2 simple LA2A questions...

i'm almost finished w/ my LA2A, & have a couple questions.

regarding SW3, in which position (closed or open) is it in "compress" mode? i think i want to leave it fixed in "compress" mode ( i can always change it later).

also, (& this probably going to seems really stupid) but on Ron's diagram, there are 3 pins/side for SW2...what are the pins/points marked "P"?

thanks in advance,
-dave

I believe that it's compressing in the closed position and limiting when open.

'P' usually stand for 'pole' if the switch is a changeover, the pole is usually the contact in the middle, though I don;t have Ron's layout to hand to check that's what he drew...

Keith

Hey SSLTech, thanks.

in Ron's diagram there are wires going to the 3 pins on either side of SW2, (which is a DPDT for meter select) & that makes perfect sense. the thing that confuses me is that there are also wires going to 2 pins/poles maked "P", one on each side of the switch (as if they were a 4th pole on either side). both of the poles marked "P" get connected to the VU meter, one directly to the "+" side of the meter, & the other to the "-" side via R24.

i tried searching the forum, it seems i'm the only jackass confused by this.
any help would be greatly appreciated.
thanks,
-dave

hey Keith,
ok i thik i can actually hear the gears turning in my head now... :grin:

both poles marked "P" are by pin 3 of SW2 in Ron's diagram.
so i guess (after re-reading what u wrote in your earlier post) in his diagram pole 3 is the switching pole, but it could differ in different switches, so it left up to the builder to figure it out based on what switch he has?

no, your not the only one.
wiring the vu sw in the LA2 is the hardest part of building that thing.
decide if you want -10 or plus 4, or whatever, and re do it from there.
most people go with the pro level, thus simplfyng the vu meter wiring.

as far as the comp/lim switch, flip a coin and wire it permanately for heads or tails since you really can not hear any difference.

Try a higher resistance value there for R7. Should do the trick. I forget what value I used for mine, but I did use something higher than 2.7K

Hi,

SW2 is a 2 pole 3 position rotary switch.

SW3 open is limit.

I also saw (not heard) a noticeable difference in limit/compress modes by increasing R7 also - I think to 2.7k - 1k did nothing.

Good luck,

Ron

hey guys,
thanks. will take it all under consideration.
i have moved away from the meter switch for now, & am just trying to get it to pass audio correctly first...its pretty close but i have 2 problems.
one seems simple (so it probably wont be), the other less so.

1) all i have to do is tap the case or the table its sitting on for that matter, & it makes a staticy type sound VERY similar to the sound of a scratchy pot. i'm chalking it up to a cold/bad solder joint somewhere...i'm gonna give it a looking over & make sure thats what it is.

2) i dont have that much gain, which seems to contradict the results that most people usually get. i remember (especially back @ TT) there were many posts about how they couldnt get past 10:00 w/ the gain knob. i dont even start to hear signal until almost 12:00. the sound is also a bit thin.

could the lack of finishing the VU switch wiring cause the gain issue? i dont think it would, as it gets its signal from the output of the output tranfmorer, & i haven't made that connection yet.

oh yeah...i used jensen iron, but didn't do the jensen mods as i just wanted to follow the diagram to get it working. i figured i could always go back to make mods later. BUT i did use a 22uf/450v output coupling cap(as jensen recommends) instead of the 10uf that the original design wants since i was out of 10uf/450 caps. could this be the culprit of the thinness in sound? (or the gain issue for that matter?)

once again, thanks in advance.
-dave

Hi anyone
Ron and I talked about 10uF capacitor.
Anyone have idea what (but not expensive) cap is best to use and does.
Duka

It sounds like an intermittant connection somewhere, or a noisy/bad tube.
Get a chopstck or pencil and tap around varous parts of the circuit to see if you can isolate the problem area, then go from there.
Remove all wires from the output transformer sec. that go to the switch wiring to eliminate the signal getting shorted out somehow in the incomplete wiring of the switch.

Hey CJ,
thanks. i got it. believe it or not it was the power fuse. i didn't have it screwed in all the way, & i guess it was making intermittent contact as i tapped it. anyway she's now passing audio & sounds quite good, although i have a low 60hz hum. its not that bad, but noticeable. its also constant (does not not vary w/ gain) so i'm pretty positive its from the heater supply.

i'm using 2 100ohm resistors from the 6.3v legs to ground since i bought the wrong power transformer that doesn't have a CT. maybe i should switch to 2 WW pots, or just get over it & order the correct transformer?

You only need one pot, 100 ohm wire or regular. Ground goes to the wiper, the two ends to the 6.3.
Hum was more acceptable in the old days, especially with AM radio still alive.
In the really old days, they didn't care about it becuase the speakers were so lo-fi that they wouldn't even reproduce it.
If all else fails, you might have to rectify the heater supply.
You could also try reversing the green wires and see if the phase reversal will help. I have gotten luck with this method once or twice.
Also, just for the heck of it, flip your power cord if you can. .

I have an AB 100ohm pot here i can use.
Thanks SO much for the suggestions CJ.
its REALLY appreciated!
i'll give them a whirl tonight.

-Dave

[quote author="cjenrick"]
as far as the comp/lim switch, flip a coin and wire it permanately for heads or tails since you really can not hear any difference.[/quote]

I would disagree with this statement, especially if you use the la2a on a parallel buss. I havent built one myself so I only have experience with old ones to base my comment on.

dave

ok....
tried flipping the phase of main AC & heater lines with no luck.
the pot i had was a 100k, not 100R so i didnt really expect it to do the trick, & it didn't. i'm now back w/ 100R resistors.

but i have noticed this, as soon as i flip the power switch the hum is completely gone. i know that sounds like a stupid statement but the unit will continue to pass audio for a few seconds after i kill the power, minus the hum. i'm thinking of trying to use an external DC powersupply to supply the heater voltage to confirm that its the source of the hum.

make sense?

[quote author="cjenrick"]
as far as the comp/lim switch, flip a coin and wire it permanately for heads or tails since you really can not hear any difference.[/quote]

Well, you're obviously not driving it into enough GR.
The difference is more apparent as GR increases (and fun begins).

Hi,

Regarding hum, I had a similar problem - for me, it was because with the chassis open, my front panel was no longer grounded (It's not hinged) - as soon as I clipped a wire from the front panel to the chassis the hum was gone.

Ron