Wal and other filter-based preamps

[sunbeast]

I have a ACG EQ-01 filter which is a concentric control that allows freq. variation but lately I have been looking at Lusithand because it's a tone filter that's more like Wal and Alembic.

I have both, and they both fulfill similar functions in slightly different ways (more similar than different in function, but sound a bit different). I find the Lusithand to have a bit more of an “aggressive” sharp tone to the peaking/Q-boost and the LPF filters seem to open to a higher frequency while the ACG sounds a bit more refined and smooth to me even with the resonance boosted (not sure if it is a difference in filter slope or if the Lusithand actually has some soft clipping going on). The Lusithand lacks any sort of high-boost filter to emulate the Attack Boost circuit on a Wal, while the ACG can do something similar using the HPF filter stack. I like them both for different reasons!

 

[Kinkh]

BTW, I am using a Sallen Key implementation rather than a SVF for economy. Similar, yet different to what @Passinwind has implemented in his design (which I find great, stumbled upon it after having designed my own Filtrum 1 preamp shown in the video).

Thanks for the info! Sallen-Key is actually a very economical solution once you figure out how to make
I tried that topology as well, worked very nice. Later I had a chance to trace the original Wal preamp, and to my surprise, they used the same topology as well.

 

[David Mochen]

Thanks for the info! Sallen-Key is actually a very economical solution once you figure out how to make
I tried that topology as well, worked very nice. Later I had a chance to trace the original Wal preamp, and to my surprise, they used the same topology as well.

Wow, I have never had a Wal in my hands, wish I could! Nice one on tracing it. I guess the first stage of mixing the coils in the pickups must be quite complex and of course it does not exist in the ACGs or Lusithands or mine (Aural Tronix)...

 

[claudel]

Wow, I have never had a Wal in my hands, wish I could! Nice one on tracing it. I guess the first stage of mixing the coils in the pickups must be quite complex and of course it does not exist in the ACGs or Lusithands or mine (Aural Tronix)...

Lusithand makes a version with buffers for discrete multicoils...

 

[Kinkh]

Wow, I have never had a Wal in my hands, wish I could! Nice one on tracing it. I guess the first stage of mixing the coils in the pickups must be quite complex and of course it does not exist in the ACGs or Lusithands or mine (Aural Tronix)...

Oh no, I've never had the chance to hold a Wal in my hands either. One person form this forum had a Wal, and took a lot of photos of the electronics, so I traced it from there. I'm not sure if I can post the schematic here or not but I did post it on another forum where he was doing a project of cloning a Wal. Not sure if I'm allowed to post links to other forums and stuff like that, but if it's allowed, I can give a link.

The mixing is quite simple actually - it's just a summing amplifier. It doses have a transistor differential input, but that's because the opamop used is old technology and needed to be "improved".

 

[David Mochen]

Oh no, I've never had the chance to hold a Wal in my hands either. One person form this forum had a Wal, and took a lot of photos of the electronics, so I traced it from there. I'm not sure if I can post the schematic here or not but I did post it on another forum where he was doing a project of cloning a Wal. Not sure if I'm allowed to post links to other forums and stuff like that, but if it's allowed, I can give a link.

The mixing is quite simple actually - it's just a summing amplifier. It doses have a transistor differential input, but that's because the opamop used is old technology and needed to be "improved".

Goes without saying I'd love to be able to take a look at that schemo

 

[SuperFunkyPete]

I think we can safely post links to the thread where I’m working on the Wal-alike.

The links I start sharing to @Kinkh’s work starts here - Building a Wal....ish

There are schematics there. Or beginning ones, he shares more later. Starting here: Building a Wal....ish

I have recorded one video with the ACG EQ-01. The link is here -

The Lusithand will be the subject of the next video, and then I will replace the neck with a multi-laminate neck and record the sonic difference with that.

