The Passinwind Open Source Preamp

[Passinwind]

I have a lump of wood put aside that was the remains of a tree from a bush fire about 30 years ago, I saw it sticking up in the bush and it was all black and burnt.
It was about 7 meters long when I dropped it and about 1/2 meter thick but fairly solid, I started to cut it up for firewood but I liked the colour of the grain so I left 5 feet and cut it up for planks and made a nice outdoor table.
I have left the exterior slab that is left from cutting planks and it is about 4 feet long by 20" wide and around 5" thick in the middle, I always thought I might try to carve a guitar out of the one piece of wood and try to keep some of the burnt edges on it.
Some of the wood has gone really hard from the heat and really rings when I tap on it, the parts I used for firewood burnt for a long time when I used it.
I wonder if I could make a slot for a truss rod and then make another piece of wood to slip into the slot so you can't see how I got it in there.
I always liked the look of those mini Les Paul guitars where the body is about 3/4 size with a full neck, maybe a mini Violin Bass build ?

Cool. Marco has a killer fire damaged acoustic guitar sitting in his living room, it could use a neck reset but is otherwise fantastic.

And he's doing some mini Jazz Basses with 18 frets but a full scale length now, I'm sure one will work its way into my shop soon enough!

 

[Tassieviking]

Those mini Jazz Basses sound cool, mini guitars with a small body but full scale are good if they are small enough to get onto planes in the normal luggage size. Maybe a short scale Bass with a mini body would be good for traveling.

I think this might be the Lithium power bank I bought, it looks very similar :12V 400A Glovebox Jump Starter and Power bank LI-PO | Jaycar Australia

I think there are smaller LiPo ones now, but if it lives under the pedals on a pedal board it should be fine.

 

[Tassieviking]

So just jumping back a page to those Fishman battery packs, those boys (and girls) over at FSB have already jumped on them.
(disected, traced, remade)
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[Passinwind]

So just jumping back a page to those Fishman battery packs, those boys (and girls) over at FSB have already jumped on them.
(disected, traced, remade)
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Did I miss the part that shows the actual battery?

 

[PeaveyPlayer]

Are you just doing filter preamps or regular 3 band Eq as well?

 

[Passinwind]

Are you just doing filter preamps or regular 3 band Eq as well?

I do one, two, three, and four band “regular” EQ preamps too, but only for a few luthier and/or pro tech friends. At one time I had grandiose plans to release many more open source designs, but by now I only expect to add two or three more utility modules and call it good.

 

[dcoyle]

Good luck on NAMM.

A question, please. Each of the circuit schematics for the three boards of the PW3B,
GitHub - Passinwind/PW3B-LPF: Open Source Filter Preamps for Bass, Guitar, Mandolin, and other musical instruments
shows the local power supply caps for that board, but I wonder if you would describe the best way to protect against reverse voltage polarity for all three boards?

I've seen diodes used in series to only pass the correct polarity and in parallel to shunt the wrong polarity to ground. How should the PW3B be set up? Do you have a particular diode recommendation for that position?

Is there any simple, acoustically transparent way to protect against over voltage?

Thanks

 

[Passinwind]

Good luck on NAMM.

A question, please. Each of the circuit schematics for the three boards of the PW3B,
GitHub - Passinwind/PW3B-LPF: Open Source Filter Preamps for Bass, Guitar, Mandolin, and other musical instruments
shows the local power supply caps for that board, but I wonder if you would describe the best way to protect against reverse voltage polarity for all three boards?

I've seen diodes used in series to only pass the correct polarity and in parallel to shunt the wrong polarity to ground. How should the PW3B be set up? Do you have a particular diode recommendation for that position?

Is there any simple, acoustically transparent way to protect against over voltage?

Thanks

Hey Dan,
I don't use any polarity or overvoltage protection in most analog builds, as it's just never proved necessary in my particular use cases. @Tassieviking included a pretty simple scheme for both polarity and overvoltage protection in his still languishing v2 pedal design, maybe he'd care to elaborate.

Apparently NAMMthrax was especially brutal this year, and I think my friends from the booth my stuff was in are only finally getting back to work this week. I'm glad I didn't go as I also heard it was even louder and more chaotic than usual.

 

[Sanj]

A question, please. Each of the circuit schematics for the three boards of the PW3B,
GitHub - Passinwind/PW3B-LPF: Open Source Filter Preamps for Bass, Guitar, Mandolin, and other musical instruments
shows the local power supply caps for that board, but I wonder if you would describe the best way to protect against reverse voltage polarity for all three boards?

I've shared a few PCB designs on OshPark that incorporate input diode protection. Each should be fairly self-explanatory, but I'd be happy to elaborate if needed. The first one is what I used for my PW3B builds.

