The Passinwind Open Source Preamp

[Jared Houseman]

I got parts and PCBs for an onboard fretless preamp on the way.

This is my first shot at an all SMD design and I'm working on building a reflow oven to go along with it

 

[Passinwind]

I still need to build mind. Hopefully, I can find the right instructions. The bits I have neatly labelled, at least.

Have I mentioned that I (a) don't like soldering and (b) I am rubbish at it? My wife's amazing at it, though...

Yeah, bribe your wife then. I still have old builds back to v1 kicking around and will help you make your build work no matter what version it is. Just PM me whenever you get going on it.

 

[Passinwind]

I heard it on the grapevine that retirement is when you stop the day job and start doing the things you love. How blessed when they are one and the same!! Best to you and yours!!

Thank you. Retiring from playing gigs several years ago brought a similar result: I still get out of the house to play with other people 1-2 times a week, but it's no longer an obligation or a meaningful part of my revenue stream.

 

[Passinwind]

And here we have a newly revamped v2 pedal, now with a 3 way HPF frequency switch:

I had been using this box as an R&D tester for acoustic guitar applications, with a fixed frequency HPF added somewhere along the way. I wondered if I could mostly keep the same response curves for guitar but port back to BG specs at the flip of a switch. Current rolloff hinge settings are 28-40-56Hz, which for me might equate to 5 string bass, 4 string bass, and guitar, respectively. Pretty much perfect for a grab and go open mike pedalboard solution, I reckon.

 

[Passinwind]

Update:

Unfortunately I had a very significant health setback in late June and it's uncertain if and when I'll ever be doing much more DIY electronics work at anything like my previous level. But so far I've exceeded my doctors' expectations quite substantially, and gotten through some fairly scary secondary medical challenges relatively unscathed, so there's plenty to be thankful for at least. I tried one pedal build last week and quickly learned that I'm not really up to that just yet, but even so, it works pretty well and if @Tassieviking or anyone else wants to exhume the small format through-hole pedal design fork I can offer better insight into the way forward now. In short, IMO it really needs SMD opamps and a bit more work on the board layout, but my most recent tuning seems to be the best yet by quite a bit, and I actually enjoy using this latest try:

There is one older 125B version that @Lo-E currently owns that I liked quite a bit too, but it uses very expensive LT through-hole opamps that just make for a stupidly expensive build. The one above uses my often preferred OPA1642, which is a very forgiving and relatively economical IC, and they seem stable enough for this application on simple adapter boards. Personally, I would just port to SAM footprints on the main board and use 1206 SMD resistors to boot, but that's just me. I had to pull the PCB out of the enclosure several times to fix a few simple mistakes, which would have only taken a few minutes with surface mount parts. I switched the bottom opamp in the above pic in about five minutes this morning, for perspective. That, with the adapter still hardwired in. OTOH, changing two through hole resistors twice meant destroying two pots and enduring two + hours of frustration.

In other news, I finally made up this new 3 way Q Switch for the preamp in my Marco Bass:

Haven't installed it yet, but I expect it to work fine and eventually make it to the OSHpark share section.

And finally, I worked out using a cheap Iniu power bank with my Cioks C4 pedal board supply, via a PD trigger board from Amazon:

This gives you the choice of 9, 12, 15, or 18V from a USB-C input, with a standard barrel adapter output. With 15V @ 2A the Cioks is good for 550mA X 4 at 9V, and proportionately less current at the higher available voltages, which are also 9, 12, 15 , or 18. You can also go USB-C to USB-C at about half the current capacity, if desired. The Cioks still steps up a 5V input to the same four output options, FWIW, and each output can be any of those voltages.

 

[edwinhurwitz]

I'm so sorry to hear of your health issues. Reach out if you need anything.

 

[-Asdfgh-]

Update:

Unfortunately I had a very significant health setback in late June and it's uncertain if and when I'll ever be doing much more DIY electronics work at anything like my previous level. But so far I've exceeded my doctors' expectations quite substantially, and gotten through some fairly scary secondary medical challenges relatively unscathed, so there's plenty to be thankful for at least. I tried one pedal build last week and quickly learned that I'm not really up to that just yet, but even so, it works pretty well and if @Tassieviking or anyone else wants to exhume the small format through-hole pedal design fork I can offer better insight into the way forward now. In short, IMO it really needs SMD opamps and a bit more work on the board layout, but my most recent tuning seems to be the best yet by quite a bit, and I actually enjoy using this latest try:

View attachment 7319032 View attachment 7319034

There is one older 125B version that @Lo-E currently owns that I liked quite a bit too, but it uses very expensive LT through-hole opamps that just make for a stupidly expensive build. The one above uses my often preferred OPA1642, which is a very forgiving and relatively economical IC, and they seem stable enough for this application on simple adapter boards. Personally, I would just port to SAM footprints on the main board and use 1206 SMD resistors to boot, but that's just me. I had to pull the PCB out of the enclosure several times to fix a few simple mistakes, which would have only taken a few minutes with surface mount parts. I switched the bottom opamp in the above pic in about five minutes this morning, for perspective. That, with the adapter still hardwired in. OTOH, changing two through hole resistors twice meant destroying two pots and enduring two + hours of frustration.

