Underhill Moonshot Preamp Review

[whitelines]

My friend Tim Bowman is the maniac behind Underhill filter preamps. I've been testing a prototype for a few months, and now have installed a release version of his new product, the Moonshot filter preamp.

The Moonshot is a drop in replacement for a Jazz bass control plate, similar to the classic Sadowsky onboard preamp. Super easy to install, you do not need a luthier to do it, it even comes with a screwdriver that fits the wire terminal screws perfectly. The pickup configuration becomes a 1961 Jazz bass V/T V/T configuration, which has a cool retro look and feel. See installation pics below.

The difference between the Moonshot and other preamps you may be familiar with is that the Moonshot (like all Underhill preamps) is a filter preamp. That means each pickup is electronically buffered and frequency filtered separately before being combined into a single signal, similar (exactly?) to what a Wal or an Alembic preamp does.

The result is that you get a subtle and movable frequency bump on each preamp. If you grew up like me playing a jazz bass and learned to use the volume controls of your neck and bridge pickup separately to blend them to get the wide range of tones, then it feels familiar, except now you have a tone control on each pickup. You can make either pickup full range, or shift the frequency hump way down to make it very sub-by. (is that a word?)

I recorded a YouTube demo. The preamp is the quietest preamp I've ever played. There is no noise gating, plugins, or external preamp in the audio, it's all recorded live and direct via an Apollo Twin X interface direct into Final Cut Pro with zero audio edits or modifications. (Video from MacBook webcam)

Since the tone spectrum is complex (2 pickups X 2 tones), it's a bit tricky to show full possibilities, but here is a taste. Headphones recommended....

 

[djmay]

I have installed Underhill preamps in both of my fretless basses, one 5-string and one 6-string. I put the Full English in the 6-string and it is now my main bass. Additionally, Tim is a great guy to do business.

 

[LowWay]

As an underhill user and filter preamp lover, I’d buy this in a second if I hade a fender shaped jazz bass. This is great to see.

 

[2minkey]

I think I am going to try an underhill preamp. Suspect the first experiment will be a Wild Pea, because I have a good P Bass (78 ash/maple) with the right pickup (Stan Hinesley vintage P) for the job. I can imagine trying a Moonshot in my (early 2000s Fender Japan 3 bolt 70s clone) J bass once I settle on pickups for it.

 

[bowthing]

I think I am going to try an underhill preamp. Suspect the first experiment will be a Wild Pea, because I have a good P Bass (78 ash/maple) with the right pickup (Stan Hinesley vintage P) for the job. I can imagine trying a Moonshot in my (early 2000s Fender Japan 3 bolt 70s clone) J bass once I settle on pickups for it.

I highly suggest split coils for the J. The output is up at normal levels, and noise will be super low for that reason plus the lack of hum. It lets you use the filters and volume blending in any way you want.

 

[2minkey]

I highly suggest split coils for the J. The output is up at normal levels, and noise will be super low for that reason plus the lack of hum. It lets you use the filters and volume blending in any way you want.

Yup, split coils are in the plan for the J. Thinking about b axis Barts or Delanos with the big pole pieces.

I ordered the Wild Pea earlier today.

 

[sunbeast]

Looking at the product page, I really like the way this was implemented! It probably essentially gives people the response they think that regular passive dual-tone/dual-volume setups gives them! Personally I might still miss a Q switch for each pickup as my experience with dual filter pres in a bass is that usually I like one of the pickups to have the bigger boost to set the character of the mids and the other to be more flat and/or round. That arrangement probably would take some more fiddling to fit in a Jazz Bass control setup though (particularly with a plate-mounted output jack)

 

[bowthing]

Looking at the product page, I really like the way this was implemented! It probably essentially gives people the response they think that regular passive dual-tone/dual-volume setups gives them! Personally I might still miss a Q switch for each pickup as my experience with dual filter pres in a bass is that usually I like one of the pickups to have the bigger boost to set the character of the mids and the other to be more flat and/or round. That arrangement probably would take some more fiddling to fit in a Jazz Bass control setup though (particularly with a plate-mounted output jack)

I went through a number of prototypes: Single Hi/Lo Q switch, filter bypass switch (not active/passive), variable Q trimmers inside, etc. I opted for simplicity, for exactly the reason you say (I wanted it to be easy and familiar) and to keep the price as low as possible. The variable Q trimmers were great, but require a lot more parts, testing, etc. so the cost and battery consumption goes way up (it's only 1 mA with the fixed filters). A big part of the process was trying many different Q tunings with other bassists. I settled on the 6 dB for the neck (mainly to have a lot of bass available) and 7.3 dB for the bridge (much more and it can get a little honky in the upper mids with typical pups). The jury is still out so, depending on feedback, those values might be tweaked. You're right, it took a lot of fiddling and layout time to squeeze all that prototype stuff in, and not break the form factor that leaves room for two batteries (if they fit in the bottom of the cavity).

