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Post by svart on Jun 29, 2018 15:18:01 GMT -6
Guesses as to what it might be?  I never really thought about this unit, but was intrigued at the sonic tone it gave guitars in a mix video I watched. I investigated and the circuit is stupid simple and there's enough parts and info available to cobble one together really quickly. I'll probably have leftover boards on this I'll sell. No kits or anything though. |
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Post by mulmany on Jun 29, 2018 15:23:14 GMT -6
Looks like a LA4 type optic compressor.
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Post by svart on Jun 29, 2018 15:23:48 GMT -6
BTW I did this schematic, parts investigation and layout in about 10 hours, so a super quick spin!
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Post by svart on Jun 29, 2018 15:24:18 GMT -6
Looks like a LA4 type optic compressor. Warmer.. |
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Post by mulmany on Jun 29, 2018 17:49:40 GMT -6
Well if I am close with an la4... Is it an la5? Cause with out a t4b it can't be a la3a😎
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Post by svart on Jun 29, 2018 18:05:27 GMT -6
Well if I am close with an la4... Is it an la5? Cause with out a t4b it can't be a la3a😎 Or can it..? |
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Post by matt@IAA on Jul 3, 2018 20:46:02 GMT -6
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Post by svart on Jul 4, 2018 11:54:12 GMT -6
I'm waiting for more guesses.. |
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Post by ragan on Jul 4, 2018 12:44:41 GMT -6
I'm waiting for more guesses.. I wish I had the knowledge to guess... Still just taking math...  |
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Post by svart on Jul 10, 2018 6:24:14 GMT -6
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Post by winetree on Jul 10, 2018 12:42:07 GMT -6
I'll be first in line.
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Post by svart on Jul 10, 2018 12:48:08 GMT -6
this one I'll sell a few boards for. I'm not going to make any units though. There are a few EL panels around out there and the CDS cells are readily available. Should be a really easy build. |
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Post by winetree on Jul 10, 2018 12:55:03 GMT -6
P.S.B.s and a BOM is good enough for me.
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Post by jeromemason on Jul 10, 2018 13:04:28 GMT -6
Nice! How much for a board?? And is the input stage close to the original??
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Post by svart on Jul 10, 2018 13:30:29 GMT -6
Nice! How much for a board?? And is the input stage close to the original?? 10$ a board. I haven't tested mine yet. I'll have 7 boards to sell. I had 10 made and I'm keeping 3. It's a direct schematic layout, no changes at all. The original type transistors are available again through Central Semi, so you can use all original active parts. You just have to use a DMM and match HFE for the input transistors. I bought a dozen or so and found a pair that were really close. they're only like 0.30$ each so it's cheaper to match than buy a matched pair from someone. You can use Hairball's transformer kit, or do like I'm doing and rig it all up with whatever you have. It'll be up to you! I'll have a rudimentary BOM, but this isn't intended to be a kit. I'm trying to make this as cheap as possible, and so far it's only a couple hundy for everything for me since I had most of the parts and I am using the cheapest options for everything. I'll cut and print my own frontpanel, cut my own chassis, etc. |
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Post by svart on Jul 10, 2018 13:33:55 GMT -6
BTW, I'm not planning on matching the CDS cells. I'm not sure the meter movement will be accurate enough to even care if they're 10 percent off or so, and since the EL panel acts more like an RMS filter, the average GR that can be calibrated via the pots is more important than anything else I would believe.
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Post by matt@IAA on Jul 10, 2018 13:41:25 GMT -6
Seems like you could fit a pair with a small power supply in a 1RU eh?
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Post by matt@IAA on Jul 10, 2018 13:49:41 GMT -6
Also, I found a post from Jim about component selection. Passed on without comment:
First, those 2N5117 transistors have to go. For Q1 and 2 I use Motorola MPSA18's. C15 should be Mica, if it's ceramic, change it to mica or a Wima FKP-2 polyprop cap. C1 is changed to .47 uf, MKS-2 Wima with a .0047 MKP-2 1kv bypass. If C2 is a tantalum, leave it. If it's electrolytic, change to 10 uf 50v Panasonic FC.
