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The Passinwind Open Source Preamp
- Thread starter Passinwind
- Start date
I have a Passinwind question that is sort of off on a tangent but I am curious.
I was recently poking around my files and happened on a manual for a Yamaha NE-1 equalizer. Now I remember the hype about this which was that at the time it was supposed to be a "secret weapon" to produce hit records. Be that as it may, what I noticed is that the NE-1 is the opposite of this preamp. Namely that instead of a resonant peak there is a resonant dip. So my pondering is to wonder if there is some kind of modification to this circuit that could be done where a toggle switch might change it from a peak to a dip in response thus giving a possibility of both options. I wouldn't be surprised if it were too complex to be practical, but nevertheless I was just wondering.
I was recently poking around my files and happened on a manual for a Yamaha NE-1 equalizer. Now I remember the hype about this which was that at the time it was supposed to be a "secret weapon" to produce hit records. Be that as it may, what I noticed is that the NE-1 is the opposite of this preamp. Namely that instead of a resonant peak there is a resonant dip. So my pondering is to wonder if there is some kind of modification to this circuit that could be done where a toggle switch might change it from a peak to a dip in response thus giving a possibility of both options. I wouldn't be surprised if it were too complex to be practical, but nevertheless I was just wondering.
- Dec 3, 2003
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- Designer/Toaster Tech @ Passinwind Electronics
I'll take a look at the possibilities, but I have a feeling it won't be that easy, given the relatively simple LPF format I went with. However, my initial design for the LPF preamp used a state variable filter, which can easily do both. Take a look at Craig Anderton's Super Tone Control for a well known and DIY friendly example of that.
There's a version that switches the NE-1 into a LPF. Since the NE-1 is a simple design it would be easy to incorporate it. switching pop noise might be an issue
Built the Super Tone Control over thirty years ago. It was a pretty cool tone circuit... very flexible!
- Dec 3, 2003
- 23,054
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- Designer/Toaster Tech @ Passinwind Electronics
Cool, that might work well for @bassbenj. Have you built one yourself?
Edit: I contacted the author, @Silent Fly , aka Max at SFX. He graciously agreed to let us include that schematic in this thread. He originally posted it on Basschat.uk.
But in any case, using that circuit would actually require a complete reboot from where the design is now. Different pot values, different opamp input used on last input stage, different scaling on the filter resistors and caps. And so far in my initial quick and dirty modeling the LPF response looks very different as well. All of which is fine if someone (else) wants to take that on.
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- Dec 3, 2003
- 23,054
- 45,929
- Disclosures
- Designer/Toaster Tech @ Passinwind Electronics
Yep, I built one a zillion years ago when Craig's book was brand new.
edwinhurwitz
Supporting Member
I still have one in a box somewhere. I should wire it up with better pots, etc. It was really fun to have built into my bass.
Was that the edition that was painted on a cave wall?
(Watch out! GOF's are everywhere. We just can't remember why.)
Still waiting on the op amps for my project, but looked at starting to wire up the pots. To my dismay the pots from the parts list are 3/8" but the holes on the bass are 6mm. I don't really want to drill the holes out so am looking at replacements, but for the 5k which is the frequency pot I'm only finding 50mW power rating. I haven't done any circuit analysis since navy school back in '89, so I'm not sure but that seems a little tight.
- Dec 3, 2003
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- Designer/Toaster Tech @ Passinwind Electronics
Are you sure the mounting holes aren't more like 7mm and change? You should be able to find 1/2 watters in that format fairly easily, but then the bushing length becomes the next potential obstacle.
- Dec 3, 2003
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Monthly update: I'm still plugging away on getting the final licensed version of my 2-band design to the luthier (just signed off on the SMT production spec, actually), and then hopefully I can make some time to improve the PW3B-LPF Wiki. But meanwhile @mnats has posted a very nice DIY friendly version of the Bajaman/Uncle Fluffy MM Stingray 2-band clone preamp, including a full single source BOM linked to Mouser. This gets a big two thumbs up from me: MM Stingray 2 band shared pcb design
- Dec 3, 2003
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Update: currently testing an opamp substitute to LT1351/1352 that draws even less current and also costs quite a bit less. These are SMD parts, but hand soldering to an adapter board is definitely workable. Some people are asking pretty stupid money for the adapter boards, but there are plenty of design shares at OSHpark; figure about a buck for three, shipping included.
Clever!
Personally, for pennies more, I would go with the machined type socket, as shown in all but the last conversion you show above. The reliability of the clip type (whatever they are called) shown in the last image, will not be as good as the machined type. Back in the DIP chip days, I replaced quite a few of the cheaper type, but never saw a problem with machined sockets. May not matter for this use, but another 50 cents more on you project is cheap insurance IMO.
Neat idea!
- Dec 3, 2003
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Thanks! Out of those approaches I think I like the perfboard one at top right of the first pic the most. But bending the IC pins adds even more fiddle factor to what already is fear of the unknown for a lot of DIY'ers. OTOH, I've successfully reworked bunk boards with wire wrap wire soldered right to the IC pins, so everything there looks doable.
I bought a bunch of inline header pins on breakable strips from an eBay vendor:
Then attached quartets to a little daughter card like this, with slightly extended pads to make hand soldering easier:
Which looks like this plugged into a standard DIP socket that end users wouldn't necessarily need to use:
But if things work out I can definitely just make an alt board revision with SMD pad layouts for the ICs rather than the current DIP-8 ones. I have something like that coming in for another project today actually. So I'll be testing opamps head to head more thoroughly in the next few days.
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- Dec 3, 2003
- 23,054
- 45,929
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- Designer/Toaster Tech @ Passinwind Electronics
It's been a lot longer than I figured on, but here's a measurement I took today of one of my NAMM boxes, Bass and Mids set flat, Res at minimum, Freq at max.:
...which jibes pretty well with my Spice models. So if you never resolved this I will be happy to try to figure out what's up.
What I wrote earlier was not very clear, so I'll try again.
As we discussed privately I planned to make a version minus the bass and treble controls. I did finish a new board using mostly surface mount parts:
Unfortunately, it behaved just like the one that I built from your board with the same roll-off at the low end. As mentioned previously, changing the electrolytic to a larger value fixed it, though I never could figure out why it behaved differently from the simulation.
I got distracted after that with a different obsession that has turned my bass world upside-down so as much as I appreciate the offer it won't be necessary. I'm concentrating my electronic efforts on making a piezo buffer with onboard HPF/LPF. Thanks again for sharing your project though!
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