The CVQ, and what does it do precisly?

[lg71]

I know about the Alembic Low pass filter and the Q-Switch, which boost at the cut off points, which is what you'd get on a music synthesizer and is called Resonance...
 
I know what Band pass, High pas, Notch Filters and so on do...
 
But the CVQ, what does it do exactly and precisely?  
 
Is it used in conjunction with the Low pass filter and Q-Switch?
or does it replace one of them, or both?
 
Any specs/details out there please?
 
Thanks,
LG

[lg71]

Ok, I think I figured by myself, maybe I am wrong...
 
If we compare the CVQ and Q-Switch to the parameter called Resonance on a music Synthesizer, we could say that:
The 3-positions Q-switch is like a preset resonance, with only three settings, flat, +6 db and +9 db (if I am right with those numbers...)
The CVQ would simply be like the full Resonance parameter, without steps, but smooth, controlled + variable, obviously.
 
So if I am right, what's the boost figure in db?  
 
I also though that it would be nice to be able to controlled the width of the Q itself, which is called Q on a full parametric EQ in fact, and I am also wondering why Alembic didn't decide to name the Q-swicth a resonance switch? When think of Q, I always think of narrow or wide Q, like on a parametric EQ...
 
Anyone?

[bsee]

The Q switch is 0dB / +6dB / +9dB on Series I and, 0dB / +8dB on non-Series basses.  The CVQ is continuously variable 0 - +15dB.  A filter with no switch, as on an Essence package, is hard-wired to +8dB.  
 
Custom builds with different parameters are always possible.

[lg71]

Thanks Bsee.
 
CVQ, offers +15db! this is quite a big difference, and a nice one.
- Do you think that it would be straight forward to alter the Q-swicth to do 0/+9 db/+15 db?
Because I hardly use the + 6db personally, it's usually flat or + 9 db...
 
- Are you certain that the Filter module has a +8 db boost?
I guess that would apply to all filters then...
 
(Message edited by LG71 on September 16, 2006)

[dfung60]

You're basically at all the answers here, but I'll add a few notes.
 
CVQ = continuously variable Q.  It is exactly as you've surmised.  The Q-switch has three resistors wired to the switch positions that yield the various frequency curves; the CVQ replaces the switch with a potentiometer which can dial up any resistance in it's range.  
 
The Q-control is controlling the amplitude of the peak at the filter's resonant frequency.  The tone knob is controlling the resonant frequency itself.  As you mention, those are two of the three functions of a fully parametric EQ.  The third is what is usually called the Q or filter width.  That's preset on this circuit, I think mostly because it would be too hard for most people to get their heads around what the three knobs were doing.  
 
You can customize your Q-switch by selecting the resistance values that give you the curves you want and replacing the ones in there now.  In an earlier discussion (which I'm too lazy to look up), I suggested that you might want to pull the middle position resistor and replace it with a small trimpot.  That will give the middle position CVQ functionality, but you'll also still be able to instantly switch between EQ curves.  If there's anything to complain about on a Series II, it's that the CVQ is hard to return to specific positions if you like different EQ settings.  This would fix that problem, quite elegantly.
 
David Fung

[lg71]

Sorry, posted twice...
 
(Message edited by LG71 on September 18, 2006)

[lg71]

Hi David, thanks for the great tips.
 
Would any trim pots or pots do the job, or would I need something very specific?
 
Is this replacement as simple and straight forward than it sounds?
 
LG

[David Houck]

LG; are you looking at doing this on your Aria or your Persuader?  The reason I ask is that, in my opinion, do-it-yourself mods with non-Alembic parts tend to significantly reduce the resale value of an Alembic bass.  But that's just me; others may have differing but reasonably valid views.

[lg71]

Good point Dave;)
I don't have the Persuader anymore, so I am thinking about the Arialembic... I am not planing to use non Alembic parts, first I need to know if it can be done as simply as David said, then I'll need to know if Mica would sell me the part(s), I am up for some DIY to keep the cost down...
You know, I am a control freak, and I know what I want but cannot afford to have it done, so I am prepare to do it myself within reason.  
 
I'd love to have a fully parametric filter for each pickup, with 15 db boost/cut and being able to use it narrow or wide, and a frequency response from around 40Hz to 8 kHz. And the option to switch back to the low pass filter at the flick of a switch... even further, having both options available at the same time for each pickups. I'll get there slowly...
 
I have my personal reason for wanting so much control, one of them is that I'd like to be able to duplicate the sound of various basses, and this just can't be done with a low pass filter and Q-switch or CVQ either. I wish I could be involved with Alembic somehow, for some interesting suggestions propositions. The engineers are not always the ones who know what is really needed. Having great knowledge is one thing, having great creativity is another one, both work together. I think it is time for Alembic to switch to the next level, Series 3...  
 
You see I was playing with synthesizers when I was younger, I was very comfortable and understood what the filters did, and the thing is, I have learnt about mixing and why not one bass will cut through every song in the world, because of the element surrounding... especially these days, with all the tools available.  
 
