The Passinwind Open Source Preamp

[Passinwind]

Thank you both! Happy to wait and order the SMD version. Also if anyone needs any SMD help please hmu, it's not as hard as one would be led to believe.

Ok, great. PM me and we can get this party started once I've done the test builds in the next few days. This is the box they'll be going in:

If anyone wants the UV print files I will be happy to set that up too. You will need to go through Amplifyfun in Portland and I haven't vetted 1590BB or 1590BB2 usage yet, just the Gorva S90 as pictured. You can order Gorvas in a variety of colors through Love My Switches and they will happily drop ship to Amplifyfun, which typically only takes a day since they're both in Portland. Since 1590BB2 is slightly bigger it'll probably print just fine, but as I said I haven't tried that yet. I highly encourage everyone to do their own artwork though!

 

[Passinwind]

100% on board to beta test these. I have extensive SMD experience.

Excellent. I am getting pretty close to closing down shop (probably after NAMM 2023) and would love to find a few people to help keep this project alive.

 

[mdalamond]

Wow, Thank you Charlie. I've had pretty good luck with JLCPCB. I've only had 1 set of boards that they messed up on and it was the very first ones I ordered. That was about 3 years and many many pcbs ago. Since then everything has been spot on. I didnt bother with reporting the error, the boards were still useable, just had to add a link. I'm sure they would have made it right though. Their customer service has always been top notch for me.
Matt

 

[Passinwind]

Wow, Thank you Charlie. I've had pretty good luck with JLCPCB. I've only had 1 set of boards that they messed up on and it was the very first ones I ordered. That was about 3 years and many many pcbs ago. Since then everything has been spot on. I didnt bother with reporting the error, the boards were still useable, just had to add a link. I'm sure they would have made it right though. Their customer service has always been top notch for me.
Matt

I've gotten a lot of duff baords from them but none were due to errors on their end. And it's just so tempting to buy 15 or 20 while you're at it!

And yeah, customer service has been very good when I needed it, they double check on things if they look like a problem and I really appreciate that.

 

[Feral Feline]

Looking forward to finding out how you reinvent yourself, as I'm sure it'll be interesting.

Also, very happy to hear you're willing to pass the torch and keep the flame burnin' on the Passinwind OSP.

Cheers,
FF

 

[mdalamond]

I've gotten a lot of duff baords from them but none were due to errors on their end. And it's just so tempting to buy 15 or 20 while you're at it!
I have had my fair share of coasters made myself. No reflection on them. I usually buy 15 to 20. Somehow I manage to be able to even use the fluffed boards. Jumper here and there and lesson learned.

And yeah, customer service has been very good when I needed it, they double check on things if they look like a problem and I really appreciate that.

 

[Passinwind]

I have had my fair share of coasters made myself. No reflection on them. I usually buy 15 to 20. Somehow I manage to be able to even use the fluffed boards. Jumper here and there and lesson learned.

I'm pretty good at board rework, just sayin'.

 

[Passinwind]

First set of the new next gen boards are stuffed and ready for wiring:

I have three beta testers lined up here in the US and two in Europe. The ones in the US will be getting bare boards and probably opamps as soon as I work through the usual details like bench testing and deciding on the actual build spec. I'll also be testing operation at 12, 15, and 18 volts now, because why not?

Some opamps I use are now showing as out of stock until 2024. I snarfed another dozen OPA145 from Digikey last night, but I will have to start digging deep to find stash somewhere outside of the usual commercial sellers next time and am working on identifying any sub parts that can work even "well enough."

Oh, and I'm looking at getting some little 3D printed boxes made to mount these things in. It would be a real time saver and would make for a much nicer looking install. But I'm not up to speed on doing a CAD file, any takers?

 

[rumblinbass]

First set of the new next gen boards are stuffed and ready for wiring:

View attachment 4771436


I have three beta testers lined up here in the US and two in Europe. The ones in the US will be getting bare boards and probably opamps as soon as I work through the usual details like bench testing and deciding on the actual build spec. I'll also be testing operation at 12, 15, and 18 volts now, because why not?

