Out of the various characters on the Nazi's side, Schultz was the intellect of the group.
John Banner - Wikipedia
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The Passinwind Open Source Preamp
- Thread starter Passinwind
- Start date
John Banner - Wikipedia
- Dec 3, 2003
- 23,054
- 45,930
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- Designer/Toaster Tech @ Passinwind Electronics
Just ran a few sims. For starters you could try changing R12 and R15 from 4.75K to 5.1K. This increases max peaking by 4dB at the max freq setting. You may want to up R13 from 1.62K to something like 1.75K as well; this knocks down peaking gain a bit (~2dB) but also widens the peak and promotes circuit stability. So there's a balancing act at work between those components, and you may be able to get away with one more standard size component value jump (ie 5.6K and 2K), but I'd definitely recommend looking at the result on an oscilloscope before moving on to listening tests. The value of R13 is especially tweaky, even a variation of a tenth of an Ohm can make a noticeable difference.
As you go to higher resonance the native pickup RLC peak becomes more important and experimenting with different input impedances to tame that peak will likely be a good idea. I really noticed something related a few weeks ago at the Seattle GTG, where one bass in our booth just shined with the LPF stomp box I brought along. Some other basses exhibited a nasty "double dip" peak when the LPF frequency was adjusted to peak at the same place as the passive peak. This particular bass didn't do that at all, which means that the damping at the input was probably just right. I have this instrument on my bench today and it reacts a good bit differently to Marco's passive tone control component choices than any of his other basses that I've worked on. Yet another rabbit hole...
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- Dec 3, 2003
- 23,054
- 45,930
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Monthly update:
After selling off my Travis Bean fretless early last year I haven't had a bass with the LPF preamp installed on hand for the last year and a half. But since my 5 string fretted Marco Bass no longer needs to serve as a tester for my 2-band design, I decided to drill another control hole and use it for working on the add-on treble module. That sounded very good, but I figured I might as well drill yet another hole and open up my options for various other test builds I have in mind. So I've finally had a chance now to use the LPF preamp onboard without any stacked pots, which I am really not a fan of at all. While I was at it I reduced overall gain (to ~1dB now when set flat), since the bass already has pretty hot humbuckers and I hope to leverage the added headroom in one way or another. For better or worse, I feel that this design sounds considerably better onboard than in a stomp box. But of course many people don't want a 6 hole control format, or to have to do a battery route, etc. etc.
After I live with this config for a month or two I'll consider either changing the official spec or maybe just posting an alt. schematic. Maybe I'll get around to doing a real demo recording as well, never know...
After selling off my Travis Bean fretless early last year I haven't had a bass with the LPF preamp installed on hand for the last year and a half. But since my 5 string fretted Marco Bass no longer needs to serve as a tester for my 2-band design, I decided to drill another control hole and use it for working on the add-on treble module. That sounded very good, but I figured I might as well drill yet another hole and open up my options for various other test builds I have in mind. So I've finally had a chance now to use the LPF preamp onboard without any stacked pots, which I am really not a fan of at all. While I was at it I reduced overall gain (to ~1dB now when set flat), since the bass already has pretty hot humbuckers and I hope to leverage the added headroom in one way or another. For better or worse, I feel that this design sounds considerably better onboard than in a stomp box. But of course many people don't want a 6 hole control format, or to have to do a battery route, etc. etc.
After I live with this config for a month or two I'll consider either changing the official spec or maybe just posting an alt. schematic. Maybe I'll get around to doing a real demo recording as well, never know...
PW, I usually deal with a 9 hole configuration every Sunday afternoon so I'm sure 6 will be fine.
- Dec 3, 2003
- 23,054
- 45,930
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
PW, I usually deal with a 9 hole configuration every Sunday afternoon so I'm sure 6 will be fine.
