The Passinwind Open Source Preamp

[Passinwind]

I've got some SMD PCB schtuff to practice on. I figure, whether I like it or not, it's the way the world is moving forward to a brighter tinier future.

I'm finally starting to gear up in earnest for SMD work. I have a microscope and new lighting incoming, and plans to turn over some old school bench gear for more relevant pieces.

In the meantime I've started working on some boards that are probably at least "DIY possible" for quite a few people. For me hand soldering 1206 parts is no big deal at this point, especially if I take a little break after doing the more demanding bits before I dive into the rest. I reckon I could build up a board like this new three bander in about an hour or so without much stress these days:

That's a test bed for a more tunable bass section, and also the second build I've done with the OPA2145. Both aspects show a lot of promise and are likely to make it into the next OS 3-band boards, I think.

 

[BassikLee]

Have you tried air soldering? At the very least, it's fun

 

[Passinwind]

Have you tried air soldering? At the very least, it's fun

Yep, but unfortunately I've not yet managed steady access to the tooling.

 

[Feral Feline]

I'd be willing to take a crack at that, but I'd need one of those air de-soldering suction pumps — just in case.

 

[SteveCS]

I can't readily find the control route dimensions but it doesn't seem to pass the eyeball test? The upcoming modular ones would probably be your best bet. If you can get me some details on the cavity route format in your bass I can at least try to accomodate that. I've been going hard at tweaks to the conventional two band section lately but I still do have standalone LPF boards waiting for their turn in the build queue.

It is difficult to measure as it is quite a convoluted shape, so I tried trace the outline and add a few key dimensions. There isn't much space in the top route, especially where it narrows down at the far end. This is looking from the top, so output is to the left and volume to the right...

...and it is only 1.25" deep...

 

[Passinwind]

Random update:

The OPA2145 has turned out to be an absolute champ so far in various builds I've tried it in. It compresses less when pushed hard than many FET opamps I've tried and scoped, and headroom is exceptionally good. It's also been quiet and very stable, and availability has been no problem thus far...yay!

Digikey are now offering a similar small quantity board production service to OSHpark. The MOQ is four boards and that costs $6 per square inch (for 4 boards), shipping included. Beyond that, you can just bump up the quantity in single unit increments, unlike OSH who only go by threes, so if you need say five or eight they can do that. The boards are red, of US production, and have the same ENIG finish for the pads as the OSHpark ones. Minimum size is 1 x 1 inches, so OSH is still the best US option for really small stuff. I'm going to order a set for a new two band build spec today, with the quoted turnaround time at ~10 days.

The standalone LPF filter board is nearly at the top of my build queue now, finally. I have all the parts on hand and it should go very quickly. I've also caught wind of a new commercial filter preamp builder in the UK and hope to have a few beta test samples in hand within the next month or so. I only have a few details but I like what I'm hearing from the builder so far. Can't really say more myself just yet, but if you sniff aorund BassChat you might find some details soon I think.

 

[Jeff Siddall]

Chip shortage is a problem for sure. I have a few 2145s in my cart, which I created more than a year ago now, but at no point has everything been in stock. A recent concerted effort to replace backordered parts with comparable substitutes (ex: different voltage/temp range/tolerance part -- invariably more expensive) has me down to a single backordered item with no suitable substitute. It should be back in stock within a few weeks, but what are the odds something else isn't out of stock by then!

 

[Passinwind]

Chip shortage is a problem for sure. I have a few 2145s in my cart, which I created more than a year ago now, but at no point has everything been in stock. A recent concerted effort to replace backordered parts with comparable substitutes (ex: different voltage/temp range/tolerance part -- invariably more expensive) has me down to a single backordered item with no suitable substitute. It should be back in stock within a few weeks, but what are the odds something else isn't out of stock by then!

Yep, I've had to resort to downgraded voltage specs, different pad spacings, etc. just to keep things rolling. And my last Mouser order took over a week to ship, but at least that matched their posted disclaimer.

 

[Passinwind]

The standalone LPF filter board is nearly at the top of my build queue now, finally. I have all the parts on hand and it should go very quickly.

And for once it did:

Actual size is 2.07 by 0.88 inches (52.6 x 22.4 mm). With SMD resistors in 1206 format it would be ~1.66 by 0.88 inches. I could also get height down to ~7mm with some different electrolytic caps, this version is right around 9mm.

