Elab LA2A - Build thread

Help Support GroupDIY:

Deepdark

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May 19, 2013
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Hi guys! Here is the official help thread for my LA2A board project, links to all documents, BOM, etc. Feel free to ask any question, post your finished unit, etc.

Where to get the board: https://www.facebook.com/elab.electronic/app/251458316228/

Documents:  https://www.dropbox.com/sh/07qjs68wgkov3q6/AABt3cKx1I3GLd67-58kTG4ha?dl=0
Mouser: https://ca.mouser.com/ProjectManager/ProjectDetail.aspx?AccessID=af1cda8839
Digikey: http://www.digikey.ca/short/3b9mjz
Input transformer clamp: http://www.digikey.ca/products/en/capacitors/accessories/63?k=capacitor
T4B: http://www.gearslut.com/index.php?main_page=product_info&cPath=67&products_id=189
Audio Transformers:  [email protected]
Toroidal power transformers: http://www.antekinc.com/as-05t240-50va-240v-transformer/
Octal T4B Socket: https://www.tubedepot.com/products/belton-8-pin-octal-pc-mount-socket-20-dot-5mm-pins
9 pins tube sockets: https://www.tubedepot.com/products/9-pin-pc-mount-socket
7 pins socket: https://www.tubedepot.com/products/7-pin-pc-mount-socket
Vu meter: http://www.hairballaudio.com/catalog/parts-store/panel-meters
Decal paper: https://www.amazon.ca/Lazer-Lazertran-Inkjet-Transfer-Paper/dp/B001LUF54E/ref=sr_1_1/163-6309199-0642268?ie=UTF8&qid=1479217539&sr=8-1&keywords=lazertran
Scale designer: http://stiftsbogtrykkeriet.dk/~mcs/Scale.html
Dial: http://ca.mouser.com/ProductDetail/Electroswitch/P118/?qs=%2fha2pyFadugkqksNnrVNmBKcIQ1qiKEoK4tJ6LM72Jo%3d

15036299_10207916211605948_8338025111569110377_n.jpg


Color of the board will vary from batch to batch. I like to try some different colors!

 

fragletrollet

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Sep 19, 2010
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Oslo
What is the difference between this and the dual La2a from Silent arts, other than being mono boards? Separate PSU pcb? Is this an advantage? Just curious  8)
 

Deepdark

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Sorry for the long reply, forgot to activate the notification replys option. Anyway. The difference between the D-LA2A and mine is that the D-LA2A is a stereo board, including the power supply on the same board. Mine is mono, and has a sepârated power supply. The poiwer supply is made to accomodate the use of toroidal power transformer or center taped EI power transformer (Like the Hammond or Allied electronic one). Also, there is a rail for DC heater for V1. Both the D-LA2A and mine are based upon the same schematic, so there shouldn't be any difference between both. AS for the noise performance, oscillation, etc. I've never used teh D-LA2A so I can't speak about it. I'm pretty sure it's really well designed and really silent when done. I've done a couple of LA2A with my own pcb and always got really low noise (around -110dbfs and less at 60hz) and never experienced oscillation. So all in all, I think you're safe to go with whatever one or teh other :)
 

Deepdark

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rprimmett said:
Some progress :)

20170117_223507.jpg

Things are coming along nicely. You could use only one psu board, though. Of course you would probably have to rework a bit the RC filter stage (which means changing the résistors values).

Basically, after the diodes, you'll be around 350v or so. you need to drop about 75v to have your B+ at 275v at about 34ma. So, 75v/34ma = 2 205ohm / 5 = 441ohm. Find the neerest resistor value and use it has your power résistors. 1W each would be plenty.
 

Deepdark

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Hi there. Basically, you need a ink printer and some Lazertan, or any water decal paper. You first draw your design in a software. Then, print it according to the setting recomendation of the paper manufacturer. Once printed, you need let it dry (again, follow the manufacturer instructions). Once dried out, you must apply one or more layer of clear, so the decal will stay strong. Once it has dried, you cut the paper around your drawing (Dial, text, whatever you printed out). Cut as close as possible to the printed drawing, So you will not have too much apparent border. Once done, dip the cited piece into some luke warm water. After a couple of second, the image will slide form the paper. You just help it slide on the panel, where the drawing is supposed to be. Adjust and let it dry. Once everything is done, you apply some layers of clear to the front panel, so the decal will stay strongly on the panel and the clear coating will protect them. Remember, you front panel must be as glossy as possible, to prevent silvering of the decal. Hope that help!
 

Deepdark

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it helps smoothing it out yes. I had actually good results by the past with it, but you have to cut out the decal really close to the lettering so the decal actually looks like a silkscreened lettering instead of a decal
 

Deepdark

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exactly, an x-acto knife and a ruler to make perfect straight cut. For round dials, I try to find the perfect glass size and use my x-acto tu cut around it so it makes a perfect round dial
 

mattmartin831

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Dec 11, 2016
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46
Would it be possible to do this build with a 2U rack chassis? I would assume the need for 3U is due to the height of the tubes. What if the tubes are mounted horizontally?
 

Deepdark

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If the tubes are mounted horizontally, it would be possible to do it in a 2U. But, you'll have to extend the lenght of sensible part like grids and heaters (you will need to hardwire them, and the more lenght you had, the more you're at risk to have oscillation or other trouble).

Personnaly, i would stick to a 3U.
 

nielsk

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Megapopulas, Florida
If there are dual footprint pads for the tube sockets so one can choose to use single pin sockets instead of a standard tube socket then 2U will work fine...
 

rsi77

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May 11, 2017
Messages
2
Thanks,

I'm still looking at this project with much interest.

Can you show a photo of your finished project? It looks like you're making a stereo unit using 2 sets of your mono boards--have you done this before? Did you find any issues with your layout that needed to be addressed?

I'm looking through your instructions and they seem very thorough, but are you interested to discuss advantages/disadvantages of various options you allow for? I.e. different types of transformers, etc.

Also, from the thread related to the stereo board there is discussion about the need to limit the input gain pot due to the extreme gain past "5" or so, and you also mention this option in your document. Did you have this same issue with this design? Did you address it in the same way? Or did you choose an input scheme which prevented the issue from appearing in the first place?

Thanks,

Ron
 

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