Active eq/pre for bass guitar?

[Tha’ToneSeaQr]

Hey all! PedalPCB has the largest and most diverse selection of circuits available of any pcb/diy instrument fx site Im aware of.. By a pretty wide margin! But unfortunately, like most others the focus is placed heavily (if not exclusively) upon electric guitar fx.. Which totally understand, because it makes a ton of sense from a practical/business standpoint.
I play guitar as well as bass and the type & number of pedals on my guitar board completely dwarfs my mini bass board!! And two of the maybe 4 fx on the bass board are a tuner & a buffered DI so..

-Anyway, Obviously “guitar-centric” preamp & eq designs can be modified in the parts selection to be more bass appropriate. But I’m not sure which PCB’s here would be best suited to this.. Could some of you folks here with more experience recommend a couple specific PCB’s as a starting point??
**What I’m looking for is ideally; A completely clean, Active (boost/cut), 3-band EQ with frequencies @ about~> 40hz, 550hz, 8khz roughly low-high. A semi-parametric sweepable midrange would really be fantastic! As would “deep/bright” switches to allow for different frequencies or hi/lo db emphasis.. But I that’d be gravy & I understand likely wouldn’t be possible anyway but.. Yeah thanks in advance!!

 

[Feral Feline]

Plenty of suggestions/threads on bass FX here.

As for your more specific bass EQ enquiries... you'll have to make some adjustments/mods if you want to fill all your tick-boxes.

Have a gander at the
- Cold Turkey EQ — Defunct HBE's boost/cut 3-band; you'll have to tweak the freqs.
- BoxandAll EQ — EQD's 3-band bax, tweaking again most likely.
- EQ, ANYONE? — Nathan East's sig parmetric; here's a PDF-promo for the NE-1. Bass-specific already, but doesn't tick all boxes.
- Equilux and Mini — Pultec style, worth a butcher's.
- Pro-Filter — Craig Anderton's super-duper tone control.

That'd be my top 5 to deliberate upon (six if you include the compact EQuilux Mini).

For what you described, I'd consider tailoring the Cold Turkey to your Freq preferences;
once satisfied with that you could then further tweak it to have sweepable midrange. Get that dialed, then it's the...
Deep/Bright switches — that's uncharted territory for me.




The best EQ-related device you could possibly get for bass, IMO, is the Frequency Interchange Filter — an HPF/LPF.
HPF was the best thing I ever purchased for bass.

 

[JTEX]

HPF was the best thing I ever purchased for bass.

I keep hearing about HPF's for bass and can't imagine why anybody would want to use one. Why would you want to filter out the bass on a... bass? Inquiring minds need to know.

 

[Passinwind]

I keep hearing about HPF's for bass and can't imagine why anybody would want to use one. Why would you want to filter out the bass on a... bass? Inquiring minds need to know.

Because the sub-fundamental content is often inharmonic, creates distortion, stresses loudspeakers, and your mom hates it.

There's also another less obvious use for an HPF: it often allows you to boost your amp's bass control more, without flub, and you can also tailor the peak frequency over a pretty wide range, sometimes allowing you to skirt nasty room nodes that manifest as boom, mud, etc.

 

[Passinwind]

-Anyway, Obviously “guitar-centric” preamp & eq designs can be modified in the parts selection to be more bass appropriate. But I’m not sure which PCB’s here would be best suited to this.. Could some of you folks here with more experience recommend a couple specific PCB’s as a starting point??
**What I’m looking for is ideally; A completely clean, Active (boost/cut), 3-band EQ with frequencies @ about~> 40hz, 550hz, 8khz roughly low-high. A semi-parametric sweepable midrange would really be fantastic! As would “deep/bright” switches to allow for different frequencies or hi/lo db emphasis.. But I that’d be gravy & I understand likely wouldn’t be possible anyway but.. Yeah thanks in advance!!

Whenever I finally finish up my through-hole open source bass EQ project there's a good chance Robert may spin off a PPCB board. Meanwhile, there's the considerably more complex part-SMD one, which is at v4: https://github.com/Passinwind/PW3B-LPF

I have another one in the works with a fully parametric EQ section for mids as well, that runs on internal +/- 15V derived from a standard 9V supply. Nearly everything I design is open source and I don't sell hardware except in a very few cases, usually when I have surplus prototypes or am doing custom builds for friends and family.

All of @Feral Feline's suggestions are worthy, might as well build them all!

