Onboard single-band paramtretric EQ??

[John Catto]

Hi there!

I'm currently finishing off building a guitar similar to the Model 1 guitar built by Turner for Lindsey Buckingham. For those who aren't familiar with this it is has a single (rotatable) pickup  and a switchable single band parametric EQ to tailor this. The EQ is the remaining issue so I'm looking for suggestions. So far the best contender I've seen has been Mike Burgundy's modded Metalzone parametric http://users.balpol.tudelft.nl/~Burgundy/bin/schem/parametricbass1a.gif with values chosen to complement the guitar (Bill have you built this or is it totally theoretical?). Ideal solutions would a: have a low battery drain b: be as low noise as possible, a pre-setable internal "Q" control would be pretty cool as well, anyone got any ideas?

Also a question for RG or anyone else who's experimented with them. I've noticed that very low current drain flashing LEDs are now available, would the "clock" of these bleed into a nearby circuit as a click or other audible artifact?

For those who are interested in this stuff, here are some shots of the guitar this is going into, strung up before final finish.

http://www.mondocatto.pwp.blueyonder.co.uk/m1preview/m1bodydry-5.jpg

http://www.mondocatto.pwp.blueyonder.co.uk/m1preview/m1bodydry-3.jpg

http://www.mondocatto.pwp.blueyonder.co.uk/m1preview/m1bodydry-2.jpg

http://www.mondocatto.pwp.blueyonder.co.uk/m1preview/m1headdry-1.jpg

Cheers JC

[Alex C]

That is an absolutely beautiful instrument!  Excellent work.

Alex

[Mike Burgundy]

That's not a modded metalzone EQ, I put that one in there to show differences and peculiarities. The EQ the link points to is a straight-forward parametric using a gyrator, with parts values lifted from an SWR amp. I experimented with the values, but ended up with really liking the originals for 5-str. bass. Go SWR.
If you use low-noise, low-consumption IC's, you should be able to keep consumption down, but if you want really long battery life, some serious discrete circuit design work is in order.
Great looking guitar. Hope it sounds half as good as it looks (I'd buy one!  )

[Mike Burgundy]

I forgot to mention:
Have a look here:
http://www.geofex.com/Article_Folders/EQs/paramet.htm

[John Catto]

Thanks mike, that was definitely my confusion there, I even remember glancing at it compared to the Metalzone and thinking there were an awful lot of changes! Out of curiosity, while this is for a guitar not a bass, which were the SWR values?

[RDV]

Here's my take on R.G.'s parametric with one band. It boosts or cuts from way low to mid. Other 10 to 1 values would take the range higher. Works pretty well. The resosnance trim should be smaller, maybe 4.7k or even 1k. I barely open up the 10k I used.


RDV

[Mike Burgundy]

the SWR values are the schem pointed at above. The original SWR (SM400 series) also had a fixed gyrator bass control (Rq=0, R1=2k2, C1=10u, C2=0.01u, and a 120k resistor for frequency (instead of the 33k and pot) and a cap-to-ground type treble control. Same boost/cut setup, but instead of the gyrator a 3k3 and .048u cap to ground.

There's also a guitar parametric at
http://users.balpol.tudelft.nl/~Burgundy/bin/schem/parametricguitarhybrid.gif
which has that type of extra controls.
The Metalzone EQ is at http://users.balpol.tudelft.nl/~Burgundy/bin/schem/parametricmetalzone.gif

RG's article is very nice: it explains how to calculate your own frequencies. I actually like to stick all that in a spreadsheet and muck about with the values  before I start building.

[gez]

If you want to go overboard on this, Rapid Electonics sell LA3607 (7-band graphic equaliser) chips.  Not that low in current consumtion though (7mA?).  Haven't tried them, but would be low parts count (apart from the pots/sliders)

www.rapidelectronics.co.uk

nice pics!!!

[John Catto]

Thanks Mike, it all becomes clear now, especially the universalness  of the circuit used. I assume when you built the preamp then you did it as a 4 band, yeah? I also assume that the buffer at the front is necessary to isolate the filter section from interacting with  high impedance sources (the pickup) in front of it.

Any idea on the flashing LED thing, can they introduce noise into the circuit? It only appeals since it knocks consumption down quite a bit since there will be an LED to show that the parametric is engaged.