The Luisthand is presently installed in the ‘Wal-ish’, and inherently has a much grittier nature than the ACG EQ-01. However it lacks a bright switch, and doesn’t go as low. It sounds fabulous though.

@David Mochen I am very interested in your preamp given it uses the same topology as the Wal preamp and has a bright switch. Does it also add some ‘grit’ to the tone the way the Lusithand does?

 

[David Mochen]

I think we can safely post links to the thread where I’m working on the Wal-alike.

The links I start sharing to @Kinkh’s work starts here - Building a Wal....ish

There are schematics there. Or beginning ones, he shares more later. Starting here: Building a Wal....ish

I have recorded one video with the ACG EQ-01. The link is here -

The Lusithand will be the subject of the next video, and then I will replace the neck with a multi-laminate neck and record the sonic difference with that.

The Luisthand is presently installed in the ‘Wal-ish’, and inherently has a much grittier nature than the ACG EQ-01. However it lacks a bright switch, and doesn’t go as low. It sounds fabulous though.

@David Mochen I am very interested in your preamp given it uses the same topology as the Wal preamp and has a bright switch. Does it also add some ‘grit’ to the tone the way the Lusithand does?

@Peter Weil thanks for your interesting! (edit)Have NOT(/edit) tried the Lusithand myself, though I can say my Filtrum is based on a pretty simple designed, entirely JFET-opamp based. It can growl if you push it hard, but my goal was to make it clear and versatile.
Here is another video in which I explain how it works.



Cheers,

David

 

[SuperFunkyPete]

The videos are helpful @David Mochen. I like the preamp; it sounds like it may be towards the cleaner side compared to the Lusithand. Amazing to see more filter preamps out there in the wild now!

 

[Passinwind]

Thanks for the info! Sallen-Key is actually a very economical solution once you figure out how to make
I tried that topology as well, worked very nice. Later I had a chance to trace the original Wal preamp, and to my surprise, they used the same topology as well.

So did/does Alembic in many if not all cases, per their own posts in the Alembic Forum.

 

[aquataur]

Greetings. This is my first post here.
@Passinwind, I hope you still monitor this thread.
I like the looks of your preamp and I contemplate building one.
In post #8 you explained that your preamp was originally destined to go directly into the instrument, but that most people use it as an external stomp box with a generic bass.
I wonder how much sense this makes.

An unloaded pickup may exhibit a resonance far up in frequency, which is good for this purpose. You place a new resonance wherever you like and adjust the peak to your like with your (on-board) preamp.

But conventional basses, particularly if they have passive cut controls but are buffered, usually have their resonance set at a pleasing frequency by means of a "voicing" capacitor and maybe a taming resistor for the Q.

So in applying your preamp (or any other), I would think that one can shift the natural resonance lower, but I don´t see how you can cancel that roll-off out and shift the peak upwards in frequency.

You say the pre-amp can to an extent. Please elaborate. It is vastly appreciated.

 

[Passinwind]

Greetings. This is my first post here.
@Passinwind, I hope you still monitor this thread.
I like the looks of your preamp and I contemplate building one.
In post #8 you explained that your preamp was originally destined to go directly into the instrument, but that most people use it as an external stomp box with a generic bass.
I wonder how much sense this makes.

An unloaded pickup may exhibit a resonance far up in frequency, which is good for this purpose. You place a new resonance wherever you like and adjust the peak to your like with your (on-board) preamp.

But conventional basses, particularly if they have passive cut controls but are buffered, usually have their resonance set at a pleasing frequency by means of a "voicing" capacitor and maybe a taming resistor for the Q.

So in applying your preamp (or any other), I would think that one can shift the natural resonance lower, but I don´t see how you can cancel that roll-off out and shift the peak upwards in frequency.
You say the pre-amp can to an extent. Please elaborate. It is vastly appreciated.