Heh! So I've been rocking this config for a while now and last week I was able to get some feedback from a very experienced studio producer friend. He doesn't have a studio right now but I'm still hoping to involve him in doing a proper demo. The local place I'd like to use is crazy busy with doing live shows in their big room at this time of the year, but it's past time to get 'er done one way or another.
I can't recall seeing a single picture in this thread of a bass with the OS preamp installed in it. Fair enough if I have to be the first, I guess. I need to get some new matching knobs made up, the black ones are just the typical Daking types you can get at your local hardware store. The resonance and frequency controls are at the bottom, with freq closest to the strings. The bass is a prototype build from Marco Bass Guitars in Oregon.
- Dec 3, 2003
- 23,054
- 45,930
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Thanks. I'm in the middle of doing a refinish, it got scratched up a bit from an overzealous dancer knocking a mic stand into it, during a solo bass set no less. It's always been hard to photograph due to all the crazy stuff going on with the burled top.
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Zombie stumbles in to a thread... had no idea.
I know I go into some tunnels, but after the last 4 days reading waaay too much of this thread and many links there from...
Fnord's IN... Will get in the Christmas Spirit and do some shopping. I'm hoping the BOM from the OP is all cool... 2 years late to a party isn't unheard of from me.
Thanks y'all for doing the work,
fnord!
you too Charlie!
(HERO)
I know I go into some tunnels, but after the last 4 days reading waaay too much of this thread and many links there from...
Fnord's IN... Will get in the Christmas Spirit and do some shopping. I'm hoping the BOM from the OP is all cool... 2 years late to a party isn't unheard of from me.
Thanks y'all for doing the work,
fnord!
you too Charlie!
(HERO)
- Dec 3, 2003
- 23,054
- 45,930
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
AFAIK the BOM is still fine. I'm about to do a small update to lower overall gain a little though. All that takes is subbing a 2K resistor for the 3K one (R4), and 12.1K for one 8.25K (R3). Just makes for a little lower noise floor and a bit more headroom. I wouldn't bother to mod existing builds though, as the plated through pads are a bit of a pain for rework even for those of us who are pretty used to dealing with that. The boards themselves tolerate rework pretty well though, FWIW.
If the noise floor isn't high enough to hear it over my tinnitus ringing floor, I don't worry about it. 
'tis tough enough to discern actual notes due to my "unique" style. Serially, I'm thinking of doing two builds. One for the J passive fiver and another for an active EMG P/J Vampire slayer Squier HM K'89 5ver.
the
the
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So, I've received the boards from OSH. Nice service.
Wow! These purple puppies are very small. I'll admit that I'm a little intimidated at such tiny things like an Elephant to a mouse. I'm pretty much going blind and I wouldn't label my fat fingers as surgical. Haven't yet ordered the mouser parts; will do in next couple of days. Imagine, I'll order solder and a thin tip for the soldering iron. I'm going to give it a shot.
f!
Wow! These purple puppies are very small. I'll admit that I'm a little intimidated at such tiny things like an Elephant to a mouse. I'm pretty much going blind and I wouldn't label my fat fingers as surgical. Haven't yet ordered the mouser parts; will do in next couple of days. Imagine, I'll order solder and a thin tip for the soldering iron. I'm going to give it a shot.
f!
- Dec 3, 2003
- 23,054
- 45,930
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Two Year Update:
Still seeing quite a few first time builders, and hoping and expecting to see more builds going into basses in the near future. I'm pretty much done with commercial onboard preamps for a while and I'll probably revisit some potential design forks I got sidetracked from right about when I originally posted this thread.
Meanwhile, I tested one of my stompbox mounted LPF units for a while this afternoon with this new bass from my friend Marco Cortes:
It'll be cool to work up a custom electronics install of whatever flavor and not have to take the bass back to Marco for a change!
Still seeing quite a few first time builders, and hoping and expecting to see more builds going into basses in the near future. I'm pretty much done with commercial onboard preamps for a while and I'll probably revisit some potential design forks I got sidetracked from right about when I originally posted this thread.