In other news, I finally made up this new 3 way Q Switch for the preamp in my Marco Bass:

View attachment 7319038

Haven't installed it yet, but I expect it to work fine and eventually make it to the OSHpark share section.

And finally, I worked out using a cheap Iniu power bank with my Cioks C4 pedal board supply, via a PD trigger board from Amazon:

View attachment 7319039

This gives you the choice of 9, 12, 15, or 18V from a USB-C input, with a standard barrel adapter output. With 15V @ 2A the Cioks is good for 550mA X 4 at 9V, and proportionately less current at the higher available voltages, which are also 9, 12, 15 , or 18. You can also go USB-C to USB-C at about half the current capacity, if desired. The Cioks still steps up a 5V input to the same four output options, FWIW, and each output can be any of those voltages.

Best wishes for your health.

 

[rumblinbass]

Update:

Unfortunately I had a very significant health setback in late June and it's uncertain if and when I'll ever be doing much more DIY electronics work at anything like my previous level. But so far I've exceeded my doctors' expectations quite substantially, and gotten through some fairly scary secondary medical challenges relatively unscathed, so there's plenty to be thankful for at least. I tried one pedal build last week and quickly learned that I'm not really up to that just yet, but even so, it works pretty well and if @Tassieviking or anyone else wants to exhume the small format through-hole pedal design fork I can offer better insight into the way forward now. In short, IMO it really needs SMD opamps and a bit more work on the board layout, but my most recent tuning seems to be the best yet by quite a bit, and I actually enjoy using this latest try:

View attachment 7319032 View attachment 7319034

There is one older 125B version that @Lo-E currently owns that I liked quite a bit too, but it uses very expensive LT through-hole opamps that just make for a stupidly expensive build. The one above uses my often preferred OPA1642, which is a very forgiving and relatively economical IC, and they seem stable enough for this application on simple adapter boards. Personally, I would just port to SAM footprints on the main board and use 1206 SMD resistors to boot, but that's just me. I had to pull the PCB out of the enclosure several times to fix a few simple mistakes, which would have only taken a few minutes with surface mount parts. I switched the bottom opamp in the above pic in about five minutes this morning, for perspective. That, with the adapter still hardwired in. OTOH, changing two through hole resistors twice meant destroying two pots and enduring two + hours of frustration.

In other news, I finally made up this new 3 way Q Switch for the preamp in my Marco Bass:

View attachment 7319038

Haven't installed it yet, but I expect it to work fine and eventually make it to the OSHpark share section.

And finally, I worked out using a cheap Iniu power bank with my Cioks C4 pedal board supply, via a PD trigger board from Amazon:

View attachment 7319039

This gives you the choice of 9, 12, 15, or 18V from a USB-C input, with a standard barrel adapter output. With 15V @ 2A the Cioks is good for 550mA X 4 at 9V, and proportionately less current at the higher available voltages, which are also 9, 12, 15 , or 18. You can also go USB-C to USB-C at about half the current capacity, if desired. The Cioks still steps up a 5V input to the same four output options, FWIW, and each output can be any of those voltages.

Sorry to hear about your continued health struggles, Charlie.

 

[emjazz]

Update:

Unfortunately I had a very significant health setback in late June and it's uncertain if and when I'll ever be doing much more DIY electronics work at anything like my previous level. But so far I've exceeded my doctors' expectations quite substantially, and gotten through some fairly scary secondary medical challenges relatively unscathed, so there's plenty to be thankful for at least. I tried one pedal build last week and quickly learned that I'm not really up to that just yet, but even so, it works pretty well and if @Tassieviking or anyone else wants to exhume the small format through-hole pedal design fork I can offer better insight into the way forward now. In short, IMO it really needs SMD opamps and a bit more work on the board layout, but my most recent tuning seems to be the best yet by quite a bit, and I actually enjoy using this latest try:

View attachment 7319032 View attachment 7319034

There is one older 125B version that @Lo-E currently owns that I liked quite a bit too, but it uses very expensive LT through-hole opamps that just make for a stupidly expensive build. The one above uses my often preferred OPA1642, which is a very forgiving and relatively economical IC, and they seem stable enough for this application on simple adapter boards. Personally, I would just port to SAM footprints on the main board and use 1206 SMD resistors to boot, but that's just me. I had to pull the PCB out of the enclosure several times to fix a few simple mistakes, which would have only taken a few minutes with surface mount parts. I switched the bottom opamp in the above pic in about five minutes this morning, for perspective. That, with the adapter still hardwired in. OTOH, changing two through hole resistors twice meant destroying two pots and enduring two + hours of frustration.