Cheers

John

[Mark Hammer]

I don't know how the hell you expect to play that thing.  I imagine it will take you 3 years just to stop looking at it!  Simply a stunningly picturesque piece a of work, John.  Haven't seen you posting here for a while, but you make a stylish re-entrance.

I think it is worth considering that what makes for a useful on-board tone-shaping circuit in one context will not necessarily be optimal in another.  In this case, the use of a single, centre-mounted,  re-orientable poickup is radically different than working with 2 or 3 pickups that span the sensing map from end-of-neck to bridge.  In those instances, radical tonal change is achieved simply by changing pickups, so the tone-control has less work to do.

I think one needs to divide up the tonal shaping workload between 3 or 4 players: your fingers, the pickups and switching, the amp controls, and stuff in between the guitar and amp (which could be on the floor, on the board, or in the guitar).  Since, for performance purposes at any rate, it is awkward to approach one's amp for tonal readjustment,  I like to have baseline/foundation tone control at the amp, fine-tuning on the floor, and wholesale re-voicing in the guitar.  I don't want to have to go to the amp and risk feedback (or bend over for that matter), and whatever substantive changes in tone I might think I need to support what I want to sound like *this minute*, I want to have instantly available.

So the more practical question is "What can you NOT do in the way of re-voicing the instrument" on the guitar itself, given the pickup and pickup arrangement?"  Personally, I've done the "Hendrix Strat" re-orientation of the bridge pickup, and there is clearly different harmonic emphasis, string-to-string, when the pickup is tilted the other way.  But tilting the pickup the other way when it is smack in the middle is probably a different beast.

Keep in mind I'm purely guessing here, but my sense is that pickup tilt would not result in the wholesale change in emphasis of upper bass that one would note in switching from neck to bridge, or from neck to middle on a Strat.  So, taking that inference at face value, I'm going to go out on a limb and suggest that maybe what you want is the following:

a) a broad resonant filter (boost and cut) that covers a lot of ground from bass to lower mids, and maybe even a little asymmetrical in its coverage so that lower mids are less affected by the boosting and cutting action than the majority of the bass end.

b) a variable lowpass filter, maybe even 2-pole, rather than traditional treble bleed at fixed frequency,

c) some degree of gain to offset the signal level change imposed by the resonant filter

Being able to broadly notch the sound and open up the lowpass filter will yield tones more in the Strat-position-2/4 zone, while goosing the resonant band a bit and rolling back the highs will yield more LP type tones.  The basic notion is that if you want to sound thin, a few tweaks will take you there, and if you want to sound fat and thick, a few tweaks will take you there too.  As has been discussed in other threads here, people tend to overlook the virtues of a broad notch, complemented by some gain control, as a means of achieving both apparent treble and bass boost.  My sense, though, is that surface-controls for doing more than simply boosting/cutting the resonant filter  (e.g., Q, center frequency) is asking for distractions.  Whether those distractions are distracting would depend on your intended use for the instrument.  Guitars vary from get-in-there-and-play instruments to recording control consoles that just happen to have the neck and strings conveniently located nearby.  Depending on where you intend to situate this beast, what I suggested may be not enough, or may well be overkill.

T'wer me, I'd go with 4 controls:
- a compensated volume control with an over-value cap to take care of bass rolloff (going higher than the usual 180-220pf cap on a standard Tele-type volume control starts to act as a bass rolloff more than merely a treble preserver - personally, I like 1500pf on a 500k pot)
- the aforementioned asymmetrical broad notch/resonant-boost
- the aforementioned variable-rolloff lowpass filter
- a gain-recovery volume control (and this would be the one mounted closest to your picking hand, rather than the other volume control)

[gez]

Whoops, sorry John didn't pay attention to the 'single' in the thread title... :oops:

[John Catto]

Thanks for all the ideas guys, here's the control layout as planned, it's pretty much straight off the Turner/Buckingham model 1 though I've switched the LED and switch positions around (easy to make an 11th hour decision about this since they use the same size hole!).

