Adding An EQ To A Circuit.

[inefficiency]

When adding an EQ or tone control to a circuit, where do you guys usually place it?

Say I picked the active bax stack. Would you just stick it at the end of the circuit, essentially on the output? Or would you pick a spot somewhere in the middle between stages or whatever?

There are various fuzzes, drives and even boosts that I thought an active EQ would add a bit of flexibility to, but I'm unsure if there's any benefit to doing anything other than just sticking it on the output.

[IvIark]

If it's replacing a different tone stack I'd put it in the same place, if I was adding a Bax to a circuit without a tone control I'd put it at the end and have a recovery stage like the last transistor stage of a muff.  You may not need that if the circuit has plenty of volume of course, but having a final recovery stage will give you a predictable output impedance which would always be an advantage.

[inefficiency]

Ah, I see. I figured because it was "active" there wouldn't be any loss. I'm aware that active means it can both cut and boost frequencies, but I figured maybe that functionality was there too.

[IvIark]

Sorry totally missed the active thing, I assumed you were just doing a passive one like the one on this page

http://amps.zugster.net/articles/tone-stacks

If it's active any losses should be recovered as part of the circuit.

[inefficiency]

Ah, cool.

Yeah, I always preferred the idea of an active tone control just for the ability to boost certain frequencies. Seemed like more versatile and thus better option.

That's a good link there, though. Might have to try some of those sometime.

[motterpaul]

Would you mind giving an example of a circuit with an active tone circuit?

Otherwise, I have found the BMP Tonestack w/ LPB1 (its a project given here) to be a very utile way to add tone control to any circuit. But it is passive with a recovery stage.

[IvIark]

If you look down this page there's an example of the active Baxandall there

http://www.learnabout-electronics.org/Amplifiers/amplifiers42.php

You'll see this in use in the Xotic AC and RC Boosters

[Silver Blues]

An active tone circuit is really just a filter tied intrinsically to some kind of amplifier (often in the feedback loop of an op-amp). My own Poinsettia is another simple example (tilt EQ). Not a plug, I promise  

[motterpaul]

Thanks! I always appreciate the theory lessons.

[inefficiency]

motterpaul, this is what I was going to use;

[motterpaul]

Thanks, I just read up on it yesterday - and in addition built the Xotic AC booster which also has a similar active tone control (in the negative feedback). It works well, but while the one I built is supposed to have a fair amount of drive it doesn't really, so I think it would work better as an EQ + boost for another overdrive circuit.

[Beaker]

Yes the AC Booster is not really an overdrive - just a boost.

Inefficiency, Fredrik's active Baxandall really is great, I've built a couple now. I'm a big fan of the Bax, as it works well, and is really versatile.

Remember Ampeg guitar amps use Baxandall tone controls, and Fredrik's layout compares very favourably to my son's Ampeg Jet.

The Runoffgroove Ginger (available on here) is a superb guitar overdrive, though it is made as a SVT in-a-box unit for bass use. It has a Baxandall tone circuit that sounds amazing.

Remember the way a Bax works though - both knobs at 12 o'clock, flat frequency. Turn knobs anti-clockwise cuts bass and treble, leaving the mids. Turn knobs clockwise increases bass and treble, scooping out the mids.

EDIT: Remember the Duncan Tone Stack Calculator has a Baxandall, so it's easy to alter it to suit your own taste.

[motterpaul]

The Xotic AC has a pretty good amount of gain - as much as many things I have built here (the RC is more of a boost than an overdrive). BUT I would like more.

People here recommended me the Thor a long time ago, and I forget why it took me a long time to get it working, but I eventually did and now I like it a lot. I have not tried the Ginger, yet, though.

What I found disappointing has been the Shin Dumulator, and I am not too impressed with JCM800. I got it working but it just doesn't light up my world, even with some mods to make it more gain.

However, I have not found anything that comes close to the AMT B1 Legend, it is by far my favorite here, and surprisingly, not many others ever mention it. It has GREAT EQ (Bass, mid, treble) and more gain on tap than anything else I have made.

[inefficiency]

When you say more gain are we talking like an "amp in a box" type Wampler thing, or just a slightly gainier overdrive?

[Beaker]

Gain as in overdrive - but there's plenty of volume too. The AC is more like a Tubescreamer than anything else - but only with the drive knob turned up about 75% if I remember right.

I built one after building the EP boost - though it never got boxed up. I do like the EP boost a lot though - but that one is purely a boost.

[motterpaul]

[quote]When you say more gain are we talking like an "amp in a box" type Wampler thing, or just a slightly gainier overdrive?


For ME, when I say gain I am referring to what most call "overdrive" - I would say "saturation" is a better definition. I prefer the tube-style harmonics; which means Jfet-style amp emulation circuits in pedals. I have not really found a fuzz or IC-based overdrive that I love.  Things like the Timmy, Xotic AC, Love Purple Plex, etc are all good enough, but don't hold up to my EVH amp, or the AMT B1 Legend.

I have a demo of the legend, it sounds unusually trebly, but I am uploading it now to YouTube.

[inefficiency]

yeah, I getcha.

One that I always really loved, but has kinda fallen out of fashion at the minute, is the Suhr Riot. I used to take it to gigs where I couldn't bring my own amp and use it as my gain channel.