Tuesday, 3 June 2014

Basic Audio Scarab Deluxe

Info about this great sounding fuzz pedal from John Lyons of Basic Audio, and thanks to him for the information he shared about the circuit.  Check out this and his other pedals here:

A straight ahead refined vintage era fuzz along the lines of the Tonebender with lots of sustain and gain.
Tone control smooths out the high end but is very usable at all settings.
All gain and tone settings remain articulate and sweet throughout their range.
Full fuzz sound with the clarity of an overdrive.

This is a "Deluxe" version of the Scarab with more control over "feel" and adjustments in bias.
This version adds in a couple knobs over the 3 knob version.

BIAS:
Tonebender type circuits vary depending on the bias of the 3rd transistor. Gritty gated tones on one end of the dial, sustaining lead tones in the middle and sweet lower gain tones at the other end of the rotation. Bias affects tone and gain.

FAT:
The low end at the input of the circuit affects fuzz amount and saturation. The feel of the pedal can be adjusted from a saturated slower responding "fat fuzz" to a snappy, fast responding, slightly less gain fuzz that has the feel of a distortion or overdrive. This helps dial in a single coil to be fat or a humbucker to clear up a bit and be more sensitive to dynamic picking.







56 comments:

  1. Finally, a Basic Audio design. Great pedal.
    More More More

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  2. Ah, I saw the thread on FSB and was waiting for your layout :D
    I'll probably build it next week-end
    Thanks !

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  3. Nice one! Added to the ever growing list.
    I could make this now but I do not have all of the POTS dang it... lol will look around cause I have to have a 50kB pot somewhere hahaah

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  4. And before anyone says it, yes I know it should say 4 links! :o)

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  5. Hey Mark, are you using the Multi-layer Ceramic Capacitor's for the 10uF value? I noticed your post on FSB about those caps... I have that seller marked on evil bay and may order several values of those... good stuff!

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    1. I've got some of those caps, but because the 10u in this layout only needs a 2.5mm pitch I probably wouldn't use them, I'd be more likely to use a tantalum.

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  6. On another note I have been meaning to make a Mctester style SI Tonebender and this layout with the mods is what I have been wanting... GOOD STUFF! hehehe
    thanks again

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  7. I've got this built and will hopefully verify shortly! Only thing that's odd is the fuzz pot is not adjusting anything... Re-checking my wiring and checking against the schematic now :)

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  8. Verified. I had a small error (4u7 cap span was wrong) fixed it and BOOM! Holy crap this thing is awesome. Move over Big Muff - this fuzz is seriously worth building even if you have a (few) dozen others... I sure do! :) Thanks IvIark for the great layout! It's a work of art! I was able to get the bigger caps to lay down without crowding. cheers, joe

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    1. Awesome, thanks for verifying Joe. I love the quick verifications! :o)

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    2. It's worth noting for those who want to build that the bias pot is most "in" at the middle of it's range - I used a 20k I had and it's fine. A 50k would do, although simply have some wasted range. No need to hold off building for lack of a 25k pot :)

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    3. My pleasure man - been wanting to do that for a while now:) Thanks for all your hard work!

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  9. Sweet! *noted*
    I was digging around and found a 50k pot in my pile of stuff so I am getting on this too... I may tinker around with the bias pot and put a resistor on there so it is in the sweet spot range since the 50k could be overkill

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    1. Personally I'd use a 10K and increase the 1K Q3 collector resistor to maybe a 4K7 (or even better socket it and test). I don't see much point in using anything bigger than a 10K for a bias pot, you get a lot of wasted rotation.

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  10. Another real nice youtube demo here:
    https://www.youtube.com/watch?v=Qj1r0uGzA5Y

    heheh this pedal really reminds me of how good SI transistors really are :-p

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  11. Well put. This is really the poster boy for SI fuzzes, IMHO. I prefer it to the Fuzz Factory - no finicky/expensive GE transistors, and LOTS more useable tones.

