Filter Preamps - anyone compared ACG, Lusithand, Passinwind, Underhill?

[mikezimmerman]

So for anyone curious, here are my thoughts on the Underhill Cali Dub preamp:

As I mentioned earlier I assumed it would be much closer to the ACG/East preamp than the Wal preamp, but once it got here I realized it's actually pretty similar to the Underhill "The Full English" preamp that's in my four string fretless. Which makes a lot of sense. @bowthing can correct me if I'm wrong, but they are the same filters in both preamps, with the only difference being that the Wal style (The Full English) preamp has a fixed Q boost on a push pull control and the Cali Dub has a variable boost.

Both are very low noise and super clean/transparent sounding. Of the two, The Full English is much easier/simpler to use and easy to dial in while the Cali Dub is significantly more versatile. The PolyVox pickups have a very distinct voice (very thick, clear, midrange heavy, and authoratative) but the filters and adjustable boosts allow you to revoice them significantly. And most interesting to me, the bass control is super useful to both boost AND cut bass. On most active basses I either leave the bass control flat or boost it. I almost never cut bass unless there's an acoustics issue. But with these pickups sculpting the bass to either add heft or lean out the tone can yield a lot of tones.

How would I compare it to the ACG? So I had an ACG EQ02 in an old Stambaugh fretless (just one filter for both pickups) and two ACGs that both had the EQ03 preamp. Both were very clear, hi-fi preamps. The ACG's treble control introduced a bit of hiss but otherwise it was very quiet. The Underhill is VERY low noise.

The ACG was hands down the most flexible preamp I've ever used. The filters were SUPER wide. I believe from 70 Hz to 7000 Hz with an adjustable 0-10 dB boost. It also had a high pass/treble control from 1.5k Hz to 10K Hz and a LOT of boost on tap (0-18 dB). And then there were fixed low and high mid boosts on a push/pull AND a passive tone knob.

It was infinitely tweak able. But that also made it difficult to recall specific tones. The filter knobs had 41 different clicks, but that was still too hard to keep track of. So while I absolutely loved that preamp, it wasn't all that easy to tweak on the fly. Alan seemed to agree, as soon after my builds he and John East released the DFM preamp which narrowed the range of the LPFs (from 70 Hz to 3.5 kHz), tweaked the treble control to be a mid/treble control (500 Hz to 5000 Hz) and added an attack boost at 8000 Hz. I think the Wal "Pick Attack" is at 7,000 Hz.

Thanks for the clear description.

That was my experience with the original ACG preamp, as well--super flexible, but less "usable" than the Wal preamp, at least for me. It sounds like one of the Underhill versions would be just about right. Maybe a "Full English" with an added bass control stack, since the one thing that the original Wal preamp was lacking (in my opinion!) was a way to tweak the lows without radically changing everyone else...

 

[Jared Lash]

Thanks for the clear description.

That was my experience with the original ACG preamp, as well--super flexible, but less "usable" than the Wal preamp, at least for me. It sounds like one of the Underhill versions would be just about right. Maybe a "Full English" with an added bass control stack, since the one thing that the original Wal preamp was lacking (in my opinion!) was a way to tweak the lows without radically changing everyone else...

Yeah, with filter preamps it's always a trade off between tonal flexibility and difficulty to dial in sounds.

I got the stock version of the Full English because I was really going after the Wal thing. And it does that very well. As I noted, the Lusithand is significantly more aggressive the filter range is also very close to a Wal. The Underhill is cleaner and more hi-fi and the filters open wider. So it's perfect for me on fretless.

But the other big advantage to the Underhill is that his designs are all modular so you can mix and match if you want. The Full English with a bass control would be awesome. He also offers the same filters with a three position mini toggle for the resonance boost. So instead of just one setting by pulling up on the filter knobs you could have two levels of boost for each filter - off, boost 1 and boost 2.

Either way, I highly recommend getting numbered knobs. It makes recalling tones way easier. There are a few options, but I really like these from Lusithand: Lusithand knobs - Lusithand Devices

Because of the difference in pot shaft sizes, you have to use brass inserts to use these knobs with Underhill preamps, but that's what I'm doing on my fretless and I love them.

 

[Passinwind]

Yeah, with filter preamps it's always a trade off between tonal flexibility and difficulty to dial in sounds.

I got the stock version of the Full English because I was really going after the Wal thing. And it does that very well. As I noted, the Lusithand is significantly more aggressive the filter range is also very close to a Wal. The Underhill is cleaner and more hi-fi and the filters open wider. So it's perfect for me on fretless.

But the other big advantage to the Underhill is that his designs are all modular so you can mix and match if you want. The Full English with a bass control would be awesome. He also offers the same filters with a three position mini toggle for the resonance boost. So instead of just one setting by pulling up on the filter knobs you could have two levels of boost for each filter - off, boost 1 and boost 2.

Either way, I highly recommend getting numbered knobs. It makes recalling tones way easier. There are a few options, but I really like these from Lusithand: Lusithand knobs - Lusithand Devices

Because of the difference in pot shaft sizes, you have to use brass inserts to use these knobs with Underhill preamps, but that's what I'm doing on my fretless and I love them.

For filter preamps I really like something like the ones in the top row of this pic, as I can tell the knob position without even looking:

The maker is on Etsy and can do many sizes, wood types, inlays, etc. He goes by “Pickknobs”, super good guy to work with too.

 

[Jared Lash]

For filter preamps I really like something like the ones in the top row of this pic, as I can tell the knob position without even looking:

View attachment 7307795

The maker is on Etsy and can do many sizes, wood types, inlays, etc. He goes by “Pickknobs”, super good guy to work with too.

I love it.

I originally thought of doing chickenhead knobs for my four strings but I didn't think they'd fit the visual vibe. But something like these knobs could be very cool.

 

[Passinwind]

I love it.

I originally thought of doing chickenhead knobs for my four strings but I didn't think they'd fit the visual vibe. But something like these knobs could be very cool.

He sent me a bunch of unfinished walnut ones so I could tweak shapes and sizes to my liking. I still need to repay that by oredering some purpleheart ones to match the fingerboard on my Marco fretless.

BTW, my current format in that bass is active Bass/Mids for the neck pickup and resonant LPF for the bridge, w/ three way Q switch. Volume pots are detented with unity gain at the detent, which makes finding settings again quite a bit easier. I can get up to 22dB of bass boost, dead clean…not that I’d really want to! But you mentioned cutting bass, and my unusual format makes that work really well for solos, for example. I have custom Marco neo sidewinders, they also behave much as you described.

 

[bowthing]

As I mentioned earlier I assumed it would be much closer to the ACG/East preamp than the Wal preamp, but once it got here I realized it's actually pretty similar to the Underhill "The Full English" preamp that's in my four string fretless. Which makes a lot of sense. @bowthing can correct me if I'm wrong, but they are the same filters in both preamps, with the only difference being that the Wal style (The Full English) preamp has a fixed Q boost on a push pull control and the Cali Dub has a variable boost.

Yup, the Underhill filters are all the same (2nd order low pass, state-variable).