In other news, I finally made up this new 3 way Q Switch for the preamp in my Marco Bass:

View attachment 7319038

Haven't installed it yet, but I expect it to work fine and eventually make it to the OSHpark share section.

And finally, I worked out using a cheap Iniu power bank with my Cioks C4 pedal board supply, via a PD trigger board from Amazon:

View attachment 7319039

This gives you the choice of 9, 12, 15, or 18V from a USB-C input, with a standard barrel adapter output. With 15V @ 2A the Cioks is good for 550mA X 4 at 9V, and proportionately less current at the higher available voltages, which are also 9, 12, 15 , or 18. You can also go USB-C to USB-C at about half the current capacity, if desired. The Cioks still steps up a 5V input to the same four output options, FWIW, and each output can be any of those voltages.

Hey Charlie...long time....sending lots of love, brother. I hope things continue on the up and up. Big hug

 

[claudel]

Be Well Soon!

 

[SteveCS]

Unfortunately I had a very significant health setback in late June

Sorry to hear this, Charlie - all best wishes for getting back to a good place as soon as possible.

 

[dcoyle]

"Unfortunately I had a very significant health setback in late June and it's uncertain if and when I'll ever be doing much more DIY electronics work at anything like my previous level. But so far I've exceeded my doctors' expectations quite substantially, and gotten through some fairly scary secondary medical challenges relatively unscathed, so there's plenty to be thankful for at least."


That's a tough way to spend your summer, Charlie, I'm glad there hasn't been more scathing. I wish you the very best, you deserve it.

Seems encouraging you feel good enough, now, to have an interest in refining your circuits and the Marco bass electronics, or even staying on it "enduring two + hours of frustration".

The art on the box in post 1665 looks pretty nice, and the purple heatshrink is way cool.

Anything new on your endeavors with the mid parametric EQ you mention in post 1657? Is it as simple as a pot trimmed by a bridging resistor to be give the desired range or are there further refinements? Does Q change with the frequency?

 

[Passinwind]

The art on the box in post 1665 looks pretty nice, and the purple heatshrink is way cool.

Anything new on your endeavors with the mid parametric EQ you mention in post 1657? Is it as simple as a pot trimmed by a bridging resistor to be give the desired range or are there further refinements? Does Q change with the frequency?

That artwork goes back directly to your input and that of a few others, and my neighbor especially loved the graphics on that color shifting enclosure you sent me. I think he may end up owning it as it suits his new very uptown Martin acoustic guitar quite well.

We also tried the PEQ/HPF pedal with that guitar, with excellent results. The next revision would probably have a dedicated buffer section for the front end, as standalone pedal format was never in the original design brief. Extending the frequency sweep was not so straightforward, and I only blundered on that tuning while trying to find headroom that I knew should be available with enough prodding. And yes, Q still changes along with frequency, but happily in a very musical way: it stays relatively constant through the midrange frequencies but then goes broader at both ends of the sweep. This makes it pretty hard to get a bad sound, actually. Strictly a happy surprise...go figure!

 

[fdeck]

Charlie, I just saw your message here, and hope your health is improving!

I've switched all of my DIY stuff to surface mount. It's really not all that bad. The SOIC chip packages are manageable. TSSOP is more trouble, but do-able under a microscope or magnifying visor. I already need those things at my age anyway.

 

[Passinwind]

Charlie, I just saw your message here, and hope your health is improving!

I've switched all of my DIY stuff to surface mount. It's really not all that bad. The SOIC chip packages are manageable. TSSOP is more trouble, but do-able under a microscope or magnifying visor. I already need those things at my age anyway.

Thanks man.

I ported to mostly SMD parts nearly a decade ago, and would never go back. I still use TH parts for most tube stuff, but am slowly changing even that habit. And yeah, magnification is surely going to be more and more important if and when I get back on the train.

 

[LowWay]

I’ve got crappy vision and no depth perception. If I had proper magnification would I be able to learn to do SMD work? My brain is still reasonably agile.

 

[Passinwind]

I’ve got crappy vision and no depth perception. If I had proper magnification would I be able to learn to do SMD work? My brain is still reasonably agile.

