also went with an 18k rather than the 15k resistor from q2 b to ground, as it was handy and i was too lazy (some things never change) to dig thru my resistor drawer for the proper size. close enough for rocknroll, right?

sound wasn't super impressive. not BAD, but not great. i found several bias points on each q that seemed to work out pretty well, still a work in process where that's concerned.

but the "fuzz" control just plain sucks. it doesn't really do much of anything, you have about 1/4 of its sweep that's actually useful, and below that, it just plain doesn't pass signal. looking at how its drawn, it looks weird to me...

so first question, can someone explain how the hell its supposed to work as drawn?

to ME, it looks like it should be varying the bias to q2, which it kinda does, if really @#$%in' poorly.
it seems to me a fixed resistor would work better.
further, the dc to the pot as its drawn damaged one pot, literally smoked the mother@#$%er.
so my spidey sense said, i bet this was drawn wrong <seen a bunch of those over the years, like the shatterbox... i know one of the guys here drew it, so i respect that and have no doubt they did it "right" to the original unit they traced, but still maintain it was a screw up by the designer in the first place that was reproduced for years by the fabricators... there's a thread here somewhere, i called mine the scatterbox cuz it sounded like shit.. but i'd found by moving ONE component, it went from useless 60's fizz to an actual decent sounding and useable fuzz>

so i looked around at the schematic, and to my understanding, that 1 meg fuzz pot should have a blocking cap at each end, really. yeah, without one, its a feedback loop for q2, but not a useful one. seems weird. i can't see any reason to add a pot that literally makes zero difference tonally...other than destroying it.

now, i am a fuzzaholic, but i'm no @#$%in purist. i don't gaf if something is "right", "original" or "correct to the period cuz i drew the mofo myself" or any of that crap.

half the damn drawings of schematics on the net are full of mistakes.... lets not go there now...lol

but anywho, looking at it, i pondered what would happen if i moved the fuzz pot second connection, on the schematic at the junction of the c resistor and c on q2 to the OTHER side of the 1u cap from q2 c to q3 b....

and bingo. suddenly, instead of a useless pot that barely does anything, it acts like a "contour" pot to the fuzztone itself. not a huge difference, but eminently useable by comparison to the schematic.

now, i'm too stupid to understand all involved in this minor circuit change... but it seems like it lets you blend some of the clean signal from the buffer stage (q1) around q2 to affect the overall tone... like a pan control like ya see in some of the super primitive fuzzes sometimes. does that seem right? it DOES make a huge diff in the overall sound of the pedal.

it went from super wooly and shitty sounding to a really nice overdrivey kind of fuzz, where adjusting the fuzz pot actually changes the tone somewhat (it didn't do anything but phart as drawn)... and the volume controls the overall level of fuzz as predicted. it also reacts properly to the guitar's knobs, which it did NOT do as drawn...

so i'm going out on a limb here, and postulating the schematic floating around the web is wrong, either because it was released wrong by olson to throw peeps off the tracks see RG's dirty tricks part of the geofex website <http://www.geofex.com/Article_Folders/dirtytrk.htm> or it was a mistake by a tracer, or it was built wrong by the original factory and nobody gave a shit cuz it was a @#$%in fuzz, and nobody cared or knew if it sounded right or not. its supPOSED to @#$% up the sound, right?

i don't have the capability of doing video these days unfortunately, but if ya mess with this circuit, its way better with the mod. in this case, on the vero, move the fuzz 1&2 connection from c1 to j17 instead, and you'll immediately see which variant works and doesn't.

also, as shown on the schematic, it SMOKED q3 at one point. i never before encountered a ge getting hot enough to burn my finger!!!!! surprisingly, tho, once it cooled down again after i swapped that one wire, the q still works. weird. fuzzes are weird. add germanium, and shit gets REALLY weird.

but anyways... this is what i done did, and the results...

so... is the fuzz control supposed to be a bias control? or do ya think the connection was inadvertently (or nefariously) moved to the wrong side of the 1u blocking cap before q3?

am i crazy? <duh> or on point? what do ya think?

look forwards to your observations, fam.

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Post by CheapPedalCollector »

Schematic looks fine to me, it's a Tone Bender copy, and the pot will vary the negative feedback to the base of Q2. If you smoked stuff at 1.5v I haven't any idea what size battery you were using. Maybe the vero layout is wrong. The 100K resistor to the base of Q2 could be high, maybe 10k would be better but hard to say. Pot is probably supposed to be LOG. Since it's using 2SB175 (btw this is also known as the fuzzder) and it's configured like a Tone Bender, they need to have sufficient leakage to bias correctly.