 

[Feral Feline]

I keep hearing about HPF's for bass and can't imagine why anybody would want to use one. Why would you want to filter out the bass on a... bass? Inquiring minds need to know.

Charlie beat me to it, and put it better than I ever could but ...

Storytime...

I lent my FDeck HPF-Pre V3 to a friend, he gave it back to me just before a gig and must've mistakenly left it plugged in — so the battery was dead (normally I don't use batteries but this was a just-Bass,-HPF-and-Tuner type of gig).
This pre is meant to attach to my bass' tailpiece, but I prefer not to have anything on the tailpiece and I put the pre on the floor. Since it's meant to stay put on the tail-piece, the battery cutoff is on the OUTPUT, not the input as per most pedals, though I told my friend to unplug it completely... Anyway, I'm not gigging at the moment, so building my own F-Deck in proper pedal-format is on hold. So, enough explaining why my friend let the battery die, back to the gig.

Of course I arrived just on the downbeat, and the HPF-Pre was dead, so I was going direct into the backline in this little club (aside: I hate Hartke alloy cones for DB!) and if I turned up enough to hear anything it was just a bunch of out-of-control boominess — low fecal-sea rumble — I couldn't hear any notes, just a low-freq smear. Myself, the band, and the club patrons all suffered throughout the first set.

Break-time: installed a new battery.

2nd Set: Dialed in my HPF to tighten up the low-end — no more deafening throbbing wubb-wubb-wubb-wubb, just clean and clear low frequencies, tight bass tones. No longer did I have to fight my DB's feedback, cause there wasn't any — no longer did the club sound like it was in a crappy sub-woofer of some shitty econo-car.
I played better because I could hear my intonation at last, I smiled, my bandmates smiled, the pub-patrons smiled...

I'd always thought HPF helped, but that gig was when I KNEW it was mandatory for me.

 

[JTEX]

Because the sub-fundamental content is often inharmonic, creates distortion, stresses loudspeakers, and your mom hates it.

There's also another less obvious use for an HPF: it often allows you to boost your amp's bass control more, without flub, and you can also tailor the peak frequency over a pretty wide range, sometimes allowing you to skirt nasty room nodes that manifest as boom, mud, etc.

Food for thought. I have to try one now. It might help keep woofer cones from flying across the room when slapping.
Still not sure about ever wanting to cut anything below about 40hz though.

I had an epiphany a few years ago. A friend of mine who's a sound engineer said that what we actually hear most of the time in a bass is not the fundamental, but its first harmonic, which is often actually louder. I didn't believe him until I put a spectrum analyzer on a bass. I, for one, like to hear my fundamental. It seems that only really good basses have it at a nice solid level relative the 1st harmonic. My Modulus had it big time. My Steinberger too.

 

[JTEX]

I'd always thought HPF helped, but that gig was when I KNEW it was mandatory for me.

Sounds like I'd want a fixed HPF set to about 30Hz.

 

[Passinwind]

Food for thought. I have to try one now. It might help keep woofer cones from flying across the room when slapping.
Still not sure about ever wanting to cut anything below about 40hz though.

I had an epiphany a few years ago. A friend of mine who's a sound engineer said that what we actually hear most of the time in a bass is not the fundamental, but its first harmonic, which is often actually louder. I didn't believe him until I put a spectrum analyzer on a bass. I, for one, like to hear my fundamental. It seems that only really good basses have it at a nice solid level relative the 1st harmonic. My Modulus had it big time. My Steinberger too.

There's a long older thread of waterfall graphs for several different basses on Talkbass, but unfortunately a software update ate many useful contributions. Somewhere in there I posted a blind A/B test, with predictably interesting results.
By the time we get to the G string the fundamental/harmonic ratios skew a lot more tight, whereas as my friend's 12 Hz and 20Hz Knuckle Bass builds definitely benefit greatly from a much higher hinge point than you might expect (ie still 30-40Hz dpensing on what cabs you have), it's the harmonic series above fundamental that make pyschoacoustics work to make it even sound like a really low note. Playing those things is pretty strange, when you finally get to 40Hz way up on thj little strings it suddenly starts sounding more like what most of think a bass sounds like.

I's suggest starting with the now common fixed second order +variable second order format, with -3dB points adjustable from say 25Hz-100Hz. The ones in my preamps and amps are a little different, as you can see in the GitHub link I posted above. There's a board share on OSHPark and I'll be posting details on the standalone one later this week. You'd already know what to do though, I think. The PPCB board @Feral Feline mentioned looks good too though.