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  12. I notice on FSB there is a discrepancy on the schematic vs the original pedal... hopefully this layout is a very close approximation - with that... hard to go wrong with a McTester based SI tone bender- building this one up tomorrow. Been too busy around here to think about a soldering iron :-p

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    1. Yes I saw there is one less cap and resistor, but we don't know whether the gut shots are old versions of the circuit which John has since changed. We probably won't know for certain until someone who is that way inclined from here, FSB or similar place gets a chance to see one up close.

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  13. Built this one and boxed it up, sounds great. I only have 2N5089s at the moment and those may have too much gain. I tried out a BC182L in Q2 and even an NPN germanium transistor in Q2 with interesting results. I suspect this pedal may like slightly lower gain transistors in the 350-450 hFE range... hmmmm anywho... swapping around different gains and this pedal was Roaring away and always sounded great!

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  14. The only issue I am having with this one is a volume drop when turning the tone pot CCW, but maybe it's normal considering the connection between vol3 and tone2.
    Do you have the same thing ?
    Other wise it sounds nice, I think I will put a fixed resistor for the bias and box a 4 knobs version

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    1. I'd expect that to happen. When the tone pot is in the fully clockwise position, the signal bypasses the tone control completely and passes straight to the volume pot. As you turn it counter clockwise the tone stack is brought more into circuit and in the far counter clockwise position you'd get around 7dB of attenuation. So yes it makes sense.

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    2. This animation of the tone control should help you visualise why it is happening.

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    3. Ok I get it, thanks Mark

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  15. wow, i'm anxious to build this. i just don't know if use a 820r or a 680r in place of the 750r resistor. Maybe i'd socket it.
    And for the 150k resistor i've got some 120k 1/8w metalfilm. will it work??

    thanks!

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  16. Well, it's done! Great fuzz. I swapped the 750r for 1k. it's maybe less gainish but i find it more pleasant. And changed the transistors to BC109. Now it sounds even better. Definitely worth the build.

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  17. Just finished boxing mine up

    Pics:
    http://johnkvintageguitars.homestead.com/Effects/Fuzz-ODs/BasicAudio/ScarabDeluxe-01.jpg

    http://johnkvintageguitars.homestead.com/Effects/Fuzz-ODs/BasicAudio/ScarabDeluxe-02.jpg

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  18. I got this one built and working, but it doesn't quite sound right and I think I need to do some biasing. Here are my voltages with the bias knob all the way up:
    Q1
    C: 4.3
    B: 1.1
    E: 0.5

    Q2
    C: 1.2
    B: 0.7
    E: 80mV

    Q3
    C: 9.27
    B: 7.9
    E: 7.5

    Q4
    C: 8
    B: 1.2
    E: 1

    Those voltages on Q3 don't seem right, but I don't have a lot to base that on with my limited knowledge. I'm going to try swapping out that one to see if it's just a bad transistor. Anyone else have any ideas just in case that doesn't help?

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  19. Okay, I scored between the tracks (I had forgotten to do that before in my excitement), and that dropped the voltages of C and E on Q3. The pedal is more manageable now, but still doesn't sound quite right. I've been swapping transistors and it's helping a little with tone, but not with control.

    Here are a couple issues: The Fat pot gets a lot quieter in the middle of the sweep; this may be normal for the circuit and isn't a big deal. I have to adjust the Bias pot after adjusting the Fuzz pot; again, not a huge deal if it's par for the course, but seems odd to me.

    The two issues that are a big deal to me is that there seems to be a secondary fuzz that sounds separate from the clean guitar signal, and turning my guitar's volume down even a hair drops out all the main fuzz and leaves me with a clean signal that sounds blended with the annoying secondary fuzz. I can't handle when fuzz, distortion, etc. sounds like it's sitting on top of my guitar signal and isn't a part of it.

    Any ideas? Could this still be the product of a bad transistor or a poorly biased one?

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  20. Great Job! Is there any chance of getting the schematic of the Basic Audio Gnarly Fuzz?

