Review: Underhill Dual Filter Onboard Preamp

[sunbeast]

Which ones are considered good?

The ones used on my Godin were made by RMC and I have used basses equipped with Graphtech Ghost saddles that sounded great (also use a guitar with Fishman piezo bridge that also sounds great blended with magnetic pickups), but a lot of what makes a good piezo sound is the preamp and filtering/EQ done to them. Most don’t sound good just amplified straight. My era of Godin had fixed sub-filtering and some internal shaping as well as a piezo-specific active 3-band preamp.

 

[bowthing]

Are you planning on adding buffering for multicoil pickups anytime?

I don't think so. Honestly, copying a Wal is not a plan at this point. I think MM pickups are pretty close for that part of the sound. Nordstrand is making one specifically for that. I do plan a bright switch.

 

[smeet]

I don't think so. Honestly, copying a Wal is not a plan at this point. I think MM pickups are pretty close for that part of the sound. Nordstrand is making one specifically for that. I do plan a bright switch.

I’m fascinated by the filter-based preamps. The sounds seem really cool. But I’m wondering about the utility. Filters seem to be a more “holistic” way to change the tone, as opposed to eq where you can change one part of the sound in relative isolation.

For instance, if I have a great sound, and on the gig I want to cut some bass, or add mids, or add/remove high end sparkle without changing the rest of the sound, how would I do that? Is the ideal setup a filter based preamp feeding into an eq-based preamp?

Also, how difficult/fiddly is it to get a sound you discovered previously? It seems that small knob movements result in big sonic changes.

 

[bowthing]

I’m fascinated by the filter-based preamps. The sounds seem really cool. But I’m wondering about the utility. Filters seem to be a more “holistic” way to change the tone, as opposed to eq where you can change one part of the sound in relative isolation.

For instance, if I have a great sound, and on the gig I want to cut some bass, or add mids, or add/remove high end sparkle without changing the rest of the sound, how would I do that? Is the ideal setup a filter based preamp feeding into an eq-based preamp?

Also, how difficult/fiddly is it to get a sound you discovered previously? It seems that small knob movements result in big sonic changes.

I think for what you describe, the new parametric filter I am releasing soon might be a good choice. It's a moderately narrow boost cut with a frequency sweep. There will be a low band (say 70-800 Hz) and a high band (say 400-5000) with some overlap. So you can do things like cut low end if the room is boomy, or boost highs, and still have the other filter to control mids. Or have wide range mid control with both filters. It will work in either pre or post mix, but pre is a lot of knobs and a real mind bender.

 

[mikezimmerman]

Honestly, you have hit upon the biggest drawback I found with filter preamps after many years playing Wals almost exclusively: it’s not really possible to just tweak one frequency range (especially bass/low mid) without affecting the others.

If you want to just fill out the lows a bit more, for instance, you have to do that at the amp.

I’m fascinated by the filter-based preamps. The sounds seem really cool. But I’m wondering about the utility. Filters seem to be a more “holistic” way to change the tone, as opposed to eq where you can change one part of the sound in relative isolation.

For instance, if I have a great sound, and on the gig I want to cut some bass, or add mids, or add/remove high end sparkle without changing the rest of the sound, how would I do that? Is the ideal setup a filter based preamp feeding into an eq-based preamp?

Also, how difficult/fiddly is it to get a sound you discovered previously? It seems that small knob movements result in big sonic changes.

 

[ctmullins]

I have one bass in which the neck pickup is directly connected to a JTEX Distiller filter unit, and the bridge pickup is directly connected to a John East BTB two-band unit. From there they both go into a three-way switch and a master volume.

It’s an interesting and flexible setup! I can obviously choose either pickup individually, but together I can sweep through the neck filter to combine with the bridge in different ways, and do the normal bass/treble adjustments on the bridge EQ.

 

[bowthing]

I’m fascinated by the filter-based preamps. The sounds seem really cool. But I’m wondering about the utility. Filters seem to be a more “holistic” way to change the tone, as opposed to eq where you can change one part of the sound in relative isolation.

For instance, if I have a great sound, and on the gig I want to cut some bass, or add mids, or add/remove high end sparkle without changing the rest of the sound, how would I do that? Is the ideal setup a filter based preamp feeding into an eq-based preamp?

Also, how difficult/fiddly is it to get a sound you discovered previously? It seems that small knob movements result in big sonic changes.