Some opamps I use are now showing as out of stock until 2024. I snarfed another dozen OPA145 from Digikey last night, but I will have to start digging deep to find stash somewhere outside of the usual commercial sellers next time and am working on identifying any sub parts that can work even "well enough."

Oh, and I'm looking at getting some little 3D printed boxes made to mount these things in. It would be a real time saver and would make for a much nicer looking install. But I'm not up to speed on doing a CAD file, any takers?

Very nice, Charlie.

 

[mdalamond]

First set of the new next gen boards are stuffed and ready for wiring:

View attachment 4771436


I have three beta testers lined up here in the US and two in Europe. The ones in the US will be getting bare boards and probably opamps as soon as I work through the usual details like bench testing and deciding on the actual build spec. I'll also be testing operation at 12, 15, and 18 volts now, because why not?

Some opamps I use are now showing as out of stock until 2024. I snarfed another dozen OPA145 from Digikey last night, but I will have to start digging deep to find stash somewhere outside of the usual commercial sellers next time and am working on identifying any sub parts that can work even "well enough."

Oh, and I'm looking at getting some little 3D printed boxes made to mount these things in. It would be a real time saver and would make for a much nicer looking install. But I'm not up to speed on doing a CAD file, any takers?

Unfortunately I have no CAD skills. I see JLC is doing 3D printing now. I may have to look into this. I think there is a forum member on here somewhere that does this sort of thing. I will see if I can find him later.
Matt

 

[mdalamond]

First set of the new next gen boards are stuffed and ready for wiring:

View attachment 4771436


I have three beta testers lined up here in the US and two in Europe. The ones in the US will be getting bare boards and probably opamps as soon as I work through the usual details like bench testing and deciding on the actual build spec. I'll also be testing operation at 12, 15, and 18 volts now, because why not?

Some opamps I use are now showing as out of stock until 2024. I snarfed another dozen OPA145 from Digikey last night, but I will have to start digging deep to find stash somewhere outside of the usual commercial sellers next time and am working on identifying any sub parts that can work even "well enough."

Oh, and I'm looking at getting some little 3D printed boxes made to mount these things in. It would be a real time saver and would make for a much nicer looking install. But I'm not up to speed on doing a CAD file, any takers?

Ah ha, found him. Maybe @DDXdesign can help you out with the CAD?

 

[JayGunn]

I agree that the OPA145 is an engineering breakthrough for bass audio. But there are several really good candidates that are only slightly in the OPA145/2145's shadow.

Using the noise test feature of LTspice I compared a bunch of op amps with 2 different circuits.

Circuit 1 is inverting, no gain, 200K load on the input, 100pF feedback cap and 470 ohm output load resistor. TI calls it Riso and for large capacitive loads it really helps stabilize the op amp from oscillating. TI usually suggests 50-100ohms, but actually for the OPA145 it needs to be higher. I have been testing with 1200p and 2000p cap loads as the worst case. Since I own a Monster cable 20' long that has > 1100p, I am trying out big numbers as a worst case.

The 4 numbers are noise at 20Hz, 1KHz and 10KHz in nV and the last number is total noise taken over 20-20KHz in uV. I am reporting only the best ones, plus two old favorites for comparison:

OPA145 82,80,50, 7.9uV
OPA180 81,81,51, 8uV
OPA202 83,83,52, 8.1uV
LT1012 85,84,53, 8.3uV
LT1097 85,84,53, 8.3uV
LT1112 85,84,53, 8.3uV

LT1351 156,129,81, 12.7uV
LM4250 136,135,110, 16.6uV

Circuit number 2 is non-inverting and this is inherently quieter. Still provides a 200K input impedance, same Cf and Riso.