 

[-Asdfgh-]

I'm hoping to find my soldering iron again this weekend, after moving. First port of call is a series of fixes of pickups, and then work on a piezo pickup for one of those short scale, six string piccolo bass things. Then I might start looking at the preamp. My wife is away so I have time, but sadly she's also vastly better at soldering!

 

[Feral Feline]

Looks great, Passinwind!

 

[Passinwind]

Just a heads up on a potential new commercial design that I caught wind of on Basschat: Experimental Prototype bass... I hope

I expect to get a couple of test boards in soon and will post a dedicated thread on it eventually if it comes to fruition. I have no affiliation with the maker, but he solicited my feedback and as always I'm happy to give that when it makes sense.

 

[Passinwind]

Looks great, Passinwind!

Thanks, here's the latest "what-if" format I came up with a couple of days ago:

 

[Feral Feline]

You gotta name these things something like: Gnat, Midge, No-Seeum... I've seen postage stamps that were bigger.



I've been collecting some smaller SMD project boards to practice on. A buffer, a 1590A reverb, and a couple others. I figure, "Sure, I'll practice soldering SMD, but I still want something useful resulting from the effort". I don't get the SMD "practice" boards I've seen... you could maybe use them as a coaster, or lightweight paperweight.


If [when] my micro-buffer and A'Verb etc work out, I'll be hitting your Oshpark page hard.

 

[Passinwind]

You gotta name these things something like: Gnat, Midge, No-Seeum... I've seen postage stamps that were bigger.



I've been collecting some smaller SMD project boards to practice on. A buffer, a 1590A reverb, and a couple others. I figure, "Sure, I'll practice soldering SMD, but I still want something useful resulting from the effort". I don't get the SMD "practice" boards I've seen... you could maybe use them as a coaster, or lightweight paperweight.


If [when] my micro-buffer and A'Verb etc work out, I'll be hitting your Oshpark page hard.

Cool. It gets easier, that last build I pictured took right around an hour and 1206 resistors would've gone just as quickly for me by now. But something was not quite right with that boy, so I built another one the next day which unfortunately manifested the same misbehavior. I've shelved them for now, but will work it out sometime next week. It's a good excuse to finally break out the microscope that @AudioTaper set me up with recently, if nothing else.

 

[A9X]

Wery interesting build PW. Aesthetically the UK build is more than a little challenging for me, but the design of his pickups is very similar to what we're prototyping now. Pre is similar in general topology and opamps ( mine summate individually, not series and are SC, 5st in the proto). If I've read it right he doesn't understand he difference between 2nd and 4th order.
My psu is almost identical to yours but 5 pin XLR. Proto pre is a current hog.

 

[Passinwind]

Wery interesting build PW. Aesthetically the UK build is more than a little challenging for me, but the design of his pickups is very similar to what we're prototyping now. Pre is similar in general topology and opamps ( mine summate individually, not series and are SC, 5st in the proto). If I've read it right he doesn't understand he difference between 2nd and 4th order.
My psu is almost identical to yours but 5 pin XLR. Proto pre is a current hog.

He hasn’t sent me the info on the volume/mixer board yet, not sure how it’ll ultimately be configured. I haven’t done a deep dive through the whole thread yet, but the whole thing looks like a definite work in progress. Nice guy though, and I always enjoy talking with fellow travelers, so to speak.

 

[Passinwind]

Digikey are now offering a similar small quantity board production service to OSHpark. The MOQ is four boards and that costs $6 per square inch (for 4 boards), shipping included. Beyond that, you can just bump up the quantity in single unit increments, unlike OSH who only go by threes, so if you need say five or eight they can do that. The boards are red, of US production, and have the same ENIG finish for the pads as the OSHpark ones. Minimum size is 1 x 1 inches, so OSH is still the best US option for really small stuff. I'm going to order a set for a new two band build spec today, with the quoted turnaround time at ~10 days.

Shipping to my PO box turned into a bit of a snafu but the service rep tells me they've now sorted things out permanently and he got back to me very quickly at least. I ordered and paid for 4 boards but actually received six, and they look quite decent:

Digikey requires a full set of Gerber files rather than a single .brd file, and unfortunately they're not set up for board shares just yet. But I'm expecting that they'll have a fully integrated modeling data/layout footprint/BOM/parts ordering/board fabrication, and maybe assembly workflow all in one place sooner than later, which would be uber cool.

 

[BassikLee]

That looks great!

 

[Passinwind]

That looks great!

Yep, I'll report back once I get one built up. I just ordered a set of new three banders to see if they have their shipping act together now. I'm optimistic, my interactions with the DigiKey support staff have always gone pretty well.