 

[JTEX]

There's a long older thread of waterfall graphs for several different basses on Talkbass, but unfortunately a software update ate many useful contributions. Somewhere in there I posted a blind A/B test, with predictably interesting results.
By the time we get to the G string the fundamental/harmonic ratios skew a lot more tight, whereas as my friend's 12 Hz and 20Hz Knuckle Bass builds definitely benefit greatly from a much higher hinge point than you might expect (ie still 30-40Hz dpensing on what cabs you have), it's the harmonic series above fundamental that make pyschoacoustics work to make it even sound like a really low note. Playing those things is pretty strange, when you finally get to 40Hz way up on thj little strings it suddenly starts sounding more like what most of think a bass sounds like.

I's suggest starting with the now common fixed second order +variable second order format, with -3dB points adjustable from say 25Hz-100Hz. The ones in my preamps and amps are a little different, as you can see in the GitHub link I posted above. There's a board share on OSHPark and I'll be posting details on the standalone one later this week. You'd already know what to do though, I think. The PPCB board @Feral Feline mentioned looks good too though.

I hadn't given it much thought before, but my Distiller filter already happens to have a subsonic filter in it (-3dB at 10Hz or so), thanks to some AC coupling caps that I didn't make much bigger than needed (btw, Alembic DC-coupled their filter to the pickups. Wierd!). Now I just have to tweak a couple of values to bring the 3dB point up to 30Hz or so, and call it a "feature" . Gotta do some listening tests. A bit concerned abot the phase shift it would add in the lowest lows vs harmonics.

 

[Passinwind]

I hadn't given it much thought before, but my Distiller filter already happens to have a subsonic filter in it (-3dB at 10Hz or so), thanks to some AC coupling caps that I didn't make much bigger than needed (btw, Alembic DC-coupled their filter to the pickups. Wierd!). Now I just have to tweak a couple of values to bring the 3dB point up to 30Hz or so, and call it a "feature" . Gotta do some listening tests. A bit concerned abot the phase shift it would add in the lowest lows vs harmonics.

That phase shift is actually your friend once you suss how to balance the tradeoffs, it's what makes pretty much all EQ even work. But you're on a good track with incorporating pre-existing rolloffs into overall system response, IMO and IME. A lot of people find it beneficial to put a small boost resonance at the lowest HPF cutoff point too, not too unlike what your Distiller or my resonant LPF implementation does at the other end.

And a variable high order HPF is definitely not a panacea, rather another tool in the box that can solve some problems but also create different ones, because no free lunch.

Also, most modern bass amps have at least a fixed HPF built in, my year old Traynor SB200 is second order at around 50Hz, and sounds fab even with my EUB, which definitely makes a ton of fundamental. Ported speakers starting unloading the cone below box tuning, which can suck up headroom in a serious way. Maybe any of this matters to you, maybe not though!

 

[Feral Feline]

Sounds like I'd want a fixed HPF set to about 30Hz.

Fits your needs = perfect!

I really didn't think I'd want anything cut above 40Hz, given Low E at 41.2Hz and I don't have anything tuned to Low B or Low A. I always set HPF as low as possible but I've been surprised by how high I've ventured — all depends on the environment. I just twist the HPF 'til it sounds good, then wiggle it a bit above and below that to make sure it's where I want it.


Do you want to try the Fdeck? I could send it over for you to play around with it.

 

[JTEX]

Do you want to try the Fdeck? I could send it over for you to play around with it.

What's an Fdeck? I'm sure it's something cool, and nice of you to offer, but I'm swamped at the moment and terrible at multi-tasking...

 

[Feral Feline]

What's an Fdeck? I'm sure it's something cool, and nice of you to offer, but I'm swamped at the moment and terrible at multi-tasking...

Francis Deck is who made my HPF; he sells them as a sideline to his regular job. Very well built, highly regarded in the bass community. Better still, he made the circuit public, so you can build one for yourself, or just breadboard it.

The Series 3 Mini is new to me! If it had been available when I bought my Series 3, I would've gone for the Mini — as you can see, the Series 3 isn't as pedalboard friendly as the Mini.


