The Passinwind Open Source Preamp

[Passinwind]

Please post your findings on this as I'm interested in the QTuners for one of my 5s. It has a cavity big enough to fit my SII (sort of) clones into.

Mine are the older BL-4s, which reputedly have a fairly big resonant peak around 4KHz that the newer ones have toned down. The Crescent Moon already has an unused 3 way switch so it's a natural for the Q switch format. It still has one of my original three band builds in it and that has always worked really well with the Q-Tuners, but I rarely use this bass these days and figure I I might as well give myself some incentive to do so a little more.

 

[Freekmagnet]

Your place or mine?

I put in a good bit of testing yesterday and have two really solid release candidate specs. I'll do an actual onboard install next, I'd like to see how the Q-Tuner pickups in my Crescent Moon fretless get on with a filter preamp and also try using the Q switch format in place of the resonance pot.

Anyhow, board shares are now up for the standalone LPF and the two breakout boards for the dual pots:

[Invalid or Expired Link Removed] (LPF board)

[Invalid or Expired Link Removed] (Frequency pot breakout)

[Invalid or Expired Link Removed] (Resonance pot breakout)

I won't have a bill of materials done until sometime next week, most likely. Due to parts supply issues I want to take a hard look at a few component subs and maybe an alternative vendor or two.

And then last night I started in on a pedal oriented variable HPF board share too:

View attachment 4327926

This is based on the ones in my DIY amps and rack preamps, it's not the variable resonance HPF design I've shelved for the moment.

Yeah, I still gotta try out those two boards you sent me. I’ve been using my test subject to try out pickups for a passive bass I’m trying to finalize. It’s been kind of a pickup building frenzy. And, I’ve been in Wyoming the last week and a half.

 

[Feral Feline]

Awersum!

Mij Oshpork hor d'oeuvre ist approachelating gigantarian Porpoise-shuns...


Moochazgrazzerage, Passinwind!

 

[shwashwa]

sign me up for a pedal version with a volume control!

 

[Passinwind]

Note: current board spec link is in the Wiki, the previous one has already gone obsolete. I’ve been working on an optional lower tuning for the second filter in per-pickup applications and made a little room for the necessary caps without changing the board size.

As of right now it looks like the default sweep ranges may end up at something like 660-8.5KHz and 40-1.2KHz.

 

[A9X]

I’ve been working on an optional lower tuning for the second filter in per-pickup applications

That makes sense. I'll be interested to see what values you come up with for the N and B filters.

 

[Passinwind]

Today’s stomp box rebuild, using the new standalone LPF board along with the newset iteration of my Bass/Mid preamp:

I settled on switched mid centers at 260, 480, and 700Hz in order to give some useful interaction feel options when the LPF is set towards the low frequency end, this particular one bottoms out around 800Hz or so. I only had thirty minutes to test it but initial results are extremely positive.

 

[Passinwind]

Since I'm about to install one of the new modular 3 band builds in one of my basses in the next couple of days I figured it was time to finally get a quote on the pots I actually want:

Sticker shock is a given for small quantity custom made, but just how big is that shock?

 

[A9X]

^^ Have a chair handy. I hope I'm wrong though experience tells me I may not be.

 

[Passinwind]

^^ Have a chair handy. I hope I'm wrong though experience tells me I may not be.

Yeah, I know from past experience in the fisheries research game where we often needed bespoke parts specs. I already got a call from the sales rep trying to steer me into a different product line that might, maybe, be doable. As I ran through my actual wish list I could hear him sigh a little, but I told him I knew this is unobtainium and I can be pretty flexible beyond needing a long enough bushing and reverse audio taper.

 

[A9X]

^^ Same experience with other parts. Most of the design work I've done in my career has been custom / bespoke and limited run so I've been there a few times. Best of luck.
I have a number of designs for other gear going through initial fitness trials at the moment and parts availability and/or cost are some of the factors that get them swiped left or right, so to say.

