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Messages - derevaun

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1
VFE Projects / Re: ALPHA DOG Question. [ANSWERED]
« on: February 16, 2024, 03:14:51 PM »
FWIW, I found some variation among legit LM308s WRT resistances between pins, using Chromesphere's test. I think the most important ones are that pin 5 isn't connected, so no resistance with any other pins, and a few megaohms between 1 and 8, although there's a range with mine. Two tests that are more dispositive are that it sounds harsh(er) with the 30pF cap removed, and the chip itself draws below 400 microAmps. In any case, I have a fake one (from Jameco) that is my absolute favorite in a DOD250  :P

2
wicked cool!

3
Open Discussion / Re: NGD
« on: February 08, 2024, 10:56:05 PM »
Whoah, that scratches a lot of itches.

4
Open Discussion / Re: Is anything real? Testing "fake" LM308s
« on: January 27, 2024, 10:54:51 PM »
Going on Chuck's post on the PPCB forum, I tested the Ebay LM308s for current. They measured between 260 - 360 microAmps, in the same range as the legit ones. So maybe they are legit. They sound fine to me, so it doesn't matter a whole lot.

The LM308N I got from Jameco is definitely fake. Actually it's mixed up with another fake LM308N that I got on Ebay a few years ago, but they both don't need the 1-8 capacitor. One is currently in a stock DOD250, where it sounds killer 8) The other I included in the test above.

I've ordered NE555s from Jameco for a couple decades, for a class. They've worked fine for our uses (blinking LEDs, Atari Punk Console, PWM) but it's been a rogue's gallery of weird/sloppy markings. Probably factory rejects or similar, and they probably would fail some test for high precision, but I haven't had a single one not work for low-stakes uses.

I guess the pinch point is that we expect a particular kind of magic from the LM308. It's certainly beyond my ear's ability to nail down, but there's always gonna be a mystique that close enough isn't quite close enough  ???

FWIW, it looks like the Ebay seller reduced the price to $8.00 for 4, plus shipping. I absolutely do not vouch for the seller or anything you might receive from them, but my experience was good and perhaps others of us like to live dangerously. Or, for science! Here's the listing:

https://www.ebay.com/itm/386701906664?hash=item5a093ad2e8:g:C9oAAOSw0-NlsP61

5
Open Discussion / Re: Prototype boards and small runs.
« on: January 26, 2024, 07:12:06 PM »
I still use OSH Park for the odd board. Their integration with Eagle is nice, and I like the After Dark boards. Plus, they're nearby, so it's fast once the board is done.

Paying by board area often led to me trying to make a layout too compact, so it's refreshing to be able to spread out and just make the board fit the end-use instead.

I don't fab a lot of boards, and I don't need 5 any more than I need 3, so I think OSH Park still makes sense. Also, having 3 of a mistake is roughly 0.6 times the pain of having 5.

All that said, I've used JLC the last couple times and it's probably the better choice overall. Except, After Dark  8)


6
VFE Projects / Re: Dragonhound LM308 substitute
« on: January 25, 2024, 12:11:42 AM »
If you can find an LM307 or LM301, they're close IMO. The 301 needs the same 30pf cap, and the 307 doesn't care about it. People say the 301 is mellower than 308, but I don't hear a difference when playing. If I wanted gnarly, I'd go for a CA3130.

AS301, a new production LM301: https://www.amplifiedparts.com/products/op-amp-as301an-alfa-single-8-pin-dip



7
Requests / Re: Connector spacing
« on: January 24, 2024, 04:35:03 AM »
I guess the first thing I'd look for is a 4 terminal version of that connector. Or, a different variation that has 2.54mm housing specs. Personally, I use 2.54mm screw terminals for that kind of connection, but a plug-in connector has its advantages.

8
Global Annoucements / Re: 2024 outlook
« on: January 23, 2024, 05:55:48 PM »
Just re-ordered the project queue, so there's every reason to not grab the boards I'm gonna grab when they come out.

9
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.

10
General Questions / Re: Diode orientation sanity check
« on: December 29, 2023, 04:23:23 PM »
As an additional data point, I got these from Retroamplis:


11
Open Discussion / Re: Happy Birthday Brian
« on: December 13, 2023, 01:14:17 PM »
Happy Rocking Birthday!

12
Open Discussion / Re: end of year zoom call?
« on: December 11, 2023, 09:53:25 PM »
I had forgotten about Skype, except for that ringtone. It does not, as they say in certain quarters, doom.

Does Zoom timeout even when there's activity? Mine times out if nobody shows up for 40 minutes, but it's a pro or something license from work.

13
Open Discussion / Re: What amp do you use to test/tune projects?
« on: December 03, 2023, 01:09:06 PM »
Monoprice 5w tube combo with a Jensen Mod swapped in, for my own stuff, because I donít get loud. My kiddo plays loud so I frequently carry a wired board,  resembling a live lobster, to the garage for testing.

14
Build Reports / Re: It's my wah and I'll cry if I want to.
« on: October 09, 2023, 02:36:27 PM »
Nice all round, but that wiring is the bomb  8)

15
Build Reports / Re: Cheap DIY Bluetooth Page Turner
« on: September 27, 2023, 12:54:15 PM »
Partly to avoid this:



A lot of musicians have their music on a Ipad Pro (because it's big) and learn to use a footswitch to turn the page.

Serving as a page turner sucks--you have to be totally up on the piece and on how the pianist plays it, including repeats and jumps to the coda at the end, etc. Music printers have to lay out instrumental parts to be easy to play through a page turn, musicians who share a stand can piss each other off about page turning, but now you can just step on a switch and it's taken care of. If it works--sometimes you see people swiping with their finger,  probably because they forgot to charge their floor turner.

Super cool project! I wondered if anybody DIYed one. PMing for the Arduino code!

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