LA2A PCB ver 2.0 build thread

[Stagefright13]

I used the Sowters on mine. I don't have an original LA2. But stuff I did many years ago on a real one sounds like it. Jensen usually makes cleaner Transformers by reputation. And their quality is outstanding. But I don't know what their LA2 style ones are like. The Sowters do sound great tho. The whole box sounds like a smooth chocolate sundae lol!

The Sowters also looks extremely well made.

 

[dripelectronics]

hi there . been lost in my research ,

i like the jensesn x formers just as good as the sowters , IMHO


as for power transformers , it seems there are some troubles

happening with the sowter power xformer ,

odd how the allied xformer ct or not works better.


one should arrive this weekend and i will be able to solve this problem.


as well as im designing a dc heater board add on for
the ver2 drip customers.


curently im in a compleate re-design of the la2a pcb .
and taking it to a whole new level .


i would wait for the new Ver 3.0 variants
that should arrive here in early
may.

a few more prototypes to go ,
but the more i skrew up , the less you will .


g.

ps. all final orders of the ver 2 / t4b's shipped .

contact me if yours hasn;t arrived/

spy photo from the opto lab :grin:

 

[IzzyRock]

Greg,
Any chances i could buy 2.0 and T4 right away? I could pay inmediately, i already emailed you. but no response yet

Cheers

Javier

 

[buschfsu]

great to hear there will be a version 3. ill take one and a T4 when they are ready!!!!!!

 

[mrclunk]

Hi all,
Just put together my first Drip V2 La2a. It sounds great but i'm having trouble with the meter.
In GR mode with no signal in it dances around a little +/- 0.3dB. It seems to be linked to the voltage regulating neon bulb that flickers also.
Do i need to adjust R25? Or could my neon be bad?
Think i read somewhere this needs to be matched with the t4b (drip version), how do i do this?

In the re-issue La-2a there is a 65v Zener diode instead of the Neon, would that stabilize things perhaps.
I'll stick some pictures up soon.
cheers
Paul

 

[mrclunk]

so i messed around a bit.
I'm measuring 80V over the neon. Is that a touch high?
Anyway I put a 100k pot for R25. Now adjusting that and the meter zero adj i can zero the meter and its stable, however the neon does not light up. Does that matter?
I've ordered some zeners anyhow so ill try that tomorrow.

 

[dripelectronics]

your running hot in the neon section ,

should be aprox 56 volts.

which power xformer are you using ,

you might need to bump up r29 4.7k to a 5 or a 6k

since the meter connects directly to the power rail through r28 (470k)

are you using one of my t4bs ,

the cells might have been dislodged in transport ,

possible that t4 octal socket connectors might be too wide,

making a poor connection with the t4b headers ,

(rare , but has happened on my la2a re0issue)

(i usually use a little plastic handle eyeglass screw driver to
tighten the octal socket crimper conectors
there might be some voltage present in pin 3 , not alot ,
but thats why i use a plastic handled screwdriver)

g.

 

[mrclunk]

thanks greg,
i may have some time this evening to mess about with it.
I'm using a Hammond 396jx transformer (500V ct) and one your t4b.
I think that the HT voltage reading was a little high off the transformer, will check later.
Dont think its a problem with the octal socket as it was really tough to push the t4b module in.
many thanks
paul

 

[mrclunk]

so...
i measure 357V after the psu diodes and 281 after R29. Thats ok isnt it? only a few volts over.
but after R28 i get 75V to 80V.
gona take out R28 and check it.

Is there a schematic for the drip v2 board somewhere, as some of the component values have changed from the original.
cheers
paul

edit: R28 is fine 468K
also i swapped out the t4b for another and get the same results.

FIXED:
I swapped the neon for a couple of 33v Zeners in series and now all checks out ok. The voltages have dropped back nearer to normal and the meters fine. I think the neons i bought must regulate at a different voltage. They were from Rapid.
ta

 

[SaMpLeGoD]

Hello,

I'm building Drip LA-2A Ver.2 and almost have my PCB full stuffed, I only need to order the transformers. I went to Sowter website, and notice that the power transformer is pretty expensive and Greg said something about problems with this transformer... am I right?

Paul, the Hammond's power transformer you have, (the 396Jx) is working well? I read something somewhere about that it has no CT and need to wired a couple of 100Ohm resistor somewhere... well, I need to read better to be sure, but is someone have any suggestion for a nice and good isolated xformer for Europe (220v - 240V) that fit in this project, please let me know!

I asked Greg to re-wire the (output +10) in a 3 position lorlin/alpha rotary switch, just to match the original one. The mod is simple: is just add a 6.8k on that position, as I saw in the La-2A's Schematic. If some one already did it and don't mind to share the wiring for this PCB (ver. 2) I appreciate!