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Post by george giblet »

I did a rough trace of the PCB. From what I can see that "factory" schematic looks more or less correct. The main difference is 100k on the input is replaced by a short on the built units. The fuzz pot is connected as shown on the schematic. On the units I saw there is a 100k resistor on the base of Q3 to the supply (-1.5V). No doubt this tweaks the Q3 collector voltage but the right value is going to depend on the transistor leakage. Start with a Q3 collector voltage in the zone -0.75V up to say -1.25V. You will soon know where to put it when playing with it.

You probably need to get Q2 biased first before you play with Q3.

If you can adjust the fuzz pot to get a good range of voltages on Q2's collector the fuzz pot should be usable. I have a feeling you might need to increase the 15k so that happens over a usable range of the pot. As is it looks like the bias is only good when the pot is nearly shorted. The important this is range of voltage on Q2's collector it doesn't matter so much how you get it. Adjust the 15k from base to ground when the fuzz pot is open. Adjust the 100k in series with the fuzz pot when the pot is closed.

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Post by george giblet »

There's a thread where LT goes through his 1.5V LRE.

Here's the schematic which is mentioned at the top of the thread.
(Has NPN and should be PNP)
https://stompboxes.co.uk/forum/download ... hp?id=1731
DSC00002.JPG

About 1/3 to 1/2 the way down the thread in post,
"by LucifersTrip » 20 Nov 2011, 12:02"
viewtopic.php?t=14884

LT mentions:
4) The 100k on the fuzz pot should be 10k.
5) He mentions the resistor on base to ground on Q3 is 5k (which I have seen).

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Post by pinkjimiphoton »

Hahahah my stoned ass forgot that i AM running this at 9v. i didn't even notice the 1.5v batt originally.

when all was said and done, i tried a bunch of fuzz pots there, most worked about the same, from 10k on up.

when all was said and done, i moved lugs 1&2 to the node after the blocking cap before q3. its not adjusting the bias as it was,
but it makes a nice softness adjustment to the fuzztone itself there. its boxed. fuck it. ;)

the vero is right, but it really does come down to needing fairly leaky germanium to work. at one point i DID have a si in q2 messing around and got it to pass signal and a decent fuzz, but the "fuzz" control worked very poorly. maybe the last 20% of the pot, below that, it was off, at least at audio frequencies.

coulda went with a smaller pot, and a big ass resistor, but wiring it the other way gave me a much more useable fuzztone.
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Post by george giblet »

Hahahah my stoned ass forgot that i AM running this at 9v. i didn't even notice the 1.5v batt originally.
Those 1.5V circuits creep up on you. There's few 3V'ers out there as well.
when all was said and done, i moved lugs 1&2 to the node after the blocking cap before q3. its not adjusting the bias as it was,
but it makes a nice softness adjustment to the fuzztone itself there. its boxed. fuck it. ;)
There's nothing saying you can't do that. I'm surprised we don't see more units with bias controls on both Q2 and Q3. Some of those Fuzzfaces sure have a lot of pots.

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Post by modman »

Please, support freestompboxes.org on Patreon for just 1 pcb per year! Or donate directly through PayPal

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Post by pinkjimiphoton »

modman wrote: 29 Apr 2021, 09:42

love it bro... but mine sounds better ;)
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Post by modman »

pinkjimiphoton wrote: 29 Apr 2021, 16:26 love it bro... but mine sounds better ;)
It's not mine :D -- just the most representative clip on youtube, it seems.
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Post by george giblet »

love it bro... but mine sounds better ;)
Running from 9V helps.

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Post by pinkjimiphoton »

george giblet wrote: 01 May 2021, 11:22
love it bro... but mine sounds better ;)
Running from 9V helps.
definitely, but it changes the bias point significantly, and the tone as well. that's why it wouldn't fire right with the stock 1m fuzz pot most likely, cuzza my stoned ape ass running it at 9v ;)
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Post by BMS1971 »

waiting for mine to arrive in a week :-). Will post gutshots of course
Ben

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Post by pmkipp »

Interestingly, the schematic that came in the box with the Olson X-78 is wrong - at least it is not what is actually happening on the circuit board on mine or others. First, there is no 100k resistor at the input. Input goes through the 3n cap directly into the base of Q1, with the 1meg going to ground as well. Then, there is a 100k resistor that goes between the 1uf cap and the base of Q3 to the power rail (that would be neg power). On the Olson X-78 that I have this 100k is attached to the solder side of the board, so was a correction to the design. Also, both 1uf caps go positive to neg.

I tried building one from the couple of unverified vero's out there which all relied on the schematic and there was always very low output. When I made these changes (I used non-polar 1uf caps) it really opened up the sound. Still not perfect as I will need to find the perfect set of transistors to use in each place, but at least this give me a fighting chance.

I have some used Matsushika transistors like those used in the originals, and some NOS NTE equivalents. We'll see what happens. My understanding is there needs to be some serious leakage in Q1 or Q3 for this to work right. Maybe I should remove and test the ones in my original...
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