LA3A 500 BUILD

[peter purpose]

If I could get the meter to zero and be accurate to 6dB I'd be happy.
I couldn't ever zero the meter with different combinations of R13, R24, and adjusting Rv23
I'm guessing the dark resistance of my LDR is way different.

R13 at 10K got me the zero no problem. Try going smaller.

 

[janczmok]

Finally got some time to look again at my unfinished module. So, some short questions:

- What's your preferred RLED value ? ( i am using now 3-PIN Led's and one red LED as planned), will try with 22OR, ok ?
- VU Meter: I have 4 (two large, marked with - and + and two small) connectors. Am i assuming right:
  - PG/MP use them on the smaller connectors,
  - M+/M- according on the meter.

- What heatsinks are needed ? Peter: Which one did you use ?

Thx

 

[peter purpose]

What's your preferred RLED value ?
That would depend on the leds being used. http://led.linear1.org/1led.wiz

Meter
PG/MP = power ground/meter power
M+/M- = meter positive/meter negative.... so you were assuming correctly.

What heatsinks are needed ?
The driver pair (metal cans) on the output amp need sinking.
I cut up an old pc heatsink and used a double sided, heat transferring pad. Get a super sticky one.
The metal cans carry plus and minus voltage, so must be seperate.

peter

 

[janczmok]

So will check the local computer surplus store for a decent heatsink plus tools Also need to file off something off the metal case, as the meter is not fitting in 100% and thereof blocking the buttons.

 

[peter purpose]

This was addressed earlier.... you just need to file a little around the bottom of the hole at the fold.

 

[janczmok]

This was addressed earlier.... you just need to file a little around the bottom of the hole at the fold.

Thanks for pointing out. Have missed this, despite that i read the whole thread 2 times yesterday.

 

[dmp]

Ok -  the meter zeros and bounces happily now as the unit compresses. Thanks for the help.
I haven't measured the accuracy, but it seems reasonable by ear. I'm very happy with it now.
I switched LDRs (although I don't think that was the problem since they had comparable dark ohms)
I have:
R24 NI
R13 10k
R22 47k
RV36 = 3.9k

 

[peter purpose]

Marvellous.

 

[mulletchuck]

is anyone supplying a complete parts kit for this?    ???

 

[Winetree]

The TB4 I took apart has a resistor on one leg of the EL Panel.
Should the resistor end go to pin #3 or Pin #4 on the
LA-3A-500 El Panel daughter board? Or does it make a difference?
Wondering which senser is meter and which one is audio? Front or Back?

 

[dmp]

Looking at the schematic, 5 & 6 are the meter. They are labeled on the pcb.
Do you realize that the numbering corresponds to the pins on the plug of your T4b? Since you took it apart, you're the only one who knows what pin the resistor was connected to. What value was the resistor?

 

[Winetree]

No, I didn't realize the pin #,s were the same. Thanks for the tip. I got it figured out.
The cap is a .0047uf@630vdc. Pin #3 goes to panel, comes out into cap to ground.

 

[dmp]

You were talking about a resistor in series with the panel. I guess it turned out to be a capacitor?
There is a 4.7nf cap in series with the panel, CT4 on Peter's schematic.

 

[gavvyt]

is anyone supplying a complete parts kit for this?    ???

I would like to know this as well.
(I am based in London)

 

[kato]

Edit to my previous post to clear up confusion - the kits I assembled do not include EL panel, opto cells, or transformers. A T4b and hairball transformer bundle is still required. There is no money savings in my parts kit - nor is there money making on my end - just the convenience of labeled parts, and not ordering from multiple sources. (And for me, the lesson that I never want the pain of running a parts kit business.)

I'm nearing the end of this parts fiasco. I've got two single channels boxed up, and 1 dual channel kit. (Plus extra two dual-channel kits with tall heatsinks that need to be trimmed to fit.)

The latest batch of kits have included these heatsinks (pictured) that fit the close spacing on the board. These are raised up a little with transistor sockets to keep from bumping into the diodes between them. In retrospect I would skip the transistor socket for a more solid connection and solder the transistors above board.

Cost is $56.41 per channel plus $5.20 priority mail for any number of kits.
(You can deduct $2.41 in paypal fees per channel if you choose the "personal tab" in Paypal and send as "payment owed" although you forfeit your Paypal buyer protection by doing this.)  Here's what's left:

1-channel kit (61.61 shipped) sold
1-channel kit (61.61 shipped)
2-channel kit (118.02 shipped) sold

I have an additional 2 channel kit assembled that with the larger heatsinks. They require a little filing at the top, and pin cutting at the bottom to fit within the race space width. PM or e-mail.

 

[duantro]

Kudos to Kato on the parts kits. Everything labeled clearly and sorted out per location. This is going to make the build a breeze! :thumbs!

 

[Winetree]

Got 2 earlier Kits. Got a part's number for the newer heatsinks?

 

[duantro]

I thought I'd post some progress. This thing has been a breeze so far. Thanks for such a great layout Peter!
I hope to get some matched cells from a friend soon. Until then I'll get the transformers and meters buttoned up.
One question, for the Cinemag 2511 input transformer, am I assuming correctly by matching the red dot from transformer to the white circled pin hole on pcb?

 

[kato]

Looking good Duane! I mailed your parts over the weekend so you're kicking some ass.

Got 2 earlier Kits. Got a part's number for the newer heatsinks?

325705B00000G

Sorry about the extra tall heatsinks.  I learned not to assemble a parts kit till I've built the thing myself.
Though the ones I shipped previously have better thermal resistance and reportedly can be made to fit with some grinding. It's always a trade off when working in tight spaces.

Info for all - important things I learned from the beta testers:

  • box caps for the unmarked caps do not fit under the amp boards without bending. Later kits shipped with half height dipped caps.
  •  heat sinks too tall for 1 rack width.
  •  RV31 and RV23 go on underside of board.

 

[duantro]

Ok, I've got my matched opto cells in hand. Tonight I plan on smearing some silicon on the el panels and soldering them in place. Should be complete. Then run some electricity thru them! ;D