 

[mikezimmerman]

I'm very excited about this! However, I do have a couple of questions: Do the stacked pots on these have long enough shafts to allow them to be removed from the control plate and installed through the top on a bass with a rear control cavity? Is there a way to combine them with something like the EPB control (used on the Cali Dub)? My fretless has space for 3 pots, and I'd love to find a way to have 2 separate filters...

 

[bowthing]

I'm very excited about this! However, I do have a couple of questions: Do the stacked pots on these have long enough shafts to allow them to be removed from the control plate and installed through the top on a bass with a rear control cavity? Is there a way to combine them with something like the EPB control (used on the Cali Dub)? My fretless has space for 3 pots, and I'd love to find a way to have 2 separate filters...

The pots have short bushings that won't work on anything thicker than a plate or pickguard. A board-only option will be up soon for pickguards (i.e. PJs). Short pots are necessary because a longer bushing would not leave enough space in the cavity for the battery, or else the knobs would be sticking way up. If the current version is popular enough, I will order a batch of custom pots to make a "long" version of the board-only setup. I will also release a volume/blend version (same layout, but one top knob is volume and the other is blend). I love this preamp, and hope it catches on, so that I can produce all four versions.

The circuits have a different layout than Gen6, to distribute the parts and make them compact enough, so they don't have the same modular "bus", and won't work with Gen6 modules. The only 3 knob option I can see on the horizon (other than the current single filter or EQ options) is a volume, blend, and stacked dual filter module, or more likely a volume/blend stack and two filters. It's tricky, because the majority of 3 knob basses have very small cavities, and both of those modules are large and "gangly". I will probably opt for a dual-filter only volume/blend stack, that doesn't allow patching EQ modules after the blend, and maybe another vol/blend stack for EQ chains like the Paradactyl 2.

 

[mikezimmerman]

The pots have short bushings that won't work on anything thicker than a plate or pickguard. A board-only option will be up soon for pickguards (i.e. PJs). Short pots are necessary because a longer bushing would not leave enough space in the cavity for the battery, or else the knobs would be sticking way up. If the current version is popular enough, I will order a batch of custom pots to make a "long" version of the board-only setup. I will also release a volume/blend version (same layout, but one top knob is volume and the other is blend). I love this preamp, and hope it catches on, so that I can produce all four versions.

The circuits have a different layout than Gen6, to distribute the parts and make them compact enough, so they don't have the same modular "bus", and won't work with Gen6 modules. The only 3 knob option I can see on the horizon (other than the current single filter or EQ options) is a volume, blend, and stacked dual filter module, or more likely a volume/blend stack and two filters. It's tricky, because the majority of 3 knob basses have very small cavities, and both of those modules are large and "gangly". I will probably opt for a dual-filter only volume/blend stack, that doesn't allow patching EQ modules after the blend, and maybe another vol/blend stack for EQ chains like the Paradactyl 2.

I understand--just figured I'd ask! Will probably grab one of the current Moonshots for my Jazz, then keep my eyes open for the other variants...

 

[sunbeast]

V

The pots have short bushings that won't work on anything thicker than a plate or pickguard. A board-only option will be up soon for pickguards (i.e. PJs). Short pots are necessary because a longer bushing would not leave enough space in the cavity for the battery, or else the knobs would be sticking way up. If the current version is popular enough, I will order a batch of custom pots to make a "long" version of the board-only setup. I will also release a volume/blend version (same layout, but one top knob is volume and the other is blend). I love this preamp, and hope it catches on, so that I can produce all four versions.

The circuits have a different layout than Gen6, to distribute the parts and make them compact enough, so they don't have the same modular "bus", and won't work with Gen6 modules. The only 3 knob option I can see on the horizon (other than the current single filter or EQ options) is a volume, blend, and stacked dual filter module, or more likely a volume/blend stack and two filters. It's tricky, because the majority of 3 knob basses have very small cavities, and both of those modules are large and "gangly". I will probably opt for a dual-filter only volume/blend stack, that doesn't allow patching EQ modules after the blend, and maybe another vol/blend stack for EQ chains like the Paradactyl 2.

