Special Edition Build Off: The Thumfinizenvette

[ctmullins]

In my experience, having all possible combinations doesn’t necessarily make a better instrument. I would start by wiring them in their “normal” configuration (series? parallel? whatever Bartolini says...). Use that as a baseline, and add options based on what your ears tell you. North coil and south coil will probably sound very similar and thus redundant. Parallel and single coil can often sound similar, especially in a live mix.

 

[Reedt2000]

In my experience, having all possible combinations doesn’t necessarily make a better instrument. I would start by wiring them in their “normal” configuration (series? parallel? whatever Bartolini says...). Use that as a baseline, and add options based on what your ears tell you. North coil and south coil will probably sound very similar and thus redundant. Parallel and single coil can often sound similar, especially in a live mix.

This was my thought too. Any instrument I've had with a huge amount of options has always ended with only a couple that were actually useful.

 

[Dark Horse]

In my experience, having all possible combinations doesn’t necessarily make a better instrument. I would start by wiring them in their “normal” configuration (series? parallel? whatever Bartolini says...). Use that as a baseline, and add options based on what your ears tell you. North coil and south coil will probably sound very similar and thus redundant. Parallel and single coil can often sound similar, especially in a live mix.

could use a rotary switch

I’d probably do ...

*outside coils (South neck, north bridge)(parallel)
*all on (parallel)
*neck
*bridge
*series (all on)
*???


Also... a while back Washburn did a pretty cool thing where they had dual coil pickups and used a pot to add/subtract one of the coils, so it was continuously variable

 

[dwizum]

I know I want a single coil mode. I would be happy with one single coil choice in each. And I am pretty sure I would choose serial humbucker and the "other" choice. I guess I'll start with that since it's compatible with the controls I already have. I may hardwire the neck pickup as parallel and see how that sounds. It would be nice to get a sort of music man tone out of this too, and the neck pickup is kind of midway between typical jazz neck position and the music man sweet spot.

I do have to admit though that a rotary switch is intriguing. I'm trying to balance the attraction of having a billion choices against the reality that I'll probably just find one or two I like and never use the rest anyways. I don't really own any basses with a billion switches...

 

[Beej]

Nothing wrong with having a dozen choices and finding only two really are ones you go to. Better that than having only one or two tones and not clicking with it.

 

[dwizum]

Pickups are here! Props to Best Bass Gear for such a quick hookup on a hard to find item during "these times."

I think I've settled on wiring. I am going to replace all 4 pots with push/pulls and set them up as a pair of pots for each pickup, with one pot doing series/parallel and the other pot doing coil tap. The best wiring diagram I can find for this does have an unfortunate "hole" in that if the series/parallel switch is in parallel mode, the coil tap switch literally does nothing. It only coil taps in series mode. I don't think this will be a big deal though, and it's better than some of the other wacky diagrams I found, which had combinations of switch positions that would have resulted in cutting the sound. At any rate, this should give me a huge level of flexibility - each humbucker can be set to series, parallel, or single coil independently, and the pickup switch will let me choose bridge, both (in series) or neck. I'm going to go with the bridge coil on the bridge and the neck coil on the neck in terms of single coils, since those are the closest to jazz positions.

I am probably going to have to scale the tone stack again since I don't think push pull pots exist for the values I have in there now. This will be like the 4th set of pots in this bass. And to complicate things even further, I've gone ahead and ordered parts for two other preamp designs, just because I'm now so hooked on fooling with preamps. One of them is a generic three band I found on the internet that seems to be based on a 2 band music man preamp with mids added, and the other one is a clone of a Bartolini NTMB which I'm excited to try since I'm expecting it to match well with the Bart pickups.

What I really need to do though is just get a setup I like in this bass so it can be "done" and then I can use something else for experiments going forwards!

