LA2A PCB ver 2.0 build thread

[emrr]

You very well might have some other problem but make sure you are using balanced cables in and out. You will lose bass if you use unbalanced cables.

There is absolutely no reason for this to be true, if wired properly. period. cage fight if necessary.

 

[crisotop]

and as for the grid , they were added only as a percaution.

seems to work well with jumps or the 1k resistors.

I didn't add the grid resistors, nor jumpered them - might that be a problem?

EDIT:

mata_haze wrote:
can anyone confirm that there should be a connection on that point please?
all the best
Mattia.


Yes. Install a jumper if you're not using the resistor.

Oops - will check that tonight!


cheers
christoph

 

[crisotop]

Another Update - Jumpered the Grid Resistor, now the unit works with huge amount of output signal! I'm still working on low frequency hum (I'm using a non-center tapped transformer, but soldered two 2W 100R resistors to the 6V legs, and connected them to ground #4 (transformer ground) - should the ground connection be shorter? I don't want to drill to many holes in my box, without actually knowing if it will make a difference. Besides the hum, there's some high frequency noise as well, which changes if I move some wires around. Btw, I'm using a Purusha case, with a powder coated front - i've read somewhere that it might help to dremel off the coating around the area where the parts touch when screwed together?

Thanks for any advice,
Christoph

 

[emrr]

Ah yes, If I read right no grid resistor or jumper. Equals no signal! Got that straight.

Wire length for hum center tap should not be critical. Are your 100 ohm resistors connected closest to the transformer? They should be, and should be away from anything else.

Do you have a verified ground connection to your AC from the wall, which encompasses the entire case?

I'd suspect induced noise from filament wire routing to the board probably last on the list. First I'd look at connection between parts of the case. Best to follow advice of Drip manual regarding solid case ground connections. Did you follow his advise about having some parts raised above the board to get them away from filament traces?

 

[crisotop]

Ah yes, If I read right no grid resistor or jumper. Equals no signal! Got that straight.

But I just jumpered the Grid resistor coming from Pin7 - left the second one unjumpered.

Are your 100 ohm resistors connected closest to the transformer? They should be, and should be away from anything else.

They are connected to the PCB, directly to the transformer pads - what do you mean by "closest to the transformer"?

Do you have a verified ground connection to your AC from the wall, which encompasses the entire case?

Yes I think so (tried two supplies, one from a furman power regulator) - i checked the case screws for connections, but will dremel some more coating of on the front panel, to ensure better connection.

Did you follow his advise about having some parts raised above the board to get them away from filament traces?

I raised all my parts as high as possible (tricky on some of the resistors, will shoot some pictures tomorrow).[/quote]

 

[crisotop]

Small update - one unit is perfectly silent now, the second one still has some low-frequency hum. My main problem was the case, i had to make sure it has good contact on all the single parts (But i have good grounding on the humming unit as well).

thanks for your advice
christoph

 

[dripelectronics]

this seems to work very well for me ,
its a little ' dc referenced heater circuit '

insted of grounding the low voltage centertap of the transformer to the
case ,

you float it in the middle of this set up .

seems stable and has been working in one of my opto 72 's
ive left on for 2 weeks now. ( no smoke
transformer operates at normal temp. etc

should definatly work for the v2 board also.



put the hum to zero ish in my test rig here.

i used a radio shack 5 tag soldering post and mounted it to the case.
then soldered the resistors and caps to it .
soldered the 220k resistor to r29 b+ side (not the 300V side)
i felt there was no reason to string 275v accross the case )
attached a wire to the resistor and connected it to the proper place
as shown below.

put the ground to the transformer star gnd.

check it out .

and report back.

(feel free to chime in on the circuit if you know a better way)

best .

g.

ps. 2 watt resistors work well here
and some folks use up to 100 uf caps.

 

[crisotop]

so here's a file with the "noise" of my unit (according to a Rhode&Schwarz UPV ~80dB SN A-weighted): crisotopLa2a

It's not perfect, but I guess pretty normal for a tube unit, I can't hear it in a full mix ant normal volume. It's only noticable at higl levels with a headphone - what's your opinion?

Two Pics of the finished units (corrected the size, to make the thread viewable again):

Thanks for all the advice
christoph

 

[dripelectronics]

ah .. thats a curable noise .

sorta like a gnd loopage problema.

ill try to pull together a list of things to try.

what x-former is that ?

looks nice .

good job on the build by the way.

g.

 

[crisotop]

ah .. thats a curable noise .

sorta like a gnd loopage problema.

Sounds promising The trafo is custom wound by a german company (rondo-mueller - thanks to silent:arts-volker and the nrg-guys for the tip) it costs 30 euros, a real cheapo compared to the sowter. It was just my noobish fault to order it without a center tap on the 6V windings.