OSH Park ~

oshpark.com

OSH Park ~

oshpark.com

OSH Park ~

oshpark.com

 

[Tassieviking]

I usually just use a schottky diode in my pedals, if it is voltage sensitive I have used a schottky diode and a zener at the same time but I don't like doing it too much.
The best is to use a Mosfet with a zener but I have never done it (yet).
My usual trick is I solder a 1N5817 diode to the power socket and the other end on the positive wire to the PCB if there is no diode on the PCB, if there is a place on the PCB for a diode then I still use a 1N5817 diode because they have a low voltage drop.
One way I have not tried is using a suitable polyswitch between the power source and the PCB and then have a zener for reverse polarity / overvoltage protection (shorting out reverse voltage)
Invalid Link Removed
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Here is an explanation for different versions:

https://barbarach.com/reverse-polarity-protection/

Edit: my last V2 pedal is not working right and is waiting for me to get my cro out and do some testing.

 

[Passinwind]

I've shared a few PCB designs on OshPark that incorporate input diode protection. Each should be fairly self-explanatory, but I'd be happy to elaborate if needed. The first one is what I used for my PW3B builds.

OSH Park ~

oshpark.com

OSH Park ~

oshpark.com

OSH Park ~

oshpark.com

I was going to link to an older version of yours, thanks for the update!

 

[dcoyle]

Thanks Charlie,

"I don't use any polarity or overvoltage protection in most analog builds, as it's just never proved necessary in my particular use cases."

I have a fear of putting the battery wrong-way-round when I go to change them, so my use case is moron proof.

I didn't notice a mention in the OP164X data sheet about what ability, if any, the IC has to handle reverse polarity. Any observations?




Thanks Sanj,

"The first one is what I used for my PW3B builds."

OSH Park ~​

I got a few of those from Osh Park when you posted about them, months ago. Thanks for sharing them, it's what I plan to use for power distribution in the pedal, whenever I get my tail back in gear.


Thanks Tassieviking,

"My usual trick is I solder a 1N5817 diode to the power socket and the other end on the positive wire to the PCB if there is no diode on the PCB, if there is a place on the PCB for a diode then I still use a 1N5817 diode because they have a low voltage drop."

Thanks for your power socket mount tip, it's the best way to mount it, lacking a board. And you hit it with the 1N5817 recommendation. If I read the chart right, the Vf is scrapping no more than 0.1VDC off the power supply at the currents the PW3B operates at. Doesn't seem too bad a headroom loss compared to
trying to change out the IC's.

 

[Passinwind]

Thanks Charlie,

"I don't use any polarity or overvoltage protection in most analog builds, as it's just never proved necessary in my particular use cases."

I have a fear of putting the battery wrong-way-round when I go to change them, so my use case is moron proof.

I didn't notice a mention in the OP164X data sheet about what ability, if any, the IC has to handle reverse polarity. Any observations?

I wouldn't be using OP1641/1642 with batteries in many cases at all, personally.

When I do use simple diode protection it's generally with a 1N5818, which seems to be slightly cheaper and easier to find than 5817 at my preferred vendors. Sometimes I attach one to the power inlet, but I often put it inline in the power cabling instead, with shrink wrap to insulate it. And then I tend to run the pedal at either 12 or 15 volts, so the diode forward voltage drop doesn't bug me as much as it does in a 9V widget.

You mentioned NAMM, I did get good feedback on both pedals I sent and especially on the per-pickup preamps in the nice singlecut Marco had me modify. Right now I'm trying to finish up an alt. body for my fretless that has my original version of what became the the singlecut's onboard electronics. The new body was a survivor of the Marco Bass shop fire and may not have been the smartest thing to take on, but here's the basic new look, with a few more tweaks sure to follow:

Center block and top wings are ash, back wings are Doug fir. The blank hole is for the Q switch, which I'd still like to do a 3 way format for. To my eyes at least, the new control layout is a little more intuitive, but let's face it, this is always going to be a tweaker's kind of a thing.

 

[dcoyle]

Really beautiful bass.

Still Mid and Bass Bax on the neck pickup and LPF frequency and Q on the bridge, using the volume pots as a mixer??

Have you chosen one frequency for the mid Bax or is there a switch for it? If one freq, what did you go with?

" ~700Hz, but I may end up wanting to take that a bit lower, I think. The new mixer format makes using mid cuts a lot more useful, since there's now makeup gain readily available. "


Is that ~700Hz still your thinking on the Mid ?

Please, what bass frequency are you using on four stringers?

I've never heard this split EQ arrangement, but am trying to imagine how it sounds/works.

Since the Mid Bax shelves, is the neck pickup upper end unthrottled in boost setting, to which you add a resonant bump from the bridge pickup?

