The Passinwind Open Source Preamp

[Passinwind]

Here is a quick pic from KiCad of the footprint.
I place the TH and the SOIC on the board with 2 VIAS and then I add the traces after.
I can make the footprint joined into one but I haven't figured out how to add the traces to the footprint so they get placed later.
I made the footprints but they might still be in the KiCad7 version on my old computer, I have to go search for them.
I also have one for the resistors and one for diodes that can be TH or SMD

Cool, I think I could make that work OK for some pedal formats, at least.

 

[Sanj]

This is the footprint I made in KiCad 6.0. It turns out that including the traces as part of the footprint causes DRC violations, so they actually have to be added separately in the board layout. Fortunately, giving the SMD and through-hole pads the same pin numbers works as one would hope.

 

[Passinwind]

Here's my current stab at an (almost) all in one through-hole part version 2 board, now at 58mm square dimensions. I have quite a few other projects in my queue before I can even think about getting any boards made. If any of the usual suspects care to take a chance on an untested layout they can PM me for the Gerbers, but maybe bear in mind that it took me three tries to get the last one right!

There's a separate little breakout board for the on-on-on toggle switch, but it's probably not especially needed for this build. Just one jumper and three flying wires from the main board, so pretty simple to hand wire.

I tested the two v2 pedals in post #1557 with my acoustic guitar for quite a while today, along with a newly revised modular v2 build in a Tayda 1590B case I've had kicking around for years. As I've mentioned several times by now, I think the v2 format is actually a bit nicer for acoustic instruments than bass guitar, but for those who already have a variable HPF somewhere else in their signal chain it works fine for BG too. And I wouldn't bother with uptown opamps, TL072 is just ducky for this application in my book.

 

[Passinwind]

I tested the two v2 pedals in post #1557 with my acoustic guitar for quite a while today, along with a newly revised modular v2 build in a Tayda 1590B case I've had kicking around for years. As I've mentioned several times by now, I think the v2 format is actually a bit nicer for acoustic instruments than bass guitar, but for those who already have a variable HPF somewhere else in their signal chain it works fine for BG too. And I wouldn't bother with uptown opamps, TL072 is just ducky for this application in my book.

Oops, that last blurt should have said 1590BB, like so:

This week I've been playing around with higher LPF max frequency tunings, up above 12kHz in some cases. It's not so much that I need to go that high, but it puts the most useful sweep range (~2k-6kHz) right between ten and two o'clock and it also makes "all knobs at noon" a very nice setting for acoustic guitar or bass guitar. The tradeoff is losing the 400-800Hz range, but the midrange controls can already handle that anyway.

 

[Passinwind]

I'm just finishing up what I expect to be my last two PW3B-LPF pedal builds for a while, since I've been sitting on these enclosures for quite a while and already had all the other needed parts on hand as well:

This one ^ will be getting a fixed frequency HPF installed tomorrow, but I could see adding a trimpot option in future board revisions. An always-on version would probably fit fine in a 125B enclosure, FWIW.

And this ^ is the first battery powered v4 build, using OPA205 and OPA2205 low current opamps as recommended by @Jerry Catanescu at JTEX. Initial bench and listening tests today were very promising, for both BG and acoustic guitar.

 

[Malak the Mad]

I'm just finishing up what I expect to be my last two PW3B-LPF pedal builds for a while, since I've been sitting on these enclosures for quite a while and already had all the other needed parts on hand as well:

View attachment 7015517

I wonder how many people will know what a "mantis shrimp" actually is, let alone what ferocious killing machines they are in nature.

 

[Passinwind]

I wonder how many people will know what a "mantis shrimp" actually is, let alone what ferocious killing machines they are in nature.

Quite a few people seem to have seen the same OBP show a few years that I learned about them from, FWIW. But yeah, I wouldn't want to mess with one.

