Pickup simulators

[RobA]

I've never played on/with a Wal bass, so I really don't know. I did just take a quick look at one of their brochures and it does describe using a resonant LP filter. It says the tone pot has a switch to invoke a 10dB gain near the rolloff freq. So, that's a bit different but probably tonally similar.

It does say that they use a flat response humbucker to start with. That's going to have a lot to do with the sound. 

[kothoma]

What does the dual pot actually do???Does it balance from one freq to the other?

It sets the cutoff frequency of the lowpass filter and its resonance peak.
You can set it anywhere from 300Hz to 4.8kHz.

[kothoma]

One other thing that has been alluded to above is that this really won't work in a straight forward way for most pickups. Since the pickup already has an input resonant LP or two, it's cutout many of the frequencies you are going to want to get another pickup's sound. Or, since it's got a resonant peak of it's own, you'll have to counter that to get a flat response to then shape yourself. The whole idea would work much better with active pickups. For guitar, the SD Blackouts are pretty ideal this way. I've got them in my Les Paul and you can shape them all over the place.

You don't necessarily need low impedance pickups. Single coils usually have a high res freq and the idea is to lower it for fatter sounds. One additional trick is to use higher value pots in the guitar to load the pickups less.
As for humbuckers you indeed need to compensate the existing lower peak, but I already wrote that above. Wiring them in parallel is also an option.

[kothoma]

One other thing that has been alluded to above is that this really won't work in a straight forward way for most pickups. Since the pickup already has an input resonant LP or two, it's cutout many of the frequencies you are going to want to get another pickup's sound. Or, since it's got a resonant peak of it's own, you'll have to counter that to get a flat response to then shape yourself. The whole idea would work much better with active pickups. For guitar, the SD Blackouts are pretty ideal this way. I've got them in my Les Paul and you can shape them all over the place.

I'm just a big Wal bass fan...I believe the Wal preamp works some how like this one...am I wrong?!

I'd guess so. If not a SVF then a similar resonant lowpass filter is used.

[kothoma]

I'm a bit confused as to why an SVF though. The main strength of the SVF is that it's got LP, BP, and HP taps in the one structure. If you aren't using those and only want the LP, there are probably better resonant lowpass filters that you could use.

Why not? It's a simple and stable topology and is able to deliver real high Q and a great sweep range for the cutoff frequency.
A biquad would need the same amount of op amps.
What other second order res lp filter do you have in mind?

[kothoma]

Another alternative would be using a combo of a high shelf cut and a PEQ filter for the resonant peak. You could set those to move independently and get a wider range of pickup simulation and tighter control of the Q and resonant peak height.

That's not needed. You just want to simulate the natural L-R-C equivalent of a pickup (a second order lowpass).

[garfo]

On my bass I use two passive humbucker, I can connect them as Single/Parallel humb/or series humb.From what I've read before, wiring it in Parallel would be better to work well with this type of circuit.
The Wal preamp is based on an Alembic preamp as well, so I assume this would be the "base" one.
Any idea on how to add that extra 10k peak to the rollof frequency?

[kothoma]

Any idea on how to add that extra 10k peak to the rollof frequency?

That's what the resonance pot is for... Seems like it's only switchable on that Wal preamp?

Here you can see that this SVF can provide >16bB gain at the peak:

[RobA]

No reason why not really. I did say I was only a bit confused . It makes sense for an on instrument situation because of the amount of control you get for the minimal number of knobs. But in the case of doing it in a box, I'd look first at parametric EQ's. I'd use a variable high-shelf in a cut only arrangement and and a pair of PEQ's. It would give you a ton of flexibility for correcting the resonance of the input signal and adding the resonant peak where ever you want it to sit. It would be much more complicated knob wise, but I've got a thing for PEQ's anyway.

There are other things that are worth experimenting with too. Lots of resonant LP filters from the synth world might be really fun to use this way. Most of them would probably be less accurate than the SVF approach but might be more colorful too.

[RobA]

[...]
That's not needed. You just want to simulate the natural L-R-C equivalent of a pickup (a second order lowpass).

No it's not needed, but it can help. Different pickups have different amounts of resonance and the rolloff isn't completely straight forward either. It's more complex than a straight LRC filter because the L, R, and C are intermixed in the same device. In addition to that, hum buckers make it even more complicated because of the way the two coils interact as two LRC filters. The PEQ approach just gives you much more flexibility to match the frequency responses of a variety of pickups.

[kothoma]

Anyway, you will always only get an approximation, good enough if you'd need to switch guitars on the fly.

I found that I don't need many different Qs, a 3-way-toggle should be enough.
If I'd build it again I probably would include parametric mids in front, perhaps with fixed Q.
OR have only maybe two presets to select, because this knob twiddling is really tricky.

BTW It was this circuit that brought me back to DIY world after many years of absence as you can't simply buy it at the next corner.

BUT: Nothing really beats having several guitars with different pickups!

[RobA]

Interesting circuit to be the one to bring you back. It makes sense though, lots of good stuff going on in there with interesting musical effects.

You are absolutely right about the complexity of using a PEQ approach and being tricky to set. It would be hard to use without some kind of preset system. Being able to flip between 3 presets would be pretty ideal.

My path for getting multiple guitar sounds in one guitar was to go with the SD P-Rails and a blend pot for pickup mixing. But even there, I've ended up with 5 toggles and a blend pot. Still kinda crazy but it has tons of tonal possibilities. I do really like the P-Rails.

[kothoma]

Yeah, I'm still considering the P-Rails. You blend the two coils (the P90 and the rail) of one pickup?

[RobA]

Yeah, I'm still considering the P-Rails. You blend the two coils (the P90 and the rail) of one pickup?

No, the blend pot replaces the pickup selector. For each pickup, I've got two toggles that let's me have P90, rail, parallel, and series. I also have a fifth toggle that puts the neck and bridge in series.

The standard series humbucker setting isn't my favorite humbucker in the world. In fact I find it a bit bland. It is good for really heavy stuff but not much else. The parallel humbucker setting is a very nice bright sounding HB though and the two rails in series make for a very nice humbucker. Both of the single coil settings on both neck and bridge are really nice. The bridge P-90 with volume bypassed is a monster. (I've got no tone controls on the guitar either.)

[kothoma]

The standard series humbucker setting isn't my favorite humbucker in the world. In fact I find it a bit bland. It is good for really heavy stuff but not much else.

That was my impression too.

The parallel humbucker setting is a very nice bright sounding HB though and the two rails in series make for a very nice humbucker. Both of the single coil settings on both neck and bridge are really nice.

So a simple on/on/on toggle per pu would be enough.
I've heard some people use them with the blades outside and P90s inside to bring forward the strat/tele single coil sound.

The bridge P-90 with volume bypassed is a monster.

But you're not using the Hot model? No toggle switch for the vol bypasss?