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Topics - derevaun

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Open Discussion / Is anything real? Testing "fake" LM308s
« on: January 14, 2024, 05:17:32 AM »
A few weeks ago I stumbled upon an Ebay listing for some LM308 "solder pulls" for pretty cheap: https://www.ebay.com/itm/386473025200  When I watch-listed it, the seller sent an even cheaper offer, with this note:

How about 25% off, eh?
What do you call a fake noodle? An impasta! :)
Thanks for checking out our new store!


Obviously, clearly, almost-came-out-and-said-it, fakes, right? Who could resist. I ordered a set, breadboarded a Rat, and waited.



When they arrived, I tested a few types of chips:
  • the maybe fakes from this Ebay listing
  • a Motorola LM308H from that "No China Bullshit" git on Ebay
  • a few AMD LM308H from a small stash I lucked into last year
  • a couple LM308N from Retroamplis
  • an LM108, PIFfed from Laundryroom David
  • a definite fake LM308N from Ebay several years ago (it has a date code that matches a lot of dubious Ebay listings)
...and...
  • LM301
  • CA3130
  • LM307 (internally compensated)
  • LM741 (internally compensated)
...and...
  • A few УД1408А (the supposed Soviet 308 equivalent)

All of the 308s (and the 108), except the fake 308, measured pin 5 not-connected and M-Ohms across 1 and 8.

I auditioned them all on the breadboarded Rat, by strumming a low chord and hammering some high notes, with the 30pF capacitor in and then out. This cap-in-or-out difference is what I listened for.

With the cap in, they all sounded pretty consistent. But removing the cap:

-the LM301 introduced some gritty, screechy artifacts on chord and note decay
-the CA3130 introduced some messy decay and a gritty, busy self noise
-the LM307 and LM741 had no difference, cap in or out, but the 741 was a lot more sensitive to touching the capacitor
-the  definite fake LM308 behaved like the LM307: no diference (it already sounds fine in a DOD 250 that doesn't have a 1-8 capacitor, also pin 5 is connected)

All of the LM308s, from the Motorola to the ones in the Ebay listing, and the УД1408А, responded to cap removal the same way: they got brighter and grittier, and a little more ragged with note decay. I didn't notice a salient difference between any of them. But the 741, 301, 3130, and 307 were each clearly different, in their own way, with regard to the external cap-in-or-out.

I also tried some a couple NTE 938 (308 replacements) that I had squirreled away, and they behaved like the 308s.

I'm not fully convinced that the Ebay "solder pull" LM308s are genuine, but they behave the same with the cap-in-or-out test, and I don't have a reliable way to compare them otherwise (I don't trust my ear to be neutral after a power-down-chip-swap-power-up interval). The real test is going to be just playing them over time and possibly developing affinity for some over others. But declare wholesale that these are fakes? I can't.

In the name of science art, I ordered 3 more sets. Some of them have identical date codes, which is another hint that they may be fakes. But all of them behaved the same as the other 308s with the cap-in-or-out test.

To be clear, I do not vouch for the Ebay seller or any suggestion of authenticity of any LM308s in the listing. I just can't distinguish the difference between the ones I got and some LM308s that I'm pretty sure are legitimate. I suspect there are other, more dispositive tests for a difference? I'd love to hear about other ways to test them. But, the more time and effort I invest in this, the less it seems to matter as a musician.

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General Questions / What the wah?
« on: August 13, 2023, 08:10:51 PM »
I grabbed a Craigslist lot that included a Crybaby wah (rev H, 2003). Never been a wah user, but no time like the present I guess.

However, it has a serious volume drop when engaged, and while I could just track down the fix, I wonder if it's a step up to build a Weener Wah to replace what's there.

Can (or should) I reuse the inductor from this board?

I think I see how to build the Weener Wah for bass or Jerry Cantrell specs. Are there other mods you like?

Thanks!

3
Build Reports / Hot Mess, finally boxed
« on: July 01, 2014, 02:22:29 AM »
I built this like 3 years ago, when GPCB was etched boards. It's an IC Big Muff. Been happily rocking it ever since, plain box taped shut, but never properly boxed it until now. The holdup was printing a label that would stick to the box and hold up to the rattle can clear coat treatment. I still need to sort out something for the LED. I think I run wires more neatly nowadays, but all of that is forgotten now that the box is shut and the screws are finally in for good  ;D




4
Build Reports / Cave Dweller (with relay switching)
« on: May 16, 2014, 02:21:59 PM »
Finally boxed up the Cave Dweller, in 1590b with top mounted jacks and relay switching.

I OSHParked a board for Mictester's relay switching scheme with a momentary stomp, using the Neutrik-alike plastic jacks from Tayda. They suck, but it works. 0805 passives on the underside (my first SMD!). Just enough room for a thinline DC jack (from BLMS). I'm gonna use low profile jacks next time I try to topmount in a 1590b.

I tried a "bicolor stone" texturized spraypaint, which came out more texturized than bicolor, but close enough. Riffed on some cave painting with India ink. The LED just points toward the hole; some hot glue works well enough to transmit its light.






5
Build Reports / Name Dropper
« on: October 16, 2013, 03:02:09 PM »
I scored three sweet OC75s from badgerific in his holiday PIF, like nearly two years ago, and finally got them into a tonebender mkii board and boxed up. I did the layout in Eagle, starting from culturejam's layout (the image is no longer online), with board mounted vertical pots from Tayda. The enclosure is a B sized trapezoid (1590TRPB); I used a laser printable clear label and hastily sprayed on a few coats of clear acrylic. It sounds great to my ears--nice and smooth. I don't get a lot of range from the Attack pot (1K), but it cleans up nicely with the guitar's volume pot.





I mounted the board so that the signal flow is left-to-right, as are the jacks. I may regret that eventually, but I doubt it. In any case, the board can be mounted right-to-left (the knobs would be farther back that way).







The board layout is shared at OSH Park. A BOM is in the works. It measures 60mm/2.3" from the pots' outside edges when they're mounted. They need at least 23mm/.9" of vertical space when mounted inside a box.





I have a few extra boards, including some that are slightly longer (70mm/2.75"; same vertical). I'd be happy to trade for similarly small and simple boards!


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