EQ circuit

[Kipper4]

Wanting to make a stand alone Eq pedal.
I discovered the tone Mender and sort o cludged together my own take on it. With my prefered tone stack.
I'm reluctant to post the schematic up yet I'd rather sort out any problems before hand.
So If anyone wants to help and give some advice about this feel free to pm and I'll email the schematic.
Basic premis is a buffer, active tone stack, Recovery stage.
It might not sound like an EE's nightmare to the seasoned but I still have a lot to learn and I want it to be good and worth building.
Theres a good chance I've made  booboo changing my one of my favorite passive tone to active too.
I'm here to improve and share.
Further to my post here

http://www.diystompboxes.com/smfforum/index.php?topic=109696.0

I will post the project when its been checked and verified, improved
Thanks (I wish I wasnt so British some days although I dont wear the bowler hat everyday)
Cheers
Rich

[Kipper4]

Here is where I'm upto
I'm still c.r.a.p at pictures here
Thanks to PB6E
Click on the pic to enlarge
s

[antonis]

Better...?? 

[Kipper4]

Thanks
How did you do that? Pm me pls

Edit; I see you saved on your photo bucket and reup loaded it
thanks appreciated


I hasten to add I have not built this yet.
I'm still working on it with some help.

[antonis]

So Kipper4 you've calculated an overall loss of more than 25dB on the tonestack...
(I suppose that it happens in the worst case....)

Does it involve the Presence pot's position or only the 3 Tone pots..

(I'm a little dummy on gain loss calculation..)

[Kipper4]

I've calculated nothing so far.
PB6E did a sim of my original. which had a make up gain of around 50 (50k pot in the NFL) and deduced that the loss was 15-20 so I changed the pot to a 20k.
When I get around to figuring out sims Maybe I might get better at calcs too
My original estimation was around 20 gain loss so I over did it after Mark Hammers advice in the thread I started with (post #1)

[bool]

For better gain staging and potentially a little better SNR I would change your input buffer into a couple-dBs boost. A fixed gain of x2 or x3 should do it - so check with your sources that the first opamp won't clip under worst case scenarios.

Also, I would add the ubiquitous "couple kOhm" and 100pF to ground input RF filter.

Likewise, a couple hundred Ohms buildout resistor at the output to play nicely with interconnects etc. And a pulldown resistor at output as well. Are you sure the 100nF at the output is enough? I would stick a 1uF for guitar and/or at least 4u7 for bass there.

There's still more room for improvement, but the above is a necessity imho.

[samhay]

bool just beat me to it, but for better signal-to-noise, you are better to boost the signal before cutting it, so you could move your adjustable gain stage to the input op-amp. If you are worried about headroom, then you can have some make-up gain at the output too, but you could also use the output op-amp for an active presense control - I suspect your current presence control will be rather interactive with your tone stack settings.

As an alternative, have you considered an active tone stack like this: http://www.diystompboxes.com/smfforum/index.php?topic=24359.msg157710#msg157710
You could add a 4th presence control at ca. 3-4 kHz in parallel to the other 3.

[antonis]

Sam I 've just caught a virus with your attachement...!! 

[samhay]

attachement? I just posted a link the another thread on DIYSB.

[Kipper4]

Thanks guys
Plenty to go at there. I saw that last night just after I made this thread Sam and Its definitly a consideration.
I also saw STM active EQ which looks good too.
I think I'm gonna have to shift the PIAI Gator off the breadboard at the weekend and experiment.
I'm off to research active presence controls
Night all and thanks again
Thanks for the ideas Bool and Antonis I'll be doing some of that too.
Rich

[Kipper4]

I found a few differant presence controls
and was wondering If something like the Flapjack OD (hotcake) presence control is what was meant by an active presence control ?
I found a few posts about it on the other forum

[bool]

You could also look into sansamp's bddi presence control. In fact, you need only to add ONE capacitor onto your second opamps' gain stage - change a couple of values, shift some things around, and you're "almost there". Of course you can leave your pot where it is now and just add a cap (recalculate the values) - the action will be different, but that may well be what you're after. Hard to tell until you breadboard it.

(The circuit around U2A)

http://i232.photobucket.com/albums/ee308/alembicplyr/Schematics/bd21_lite_v10.png

[samhay]

Rich - if by a presence control you want to boost frequencies above ~ 3 kHz (that's my definition, which I borrowed from Fender), then a 47n cap in series with R1 will make IC1_B a presence control in your design.

[Kipper4]

Thanks guys
That's some brilliant stuff to try out on the breadboard this weekend

[Kipper4]

Quick question.
Has anyone tried an Active E series tone stack.
I've been messing with the duncan tonestack calc
I tried the above circuit on the breadboard and its ok. but stil very interactive depending on where the pots are set.
Matbe i was thinking of something a little more seperated and extreme.
I have a ways to go
IIRC i removed R1 too

[samhay]

Fancy posting a schem of the 'E series' tone stack? - can't find one, nor run the Duncan tone stack calculator.

[Kipper4]

Certainly can tomorrow.
I'll take a snapshot of the response curves and values hopefully.

[amptramp]

Let your computer do the drudgery:

http://www.duncanamps.com/tsc/index.html

This is a tone stack calculator that allows you to move the controls and determine the frequency response.  Just hit the download at the bottom of the page.

[PRR]

> the 'E series' tone stack? - can't find one, nor run the Duncan tone stack calculator.

It's right there in my Duncan's.

> an Active E series tone stack.

It is a fine-yet-funky *passive* network. What are you going to do to make it "active"? Feed it coffee? Buy it a gym membership?

OTOH, "all" passive tone-changers are lossy, so you always need some added amplification, which I suppose adds a touch of "active". But if you do more than make-up gain you really come out with some very different tonestack; and if you know what you want you might start with a clean sheet instead of a minor Fender hack.