EQ blending help

[acehobojoe]

Let's say I had an EQ circuit that I liked, looking like this :
I could probably easily make something like this with the AMZ RC calculator..

then, I would probably want a brighter sounding one with a circuit like this:

The question is, can I blend these two with a single pot? input on lug 2 and circuit 1 on lug 1 and circuit 2 on lug 3, both being connected to the output. Only one would be in use though, because of the resistivity of the pot.

am I thinking about this right?

I also want to try to put this Pre-overdrive in a circuit, for funsees. Does anyone have experience with that?

Am I fine with just the capacitor resistor networks, or do I need anything else?

[PRR]

> I could probably easily make something like this with the AMZ RC calculator..

That's got 8 poles (bends). The basic R-C calculation will get one bend. If you cascade eight simple passive R-C they will interact, action will be very mild. If you buffer between, that's eight buffers, a LOT of amplifiers.

You also have a 15dB/Oct slope, which is hard to get with any sane number of slopes that get to 6dB/Oct at infinity, are ~~2dB/Oct near the corner.

At 8 amplifiers you could basically build a Graphic EQ, which will do this plus MANY other curves.

And having "many other curves" on tap might make your blend question moot. From curve A, bump-up 1KHz 2KHz 4KHz 4dB to 8dB each. I used to do that with my thumb.

[acehobojoe]

yea, maybe not something that involved, but I was thinking of something simple with a low cut but a boost around those regions. probably could run a high pass with 68nF or something initially then try to bring down some of the highs, the only remaining part would be to cut the 200 range. It's not completely necessary, but it can definitely clean up a guitar signal.

The second is simply a smooth slope on a hi pass circuit, allowing in the higher frequencies. to add a bit of "sparkle" at the top.


Do you think it would be better to do such a thing with 8 amplifiers or maybe even less to keep it simple?

[WhiskeyMadeMeDoIt]

Your first eq setting looks very much like a cab simulation curve with a bump at around 400hz.
Check out this thread and look for the simple cab sim circuit.  That will be a nice starting point for sure. 
http://www.diystompboxes.com/smfforum/index.php?topic=106185.msg959449#msg959449

[ubersam]

RC filters will just cut, no boost. If you want boost you'll need something like an eq. Check this out: http://www.geofex.com/article_folders/eqs/paramet.htm

[antonis]

The question is, can I blend these two with a single pot? input on lug 2 and circuit 1 on lug 1 and circuit 2 on lug 3, both being connected to the output.
Only one would be in use though, because of the resistivity of the pot.

This would practicaly work only for full pot rotation (and for a BIG pot value)...

At any indermediate slider's position (except at precisely centered one) you'll have two "unequal" signals which are straightly mixed after their own obtained gain (or loss)...

I think it's better to split the incoming signal right before the two circuits (if their input impedances are equal) and then bled the two outputs via a pot..

[WhiskeyMadeMeDoIt]

That is what is what I was suggesting but didn't type it out build a buffer and split the signal to a tweaked cab sim for the top graph and then another active opamp style eq to match his bottom graph and then blend them with a pot into an output buffer.

[acehobojoe]

so it will work properly if they are blended after they are split. With something like a dual transistor setup. That makes sense, I can see why it wouldn't work if you were blending the path, it would be unequal.

[acehobojoe]

Whiskey, I really like all of the cab sims mentioned on that thread!

[PRR]

To state the obvious: your softy tool interface "IS" classic analog filters, just implemented digitally.

So go across the top icons. You have a low-cut, a shelf, several band-pass, a shelf, a high-cut.

Go across the bottom. These are the numbers you put in your filter calculations. (I just noticed these are not in order; you must have a way to diddle the frequencies.)

That is a LOT of bandpass and similar filters to implement with op-amps. At least 10 opamps plus an input buffer and maybe a summer.

OTOH you have a lot of trivial Qs. Q like 0.3 can -probably- be omitted and a similar curve gotten with shift of an adjacent filter.

24dB/Oct hi/lo-pass filters are VERY steep. Unless you have major crap just outside the desired band, you do not need such steep filters.

For any stage use, I'd think a 60hz 12dB bass-cut, a narrow -15dB 170Hz dip, then a broad 200hz +20 boost, would sound very similar.

PC-based digital filters reduce the per-section cost to zero, so are not good models for filters you have to hand-build stage-by-stage, until you work to minimize the filter.

[acehobojoe]

is there a good online tool or software that can help me figure out the shape of the sound desired and how to easily implement it? Something visual would be nice.

[Quackzed]

i would try prr's suggestion ,which is an approximation (3 band) of your more complicated (8 band?) eq curve...
try it right in another instance of the same 'channel eq' plug-in that you did the original in...
the point is to use less bands to make it reasonably practical to build in the real world, without a ton of parts...
try to limit yourself to just 3 bands and get 'close as you can' to your original curve... start with the suggested low end cut, notch, and wide q boost, then tweak till its close as you can get it...
then you can calculate op-amp filters to do each 'band' once you've got your info from the plug-in's individual 'bands'... the individual frequency, q for bandpass or per octave rolloff for low cut,and  cut or boost amount etc...
does that make sense? that way you keep the less significant details of the eq curve you want from making a realworld circuit too big and complicated to actually build...

[ubersam]

There is this:

OK, now I'm posting a circuit I did build, and that is very good and controllable.  No savings here on opamps, this is the no-compromise version, meaning that I am not trading functionality or performance for simplicity. Anyway, it is easier to understand and tweak in comparison to the gyrator based eqs., and eventually could be extended to more stages.



Be advised that a buffer stage is needed BEFORE in case you are going to feed it directly with your guitar, and eventually a gain control stage AFTER to match your setup level.

EDIT: Note the 10:1 ratio in the capacitors of each stage.  I optimized the resistor values (using MicroCap 7 optimizer) and the cap ratio to maximize the Q or peakedness of the bands, so this Eq has a much more definite mid band in comparison to a 2-band baxandall tonestack.

It's from this thread: http://www.diystompboxes.com/smfforum/index.php?topic=24359.0 - WARNING: my anti-virus seem to think that there is a virus on that page, something to do with "Joe Hart"

is there a good online tool or software that can help me figure out the shape of the sound desired and how to easily implement it? Something visual would be nice.

LTSpice is a free simulation software. Draw up the schematic and run the simulation, see the curves. Took me a while to figure out how to use it though.

[acehobojoe]

That makes a lot of sense. Thank you!

I'll download LTSpice

[acehobojoe]

Great. There's three buttons.. . I have a lot of work to do.