Beginner breadboarded fuzz issue

[Locrian99]

So I am new this, I've built an op amp muff kit I got off Amazon and it works great.   I figured next step would be bread boarding a fuzz face and tweaking it til I like it and then putting it in vero and boxing it up.   I've made it to the breadboarding part lol.   So the effect works, I get fuzz.   The weird thing is I don't get anything til about 7 on the guitar volume knob.  7-9 is quiet 10 is full volume.   I've tried adjusting the bias of the collector for Q2 same results and I've tried several different transistor combinations same results.   I'm using the beavis board fuzz layout which looks about the same as the small bear one.   If I crank the fuzz pot all the way I can hear further down on the guitar volume knob but it sounds hollow.   

Any advice would be greatly appreciated. 

[GibsonGM]

Hi Locrian, and welcome.     I'm assuming you're looking for the famous 'roll-back' of a fuzz, and would like to have mostly the full range of your vol control?

Can you post a like to the schematic you used, and also, can you take a pic of the breadboard so we can see what you built?  That would be helpful for us to get a fast answer for you!

[Locrian99]

Yes I would like to be able to use the volume knob to roll back, as well as just control the volume.   

http://beavisaudio.com/beavisboard/projects/bbp_FuzzFace_Rev1_1.pdf

This is the schematic/breadboard layout I used.   I am using a 500k volume pot as the schematic says not the 100k shown in the breadboard diagram.   As you can see from my picture I put a trim pot in in place of the 8.2k resistor.    Though i had the same issue when using the resistor and swapping different values to bias.    I have not tried biasing the collector of q1 at this point.   

[antonis]

Hi & Welcome, also..

You can try last Beavis mod suggestion:
Experiment with different values for R1. Try values from 1K up to 470K.

[Locrian99]

Didn't fix the volume issue but the changes are awesome.   For sure something to tinker with.   Tried a 33k and a 220k.   May even try a 500k linear pot there later once I figure out this guitar volume knob thing. 

[GibsonGM]

Weird, my program won't open the schematic PDF (WPS Office).  I'm just wondering what interaction between the input and your volume knob might be going on.  Do you know what your vol. pot is in the guitar?  Ideally it will clean up when rolling back, but on some (like mine, with treble bleed caps) it will get thin as you go past 6 or 5 on the knob.   Below "5", I wouldn't want to use the vol as it's too bright/weak, but I never go there anyway.

Maybe get it biased with voltages, and see if anything changes?

[antonis]

Weird, my program won't open the schematic PDF (WPS Office).

For your convenience, Sir..

[Locrian99]

Thank you.

Not sure what the pot is in the guitar it's a 2020 players strat.  I grabbed my les paul and tried it and it's functioning as you stated  below about 5/6 it gets thin but there's sound even when the fuzz is not maxed.   So it's the guitar or the combination of the two.   Think I'll change the fuzz knob from a type c to a b.   Not sure why I would want it to be set so it climbs so quick at the end but that's what it called for.     So I guess that answers that.  I'll continue tweaking and see if it gets better with the bias changes and transistor combinations.   I was messing around last night and it's got a 796 hfe 2n5089 in it right now way too much lol.   

Again thanks!.   

[Locrian99]

Actually I've got your attention if you don't mind.   Endgame I was planning on putting the fuzz on vero perhaps following the pictures lay out.

https://4.bp.blogspot.com/-GpJOulSONK4/UW1OFmyB5sI/AAAAAAAAFaA/s2OGVrgP-Fg/s1600/Creepy+Fingers+Effects+Si+Fuzz+Face+-+smaller.png

I notice the pins on one of the transistors is rotated looks like the base and collector switch spots.   Do I just twist those and maybe put some electrical tape on there?   I will be socketing the transistors.   Again thanks. 

[antonis]

Do I just twist those and maybe put some electrical tape on there?

Yes..

But after your final mod, smear a drip of solder on each BJT leg, securing it in its respective socket..