When the EQ is switched out all the active circuitry is right out, it acts more or less like a Les Paul Junior. In fact since this is a 24 fret guitar the pickup isn't as far forward as it initially looks, it's more where the middle pickup would be in a Les Paul (if it had one), Mark I think you're right in thinking that rotating the pickup won't make much easily discernable difference, it's more of a "trick" detail to play with, it's locked in place with an allen keyed bolt.  The idea (as explored on the Turner guitars it's modeled on) is to be able to just tweak the tone for a second switchable sound with a pretty wide "Q" ie. depending on what the cut/boost and sweep controls are doing to say thin the mids, or add a bit of high end, or exaggerate the bottom end, add a wah like mid vowel sound, hook into a feedback sweet spot etc. I think adding an internally adjusted "Q" would be a good idea as would (depending on how gainy the circuit turns out to be) an internal trimpot for gain so when the cut/boost is centred it's at unity gain. This of course isn't an original idea, it's Turners,  but I think it's going to be fun to develop and play with.

BTW thanks for all the nice comments on the guitar! If you click on my www link it takes you to a page with some of the other guitars I've built including my most recently finished one which is a Zemaitis style Metaltop.

[Ge_Whiz]

Lovely guitars, John. Could I ask how you engraved that gorgeous metaltop?

[Rob Strand]

John, the gyrator types like the SWR are the simplest and do a reasonable job provided you keep the range of frequency adjustment to a minimum (say a range of 4:1).  The Q on these units actually varies with both frequency and the amount of boost (Q can vary a *lot* here).

The next type is that used MusicMan bass amps.  The Q on these varies less with boost and does not vary with frequency.  This design still has minimal opamp count.  Frequency adjustment requires a dual frequency pot.  Variable Q requires switching-in a different pair of caps.

The next type is the state variable based parametric.  These are similar in characteristics to the Music man type.  This design requires more opamps but it has the added feature of variable Q - but it requires a dual Q pot (so no interally Q adjustment with a trimmer).

Yet another type is that used be the Rane company.  The Rane circuit (and others) use a tapped gain pot, which are hard to get.  The tapped gain pot helps reduce Q variations with the amount of boost and cut.

Another circuit to check out is that used on later Fender Bass amplifiers.

You will find many other circuits.  Most of these are a little dodgy in on way or another.   The above bunch are IMHO are the least problematic, and amongst them you can see a direct trade of between functionality and complexity.

Putting that aside, if you don't get your frequency range, amount of boost/cut and Q's right, it doesn't matter what circuit you use it won't sound right!

[petemoore]

When you said homemade, I'd not envisioned what the pic is of: What a guitar!! 11..off the hook.
  Just had to comment on the Axe...Stunningly Beautiful.

[John Catto]

Lovely guitars, John. Could I ask how you engraved that gorgeous metaltop?

Sure, It's actually all acid etched. I did all the artwork for the flat metal parts (top, truss cover and jackplate) in Illustrator and Photoshop then had a commercial etcher/engraver (Mercury Engraving in London) do the work, they did a fantastic job IMO, I chose them because they were one of the few who understood what I was looking to achieve in this.

[gez]

I did all the artwork for the flat metal parts (top, truss cover and jackplate) in Illustrator and Photoshop then had a commercial etcher/engraver (Mercury Engraving in London) do the work, they did a fantastic job IMO, I chose them because they were one of the few who understood what I was looking to achieve in this.

If you don't mind John, how much do they charge for such a job? (I'm looking to get some boxes engraved a little further down the line).

PS  Had a look at your website, outstanding!  Do you do this for a living?

[John Catto]

All in all including cutting out and drilling the stainless steel it was a tad under £200 (£145 plus VAT plus some extra I paid them to drill all the control and mounting holes, I was going to do that myself but got stumped by the stainless steel  :wink:). Looking at the original quote the etch job by itself including materials was £115 plus VAT so I guess you could get a bunch of top plates for boxes done for that on one sheet. A lot of the cost is in the setup so it should get cheaper the more you get done. Materials they work with include Brass, anodised Aluminium, satin stainless (what I used) and high polish stainless (looks like chrome), non anodised Aluminium seems to be a problem since it etches out of control and it's hard to get a good result with fine detail.

I'm a total hobbyist though I've built guitars off and on as long as I've played them.

[gez]

Thanks!