Eq for both bass and guitar?

[iainpunk]

i honestly think that a little bit of gain (up to 4x) is a useful addition, but not necessary, and if you choose to add some gain, a volume control BEFORE the 'flat' gain stage is paramount to make sure you don't make anything clip unintentionally.

Example: his chart shows that, if we use both C as 22nF cap, f=1/(2*pi*R*C) should give me the a frequence of around 700 using a 100k resistor but i get 70 [1/(2*3.14*100000*0.000000022)]
I mean, bigger caps=lower freq. If he used a C of 7.8nF to have a 200-2000Hz band then it's quite weird to me that using a larger 22nF i get 700-7000Hz (which is of course higher)

i think there is a small error on that website.

cheers, Iain

[ghiekorg]

I updated the schematic using the values i found.

Here is iainpunk's version (do i need a pulldown resistor before going out?):

and here is Rob Strand version (i just added the gain stage resistors as before and a vol pot at the end, which could also be before the EQ of course):


Would they work the same way?

[iainpunk]

I updated the schematic using the values i found.

Here is iainpunk's version (do i need a pulldown resistor before going out?):

and here is Rob Strand version (i just added the gain stage resistors as before and a vol pot at the end, which could also be before the EQ of course):


Would they work the same way?

1> i forgot the output capacitor in my drawing, yes, im an idiot (no im not, i am working with a lot of bipolar supplies recently which generally don't need an output DC blocker)



2> i strongly recommend putting the volume control at the start of the circuit, because if the input signal is large, then boosted 12dB and also boosted by both eq's, it could clip the op amps. reducing the signal before that prevents that.

3> yes they work the same way, but having a buffer at the 4.5V makes the filters work more cleanly, which you probably want.

cheers, Iain

[ElectricDruid]

Example: his chart shows that, if we use both C as 22nF cap, f=1/(2*pi*R*C) should give me the a frequence of around 700 using a 100k resistor but i get 70 [1/(2*3.14*100000*0.000000022)]
I mean, bigger caps=lower freq. If he used a C of 7.8nF to have a 200-2000Hz band then it's quite weird to me that using a larger 22nF i get 700-7000Hz (which is of course higher)

i think there is a small error on that website.

I think that's unlikely. This circuit we're looking at uses cap values that are different, whereas his example uses cap values that are equal. He also talks about this in the article, and moving the cap values apart like that changes both the Q and the frequency formula. So it's quite possible that his results are fine for his equal-caps case, and yours are correct for the Giblet EQ version.

One way of getting the frequency range you want is to simply scale either the R's or the C's. In the ESP article, he keeps the R's the same, and scales the C. So if you change from 47n to 22n, you go up by an octave (close enough). If you go from 47n to 100n you go down by an octave (again, close enough). This is often easier than doing all the sums.

PS: BTW, your gain calculation for the non-inv buffer from a few posts ago was exactly right.

[ghiekorg]

Hi guys, thank you for your posts.
I updated the schematic:
i am not sure about the cap before the output. Is it 33, 330 or 3300nf?



And i breadboarded and.... of course it doesn't work. I suck at breadboarding. I REALLY do. I made like 5-6 pedals on breadboard and only one worked. Badly too. I don't know what i do wrong all the time, so i just drew what i did, maybe you can hellp me understand...
Couple of notes:
- I didn't draw the connection between RV2b lug1-2 and and RV1 lug2 as i did it offboard.
- I don't have 33nf so i used 47nF instead.
- I don't have dual gangs so i used B100k and rotated them at the same time.
- I only made the BASS part, as i was thinking it would have worked without the treble part anyways so i jumped from the TL072 out directly to C7
- I don't get any sound. If i unplug ground and 9v from the tl02 on the right i get something but the controls are not working like they should
- Like always, i have no clue about lug1-3 of the lugs but i guess they would just work in reverse if they are switched

So if you change from 47n to 22n, you go up by an octave (close enough). If you go from 47n to 100n you go down by an octave (again, close enough). This is often easier than doing all the sums.

I actually made a small chart:



the C doubles at every line while the freq halves.
Starting from the page's values (4.7nF, 12nF, 200Hz and 2000Hz) i get:
C2=18.8 C1=48 for 50-500Hz
C2=1.175 C1=3 for 800-8000Hz
The same results i get using the formula.