While I originally wanted to build a PB-friendly "FDeck", there are a lot more DIY options out there now. Even though I have the Series 3 already, I'm still thinking of building an FDeck, something from Passin' Wind's camp, and I have the PPCB HPF/LPF to build and similar HPF/LPF stuff from SchallTechnik_04.

 

[JTEX]

Francis Deck is who made my HPF; he sells them as a sideline to his regular job.

I read up a litle bit and noticed that this was mostly intended for double bass with piezo pickups. Now it all makes sense. Big thumps from body hits to piezo-equipped instruments could totally ruin woofers. It's less of a problem for electromagnetic pickups, but it can still be an issue. A good bass amp ought to be designed to deal with anything that comes out of a bass, though - thumps, thwacks, strings crashing into pickups and all.

 

[Passinwind]

I read up a litle bit and noticed that this was mostly intended for double bass with piezo pickups. Now it all makes sense. Big thumps from body hits to piezo-equipped instruments could totally ruin woofers. It's less of a problem for electromagnetic pickups, but it can still be an issue. A good bass amp ought to be designed to deal with anything that comes out of a bass, though - thumps, thwacks, strings crashing into pickups and all.

Only his first couple of versions were primarily URB centric. The latest one is definitely more useful for bass guitar too, and the next one that’s on the way even more so from what he’s told me. But you’re correct IMO, which is why so many contemporary manufacturers like Mesa, Genzler, Bergantino, etc. include variable 4th order HPFs in their amps’s feature sets these days. I came up when DC coupled power amps were common, and a whole lot of stuff done got blowed up back in the Stoned Ages.

I often run a 700 watt @4ohm head into a single 4 ohm 112 cab with box tuning in the low 50Hz range. Thermal rating of the custom driver is 450 watts RMS, but the realistic mechanical rating would be considerably less, especially below box tuning. If you look at the cab plans Eminence publishes many explicitly state power ratings dependent on using an HPF at some specific cutoff frequency. There’s quite a bit to unpack here, but the bottom line is that it can be a useful tool in many scenarios, especially with the prevalence of very high power bass amps these days.

 

[Feral Feline]

Yeah, Series 3 (the one I have) is also suitable for slabs.

 

[phi1]

The Unicab has gotten a few good mentions on the forum for bass

 

[Tha’ToneSeaQr]

Only his first couple of versions were primarily URB centric. The latest one is definitely more useful for bass guitar too, and the next one that’s on the way even more so from what he’s told me. But you’re correct IMO, which is why so many contemporary manufacturers like Mesa, Genzler, Bergantino, etc. include variable 4th order HPFs in their amps’s feature sets these days. I came up when DC coupled power amps were common, and a whole lot stuff done got blowed up back in the Stoned Ages.

I often run a 700 watt @4ohm head into a single 4 ohm 112 cab with box tuning in the low 50Hz range. Thermal rating of the custom driver is 450 watts RMS, but the realistic mechanical rating would be considerably less, especially below box tuning. If you look at the cab plans Eminence publishes many explicitly state power ratings dependent on using an HPF at some specific cutoff frequency. There’s quite a bit to unpack here, but the bottom line is that it can be a useful tool in many scenarios, especially with the prevalence of very high power bass amps these days.

First off thank you so much for offering to share your eq circuit design projects with me!
Reading through your posts left me with the very strong impression that you’re knowledgeable on the nitty gritty aspects of speaker cone/magnet materials or theoretical aspects of how differing dimensions in cabinet construction effects sound production levels @specific frequencies… For example
-How crafty are you at identifying specific components in a preamp schematic that you want to alter in resistance & capacitance to raise or lower a certain frequency..? And can you work around/compensate for unknown variables or values when calculating those frequencies??

**I realize some of this may sound like the kind of thing where; “if you have to ask the question, you probably shouldn’t be attempting this project yet”. Which is something I’ve been told many times in forums & by the robots.. Um, I mean people working at GC (The Centers for Guitars ) but Ive always soldiered on despite them l and in doing so have come a REALLY long way from the time I called up Paul Cochrane to ask him if a 275v 22awg stranded wire would work in place of the 600v 22awg stranded wire I’d broken deoxit’ing the pots.. Haha!!

 

[Tha’ToneSeaQr]

@Feral Feline Thanks!! This definitely gives me a really good starting point. Obviously there’s some things I need to work out if I hope to get in the ballpark of what I want from these circuits. And I very likely will need the help of all the folks here throughout the process if I want any chance of success!