Hey guys. Sorry to ask questions all the time but I'm almost done building my first pedal and I have some more questions.
So, here is the schem I made
(http://i.imgur.com/nQjEFbV.png)
The project is a Big Muff
C16 is a a low pass (that's what I'be been told) to reject high frequencies. My question is, Is it ok if[/img] its connected to R1 (which is a pull down resistor) by ground or it should be connected to ground from the source?
C17 is the power supply bypass (that's what I'be been told too :icon_mrgreen:) and D15 is the reverse polarity protection. Again, I'll have it connected to ground from the source, is it necessary?
Finally, is it Ok if I connect R27 -28 and 29 to positive BEFORE R24? Or will it change anything
Thanks guys! And I hope to finish my pedal soon.
There are many ways to answer those questions, but I'll give you the most practical answer:
It won't matter where or in what order you connect those.
A couple of things about these questions are confusing, so let's do some clarification. C16 and R2 form a high-pass filter (not low-pass). A resistor in the signal path with a capacitor connected from signal to ground, is the simplest passive filter circuit. Capacitor before resistor=high-pass. Capacitor after resistor=low-pass. R1 is unrelated to the filter circuit.
With C17, it's important to note that DC power doesn't flow through capacitors. It does "charge" them up to the supplied voltage. Purpose, when little fluctuations in the power supply occur, which can cause noise, C17 will charge or discharge accordingly to "smooth" those spikes and dips. D15 is positioned to allow current to flow if the polarity were reversed. Neither C17 nor D15 are necessary, but you gain nothing by removing them, and C17 can help reduce noise.
Electrically speaking, R27, 28, and 29 are connected to the power supply at the same point as R24. If you're referring to the physical position of the connection, that never matters. All four of those resistors are connected to the power supply on one end. How you physically orient them is irrelevant. Good luck!
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Well, being picky...
C16 and R2-R1 are a low pass filter, since frequencies higher than the filter's knee (cutoff frequency) go to GND by C16 itself;
btw R1 is very high value to influence heavily the cutoff, but it's there, and does its job nevertheless.
This is Mat's first pedal, I think it's a good time to learn stuff...
I guess he will design a PCB of some sort, then, especially with high gain circuits, follow the signal and GND and power supply flow, is a good thing, it will help with problematic circuit, first of all tube circuits...
Don't be cheap on filter capacitors, you never know what power supply you have at hand....
The best way to do this is to use a star ground system. You can find more information by searching the internet, but basically it means that power supply things, like C17, run to the point where your battery "-" , which is ground, will connect to the PCB.
Then, each stage's grounds such as R1, R3, R5 also run to that point.
R7, R9, R11, likewise.
So, you are making several "stars", which all connect back to the "main ground", the place on the PCB where your ground attaches. Grouping them this was assures that you are not connecting a section that has high ground currents flowing (power supply filter...) to one that is amplifying a low-level signal (input stage), which helps to avoid picking up noise.
There are many times that this will make little difference, but it is good practice, especially with tube equipment, which will have higher currents flowing around ground paths.
See what I mean? :icon_wink:
So I came up with something like this
(http://i.imgur.com/mRofbEt.png)
Red dots are ground connections. I think I can get the all together but the one from R30 goes to a led and I was told to have that connected apart from the circuit and C17 (A cap for power supply ripple) and D5 (Polarity protection) seemed at the time safer to have them apart from the circuit. This will all go to - in the DC jack but seeing your responses now I don't know if it's the right thing to do. Should I connect all of these together? Except the leds I guess.
hi Mat,
it's good to have the LED ground as close to the power supply ground as possible, so any "pop" goes straight to the power supply and not via. a ground that's connected to signal. both places will probably cause some pop, but having the LED ground share a wire with signal ground will be louder. for a similar reason, it's also good to have the power supply filter cap grounds near the input, so no ripple or hiss from your adapter will contaminate the signal either.
it's also beneficial to have the protection diode near both the power supply + and -, so if it's ever needed, the diode can short those two sides together more directly (i think because there's less resistance from the length of the traces).
you can get away with a lot of things with ground placement when building pedals, it'll all still work even if you place grounds randomly. each individual guideline may not matter much, in individual pedals, but together they add up to reduce a lot of noise in a pedalboard at a loud gig.
