Obsidian-T modification

[sixfeet5512]

Hello,

I'm a beginner in electronics, so far i made the deluxe bazz fuss and the obsidian-T.
I work in an after-sale service of a big company, so i have access to plenty of material to work on 

I'm currently willing to mod my Obsidian-T as i wish to add some options to it...

I wanted to add hard clipping diodes activated by a switch, so i've done it, but with no change at all on the sound !

I don't know if my schematic is wrong or if i'm using bad components, or if it can't be adapted on this circuit.

The basic schematic is here : http://www.google.fr/imgres?imgurl=http://i124.photobucket.com/albums/p34/Baktown/Obsidian-T.gif&imgrefurl=http://www.diystompboxes.com/smfforum/index.php?topic%3D61692.0&h=459&w=799&tbnid=pgnFGaOYCQ3IhM:&zoom=1&tbnh=90&tbnw=157&usg=__EcwTp2ExmZLcu0JVnPQ_HvHFDsw=&docid=kZSespM0hTkYKM&client=firefox-a&sa=X&ei=HjlyU_qMK6XM0AXQ2oD4Dw&ved=0CDgQ9QEwAg&dur=1319

Here is the modification I made : http://hpics.li/2c22862

(sorry i can't manage to put images into my message).

I've tried using 1N914, red leds, green leds...

Also i've tried to get the signal from Gain 2d pin or Volume 1st pin, with no more effects.

Please help !

[duck_arse]

hello sixfeet, and welcome.

try another 100nF cap after the switch, before the 33k. it might work. do you have any germanium or schottky diodes?

[sixfeet5512]

Thanks for your answer i'll try it asap

Could you explain why adding a capacity would make it work? I'm trying to understand what i'm doing 

About diodes, i have silicium (1N914, 1N4007...), or leds

[duck_arse]

I'm not an expert (on anything) by a long shot. if you're lucky, one will come along and correctly explain. anyway ....

diodes will only conduct when they are forward biased, being more positive on their Anode end than their Kathode end. the 100nF that is already in circuit isolates the tone stack following it from the DC that appears on the collector of Q4. that means the output is then dc referenced to ground, exactly the conditions we want for whatever is following.



when you switch your diodes, as drawn, they have 0V on both ends (follow the string of resistors, one will end at ground), so neither diode can forward bias, neither can conduct, no hard clipping, questions are asked on forums. by putting the second capacitor after the switch point, you have isolated the diodes from any dc bias. this means the signal is now going (+) and (-) about 0V, and when it goes above the diode forward voltage, (or below the other diodes forward voltage), they get angry, turn on, clip the signal, create happy campers.

besides, whenever I see the back-to-back clippers in circuits that work, they are isolated between capacitors. one thing to note, because you now have 2 capacitors in series, their values are calculated as for resistors in parallel. so, 100nF in series w/ 100nF = 50nF. double the caps to 220nF and the end result will look like 100nF for frequency calculations.

as for Silicon, diodes or transistors it has a Vf of about 0V6. Germanium has a much lower Vf of about 300mV, so it conducts/clipps sooner and for longer. schottky diodes are made from silicon, but the have a forward voltage about the same as germaniums. and the leds are a mixture of different elements, and have differing Fv depending on their colour, which is a function of the elemental mix. red leds are abot 1V6, blue leds can be as high as 3V, so you'd need buckets of signal to get them to clip.

I hope some of this helps. what does your big company deal in?

[sixfeet5512]

Thanks for your answer i think i understand a bit :-)

I'll try it when my son sleeps... i'm desperate for free time lol

I work at Somfy, i think they are kinda world known now... main activity is motorising roller shutters, but they make plenty of electronics products too.

I found schotty diodes today, on a dead radio keypad. Is that kind of diode better for that circuit?

My goal when i began to play with electronics was to use as often as possible the components i throw garbage every day in my work... i even created a simple fuzz pedal with 0 buying, on a PCB i found, and i even made homemade jack inputs huhuh. That did not work very well, veeeery bad sounding, but that was fun.

[duck_arse]

no one type diode is "better" than the other. the lower Vf ones clip at a lower voltage, so clip sooner and provide more apparent sustain. the leds will tend to only clip the peaks of your signal, because the level falls below their Vf quickly. most people like germaniums, they are used in things like the super fuzz, but it comes down to what sound you like. so, try them all. you can also have a look at the amz site (linked at page top) for the "warp controls" and the page on clipping, plenty there.

if you have an endless supply of junk as a resource, you're laughing. is it through hole parts, or surface mount? do you get enclosures as well? have you sighted the "bazz fuss" circuit yet? that is a perfect build for junk parts, so many options.