 

[JayGunn]

a generic three band I found on the internet that seems to be based on a 2 band music man preamp with mids added

Interesting! If you can publish here or PM me an image of the schematic for this EQ/preamp, I'd set it up in LTSpice and show you the sweeps of the 3 bands. Not only do you find out where the peaks are, but you get to see how they interact, which sometimes can be pretty odd.

 

[dwizum]

Hey @JayGunn! Here's the schematic for the supposed stringray based preamp. I found it on another forum as a perfboard layout and drew the schematic from that:

I'm wondering about a few things. I don't really want an actual musicman style tone. Would the cap values on the input have the biggest influence on the overall tone? Such as the 2.2nF from input to ground.

The Bartolini based design I'm working on seems like it's made it's rounds a few times over the years. I'll post it here too for completeness. I'm not used to seeing inductors in an eq like this, but I am pretty new at it. Does the resistance of those components on the wiper of the mid pot set the Q for the mid pot? I'm wondering because the inductors I ended up with are higher resistance than the ones on the original schematic. I'm wondering if I should drop the resistor in series down in resistance to end up with the same total resistance.

 

[MPU]

If that’s the same preamp that was talked about on Pickups that 2,2nF makes quite a difference. I have MM 3-band preamp clone on my Mungo and I swapped that 2,2nF to 1nF. Much more highs to boost, muck more natural than a bit muffled highs with 2,2nF.

 

[dwizum]

Good to know, thanks! I like a good, full spectrum response without muffled highs, but I'm not a fan of overly bright sounds either. Maybe I'll get a few values and experiment.

 

[JayGunn]

I'll get to the LTSpice promise I made in a few days. Today I had a bizarre nail gun accident which has switched me from wall building for at least a few days over to doing my taxes. They are usually dirt simple for me but this year I have to add up the cost of a house I built, by going through receipts spread over 5 years of construction time before it could become occupied.

Meanwhile check out Robbie K's comments in post #2 of the thread linked to below about the MM 3-band preamp.

MM preamp resonant peak cap/res value for passive MM setup application?

 

[dwizum]

Okay so now I'm reading about sallen-key filters. And I guess that, plus the 2.2n cap across the pickups, explains the distinctive music man tone.

I'm trying to understand the component values for that filter. The problem I'm having is that most of the examples I'm finding seem to have the R2 equivalent connected to ground (not vref) and don't have an R4. Here's one:

Link Removed

I'm going to keep looking, because I'd like to be able to understand how that filter works well enough to play with the component values and have some idea of what's going to happen. I agree with Robbie K's comment in that thread you linked, the typical MM style preamp seems to cut the bass too much and I'd like to fix that. This bass build aside, I'd like to get a music man-ish preamp put together that I like. I have an Ibanez ATK that is sort of a music man knockoff, and it suffers from the bass cut symptom really badly. It's almost like Ibanez copied the music man preamp and magnified the worst parts of it. I like the tone but it's one step too far. Even if I don't end up using this preamp in my buildoff bass I'd like to put it in that one.

I suppose I could just cut all of that out and use the first op amp as a unity gain buffer?

Also - sorry to hear about your accident!

Maybe I need to finally figure out ltspice for myself...

 

[JayGunn]

Here's a calculator for the HPF part, from Japan but in English:

Sallen-Key High-pass Filter Design Tool

If you replace each cap with a resistor and each resistor with a cap, you convert the HPF to a LPF, like passinwind uses in his preamp. I haven't ever created a circuit with a HPF, but I'm tempted to try it for a bass I will some day finish that has piezo pickups built into the bridge saddles. If you knock a piezo you get a huge thump, and the HPF would block the low freq part of that. "First finish the bass, then try out the HPF," that is my Big Plan.

 

[dwizum]

Thanks for the link. And I've been looking at the passinwind design too, for reference at least.

The thing I'm struggling with is that the design in the schematic I had drawn above doesn't really seem to match the typical sallen-key designs. In the sallen-key LPF designs, one resistor connects from output back to the junction of the caps, and the other resistor connects from the positive input to ground.