Meanwhile, I tested one of my stompbox mounted LPF units for a while this afternoon with this new bass from my friend Marco Cortes:
It'll be cool to work up a custom electronics install of whatever flavor and not have to take the bass back to Marco for a change!
All the credits to you Charlie!
The OS Preamp is a great idea, I'm sure it can be the blueprint for some really cool stuff from users!
The OS Preamp is a great idea, I'm sure it can be the blueprint for some really cool stuff from users!
I only stumpled upon this thread some days ago and I couldn't believe my eyes. Absolutely excited since I own a guitar with a Lemme's SVF inside which I like very much ... but I always wished to not only have a filter but also Bass&Mid controls. And if one could make the mids switchable ... Bäm! It's all here! So I can't wait to try out this one. I have two questions though ...
a) I have seen the spec sheet providing the values for altering the mid frequencies - is there a combination of frequencies for bass guitar / guitar that you can recommend as a starting point?
b) I love the Lemme's SVF for playing around at home but in a live playing situation I always felt the two-pot-filter as not being intuitive enough. So I sold the original SVF and got me his version with switchable resonant peaks which in my opinion are way easier to handle.
So talking about your preamp design: Would it be hard to replace the resonance pot by a 3 position mini-switch? Any hint on how to obtain that and what resistor values to useas a starting point?
Thank you for any hints and the generosity to share this design!
a) I have seen the spec sheet providing the values for altering the mid frequencies - is there a combination of frequencies for bass guitar / guitar that you can recommend as a starting point?
b) I love the Lemme's SVF for playing around at home but in a live playing situation I always felt the two-pot-filter as not being intuitive enough. So I sold the original SVF and got me his version with switchable resonant peaks which in my opinion are way easier to handle.
So talking about your preamp design: Would it be hard to replace the resonance pot by a 3 position mini-switch? Any hint on how to obtain that and what resistor values to useas a starting point?
Thank you for any hints and the generosity to share this design!
- Dec 3, 2003
- 23,054
- 45,930
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
a) Most popular has been 800/1.6K/2.4K Hz. I personally prefer just 700/1.6K. Without an extensive switching network both gain and bandwidth vary pretty greatly by frequency and we start to see pretty big compromises just for the sake of more flexibility. But if you give me a target range I can try to help mitigate the necessary compromises a bit.
b) Yes, I think many people find variable resonance/variable frequency to be a bit much. But IMO and IME it also works considerably better than a simple switched resonance format. At the least, I suggest starting with a stompbox build, measuring where the resonance pot settings work for you, and then port those resistance values to a switch. But I will work up a simple 0dB/+3dB/+6dB switching scheme, which I have found to be in the general vicinity of the most useful settings for me in my actual ensemble playing situations.
Note: I may not get to much of anything until after the NAMM show starts in just over two weeks. Even though I'm not going this year, quite a few of my builds are, and many are still to be built, much less installed...
Thank you Charlie. No hurry though. I already ordered the boards and will look now to source the missing parts so I don't think to be able to begin before the NAMM ...
Ah, in the meantime ... you wrote somewhere that you tried out alternatives for 1351/1352 and that some were promising. Couldn't find though what you tried out ... are there any valid alternatives you can recommend? Thanks again, Ralf
Ah, in the meantime ... you wrote somewhere that you tried out alternatives for 1351/1352 and that some were promising. Couldn't find though what you tried out ... are there any valid alternatives you can recommend? Thanks again, Ralf
- Dec 3, 2003
- 23,054
- 45,930
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Hi Ralf, and welcome to Talkbass BTW. The ADA 4062-2 has a little less headroom but also less current consumption and a bit of the FET clipping mojo going on. You'd need an SO-8 to DIP-8 converter board though. And unfortunately I still have not identified a single opamp chip that is quite comparable so far. ADA 4177-1 was about the closest out of the ones I tried last time around.