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  21. Run out of 2N5088 at the momment but i have BC547, BC548 and MPA18. Which one you guys think will work best? Sorry for asking but every time i have to build a vero from this blog i have to etch the board, we dont have that in my country. so, Photoshop and etch :)

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  22. I built this, using BC549s. I've done a few fuzzes by now, and this is possibly the nicest one so far. Great stuff! I'm having some trouble though. Maybe someone can help me out here?

    When I turn the volume knob on my guitar to zero with the pedal on, I get a crazy noise of some kind. It gradually disappears as I turn my guitar volume up. I can also get rid of it by slightly underbiasing the Q3 with the BIAS knob, but I would like to be able to use the pedal at higher bias settings without it turning my quieter parts into wild, uncontrollable cacophony. Right now I can't use the volume control on my guitar as I'm used to, unless it's underbiased.

    What do you think I've done wrong here? Is this a part of how the circuit functions or can I fix it somehow?


    Thanks for this wonderful resource!

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    1. It it an oscillation (like the circuit is oscillating), or does it sound more like radio interference? A lot of fuzzes will pick up radio really well when your volume pot is down...

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    2. mine doesn't have that issue so that's not the nature of the circuit.

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    3. I don't think that it's my guitar doing it. I've built and used other as loud fuzzes without these issues. The guitar is well shielded and I play inside a giant metal container, so I must've done something on the circuit that makes this happen. I don't know, it disappears if I underbias the circuit with the BIAS knob, so I thought maybe I should be looking for something in that region of the circuit board? Any suggestions?

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    4. OK, so I've tinkered some more with it and found that the best way to describe it is as a high pitched squeal with a lower motor like sound at the same time. It's running the whole time as the circuit is engaged and will be shut off with the bypass switch, so I've narrowed it down to the wiring. I looked for a ground loop, but can't find any.

      I think you may be correct joedoc, saying it could be some kind of oscillation. I tried tying another 100uF cap across the power plug and the pitch of the noise changed. I guess I have two 100uFs in parallel now, making it 200uF? Should I just add bigger cap value until I get rid of the problem? There must be a better way, right?

      Is the circuit too gainy? It doesn't make sense to me. I've tried it with BC108s, BC549s, 2n5088s, 2n5089s and 2n4123, but I'm just getting different versions of the same problem.

      I read somewhere that you could lower (or raise?) the resistor between emitter and ground on Q2 in a Fuzz Face to fix the squealing by lowering the gain. That would translate to Q3 in this circuit, right? Would changing this possibly mend my troubles?

      It's unbearable! The fuzz is, apart from the feedback/noise, just the dream fuzz really, but it's almost useless now, unless I Bias it to a farty, gated sound. That's a cool sound, but I need the rest of the range also...

      Thank you for helping out so far!

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    5. Alright, so I found that the wires for the FAT control at the inout of the circuit was crazy microphonic. Touch the wires and it oscillates. I tried tying down bigger caps across the power rails to no avail. I actually went as far as to do a whole new circuit to see if I could replicate the problem, but omitted the input tone filter and the output tone control completely and replaced them with a 100n on both ends.
      And the problem persist. Only solution I've found was to hook it all up to battery power instead and that works perfectly well. It's strange, cause this is the only pedal I have that seems to not take the power supply. It's just a standard boss wall wart, but it's never caused me trouble before. I tried with a bunch of identical once with the exact same result. So I guess we can say I found a remedy, using battery power, but I still don't know what's causing the noise...

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    6. Hi

      I have the exact same issue aka high pitch all the way but i when turning the bias pot CW it suddenly jumps in volume. Maybe thats the sweet spot ? Anyway that pitch is annoying and i have the same microphonic fat pot. Mine is not boxed atm but is in my wooden test box. Maybe a metal enclosure would isolate that ?

      Any thoughts ?

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  24. In the middle of troubleshooting -- just wanted to confirm; are bias lug 1 and volume lug 3 left unconnected?

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    1. Derp. Had tone 3 going to volume 1 instead of 3. All good now.

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  25. Just built this one - sounds great! Shouldnt the outer lugs of the fat pot be swapped? Mine works in opposite way compared with the vid..