 

[Tassieviking]

I had a quick look at the local "Silicon Chip" electronic magazine while I was in the shops today, there was a pick guard build where the pick guard was a PCB and any electronics was SMD on the inside of the pickguard, even the pots were soldered to the inside of the pickguard.
It looked interesting and I straight away thought of Charlie and all his inboard preamps, no internal PCB needed since its all on the pickguard.
I might have to buy the magazine when I go to the shops next time because the idea is growing on me.
You can see the front only on the online preview of the magazine:

Electric Guitar Pickguards - September 2024 - Silicon Chip Online

The control circuitry on electric basses has remained remarkably simple since Leo Fender first introduced the instrument over 70 years ago. These modern PCBs offer more advanced features and a cool aesthetic. They suit many popular models of electric bass as well as the Fender Telecaster...

www.siliconchip.com.au

 

[Passinwind]

I'm just finishing up what I expect to be my last two PW3B-LPF pedal builds for a while, since I've been sitting on these enclosures for quite a while and already had all the other needed parts on hand as well:

View attachment 7015517

This one ^ will be getting a fixed frequency HPF installed tomorrow, but I could see adding a trimpot option in future board revisions. An always-on version would probably fit fine in a 125B enclosure, FWIW.

View attachment 7015519

And this ^ is the first battery powered v4 build, using OPA205 and OPA2205 low current opamps as recommended by @Jerry Catanescu at JTEX. Initial bench and listening tests today were very promising, for both BG and acoustic guitar.

Just a quick follow up: both those builds have worked out extremely well and the battery powered one is now in my travel kit for open mics and the like, for both bass and acoustic guitar. Back to onboard builds now, as my old BSX EUB is long overdue for a freshening of the bespoke Bart preamp that lives in it. I'm thinking Bass/LPF, master volume...done. But it has individual piezo sensors per string, so it may easily end up being a lot more complicated than that. And since I do play with a bow fairly often, there are a lot of interesting tradeoffs to work through.

 

[Dirk Diggler]

Mantis Shrimp is the new Honey Badger, well of the sea at least.
LOL

Still absolutely enjoying my PW 2 band pre in the OLP by the way.

Cheers,
Dirk

 

[ctmullins]

Haven't gotten caught up on this thread in a while, but I noticed the Wiki pages are gone.

Is somebody working on that?

 

[dcoyle]

The info you may want is at GitHub - Passinwind/PW3B-LPF: Open Source Filter Preamps for Bass, Guitar, Mandolin, and other musical instruments

 

[Passinwind]

Haven't gotten caught up on this thread in a while, but I noticed the Wiki pages are gone.

Is somebody working on that?

It's in flux at the moment for a variety of reasons. TB Admin couldn't even manage to fully delete the old very obsolete one and my focus has mostly shifted to non-bass instruments, so a Github repository seemed like a decent interim solution. I'm also seemingly around here for a little while yet, so feel free to PM me or ask whatever here in this thread.

 

[dcoyle]

" I'm also seemingly around here for a little while yet, so feel free to PM me or ask whatever here in this thread."

Charlie, I don't know if it's stated somewhere else and I missed it, but could you post the specs for this now finalized OS PW3B version?

> HPF frequency sweep range

> The amount of bass max boost and max cut, and at what frequency

> The frequencies of the three midrange settings of the switch, and

> The amount of midrange max boost and max cut

> The frequency sweep range of the LPF

> The amount of max peak and max dampening of the RESO control at some useful frequency, say ?4KHz ?

> The max amount of make-up gain or cut

I think this would be useful to document for archival reasons, but also just to help folks (me) calibrate our ears.

Thanks

 

[Passinwind]

" I'm also seemingly around here for a little while yet, so feel free to PM me or ask whatever here in this thread."

Charlie, I don't know if it's stated somewhere else and I missed it, but could you post the specs for this now finalized OS PW3B version?

> HPF frequency sweep range

> The amount of bass max boost and max cut, and at what frequency

> The frequencies of the three midrange settings of the switch, and

> The amount of midrange max boost and max cut

> The frequency sweep range of the LPF

> The amount of max peak and max dampening of the RESO control at some useful frequency, say ?4KHz ?

> The max amount of make-up gain or cut

I think this would be useful to document for archival reasons, but also just to help folks (me) calibrate our ears.