[sixfeet5512]

Yeah for enclosures i use intercoms call station, aluminum box around 15x20cm it's very handy

Many products now have CMS components, so it sux. I found treasures in older stuff!
For the bazz fuss i buyed the components and made the "deluxe" version that sounds pretty good, but now i see i'm able to make something working good i'm looking for using junks again

I just modified the circuit now with 2 x 220nf capacitors in serial, and signal going to diodes between them. I have put sockets for the diodes so i will try different ones

Thanks for your advices, i will tell you if that works!

[sixfeet5512]

Heyyy, cheers mate that's working!!
I had little time to test so i have no idea of what is sounding best, my idea was to have an option to "tighten" the signal, making it less fuzzy while keeping the power... Any idea of a combination that could make that?
It was fun to see led glowing as i played :-)

I think i have some bias problem too, when i don't play the pedal would sustain infinitely any noise while adding some oscillating effect. So i'm gonna replace a resistor by a trim, but i wonder if it's best to trim the 10K resistor of Q4's collector, or the 3.3K of Q4's emitter ?

(When i touch Q4's solders, the strange noise disappear so i guess the problem is here)

Sorry for my english btw, i'm French and school is over since a long time

[duck_arse]

glad to hear it works. sad to hear it feedbacks.

as Q3 and Q4 are setup much like a fuzzface, you can reduce the 10uF across the 3k3 on Q4. this will reduce the fuzz-gain on the low end, help reduce some mush. try 1uF or 470nF maybe, see what happens. if you go too low a cap value, it can go bazzurkk oscillate, I have found. if it gets outta control, you can remove that cap, it will reduce fuzz even more, but still work. with the cap out, you can then increase some gain by reducing the 3k3.

confused yet? do you have a multimeter? measure for about 1/2 battery volts at the collector of Q4, with no signal. this is the general vicinity for "cleanest" output. you can probably trim the 10k collector, but don't let it go down to 0R, or you may smoke Q4. user "gus" has quite a bit on trimming methods for the fuzzface-alikes, you could search some of that hereabouts.

you can also mess with the value of the 100nF caps betweeen Q2 and Q3. reducing them will cut some flab, maybe "tighten" like you want. go as low as you like, 2n2 is sometimes sighted.

as for the oscillatings, hope they disappear with the gain reductions. otherwise, check all your grounds and lead-dress and input/output seperations. see how that goes.

I was thinking, if you work with motor controls et al, you might be geting some power mosfets, driving relays and motors. you can pull them and use them as clippers as well (search again), or try them in ordinary mosfet booster circuits. there is an obsidian that uses mosfets, but check the polarities with that one.

yr english is fine if you can understand the rubbish I type. my school also long gone. good luck, have fun.

[sixfeet5512]

Rubbish? i thought you were american :p

This morning i put a trimpot in place of 10K Q4 collector's resistor, and by lowering it the oscillating noise disappeared. I have around 7V now on Q4, but no smoke sighten :p

I will keep your ideas about capacitors for a future project, seems interesting enough but I'm done modifying my obsidian now : i made it on a "naked" copper pinboard and copper is beginning to oxydate, now soldering is hard! I was afraid to damage the circuit while manipulating as well so i've put it in it's box.

I had much fun messing with diodes this afternoon, I still have to test further but found some clues about what I want.

I definitely prefer assymetrical clipping, and adding a capacity in serial with the lone diode brings a lot of warmth to the sound. Still have to find the best value tho.
Orange LEDs were my favorite for the moment

Thanks again for your explanations 

[duck_arse]

Rubbish? i thought you were american :p

...... I'll let this insult pass. geeze, mate, all australia here, cobber! does le tour pass your house this year?

we want to see pictures of your completed box, post in one of the pictures threads, you'll get EXTRA bonus points for all parts from junk. I'm so glad the osc stopped, cause I had no ideas.

"naked" copper pinboard and copper is beginning to oxydate

do you mean pad-per-hole perfboard? (oxidise/oxidize)

[sixfeet5512]

Kinda, 3 holes-perfboard in fact. I think this is a good compromise between pad per hole and whole stripes. And yes, that oxydizes!!

"Le tour" is not passing by, and hopefully.   

I'll try to take some pictures this week-end, but this pedal is almost all buyed, only a few resistors and the enclosure are saved from junk.

Finally i could not resist modifying my circuit, so now I have soft clipping on Q3 and i think this fits much better my needs. Still have to test further but 2xwhite leds in series against a silicon diode was making a nice overdrive sound with almost no loss in volume.

And for the oscillating, i found the board was touching a screw under it, so i removed all screws from enclosure and trimmed back Q4 to 4,5V again, and it sounds much better.