Cheers :guinness:

Eddie :thumb:

 

[mrclunk]

Hi Eddie,
the Hamond 396jx is fine, seems to be the european choice, and does have a center tap, think your confusing it with the 269jx.
Bought mine from here:
http://www.tube-town.net/ttstore/index.php/cat/c155_300-Series-Classic-Tube.html if you can find one cheaper let me know!
There is also a custom transformer that Silent arts is having made that will work. check this thread:
http://www.groupdiy.com/index.php?topic=27273

Another good source for parts is for this project is http://www.banzaieffects.com/ btw.

happy squashing

 

[SaMpLeGoD]

Hello Paul!
Thanks man, I'll order that power transformer, did you mean 369JX isn't it?!
About the intput/output xformers, I went to sowter website, looking for the 4383 and 8940, and found near those the 1009 and 1010 that they're telling us those are kind of reissues from 1968's LA-2A, if I'm not mistaken. they have diferent impedance and gain! Are they suitable for the LA-2A's Drip Opto version? Hey Greg! say something hehehe
I need to order the xformers :wink: just kiding! If someone have any idea, I'll apreciate!!

Cheers :guinness:

Eddie :thumb:

 

[mrclunk]

I looked into the transformer options.
Briefly:-
If u want as close to the original sound u need the original UTC xforms.
The drip boards are designed for the Sowter 4383 and 8940, thats what i used. The 4383 give aprox 12dB less gain on the input than the UTC or Sowter 1009.
But its also worth exploring whether a 1:1 input transformer would suit your needs better (even less gain). The original La2a input was rated for levels of -20dB, so with modern equipment they will overload easy.
The next pair of La2a i do i'll try 10K:10k intput xforms as i have a box of nice Sowters gathering dust.
Theres tons of info in the forum about xform choices, reducing gain etc...
some good info in this one
http://www.groupdiy.com/index.php?topic=22288

Jensen detail the 10k input mod here.
http://www.jensen-transformers.com/as/as091.pdf

btw there was a 3 week lead time on the sowters when i ordered them.

these were the first LA2As i've built so don't take my words as gospel. Cj an ssltech are the LA2a daddies as far as i can tell.

some pics of my first one.
http://twin-x.com/groupdiy/displayimage.php?pos=-2223
http://twin-x.com/groupdiy/displayimage.php?pos=-2222
http://twin-x.com/groupdiy/displayimage.php?pos=-2221

 

[SaMpLeGoD]

Hey Paul,

Thanks for the explanation!
The pics from your gear are awesome! looks great! good job!
my LA-2A looks like the original too! I'll put some pics when it's finished too!
Have some in my site, take a look Here
Let's keep on contact!
Cheers :guinness:

Eddie :thumb:

 

[mrclunk]

cheers, nice to be of some help for once.
I'm getting bored of copying the original graphics, will try some of my own designs in the future.
paul

 

[IzzyRock]

I need some help here.

I bought all components shown on the opto manual and it says 3 - 220k resistors. However, there is place for 4 220k on the pcb. Did I do something wrong or greg just mispelled the qty number in the part list?

 

[SaMpLeGoD]

Hey,
I bought the Hammond 369JX, and noticed that it has no "Grey Wire" (supposed to be the core's shield wire). In the Hammond's website the wiring scheme's actualy don't have that wire too... well, in the 200's series all transformers have that wire... is the internal ground wire's already connected to the transformer's chassi? there's no FAQ about that in the Hammond's website, and I just only want to know if this it's normal. I'll wire the xformer in my LA-2A without that wire... hope everything goes right :?

Cheers :guinness:

Eddie :thumb:

 

[Stagefright13]

The grey wire is the shield and goes to ground. You don't need one.

 

[SaMpLeGoD]

Hi all!!

Finally I finished my LA-2A, I think all is working, I powered up without the tubes first, all ok the NE-2 (neon Lamp) lighted up, mesure the voltages from the power xformer, and have 228V (Portugal AC 230V) at the AC Input, 228V at the "Black wires" and 502V at the "red Wires" (High Voltage). Put the tubes, the 12AX7 lighted up, all fine, put the selector in "Gain Reduction Mode" and correctly set the zero at the VU Meter. All fine and working... but... yeah... but... when I change the selector to +4 or +10, the VU's pointer goes to the right side very quick it really strike to the right, like if there is some extra voltage unsupported by the VU. It's supposed to be at the full left, isn't it? I'm puting no Input signal at all.

Well, the only thing I made, by my own, was to put a lorlin rotary switch 2pole 3 positions insted the spdt switch to get the +10 metering too... it's just to be like the original one. I saw the LA-2A schematic and realize that the difference is in +10 mode I have a 6.8k resistor (in series with the R24 3.9K). I tested the functionality before connect, and seemed to be all right...
The meter is a Sifam AL39WF, the largest one from that series. I Didn't fit the T4B yet!
Where do I start to troubleshoot? Any Ideas??
All the parts value and connections are all right... I carefully tested all the resistor's values before soldering :roll:
Need really help :?

Cheers :guinness: :guinness: :guinness:

Eddie :thumb:

 

[crisotop]

did you terminate the meter with a 3k6 resistor (there has to be a sticker on your sifam somewhere)?

cheers
christoph