I apologize if I'm missing something, but for 3 pot holes and 2 filters paired with passive pickups couldn't someone grab two of your BP buffer boards, two of the FV Variable Q Filter stacks and something like a stacked 25KA pot (or whichever value volume pots you'd recommend) for a dual volume placed after the filters and buffers?

 

[bowthing]

V

I apologize if I'm missing something, but for 3 pot holes and 2 filters paired with passive pickups couldn't someone grab two of your BP buffer boards, two of the FV Variable Q Filter stacks and something like a stacked 25KA pot (or whichever value volume pots you'd recommend) for a dual volume placed after the filters and buffers?

To do that you would also need some decoupling caps and summing resistors after the FV outputs (they are at bias voltage). The decoupling caps should be at least 3.3 µF and ideally film for lowest distortion. I wouldn't go lower than 2k for the summing resistors. 25k pots would be fine, or 10k. With either one there will be a volume drop, but you can compensate with buffer gain.

 

[sunbeast]

To do that you would also need some decoupling caps and summing resistors after the FV outputs (they are at bias voltage). The decoupling caps should be at least 3.3 µF and ideally film for lowest distortion. I wouldn't go lower than 2k for the summing resistors. 25k pots would be fine, or 10k. With either one there will be a volume drop, but you can compensate with buffer gain.

Is that essentially what are found on your blending board?

 

[bowthing]

Is that essentially what are found on your blending board?

No, the active blend is a different circuit with equal volume for the whole sweep, and the ability to drive a filter or EQ after the blend.

 

[sunbeast]

No, the active blend is a different circuit with equal volume for the whole sweep, and the ability to drive a filter or EQ after the blend.

Ah cool- I imagined the blend would come post-filters as it does in my ACG/East dual filter pre. So yours are arranged pickup-buffer-blend-filters-volume? I really need to try one of your preamps!

 

[bowthing]

Ah cool- I imagined the blend would come post-filters as it does in my ACG/East dual filter pre. So yours are arranged pickup-buffer-blend-filters-volume? I really need to try one of your preamps!

Pickup>buffer>filter>blend>EQ, pickup>buffer>EQ>blend>filter>EQ, etc., etc. Pretty much any crazy scheme your heart desires. The treble boost is the only module that forces the order somewhat.

 

[sunbeast]

Pickup>buffer>filter>blend>EQ, pickup>buffer>EQ>blend>filter>EQ, etc., etc. Pretty much any crazy scheme your heart desires. The treble boost is the only module that forces the order somewhat.

Nice- I’m definitely a fan of your general modular philosophy, and I hope you are able to continue offering parts in a modular form! I’d guess the kits are probably more popular, but being able to configure things myself is very attractive.

One thing I don’t think I’ve seen mentioned about your filter pres- Are your filters capable of intentional saturation or are they naturally very clean/high-headroom? That is one thing I’ve noticed with an Alembic filter pre I had as well as the Lusithand filters when run at 9V- I can dial in a nice slightly gritty filter texture with hot enough pickups. My ACG filter pre seems much more “hi-fi” and clean in general even at 9V

 

[bowthing]

Nice- I’m definitely a fan of your general modular philosophy, and I hope you are able to continue offering parts in a modular form! I’d guess the kits are probably more popular, but being able to configure things myself is very attractive.

One thing I don’t think I’ve seen mentioned about your filter pres- Are your filters capable of intentional saturation or are they naturally very clean/high-headroom? That is one thing I’ve noticed with an Alembic filter pre I had as well as the Lusithand filters when run at 9V- I can dial in a nice slightly gritty filter texture with hot enough pickups. My ACG filter pre seems much more “hi-fi” and clean in general even at 9V

The circuits are very low noise and low distortion within the operating range, but there is more than enough "rope to hang yourself with" if you want, by turning up the buffer gains, using very high Qs, super hot pups, etc.. The same thing can be done with lower voltage (i.e throw in a battery that is at 5V). The fundamental problem with doing that onboard (as opposed to a pedal) is that the distortion will change as the battery voltage goes down (or up). My personal preference is to do that outboard, so you can turn it on or off and avoid having a bass that is a "one trick pony", and so it's consistent. Incidentally, the FS filters have a secret hack: Unplug the switch and you can turn both the high and low Q trimmers up and get 20dB or so of resonant peak. It's pretty ridiculous at that level, but it should distort a lot!

Getting near clipping with the Moonshot is probably not too practical, as the gain is kept near unity and the Qs are not very high. There is lots of headroom for J pups even down around 7V.