[GibsonGM]

Yeah, sometimes a project like this shows off something in a guitar or other equipment we weren't aware of. Fuzzes really work with the guitar electronics, where most other stomps have higher input impedance so are more immune.   I just 'get used to' where 'clean' is when I use a fuzz, and go with the flow.  They're just about the only time I even use the vol knob! 

[Locrian99]

Is there a way to test the output from the guitar and see if it is a pot issue ?   Since it's happening on all 3 pickups I would think it wouldn't be an issue with the pick up.  Moving away from a stomp box issue here I realize. 

[GibsonGM]

Strat (?) all going to one volume pot.  If you have a humbucker in the bridge, they may have compromised and put in a 500k pot for it instead of the customary 250k, tho what wouldn't cause your problem.   OR, the taper may be different than what we'd expect, cutting you off sooner than another pot would.  A vol. pot should be log taper, but may vary from one manufacturer to another.   Or a previous owner (if it had one) may have played around in there.... 

If it's a strat you can take a look next time you change strings (take out the 30 screws, lol)...if a Les Paul type, of course just take off the back plate!   I hesitate to think there is 'something wrong' with your vol. pot...I think of these variations as 'features', lol.   But if it's REALLY bad, yes, explore further.  Maybe there is a wiring error in there or something (?)

[Locrian99]

Copy that may just have to chalk it up as a feature of this pedal.   I did wonder if maybe it's a c type or something weird like that, as it does seem to really have a difference in that last bit of turn.   Anyways thank you.   I'm just going to fine tune it for now and hopefully get it committed to vero and boxed up.   

[Locrian99]

Well I couldn't stop tinkering with it.   Tried several things the input pot like an axis.   Dropped the volume pot to a 100k etc.   then decided if it was not enough output from the strat I'll just put a booster in front did up a little lpb-1 in front of the fuzz and my volume knob works!   I also get that roll off I was looking for.   

[GibsonGM]

What that suggests is some 'interplay' between your volume pot and the fuzz input. The LPB is raising the input impedance of the fuzz (and boosting the signal of course!).   Have you biased the fuzz, adjusted the transistor voltages?

One thing that just occurred to me is that if the bypass cap isn't connected properly, you'd have far less gain - I just wonder if something could be going on there. Maybe take a look around the 1k pot and make sure all is wired right, and also be sure the pot taper is a "B" taper...just a thought.

[Locrian99]

It does have a 1kC style pot for the fuzz control which makes the taper less than ideal. My understanding is it should just effect the taper.   I have new pots arriving today so I'll change that out, the original directions from small bear call for a reverse audio which is why I used that.  I've got the collector of q2 transistor biased at 4.6 but the volume thing was happening with all transistor combinations I tried before I settled on the 2 2n2222a's.   I'll try the pot thing out tonight hopefully that changes it.   As far as the wiring I'm pretty sure I've got everything right I've gone over it several times literally made a second one on another breadboard I had, did use same pot though same thing. 

Thanks for the direction.

[antonis]

Let's see what's happening here..

100k feedback resistor interacts with input signal impedance, setting Q1 stage gain..
(just lift it from Q2 Emitter and place it on Q1 Collector)

Overall FF gain formula is complicated a bit but, in general terms, it can be tweaked by altering R1/Rsource ratio (besides VR1 pot)..

LPB-1 output impedance is considered about 10k so you need a similar resistane pot - in case of your FF build is correct..!!

Could you plz post some voltage measurements..??

[anotherjim]

If you're in a hurry to look inside a Strat, a hack is to clamp the strings to the fingerboard with capo or cable ties then slacken the strings, remove the neck screws and then you have access. Not actually ideal and still not super quick  ('cause all them screws) and you have to make sure any shims in the neck pocket don't fall out of place. It's the way to go if you need to test and try different changes to the electrics.

[Locrian99]

Hey guys I'll post some voltage measurements tonight.   I made a little audio probe last night and was thinking I'd probe the signal tonight to see if there's a point where it loses the volume.    I know off the top of my head q2 collector is between 4.6-4.7, base is right around .5 I don't remember the emitter.   The q1 collector was i 1.17 and the emitter was 0 I don't recall the base.  Both are 2n2222a right around 200 hfe.   Q2 was slightly higher than q1.