If you knock the preamp input impedance down to a very pickup specific range you can more or less neutralize the native resonance peaking and then interpose a new peak anywhere you like. Sometimes this sounds quite natural and sometimes it doesn't though. I've found something around 220k ohms to work pretty well in many cases, but some pedal builders have pushed back and wanted to retain some or all of the native voicing, which can sound fine too, especiallf if cutting treble is your primary goal. And then more recently I've been doing boxes for piezo pickups as well, which I've still found to benefit from a lower impedance load than normally expected. For example, the Fishman BP-100 upright bass pickup is often cited as sounding best with a 10 meg ohm load, but I found something around 700k to work best for the specific bass and player I built it for. One friend's piezo equipped acoustic guitar seems to like 500k best too, go figure.

I'd suggest you post this query in the long thread in the Pickups and Electronics forum as well, there are finally several new builders giving good feedback on the newer design and hopefully carrying the torch as I move toward retirement and concentrating on other instruments than bass as my primary focus. I am still monitoring TB almost daily for the moment though.

Oh, and finally: I feel that starting with purpose built low-ish impedance pickups would be preferable for onboard builds, and one of my luthier friends has promised to wind me some once his workload stabilizes a bit more.

 

[aquataur]

If you knock the preamp input impedance down to a very pickup specific range you can more or less neutralize the native resonance peaking and then interpose a new peak anywhere you like.

I suppose this works if the pickup is directly wired to the pre-amp, but not if there is active electronics (like a buffer of sorts) in between.
Incidentally, this is exactly the load value fender-ish single coil pickups "see" by means of the subsequent pots.
500k in Gibson style guitars (and probably other hum-bucker equipped guitars).

Fellow musicians have written how much they like amp XY and how great it sounds. I reckon, this is highly subjective. I guess I have to try it and see for myself, or I will never know.

I like your work and your approach. I understand that you want to move on. I can see some similarity between you and me.

 

[Passinwind]

I suppose this works if the pickup is directly wired to the pre-amp, but not if there is active electronics (like a buffer of sorts) in between.
Incidentally, this is exactly the load value fender-ish single coil pickups "see" by means of the subsequent pots.
500k in Gibson style guitars (and probably other hum-bucker equipped guitars).

Fellow musicians have written how much they like amp XY and how great it sounds. I reckon, this is highly subjective. I guess I have to try it and see for myself, or I will never know.

I like your work and your approach. I understand that you want to move on. I can see some similarity between you and me.

My load impedance assumes a passive bass with the usual volume and tone control, so the actual pickup loading will be considerably lower. If the bass is active then volume controls and/or blend in front of the preamp, followed by a low-ish value input shunt. 220k or so works fine for thevpedal in both those scenarios, but with an actiive bass we can go lower as desired, I just did a 100k one for my active acoustic guitar yesterday actually.

I’ve put a lot of time into these things for the last seven years, have what I need for myself by now, and have many other interests beckoning.

 

[aquataur]

I'll give it a shot and report back, FYI. This may take a few weeks. Thanks for chiming in.

 

[Jerry Catanescu]

Indeed, if you can place a preamp directly after a pickup, the preamp has the latitude to effectively revoice it over a very wide range. It just needs to play around with the resistive and capacitive loading, and perhaps add its own resonant peak, to taste. Sky's the limit. Worst kept secret in the biz! I really don't care much about what particular pickups I use anymore, so long as they're not noisy, they make a good thumb rest (on a bass) and have good string to string balance. The rest is negotiable.

 

[aquataur]

I just realize that I can toggle my L-2000 to passive. Didn´t think because I never saw a reason to use this.
This is going to be interesting. I made up a PCB with Version 2, so I can say within a few days how it works.

I had thought that the input impedance of the amp was rather low, but after Charlie pointed out that this was deliberate to dampen the pickup this sheds a different light on it.

Actually, it is not such a well kept secret: C-Switch vs State-Variable Filter (SVF)
However, the guy uses a SVF to revoice a pickup.

But I agree, the fact is not necessarily hung on the big bell by any manufacturer of pickups