C14 is either mica or Wima FKP-2, C3 is another Panasonic 10 uf 50v FC. R14 is now 15k, C4 is now 220 pf Wima FKP-2 or a mica. C5 is changed to a 1000 uf 25v Panasonic FM bypassed with a .1 uf 250v MKP-2 Wima. C8 is another 10 uf 50v FC and C9 is a 100 uf 50v FM. C12 is changed to a 2200 uf 35v and C10 is 4700 uf 50 v Nichicon.
Last, change Q5 to a 2N6716 and Q6 to a 2N6728 for a faster sound.
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Post by jeromemason on Jul 10, 2018 13:51:32 GMT -6
If it all test’s well please put me down for one, I love the sound of the 3A’s amp section on guitars.
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Post by svart on Jul 10, 2018 13:52:52 GMT -6
Seems like you could fit a pair with a small power supply in a 1RU eh? possible! I'm doing 2u simply because of the size of the meters I bought. |
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Post by svart on Jul 10, 2018 14:03:48 GMT -6
Also, I found a post from Jim about component selection. Passed on without comment: First, those 2N5117 transistors have to go. For Q1 and 2 I use Motorola MPSA18's. C15 should be Mica, if it's ceramic, change it to mica or a Wima FKP-2 polyprop cap. C1 is changed to .47 uf, MKS-2 Wima with a .0047 MKP-2 1kv bypass. If C2 is a tantalum, leave it. If it's electrolytic, change to 10 uf 50v Panasonic FC. C14 is either mica or Wima FKP-2, C3 is another Panasonic 10 uf 50v FC. R14 is now 15k, C4 is now 220 pf Wima FKP-2 or a mica. C5 is changed to a 1000 uf 25v Panasonic FM bypassed with a .1 uf 250v MKP-2 Wima. C8 is another 10 uf 50v FC and C9 is a 100 uf 50v FM. C12 is changed to a 2200 uf 35v and C10 is 4700 uf 50 v Nichicon. Last, change Q5 to a 2N6716 and Q6 to a 2N6728 for a faster sound. I'm not sure what he was looking at but the original UREI document I used has 2n5089, 2n5087, 2n3053, 2n4037, 2n3417.. I don't see anything with 2n5117. I also don't care about the rest of that. I don't want a different compressor, I want the LA3A sound.. It makes no sense to me to want a certain sound and then go to great measures to change it into something it's not. Folks can do whatever they want once they get the boards though. |
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Post by NoFilterChuck on Jul 10, 2018 14:18:48 GMT -6
Interesting that you borrowed the T4B replacement design from Peter Purpose's LaZ-La3A from GroupDIY. His PCB has been discontinued for years, but the idea for dealing with the optical cells is cool. Nice Lil project! Are you gonna do a front panel for it?
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Post by svart on Jul 10, 2018 14:22:35 GMT -6
Interesting that you borrowed the T4B replacement design from Peter Purpose's LaZ-La3A from GroupDIY. His PCB has been discontinued for years, but the idea for dealing with the optical cells is cool. Nice Lil project! Are you gonna do a front panel for it? Interesting, I hadn't actually seen his project. The T4B thing was really just the best and most sensible way to do it. I found cheap little boxes to use for the cover, and a little foam between the lid and the EL panel should hold it in place. I was going to cut out my own panel and just print stickers for the controls. I can certainly make the stickers available for people to download though. |
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Post by matt@IAA on Jul 10, 2018 14:30:55 GMT -6
I'm game for a pair.
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Post by johneppstein on Jul 10, 2018 14:32:18 GMT -6
10 bucks for the board? I'm in. Haven't built anything in a while, could use an LA3A style comp.
Edit: I'd go for 2 if you have enough.
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