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Messages - smadin

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1
Schematics and Layouts / Electrosmash 1Wamp
« on: January 05, 2022, 09:47:55 AM »
Anyone familiar with this one? I came across it a little while ago, though judging by the forum posts it was published back in the early '10s. It's another LM386-based design, a bit more complex than the Honey, with a very thorough article breaking down the design and math for each section. The author even includes Teemu's book in the list of references at the end: https://www.electrosmash.com/1wamp

Kits and PCBs are no longer available for order, but the KiCad project, BOM, and layout transfers are hosted in the forum at https://www.electrosmash.com/forum/1wamp/92-1wamp-schematic-layout-open-hardware-files, so I was thinking of it as a potential next project.

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Honey Amp / Re: Got my kit!
« on: December 02, 2021, 12:33:46 PM »
thanks! they are soldered, but could use a little touch-up.

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Honey Amp / Re: Got my kit!
« on: November 30, 2021, 04:33:37 PM »
Photos of the build—I have a couple of these Trader Joe's tins, which I kept because I like the shape and size, a little more room to maneuver inside than an Altoids tin. I used some nylon standoffs and screws to hold it off the metal, which works well enough.

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Honey Amp / Re: Got my kit!
« on: November 29, 2021, 07:31:53 PM »
Finally got a chance to actually build the kit! Kudos to Joe for a really nicely designed PCB, soldering it all up was a snap. I'll post a couple photos when I get them off my phone; I wired up the speaker outputs to a Speakon jack and the power supply connections to a 2.1mm barrel jack. I have a couple of cheap small speakers, and a proper 10" guitar speaker as well, and both a 9V battery clip with a 2.1mm plug and a 12V wall wart, so I can swap things around and compare.

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Honey Amp / Re: Got my kit!
« on: May 03, 2021, 06:23:23 PM »
I checked my box and it does look like I'm missing the sticker as well. I'll message you on Kickstarter. Thanks!

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Honey Amp / Got my kit!
« on: May 02, 2021, 04:41:40 PM »
Hello folks,

I used to hang out on here, many years ago, though I lurked more than I posted, so when I got the email about the Kickstarter launch, I was thrilled to back it. My kit arrived yesterday — thanks @joecool85! — and I'm excited to start work on it soon. I'm curious what other folks are planning for enclosures!

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Amplifier Discussion / Re: Pictures
« on: October 22, 2008, 07:40:44 PM »
Agreed — that looks fantastic!  Very nice work.

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Amplifier Discussion / Re: Crate schematic
« on: June 26, 2008, 11:30:08 AM »
(Thank you, Teemu!  Much appreciated.  Now to try to find the time to study it...)

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Amplifier Discussion / Re: Crate schematic
« on: June 24, 2008, 11:46:25 AM »
This thread's been dormant for a while, but I guess it can't hurt to ask...

I picked up my old Crate GX-20M from my folks' attic over the weekend, after not even thinking about it for about a decade, and now I'm thinking that I'd like to know more about its guts, and possibly look into some modifications.  Teemu, from your post it sounds like this might be a model that falls in the range of schematics you mentioned; if you've got it in convenient electronic form and wouldn't mind sharing (or if anyone else does) I'd certainly appreciate it.

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The Newcomer's Forum / LM386 bypass
« on: May 30, 2008, 07:01:37 PM »
(I wasn't sure whether this should have gone in the main Amplifiers section instead, but I think it's a newbie-ish enough question...)

I've noticed that although the Ruby uses only a 100nF, and the Little Gem and Little Gem 2 don't use any at all, some cursory Googling suggests that a 10uF or so cap from pin 7 to ground on the LM386 goes a long way to reducing noise, and I see that (for example) n9voc tends to use them in his schems.  Is there any reason not to add those in to the Fetzer-Little Gem MkII I'm building?

11
For the speakers I've been looking at, Jensen MODs, at least, http://www.tubedepot.com/ has better prices than most other places I've looked.  I haven't actually done any business with them yet, though, so take that with a grain of salt unless someone else knows more about them...

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That makes sense, Teemu.  I'm still inclined to build a few different circuits, because I'm interested in comparing how they sound as well, and once I have a little more experience, trying out different designs, but starting out bigger is probably a good idea.  Thanks again, and thanks also for making your excellent book available; I haven't had time to read very much of it yet, but I expect I will be referring back to it frequently for as long as I'm building these things.

13
Well, the chances that I'll ever actually need an amp powerful enough to play live with a drummer are probably slim, but I'll keep that in mind!  For the time being this is just a fun hobby and a way to learn interesting things, for me -- and I enjoy making things.

I'll start looking around for 160ish transformers.  This is turning out to be a sizable project, so to tide me over I've picked up supplies to build a wall-wart powered Little Gem MkII with the buffer replaced with a Fetzer, a la the Fetzer-Ruby.

Thanks for the input!  I'm constantly impressed by what a great resource this forum is.

14
Ah, with a bit more reading it looks like my math was wrong.  I misunderstood the conversion factor going from AC to DC (and so was rather confused by some of the PSU schematics I'd been looking up...).  So to supply +-30VDC I should need a 21-0-21 transformer, and with an LM1875 160VA should be plenty -- and now that I think about it, the formula in the LM2876 data sheet is for peak current.  So even with a 3886 in there, a 200VA transformer should be enough.  Does that sound reasonable?  (I'm sure this is really basic stuff for most of you, so I apologize for undoubtedly covering the same ground as countless other newbies...I feel like I'm getting a much better understanding, though, so hopefully I'll become rapidly less burdensome.)

15
Quote
You could likely build a basic supply but swap in different mains transformers depending on the required rail voltage and VA rating. The rectifier and filter capacitor circuitry is pretty universal anyway so you only would need to rate those components for the worst-case scenario (highest rail voltage and current demand). Conversion between single- and bipolar supply of course requires a bit more planning and rewiring. Fusing should, of course, be done according to circuit but fuses are easy to swap so that’s not a problem.

Thanks!  That sounds likely to be the best option.

I forgot to mention current in my initial post, but I was thinking about that.  Based on the equations in the LM2876 datasheet, at 40W output I'd need +-30V supply rails at about 3.16A.  On the other hand, the 2876 can run on +-25V, which looks like it would mean about 27W output and 2.63A.  Assuming I did the math right, that is.  So looking at those numbers (and considering my budget!) perhaps I should start with +-25V, and I think I should then be able to swap in either an LM2876 circuit or an LM1875 without changing the power supply, is that right?  Would a 250VA transformer be about what I'd need for that?

Thanks again for the help!

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