Thanks

I think all that info belongs in the Github repository, for sure. And now that I can do RTAs again I plan to post more actual measurements eventually, but I doubt I have anything built to the current OS spec on hand right now. I also need to post a mid tuning spreadsheet, because alt tunings hugely impact the overall play feel of the pedals. But for now, let's call these preliminary specs, which are modeled and not actually measured:

HPF, -3dB points at 26-100Hz with Bass control at nominal flat, which is at roughly 10 o'clock position.

Bass: +/-13.5dB @ 38Hz with HPF at 3 o'clock, peak frequency will be higher at any other Bass control setting. With Bass control at noon, HPF at 3 o'clock, Mids at noon, LPF res at 9 o'clock, and LFR freq at max, Bbass response is +3dB@56Hz. I'd suggest that the other end of the bass curve is more important (i.e. where do we start to hear the control kick in), but a posted graph will tell much more than anything written. But let's call it +3dB @266Hz with Bass at max, other control settings as above. If we take the midpoint that gives us a nominal 100Hz bass frequency spec, this is how Audere and some others spec their curves. But again, that's only at max boost, which very few people actually use IME.

Nominal Mid switch frequencies with all other controls as above, 240Hz, 408Hz, 1.6kHz.
Boost/cut at right/top position: +/ -14dB @ 1.6kHz
Boost cut at mid position: +/-8dB @ 480Hz
Boost cut at left/bottom position: +/- 4dB @ 240Hz
This looks goofy but works out really well in practice given interactions with various other controls.

LPF sweep with Res at max: 285Hz-8.2kHz.
LPF sweep, Res at min: -3dB @ 300Hz-6kHz

LPF gain at 4kHz peak setting: +15dB
LPF, w/Freq as above, Res at min: -3db @ 3.6kHz

Nominal boost/cut, all other controls at nominal flat settings: +5.3dB / - 6dB

I expect this will require some clarification, these specs are very far from straightforward in so many ways. And of course your first build is completely different than the OS spec, by your request at the time.

 

[dcoyle]

Wow! I had no idea it was so very interactive. I mean I did from the graphs on p.1 of the post that show that iteration's behavior, but when I listen/twist knobs, I only think about/notice the effect on the band I'm paying attention to. It's the engineer's vrs musician's mind set. Then you start playing again and have your musician's impression. I guess I do need a little aural calibration.

Thanks for taking the time to share all that.

 

[dcoyle]

" when I listen/twist knobs, I only think about/notice the effect on the band I'm paying attention to. It's the engineer's vrs musician's mind set. Then you start playing again and have your musician's impression"

You have your musician's impression, which is 'Oh that's nice', or 'That's not it' but you think that's the effect of tweaking XXX frequency, but it's not isolated like a 1/3 octave graphic equalizer, so you've really changed a whole lot of things in the EQ.

 

[Passinwind]

Meanwhile, my janky but great sounding Cabintech "Digital BBD" test box:

Top row: modulation frequency, modulation depth, feedback/regeneration.

Middle row: Left channel (Ch4) time, Master time base, Ch1 time, Ch2 time, C3 time. Ch1-3 all routed to Right channel output for now.

Bottom row: Dry volume, Ch1 vol, Ch2 vol, Ch3 vole, Input volume.

And yes, it could use at least a couple more knobs and a switch or three.

The production version of the Cabintech board is much smaller and all that functionality should easily fit in a 1590BB enclosure now. But of course I'm looking at using two boards next time and doing 8 taps with a full mono-->stereo mix matrix, so another mondo box is probably in the works.

 

[dcoyle]

"And yes, it could use at least a couple more knobs and a switch or three."

Well it looks like you've picked up a sponsor, anyway.

 

[Passinwind]

"And yes, it could use at least a couple more knobs and a switch or three."

Well it looks like you've picked up a sponsor, anyway.

More like "a free sticker is a good sticker." I think it's covering another pot hole, but IIRC there's no room to implement that at the moment due to all the various individual test modules. There are a few different gain and mix board versions in there, it's just way too convoluted. I'm really surprised that the noise floor is so good, but I'll take it!