Thanks Greg!
Christoph

 

[mfdu]

i finally have channel one of my la2a .1 boards up and running.

here's the voltages (no tubes or t4b) - somwhat over spec :
12ax7#1
pin 1 = 476vac
pin 2 = 476vac
12bh7a
pin 6 = 759vac
12ax7#2
pin 1 = 525vac
pin 6 = 526vac
6aq5a
pin 5536vac
pin 6 = 534vac
t4b
pin 5 = 12.1vac

am i, like, too far out on them? should i worry? or can i proceed?

now the pr*n. internal shot. a little messy. better shots to follow.

mfdu

 

[CJ]

thats all wrong..

where did you buy this?

 

[dripelectronics]

wow , a ver 1 board ,


EDIT * what is your transformer specs * ?
is it a 250-0-250 ?

some of those voltages seem hot .



:shock:

if all the caps and resistors are in their proper places ,
and your using a 250-0250 xformer .

put the tubes in ,

the voltages will always be correct if the proper resistors are in place .

there is no load with out the tubes .

so the voltages will be very high.

if the fuse didnt blow on power up with out the tubes ,
i feel you are safe to fire her up with tubes .

i lost my voltage charts for the ver 1 , when i got rid of my
old web site .

g.

 

[mfdu]

hey, whoa everyone.

philosophically, what is different b/w the 1176 clones (eg. mNats, of which i have four working units, thanks) and the boards / t4b's that g. is doing as drip electronics? or the gyraf SSL? or how about fabio's built 2520'2 (it's been 18 months and im still waitin . . .)

if you allow one, you allow all? i don't have the knowledge time or gear to make my own boards - should that disclude me from getting to build my own WITH the help and experience of the online community?

g - thanks for the support - i'll try with tubes (no t4b) and report back.
trannies on this unit are billington. unit 2 is sowter i/o.

thanks for the support this forum provides me in support of my DIY'ing.

chris
mfdu

 

[lofi]

[quote author="mfdu"]hey, whoa everyone.

philosophically, what is different b/w the 1176 clones (eg. mNats, of which i have four working units, thanks) and the boards / t4b's that g. is doing as drip electronics? or the gyraf SSL? or how about fabio's built 2520'2 (it's been 18 months and im still waitin . . .)
[/quote]

from a personal point of view, nothing. P2P might be the traditional way to do it, then again steam trains are traditional. i built a guitar amp P2P, enjoyed it, but unless somebody can prove that it was the only way to get the sonics necessary I'd have preferred PCB.

Its nice to do stuff the traditional way, and fun, but some times i get the feeling its just a marketing tool (Marshall re-issue?). I think CJ keeps going off on one at the apparent 'commercial' attitudes of some of the designers here. I think he fails to see that people need different levels of accessibility, most are building to use. We all want to learn, and building is the quick way to do it, no matter how you go about it.

I've just ordered some Turrets to P2P a LA2A via CJ's site, but i have also bought the Drip board Nick Godfrey (Godders) had for sale in the Black Market, think that will be finished first.

Iain

 

[Bluzzi]

[quote author="lofi"]
I've just ordered some Turrets to P2P a LA2A via CJ's site, but i have also bought the Drip board Nick Godfrey (Godders) had for sale in the Black Market, think that will be finished first.

Iain[/quote]

Iain, where on CJ's site did you order the Turrets? I couldn't find any items for sale just info on LA2A, Pultecs etc.

jim

 

[lofi]

sorry, my bad english

i am going to P2P the LA2A as per CJ's site, i ordered the Turrets from here

 

[Bluzzi]

Thats ron's drawing right? (Cayocosta)

I used it for my 2 LA2As. Great gift to our group! I modified mine slightly to exclude some parts (terminal strips for one).

P2P is easy really. The only part I find a bit hard is the tube wiring as it gets tight in there. On my second one I used smaller gage wire and that helped.

I think both ways are equally valid. But I'm sure many people that were afraid to tackle LA2A P2P are happily using theirs now and that is a positive thing.

Have fun.

jim

 

[lofi]

[quote author="Bluzzi"]

P2P is easy really. The only part I find a bit hard is the tube wiring as it gets tight in there. On my second one I used smaller gage wire and that helped.

jim[/quote]

the first time i made an amp p2p i used household electrical wire (i knew just less than nothing :grin: ) Hell you should have heard the cussing at that!!

made it with 22 guage the second time, much better :grin: :grin:

Iain

 

[IzzyRock]

Hello.
I havent posted before here but I've been reading a lot!!
Im planning on doing the PCB 2.0 but I got a queestion about the trannies.

How could u compare the sowters and the Jensens? Have any of u tried both? Which ones sound better? Or what are the noticeable differences.

Hope you could help me, I'm still deciding which way to go.

PD: Greg, are you still selling the PCBs and the T4 ?

Thanks a lot