DIY EQ

[aviherman5]

Hi all,

Will this

Work as a three-band EQ?

This is the full schematic:


Thank you!

[bushidov]

I am not sure of your common-source JFET boost circuit (doesn't look quite right, maybe that's just me), but as of the rest of your circuit, here's what I think you are trying to do, but maybe I am incorrect.

I had to redraw your schematic to make sense to my eyes and got this:


Because when capacitors are in parallel, you add the values together, I redrew it like this:


So, I think you are doing a Marshall/Fender-esque style of passive tone control/tone stack. If that is the case, we need to change the value of R3 from 50k down to something like 1k, and add resistor R4 and set that to the 50k I think you were going for:


However, in this style of tone stack, if this is the tone stack style you were going for, then you also have the mids and bass pots flipped (and most likely your caps for those filters flipped as well). I redrew that to what I think you were actually going for:


which would generate this sweep:


Sorry, I made a lot of assumptions, and if I am incorrect on any of them, let me know.

[aviherman5]

Ok wow. Thank you so much for these suggestions!

So just one questions then:

I did the math for frequency: 1/2(3.14)*r*c. And I have changed some of the values of the components to make them more commonly available and better suited to my needs.

Pots:
100k linear
.005uf bass capacitor
.00124uf mid capacitor (2 620s' in parallel)
.00047 treble capacitor

Ideally when the pot is turned halfway (100k pot so 50k plus the 56k we already have) I should be at these frequencies:
Bass: 300hz
Mid: 1.2khz (1211 but close enough)
High: 3.2khz (3194 but close enough)

Are my calculations correct?

Thank you so much!

[aviherman5]

Oh and by the way...those calculations are relative to R4 being 56k. Is that ok if it stays that instead of 50k? Thank you!!

[Keeb]

This might be beside the point if you don't intend to build the entire circuit but the boost section will invert the signal. That means the two signals that will blend are out of phase - which will lead to a weaker signal.

[aviherman5]

What if I put the EQ before the boost?

Or can I use this signal inverter before the EQ and after the boost?

[antonis]

First of all, draw a sensible booster..

[iainpunk]

hey, welcome to the forum,
i get some very strong 're-inventing the wheel' vibes

if you stack filters like this, they are going to interact, if you don't know how to put together such complex formula's, just use ToneStack Calculator in the web: https://www.guitarscience.net/tsc/fender.htm

the last schematic, that Sbus signal inverter, is for very specific systems, it won't work for guitar.
if you want to cleanly invert the signal after or before the gain and filter, just use a phase splitter:

Rc and Re shoud be both 10k
R1 i'd say 560k and R2 150k
the caps can be 100nF

the blender could be done more cleanly as well, since its shunting signal to ground, which is for various reasons considered bad practice.


another point about schematics,
we generally draw them with the signal going left to right, not up/down or right to left.

cheers, Iain

[antonis]

if you want to cleanly invert the signal after or before the gain and filter, just use a phase splitter:

Rc and Re shoud be both 10k
R1 i'd say 560k and R2 150k
the caps can be 100nF

I'd argue for Rc & Re 4k7 and R2 220k..

Halving splitter's output impedance and getting closer to about 1/2 Vcc Emitter & Collector swing..

[aviherman5]

Thank you

if you want to cleanly invert the signal after or before the gain and filter, just use a phase splitter:

Rc and Re shoud be both 10k
R1 i'd say 560k and R2 150k
the caps can be 100nF

So do I first go into the signal inverter, then from each output go into the boost and EQ, then combine the outputs at the end?

[antonis]

I think we all are confused a bit..

Boosters invert - that's for sure - but this doesn't mind at all as long as there isn't any other anti-phase signal (180^o phase difference, either leading or lagging..) mixed at some further down point..

In case you wish to mix the inverted signal with another "clean" one, just re-invert the former..
(via a CE amp or inverting op-amp with some gain, to recover EQ loss..)

P.S.1
I can't see the reason for Iain suggesting you the use of phase splitter..
(maybe I didn't get some devastating point of your query..)

P.S.2
One 1.2nF (E12 series) is much cheaper and space saver (not the tyres type, Stephen..  ) than 2 X 620pF (E24 series)

[iainpunk]

Thank you

if you want to cleanly invert the signal after or before the gain and filter, just use a phase splitter:

Rc and Re shoud be both 10k
R1 i'd say 560k and R2 150k
the caps can be 100nF

So do I first go into the signal inverter, then from each output go into the boost and EQ, then combine the outputs at the end?

yes, the top one is to be the boosted and eq'd one and the bottom one the clean channel.

antonis, its so you have a buffered clean signal for mixing and an out of phase signal to be put back in phase by the booster.
also, yes those values make more sense, i forgot to take the Vf in to account, and lower impedance is more better.

cheers, Iain

[antonis]

its so you have a buffered clean signal for mixing and an out of phase signal to be put back in phase by the booster.

Very true and correct but does OP intend to do such a thing..??
(honestly, I'm puzzled over those drawings..) 

[11-90-an]

Me, I wonder why mixing un-EQ'd signal would be needed here... but only my preference...

Drawing a schem... hold on 

EDIT:

Here ya go...


Untested, but should work... i think 

JFET booster from here

Choose 1 of the "ends"... end 1 has lots more volume and might even distort...(untested) if that happens scrap end 1 and go with end 2

EQ pot should probably be moved and replace the 100k resistor at the end of the EQ section... however I don't putting it before the EQ would have any drastic disadvantages...(again, just an assumption)

The resistor circled in orange adjusts the volume of the "dry" signal (seems redundant but hear me out) set it by turning all knobs to max, then adjust it until you can hear the EQ'd signal is almost equally as loud as the "dry" signal

Hope that helps...

[iainpunk]

EQ pot should probably be moved and replace the 100k resistor at the end of the EQ section... however I don't putting it before the EQ would have any drastic disadvantages...(again, just an assumption)

that should work fine, but in this case, a linear pot would work fine, since there is loading on the pot from the tone stack!

Very true and correct but does OP intend to do such a thing..??
(honestly, I'm puzzled over those drawings..) 

the trick is looking from right to left in his drawings.
you can see the label input directly connected to ''source A'' which goes in to the mixer, and ''source B'' comes from the tone stack and goes to the mixer.

also, the powersupply block looks off,,, the crowbar has no fuse-resistor,

cheers, Iain

[aviherman5]

Me, I wonder why mixing un-EQ'd signal would be needed here... but only my preference...

Drawing a schem... hold on 

EDIT:

Here ya go...


Untested, but should work... i think 

JFET booster from here

Choose 1 of the "ends"... end 1 has lots more volume and might even distort...(untested) if that happens scrap end 1 and go with end 2

EQ pot should probably be moved and replace the 100k resistor at the end of the EQ section... however I don't putting it before the EQ would have any drastic disadvantages...(again, just an assumption)

The resistor circled in orange adjusts the volume of the "dry" signal (seems redundant but hear me out) set it by turning all knobs to max, then adjust it until you can hear the EQ'd signal is almost equally as loud as the "dry" signal

Hope that helps...

Oh Lord you are the best. This is perfect can't thank you enough