The parts in my open source designs are all on the largish side and pretty easy for me, even with no magnification. I do highly recommend using properly small soldering iron tips though.

 

[Tassieviking]

I would also suggest to use very small solder wire, I usually use 0.5mm for both TH and SMD components for my jobs.
I sometimes go up to 0.8mm but I think 0.5mm suits me better once I got used to it, it can feel strange when you keep feeding the solder onto a TH solder joint but I usually use at least 1/4" of solder for TH components
0.5mm is approx 0.02 inches I think.

You might also need some good tweezers to hold the components in place.

 

[dcoyle]

In addition to the small diameter solder, and the fine, curved point tweezers, a syringe of no-clean solder, desolder wick, a bit of brass wool or a wet sponge to clean the tip on, three to six power magnification, good lighting, and the habit on cleaning and fluxing the tip immediately before use are enough to work on the scale of this project, IME.

I use an empty soup can to gently rap the solder pen against to remove solder, push it into the brass wool to clean slag, touch fresh solder to wet the tip just slightly and then touch prefluxed work.

Eyesight-wise, it's hard for everybody to have depth perception when using magnification because of parallax, but one stumbles through.

The biggest surprise for me was at this scale the surface tension of the solder is a significant factor, enough to make too much solder on the tip glob up or actually move the resistor around.

If something messes up, heat it up, brush the component off, clean the pad with fluxed desolder braid and try again.

There's a learning curve the first hour, but if you have solder skills at through-hole component scale, you'll zero in on this scale, I expect.

 

[Estevanbass]

Disclaimer: For a while I've been wanting to put one or another of my DIY onboard preamp designs into an open source DIY oriented format that other TB'ers can build and readily tweak to their particular wants and needs. I've finally settled on a specific concept and am well into testing a few different versions. I'm about to send out a build kit to my first beta tester, and I will also have a few builds mounted in stompboxes and a bass or two at NAMM in a few weeks. I'm hoping to have v1.0 wrapped up a few weeks after the show, at which point I will release a board share at OSHpark.com, where anyone can order up three boards at a time at OSHpark's usual DIY-friendly rates. I'll have zero financial stake in that, and likewise for the BOMs for Mouser and Digikey that I will also provide. All of this has already been vetted by the TB Admins, and I recently ported my status to Commercial User in anticipation of eventually licensing this or some other of my designs to one or more OEMs. I think that puts everything up front, but please just ask if anything seems shady in any way. This is new territory for me and I want everything to be fun for all involved. View attachment 2562845

Intro: OK, so what about the pie, already? The design features pretty standard bass and midrange control circuits, with a treble section using a swept frequency, variable resonance low pass filter. Here's a graphical representation of various treble control sweeps modeled in LTspice:

View attachment 2562846

And here's a look at the Resonance control function, with Frequency set at the lowest setting:

View attachment 2562847

These are just sample filter alignments and overall gain settings, there is a fair bit of adjustability available with a few component value tweaks.

Here's the first gen circuit board, which has already been superseded by a new one of the same size, which is roughly 2.2" x 1.67":

View attachment 2562848

Current cost from OSHpark shows three boards at $18.30, shipping to nearly anywhere included. Things like board sharing or group buys on pots or other parts will be up to whatever community evolves from this thread. Open Source means that any or all of you are free to do your own perfboard or PCB layouts, mods, ruthless criticism, and so on -- as long as you share all that stuff here. I'll be happy to provide tech support until a mature build spec is reached, and hopefully we can then have a TB Wiki featuring collective wisdom on best building practices, wins and losses with specific pickups and instruments, sound samples, and of course build pics.

As far as overall cost, I anticipate that $50-100 will cover most build specs. Shipping from at least two or three parts sources will likely suck up a fair amount of that at first, but hopefully we can eventually figure out a way to mitigate that some.

I've gone out of my way to use simple "cookbook" type public domain circuits and to avoid using hard to source parts like reverse audio taper dual pots. I have spec'ed fairly expensive and somewhat obscure opamps, but many cheaper and more common subs will probably also work pretty well. If that proves to be true then paring the BOM down to a single source list will be a lot more feasible.

There you have it, my Christmas present to TB, the PW3B-LPF. If any of you are not familiar with Creative Commons licensing, here's a link to the specific license. View attachment 1020173

The license link will always give access to the current schematic version. Please use that link and do not post the schematic in this thread, since TB will cache it and it will inevitably become outdated.

The TB Wiki for this project starts here.

Hello Mr. Escher, very interested in your stomp box preamps. I saw a pic on Marco Bass Instagram and wanted to purchase your preamp pedal. If available for purchase, how would I go about it. Seems like a neat idea. Thanks so much, cheers!