Thanks again guys. I feel we are close once it's breadboarded i will do a layout and i will build it. But first it should work 

[iainpunk]

i am not sure about the cap before the output. Is it 33, 330 or 3300nf?

i meant 330nf, but 100nf should be enough

[iainpunk]

i recommend to start breadboarding part by part, not a whole lot at once, and then just build it up until you have added everything.

start with one of the buffers on one side of the 072, without the input volume control, leave one op amp off of the breadboard. keep in mind that bias and dc-blocking are still necessary. then add another part, the first eq and get that to work, then the other eq and the 4.5v buffer
(the buffer is mainly important to keep the filters from interacting and oscillating, i suspect that if you have one filter, it'll be alright without the buffer)

success and cheers, Iain

[11-90-an]

and if it still doesn't work, you can always use your JACK OUT wire as an audio probe and trace out the signal...

saved me lots of times. most of the problems are a component one hole off to the side, not plugging in my PSU, and best of all, not even plugging my guitar in...

[ghiekorg]

Hi guys
today i had a but of time (and will) to start all over. I breadboarded the layout without the 2 eq parts, like this:



I can hear the sound from the amp but there is a lot of noise. Also the guitar behaves like this:

https://youtu.be/JqnnDL-5_D4

Is there already something wrong or is it a normal behave and i should just go on?
Thanks

[antonis]

I wonder how you get signal sound..!! 

C5 / Upper op-amp non-inverting input join is practically grounded via lower op-amp output..
(in the absence of Volume pot..)

[iainpunk]

try this


cheers, Iain

[ghiekorg]

try this


cheers, Iain

i tried but still same noise.
here is exactly my breadboard...

[iainpunk]

sorry for being an idiot, i missed something!

the green circle!

also, post voltages

cheers, Iain

[ghiekorg]

Nothing, still noise and no sound. I made a 2 min video where is show exactly what i did. Maybe it's me doing something wrong?
https://youtu.be/9FXekn-r0CQ

[iainpunk]

have you connected the guitar ground to the circuit ground?
that might be a good idea to begin with.

you could make a base/housing for your breadboard that allows for a more permanent jack and power connection,
i used a metal cookie tin which was 3x the size of the breadboard for ease of use, i drilled holes for 2 guitar jacks, 2 BNC connectors, a guitar pedal power connector and mounted everything permanently. all connectors have their own permanent jumper wires connected, this makes it easier to build on breadboard and transport prototypes. i used them for gigs and jam sessions. a lot of extra holes for potentiometers is a good idea too!! and don't forget a ground connection from the chassis to the 0V and the signal ground etc...

that pick guard on the guitar looks cool, do you have a full picture?

cheers, Iain

[ghiekorg]

omg i'm so stupid... i'm sorry. Yes i forgot to connent the jacks to the ground, thank you...

About the chassis: i was actually thinking abou that after seeing wampler's breadboard. This weekend i will go search for some metal waste

the guitar is only like stickers here a couple i did:





today i will try to go on with the first eq section. I will keep you posted. Be patient please <3

[ghiekorg]

so... It actually seems to work
Here is a clip with only the bass section
https://youtu.be/ATKJPjTUY3o
and here one with only the high section:
https://youtu.be/h_rr8tDILCY
Do you think i can proceed to layouting the PCB or shall i first build it completely with the volume knob and both stages together?
I am really excited now

[11-90-an]

so... It actually seems to work
Here is a clip with only the bass section
https://youtu.be/ATKJPjTUY3o
and here one with only the high section:
https://youtu.be/h_rr8tDILCY
Do you think i can proceed to layouting the PCB or shall i first build it completely with the volume knob and both stages together?
I am really excited now

hold yer horses... breadboard everything first 

It can save you lots of debugging time and effort... but then again, this is a rather simple circuit (compared to many others, of course...) so you can probably go straight to pcb...

good luck...

[iainpunk]

well, first breadboard it and check if everything works together, i have build a fuzz once and on the fly added an powerful active eq and it didn't work together what so ever, so i had to go back to the drawing board to get it to work.

i really like the look of the guitar, but the bass is a bit to bright/boldly colored for my taste.

desinging a pcb is one way to go, you could also look in to perf or vero board, those are prototyping boards which makes them super flexible to use. i personally really like perf (pad per hole), and really dislike vero (strip board), but that is a matter of preference.

cheers, Iain

[ghiekorg]

I just finished breadboarding it all and it seems to work
https://www.youtube.com/watch?v=FqKZbostGoE&ab_channel=ghiekorg

It's bit noisy though (here is a clip after adding the 500k vol pot (didn't have a 1M)):
https://www.youtube.com/watch?v=7M9h_fywFFU&ab_channel=ghiekorg

Do you think it will get better when boxed?

Thank you guys, I'm reall excited about building it up