Or does "using mid cuts" mean you use the mid to shut off the neck above 700Hz, where the bridge takes over?

"Center block and top wings are ash, back wings are Doug fir."

Uh, front wings are fir, que no?

 

[Passinwind]

Really beautiful bass.

Still Mid and Bass Bax on the neck pickup and LPF frequency and Q on the bridge, using the volume pots as a mixe

Is that ~700Hz still your thinking on the Mid ?

I think a switch may be in order, but 700 is magic for my fretless EQ preferences

Please, what bass frequency are you using on four stringers?

Typically between 41-43Hz at full boost, which gives 50-ish or a little below at the mild boost settings I might use. But there's always an HPF somewhere downstream. But for this new one I think it's 38Hz at full boost, which puts it back around the low forties at rational (<12dB) boost settings.

I've never heard this split EQ arrangement, but am trying to imagine how it sounds/works.

Since the Mid Bax shelves, is the neck pickup upper end unthrottled in boost setting, to which you add a resonant bump from the bridge pickup?

Or does "using mid cuts" mean you use the mid to shut off the neck above 700Hz, where the bridge takes over?

"Center block and top wings are ash, back wings are Doug fir."

Uh, front wings are fir, que no?

The Bax Mid section is bandpass, not shelving. Same as for my standard two band preamps. But yeah, I haven't gotten to dealing with a possible passive tone or some other simple LPF for the neck side. I thought about doing that for the fretted NAMM bass as a first test, as I virtually never use treble cut on my fretless onboards, especially on that pickup. The way the two channels sum lends itself to a lot of different EQ strategies, including more or less both the possibilities you mentioned. Full mid cut will shut off highs on the neck side pretty effectively, especially for tweeterless cabs.

According to Marco the front of that body is all ash, with the center block having a completely different grain orientation. I had to do quite a bit of carving/shaping, the back wood is a lot softer and has that reddish tint of fir for sure.

 

[dcoyle]

"According to Marco the front of that body is all ash..."

Sorry to waste time.

"The Bax Mid section is bandpass, not shelving."

Please, around what F3 are you shutting down the Mid Bax ?

Thanks

 

[Passinwind]

"The Bax Mid section is bandpass, not shelving."

Please, around what F3 are you shutting down the Mid Bax ?

Thanks

At max Mid boost -3dB points (3dB below the +14db of mid boost at 700) are ~350Hz and 1.4kHz. But I never use anything close to that much Mid boost, personally. At a more useful +6dB of mid boost the 3dB down point moves up to more like 3kHz. All of this ignores the final mixing section, which by design allows more or less divorcing the Bax relationship between Q and gain. The composite curves for the two pickup summing are pretty darned interactive and hard to characterize with a simple Spice model.

Not surprisingly, I found out today that at least one potential buyer for the singlecut bass at NAMM with my preamp in it passed because he couldn't wrap his head around how to get where he needed to go intuitively. I find it much easier and way more effective for myself than a straight B/M/T Bax or any of the usual EQ suspects I've worked with, but I then again I didn't have to figure it out in the horrendous audition space that is NAMM.

 

[Passinwind]

Hey my friends,

In two weeks I will finally be retiring completely, for real this time. No more support from me for this project or any others. It's been a lot of fun and a great learning experience on my side, and hopefully for at least some of you. Not looking for props or anything like that at all please, as I have already gotten way more love and attention on TB over the years than I could possibly deserve. So I just want to canvas for any wanted last minute additions to my GitHub repository at GitHub - Passinwind/PW3B-LPF: Open Source Filter Preamps for Bass, Guitar, Mandolin, and other musical instruments

The only addition I currently have on my plate is a simple midrange frequency spreadsheet for the mid switch option, and an optimized 700Hz format for non-switched applications. Anything else you all want as far as the v4 pedal only? All the older versions are obsolete and have been removed, build 'em now or lose 'em, I'm afraid.

As far as the onboard ones, there are now so many excellent commercial ones out there that I'd highly recommend just buying whichever one suits your needs, the modular builds I've been doing are ridiculously time intensive and wouldn't save you enough in parts cost to be remotely worth it IMO. Out of deference to the various commercial builders who have greatly helped me over the years I'm not going to show my homework at this time, I hope you all understand.

Last call, ask now or it's not going to happen!

 

[Jared Houseman]

This project has been such an inspiration over the years. I'm just about to graduate with my electrical engineering degree. This thread definitely contributed to my decision to go to college and take up engineering.

I'm on spring break this week. Hopefully I'll finally get around to knocking out my fretless preamp

 

[Passinwind]

This was my last official onboard preamp install, finished a few minutes ago. But my best "civilian" customer may get one in under the wire.