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Any Filter-based outboard preamps other than Alembic?

rogerbmiller

rogerbmiller

Gold Supporting Member
Sep 16, 2003
7,103
5,922
NYC
#1
So I am trying to marry my love of my passive basses with my love of filter-based electronics without modding and wondering if there are any outboard preamps that employ filtering other than the Alembic models.

Mind you I have nothing against Alembics, in fact they are in many ways the benchmark but I don't want to spend $1200 on an SF2.

Any suggestions are quite welcome.

Thanks.


Roger
 
#4
If you know someone who can read a schematic, I posted a design for a simplified filter pre a month or two ago.

Here's the post. I've since made three or four versions of this idea, tweaked for various basses etc. I made one for a stingray(ish) bass the other day, but I've lent it to a mate. I'll post some sounds in a few days when I get it back.

Instead of a pot for resonance, there's just a switch. There's only two settings shown, but there's no reason you couldn't have a rotary switch for 5 or 6. And the sweep control has to be a dual gang, reverse log pot, but you can get these on e bay pretty easily. There's no reason you couldn't make this into a pedal.
 
#6
Technically all preamps are "filter based" but if you want the exact kind of filter that Alembic uses I believe the article that RobbieK linked to has a lot of information about them. I am seriously thinking about putting a homemade Sallen-Key preamp in my fretless Jazz. However, if AGC or someone else has the preamp you want as an in-bass version you can indeed put the preamp in an outboard box or an old pedal housing. You would think that someone would be making one you could just buy in pedal form by now and maybe they do, I am just not that familiar with the pedal marketplace. I do have a couple of Zoom multieffects pedals but if any of them have a variable Q LPF type preamp/filter you never would know that from the rather spartan descriptions that Zoom gives you. One of these days I will sit down with these pedals and a digital oscilloscope to figure out what the filter models actually do....
 
#10
Are you talking about a "variable Q" tone filter (sometimes called "sweepable") vs the more usual T/B boost & cut variety?

FWIW there's many onboard preamps that include a sweepable midrange control that'll give you that, plus the regular bass and treble boost & cut, all in one neat package.
 
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#11
Feel free to check out my recent thread on my Craig Anderton Super Tone Control:

Now liking a SS preamp... | TalkBass.com

It's a three band state variable filter with separate mix controls for LP, BP and HP and the BP region can be anywhere in the audio band. Also has resonance.

Unfortunately, PAiA electronics no longer sells that parts kit and circuit board. I built two of them about 30 years ago and still use one daily.

Otto
 
#12
Dtar Equinox by Rick Turner (Alembic cofounder). It's intended as an acoustic guitar pre but I use it in my effect loop just for the filters. Has two notch filters and three band pass filters (center freq, band width and gain controls for each filter). It's smaller than rack units and does everything I ever used my SF2 for and cost me $165 used on the 'bay. Not sure where to buy one new but it's a bona fide cool, cheap, effective substitute for the Sf2.
 
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#13
Whoa okay hold on. I am not a technical person at all but by understanding is that most onboard preamps are boost/cut based. I.e. the preamp has 2 or more bands (lows, highs, mids, low mids, for example) and within those frequencies you can boost or cut.

Like I said I am not technical but that seems very different to me than a low pass, hig pass, or mid pass filter. I could be wrong but they sound nothing alike. If you sweep a filter control tback and forth to its extremes you hear a "whah whah whah" type sound that doesn not exist when boosting or cutting treble for example.

So forget Alembic. Some other systems that come to mind are Ibanez Varimid, Wal Basses, Heartfield basses, the EMG BQS, etc.

Maybe the better question to ask here is who in TB can make me a preamp pedal out of an onboard preamp I select cause there are plenty of filter based OBPs!
 
#14
q actually stands for quality. and refers to the bandwidth or resonance of a filter. ask anyone who's into analogue synths and they'll tell you that it doesn't matter if a filter is high pass, band pass, or low pass, if you crank the resonance, when you sweep the frequency you get that that wah wah sound. in fact a wah wah pedal is a sweepable resonant band pass filter. and if you listen to the famous 70's Dr who theme you'll hear a massive synth filter sweep right at the start. sounds like a space ship landing! really any preamp with a resonant filter, even if it doesn't have an adjustment for q, is referred (rightly or wrongly) as a filter based pre these days.

the Craig anderton super tone control is a well known implementation of the state variable filter. this requires 3 opamps but gives you high, band and low pass outputs plus resonance and of course frequency controls.

as is, the anderton circuit needs a bipolar supply, but you could do that with 2 batteries I guess. it also has a fairly low input z, but that could be tweaked if your bass is passive. I'd also use modern opamps.