OPA145 17,12,12, 1.7uV
OPA180 17,13,13, 1.8uV
OPA202 18,14,13, 1.9uV
LT1012 21,17,17, 2.4uV
LT1097 85,84,53, 8.3uV
LT1112 85,84,53, 8.3uV

LT1351 35,17,17, 2.4uV
LM4250 54,53,66, 9.9uV

My takeaways: LT1351 is fine for a low source impedance, lousy for a buffer or an MM 2-band EQ.
OPA991 is a nice product but I left it out because it uses too much battery. Comparable noise to 145, 180.
OPA202 is awesome, uses a little bit more battery than the OPA145 and laughs at capacitive loads.
OPA180 is the also-ran that would be great except that the OPA145 is even a bit better.
LT1012, LT1097, LT1112 must share some architecture to have such matching noise figures, or maybe someone just cut and pasted the same parameters into the 3 Spice models(?) BUT they all use a lot less battery that the OPA products shown, so they would be a good choice for a circuit with a lot of amps.

p.s. Did I emphasize enough that the OPA202 is really great? Hope this helps!

 

[Passinwind]

p.s. Did I emphasize enough that the OPA202 is really great? Hope this helps!

Thanks for all that! I was just looking that the 202 data sheet a day or two ago actually. The low slew rate and modest GBW knocked it down a notch in my mental ranking but I guess I'll buy a few anyway.

I bought several OPA207 to see if I can make them work as a sub in the LPF section, or maybe for my little gain/mixer boards. Easy on batteries, seems like it might work out as an OK sub in some things for now.

BTW, I've generally been using between 220-330 ohms inline at the output for most of my opamp circuits for many years, with some opamps it's helps stability a bunch.

 

[Passinwind]

Hard at work on the next gen testers, the first one should be making noise later today:

I've taken a pretty big swing at changing up frequency centers, sweep range, native gain...pretty much everything. And this particular box has been optimized for use with active basses, or after some other pedal(s) in the signal chain.

 

[Bemo9]

Hey Charlie, since I can't get mine working yet, any chance you're going sell some?

 

[deepestend]

Def interested if you do any more kits.

 

[Passinwind]

Def interested if you do any more kits.

I never actually offered any kits, just a board share and a BOM. Those are still in place but many changes are in the works right now and I wouldn't really recommend building to the old spec at this time, even if you could scare up all the parts somehow.

Briefly: new default spec for the original design is just awaiting testing by a beta tester or two, one board will probably be in a tester's hands later today. More resonant gain available, wider frequency sweep range, and somewhat different bass and mid voicings.

Next gen boards: "easy" surface mount parts used for resistors and opamps, hand soldering will be no problem for reasonably experienced hands. More of everything available gain wise, including up to 16dB of resonant gain. There will be many more tuning options too. Consumes considerable more current, so for most people I see this as a pedal thing. I will be offering pedal graphics via a US vendor for those who might want that. No business interest on my part, as usual. Here are a couple of goofy testers I had made last week as proof of concept:

And then there's a more fully featured one in the works, but I doubt it'll go live until the next NAMM show. I've already been testing the new parts, but I expect I can improve what I've got right now by quite a lot.

 

[Passinwind]

Update:

Yesterday I built up a new one for OPA1692/OPA207 testing:

So I now have three different boxes on hand to work through the final details before I decide on a default spec for the next gen preamp. The OPA207 appears to work just fine in this application, which is very good news since there are still some in stock at the usual vendor sites for the moment.

 

[Passinwind]

Update:

The spec is now settled and the BOM for the next gen boards is nearly done, hoping to get it to the beta test builders later today. Still working on opamp subs, but I did find some OK options for now, especially for pedal builds.

I'm looking into having one of the well known DIY pedal effects board vendors do a layout and sell boards once I completely retire, which is likely to be around six months from now. There are substantial parts issues there too unfortunately, since most pedals use board mounted pots, but this guy is one of the best at dealing with that stuff. It may or may not pan out, but it seems worth a shot at least.

Edit: the PCB guy came back with an enthusiastic yes very quickly. I'll keep his identity private for now, but he's known in the DIY pedal community and should do a great job.

 

[ThisBass]

Very brilliant work Charlie. Sorry to say that I noticed all that work you did just now
It is pity to hear that you plan to quit all that working in a couple of months