 

[fdeck]

I inquired on a custom pot with Taiwan Alpha. They told me MOQ of 1000 parts, and 75-90 days ARO. It was before the pandemic, so I have no idea what the present situation is.

That's why I'm still using the bass-ackwards frequency knob. Just have to rationalize it. Clockwise should be "more bass."

 

[Passinwind]

25466960[/URL], member: 40185"]I inquired on a custom pot with Taiwan Alpha. They told me MOQ of 1000 parts, and 75-90 days ARO. It was before the pandemic, so I have no idea what the present situation is.

That's why I'm still using the bass-ackwards frequency knob. Just have to rationalize it. Clockwise should be "more bass."

Yep, that’s how I do my HPFs too, just call it “sub bass.” And I have posted the backwards wired audio taper pot hack in this thread a few times over the years.

Besides the RFQ from potentiometers.com posted above I put one in with Omeg too, they at least have the prerequisite feaures I need all listed in their dropdown menues, and profess to welcome inquiries on small quantities.

 

[Jeff Siddall]

Depending on how your circuit tolerances work you might be able to use digitpots. You can closely match 1-2 or 2-3 resistance between pots using programmable calibration (probably within 1%), but 1-3 resistance is fixed and typically varies significantly (20% or more) between devices. That may not work for your purpose.

Overall they are relatively inexpensive but do require a controller with the associated programming work plus board redesign for the not-insignificant footprints involved.

 

[Passinwind]

Depending on how your circuit tolerances work you might be able to use digitpots. You can closely match 1-2 or 2-3 resistance between pots using programmable calibration (probably within 1%), but 1-3 resistance is fixed and typically varies significantly (20% or more) between devices. That may not work for your purpose.

One end is tied to 2 in both cases, so this could actually work very well. I'm more inclined to try it for a pedal though.

And after a deep rabbit hole dive last night I've come up with a quick and dirty solution for using the Tayda pots in my next onboard install. Since the threaded bushings are a few mm short and the control shaft is a few mm longer than needed I'm just going to cut up a couple of lengths of threaded lamp tube from my local hardware store:

The inner diameter is just slighly bigger than the 7mm pot bushing and there's plenty of surface area for something like JB Weld or urethane adhesive to adhere to. The thread pitch of the 3/8 threaded section is slightly different from a standard pot but the store has brass or zinc plated nuts that will work fine. I could and probably will also just buy a tap set and use thick walled brass tube for an A1 job, but I think this should suffice for the moment.

 

[Passinwind]

I could and probably will also just buy a tap set and use thick walled brass tube for an A1 job, but I think this should suffice for the moment.

It turns out that a vendor I've used before stocks this: Invalid Link Removed

The ID is within .001" of the standard tap spec for 7mm 0.75 pitch threading, and they stock that size in both brass and aluminum. So I think it's probably going to be worth investing in a tap and die set if this becomes an ongoing need.

 

[Passinwind]

^^ Have a chair handy. I hope I'm wrong though experience tells me I may not be.

I did just get a shock, but not in the way I expected. My price quote on a dozen dual antilog conductive plastic pots from the UK vendor's simple web inquiry form came back at a bit under twelve dollars per unit with a 4-5 week lead time, shipping incuded. And their track options include 25K ohms, which is pretty ideal for the alignments I'm currenty playing with. I spec'ed a 12mm bushing length, which will save me a lot headaches. Didn't ask about tighter tolerances, I reckon I'll just try their stock production mode first.

 

[A9X]

That's pretty good, a lot better than I expected.

 

[Passinwind]

Tayda/Alpha reverse taper dual pots redux:

 

[shwashwa]

Today’s stomp box rebuild, using the new standalone LPF board along with the newset iteration of my Bass/Mid preamp:

View attachment 4334859


I settled on switched mid centers at 260, 480, and 700Hz in order to give some useful interaction feel options when the LPF is set towards the low frequency end, this particular one bottoms out around 800Hz or so. I only had thirty minutes to test it but initial results are extremely positive.

oohhh, i want it!