Review: Underhill Dual Filter Onboard Preamp

[bowthing]

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?

Yes, vol and blend pot.
The two trim pots are gain adjustment for each pickup. For a Wal-like setup you need two FS5 filter packages. They can be set to fixed Q, dual Q, or triple Q (with no switch, 2-way switch, or 3-way switch). For full Wal-like functionality you can also use an FT Treble boost filter (typically operated by volume push-pull).

 

[bowthing]

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.

Yup, that's a nice simple setup, and fully variable Q.

 

[5StringPocket]

I’m not interested in sounding like a Waal but like the tonal flexibility a filter preamp provides. I see The Full English Multicoil preamp asks whether your bass is 4 or 5 string. Is this the right match for a set of Nordstrand PolyVox pickups?
https://www.underhillbass.com/product-page/the-full-english-multicoil-version
Here are some relevant PolyVox links:
https://www.talkbass.com/threads/nordstrand-poly-vox.1643176/page-4
From this linked image below, does this 4-string model have two 3-conductor wire bundles, each consisting of 2 signal wires plus ground?
https://www.talkbass.com/attachments/polyvox4-jpg.5466975/
Poly Vox 5

 

[bowthing]

The PolyVox as I understand it has a signal, ground, and shield wire, so you use the standard pickup Full English (not multicoil) for any of them.

 

[5StringPocket]

The PolyVox as I understand it has a signal, ground, and shield wire, so you use the standard pickup Full English (not multicoil) for any of them.

Thanks, I think this pickup/preamp pair would be killer.

 

[bowthing]

I’m not interested in sounding like a Waal but like the tonal flexibility a filter preamp provides. I see The Full English Multicoil preamp asks whether your bass is 4 or 5 string. Is this the right match for a set of Nordstrand PolyVox pickups?
The Full English (Multicoil Pickups) | Underhill Bass
Here are some relevant PolyVox links:
https://www.talkbass.com/threads/nordstrand-poly-vox.1643176/page-4
From this linked image below, does this 4-string model have two 3-conductor wire bundles, each consisting of 2 signal wires plus ground?
https://www.talkbass.com/attachments/polyvox4-jpg.5466975/
Poly Vox 5

The PolyVox are wired out like regular pickups, so you use the version for standard pickups. All reports so far say that they sound really great!

 

[5StringPocket]

Still mulling this over. Here is the link for the Full English Standard version. I guess you order the pot nuts if you're not sure the existing nuts would fit these pots? $20 is pricey for 4 nuts... What cavity depth is required to mount this? It would be helpful to know if routing would be required.

The Full English (Standard Pickups) | Underhill Bass

 

[sunbeast]

Still mulling this over. Here is the link for the Full English Standard version. I guess you order the pot nuts if you're not sure the existing nuts would fit these pots? $20 is pricey for 4 nuts... What cavity depth is required to mount this? It would be helpful to know if routing would be required.

The Full English (Standard Pickups) | Underhill Bass

There is a section under the Help-Preamp Support tab about the nuts. I was curious about the necessary depth as well as I have a bass with a shallow cavity that I was considering a filter pre for and the ACG I have is too deep. I found this comment from Underhill on Facebook with a Google search (in response to a potential customer with a very shallow control cavity): "All of the modules will fit in 7/8", but not 3/4". That's really tight!" Unfortunately my cavity is too small as well (not surprising though, as these types of pres require some special pots!)

 

[bowthing]

Still mulling this over. Here is the link for the Full English Standard version. I guess you order the pot nuts if you're not sure the existing nuts would fit these pots? $20 is pricey for 4 nuts... What cavity depth is required to mount this? It would be helpful to know if routing would be required.

The Full English (Standard Pickups) | Underhill Bass

For clarification on the pot nuts, they are for two situations. First, when the holes are 3/8", they fill in the space and center the 7mm pots. Second, the bushings on the pots are not long enough to reach through a typical body panel (fine with a pickguard). BUT... As of this week I have new pots with long bushings, so you can body-mount them directly in 7mm holes. You will still probably want pot nuts for 3/8" holes, because using washers doesn't work very well, as the large thin washers required will bend into a cup shape. and the pot will work loose pretty easily. You can always fill the holes with wood and re-drill to 7mm, but pot nuts will hold very securely without the luthier work.

So apologies on the price, I know they are ridiculously expensive, but I make them one at a time by hand and actually loose a little money time-wise. This year I will farm out a proper batch to a machine shop, and the price will go way down. I may just include them with every preamp after that!

 

[millahh]

So, I'm about to embark on adventure! I just snagged a spectacular deal on a G&L L2k Tribute, and am going to be putting a Calistan into it. Well, more accurately, my local Luther is going to be putting it in, as it is going to require drilling a hole for the fourth knob. I'm figuring I'll need to have a new battery compartment routed, as the space for the current battery will be needed to accommodate the fourth knob; assuming that's the case, I'll take the opportunity to go for 18v instead of 9v, as I tend to play rather aggressively and want to avoid undesired clipping.

My one remaining question is what to do with the hole for the third switch...I could have a small LED put in, or maybe a switch for coil options, but the latter seems like overkill, given the options and flexibility of the filter preamp.

I'll post updates here as the situation develops!

Also, Tim is great to work with, very patient in answering all my questions!