To my mind, the main thing is to be able to filter BEFORE the blend, and to a lesser extent the type of filter. You just can't do that any other way save for a stereo cable. The low-pass filters indeed have the tradeoffs you guys mention (fiddly and phase interactions), but make for a lot of interesting sounds. The goal of my design is to be kind of like an onboard pedal board. Plug in one pedal for this pickup, another for that, and maybe a third on the blended signal. When I get a traditional bass/treble/mid eq done, you could have the per-pickup filters and the post eq all onboard. It becomes a question of how much you can really deal with in a limited space for control knobs (and limited power), though, and how much you will actually use long term.

 

[bowthing]

I have one bass in which the neck pickup is directly connected to a JTEX Distiller filter unit, and the bridge pickup is directly connected to a John East BTB two-band unit. From there they both go into a three-way switch and a master volume.

It’s an interesting and flexible setup! I can obviously choose either pickup individually, but together I can sweep through the neck filter to combine with the bridge in different ways, and do the normal bass/treble adjustments on the bridge EQ.

That's cool! The three-way switch is an under appreciated solution for all sorts of great basses!

 

[Johno Dunn]

Playing at church this morning and at run through had a buzz on my bridge pu, probably something I miss wired combined with the funky wiring in the church! I rolled it back to the neck pu, no buzz, and was able to dial in an amazing tone. Best IE tone I’ve had! I may go back to a one pu set up once the Zen Blade gets here! Neck pu only?

 

[sunbeast]

I’m fascinated by the filter-based preamps. The sounds seem really cool. But I’m wondering about the utility. Filters seem to be a more “holistic” way to change the tone, as opposed to eq where you can change one part of the sound in relative isolation.

For instance, if I have a great sound, and on the gig I want to cut some bass, or add mids, or add/remove high end sparkle without changing the rest of the sound, how would I do that? Is the ideal setup a filter based preamp feeding into an eq-based preamp?

Also, how difficult/fiddly is it to get a sound you discovered previously? It seems that small knob movements result in big sonic changes.

As a longtime user of mostly passive instruments, a filter preamp to me basically offers a wider and adjustable palette of the character of what differentiates passive pickups- the peak at the resonant frequency (after which high frequencies drop dramatically) of a pickup is a large part of what gives a particular passive pickup its characteristic tone, and a filter preamp just emulates this character but in a sweepable form (which does depend on the pickup you pair it with having a relatively wide response- the filter can't create much of an audible peak past the natural drop-off of the pickup used, so generally "sterile" wide-range pickups seem to pair best IME). Since I'm used to doing most EQ later in my chain anyway, a filter pre works well for me to just set this initial character of my sound.

For the last year I've actually been running a sort of "Master" resonant filter preamp built into a box on my pedalboard to be used with all my basses, both passive and active (right now its a Lusithand pre that works great in this role, though I plan to build a J-tex I have then possibly at some point Underhill into boxes to compare as well). This way I can use a filter with all of my instruments without having to make them all active (my original plan was to build a belt-loop preamp, but I prefer the security of keeping it on the board and don't find it too inconvenient for my uses to reach down and adjust as necessary). I then run into a pedal preamp (or multiple) for added versatility (the filter basically helping mold the base character of the tone if the resonance is boosted and set somewhere in the midrange, or more as a high-end attack boost if set higher) or when using an active bass with more traditional onboard preamp I have midrange and bass shaping on the bass run before the filter and they don't really fight each-other unless I set the filter frequency too low where the controls might clash.

 

[MilkyMcMilkMilk]

Is there a way to get this in a pedal form?
I'm interested in the sound but not really willing to change out my preamp.

 

[bowthing]

Is there a way to get this in a pedal form?
I'm interested in the sound but not really willing to change out my preamp.

You would have to have a bass with two cables, one for each pickup, and two pedals. The filters are applied separately to each pickup before they are blended, which is why it has some unique sounds. Look at the @Passinwind preamp for something similar, or an Alembic preamp.

 

[Passinwind]

You would have to have a bass with two cables, one for each pickup, and two pedals. The filters are applied separately to each pickup before they are blended, which is why it has some unique sounds. Look at the @Passinwind preamp for something similar, or an Alembic preamp.

You could do one 3 conductor cable off the bass with a TRS connector set (or an XLR) and build two of my LPF modules into the same box, but a bass with a regular format preamp already installed would work OK with any of the regular design forks on my open source project. But all of this is DIY for the most part, as I very rarely sell hardware. Just buying someone else's premade solution is going to be a lot less work...

