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The Passinwind Open Source Preamp

#281
Just got my OSH Park package Friday. First application for the PW3BLPF preamp will be onboard in a bass with 2 pickups. The bass is under construction now.

If I want the signal path to be (2) pickups -> blend control -> preamp -> volume control (25K or 10K preferred?) do you suggest I go for an ungrounded 100K MN blend control, or a grounded 250K MN blend?

Note: I am planning to wind the pickups. Does it cause impedance matching problems if I wind them with about half the turns that are customary? Like, e.g., a split coil with 3000-4000 turns. This will put the resonant peak of the pickup oddly high compared to a more standard P-bass pickup. I would adjust the first stage resistor values to get some extra gain. If low impedance + blend is a deal killer with the preamp as designed, I am completely free to change the pickup configuration. I am more determined to use this preamp than any particular pickup combo at this point.

John
 
#282
JayGunn said:
Just got my OSH Park package Friday. First application for the PW3BLPF preamp will be onboard in a bass with 2 pickups. The bass is under construction now.

If I want the signal path to be (2) pickups -> blend control -> preamp -> volume control (25K or 10K preferred?) do you suggest I go for an ungrounded 100K MN blend control, or a grounded 250K MN blend?

Note: I am planning to wind the pickups. Does it cause impedance matching problems if I wind them with about half the turns that are customary? Like, e.g., a split coil with 3000-4000 turns. This will put the resonant peak of the pickup oddly high compared to a more standard P-bass pickup. I would adjust the first stage resistor values to get some extra gain. If low impedance + blend is a deal killer with the preamp as designed, I am completely free to change the pickup configuration. I am more determined to use this preamp than any particular pickup combo at this point.
Click to expand...

Hey John,

Good questions. These loading effects are going to take a while to work through on a case by case basis at first, I think.

I ran into some similar things with the Marco Bass we installed one of these preamps into for NAMM. I will get with Marco and try to suss the specifics of the winds he uses in those pickups, which also have a pretty high resonant frequency. In general, my gut feeling is that lower impedance is likely to be better. An ungrounded 250K MN pot in front and 10K in back didn't work quite as well as just using two 250K volume pots in front for my Travis Bean, FWIW. That combo worked OK on the Marco Bass, but to my ears 250K MN grounded followed by a 500K volume in front of the preamp worked better. But the preamp specs were also changed quite a bit at the same time, so for now I'll have to say I don't know.
 
#284
40Hz said:
Well,got an hour free and clear and got the resistors and sockets installed. Hopefully get the rest soldered in and be able to test it over the weekend if all goes well. Yay! :hyper:
Click to expand...

Cool. I need to put up a diagram of the pot wiring scheme for the bass and mid controls. I'll try to get to that by this evening.
 
#286
Passinwind said:
Cool. I need to put up a diagram of the pot wiring scheme for the bass and mid controls. I'll try to get to that by this evening.
Click to expand...

Slightly OT - but you were right. This new Hakko FX888D station I got is a dream to work with.

I have used (slightly) better. But not at this price point. And nothing I would buy for the amount of use an iron gets around my place. But man! Coming off my old Weller it's a whole new world. Recovery on this thing is almost instantaneous. Recommended.
 
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#289
DrummerwStrings said:
^ ah, this Yankee just learned something. More than a local drive, but I'm looking forward to hearing from ppl who can go.
Click to expand...

I was hoping to go to the New England GTG in May, but couldn't swing it because of the timing. Maybe next year, or maybe for something like the Philly Phall guitar show I've been to a few times.
 
#290
OK, tried a new switchable midrange alignment yesterday that actually works to my satisfaction for 250/500/800 Hz. I also knocked the overall gain down to about 1dB to make the stompbox play nicer with active basses. I'll have it at the BassCon for user feedback and if it passes muster I'll post it as either an alt version or even the primary. This is a tricky balancing act, as the bass section interacts a lot with the mid alignment as the mid freq gets shifted lower, and as usual there's really no free lunch.
 
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#292
ric426 said:
I'll be interested to see it!
Click to expand...

No doubt. Your feedback and that of a couple of other guys got me to revisit this. I knew I could get it better than the first couple of tries, since lower mid frequency centers have never been any problem with my very similar amp and rack preamp builds. The headroom aspect is a lot trickier with a 9V battery supply though, which is mostly what had been tripping me up. Just a matter of balancing tradeoffs, which feels like my never ending lot.
 
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#293
Weekly update:

Did that aforementioned tech presentation / demo of the PW3B-LPF and PW1B at the Emerald City Bass Convention last weekend:

BassCon1a.jpg


I also brought along a new stompbox mounted FET buffer/preamp that I only finished up around midnight the night before I drove up to Seattle. This is basically just the Tillman/Kreutzer preamp, which in turn is basically just a classic cookbook circuit. My test board layout came in at .8 x .8 inches and I thought the preamp sounded great with my friend's new passive J. I was surprised to not find a board share already up on OSH Park, but my search-fu may have been lacking, I guess.
 
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#294
Passinwind said:
Weekly update:

Did that aforementioned tech presentation / demo of the PW3B-LPF and PW1B at the Emerald City Bass Convention last weekend:

BassCon1a.jpg


I also brought along a new stompbox mounted FET buffer/preamp that I only finished up around midnight the night before I drove up to Seattle. This is basically just the Tillman/Kreutzer preamp, which in turn is basically just a classic cookbook circuit. My test board layout came in at .8 x .8 inches and I thought the preamp sounded great with my friend's new passive J. I was surprised to not find a board share already up on OSH Park, but my search-fu may have been lacking, I guess.
Click to expand...
Looking at all the rack gear in the background, plus the unrelated clutter in front of it, reminded me of a tour through AT&T's Zunai, Denver facility back in the mid-90's.

Lots of memories (good and bad) from 21 years in industrial telecommunications...

Just wondering where the Emeral City event was held?
 
#295
steve_rolfeca said:
Looking at all the rack gear in the background, plus the unrelated clutter in front of it, reminded me of a tour through AT&T's Zunai, Denver facility back in the mid-90's.

Lots of memories (good and bad) from 21 years in industrial telecommunications...

Just wondering where the Emeral City event was held?
Click to expand...
That's not rack gear in the background, it's stacked pallets of beer cans.

Event was at Odin Brewing Company.
 
#296
steve_rolfeca said:
Looking at all the rack gear in the background, plus the unrelated clutter in front of it, reminded me of a tour through AT&T's Zunai, Denver facility back in the mid-90's.

Lots of memories (good and bad) from 21 years in industrial telecommunications...

Just wondering where the Emerald City event was held?
Click to expand...

@ak56 answered your question, but I worked in field service for corporate and institutional sound installs for a while and certainly saw my share of big racks...and then there were all those sound provider gigs, and...well, nevermind.
Yel_wink.gif


Here is more or less the view I had from my corner at the GTG:

OdinBrewhouse.jpg


That's a 60 barrel brew system, and they know how to use it. Thanks to E. Pruitt for the pic.
 

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