DIY Dist Pedal: Is this schem correct?

[Earthscum]

Hello all. I've been trying to find a forum that someone may be able to answer some questions about a circuit I'm building.

First point from the input is a JFET buffer which will always be on, then a switch to switch between the next stages or straight out. The next stage is a NPN Transistor booster that feeds the final stage, a single transistor distortion.

I built the distortion circuit once, and confirm that it works (not sure if it works fully as intended though). My guitfiddle (Db tuning... like Deftones) didn't get any distortion from the high strings, but as I struck the lower strings, I got a nice diode-only clipping akin to a slight overdrive. Nothing that would scare an old lady, though.

Last night I built the buffer (confirmed working from a headphone amp I built) and the booster circuit to confirm they worked together. I haven't combined all 3 yet... maybe tonight.

What I want to know is if there are any caps or resistors that seem to be the wrong value, not needed, or missing. This is a combined circuit from 2 different sources.

The transistor distortion is from Cook Your Own Distortion .

The buffer and clean booster are from AMZ-FX .

Here's the schem:



What I noticed was that if I changed the .1u caps from the inputs of the stages to .068u or .047u I can get more bass through (I'm actually building this for my bass, but would like to keep it versatile enough to use it for my guitar as well).

Are these caps critical?
Does this circuit look sound?
Any ideas on components or values I can change safely to tune the tone?

I am thinking of adding a Big Muff style tone control at the input and output of the booster/distortion stage to shape more bass going in, and to bring the highs back up at the end. If I do this, can I eliminate any of the caps?

I apologize for the crappy half spice (oregano) half Illustrator picture. Illustrator kept crashing on me (I'm on Ubuntu) and just don't have the patience today, lol.

[Earthscum]

Another thing I was wondering is if each stage is getting 9V, or if it drops for some reason. I'm fairly new to electronics, in a sense. I just recently decided to start building my own circuits, so even though it looks to me that each stage gets a full 9V (or probably more realistically around 8.6V) I figure I'd double-check with someone else. I only know 1 person in RL that knows what I'm asking, and I only see him about once every 2 years, lol. Thanks in advance!

[unclejed613]

take out the diode pair from the base of Q3. they will cause Q3 to go into saturation and you won't get any signal out distorted or otherwise. move the high side of R7 to the 9v rail. this will increase Q3's gain. put a cap between the wiper of the drive pot and the base of Q3 this will keep the drive pot from removing q3's bias at the bottom of it's travel. you won't have any problems with voltage drops in the supply rail. the only problem you will have there is battery life issues and looks at a glance that you're drawing a couple of mA at most, so that shouldn't really be a problem

[mjf]

hello.
i think one distortion circuit is enough.......
is your psu voltage 9v (battery or accumulator)?
what fet transistor do you want to use (bf245 or so)?
i think you need a cap in the line between the 10k pot and the crosspoint r3/r4 (or you will bias q2 with the pot..........).
if you want to hear more bass tones you must increase (make bigger) the coupling caps.
greetings..........

[Earthscum]

you mean the D3/D4 pair? When I ran that circuit by itself, I got great clipping from them (after I turned the transistor around... one of my first debugging lessons). It sounded a lot cleaner and had more headroom. I'll have to try out that stage by itself again to make sure I wasn't mistaken, but I lifted one end and got almost clean tone. The diodes in the feedback didn't sound as good... actually sounded similar to my DS-1 before I modded it. Really fuzzy and tinny, but since it's a simple circuit I could probably clean that up with pre and post tone controls.

Basically, I kinda want a clean boost that I can clip at the end. I don't want fuzz from an overdriven transistor, although that's probably what I'll get when I boost into the third stage, aye? Should I just take that last distortion stage completely out and clip in the booster stage?

[Earthscum]

Another thing, if someone could explain, why the distortion stage doesn't have a resistor dropped to ground before the base like the gain stage? I'm still trying to understand biasing (I know the definition, but I need hands-on to completely understand something... if you don't know how to break it good, you don't know how to fix it good, as I've always said). It has a 47k from the power source, but in the booster the 47k helps create the bias? Maybe just build 2 booster stages, and use one to overdrive the other? Or just clip the booster feedback?

[Earthscum]

Thanks unclejed, very much. Should there be a cap between the base and resistors, or wiper to resistors in the Q2 stage as well, or in front of the buffer, or are those biases fairly stable?

I'm still under moderation, so my posts won't be showing up for a bit. Noticed you added the other info after I replied (with more questions, of course). I'm going to go read more about biasing... maybe beating it into my head will help, lol. At least I can open up a box and comprehend what the circuit is supposed to do now. Much better than when I started this whole thing a couple weeks ago. Been playing bass/guitar and using all the gear from studio to road for 20 years and just now getting into this aspect.

[Earthscum]

lol, mjf... you answered my question (I was getting tired last night and somehow missed your post, sorry!). So, yes... I DO need a cap before the resistors.

Just out of curiosity, what would be the effect of placing a cap AFTER the R3/R4? Would that cause it to act as a (high pass?) filter, or just have no useful effect?

FET will be MF102 (what I've been using). I am always open to alternatives, especially if it comes to added noise... one thing that has driven me crazy over the years is when you kick on a pedal and hear white noise hissing in the background. I hear people kick on their flanger or phaser with a distortion, and of course it gets amplified and becomes a whooshing sound... AARGH!!! I use a KMD phaser in front of my distortion (gives it more of a dimensional depth than running after dist) and want clean sound as much as possible.

I'm going to run on battery hopefully. If I start running through a battery every 3rd or 4th practice/show, I'm gonna bust out a wall wart or build a pedal board with some regulated (and filtered) 9V dc. I already have both my guitarists using Boss pedals that plug in (ME-8 and ME-50). It's hard to find an open plug on the bar sometimes. Would pulling out the distortion stage and clipping the feedback path of the booster stage make a significant difference in battery life?

[Earthscum]

I was just looking at the schem and making considerations when it occurred to me... the diode pair (D3/D4) that would presumably send Q3 into saturation... isn't that what the C4 is for, so it doesn't change the bias? That's just based on the recommendation to place a couple other caps in to keep from changing the bias. If not, what purpose does that cap (C4) serve?

Edit to add: quickie question... I assume the cap on the V+ smooths out DC ripple? If not, what function does it serve? Would changing the value of this cap do anything to the unit as a whole? I have been just using it as per schematics, but don't know (or at least I assume I don't know) it's function.

[mjf]

hello.
i think there will be a little effort to get this amp working.........

with a cap after r3/r4 the transistor cannot work because there cannot flow base current in it........

did you thougt about fet mpf 102 ? there is a preamp schematic available .....

greater voltage amplification gives usually greater noise.so do not exceed amplification...........

when the amp is finished you can measure the current consumption - before that it is not easy to answer.........

d1/d2 is the diode pair at the base of q3 that you can leave away.


you need c4 to isolate the bias current of q3 from other gain stages and so...............

c1 is a decoupling cap - it should lower the output resistance of the battery and stabilise the circuit against oscillations and so......
greetings.............