first distortion design, please proof for me !!

[TimWaldvogel]

ok, so i am still learning about pedals and what components do what. i have a tl082 dual op amp here i have been wanting to use lately, so i designed a circuit similiar to a modded mxr distortion + but is the front i placed a simple op amp booster circuit i found.

see the thing is, i dont full understand biasing too much yet. and this was my first time using this program... i am aware the schematic jumps around a little, but thats how it made sense to me in my head as i was placing things on here... PLEASE PLEASE PLEASE look over this and give me some feedback and suggestions ASAP... i would really appreciate it

RED lines represent the 9v power into the circuit
GREEN is where the Circuit inputs

below are the link to the two schematics i used for each op amp section

http://www.jer00n.nl/pics/opampbooster.png

http://www.experimentalistsanonymous.com/diy/Schematics/Distortion%20Boost%20and%20Overdrive/MXR%20Distortion%20Plus.gif


THANKS, TIM !!

[GibsonGM]

Hi Tim,
Good work so far...I think, given just a quick look, that you might need to add a cap from op amp OUT1 to the input to opamp section 2 (The connection under the IC on your layout). 

There is a DC level present from the operation of the 1st section that is passed to the 2nd and may interfere with its operation without the cap there to block it.  Values from about .47uF to 10uF should work ok, and can be chosen to either reduce or enhance bass (respectively). Experiment for good sound!  Then, you'll still need to add the bias section from the Dist+ (the 1M resistors, there are 3 of them....) to your 2nd stage input in order to get that "Distortion plus sound".  Think of it as connecting 2 pedals together, really.

Second, maybe you need a better means of controlling how much boost you're going to feed the Dist +?   As shown, the booster will output a lot of noise as the volume is rolled back, and you could lose high freq's.   The best way to control the volume there is with a pot in the feedback path of the opamp's 1st section....an output vol. control would add a lot of noise unless it's last in the circuit.  Alternatively, you could just decide on a 'permanent boost', and adjust the feedback resistor accordingly, but a 'pre level' control is definitely cool!   Start with a 500k or 1M pot in the feedback loop and adjust accordingly....look up a Tube Screamer schem to see what I mean....it would go where the 220k resistor is on your boost schematic, wired as a variable resistor. 

Keep modding and adjusting, and you'll end up with a nice Dist+!   

~Mike 

[TimWaldvogel]

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ok so i revised it with your suggestions.... and once again i apologize for the mess on the perf layout, hope to have neater layouts in the future... PLEASE proof for me to verify my changes? and thank you soooo much for your help

[TimWaldvogel]

sorry link didnt work

[aron]

The output cap doesn't need to be that big. It can be a smaller film cap value. .1uF is fine.
It might be helpful if you redrew the schematic with your additions.

[TimWaldvogel]

so c7 can be a .1 uf film cap? good to know, i though since it was supposed to filter voltage it had to be electrolytic

[TimWaldvogel]

ok everyone who is being nice enough to help me, i redid it, tried to think a little bit more, but i think its neater than the other two lol. anyways this is my revamped and revise layout with the modifications and suggestions i have got. please check this out and let me know  if i need to change anything else

[aziltz]

Hey Friend, it doesn't look like your tone control is wired quite right.  I'm seeing it wired as a Volume control, and then run into the volume control.  I think theres a cap to ground missing somewhere in there.

I could be wrong.

[JKowalski]

I think there might be some things I would change, but it's hard for me to anaylze the circuit when it's in a perf layout form. If you could make it into a schematic form, that would be helpful, for me, and probably everyone else checking it out. 

[TimWaldvogel]

well i forgot a cap, i just fixed it, but this link here at premier guitar says to wire a cap in series with a 1meg audio pot. so shouldnt the variable is the resistor combined with the cap running into the input change the tone?. i am very new, the closest thing to tone pots ive done is treble bleed caps on my guitar

[TimWaldvogel]

i have since put that cap to ground i was missing however c8 should act as a tone cap right?

[TimWaldvogel]

OOOOOOOOOOOOKKKK lol, just looked it up, i think c8 should jumping from the middle lug on the tone to the input lug on the volume... i think, gosh this is confusing stuff lol

[JKowalski]

OOOOOOOOOOOOKKKK lol, just looked it up, i think c8 should jumping from the middle lug on the tone to the input lug on the volume... i think, gosh this is confusing stuff lol

It'd probably be less confusing in schematic form 

[TimWaldvogel]

do you have an free programs for schematics?

[aziltz]

without a schematic I can't be certain, but it looks to me that output is taken from C8 through the tone cap and then to the Volume.

As drawn, C8 would be a coupling cap to block DC from the opamp getting to the output as well as shaping the bass.  It would have no effect on the highs which is why I was looking for a cap-top-ground from the Tone Control.

*I think c8 is where it belongs...  The way you have it wired now, I would take the rightmost tone lug and send it to the Volume control input, instead of ground.  Then I would take a cap to ground off the middle lug and leave the 3rd lug and c8 alone.

search "stupidly wonderful tone control" for a good example.

I use "eagle" for schematics, but its got a steep learning curve.  It's free though, and you can make PCB layouts.  just google "eagle" and "cad" and it should come up

[JKowalski]

do you have an free programs for schematics?

LTSpice is a good computer circuit simulator, schematics are easy to draw on it.

Also a piece of paper will do in a pinch 

[TimWaldvogel]

ok so i ATTEMPTED to put the general circuit schematic into perspective on paint... hahaha
anyways, it should be too hard to read. and might give you more insight to my perf layout too. i can figure out the tone controls, just wanna make sure everything else within the general circuit is good

[TimWaldvogel]

hahah wrong picture, here ya go

[PRR]

> circuit schematic into perspective on paint...

Thank you. The pictoral is needed for building, but for thinking the abstract schematic (no matter how rough-drawn) is often clearer.

Your DC bias for the second stage is typo: you have forced the input to the +9V which generally won't work. There are several ways to do this; I simply stole the scheme you used on the first stage.



HOWever: in fact you may not need it. The DC out of the first stage will be half of 9V, which is just what the second stage needs. So, at least for non-distorted zone, in this case you may omit all these parts and just wire first to second.

In heavy distortion, the cap-coupled and the dirct-coupled may overload differently. Depends on several imponderables. If you were going to sell a million, you would try without these parts, save a few cents. For one-off DIY, just use them.

When turned-up, this is a HIGH! gain circuit. Layout will be critical. Keep outputs AWAY from inputs. You will still have signals sneaking though ground and power rail. It may just be impractical to have this much gain inside one box until you have years of layout experience.

[TimWaldvogel]

ok heres the thing, how can i lower the gain from the distortion circuit to make the boost circuit a little more effective, and originally i did not have the bias for the 2nd stage, however someone in this thread above told me i needed it for the proper tone and said i needed a cap between stages for voltage leaks. how can i change values to make this a more functional pedal. maybe lower the gain of the distortion stage. and from what i understand the boost is only a 10db boost circuit