This preamp has the two caps, and it has the feedback resistor from output back to the junction of the two caps. But the resistor connected to the positive input goes to vref, not to ground. Does that change anything? Can you still use the same calculations to determine the values for the parts?

 

[JayGunn]

Okay time to have some fun with LTSpice. I'm not an expert but you'll see that you can get a lot of research done without being a complete master of it.

Here is my model of the pickup and the 3-band circuit you posted above:

Top left is a model of the pickup. Middle right is the model of the power supply. The LT1012 op amp left center could be any single op amp, as could the LT1351. These are not unreasonable choices, and because they are Linear Technology products, they come with the software.

When you install the program (it's free) you can start a new project and draw this my hand. The only problem you'll have is to get a copy of aud.sub and potentiometer.sub. I found them online. Aud.sub is an audio taper pot, and potentiometer.sub is linear taper. The output volume pot is the audio taper, naturally.

When you fire this up in LTSpice by clicking the Run button (silhouette of a running man) nothing happens at first. LTS is waiting for you to place the cursor over the wire at which you want to display the voltage. Click between C6 at the output and the top of "Vol." The cursor will turn into a cute little probe.

I'll continue in a following set of posts to show you the real fun!

 

[JayGunn]

Here's what comes out when you probe the output as it is currently set up.

What you're seeing is the output, swept from 20Hz to 20K Hz. This is dictated by the .AC command on the screen, to the right of the Mid pot. Meanwhile instead of a single line you see those 11 colored lines because of the .STEP commands on the screen, top right. If you want to see a single line (less fun but sometimes very useful, you would right click on the command you want to change and comment out the .STEP by starting it with a semi-colon, and uncommenting out the .PARAM command below it by removing its semicolon. As shown, parameter {R1} is stepped and {R2} is kept at a fixed value of 0.5, which means the linear pot is turned to the middle.

The bass section is following R1. So is the treble pot. But the Mid pot is following 1-{R1} so it is stepping in reverse. The green line is the Bass pot at 0.01 (counter-clockwise), then it becomes the highest line in the mids (fully clockwise at 0.99) and then lowest again on the treble pot (back to counter clockwise). It is best to start stepping at 0.01, not 0.00. Also best to stop a hair below 1.0 for fully clockwise...

Is this effing cool?

 

[JayGunn]

One more demo for today. Not fair to people who aren't into this to turn a build thread into an electronics thread, but you DID ask about the MM 3-band pre. Apologies for the diversion to all.

In this one we'll step only the Mid pot. Bass and Treb at 0.5. You will see how much the range of the mid adjustment is altered by interaction with Bass and Treb adjustments. Note how much more range there is sweeping the Mid pot if Treb and Bass stay fixed as compared to the one above. From maybe +-4dB at 400Hz in the first plot to more like +-8dB in this one.

And here is the section of the schematic I changed to do this plot. Changed Mid wiper from 1-{R1} to plain {R1}. Changed Treb and Bass to use {R2} which is set to 0.5

TB readers: please DO complain if you don't want me to say more about this. I have a lot up my sleeve but I don't want to impose it.

 

[dwizum]

This is really cool, I don't mind the "hijack" at all! Selfishly, I'm learning a lot, so I'm totally happy with you sharing this.

It looks like you changed some of the component values in the front end, the two caps went from 8.2n to 20n and two resistors went from 150k and 10k to 82k and 6.8k respectively. Was there a reason for that?

That's a big peak at roughly 4k!

 

[Beej]

More power to the nerds!

This is useful stuff to an idiot like me.

 

[dwizum]

Back in the shop for the next (maybe last?) round of surgery. In goes the Bartolini clone preamp I just finished soldering, along with the bart pickups and push pull pots for switching. I'm gonna leave the MM 3 band preamp for my old Ibanez and just "finish" this buildoff bass with the bart parts.