I'm really surprised there isn't a pedal with this sort of filter, or something similar going around.
 
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#15
RobbieK said:
the Craig anderton super tone control is a well known implementation of the state variable filter. this requires 3 opamps but gives you high, band and low pass outputs plus resonance and of course frequency controls.

as is, the anderton circuit needs a bipolar supply, but you could do that with 2 batteries I guess. it also has a fairly low input z, but that could be tweaked if your bass is passive. I'd also use modern opamps.

I'm really surprised there isn't a pedal with this sort of filter, or something similar going around.
Click to expand...

I run these devices with either an AC powered bipolar supply or more often with a battery-powered, switched bipolar supply. I run one of his compressor/limiters as a front end, so the tone control input Z isn't an issue and it has plenty of signal to work with.

Mine isn't exactly a pedal, since it lacks a stomp switch, but I don't really use it as an add on effect, but rather as an EQ that is always in use.

BTW, all these kits were about $25 each, back in the day. I built two preamps, two compressors, two tone controls and three mono mixers for about $200 and a bit of time with a soldering iron.

Otto
 
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#16
dincz said:
That would be my take too - at least for preamps with EQ controls. So what does "filter based" actually mean in TB-speak?
Click to expand...

It usually refers to the Alembic filter or a variation thereof. They are state variable filters so they can provide high-, low-, and band-pass functions by tapping off at various points. They can provide combinations of these too by mixing the tap points as Alembic claims to do and while bass guitar preamps may not use or need this feature by doing a proper weighting of the feedback and output summer paths they can provide a completely general filter response. Anything you can describe as the ratio of two polynomials can be implemented. Most of us are most interested in the LPF configuration which provides a variable cutoff frequency and a variable damping ratio. To borrow StellarTone's marketing line a variable LPF will "cut the highs while preserving the mids" and when you throw in the variable damping feature you can even emphasize the high mids. The Sallen-Key approach that we cooked up will give you a variable cutoff and damping in a simple dual opamp design.
 
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#17
So, here's an example. Just now I was playing the SX P thru the Super Tone Control. LP at unity, BP at -5 dB and centered about 200. No resonance. Just turning the HP section down from unity to -5 dB (basically shelving everything above 400 or so by that much) gave a much mellowed tone, but without the same dulling effect that turning a standard tone way down would produce. In fact it still sounded nice and fat with the standard tone all the way up.

An example of how an EQ like this can do good things in a slightly different way. Of course, I still will typically use the Q-filter and standard tone controls of the P or Ripper or the active controls of the Sterling in combination, but sometimes to a lesser degree while the outboard EQ does part of the sculpting.

Otto
 
#18
dincz said:
So what does "filter based" actually mean in TB-speak?
Click to expand...

khutch offered a good explanation above; another way to explain the TB nomenclature would be to say that "filter-based" refers to preamps with n-pass (where n=high, low, or band) filters that provide infinite attenuation (at some slope) below, above, or outside of their cutoff frequency...as differentiated with the much more common bass preamps whose high and low filters are usually shelving filters with a user-determined amount of boost or cut below or above their cutoff frequency, but no additional attenuation beyond that. E.g., a low-pass filter versus a low shelving EQ.

The thing that makes the Alembic SF-2 somewhat unique in terms of outboard filters/EQs is that the n-pass filters are in parallel with the dry signal, so you can actually mix the filtered signal with the unfiltered signal...or, mute the unfiltered signal entirely. With a conventional parametric or graphic EQ, all the filters are in series -- which causes them to interact more -- and there's no way (without additional hardware) to bleed some unfiltered signal around the filtered signal.
 
#19
ofajen said:
So, here's an example. Just now I was playing the SX P thru the Super Tone Control. LP at unity, BP at -5 dB and centered about 200. No resonance. Just turning the HP section down from unity to -5 dB (basically shelving everything above 400 or so by that much) gave a much mellowed tone, but without the same dulling effect that turning a standard tone way down would produce. In fact it still sounded nice and fat with the standard tone all the way up.

An example of how an EQ like this can do good things in a slightly different way. Of course, I still will typically use the Q-filter and standard tone controls of the P or Ripper or the active controls of the Sterling in combination, but sometimes to a lesser degree while the outboard EQ does part of the sculpting.

Otto
Click to expand...

Does anyone sell Super Tone Controls all assembled? I am not handy with electronics.
 

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