 

[sunbeast]

Is there a way to get this in a pedal form?
I'm interested in the sound but not really willing to change out my preamp.

As I mentioned in a post above yours, a single filter pre is totally possible to install in a pedal form and I have done it with a few different filter pres at this point to great success.

As @bowthing points out though, part of the attraction of the more sophisticated filter preamps (as used in some Alembics, Wals, etc) is having independent filters per pickup and blending them to taste and this becomes more complicated to do outside the instrument. I also have a bass with dual filters (ACG preamp) and it is capable of tones that are otherwise inaccessible for me using other methods

 

[Johno Dunn]

As I mentioned in a post above yours, a single filter pre is totally possible to install in a pedal form and I have done it with a few different filter pres at this point to great success.

As @bowthing points out though, part of the attraction of the more sophisticated filter preamps (as used in some Alembics, Wals, etc) is having independent filters per pickup and blending them to taste and this becomes more complicated to do outside the instrument. I also have a bass with dual filters (ACG preamp) and it is capable of tones that are otherwise inaccessible for me using other methods

With the Underhill pre, I am able to achieve "my" tone in every siyuation I find myself in. I hear things my fretless was not capable of before!

 

[MilkyMcMilkMilk]

You would have to have a bass with two cables, one for each pickup, and two pedals. The filters are applied separately to each pickup before they are blended, which is why it has some unique sounds. Look at the @Passinwind preamp for something similar, or an Alembic preamp.

I appreciate everyone's input. I prefer to use one pickup in the bridge position mostly.
I have a tune bass that I love, the preamp is the only thing kind of lacking. I can get good sound but
I need my sans amp geddy lee pedal to give it a bit of oomph.
The way my preamp is now is, bass, treble and mids eq knobs with pickup selection and volume. it also has 2 switches. one goes between active and passive, the other goes parallel, series and
single coil.

I'd be concerned I may lose some functionality
installing a different preamp.

 

[bowthing]

I appreciate everyone's input. I prefer to use one pickup in the bridge position mostly.
I have a tune bass that I love, the preamp is the only thing kind of lacking. I can get good sound but
I need my sans amp geddy lee pedal to give it a bit of oomph.
The way my preamp is now is, bass, treble and mids eq knobs with pickup selection and volume. it also has 2 switches. one goes between active and passive, the other goes parallel, series and
single coil.

I'd be concerned I may lose some functionality
installing a different preamp.

You could put a filter on the bridge pickup and a 3 band parametric EQ on an Underhill, but it would be a little wild with four control knobs (in addition to vol & blend). Too much functionality! The filter would be first in series so if you wanted the bridge to have full eq you would need to turn the filter frequency up all the way (kind of a one or the other situation). The coil switch would be unchanged, and the active/passive would become a filter bypass switch. Finding a low pass filter pedal sounds like the easiest option.

 

[MilkyMcMilkMilk]

I do have a 6 string that I don't play a lot cause it's hard to eq. Boomy on B string and way to high on the C string. I'm able to tame it some with a couple of pedals but maybe this bass would be a better option for a new preamp.
2 humbucker pickups, Treble and bass knob as well as volume knob for each pickup.
Would this work better?

 

[bowthing]

I do have a 6 string that I don't play a lot cause it's hard to eq. Boomy on B string and way to high on the C string. I'm able to tame it some with a couple of pedals but maybe this bass would be a better option for a new preamp.
2 humbucker pickups, Treble and bass knob as well as volume knob for each pickup.
Would this work better?

The two band parametric would work (or the 3 band but that's an extra knob). It's made to cut boominess when rolled all the way down, so you could leave the bass freq all the way down and treble all the way up, then just cut with the upper two knobs.

With a fully active preamp a vol/vol setup doesn't work, so it would be volume/blend. (Actually vol/vol does work, but it's like a mixing console: The bass is twice as loud with both pickups on full as it is with one on full. So I only make a blend, but it actually works over the whole range, being active).

 

[MilkyMcMilkMilk]

I'm interested in this to get close to a Wal tone.
Volume and blend would be fine by me.
So i'm pretty dumb when it comes to fancy electronics.
So on your PD4 dual Preamp Package you have a volume and pick up blend pot.
The 2 internal trim pots, those are the filters?

So after reading a little more, maybe for a 4 knob bass, I could do the PD4
and a fv4 q filter for each pickup, does that make sense.