Ok. So I think that if I made a conection from the C17 ground to maybe R1 ground it will do. Thanks guys!
i think that would be fine. if you imagine swapping the locations of R1 and C17, then it would be less ideal.
IMO you should move C16 to be closer to C17, so they work more like 1 capacitor, and maybe move the V+ input pad closer to D5. it should still work either way, though.
tip: if you connect your ground output only to the power socket negative, and make a 2nd pad connected to ground, then you don't need to connect the power socket to the rest of ground later.
let us know how it goes, whatever you do!
Guys..!!
(plz correct me if I'm wrong..) :icon_redface:
C16 doesn't mind for R2 and/or R1 'cause it forms a LPF with the previous stage output impendance..
(signal source internal resistance..)
To be more specific, it actually minds a little bit for R1 'cause they're placed in parallel..
@Alex83tele: Divider's point is on C16/R2/R1 common point and signal is then taken out of the other R2 edge, so R2 "divides" nothing in that specific arrangement..
(what you've said stands for cap(s) AFTER R2..) :icon_wink:
ah! i forgot there was a schematic and made too many guesses from the PCB. forget what i said about C16. thanks for pointing that out, Antonis.
So, is it ok if I leave it like that? :-\ Hey guys, any recomendation? It seems that I need to get the PCB even smaller, it fits in the case but I'm worriend about the other thing like the swithces or the pots. The pots will have to go above the PC and some of the imput jack too. I'm not getting the components too tigh but maybe I can make some more space. Can you give me some advises froms your experiences? I'm trying to look at pictures at other peoples boxes to see how do they do it.
yes, the grounds should work like that (but we haven't checked the rest). i think moving V+ input closer to D5 would improve safety slightly, but it's not too important. all the things i said were just ideas, those parts of the circuit should already work the way it is now.
i'm sorry for the mistake, btw! i wrongly thought C17 was another power filter cap. usually a ceramic cap is placed in parallel with an electrolytic power filter cap, because it works better with higher-frequency noise. somewhere between 10-100nF is a good value.
fitting components into boxes is almost a whole other science, and it would be difficult to suggest everything in one post. do you have a photo of your board in the enclosure? Or the enclosure datasheet and circuit board size? maybe it would help us give suggestions. here are some random tips:
Circuit boards with components are around 1.5-2cm high, and in most enclosures, will fit underneath pots and toggle switches. Sometimes sockets and footswitches, if the enclosure is 4cm+.- You can reduce the height by using microminiature capacitors and avoiding transistor sockets, but i don't recommend that for your first pedal as heat may damage the transistors.
- You can put your traces slightly closer to the edges, if you must, but don't put them at the very edge.
- A sheet of plastic (cut from food packaging etc) can be placed under the board to insulate it.
- Your footswitch can be in a bottom corner, it doesn't have to be in the centre.
- There are smaller 3PDT footswitches available, i can provide links if you're interested.
- If you shrink the layout, try to make sure the input signal is kept away from any stages where the signal is high-gain. I THINK this shouldn't be a problem after the signal comes out of Q1
- Not using a battery means much more space and much less waste!
I think I got it. I reduced some space and made the conection points closer to where the cables will have to go in the case.
The case Ill use is a 150 bB. Al my measures are in mm (milimiters, sory amercans but metric sistem rules :icon_mrgreen:)
150 BB: 120mm x 95mm x 35mm
Here's the new trace
(https://s3.postimg.org/lel8n3cqn/Sin_t_tulo.png) (https://postimg.org/image/lel8n3cqn/)
And here is the print
(https://s1.postimg.org/vdxj4fhnv/image.jpg) (https://postimg.org/image/vdxj4fhnv/)
No mather how I try, there doesn't seem to have enough space for the PCB and the jacks, so it might to have to be under the jacks and the pots. Is it OK?
Sorry for the late reply! This should be fine, if there is enough vertical space, but you may need to insulate the board and possibly secure it. Have you made this already?
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Quote from: MrStab on July 12, 2017, 12:07:13 PM
Have you made this already?
Oh boy. It's taking me so much time. I made another version but now I have to make yet another one. I'm sure its gonna fit and there is also a nice space fr the soldering.