 

[Johno Dunn]

So, I'm about to embark on adventure! I just snagged a spectacular deal on a G&L L2k Tribute, and am going to be putting a Calistan into it. Well, more accurately, my local Luther is going to be putting it in, as it is going to require drilling a hole for the fourth knob. I'm figuring I'll need to have a new battery compartment routed, as the space for the current battery will be needed to accommodate the fourth knob; assuming that's the case, I'll take the opportunity to go for 18v instead of 9v, as I tend to play rather aggressively and want to avoid undesired clipping.

My one remaining question is what to do with the hole for the third switch...I could have a small LED put in, or maybe a switch for coil options, but the latter seems like overkill, given the options and flexibility of the filter preamp.

I'll post updates here as the situation develops!

Also, Tim is great to work with, very patient in answering all my questions!

I bugged him for months! Very patient man.

 

[sunbeast]

So, I'm about to embark on adventure! I just snagged a spectacular deal on a G&L L2k Tribute, and am going to be putting a Calistan into it. Well, more accurately, my local Luther is going to be putting it in, as it is going to require drilling a hole for the fourth knob. I'm figuring I'll need to have a new battery compartment routed, as the space for the current battery will be needed to accommodate the fourth knob; assuming that's the case, I'll take the opportunity to go for 18v instead of 9v, as I tend to play rather aggressively and want to avoid undesired clipping.

My one remaining question is what to do with the hole for the third switch...I could have a small LED put in, or maybe a switch for coil options, but the latter seems like overkill, given the options and flexibility of the filter preamp.

I'll post updates here as the situation develops!

Also, Tim is great to work with, very patient in answering all my questions!

Separate coil switches per pickup is pretty useful IMO as someone who did that mod on a number of different L-series instruments. I also made my L-series basses Volume/Volume using a stacked potentiometer. Or leave it as an active/passive switch in case of battery failure.

 

[millahh]

Separate coil switches per pickup is pretty useful IMO as someone who did that mod on a number of different L-series instruments. I also made my L-series basses Volume/Volume using a stacked potentiometer. Or leave it as an active/passive switch in case of battery failure.

So, I wired up my other L2K to be able to do series, parallel, inner & outer (though not independently per pickup)...I seem to recall you being one of the other tinkerers back when we had the G&L subforum?

In this instance, if I did the switch for coil configuration, I'd probably go for outer/parallel/inner. I partly feel like this would be cool, and partly like it would be absurd overkill. Though I do love running inner coils on my other one!

 

[sunbeast]

So, I wired up my other L2K to be able to do series, parallel, inner & outer (though not independently per pickup)...I seem to recall you being one of the other tinkerers back when we had the G&L subforum?

In this instance, if I did the switch for coil configuration, I'd probably go for outer/parallel/inner. I partly feel like this would be cool, and partly like it would be absurd overkill. Though I do love running inner coils on my other one!

Yes I was definitely tinkering heavy on my G&Ls back then. I was big on the “single coil with bass boost” mode (series with capacitor or “OMG) and added that to all my modern G&Ls. I always preferred the outer coils for single-coil mode

 

[jfiver]

My one remaining question is what to do with the hole for the third switch...I could have a small LED put in, or maybe a switch for coil options, but the latter seems like overkill, given the options and flexibility of the filter preamp.

Filter bypass switch? Tim was able to accommodate my request for one. Being able to flick between filtered and open tones without needing to change anything is pretty rad. I think there's also been 3-position switches, with one filter on and the other off in the middle position, done in the past.

 

[bowthing]

My one remaining question is what to do with the hole for the third switch...I could have a small LED put in, or maybe a switch for coil options, but the latter seems like overkill, given the options and flexibility of the filter preamp.

I do have an external switch (SB) that plugs into the treble boost in lieu of the volume push-pull.

 

[millahh]

Thanks all for the stimulating discussion. I have 2-3 options that I've narrowed down to:

1). Outer/parallel/inner coils switch, using a variant of the k-mod wiring. That's my preferred functionality on my "normal" L2K. There's so much flexibility in how the pickups are voiced from the filters, but at the same time, why not?

2). Treble boost switch. The more I think about this, the more intrigued I am. Tim, from what you've seen, do folks like having this additional functionality? I started off thinking of doing a pseudo-Wal, so it would be in line with that.

3). Does a long-shaft version of the Full English p/p volume module exist? If so, I could have both 1 & 2 together. It would be truly absurd, but I also feel like restraint is far in the rear view mirror at this point.

I'll chew on it for a couple of days and make a decision. I figure it will be tough to get the work done I've the holidays, so I've got time to work with...

 

[Brian Patterson]

If those trim dials were rigidly mounted inside the cavity and were accessible through some tiny openings for adjustment, I'd be much more impressed.

All those parts left loose is not a compelling approach.

 

[Memnochthebass]

2). Treble boost switch. The more I think about this, the more intrigued I am. Tim, from what you've seen, do folks like having this additional functionality? I started off thinking of doing a pseudo-Wal, so it would be in line with that.

I have the treble boost on three of the preamps I have(I favor the Cali models), so I'm at least one of the folks that loves it.

 

[Memnochthebass]

If those trim dials were rigidly mounted inside the cavity and were accessible through some tiny openings for adjustment, I'd be much more impressed.

All those parts left loose is not a compelling approach.

I mount the buffers and treble filters with double sided tape that Mr. Bowman provides with his preamps and no worries. If I wanted to, I could drill a couple of holes in the cavity cover to adjust the trims with a small fladhead because the tape is pretty strong, but I'm more of a "set and forget" type.