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  27. Hello!
    I´m having a problem with the bias pot. If we number it as a traditional pot (from 0 to 10) mine is only useful from 9 to 10. Below 9 I have no sound at all from the pedal.
    In that short movement I can hear variation in the tone, if I continue going down I hear some crackes (little) and then the silence.

    Anyone knows what´s happening, or what could I do?

    Thanks!!!

    P.D. Sorry but my english is very rusty

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  28. This thing is drivning me nuts. I am on my second scarab build - the first one worked like a charm - but this time I have problems with the volume control which doesn't do anything. The effect seems to be stuck on maximum. I have done the usual trouble shooting, tested the pot and it definitely works. I don't see how it is even possible to 'bypass' the volume control when it is placed like it is on this build. Any help would be much appreciated

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  29. This thing is drivning me nuts. I am on my second scarab build - the first one worked like a charm - but this time I have problems with the volume control which doesn't do anything. The effect seems to be stuck on maximum. I have done the usual trouble shooting, tested the pot and it definitely works. I don't see how it is even possible to 'bypass' the volume control when it is placed like it is on this build. Any help would be much appreciated

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    1. Volume pot's lug 1 is connected to all other grounds and definitely grounded?
      +m

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  30. Yes all the connection seem to be in place. I have a wire going from lug 1 on the volume pot to the ground lug on the input jack. I have testet the connection for continuity and it seems solid. All cuts and links on the board appear right. Same thing with components. But I must be missing something.

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    1. If the full output is at volume pot 3 and there is definitely ground at lug 1, then only possibility is that the wiper of the pot doesn't work. When CCW, the output must be completely grounded if lug is ground.
      +m

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  31. Working! It seems to have been a combination of two problems. The pot was broken, but measured fine when it was sitting in the enclosure because for some reason the way my board was placed somehow made a connection to bypass the volume. I replaced the pot and flipped the board, so now everything is peach! This really is a killer fuzz this version has BC109's in it. Awsome.

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  32. I have built this pedal and it sounds great. It is one of the best sounding pedals that I have built.

    However, I find that when the fat knob is in the middle of its range I pick up radio stations in an almost unusable way. If I turn the bias knob to 3:00 or 9:00, this will cut out the stations, but it would be nice to fix this.

    Also, I have a strange issue with my volume pot. My volume pot, when cranked, actually drops in volume. This is only in the last little bit of its rotation. It seems like it needs to be up higher than demo vids that I have seen.


    All in all, sounds great, but I would love to be able to make sure it is perfect.

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    1. I'm not sure if I made clear, but the volume on mine is less than unity until around 2:00. Then it rapidly goes up from there.

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    2. To cure the radio interference, just take a small cap around 47pF - 150pF and solderer that from input (aka fat2) to ground. This will dump the inaudible high frequencies to ground and kill the radio signal from getting past the input. That should do it. If not, then use shieded wiring.

      As for volume, that is on par with logarithmic pot behaviour. There are two possible solutions.

      First, ignore all demo videos as those vary rarely give real life examples of the sound or pedal behaviour. Those are good for referencing the overall tone, but not much else. To match the demo video, you would need the same guitar with the same pickups, the same amplifier and even more importantly, the same playing style and the same dynamic touch.

      Second (which is the one i would do), you could swap the log pot for linear taper. http://www.geofex.com/Article_Folders/potsecrets/pottaper.gif
      With log pot, you'll have 10K of resistance between the signal and ground when the pot is set to middle position. As with linear, you'll have 50K with pot set at middle. I myself use log pots for volume rarely. Only when the output level is way too massive to hadle with linear taper.
      +m

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    3. Thank you so much for your help here and in other threads, mirosol. That was a great post, and your posts have helped me in the past as well.

      Mark

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  33. just finished and tested it, sounds amazing, subbed a b50k for the bias. i've tested many of the fuzz circuits,and this one is my favorite so far!

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  34. Hello. I build and love this pedal, it's really good weapon on my board. But now i'm wondering if it's possible to add a momentary feedback switch on it, like the caroline guitars "havoc"... Is it possible ? If yes what i need to do ?

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