For instance, My Aria SB1000 doesn't sound like my Arialembic,  
the pickups design is similar in bracket, but the tone control is day and night... the SB1000 has got six preset notch filters you see, and it is a real pleasure to flick through... As I said, it is day and night, but for someone like me who cannot afford every bass in the world, and most importantly, I WANT to play one bass and only, the one that will give me the biggest palette of sound + great feel, I don't want to keep swapping basses, because they all sound different, wide fingerboard, narrow, heavy, light and so on... you see, I don't want that, so gradually, one of little dream is to have my Alembic electronics taken beyond custom, ASAIK there is no Alembic out there with the features I am after, yet, I KNOW that for someone like Ron, it would be Piece of Cake to make it happen. What else, if it cannot be done with the Alembic electronics for some reason, I'll hunt elsewhere... And if I get tired, I'll take a break  LOL

[dfung60]

A trimpot is just a small size potentiometer which is adjusted with a screwdriver rather than having a shaft and knob.  You would put this somewhere inside the control cavity, and pull the back plate to tweak it.  There's no reason you couldn't put a regular potentiometer there too, but then you'd need to drill a hole for the shaft.  These trimpots are intended to allow for calibration and adjustment, so they're not designed to be turned a lot - many of them are only spec'ed for a couple of hundred turns before they need to be replaced.
 
I don't think the brand of the trimpot matters too much.  An expensive one will be more precise but it's unlikely that precision will really matter much in this application.  You want to select the same value of trimpot as the CVQ pot for starters, which is...  well, I don't know what it is off the top of my head.  My Series IIs are hidden in the back of the closet right now, so hopefully somebody else can take a peek more quickly than I can.  
 
These parts aren't very expensive - I believe that Alembic is using the fanciest conductive plastic Bourns parts in their circuits (these are the little blue boxes) and they probably are no more than a couple of bucks each (less than a dollar each when purchased at a electronics parts dealer, but you may have a hard time buying less than 500 of them!).  Since the kind of mod I'm talking about here isn't something that Alembic normally does, they may not stock the value you'd need.  This mod would only be a couple of bucks - you simply wire the trimpot in where a resistor is now, then glue the trimpot down somewhere so it doesn't short out.
 
I think a fully parametric EQ is an interesting idea too (and probably not all that hard to do), but the problem is that it spawns many switches and knobs which can't be described or tweaked easily.  On the occasions that I find an instrument with a varitone knob (an old BC Rich or Haegstrom), I find it interesting for a few minutes, but pretty quickly flip to the position with the least effect and leave it there for the rest of the time I'm playing with it.
 
The dream EQ you talk about is interesting too, but pretty hard to do.  Because different basses are mechanically different (different woods, through-body, bolt-on, etc.) it's very hard to replicate different instruments with simple filters like this.  One part of the problem is that it would take a cascade of tunable filters to recreate the resonsances and formants of a particular instrument.  Even then, filters can't very easily model the envelope of the note which is much more distinctive than the tone.  
 
This kind of modelling can be attempted digitally, which is what something like a Line 6 Variax bass is doing.  In the DSP, they can build very complex filter models that have both fixed frequency and frequency-related functionality.  To really make it a convincing duplicate, you need a lot more horsepower and software than something like a Variax and it may be challenging on even a very powerful ProTools system.

[adriaan]

AFAIK, Alembic will only add CVQ to Series electronics. Sounds like it's not quite as simple as substituting a potentiometer for a switch.

[lg71]

Dave, I know what your saying about differences in woods, pickups and so on... I didn't mean 100% cloning though. I know about DSP being an other option, but this would be emulating the characteristic digitally, and I am not thinking about that. I want the Analog option, and by myself I won't be able to achieve this. I can solder, I have got ideas, but that's it really, if know one show me what to replace with what, I wouldn't go far... lol  
 
Here are some of my ideas;
 
Take the Alembic low pass filter and the Q-switch, add a CVQ, so we have three parts...
 
The Filter gets upgraded/tweaked to act as a low pass filter as well as a peaking filter.
The Q-switch get tweaked to offer three different function that work in conjunction with the CVQ like so;
- setting 1 on the switch makes the filter act as a low pass filter (as before) and the CVQ does what it did...
- setting 2 on the switch makes the filter act as a peaking filter and the CVQ will boost the chosen frequency by
the filter, from 0 to whatever is useable...
- setting 3 on the switch still makes the filter act as a peaking filter, but REVERSED  so cuts instead of boosting,
in conjunction with the CVQ.  
 
So in fact the CVQ keeps doing what is was doing, going from 0 db to + 15 db for instance, but the filter becomes
a dual filter on the same board, and the Q-switch becomes a filter selector, low pass, boost/PEAK or cut/NOTCH...
 
Further the Alembic pan/balance, can become a Boost Cut and giving 0 db at the centre. So, it could replace the CVQ pot.
 
Still further, make two filters instead of one, so you get a low pass filter as well as a parametric filter at the same time.
 
Beyond further... make the slope adjustable on the Low pass filter, and the parametric filter becomes fully parametric.
 
I know that most of you might be thinking this is ridiculous: BUT, believe me, once you know exactly what everything does,
and how it would shape the sound of your instrument... you'll probably start thinking like me.
 
THIS is possible, Ron can EASILY do it, and I know so, just by seeing what he's already done, like the SF-2 for example...

[lg71]

I just came across this VERY interesting page on the subject; Over here!